Influence of Cu content on optical spectra of Cu/Mg co-doped ZnO films by Kramers–Kronig

Influence of Cu content on optical spectra of Cu/Mg co-doped ZnO films by Kramers–Kronig | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Influence of Cu content on optical spectra of Cu/Mg co-doped ZnO films by Kramers–Kronig Mahsa fakharpour This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5223491/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 17 Jan, 2025 Read the published version in Optical and Quantum Electronics → Version 1 posted 13 You are reading this latest preprint version Abstract Mg and Cu co-doped ZnO thin films were fabricated on a FTO glass substrate by the electrochemical method at a constant current density of 3.5 mA/cm². Mg:Cu:ZnO films with a 3 wt.% Mg concentration and varying concentrations of 0, 2, 3, and 4 wt.% Cu are designated as ZM3, ZM3C2, ZM3C3, and ZM3C4, respectively. The thin films were subjected to analysis using XRD, SEM, FTIR and UV-vis spectroscopy. The structural and optical parameters of Mg:Cu:ZnO thin films for photonic applications were investigated in detail. The results of the structural and morphological analysis demonstrated that the structural parameters and grain size are dependent on the concentration of dopants. The grain size was calculated to be 55.20, 36.43, 32.64, and 32.57 nm for the ZM3, ZM3C2, ZM3C3, and ZM3C4 films, respectively. The results of the spectroscopy analysis indicated a reduction in the band gap, from 3.9 eV to 3.6 eV, as the concentration of Cu in Mg:Cu:ZnO increased from 0–4%. The optical parameters of the films were obtained through the utilization of FTIR transmission spectrum data and the application of Kramers–Kronig (K-K) relations. The findings indicated that the ZM3C3 film exhibited the highest energy storage capacity and the lowest energy loss when compared to the other samples. Mg:Cu:ZnO thin films Structural study Optical study Electrochemical Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction Zinc oxide is an n-type semiconductor in the II-VI group, exhibiting high mobility and crystallinity, as well as excellent mechanical properties and transparency in the visible region. Its energy band gap is 3.37 eV (Nimbalkar and Patil 2017 ). Due to its distinctive properties, ZnO is employed in a variety of commercial applications, including displays, optoelectronic devices, antireflection coatings, transistors, solar cells, light-emitting diodes, and others (Vyas 2020 ; Ahmaruzzaman and Raha 2022 ; Maqsood et al. 2023 ; Saha et al. 2020 ). A number of researchers have devised various techniques for the preparation of zinc oxide thin films (Noman et al. 2021 ; Tamulevičius et al. 2023 ; Amakali et al. 2020 ; Rashid et al. 2021 ). The electrochemical method offers several advantages over other methods, including simplicity, cost-effectiveness, and the ability to create homogeneous films with controlled grain size. The electrochemical method allows for the alteration of composite morphology, distribution, and grain size during synthesis, thereby enabling the customization of samples to satisfy specific properties for a range of applications. The incorporation of metal dopants, including Al, Mg, Cu, and Fe, has been demonstrated to enhance the optical, electrical, and mechanical properties of ZnO thin films (Goktas et al.2018; Sowmya et al. 2023 ; Kumaresan et al. 2017 ). The various techniques, including sol-gel, sputtering, chemical vapor deposition, and electro-deposition, have been presented as methods for the addition of dopants to nanostructures and thin films. Among the various doping techniques employed in ZnO, Cu doping has been shown to enhance the properties of ZnO due to the small difference in atomic radius between Cu and ZnO, as well as the proper substitution of Cu atoms within the atomic lattice of ZnO. Consequently, Cu doping can influence the optical properties of ZnO films, including the band gap, absorption, and photoluminescence. In our previous research, we have demonstrated that the optical properties of the films undergo changes in response to alterations in the morphology of the nanostructure during the deposition process (Fakharpour and Karimi 2022; Fakharpour and Savaloni 2017 ; Fakharpour et al. 2016 ; Gholizadeh and Fakharpour 2023). Recently, some literature has been published on the modification of the optical band gap and optical properties of ZnO films by Cu doping (Karimi Tafti and Fakharpour 2023 ; Asikuzun et al. 2018 )]. Nevertheless, an increase in the concentration of Cu dopants in ZnO results in a reduction in the transparency of the film in the visible region. However, the optical band gap of Cu-doped ZnO thin films is observed to decrease, while the Urbach energy increases (Asikuzun et al. 2018 ). In a related study, Debir et al. (2020) developed ZnO films doped with Al and Cu using the sol-gel method. The findings revealed that the size of ZnO particles not only increases with Al and Cu doping, but also that the energy band gap and photoluminescence properties of ZnO films decrease. The incorporation of Mg and Cu dopants markedly enhances the electro-optical characteristics of ZnO. The atomic radius of Mg is also similar to that of ZnO. However, Mg doping in the ZnO lattice and substitution of the Mg ion with the Zn ion results in lattice distortion. The innovative application of Mg doping in ZnO has resulted in its extensive utilization in optoelectronic and electronic devices. The energy band gap of MgO is 7.8 eV (Heo et al. 2015 ), while the transition region of ZnO films can be increased through the introduction of Mg doping in ZnO, as evidenced by previous research (Minemoto et al. 2000 ; Hsu et al. 2006 ). However, the engineering of the energy band gap and the Urbach parameter of ZnO is contingent upon the quantity of Mg dopant employed. Razooqi et al. ( 2021 ) demonstrated that the energy band gap of Mg-doped ZnO films with Mg concentrations ranging from 0 to 0.42 at% exhibited a variation between 3.26 eV and 3.82 eV. The energy band gap of a ZnO thin film increases with increasing Mg content; however, this increase is not linear (Mia et al. 2017 ; Huang et al. 2012 ). In contemporary practice, the use of two or more dopants in thin films or nanostructures allows for the modification of multiple physical properties of a compound in a simultaneous manner. Kumar et al. ( 2021 ) investigated the optical properties of a ZnO thin film with Mg and Se co-doping. In another literature, it was reported that magnesium can adjust the energy gap of a ZnO thin film in the range of 3.7 to 7.2 eV (Kim et al. 2008 ). Ivansyah et al. ( 2023 ) successfully synthesized a new photocatalyst of triple doped ZnO, namely Mg, Cu, N-doped ZnO and Mg, Cu, B-doped ZnO, through a solid-state method. The resulting materials exhibited promising antibacterial properties and photocatalytic activity. The proximity of the ionic radii of the dopants and the matrix material results in the formation of composites with minimal lattice distortion. The ionic radii of Mg 2+ (0.57 Å) and Cu 2+ (0.73 Å) are comparable to Zn 2+ (0.60 Å), indicating that the dopants can be readily substituted in the Zn lattice. It is therefore proposed that the addition of dopants at varying concentrations represents an effective method for adjusting the band gap in the ZnO lattice. Furthermore, it is important to note that the addition of a high concentration of dopants in ZnO leads to phase separation (Hu et al. 2016 ). In addition, the solubility of dopants in ZnO is a significant challenge, which can impact the composite's crystallinity (Pan et al. 2013 ). It is therefore important to control a number of parameters and dopant concentrations in order to obtain unique properties for use in photonics and optoelectronics applications (Chen et al. 2022 ; Asikuzun et al. 2018 ). In the electrochemical technique, the structural and optical properties of ZnO thin films doped with Mg and Cu are found to be dependent on a number of factors, including the current density, the time of current application, temperature, and the concentration of the dopants. Previous researchers have prepared ZnO, Mg-ZnO and Cu-ZnO thin films using a variety of techniques, as outlined in references (Asikuzun et al. 2018 ; Dabir et al. 2020 ; Heo et al. 2015 ; Minemoto et al. 2000 ; Hsu et al. 2006 ; Razooqi et al. 2021 ; Mia et al. 2017 ). Furthermore, the optical and structural properties of these films have been investigated. Nevertheless, the investigation of the properties of ZnO thin films with Cu and Mg co-doping prepared by the electrochemical technique has yet to be reported. The objective of this paper is to present the findings of an investigation into the properties of ZnO thin films doped with Mg and ZnO films co-doped with Mg and Cu. A thin film of Mg:ZnO (Mg: 3wt. %) was prepared as a control sample, and Cu:Mg:ZnO (Mg: 3 wt. % and Cu: 2, 3, 4 wt. %) thin films were prepared on the FTO glass substrate using the electrochemical technique. It is assumed that the temperature, time and density of the current applied to the prepared solutions are identical. The characterization of all samples was conducted using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and UV-Vis spectroscopy. The energy band gap, Urbach energy, and refractive indices of the samples were calculated and subjected to analysis. Experimental procedures 2.1 Sample preparation In this study, a Mg:ZnO thin film was prepared as a control sample, and Cu:Mg:ZnO films with varying weight percentages of Cu on FTO glass substrates were fabricated for comparison using the following method. To prepare the control sample, 2 g of zinc acetate (Zn(CH 3 COO) 2 -2H 2 O) (Merck-98%) as Zn precursor and 60 mg of magnesium acetate tetrahydrate (Mg(CH 3 COO) 2 -4H 2 O) (Merck-98%) as doping agent were dissolved in 100 ml of ethanol (Merc-98%). To prepare the remaining samples, copper nitrate trihydrate (Cu(NO3)2-3H2O) (Merck-98%) was added to the control sample solution at varying concentrations of 2 wt.%, 3 wt.%, and 4 wt.% of Zn. Subsequently, the solutions were subjected to ultrasound for a period of 20 min. Finally, the solutions were stirred for 2 hours at a temperature of 60°C using a magnetic stirrer in order to prepare a clear solution. The solutions were brought to a volume of 1000 ml and stirred again for a further 20 min. The FTO glass substrates (with a resistance of less than 7 Ω) were cut to a size of 2 cm × 2 cm and cleaned with acetone and ethanol in an ultrasonic bath for a period of 20 min. Two graphite electrodes were employed for the deposition of Mg:ZnO and Cu:Mg:ZnO composites on FTO glass substrates by the electrochemical method. In this context, the anode, cathode and ionic electrolyte are to be understood as the graphite electrode, the FTO glass and the solution, respectively. The schematic representation of the electrochemical synthesis is presented in Fig. 1 . A constant current density of 3.5 mA/cm² was applied to the electrodes by the power supply for a period of 20 min. By modifying the current density and the duration of the synthesis, it is possible to regulate the thickness of the films and the size of the grains. Subsequently, the prepared films were subjected to structural and optical characterization. The Mg:ZnO films were designated as ZM3, whereas the Cu-doped Mg:ZnO samples, ZM3C2 (2 wt. %), ZnM3C3 (3 wt. %) and ZM3C4 (4 wt. %), were designated ZM3C2, ZM3C3 and ZM3C4, respectively. 2.2 Analysis methodology Phase identification was conducted using X-ray diffraction (XRD) in a Philips PW1730 model with Ka-Cu radiation at λ = 1.5406 Å and the range of 2θ = 30–75º. This was employed to ascertain the structural properties of ZM3, ZM3C2, ZM3C3, and ZM3C4 films. The morphological properties of the manufactured films were examined using scanning electron microscopy (SEM) (Philips, model XL30). Fourier transform infrared spectroscopy (FTIR-Spectrum 400FT-IR/FIR) was employed to ascertain the functional group present in the films, operating within the wavenumber range of 400–4000 cm − 1 . The optical spectra of the films were recorded using a UV-Vis-Lambda 750 Perkin Elmer spectrophotometer in the wavelength range of 200–1100 nm. Results and discussion 3.1 Structural properties The preparation of Cu:Mg:ZnO films with various Cu-doping levels of 0, 2, 3, and 4 wt.