Thickness-Dependent Structural and Optical Properties of WS₂ Thin Films Prepared by RF Magnetron Sputtering

Thickness-Dependent Structural and Optical Properties of WS₂ Thin Films Prepared by RF Magnetron Sputtering | 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 Thickness-Dependent Structural and Optical Properties of WS₂ Thin Films Prepared by RF Magnetron Sputtering samira Bahadivand Chegini1, mohammad reza khanlary, zahra pasalari, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8731932/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 4 You are reading this latest preprint version Abstract In this study, the thickness-dependent structural, vibrational, optical, and electrical properties of sputter-deposited WS₂ thin films were systematically investigated. Two film thicknesses, 10 nm and 100 nm, were deposited and subsequently annealed to evaluate the influence of thickness and post-deposition thermal treatment on material performance. X-ray diffraction analysis revealed thickness-dependent variations in interlayer ordering and crystallographic coherence. Raman spectroscopy confirmed the characteristic vibrational modes of WS₂ along with defect-related features, indicating the polycrystalline nature of the films. Photoluminescence spectroscopy showed that the optical response of the films is dominated by excitonic recombination. A thickness-dependent red-shift of the A-excitonic emission was observed, while the appearance of the B-excitonic transition in the annealed 100 nm film indicated improved electronic homogeneity after annealing. Diffuse reflectance spectroscopy further supported these findings, revealing a gradual decrease in the effective optical bandgap with increasing film thickness due to reduced confinement effects and enhanced interlayer electronic coupling. Hall effect measurements demonstrated n-type conductivity for both samples, attributed to intrinsic donor-like defects such as sulfur vacancies. The 10 nm film exhibited lower resistivity, higher conductivity, and slightly higher carrier mobility compared to the 100 nm film, highlighting the importance of thickness control for optimizing charge transport in WS₂ thin films. Overall, this work provides a comprehensive understanding of how thickness and thermal treatment govern the excitonic behavior, band structure, and electronic transport properties of sputter-deposited WS₂ thin films. The results offer valuable insights for the design and optimization of WS₂-based electronic and optoelectronic devices. WS₂ thin films Sputtering deposition Thickness dependence Excitonic transitions Photoluminescence Diffuse reflectance spectroscopy Optical bandgap Hall effect Carrier mobility Annealing effect Two-dimensional materials Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction The discovery of graphene ignited a research revolution in two-dimensional (2D) materials, leading to the exploration of a wider family of compounds, notably transition metal dichalcogenides (TMDs) [ 1 ]. While graphene boasts exceptional electronic properties, its lack of a natural bandgap limits its application in digital electronics and photonics. TMDs, with the general formula MX₂ (where M is a transition metal such as Mo or W, and X is a chalcogen such as S, Se, or Te), overcome this limitation by possessing layer-number-dependent bandgaps [ 2 , 3 ]. Among the TMDs, tungsten disulfide (WS₂) has emerged as a particularly compelling material due to its unique combination of properties: a crossover from an indirect bandgap of approximately 1.3 eV in the bulk to a direct bandgap approaching 2.1 eV in the monolayer limit [ 4 , 5 ], strong spin-orbit coupling, and high quantum efficiency [ 6 ]. These characteristics make WS₂ an ideal candidate for a wide array of applications, including field-effect transistors [ 7 ], photodetectors [ 8 ], catalysts for the hydrogen evolution reaction (HER) [ 9 ], and components in advanced optoelectronic devices [ 10 ]. A critical aspect of WS₂ is its polymorphism. The most common phases are the trigonal prismatic (2H, semiconducting) and the octahedral (1T, metallic) phases. The 1T phase is typically metastable but can be stabilized during specific synthesis routes. The ability to control the phase is paramount, as it dictates the electronic and catalytic properties of the material [ 11 ]. While chemical vapor deposition (CVD) is widely used for synthesizing high-quality 2D TMDs, it often faces challenges in achieving uniform large-area coverage, precise thickness control, and phase purity [ 12 , 13 ]. In this context, RF magnetron sputtering presents a highly attractive alternative. It is an industry-proven, scalable technique capable of depositing uniform, pinhole-free films over large areas with excellent control over thickness and composition, all at relatively low substrate temperatures [ 14 , 15 ]. However, sputter-deposited TMD films are often amorphous or nanocrystalline and may contain a high density of defects and mixed phases. Post-deposition thermal annealing is a crucial processing step to enhance crystallinity, reduce defects, and induce phase transformations [ 16 , 17 ]. The response to annealing is not universal and can be strongly influenced by initial film properties, with thickness being a key parameter. A systematic study elucidating how the thickness of sputter-deposited WS₂ films governs their structural evolution and optoelectronic response upon annealing is still lacking. Despite the growing interest in WS₂ as a promising two-dimensional semiconductor for electronic and optoelectronic applications, a comprehensive understanding of how film thickness and post-deposition thermal treatment influence its excitonic behavior, optical band structure, and charge transport properties in sputter-deposited thin films remains limited. Most previous studies have focused on either exfoliated or CVD-grown WS₂, while systematic investigations on sputtered WS₂ layers with controlled thickness are still scarce. In this work, we address this gap by systematically investigating the structural, vibrational, optical, and electrical properties of WS₂ thin films with thicknesses of 10 and 100 nm, both in as-deposited and annealed states. By combining XRD, Raman spectroscopy, photoluminescence, diffuse reflectance spectroscopy, and Hall effect measurements, we provide a comprehensive thickness-dependent analysis that elucidates the interplay between microstructural order, excitonic transitions, optical bandgap modulation, and charge transport in WS₂ thin films. The insights gained from this study offer valuable guidance for the rational design and optimization of WS₂-based thin-film devices. 