% was confirmed by powder X-ray diffraction pattern using Cu-Ka radiation (λ = 1.54061 Å) at room temperature, as illustrated in Fig. 2 . The scattering of X-rays by different crystallographic planes resulted in the observation of peaks in the diffraction pattern, which indicates a successful synthesis of the films (Pan et al. 2013 ; Chen et al. 2022 ). By matching the relative intensity and diffraction angle of the created peaks with those of the JCPDS card, the structure of the thin films was confirmed to be free of any additional impurities for all the different weight percentages of the studied Cu. The peaks obtained in the XRD pattern at different 2θ angles indexed to the diffraction planes are listed in Table 1 . The diffraction peaks of Zn and Mg indicate a hexagonal wurtzite structure, with peak positions corresponding to JCPDS No. 01-087-0713 and 00-035-0821, respectively. The diffraction peaks (100), (101), (102), and (110) can be attributed to Zn with the hexagonal structure at 2θ = 38.7°, 43°, 54.4°, and 70.5°, respectively. The diffraction peaks (100) and (101) can be attributed to Mg, with a 2θ value of 32.3° and 36.6°, respectively. The Cu-doping process yielded a single peak at 43°, which aligns with the JCPDS standard No. 00-004-0836. The chemical reaction of the dopant affects the crystal growth kinetics, resulting in a decrease in diffraction peak intensity with an increase in the weight percentage of Cu dopant (Karunakaran et al. 2011 ). The reduction in intensity is attributed to the distortion of the crystalline lattice of Mg:ZnO caused by the Cu dopant. The intensity of the principal peak at approximately 43° progressively decreases, broadens, and shifts to lower values with increasing Cu dopant, as illustrated in Table 1 . This is due to the fact that the crystallinity of the Mg:ZnO films was found to decrease with the increase of Cu dopant, which resulted from the substitution of Cu 2+ into the Zn 2+ site (Yadav et al. 2016). The crystallite size (D) was calculated using the Scherer formula, based on the XRD data, as shown in Table 1 . The results demonstrate that the crystallite size decreases with the increase of Cu dopant levels, which is consistent with the aforementioned explanations. The crystallite size of the ZM3, ZM3C2, ZM3C3, and ZM3C4 films was determined to be 28.42 nm, 22.55 nm, 22.19 nm, and 19.20 nm, respectively. Table 1 Structural data of Mg:ZnO and Cu:Mg:ZnO films with different Cu concentrations Samples 2θ (°) β (°) D (nm) ZM3 43.24 0.34 28.42 ZM3C2 43.04 0.37 22.55 ZM3C3 43.10 0.38 22.19 ZM3C4 43.05 0.44 19.20 3.2 Surface morphological analysis A morphological study of Mg:ZnO and Cu:Mg:ZnO films was conducted using scanning electron microscopy (SEM) images. The objective was to investigate the size, shape, and size distribution of the grains. The average grain size was determined using the Image J software for more than 100 grains. The SEM images for Cu:Mg:ZnO films with varying Cu-doping levels (0, 2, 3, and 4 wt.%) are presented in Fig. 3 . The SEM images of composite films with varying Cu weight percentages reveal the presence of aggregated grains, a spherical morphology, and a homogeneous distribution of grains. The grain boundaries between grains are clearly defined in all samples. The grain size (d) was found to be 55.20, 36.43, 32.64, and 32.57 nm for the ZM3, ZM3C2, ZM3C3, and ZM3C4 films, respectively. The accumulation phenomenon in the ZM3C4 films is less pronounced than in the other samples. The formation of agglomerates of nanoparticles was observed in both Mg:ZnO and Cu:Mg:ZnO films. Nevertheless, the degree of agglomeration is greater for the Cu:Mg:ZnO films than for the Mg:ZnO films. The type of doped material and the different concentrations can affect the grain size and the growth process of the grains (Golshan et al. 2022 ). Given that the ionic charge of Zn 2+ and Mg 2+ is identical, and that Cu can assume an ionic charge of + 1 to + 3 (Cu + , Cu + 2 , Cu + 3 ), contingent on the weight percentage of doped Cu, it follows that the concentration of dopants may also exert an influence on particle growth (Mouritys et al. 2016 ). 3.3 Optical properties The investigation of the transmittance properties of Cu:Mg:ZnO thin films with varying Cu doping levels is of significant importance for a number of potential applications. Consequently, the optical properties of ZM3, ZM3C2, ZM3C3, and ZM3C4 films, including transmittance, band gap, and Urbach energy, were examined through the utilization of UV-Visible spectroscopy. Figure 4 shows the UV-Visible transmittance spectra of ZM3, ZM3C2, ZM3C3, and ZM3C4 films deposited by the electrochemical deposition method at a constant current density of 3.5 mA/cm². An increase in the concentration of Cu in the ZM3 film results in a reduction in transmittance, which in turn affects the direct band gap of Cu:Mg:ZnO films. The observed decrease in transmittance can be attributed to an increase in scattering caused by a reduction in grain size and film thickness (Tsay et al. 2013). As the grain size decreases, the number of grain boundaries rises, thereby increasing light scattering and reducing transmission (Nobbmann and Morfesis 2009 ; Gholizadeh Arashti and Fakharpour 2020 ). In this work, with the increase of Cu doping, the grain size is reduced compared to the wavelength of the irradiated light, as a result, the transmission is reduced. It has been demonstrated that all films exhibit high absorption in the ultraviolet region. However, it has also been observed that as the concentration of Cu in the film increases, the transmission of light in the visible and infrared regions decreases. The transmittance demonstrates an increase in the visible region (300–700 nm) and a subsequent decrease in the infrared region (750–1100 nm). The transmission spectra of the samples indicate that the absorption edge is approximately 300 nm for all samples. The substantial reduction in UV transmission observed in these films renders them suitable for use as protective coatings in optoelectronic devices (Zhang et al. 2016 ). \(\alpha =\frac{1}{t}\ln (1/T)\) The absorption coefficient (α) can be expressed from the following equation (Tauc 1970 ): (1) where t and T are the thickness and transmittance of ZM3, ZM3C2, ZM3C3, and ZM3C4 films, respectively. The direct band gap (E g ) of the films was obtained from the Tauc relationship (Tauc 1970 ): $$\alpha h\upsilon =\beta {\left( {h\upsilon - {E_g}} \right)^n}$$ 2 where β is a constant, h is the Planck’s constant, ν is the photon frequency, and n is ½ for direct band gap of semiconductor. Figure 5 a shows the Tauc plots for ZM3, ZM3C2, ZM3C3, and ZM3C4 films. The band gap is observed to decrease from 3.90 to 3.60 eV with an increase in the Cu content of the composite, from 0 to 4 wt.%. The reduction in the band gap can be attributed to the decline in optical absorption. The band gaps of MgO and ZnO semiconductors have been determined to be approximately 6.7 eV and 3.37 eV, respectively. The incorporation of Mg resulted in an expansion of the band gap of the ZnO film, which can be attributed to the high band gap of MgO. Consequently, the calculated band gap of the ZM3 film is approximately 3.9 eV, which is in accordance with the findings reported by Kaushal et al. (2009). Conversely, the band gap of the CuO film is approximately 1.48 eV (Gnatenko et al. 2023 ). Furthermore, Cu doping of ZnO results in a reduction of the band gap due to the low band gap of CuO (Nimbalkar and Patil 2017 ; Asikuzun e al. 2018). Consequently, the band gap of ZM3 composite films undergoes a red shift as the quantity of Cu is increased. In addition, the reduction in energy band gap observed in films with increasing Cu doping concentration can be attributed to the presence of localized states in the forbidden gap near the conduction band, which are a consequence of the dopants and lattice defects present (Martı́nezF et al. 1999; Vempati et al. 2012 ). The introduction of an impurity into the semiconductor material results in the formation of a band tail within the band gap. The width of the band tail is calculated from the inverse of the line slope of the ln(α) as a function of photon energy curve using the following equation (Caglar et al. 2011 ; Ilıcan et al. 2010 ): $$\alpha ={\alpha _0}+\exp \left( {\frac{{h\upsilon }}{{{E_u}}}} \right)$$ 3 where a 0 is a constant. Figure 5 b shows the ln(α) as function of photon energy curve. The Urbach energy of the films demonstrates an increase with increasing of Cu concentration in the composite, from 179 mV to 233 mV. The number of defects in the composite increases with rising Cu concentration in the composite, thereby raising the Urbach energy (Bindu and Thomas 2014 ). Furthermore, the Urbach energy is observed to increase with a reduction in crystallite and grain size, which is in accordance with the findings of the XRD pattern and SEM images presented in this study (Bindu and Thomas 2014 ; Speaks 2020 ). The steepness parameter (S) at a constant temperature has an inverse relationship with the Urbach energy and decreases with increasing Cu concentration, which is defined as follows: $${E_u}={\raise0.7ex\hbox{${{K_B}T}$} \!\mathord{\left/ {\vphantom {{{K_B}T} S}}\right.\kern-0pt}\!\lower0.7ex\hbox{$S$}}$$ 4 where K B is the Boltzmann constant and T is the temperature (300 K). Table 2 Optical data, thickness, and grain size of ZM3, ZM3C2, ZM3C3, and ZM3C4 films Sample Thickness (nm) Grain size (nm) E g (eV) E u (mev) Steepness parameter S × 10 − 2 ZM3 570 ± 5 55.20 3.9 180 1.43 ZM3C2 568 ± 6 36.43 3.72 179 1.44 ZM3C3 558 ± 5 32.64 3.61 193 1.33 ZM3C4 549 ± 4 32.57 3.60 233 1.10 3.4 FTIR analysis The FTIR spectra of Cu:Mg:ZnO thin films with various Cu-doping concentrations of 0, 2, 3, and 4 wt.%, in the range of 400–4000 cm − 1 is shown in Fig. 6 . The broad absorption bands observed at 3417, 3297, 3340 and 3320 cm − 1 for ZM3, ZM3C2, ZM3C3 and ZM3C4 are attributed to the stretching vibrational mode of the hydroxyl group. This is due to the absorption of water during the process of sample fabrication (Rahman et al. 2021 ). The weak peaks in the range of 1403 to 1492 cm − 1 all samples are related to the H–O–H bending vibrations. The peaks at 890, 894, 917, and 917 cm − 1 indicate metal stretching vibrations in the v 1 band for ZM3, ZM3C2, ZM3C3, and ZM3C4, respectively. The peaks also at 482, 478, 489, and 485 cm − 1 are responsible for metal stretching vibrations in the v 2 band for ZM3, ZM3C2, ZM3C3, and ZM3C4, respectively (Rosnan et al. 2016 ). 3.5 Optical constants The optical parameters of the synthesized samples of ZM3, ZM3C2, ZM3C3, and ZM3C4, including the refractive index n(ω) and extinction coefficient k(ω), were obtained using FTIR transmission spectrum data and Kramers–Kronig (K-K) relations. The details of the relations employed in this study are derived from references (Khorrami et al. 2012 ; Simmons and Potter 2000 ). The absorption can be calculated by employing Lambert's law in conjunction with the transmission (T) data. The reflection R(ω) values were obtained in terms of wavenumber from the equation R(ω) = 100-T(ω)-A(ω), which was derived from the data. The optical constants n(ω) and k(ω), respectively, are the real and imaginary parts of the complex refractive index derived as follows: $$n(\omega )=\frac{{1 - R(\omega )}}{{1+R(\omega ) - 2\sqrt {R(\omega )} \cos \varphi (\omega )}}$$ 5 $$k(\omega )=\frac{{ - 2\sqrt {R(\omega )} \sin \varphi (\omega )}}{{1+R(\omega ) - 2\sqrt {R(\omega )} \cos \varphi (\omega )}}$$ 6 The phase change between the incident and reflected beams, denoted by φ(ω), can be obtained from the K-K dispersion relation as follows (Lucarini et al. 2009 ): $$\varphi (\omega )=\frac{{ - \omega }}{\pi }\int\limits_{0}^{\infty } {\frac{{\ln R(\omega ^{\prime}) - \ln R(\omega )}}{{{{\omega ^{\prime}}^2} - {\omega ^2}}}d\omega ^{\prime}}$$ 7 Figure 7 shows n(ω) and k(ω) as a function of wavenumber for ZM3, ZM3C2, ZM3C3, and ZM3C4 films in the range of 400–4000 cm − 1 . The interaction of light with the atomic structure of materials becomes more evident at shorter wavelengths (higher wavenumber), which is why there are peaks in the n and k spectra as a function of the wavenumber. The synthesized composite, comprising three elements (Zn, Mg and Cu) with varying electronic structures and ionic radii, exhibits distinct interactions with light across different wavenumbers. Consequently, the formation of n peaks at varying wavenumbers is the result. The intensity of the n peaks has been observed to increase with the addition of Cu concentration in samples ZM3C3 and ZM3C4. A gradual shift was observed in the n peaks, which may be attributed to the disparity in ionic radius between Cu 2+ (0.73 Å), Mg 2+ (0.57 Å) and Zn 2+ (0.60 Å). Furthermore, the SEM images revealed that the grain sizes of composites ZM3C3 and ZM3C4 exhibited a slight discrepancy compared to ZM3 and ZM3C2. This could be another contributing factor to the observed increase in intensity and shift of the n peaks against wavenumber. The peaks of 505, 1080, 1666, 2341, and 3590 cm − 1 in the k plot indicate the absorption in these wavenumbers, which is consistent with the data obtained from the FTIR spectra. It can thus be concluded that the absorption in specific wavenumbers can be regulated and modified by increasing the concentration of Cu in the composite. The real ( ε 1 ) and imaginary parts ( ε 2 ) of the dielectric constants for the composite samples were obtained from the following relations (Omar 2011 ): $$\left\{ \begin{gathered} {\varepsilon _1}={n^2}(\omega ) - {k^2}(\omega ) \hfill \\ {\varepsilon _2}=2n(\omega )k(\omega ) \hfill \\ \end{gathered} \right.$$ 8 The real and imaginary parts of dielectric constants are shown in Fig. 8 . The real part of the dielectric constant, ε 1 , represents the capacity of the material to store electric energy in an electric field, which is directly correlated with the refractive index of the material. The absorption of light is markedly enhanced at wavenumbers of approximately 930 and 3500 cm⁻¹. This characteristic is of significant importance for applications involving capacitors and insulation. The values of ε 1 in the wavenumbers of approximately 520 and 3250 cm − 1 reach zero, indicating a transition in the material's behavior from dielectric to metal. The imaginary part of the dielectric constant, ε ₂ , is employed to quantify the energy loss within the material as a consequence of absorption when an electric field is applied. This characteristic is of particular significance in the context of optical device applications, where the minimization of absorption losses is a crucial consideration. The findings indicate that composite ZM3C3 exhibits the greatest energy storage capacity and the lowest energy loss in comparison to the other samples. Conclusion The objective of this study was to investigate the effect of the concentration of Mg (3 wt.%) and Cu (0 wt.%, 2 wt.%, 3 wt.%, and 4 wt.%) on the microstructural and optical properties of a ZnO thin film. The grain size obtained by SEM images decreased with increasing Cu concentration from 55.20 nm to 32.57 nm. The results of the UV–Vis spectroscopy demonstrated that all films exhibited high absorption in the ultraviolet region. Furthermore, the transmission of light was observed to decrease in the visible and infrared regions as the concentration of Cu increased. The band gap of the synthesized films showed a decrease from 3.90 eV to 3.60 eV, while the Urbach energy demonstrated an increase from 179 mV to 233 mV with an increase in Cu concentration from 0 to 4 wt.%. The optical constants were obtained through the utilization of FTIR spectra data and the application of K-K relations. The n peaks of films ZM3C3 and ZM3C4 exhibited a pronounced increase in comparison to the other samples. This phenomenon may be attributed to the discrepancy in grain size between the films and the ionic radii of the constituent elements. The real and imaginary parts of the dielectric constants of the films demonstrated that film ZM3C3 exhibits the highest energy storage capacity and the lowest energy loss. It can therefore be concluded that the doping of ZnO thin films with Mg and Cu at varying concentrations in order to control the band gap, storage and loss of light may prove to be a pivotal technique in the future of the optoelectronic industry. Declarations Research funding : This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Author contributions : The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Data availability : Data will be made available on request from the corresponding author. Conflict of interest : The authors declare no conflict of interest regarding this article. References Ahmaruzzaman, M., Raha, S.: ZnO nanostructured materials and their potential applications: Progress, Challenges and Perspectives. Nanoscale Advances. 4, (2022). https://doi.org/10.1039/d1na00880c Amakali, T., Daniel, L.S., Uahengo, V., Dzade, N.Y., Veikko, N.H. de: Structural and Optical Properties of ZnO Thin Films Prepared by Molecular Precursor and Sol–Gel Methods. Crystals. 10, 132–132 (2020). https://doi.org/10.3390/cryst10020132 Asikuzun, E., Ozturk, O., Arda, L., Terzioglu, C.: Preparation, growth and characterization of nonvacuum Cu-doped ZnO thin films. Journal of Molecular Structure. 1165, 1–7 (2018). https://doi.org/10.1016/j.molstruc.2018.03.053 Bindu, P., Thomas, S.: Estimation of lattice strain in ZnO nanoparticles: X-ray peak profile analysis. Journal of Theoretical and Applied Physics. 8, 123–134 (2014). https://doi.org/10.1007/s40094-014-0141-9 Caglar, Y., Caglar, M., Ilican, S.: Microstructural, optical and electrical studies on sol gel derived ZnO and ZnO:Al films. Current Applied Physics. 12, 963–968 (2011). https://doi.org/10.1016/j.cap.2011.12.017 Chen, L., Lü, S., Guo, W., Li, J., Wu, S.: High thermal conductivity of highly alloyed Mg-Zn-Cu alloy and its mechanism. Journal of Alloys and Compounds. 918, 165614–165614 (2022). https://doi.org/10.1016/j.jallcom.2022.165614 Dabir, F., Esfahani, H., Bakhtiargonbadi, F., Khodadadi, Z.: Study on microstructural and electro-optical properties of sol–gel derived pure and Al/Cu-doped ZnO thin films. Journal of Sol-Gel Science and Technology. 96, 529–538 (2020). https://doi.org/10.1007/s10971-020-05269-0 Fakharpour, M., Babaei, F., Savaloni, H.: Engineering Mn as Tetragonal-Like Helical Sculptured Thin Film for Broadband Absorption. Plasmonics. 11, 1579–1587 (2016). https://doi.org/10.1007/s11468-016-0213-6 Fakharpour, M., Karimi Tafti, M.H.: The energy band gap of the manganese oxide pyramidal nanostructures. Journal of Modern Optics. 69, 911–916 (2022). https://doi.org/10.1080/09500340.2022.2095050 Fakharpour, M., Savaloni, H.: Fabrication of graded helical square tower-like Mn sculptured thin films and investigation of their electrical properties: comparison with perturbation theory. Iranian physical journal. 11, 109–117 (2017). https://doi.org/10.1007/s40094-017-0242-3 Gholizadeh Arashti , M., Fakharpour, M.: Theoretical investigation of optical properties of Aluminum zig-zag thin films. Journal of Nanoanalysis. 10, 415–427 (2023). https://doi.org/10.22034/jna.2020.1907296.1226 Gholizadeh Arashti, M., Fakharpour, M.: Fabrication and characterization of Al/glass zig-zag thin film, comparing to the discrete dipole approximation results. The European Physical Journal B. 93, (2020). https://doi.org/10.1140/epjb/e2020-100581-0 Gnatenko, Yu.P., Bukivskij, P.M., Gamernyk, R.V., Yevdokymenko, V.Yu., Opanasyuk, A.S., Bukivskii, A.P., Furyer, M.S., Tarakhan, L.M.: Study of optical and photoelectric properties of copper oxide films. Materials Chemistry and Physics. 307, 128175–128175 (2023). https://doi.org/10.1016/j.matchemphys.2023.128175 Goktas, A., Aslan, F., Yeşilata, B., Boz, İ.: Physical properties of solution processable n-type Fe and Al co-doped ZnO nanostructured thin films: Role of Al doping levels and annealing. Materials Science in Semiconductor Processing. 75, 221–233 (2018). https://doi.org/10.1016/j.mssp.2017.11.033 Golshan, V., Mirjalili, F., Fakharpour, M.: Self-Cleaning Surfaces with Superhydrophobicity of Ag–TiO2 Nanofilms on the Floor Ceramic Tiles. Glass Physics and Chemistry. 48, 35–42 (2022). https://doi.org/10.1134/s1087659622010059 Heo, S., Cho, E., Lee, H.-I., Park, G.S., Kang, H.J., Nagatomi, T., Choi, P., Choi, B.-D.: Band gap and defect states of MgO thin films investigated using reflection electron energy loss spectroscopy. AIP Advances. 5, 077167 (2015). https://doi.org/10.1063/1.4927547 Hsu, H.-C., Wu, C.-Y., Cheng, H.-M., Hsieh, W.-F.: Band gap engineering and stimulated emission of ZnMgO nanowires. Applied Physics Letters. 89, 013101 (2006). https://doi.org/10.1063/1.2218813 Hu, Y., Zeng, H., Du, J., Hu, Z., Zhang, S.: The structural, electrical and optical properties of Mg-doped ZnO with different interstitial Mg concentration. Materials Chemistry and Physics. 182, 15–21 (2016). https://doi.org/10.1016/j.matchemphys.2016.05.065 Huang, K., Tang, Z., Zhang, L., Yu, J., Lv, J., Liu, X., Liu, F.: Preparation and characterization of Mg-doped ZnO thin films by sol–gel method. Applied surface science. 258, 3710–3713 (2012). https://doi.org/10.1016/j.apsusc.2011.12.011 Ilıcan, S., Çağlar, M., Çağlar, Y.: Sn doping effects on the electro-optical properties of sol gel derived transparent ZnO films. Applied Surface Science. 256, 7204–7210 (2010). https://doi.org/10.1016/j.apsusc.2010.05.052 Ivansyah, A.L., Amelia, S.R., Rohmatulloh, Y., Sanusi, N., Listiani, P., Ichikawa, Y., Honda, M., Sudiarti, T.: Insight into novel triple doping (Mg, Cu, N and Mg, Cu, B) on the structural, optical, photocatalytic, and antibacterial properties of ZnO. Colloids and Surfaces A Physicochemical and Engineering Aspects. 678, 132454–132454 (2023). https://doi.org/10.1016/j.colsurfa.2023.132454 Karimi Tafti, M.H., Fakharpour, M.: Optical Properties of NiO Columnar Nanostructure Prepared by OAD Technique. Journal of Optoelectronical Nanostructures. 8, 51–67 (2023). https://doi.org/10.30495/jopn.2023.31332.1277 Karunakaran, C., Rajeswari, V., Gomathisankar, P.: Combustion synthesis of ZnO and Ag-doped ZnO and their bactericidal and photocatalytic activities. Superlattices and Microstructures. 50, 234–241 (2011). https://doi.org/10.1016/j.spmi.2011.06.005 Kaushal, A., Kaur, D.: Effect of Mg content on structural, electrical and optical properties of Zn1−xMgxO nanocomposite thin films. Solar Energy Materials and Solar Cells. 93, 193–198 (2009). https://doi.org/10.1016/j.solmat.2008.09.039 Khorrami, Gh.H., Khorsand Zak, A., Kompany, A., yousefi, R.: Optical and structural properties of X-doped (X=Mn, Mg, and Zn) PZT nanoparticles by Kramers–Kronig and size strain plot methods. Ceramics International. 38, 5683–5690 (2012). https://doi.org/10.1016/j.ceramint.2012.04.012 Kim, T.H., Park, J.J., Nam, S.H., Park, H.S., Cheong, N.R., Song, J.K., Park, S.M.: Fabrication of Mg-doped ZnO thin films by laser ablation of Zn:Mg target. Applied Surface Science. 255, 5264–5266 (2008). https://doi.org/10.1016/j.apsusc.2008.07.105 Kumar, P., Dev, S., Singh Dhayal, S., Acharya, V., Kumar, S., Kumar, S., Singh, N., Dhar, R.: Synergistic effect of Mg and Se co-doping on the structural, optical and anti-bacterial activity of ZnO thin films. Inorganic Chemistry Communications. 131, 108801 (2021). https://doi.org/10.1016/j.inoche.2021.108801 Kumaresan, S., Vallalperuman, K., Sathishkumar, S., Karthik, M., SivaKarthik, P.: Synthesis and systematic investigations of Al and Cu-doped ZnO nanoparticles and its structural, optical and photo-catalytic properties. Journal of Materials Science Materials in Electronics. 28, 9199–9205 (2017). https://doi.org/10.1007/s10854-017-6654-7 Lucarini, V., Saarinen, J.J., Peiponen, K.-E., Vartiainen, E.M.: Kramers-Kronig Relations in Optical Materials Research. Springer (2009) Maqsood, S., Ali, Z., Ali, K., Ishaq, M., Sajid, M., Farhan, A., Rahdar, A., Pandey, S.: Assessment of different optimized anti-reflection coatings for ZnO/Si heterojunction solar cells. Ceramics International. 49, 37118–37126 (2023). https://doi.org/10.1016/j.ceramint.2023.08.313 Martı́nezF.L., del Prado, A., Mártil, I., González-Dı́azG., Selle, B., Sieber, I.: Thermally induced changes in the optical properties of SiNx:H films deposited by the electron cyclotron resonance plasma method. Journal of Applied Physics. 86, 2055–2061 (1999). https://doi.org/10.1063/1.371008 Mia, M.N.H., Pervez, M.F., Hossain, M.K., Reefaz Rahman, M., Uddin, M.J., Al Mashud, M.A., Ghosh, H.K., Hoq, M.: Influence of Mg content on tailoring optical bandgap of Mg-doped ZnO thin film prepared by sol-gel method. Results in Physics. 7, 2683–2691 (2017). https://doi.org/10.1016/j.rinp.2017.07.047 Minemoto, T., Negami, T., Nishiwaki, S., Takakura, H., Hamakawa, Y.: Preparation of Zn1−xMgxO films by radio frequency magnetron sputtering. Thin Solid Films. 372, 173–176 (2000). https://doi.org/10.1016/s0040-6090(00)01009-9 Mouritys, I., Byzynski, G., Ribeiro, C., Longo, E.: Different dye degradation mechanisms for ZnO and ZnO doped with N (ZnO:N). Journal of Molecular Catalysis A-chemical. 417, 89–100 (2016). https://doi.org/10.1016/j.molcata.2016.02.027 Nimbalkar, A.R., Patil, M.G.: Synthesis of highly selective and sensitive Cu-doped ZnO thin film sensor for detection of H 2 S gas. Materials Science in Semiconductor Processing. 71, 332–341 (2017). https://doi.org/10.1016/j.mssp.2017.08.022 Nobbmann, U., Morfesis, A.: Light scattering and nanoparticles. Materials Today. 12, 52–54 (2009). https://doi.org/10.1016/s1369-7021(09)70164-6 Noman, M.T., Amor, N., Petru, M.: Synthesis and applications of ZnO nanostructures (ZONSs): a review. Critical Reviews in Solid State and Materials Sciences. 47, 99–141 (2021). https://doi.org/10.1080/10408436.2021.1886041 Omar, M.A.: Elementary solid state physics (英文影印版) : principles and applications / Elementary solid state physics (ying wen ying yin ban) : principles and applications. Beijing World Publishing Corporation, Beijing (2011) Pan, H., Pan, F., Wang, X., Peng, J., She, J., Zhao, C., Huang, Q., Song, K., Gao, Z.: High conductivity and high strength Mg–Zn–Cu alloy. Materials Science and Technology. 30, 759–764 (2013). https://doi.org/10.1179/1743284713y.0000000400 Rahman, A., Tan, A.L., Harunsani, M.H., Ahmad, N., Hojamberdiev, M., Khan, M.M.: Visible light induced antibacterial and antioxidant studies of ZnO and Cu-doped ZnO fabricated using aqueous leaf extract of Ziziphus mauritiana Lam. Journal of Environmental Chemical Engineering. 9, 105481–105481 (2021). https://doi.org/10.1016/j.jece.2021.105481 Rashid, T.M., Nayef, U.M., Jabir, M.S., Mutlak, F.A.-H. .: Synthesis and characterization of Au:ZnO (core:shell) nanoparticles via laser ablation. Optik. 244, 167569–167569 (2021). https://doi.org/10.1016/j.ijleo.2021.167569 Razooqi, M.A., Koirala, P., Phillips, A.B., Liyanage, G.K., Awni, R.A., Sapkota, D.R., Ramanujam, B., Heben, M.J., O’Leary, S.K., Podraza, N.J., Collins, R.W.: Optical Properties of Magnesium-Zinc Oxide for Thin Film Photovoltaics. Materials. 14, 5649–5649 (2021). https://doi.org/10.3390/ma14195649 Rosnan, R.M., Othaman, Z., Hussin, R., Ati, A.A., Samavati, A., Dabagh, S., Zare, S.: Effects of Mg substitution on the structural and magnetic properties of Co 0.5 Ni 0.5− x Mg x Fe 2 O 4 nanoparticle ferrites. Chinese Physics B. 25, 047501 (2016). https://doi.org/10.1088/1674-1056/25/4/047501 Saha, J.K., Bukke, R.N., Mude, N.N., Jang, J.: Significant improvement of spray pyrolyzed ZnO thin film by precursor optimization for high mobility thin film transistors. Scientific Reports. 10, (2020). https://doi.org/10.1038/s41598-020-65938-6 Simmons, J.H., Potter, K.S.: Optical materials. Academic Press, San Diego (2000) Sowmya, K., Aparna, Y., Chendra Prakash, A., Thotakura, R., Bhaskar, A.: Influence of Metal (Al, Mg, Sm, and Cu) Dopants on Structural, Optical, Magnetic, and Antimicrobial Properties of ZnO Nanopowders Synthesized by Coprecipitation Method. physica status solidi (a). 221, (2023). https://doi.org/10.1002/pssa.202300628 Speaks, D.T.: Effect of concentration, aging, and annealing on sol gel ZnO and Al-doped ZnO thin films. International Journal of Mechanical and Materials Engineering. 15, (2020). https://doi.org/10.1186/s40712-019-0113-6 Tamulevičius, T., Laurikėnas, P., Juodėnas, M., Mardosaitė, R., Abakevičienė, B., Pereyra, C.J., Račkauskas, S.: Antireflection Coatings Based on Randomly Oriented ZnO Nanowires. Solar RRL. 7, (2023). https://doi.org/10.1002/solr.202201056 Tauc, J.: Absorption edge and internal electric fields in amorphous semiconductors. Materials Research Bulletin. 5, 721–729 (1970). https://doi.org/10.1016/0025-5408(70)90112-1 Tsay, C.-Y., Lee, W.-C.: Effect of dopants on the structural, optical and electrical properties of sol–gel derived ZnO semiconductor thin films. Current Applied Physics. 13, 60–65 (2013). https://doi.org/10.1016/j.cap.2012.06.010 Vempati, S., Mitra, J., Dawson, P.: One-step synthesis of ZnO nanosheets: a blue-white fluorophore. Nanoscale Research Letters. 7, (2012). https://doi.org/10.1186/1556-276x-7-470 Vyas, S.: A Short Review on Properties and Applications of Zinc Oxide Based Thin Films and Devices : ZnO as a promising material for applications in electronics, optoelectronics, biomedical and sensors. Johnson Matthey Technology Review. 64, 202–218 (2020). https://doi.org/10.1595/205651320x15694993568524 Yadav, A., Varshney, D.: Structural and Dielectric Properties of Copper-Substituted Mg–Zn Spinel Ferrites. Journal of Superconductivity and Novel Magnetism. 30, 1297–1302 (2016). https://doi.org/10.1007/s10948-016-3931-2 Zhang, Q., Zhao, Y., Jia, Z., Qin, Z., Chu, L., Yang, J., Zhang, J., Huang, W., Li, X.: High Stable, Transparent and Conductive ZnO/Ag/ZnO Nanofilm Electrodes on Rigid/Flexible Substrates. Energies. 9, 443 (2016). https://doi.org/10.3390/en9060443 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 17 Jan, 2025 Read the published version in Optical and Quantum Electronics → Version 1 posted Editorial decision: Revision requested 06 Nov, 2024 Reviews received at journal 06 Nov, 2024 Reviews received at journal 02 Nov, 2024 Reviews received at journal 27 Oct, 2024 Reviewers agreed at journal 19 Oct, 2024 Reviewers agreed at journal 16 Oct, 2024 Reviewers agreed at journal 15 Oct, 2024 Reviewers agreed at journal 14 Oct, 2024 Reviewers agreed at journal 14 Oct, 2024 Reviewers invited by journal 14 Oct, 2024 Editor assigned by journal 09 Oct, 2024 Submission checks completed at journal 08 Oct, 2024 First submitted to journal 08 Oct, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5223491","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":375030882,"identity":"4d767ffa-dba8-4c18-b0c1-8f2643fa4bde","order_by":0,"name":"Mahsa fakharpour","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABDklEQVRIiWNgGAWjYFACHhAhxyAhAeXzMzCwEaPFGKFFsoFkLQYHCGjRbT97+MMPBgN5ydnNzz4XVBzON76R/OzBhwoGeX6xA1i1mJ3JS5PsYTAwnC1zzHj2jDOHLbfdSDM3nHGGwXDm7ATsWg7kmAHd9odxnkSCMTNv22EDsxsJZtK8bQwJBrdxaDn/xvjjHwYD+3kS6Z/BWoxnpH/Dr+VGjoE0D4NB4myJHIgtBhI5BGy58cZMWsbAIHnmjJxi5hln0g0kzrwpk5xxRgK3X87nGH98U2FgO+NG+mbmggprA/729G0SHyps5PmlsWuBAAMIxQwmBcAqJXCpRQUQLfwHiFM9CkbBKBgFIwYAAKpvWOGj/EJEAAAAAElFTkSuQmCC","orcid":"","institution":"Islamic Azad University Maybod","correspondingAuthor":true,"prefix":"","firstName":"Mahsa","middleName":"","lastName":"fakharpour","suffix":""}],"badges":[],"createdAt":"2024-10-08 08:38:27","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5223491/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5223491/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11082-024-07994-0","type":"published","date":"2025-01-17T15:56:55+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":69924258,"identity":"4dadf2c4-0aac-453b-a8c3-d21d30378084","added_by":"auto","created_at":"2024-11-26 16:03:16","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":184702,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic representation for the fabrication of Mg:ZnO and Cu:Mg:ZnO films with different Cu concentrations\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-5223491/v1/32ebdbc068ed25fd5d93b1e0.png"},{"id":69923088,"identity":"f3fcc32a-ad6f-4a15-959f-123f3b4fd2f6","added_by":"auto","created_at":"2024-11-26 15:47:16","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":115332,"visible":true,"origin":"","legend":"\u003cp\u003eXRD Patterns of pure and Cu-doped Mg:ZnO films at different doping concentrations\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-5223491/v1/999eaa403e48b54e93c9aa3c.png"},{"id":69923090,"identity":"77e3d8b3-e381-4a13-8bb0-5a88b2a9ee93","added_by":"auto","created_at":"2024-11-26 15:47:16","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":532824,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of \u003cstrong\u003ea\u003c/strong\u003e ZM3, \u003cstrong\u003eb\u003c/strong\u003e ZM3C2, \u003cstrong\u003ec\u003c/strong\u003e ZM3C3, and \u003cstrong\u003ed\u003c/strong\u003eZM3C4 films\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-5223491/v1/890281b8f779d5dc0ad2a8ef.png"},{"id":69924259,"identity":"cc2b5805-2c44-48a1-94fb-dcb0e89a246a","added_by":"auto","created_at":"2024-11-26 16:03:16","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":189415,"visible":true,"origin":"","legend":"\u003cp\u003eUV-Visible transmittance spectra of ZM3, ZM3C2, ZM3C3, and ZM3C4 films\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-5223491/v1/1aeac13ed22c36fc8a214960.png"},{"id":69923093,"identity":"9e0ce650-70b8-4279-8db4-ac44cbe9a8b3","added_by":"auto","created_at":"2024-11-26 15:47:16","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":264339,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e Band gap and \u003cstrong\u003eb\u003c/strong\u003e Urbach energy curves of ZM3, ZM3C2, ZM3C3, and ZM3C4 films\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-5223491/v1/5bebf29e913524e3ef570199.png"},{"id":69923089,"identity":"abe47092-0d52-4b42-b198-fd8f86ed5fad","added_by":"auto","created_at":"2024-11-26 15:47:16","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":295056,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of ZM3, ZM3C2, ZM3C3, and ZM3C4 films\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-5223491/v1/0f74a7ef757cdfdec8b3e3ed.png"},{"id":69923961,"identity":"bd069f4b-9dee-4154-8354-b148721eda69","added_by":"auto","created_at":"2024-11-26 15:55:16","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":323624,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e refractive index and \u003cstrong\u003eb\u003c/strong\u003e extinction coefficient of ZM3, ZM3C2, ZM3C3, and ZM3C4 films\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-5223491/v1/94553da57434dfa646d7dc55.png"},{"id":69923964,"identity":"b2678e50-7fa4-4241-8c2e-8dd24b60ca2d","added_by":"auto","created_at":"2024-11-26 15:55:16","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":327379,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e Real part and \u003cstrong\u003eb\u003c/strong\u003e imaginary part of dielectric constant of ZM3, ZM3C2, ZM3C3, and ZM3C4 films\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-5223491/v1/45a557e701d07ad4d3e0932f.png"},{"id":74284444,"identity":"2c3c1e0a-dbef-4f8a-8a60-4ff5dcae6870","added_by":"auto","created_at":"2025-01-20 16:05:29","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2877675,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5223491/v1/3c8e80d5-6a81-4abc-ad6b-850a9c968cb5.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Influence of Cu content on optical spectra of Cu/Mg co-doped ZnO films by Kramers–Kronig","fulltext":[{"header":"Introduction","content":"\u003cp\u003eZinc oxide is an n-type semiconductor in the II-VI group, exhibiting high mobility and crystallinity, as well as excellent mechanical properties and transparency in the visible region. Its energy band gap is 3.37 eV (Nimbalkar and Patil \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Due to its distinctive properties, ZnO is employed in a variety of commercial applications, including displays, optoelectronic devices, antireflection coatings, transistors, solar cells, light-emitting diodes, and others (Vyas \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Ahmaruzzaman and Raha \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Maqsood et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Saha et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). A number of researchers have devised various techniques for the preparation of zinc oxide thin films (Noman et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2021\u003c/span\u003e;\u003c/p\u003e \u003cp\u003eTamulevičius et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Amakali et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Rashid et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The electrochemical method offers several advantages over other methods, including simplicity, cost-effectiveness, and the ability to create homogeneous films with controlled grain size. The electrochemical method allows for the alteration of composite morphology, distribution, and grain size during synthesis, thereby enabling the customization of samples to satisfy specific properties for a range of applications.\u003c/p\u003e \u003cp\u003eThe incorporation of metal dopants, including Al, Mg, Cu, and Fe, has been demonstrated to enhance the optical, electrical, and mechanical properties of ZnO thin films (Goktas et al.2018; Sowmya et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Kumaresan et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The various techniques, including sol-gel, sputtering, chemical vapor deposition, and electro-deposition, have been presented as methods for the addition of dopants to nanostructures and thin films. Among the various doping techniques employed in ZnO, Cu doping has been shown to enhance the properties of ZnO due to the small difference in atomic radius between Cu and ZnO, as well as the proper substitution of Cu atoms within the atomic lattice of ZnO. Consequently, Cu doping can influence the optical properties of ZnO films, including the band gap, absorption, and photoluminescence. In our previous research, we have demonstrated that the optical properties of the films undergo changes in response to alterations in the morphology of the nanostructure during the deposition process (Fakharpour and Karimi 2022; Fakharpour and Savaloni \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Fakharpour et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Gholizadeh and Fakharpour 2023). Recently, some literature has been published on the modification of the optical band gap and optical properties of ZnO films by Cu doping (Karimi Tafti and Fakharpour \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Asikuzun et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2018\u003c/span\u003e)]. Nevertheless, an increase in the concentration of Cu dopants in ZnO results in a reduction in the transparency of the film in the visible region. However, the optical band gap of Cu-doped ZnO thin films is observed to decrease, while the Urbach energy increases (Asikuzun et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). In a related study, Debir et al. (2020) developed ZnO films doped with Al and Cu using the sol-gel method. The findings revealed that the size of ZnO particles not only increases with Al and Cu doping, but also that the energy band gap and photoluminescence properties of ZnO films decrease.\u003c/p\u003e \u003cp\u003eThe incorporation of Mg and Cu dopants markedly enhances the electro-optical characteristics of ZnO. The atomic radius of Mg is also similar to that of ZnO. However, Mg doping in the ZnO lattice and substitution of the Mg ion with the Zn ion results in lattice distortion. The innovative application of Mg doping in ZnO has resulted in its extensive utilization in optoelectronic and electronic devices. The energy band gap of MgO is 7.8 eV (Heo et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), while the transition region of ZnO films can be increased through the introduction of Mg doping in ZnO, as evidenced by previous research (Minemoto et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Hsu et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). However, the engineering of the energy band gap and the Urbach parameter of ZnO is contingent upon the quantity of Mg dopant employed. Razooqi et al. (\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) demonstrated that the energy band gap of Mg-doped ZnO films with Mg concentrations ranging from 0 to 0.42 at% exhibited a variation between 3.26 eV and 3.82 eV. The energy band gap of a ZnO thin film increases with increasing Mg content; however, this increase is not linear (Mia et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Huang et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). In contemporary practice, the use of two or more dopants in thin films or nanostructures allows for the modification of multiple physical properties of a compound in a simultaneous manner. Kumar et al. (\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) investigated the optical properties of a ZnO thin film with Mg and Se co-doping. In another literature, it was reported that magnesium can adjust the energy gap of a ZnO thin film in the range of 3.7 to 7.2 eV (Kim et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Ivansyah et al. (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) successfully synthesized a new photocatalyst of triple doped ZnO, namely Mg, Cu, N-doped ZnO and Mg, Cu, B-doped ZnO, through a solid-state method. The resulting materials exhibited promising antibacterial properties and photocatalytic activity. The proximity of the ionic radii of the dopants and the matrix material results in the formation of composites with minimal lattice distortion. The ionic radii of Mg\u003csup\u003e2+\u003c/sup\u003e (0.57 \u0026Aring;) and Cu\u003csup\u003e2+\u003c/sup\u003e (0.73 \u0026Aring;) are comparable to Zn\u003csup\u003e2+\u003c/sup\u003e (0.60 \u0026Aring;), indicating that the dopants can be readily substituted in the Zn lattice. It is therefore proposed that the addition of dopants at varying concentrations represents an effective method for adjusting the band gap in the ZnO lattice. Furthermore, it is important to note that the addition of a high concentration of dopants in ZnO leads to phase separation (Hu et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). In addition, the solubility of dopants in ZnO is a significant challenge, which can impact the composite's crystallinity (Pan et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). It is therefore important to control a number of parameters and dopant concentrations in order to obtain unique properties for use in photonics and optoelectronics applications (Chen et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Asikuzun et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the electrochemical technique, the structural and optical properties of ZnO thin films doped with Mg and Cu are found to be dependent on a number of factors, including the current density, the time of current application, temperature, and the concentration of the dopants. Previous researchers have prepared ZnO, Mg-ZnO and Cu-ZnO thin films using a variety of techniques, as outlined in references (Asikuzun et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Dabir et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Heo et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Minemoto et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Hsu et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Razooqi et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Mia et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Furthermore, the optical and structural properties of these films have been investigated. Nevertheless, the investigation of the properties of ZnO thin films with Cu and Mg co-doping prepared by the electrochemical technique has yet to be reported. The objective of this paper is to present the findings of an investigation into the properties of ZnO thin films doped with Mg and ZnO films co-doped with Mg and Cu. A thin film of Mg:ZnO (Mg: 3wt. %) was prepared as a control sample, and Cu:Mg:ZnO (Mg: 3 wt. % and Cu: 2, 3, 4 wt. %) thin films were prepared on the FTO glass substrate using the electrochemical technique. It is assumed that the temperature, time and density of the current applied to the prepared solutions are identical. The characterization of all samples was conducted using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and UV-Vis spectroscopy. The energy band gap, Urbach energy, and refractive indices of the samples were calculated and subjected to analysis.\u003c/p\u003e"},{"header":"Experimental procedures","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Sample preparation\u003c/h2\u003e \u003cp\u003eIn this study, a Mg:ZnO thin film was prepared as a control sample, and Cu:Mg:ZnO films with varying weight percentages of Cu on FTO glass substrates were fabricated for comparison using the following method. To prepare the control sample, 2 g of zinc acetate (Zn(CH\u003csub\u003e3\u003c/sub\u003eCOO)\u003csub\u003e2\u003c/sub\u003e-2H\u003csub\u003e2\u003c/sub\u003eO) (Merck-98%) as Zn precursor and 60 mg of magnesium acetate tetrahydrate (Mg(CH\u003csub\u003e3\u003c/sub\u003eCOO)\u003csub\u003e2\u003c/sub\u003e-4H\u003csub\u003e2\u003c/sub\u003eO) (Merck-98%) as doping agent were dissolved in 100 ml of ethanol (Merc-98%). To prepare the remaining samples, copper nitrate trihydrate (Cu(NO3)2-3H2O) (Merck-98%) was added to the control sample solution at varying concentrations of 2 wt.%, 3 wt.%, and 4 wt.% of Zn. Subsequently, the solutions were subjected to ultrasound for a period of 20 min. Finally, the solutions were stirred for 2 hours at a temperature of 60\u0026deg;C using a magnetic stirrer in order to prepare a clear solution. The solutions were brought to a volume of 1000 ml and stirred again for a further 20 min.\u003c/p\u003e \u003cp\u003eThe FTO glass substrates (with a resistance of less than 7 Ω) were cut to a size of 2 cm \u0026times; 2 cm and cleaned with acetone and ethanol in an ultrasonic bath for a period of 20 min. Two graphite electrodes were employed for the deposition of Mg:ZnO and Cu:Mg:ZnO composites on FTO glass substrates by the electrochemical method. In this context, the anode, cathode and ionic electrolyte are to be understood as the graphite electrode, the FTO glass and the solution, respectively. The schematic representation of the electrochemical synthesis is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. A constant current density of 3.5 mA/cm\u0026sup2; was applied to the electrodes by the power supply for a period of 20 min. By modifying the current density and the duration of the synthesis, it is possible to regulate the thickness of the films and the size of the grains. Subsequently, the prepared films were subjected to structural and optical characterization. The Mg:ZnO films were designated as ZM3, whereas the Cu-doped Mg:ZnO samples, ZM3C2 (2 wt. %), ZnM3C3 (3 wt. %) and ZM3C4 (4 wt. %), were designated ZM3C2, ZM3C3 and ZM3C4, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Analysis methodology\u003c/h2\u003e \u003cp\u003ePhase identification was conducted using X-ray diffraction (XRD) in a Philips PW1730 model with Ka-Cu radiation at λ\u0026thinsp;=\u0026thinsp;1.5406 \u0026Aring; and the range of 2θ\u0026thinsp;=\u0026thinsp;30\u0026ndash;75\u0026ordm;. This was employed to ascertain the structural properties of ZM3, ZM3C2, ZM3C3, and ZM3C4 films. The morphological properties of the manufactured films were examined using scanning electron microscopy (SEM) (Philips, model XL30). Fourier transform infrared spectroscopy (FTIR-Spectrum 400FT-IR/FIR) was employed to ascertain the functional group present in the films, operating within the wavenumber range of 400\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The optical spectra of the films were recorded using a UV-Vis-Lambda 750 Perkin Elmer spectrophotometer in the wavelength range of 200\u0026ndash;1100 nm.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Structural properties\u003c/h2\u003e \u003cp\u003eThe preparation of Cu:Mg:ZnO films with various Cu-doping levels of 0, 2, 3, and 4 wt.% was confirmed by powder X-ray diffraction pattern using Cu-Ka radiation (λ\u0026thinsp;=\u0026thinsp;1.54061 \u0026Aring;) at room temperature, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The scattering of X-rays by different crystallographic planes resulted in the observation of peaks in the diffraction pattern, which indicates a successful synthesis of the films (Pan et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Chen et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). By matching the relative intensity and diffraction angle of the created peaks with those of the JCPDS card, the structure of the thin films was confirmed to be free of any additional impurities for all the different weight percentages of the studied Cu. The peaks obtained in the XRD pattern at different 2θ angles indexed to the diffraction planes are listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The diffraction peaks of Zn and Mg indicate a hexagonal wurtzite structure, with peak positions corresponding to JCPDS No. 01-087-0713 and 00-035-0821, respectively. The diffraction peaks (100), (101), (102), and (110) can be attributed to Zn with the hexagonal structure at 2θ\u0026thinsp;=\u0026thinsp;38.7\u0026deg;, 43\u0026deg;, 54.4\u0026deg;, and 70.5\u0026deg;, respectively. The diffraction peaks (100) and (101) can be attributed to Mg, with a 2θ value of 32.3\u0026deg; and 36.6\u0026deg;, respectively. The Cu-doping process yielded a single peak at 43\u0026deg;, which aligns with the JCPDS standard No. 00-004-0836. The chemical reaction of the dopant affects the crystal growth kinetics, resulting in a decrease in diffraction peak intensity with an increase in the weight percentage of Cu dopant (Karunakaran et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). The reduction in intensity is attributed to the distortion of the crystalline lattice of Mg:ZnO caused by the Cu dopant. The intensity of the principal peak at approximately 43\u0026deg; progressively decreases, broadens, and shifts to lower values with increasing Cu dopant, as illustrated in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. This is due to the fact that the crystallinity of the Mg:ZnO films was found to decrease with the increase of Cu dopant, which resulted from the substitution of Cu\u003csup\u003e2+\u003c/sup\u003e into the Zn\u003csup\u003e2+\u003c/sup\u003e site (Yadav et al. 2016). The crystallite size (D) was calculated using the Scherer formula, based on the XRD data, as shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The results demonstrate that the crystallite size decreases with the increase of Cu dopant levels, which is consistent with the aforementioned explanations. The crystallite size of the ZM3, ZM3C2, ZM3C3, and ZM3C4 films was determined to be 28.42 nm, 22.55 nm, 22.19 nm, and 19.20 nm, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eStructural data of Mg:ZnO and Cu:Mg:ZnO films with different Cu concentrations\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2θ (\u0026deg;)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eβ (\u0026deg;)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eD (nm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZM3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e43.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e28.42\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZM3C2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e43.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e22.55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZM3C3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e43.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e22.19\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZM3C4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e43.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e19.20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Surface morphological analysis\u003c/h2\u003e \u003cp\u003eA morphological study of Mg:ZnO and Cu:Mg:ZnO films was conducted using scanning electron microscopy (SEM) images. The objective was to investigate the size, shape, and size distribution of the grains. The average grain size was determined using the Image J software for more than 100 grains. The SEM images for Cu:Mg:ZnO films with varying Cu-doping levels (0, 2, 3, and 4 wt.%) are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The SEM images of composite films with varying Cu weight percentages reveal the presence of aggregated grains, a spherical morphology, and a homogeneous distribution of grains. The grain boundaries between grains are clearly defined in all samples. The grain size (d) was found to be 55.20, 36.43, 32.64, and 32.57 nm for the ZM3, ZM3C2, ZM3C3, and ZM3C4 films, respectively. The accumulation phenomenon in the ZM3C4 films is less pronounced than in the other samples. The formation of agglomerates of nanoparticles was observed in both Mg:ZnO and Cu:Mg:ZnO films. Nevertheless, the degree of agglomeration is greater for the Cu:Mg:ZnO films than for the Mg:ZnO films. The type of doped material and the different concentrations can affect the grain size and the growth process of the grains (Golshan et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Given that the ionic charge of Zn\u003csup\u003e2+\u003c/sup\u003e and Mg\u003csup\u003e2+\u003c/sup\u003e is identical, and that Cu can assume an ionic charge of +\u0026thinsp;1 to +\u0026thinsp;3 (Cu\u003csup\u003e+\u003c/sup\u003e, Cu\u003csup\u003e+\u0026thinsp;2\u003c/sup\u003e, Cu\u003csup\u003e+\u0026thinsp;3\u003c/sup\u003e), contingent on the weight percentage of doped Cu, it follows that the concentration of dopants may also exert an influence on particle growth (Mouritys et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Optical properties\u003c/h2\u003e \u003cp\u003eThe investigation of the transmittance properties of Cu:Mg:ZnO thin films with varying Cu doping levels is of significant importance for a number of potential applications. Consequently, the optical properties of ZM3, ZM3C2, ZM3C3, and ZM3C4 films, including transmittance, band gap, and Urbach energy, were examined through the utilization of UV-Visible spectroscopy. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the UV-Visible transmittance spectra of ZM3, ZM3C2, ZM3C3, and ZM3C4 films deposited by the electrochemical deposition method at a constant current density of 3.5 mA/cm\u0026sup2;. An increase in the concentration of Cu in the ZM3 film results in a reduction in transmittance, which in turn affects the direct band gap of Cu:Mg:ZnO films. The observed decrease in transmittance can be attributed to an increase in scattering caused by a reduction in grain size and film thickness (Tsay et al. 2013). As the grain size decreases, the number of grain boundaries rises, thereby increasing light scattering and reducing transmission (Nobbmann and Morfesis \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Gholizadeh Arashti and Fakharpour \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). In this work, with the increase of Cu doping, the grain size is reduced compared to the wavelength of the irradiated light, as a result, the transmission is reduced. It has been demonstrated that all films exhibit high absorption in the ultraviolet region. However, it has also been observed that as the concentration of Cu in the film increases, the transmission of light in the visible and infrared regions decreases. The transmittance demonstrates an increase in the visible region (300\u0026ndash;700 nm) and a subsequent decrease in the infrared region (750\u0026ndash;1100 nm). The transmission spectra of the samples indicate that the absorption edge is approximately 300 nm for all samples. The substantial reduction in UV transmission observed in these films renders them suitable for use as protective coatings in optoelectronic devices (Zhang et al. \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\alpha =\\frac{1}{t}\\ln (1/T)\\)\u003c/span\u003e \u003c/span\u003eThe absorption coefficient (α) can be expressed from the following equation (Tauc \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e1970\u003c/span\u003e):\u003c/p\u003e \u003cp\u003e(1)\u003c/p\u003e \u003cp\u003ewhere t and T are the thickness and transmittance of ZM3, ZM3C2, ZM3C3, and ZM3C4 films, respectively.\u003c/p\u003e \u003cp\u003eThe direct band gap (E\u003csub\u003eg\u003c/sub\u003e) of the films was obtained from the Tauc relationship (Tauc \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e1970\u003c/span\u003e):\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\alpha h\\upsilon =\\beta {\\left( {h\\upsilon - {E_g}} \\right)^n}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere β is a constant, h is the Planck\u0026rsquo;s constant, ν is the photon frequency, and n is \u0026frac12; for direct band gap of semiconductor. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea shows the Tauc plots for ZM3, ZM3C2, ZM3C3, and ZM3C4 films. The band gap is observed to decrease from 3.90 to 3.60 eV with an increase in the Cu content of the composite, from 0 to 4 wt.%. The reduction in the band gap can be attributed to the decline in optical absorption. The band gaps of MgO and ZnO semiconductors have been determined to be approximately 6.7 eV and 3.37 eV, respectively. The incorporation of Mg resulted in an expansion of the band gap of the ZnO film, which can be attributed to the high band gap of MgO. Consequently, the calculated band gap of the ZM3 film is approximately 3.9 eV, which is in accordance with the findings reported by Kaushal et al. (2009). Conversely, the band gap of the CuO film is approximately 1.48 eV (Gnatenko et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Furthermore, Cu doping of ZnO results in a reduction of the band gap due to the low band gap of CuO (Nimbalkar and Patil \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Asikuzun e al. 2018). Consequently, the band gap of ZM3 composite films undergoes a red shift as the quantity of Cu is increased. In addition, the reduction in energy band gap observed in films with increasing Cu doping concentration can be attributed to the presence of localized states in the forbidden gap near the conduction band, which are a consequence of the dopants and lattice defects present (Martı́nezF et al. 1999; Vempati et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe introduction of an impurity into the semiconductor material results in the formation of a band tail within the band gap. The width of the band tail is calculated from the inverse of the line slope of the ln(α) as a function of photon energy curve using the following equation (Caglar et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2011\u003c/span\u003e;\u003c/p\u003e \u003cp\u003eIlıcan et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2010\u003c/span\u003e):\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\alpha ={\\alpha _0}+\\exp \\left( {\\frac{{h\\upsilon }}{{{E_u}}}} \\right)$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003ea\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e is a constant. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb shows the ln(α) as function of photon energy curve. The Urbach energy of the films demonstrates an increase with increasing of Cu concentration in the composite, from 179 mV to 233 mV. The number of defects in the composite increases with rising Cu concentration in the composite, thereby raising the Urbach energy (Bindu and Thomas \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Furthermore, the Urbach energy is observed to increase with a reduction in crystallite and grain size, which is in accordance with the findings of the XRD pattern and SEM images presented in this study (Bindu and Thomas \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Speaks \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe steepness parameter (S) at a constant temperature has an inverse relationship with the Urbach energy and decreases with increasing Cu concentration, which is defined as follows:\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$${E_u}={\\raise0.7ex\\hbox{${{K_B}T}$} \\!\\mathord{\\left/ {\\vphantom {{{K_B}T} S}}\\right.\\kern-0pt}\\!\\lower0.7ex\\hbox{$S$}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere K\u003csub\u003eB\u003c/sub\u003e is the Boltzmann constant and T is the temperature (300 K).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eOptical data, thickness, and grain size of ZM3, ZM3C2, ZM3C3, and ZM3C4 films\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eThickness (nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGrain size (nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eE\u003csub\u003eg\u003c/sub\u003e (eV)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eE\u003csub\u003eu\u003c/sub\u003e (mev)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSteepness\u003c/p\u003e \u003cp\u003eparameter\u003c/p\u003e \u003cp\u003eS \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZM3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e570\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e55.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.43\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZM3C2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e568\u0026thinsp;\u0026plusmn;\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e36.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.72\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e179\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.44\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZM3C3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e558\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e32.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e193\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.33\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZM3C4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e549\u0026thinsp;\u0026plusmn;\u0026thinsp;4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e32.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e233\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.4 FTIR analysis\u003c/h2\u003e \u003cp\u003eThe FTIR spectra of Cu:Mg:ZnO thin films with various Cu-doping concentrations of 0, 2, 3, and 4 wt.%, in the range of 400\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The broad absorption bands observed at 3417, 3297, 3340 and 3320 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for ZM3, ZM3C2, ZM3C3 and ZM3C4 are attributed to the stretching vibrational mode of the hydroxyl group. This is due to the absorption of water during the process of sample fabrication (Rahman et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The weak peaks in the range of 1403 to 1492 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e all samples are related to the H\u0026ndash;O\u0026ndash;H bending vibrations. The peaks at 890, 894, 917, and 917 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e indicate metal stretching vibrations in the v\u003csub\u003e1\u003c/sub\u003e band for ZM3, ZM3C2, ZM3C3, and ZM3C4, respectively. The peaks also at 482, 478, 489, and 485 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are responsible for metal stretching vibrations in the v\u003csub\u003e2\u003c/sub\u003e band for ZM3, ZM3C2, ZM3C3, and ZM3C4, respectively (Rosnan et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Optical constants\u003c/h2\u003e \u003cp\u003eThe optical parameters of the synthesized samples of ZM3, ZM3C2, ZM3C3, and ZM3C4, including the refractive index n(ω) and extinction coefficient k(ω), were obtained using FTIR transmission spectrum data and Kramers\u0026ndash;Kronig (K-K) relations. The details of the relations employed in this study are derived from references (Khorrami et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Simmons and Potter \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2000\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe absorption can be calculated by employing Lambert's law in conjunction with the transmission (T) data. The reflection R(ω) values were obtained in terms of wavenumber from the equation R(ω)\u0026thinsp;=\u0026thinsp;100-T(ω)-A(ω), which was derived from the data. The optical constants n(ω) and k(ω), respectively, are the real and imaginary parts of the complex refractive index derived as follows:\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$n(\\omega )=\\frac{{1 - R(\\omega )}}{{1+R(\\omega ) - 2\\sqrt {R(\\omega )} \\cos \\varphi (\\omega )}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ5\" name=\"EquationSource\"\u003e\n$$k(\\omega )=\\frac{{ - 2\\sqrt {R(\\omega )} \\sin \\varphi (\\omega )}}{{1+R(\\omega ) - 2\\sqrt {R(\\omega )} \\cos \\varphi (\\omega )}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e6\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe phase change between the incident and reflected beams, denoted by φ(ω), can be obtained from the K-K dispersion relation as follows (Lucarini et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2009\u003c/span\u003e):\u003cdiv id=\"Equ6\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ6\" name=\"EquationSource\"\u003e\n$$\\varphi (\\omega )=\\frac{{ - \\omega }}{\\pi }\\int\\limits_{0}^{\\infty } {\\frac{{\\ln R(\\omega ^{\\prime}) - \\ln R(\\omega )}}{{{{\\omega ^{\\prime}}^2} - {\\omega ^2}}}d\\omega ^{\\prime}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e7\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e shows n(ω) and k(ω) as a function of wavenumber for ZM3, ZM3C2, ZM3C3, and ZM3C4 films in the range of 400\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The interaction of light with the atomic structure of materials becomes more evident at shorter wavelengths (higher wavenumber), which is why there are peaks in the n and k spectra as a function of the wavenumber. The synthesized composite, comprising three elements (Zn, Mg and Cu) with varying electronic structures and ionic radii, exhibits distinct interactions with light across different wavenumbers. Consequently, the formation of n peaks at varying wavenumbers is the result. The intensity of the n peaks has been observed to increase with the addition of Cu concentration in samples ZM3C3 and ZM3C4. A gradual shift was observed in the n peaks, which may be attributed to the disparity in ionic radius between Cu\u003csup\u003e2+\u003c/sup\u003e (0.73 \u0026Aring;), Mg\u003csup\u003e2+\u003c/sup\u003e (0.57 \u0026Aring;) and Zn\u003csup\u003e2+\u003c/sup\u003e (0.60 \u0026Aring;). Furthermore, the SEM images revealed that the grain sizes of composites ZM3C3 and ZM3C4 exhibited a slight discrepancy compared to ZM3 and ZM3C2. This could be another contributing factor to the observed increase in intensity and shift of the n peaks against wavenumber. The peaks of 505, 1080, 1666, 2341, and 3590 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the k plot indicate the absorption in these wavenumbers, which is consistent with the data obtained from the FTIR spectra. It can thus be concluded that the absorption in specific wavenumbers can be regulated and modified by increasing the concentration of Cu in the composite.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe real (\u003cem\u003eε\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e) and imaginary parts (\u003cem\u003eε\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e) of the dielectric constants for the composite samples were obtained from the following relations (Omar \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2011\u003c/span\u003e):\u003cdiv id=\"Equ7\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ7\" name=\"EquationSource\"\u003e\n$$\\left\\{ \\begin{gathered} {\\varepsilon _1}={n^2}(\\omega ) - {k^2}(\\omega ) \\hfill \\\\ {\\varepsilon _2}=2n(\\omega )k(\\omega ) \\hfill \\\\ \\end{gathered} \\right.$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e8\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe real and imaginary parts of dielectric constants are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. The real part of the dielectric constant, ε\u003csub\u003e1\u003c/sub\u003e, represents the capacity of the material to store electric energy in an electric field, which is directly correlated with the refractive index of the material. The absorption of light is markedly enhanced at wavenumbers of approximately 930 and 3500 cm⁻\u0026sup1;. This characteristic is of significant importance for applications involving capacitors and insulation. The values of ε\u003csub\u003e1\u003c/sub\u003e in the wavenumbers of approximately 520 and 3250 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e reach zero, indicating a transition in the material's behavior from dielectric to metal. The imaginary part of the dielectric constant, ε\u003csub\u003e₂\u003c/sub\u003e, is employed to quantify the energy loss within the material as a consequence of absorption when an electric field is applied. This characteristic is of particular significance in the context of optical device applications, where the minimization of absorption losses is a crucial consideration. The findings indicate that composite ZM3C3 exhibits the greatest energy storage capacity and the lowest energy loss in comparison to the other samples.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":" \u003cp\u003eThe objective of this study was to investigate the effect of the concentration of Mg (3 wt.%) and Cu (0 wt.%, 2 wt.%, 3 wt.%, and 4 wt.%) on the microstructural and optical properties of a ZnO thin film. The grain size obtained by SEM images decreased with increasing Cu concentration from 55.20 nm to 32.57 nm. The results of the UV\u0026ndash;Vis spectroscopy demonstrated that all films exhibited high absorption in the ultraviolet region. Furthermore, the transmission of light was observed to decrease in the visible and infrared regions as the concentration of Cu increased. The band gap of the synthesized films showed a decrease from 3.90 eV to 3.60 eV, while the Urbach energy demonstrated an increase from 179 mV to 233 mV with an increase in Cu concentration from 0 to 4 wt.%. The optical constants were obtained through the utilization of FTIR spectra data and the application of K-K relations. The n peaks of films ZM3C3 and ZM3C4 exhibited a pronounced increase in comparison to the other samples. This phenomenon may be attributed to the discrepancy in grain size between the films and the ionic radii of the constituent elements. The real and imaginary parts of the dielectric constants of the films demonstrated that film ZM3C3 exhibits the highest energy storage capacity and the lowest energy loss. It can therefore be concluded that the doping of ZnO thin films with Mg and Cu at varying concentrations in order to control the band gap, storage and loss of light may prove to be a pivotal technique in the future of the optoelectronic industry.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eResearch funding\u003c/strong\u003e: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e: The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e: Data will be made available on request from the corresponding author.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e: The authors declare no conflict of interest regarding this article.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAhmaruzzaman, M., Raha, S.: ZnO nanostructured materials and their potential applications: Progress, Challenges and Perspectives. Nanoscale Advances. 4, (2022). https://doi.org/10.1039/d1na00880c\u003c/li\u003e\n\u003cli\u003eAmakali, T., Daniel, L.S., Uahengo, V., Dzade, N.Y., Veikko, N.H. de: Structural and Optical Properties of ZnO Thin Films Prepared by Molecular Precursor and Sol\u0026ndash;Gel Methods. Crystals. 10, 132\u0026ndash;132 (2020). https://doi.org/10.3390/cryst10020132\u003c/li\u003e\n\u003cli\u003eAsikuzun, E., Ozturk, O., Arda, L., Terzioglu, C.: Preparation, growth and characterization of nonvacuum Cu-doped ZnO thin films. Journal of Molecular Structure. 1165, 1\u0026ndash;7 (2018). https://doi.org/10.1016/j.molstruc.2018.03.053\u003c/li\u003e\n\u003cli\u003eBindu, P., Thomas, S.: Estimation of lattice strain in ZnO nanoparticles: X-ray peak profile analysis. Journal of Theoretical and Applied Physics. 8, 123\u0026ndash;134 (2014). https://doi.org/10.1007/s40094-014-0141-9\u003c/li\u003e\n\u003cli\u003eCaglar, Y., Caglar, M., Ilican, S.: Microstructural, optical and electrical studies on sol gel derived ZnO and ZnO:Al films. Current Applied Physics. 12, 963\u0026ndash;968 (2011). https://doi.org/10.1016/j.cap.2011.12.017\u003c/li\u003e\n\u003cli\u003eChen, L., L\u0026uuml;, S., Guo, W., Li, J., Wu, S.: High thermal conductivity of highly alloyed Mg-Zn-Cu alloy and its mechanism. Journal of Alloys and Compounds. 918, 165614\u0026ndash;165614 (2022). https://doi.org/10.1016/j.jallcom.2022.165614\u003c/li\u003e\n\u003cli\u003eDabir, F., Esfahani, H., Bakhtiargonbadi, F., Khodadadi, Z.: Study on microstructural and electro-optical properties of sol\u0026ndash;gel derived pure and Al/Cu-doped ZnO thin films. Journal of Sol-Gel Science and Technology. 96, 529\u0026ndash;538 (2020). https://doi.org/10.1007/s10971-020-05269-0\u003c/li\u003e\n\u003cli\u003eFakharpour, M., Babaei, F., Savaloni, H.: Engineering Mn as Tetragonal-Like Helical Sculptured Thin Film for Broadband Absorption. Plasmonics. 11, 1579\u0026ndash;1587 (2016). https://doi.org/10.1007/s11468-016-0213-6\u003c/li\u003e\n\u003cli\u003eFakharpour, M., Karimi Tafti, M.H.: The energy band gap of the manganese oxide pyramidal nanostructures. Journal of Modern Optics. 69, 911\u0026ndash;916 (2022). https://doi.org/10.1080/09500340.2022.2095050\u003c/li\u003e\n\u003cli\u003eFakharpour, M., Savaloni, H.: Fabrication of graded helical square tower-like Mn sculptured thin films and investigation of their electrical properties: comparison with perturbation theory. Iranian physical journal. 11, 109\u0026ndash;117 (2017). https://doi.org/10.1007/s40094-017-0242-3\u003c/li\u003e\n\u003cli\u003eGholizadeh Arashti , M., Fakharpour, M.: Theoretical investigation of optical properties of Aluminum zig-zag thin films. Journal of Nanoanalysis. 10, 415\u0026ndash;427 (2023). https://doi.org/10.22034/jna.2020.1907296.1226\u003c/li\u003e\n\u003cli\u003eGholizadeh Arashti, M., Fakharpour, M.: Fabrication and characterization of Al/glass zig-zag thin film, comparing to the discrete dipole approximation results. The European Physical Journal B. 93, (2020). https://doi.org/10.1140/epjb/e2020-100581-0\u003c/li\u003e\n\u003cli\u003eGnatenko, Yu.P., Bukivskij, P.M., Gamernyk, R.V., Yevdokymenko, V.Yu., Opanasyuk, A.S., Bukivskii, A.P., Furyer, M.S., Tarakhan, L.M.: Study of optical and photoelectric properties of copper oxide films. Materials Chemistry and Physics. 307, 128175\u0026ndash;128175 (2023). https://doi.org/10.1016/j.matchemphys.2023.128175\u003c/li\u003e\n\u003cli\u003eGoktas, A., Aslan, F., Yeşilata, B., Boz, İ.: Physical properties of solution processable n-type Fe and Al co-doped ZnO nanostructured thin films: Role of Al doping levels and annealing. Materials Science in Semiconductor Processing. 75, 221\u0026ndash;233 (2018). https://doi.org/10.1016/j.mssp.2017.11.033\u003c/li\u003e\n\u003cli\u003eGolshan, V., Mirjalili, F., Fakharpour, M.: Self-Cleaning Surfaces with Superhydrophobicity of Ag\u0026ndash;TiO2 Nanofilms on the Floor Ceramic Tiles. Glass Physics and Chemistry. 48, 35\u0026ndash;42 (2022). https://doi.org/10.1134/s1087659622010059\u003c/li\u003e\n\u003cli\u003eHeo, S., Cho, E., Lee, H.-I., Park, G.S., Kang, H.J., Nagatomi, T., Choi, P., Choi, B.-D.: Band gap and defect states of MgO thin films investigated using reflection electron energy loss spectroscopy. AIP Advances. 5, 077167 (2015). https://doi.org/10.1063/1.4927547\u003c/li\u003e\n\u003cli\u003eHsu, H.-C., Wu, C.-Y., Cheng, H.-M., Hsieh, W.-F.: Band gap engineering and stimulated emission of ZnMgO nanowires. Applied Physics Letters. 89, 013101 (2006). https://doi.org/10.1063/1.2218813\u003c/li\u003e\n\u003cli\u003eHu, Y., Zeng, H., Du, J., Hu, Z., Zhang, S.: The structural, electrical and optical properties of Mg-doped ZnO with different interstitial Mg concentration. Materials Chemistry and Physics. 182, 15\u0026ndash;21 (2016). https://doi.org/10.1016/j.matchemphys.2016.05.065\u003c/li\u003e\n\u003cli\u003eHuang, K., Tang, Z., Zhang, L., Yu, J., Lv, J., Liu, X., Liu, F.: Preparation and characterization of Mg-doped ZnO thin films by sol\u0026ndash;gel method. Applied surface science. 258, 3710\u0026ndash;3713 (2012). https://doi.org/10.1016/j.apsusc.2011.12.011\u003c/li\u003e\n\u003cli\u003eIlıcan, S., \u0026Ccedil;ağlar, M., \u0026Ccedil;ağlar, Y.: Sn doping effects on the electro-optical properties of sol gel derived transparent ZnO films. Applied Surface Science. 256, 7204\u0026ndash;7210 (2010). https://doi.org/10.1016/j.apsusc.2010.05.052\u003c/li\u003e\n\u003cli\u003eIvansyah, A.L., Amelia, S.R., Rohmatulloh, Y., Sanusi, N., Listiani, P., Ichikawa, Y., Honda, M., Sudiarti, T.: Insight into novel triple doping (Mg, Cu, N and Mg, Cu, B) on the structural, optical, photocatalytic, and antibacterial properties of ZnO. Colloids and Surfaces A Physicochemical and Engineering Aspects. 678, 132454\u0026ndash;132454 (2023). https://doi.org/10.1016/j.colsurfa.2023.132454\u003c/li\u003e\n\u003cli\u003eKarimi Tafti, M.H., Fakharpour, M.: Optical Properties of NiO Columnar Nanostructure Prepared by OAD Technique. Journal of Optoelectronical Nanostructures. 8, 51\u0026ndash;67 (2023). https://doi.org/10.30495/jopn.2023.31332.1277\u003c/li\u003e\n\u003cli\u003eKarunakaran, C., Rajeswari, V., Gomathisankar, P.: Combustion synthesis of ZnO and Ag-doped ZnO and their bactericidal and photocatalytic activities. Superlattices and Microstructures. 50, 234\u0026ndash;241 (2011). https://doi.org/10.1016/j.spmi.2011.06.005\u003c/li\u003e\n\u003cli\u003eKaushal, A., Kaur, D.: Effect of Mg content on structural, electrical and optical properties of Zn1\u0026minus;xMgxO nanocomposite thin films. Solar Energy Materials and Solar Cells. 93, 193\u0026ndash;198 (2009). https://doi.org/10.1016/j.solmat.2008.09.039\u003c/li\u003e\n\u003cli\u003eKhorrami, Gh.H., Khorsand Zak, A., Kompany, A., yousefi, R.: Optical and structural properties of X-doped (X=Mn, Mg, and Zn) PZT nanoparticles by Kramers\u0026ndash;Kronig and size strain plot methods. Ceramics International. 38, 5683\u0026ndash;5690 (2012). https://doi.org/10.1016/j.ceramint.2012.04.012\u003c/li\u003e\n\u003cli\u003eKim, T.H., Park, J.J., Nam, S.H., Park, H.S., Cheong, N.R., Song, J.K., Park, S.M.: Fabrication of Mg-doped ZnO thin films by laser ablation of Zn:Mg target. Applied Surface Science. 255, 5264\u0026ndash;5266 (2008). https://doi.org/10.1016/j.apsusc.2008.07.105\u003c/li\u003e\n\u003cli\u003eKumar, P., Dev, S., Singh Dhayal, S., Acharya, V., Kumar, S., Kumar, S., Singh, N., Dhar, R.: Synergistic effect of Mg and Se co-doping on the structural, optical and anti-bacterial activity of ZnO thin films. Inorganic Chemistry Communications. 131, 108801 (2021). https://doi.org/10.1016/j.inoche.2021.108801\u003c/li\u003e\n\u003cli\u003eKumaresan, S., Vallalperuman, K., Sathishkumar, S., Karthik, M., SivaKarthik, P.: Synthesis and systematic investigations of Al and Cu-doped ZnO nanoparticles and its structural, optical and photo-catalytic properties. Journal of Materials Science Materials in Electronics. 28, 9199\u0026ndash;9205 (2017). https://doi.org/10.1007/s10854-017-6654-7\u003c/li\u003e\n\u003cli\u003eLucarini, V., Saarinen, J.J., Peiponen, K.-E., Vartiainen, E.M.: Kramers-Kronig Relations in Optical Materials Research. Springer (2009)\u003c/li\u003e\n\u003cli\u003eMaqsood, S., Ali, Z., Ali, K., Ishaq, M., Sajid, M., Farhan, A., Rahdar, A., Pandey, S.: Assessment of different optimized anti-reflection coatings for ZnO/Si heterojunction solar cells. Ceramics International. 49, 37118\u0026ndash;37126 (2023). https://doi.org/10.1016/j.ceramint.2023.08.313\u003c/li\u003e\n\u003cli\u003eMartı́nezF.L., del Prado, A., M\u0026aacute;rtil, I., Gonz\u0026aacute;lez-Dı́azG., Selle, B., Sieber, I.: Thermally induced changes in the optical properties of SiNx:H films deposited by the electron cyclotron resonance plasma method. Journal of Applied Physics. 86, 2055\u0026ndash;2061 (1999). https://doi.org/10.1063/1.371008\u003c/li\u003e\n\u003cli\u003eMia, M.N.H., Pervez, M.F., Hossain, M.K., Reefaz Rahman, M., Uddin, M.J., Al Mashud, M.A., Ghosh, H.K., Hoq, M.: Influence of Mg content on tailoring optical bandgap of Mg-doped ZnO thin film prepared by sol-gel method. Results in Physics. 7, 2683\u0026ndash;2691 (2017). https://doi.org/10.1016/j.rinp.2017.07.047\u003c/li\u003e\n\u003cli\u003eMinemoto, T., Negami, T., Nishiwaki, S., Takakura, H., Hamakawa, Y.: Preparation of Zn1\u0026minus;xMgxO films by radio frequency magnetron sputtering. Thin Solid Films. 372, 173\u0026ndash;176 (2000). https://doi.org/10.1016/s0040-6090(00)01009-9\u003c/li\u003e\n\u003cli\u003eMouritys, I., Byzynski, G., Ribeiro, C., Longo, E.: Different dye degradation mechanisms for ZnO and ZnO doped with N (ZnO:N). Journal of Molecular Catalysis A-chemical. 417, 89\u0026ndash;100 (2016). https://doi.org/10.1016/j.molcata.2016.02.027\u003c/li\u003e\n\u003cli\u003eNimbalkar, A.R., Patil, M.G.: Synthesis of highly selective and sensitive Cu-doped ZnO thin film sensor for detection of H 2 S gas. Materials Science in Semiconductor Processing. 71, 332\u0026ndash;341 (2017). https://doi.org/10.1016/j.mssp.2017.08.022\u003c/li\u003e\n\u003cli\u003eNobbmann, U., Morfesis, A.: Light scattering and nanoparticles. Materials Today. 12, 52\u0026ndash;54 (2009). https://doi.org/10.1016/s1369-7021(09)70164-6\u003c/li\u003e\n\u003cli\u003eNoman, M.T., Amor, N., Petru, M.: Synthesis and applications of ZnO nanostructures (ZONSs): a review. Critical Reviews in Solid State and Materials Sciences. 47, 99\u0026ndash;141 (2021). https://doi.org/10.1080/10408436.2021.1886041\u003c/li\u003e\n\u003cli\u003eOmar, M.A.: Elementary solid state physics (英文影印版) : principles and applications / Elementary solid state physics (ying wen ying yin ban) : principles and applications. Beijing World Publishing Corporation, Beijing (2011)\u003c/li\u003e\n\u003cli\u003ePan, H., Pan, F., Wang, X., Peng, J., She, J., Zhao, C., Huang, Q., Song, K., Gao, Z.: High conductivity and high strength Mg\u0026ndash;Zn\u0026ndash;Cu alloy. Materials Science and Technology. 30, 759\u0026ndash;764 (2013). https://doi.org/10.1179/1743284713y.0000000400\u003c/li\u003e\n\u003cli\u003eRahman, A., Tan, A.L., Harunsani, M.H., Ahmad, N., Hojamberdiev, M., Khan, M.M.: Visible light induced antibacterial and antioxidant studies of ZnO and Cu-doped ZnO fabricated using aqueous leaf extract of Ziziphus mauritiana Lam. Journal of Environmental Chemical Engineering. 9, 105481\u0026ndash;105481 (2021). https://doi.org/10.1016/j.jece.2021.105481\u003c/li\u003e\n\u003cli\u003eRashid, T.M., Nayef, U.M., Jabir, M.S., Mutlak, F.A.-H. .: Synthesis and characterization of Au:ZnO (core:shell) nanoparticles via laser ablation. Optik. 244, 167569\u0026ndash;167569 (2021). https://doi.org/10.1016/j.ijleo.2021.167569\u003c/li\u003e\n\u003cli\u003eRazooqi, M.A., Koirala, P., Phillips, A.B., Liyanage, G.K., Awni, R.A., Sapkota, D.R., Ramanujam, B., Heben, M.J., O\u0026rsquo;Leary, S.K., Podraza, N.J., Collins, R.W.: Optical Properties of Magnesium-Zinc Oxide for Thin Film Photovoltaics. Materials. 14, 5649\u0026ndash;5649 (2021). https://doi.org/10.3390/ma14195649\u003c/li\u003e\n\u003cli\u003eRosnan, R.M., Othaman, Z., Hussin, R., Ati, A.A., Samavati, A., Dabagh, S., Zare, S.: Effects of Mg substitution on the structural and magnetic properties of Co \u003csub\u003e0.5\u003c/sub\u003e Ni \u003csub\u003e0.5\u0026minus; \u003cem\u003ex\u003c/em\u003e \u003c/sub\u003eMg \u003cem\u003e\u003csub\u003ex\u003c/sub\u003e\u003c/em\u003e\u003csub\u003e \u003c/sub\u003eFe \u003csub\u003e2\u003c/sub\u003e O \u003csub\u003e4\u003c/sub\u003e nanoparticle ferrites. Chinese Physics B. 25, 047501 (2016). https://doi.org/10.1088/1674-1056/25/4/047501\u003c/li\u003e\n\u003cli\u003eSaha, J.K., Bukke, R.N., Mude, N.N., Jang, J.: Significant improvement of spray pyrolyzed ZnO thin film by precursor optimization for high mobility thin film transistors. Scientific Reports. 10, (2020). https://doi.org/10.1038/s41598-020-65938-6\u003c/li\u003e\n\u003cli\u003eSimmons, J.H., Potter, K.S.: Optical materials. Academic Press, San Diego (2000)\u003c/li\u003e\n\u003cli\u003eSowmya, K., Aparna, Y., Chendra Prakash, A., Thotakura, R., Bhaskar, A.: Influence of Metal (Al, Mg, Sm, and Cu) Dopants on Structural, Optical, Magnetic, and Antimicrobial Properties of ZnO Nanopowders Synthesized by Coprecipitation Method. physica status solidi (a). 221, (2023). https://doi.org/10.1002/pssa.202300628\u003c/li\u003e\n\u003cli\u003eSpeaks, D.T.: Effect of concentration, aging, and annealing on sol gel ZnO and Al-doped ZnO thin films. International Journal of Mechanical and Materials Engineering. 15, (2020). https://doi.org/10.1186/s40712-019-0113-6\u003c/li\u003e\n\u003cli\u003eTamulevičius, T., Laurikėnas, P., Juodėnas, M., Mardosaitė, R., Abakevičienė, B., Pereyra, C.J., Račkauskas, S.: Antireflection Coatings Based on Randomly Oriented ZnO Nanowires. Solar RRL. 7, (2023). https://doi.org/10.1002/solr.202201056\u003c/li\u003e\n\u003cli\u003eTauc, J.: Absorption edge and internal electric fields in amorphous semiconductors. Materials Research Bulletin. 5, 721\u0026ndash;729 (1970). https://doi.org/10.1016/0025-5408(70)90112-1\u003c/li\u003e\n\u003cli\u003eTsay, C.-Y., Lee, W.-C.: Effect of dopants on the structural, optical and electrical properties of sol\u0026ndash;gel derived ZnO semiconductor thin films. Current Applied Physics. 13, 60\u0026ndash;65 (2013). https://doi.org/10.1016/j.cap.2012.06.010\u003c/li\u003e\n\u003cli\u003eVempati, S., Mitra, J., Dawson, P.: One-step synthesis of ZnO nanosheets: a blue-white fluorophore. Nanoscale Research Letters. 7, (2012). https://doi.org/10.1186/1556-276x-7-470\u003c/li\u003e\n\u003cli\u003eVyas, S.: A Short Review on Properties and Applications of Zinc Oxide Based Thin Films and Devices : ZnO as a promising material for applications in electronics, optoelectronics, biomedical and sensors. Johnson Matthey Technology Review. 64, 202\u0026ndash;218 (2020). https://doi.org/10.1595/205651320x15694993568524\u003c/li\u003e\n\u003cli\u003eYadav, A., Varshney, D.: Structural and Dielectric Properties of Copper-Substituted Mg\u0026ndash;Zn Spinel Ferrites. Journal of Superconductivity and Novel Magnetism. 30, 1297\u0026ndash;1302 (2016). https://doi.org/10.1007/s10948-016-3931-2\u003c/li\u003e\n\u003cli\u003eZhang, Q., Zhao, Y., Jia, Z., Qin, Z., Chu, L., Yang, J., Zhang, J., Huang, W., Li, X.: High Stable, Transparent and Conductive ZnO/Ag/ZnO Nanofilm Electrodes on Rigid/Flexible Substrates. Energies. 9, 443 (2016). https://doi.org/10.3390/en9060443\u003cspan dir=\"RTL\"\u003e \u003c/span\u003e\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"optical-and-quantum-electronics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"oqel","sideBox":"Learn more about [Optical and Quantum Electronics](https://www.springer.com/journal/11082)","snPcode":"11082","submissionUrl":"https://submission.nature.com/new-submission/11082/3","title":"Optical and Quantum Electronics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Mg:Cu:ZnO thin films, Structural study, Optical study, Electrochemical","lastPublishedDoi":"10.21203/rs.3.rs-5223491/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5223491/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eMg and Cu co-doped ZnO thin films were fabricated on a FTO glass substrate by the electrochemical method at a constant current density of 3.5 mA/cm\u0026sup2;. Mg:Cu:ZnO films with a 3 wt.% Mg concentration and varying concentrations of 0, 2, 3, and 4 wt.% Cu are designated as ZM3, ZM3C2, ZM3C3, and ZM3C4, respectively. The thin films were subjected to analysis using XRD, SEM, FTIR and UV-vis spectroscopy. The structural and optical parameters of Mg:Cu:ZnO thin films for photonic applications were investigated in detail. The results of the structural and morphological analysis demonstrated that the structural parameters and grain size are dependent on the concentration of dopants. The grain size was calculated to be 55.20, 36.43, 32.64, and 32.57 nm for the ZM3, ZM3C2, ZM3C3, and ZM3C4 films, respectively. The results of the spectroscopy analysis indicated a reduction in the band gap, from 3.9 eV to 3.6 eV, as the concentration of Cu in Mg:Cu:ZnO increased from 0\u0026ndash;4%. The optical parameters of the films were obtained through the utilization of FTIR transmission spectrum data and the application of Kramers\u0026ndash;Kronig (K-K) relations. The findings indicated that the ZM3C3 film exhibited the highest energy storage capacity and the lowest energy loss when compared to the other samples.\u003c/p\u003e","manuscriptTitle":"Influence of Cu content on optical spectra of Cu/Mg co-doped ZnO films by Kramers–Kronig","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-26 15:47:11","doi":"10.21203/rs.3.rs-5223491/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-11-06T21:55:43+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-06T19:42:02+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-02T17:13:54+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-10-27T21:38:04+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"2220811234031599608201184558403767894","date":"2024-10-19T11:29:32+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"204842325750362051839654345578952394830","date":"2024-10-16T12:16:54+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"53816603856719579642995818546133918258","date":"2024-10-15T17:41:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"328366974532922660740036608433434461","date":"2024-10-14T11:14:30+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"117778567287659420238814417490178420549","date":"2024-10-14T10:57:09+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-10-14T10:27:39+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-10-09T07:19:06+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-10-09T03:07:49+00:00","index":"","fulltext":""},{"type":"submitted","content":"Optical and Quantum Electronics","date":"2024-10-08T08:34:01+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"optical-and-quantum-electronics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"oqel","sideBox":"Learn more about [Optical and Quantum Electronics](https://www.springer.com/journal/11082)","snPcode":"11082","submissionUrl":"https://submission.nature.com/new-submission/11082/3","title":"Optical and Quantum Electronics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"8e7cb00e-a039-47e4-bc51-56603274d8b0","owner":[],"postedDate":"November 26th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-01-20T15:58:41+00:00","versionOfRecord":{"articleIdentity":"rs-5223491","link":"https://doi.org/10.1007/s11082-024-07994-0","journal":{"identity":"optical-and-quantum-electronics","isVorOnly":false,"title":"Optical and Quantum Electronics"},"publishedOn":"2025-01-17 15:56:55","publishedOnDateReadable":"January 17th, 2025"},"versionCreatedAt":"2024-11-26 15:47:11","video":"","vorDoi":"10.1007/s11082-024-07994-0","vorDoiUrl":"https://doi.org/10.1007/s11082-024-07994-0","workflowStages":[]},"version":"v1","identity":"rs-5223491","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5223491","identity":"rs-5223491","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}