2. Materials and Methods 2.1. Substrate Preparation and Film Deposition P-type silicon substrates with (100) crystallographic orientation and a thermally grown SiO₂ layer were used as the supporting substrates. They were meticulously cleaned through a sequential ultrasonic process in analytical-grade acetone for 15 minutes, followed by ethanol for 15 minutes, and finally deionized water for 10 minutes to remove organic and particulate contaminants. The substrates were then dried in a clean ambient environment using a nitrogen gun and subsequently baked on a hotplate at 100°C for 5 minutes to ensure complete removal of moisture. The WS₂ thin films were deposited using a high-vacuum RF magnetron sputtering system (DST 3 -A). A 2-inch diameter WS₂ target with a high purity of 99.99% was used as the source material. The chamber was first evacuated to a base pressure of 1 × 10⁻ 5 Torr to minimize impurities. High-purity argon (99.9%) was introduced as the sputtering gas at a constant flow rate of 15 sccm, maintained by a mass flow controller. Prior to each deposition, the target was pre-sputtered for 5 minutes with a shutter shielding the substrates to remove any native oxide or surface contamination. The depositions were carried out at room temperature with a constant RF power of 32 W, resulting in a deposition pressure of 8 mTorr. The distance between the target and the substrate holder was fixed at 70 mm. Film thicknesses of 10 nm and 100 nm were precisely controlled using an in-situ quartz crystal thickness monitor. 2.2. Post Deposition Annealing The as-deposited samples were subjected to post-deposition annealing in a horizontal tube furnace. The annealing was performed at 400°C (673 K) for a duration of 30 minutes. The samples were placed in a quartz boat at the center of the hot zone. A continuous flow of high-purity argon gas (100 sccm) was maintained throughout the heating, soaking, and cooling cycles to prevent any oxidation of the films. The heating process were programmed so that the target temperature of 400°C was reached within 20 minutes, ensuring minimal thermal stress during annealing. 2.3. Characterization The structural characterization of the films was performed using X-ray diffraction (XRD) on a diffractometer with Cu Kα radiation (λ = 1.5406 Å), operating in the θ–2θ scan mode over a range of 10° to 80°. Micro-Raman spectroscopy was conducted using a spectrometer equipped with a 532 nm Nd:YAG laser as the excitation source. The laser spot size was kept below 1 µm, and the power was maintained below 1 mW to avoid laser-induced heating. Photoluminescence (PL) spectra were acquired using a spectrophotometer with excitations at 420 nm and 532 nm. Diffuse Reflectance Spectroscopy (DRS) was carried out using a UV-Vis-NIR spectrophotometer equipped with an integrating sphere, with BaSO₄ used as a 100% reflectance standard. The optical bandgap was estimated from the DRS data using the Kubelka-Munk transformation. The surface morphology and microstructure of the films were examined by Field Emission Scanning Electron Microscopy (FESEM) using a microscope operating at 15 kV. The electrical properties, including resistivity (ρ), carrier concentration (n), and Hall mobility (µ), were determined at room temperature using the van der Pauw configuration for Hall effect measurements under a magnetic field of 0.5 T. 3. Results and Discussion 3.1. Grazing-incidence X-ray diffraction (GIXRD) The structural characteristics of the WS₂ thin films with thicknesses of 10 nm and 100 nm were investigated using grazing-incidence X-ray diffraction (GIXRD), which is particularly suitable for thin and ultrathin films due to its enhanced surface sensitivity and reduced contribution from the silicon substrate. Consequently, the diffraction features discussed below predominantly originate from the deposited layers. For the 100 nm thick WS₂ film (Figure 1a), the GIXRD pattern exhibits multiple well-resolved diffraction peaks, indicating the development of a comparatively higher degree of crystallographic ordering. The most intense reflection appears at 2θ ≈ 11.2°, which can be indexed to the (002) basal-plane reflection of layered WS₂. In addition, several reflections are observed at approximately 24.1°, 28.4°, 34.1°, 49.3°, 55.3°, and 61.1°, corresponding to the (004), (101), (103), (105), (110), and (114) planes, respectively [18,19]. The positions of the non-basal reflections at 49.3°, 55.3°, and 61.1° are consistent with reported diffraction data for layered WS₂ and primarily reflect the in-plane W–S atomic arrangement. Compared with bulk crystalline 2H-WS₂, for which the (002) reflection is typically located at 2θ ≈ 14.2°–14.4° [20], the pronounced shift of the (002) peak toward lower angles indicates an expanded interlayer spacing in the 100 nm film. Such expansion is frequently observed in sputter-deposited WS₂ thin films and is commonly attributed to stacking disorder, residual strain, point defects, and non-equilibrium growth effects [21,22]. It should be emphasized that, despite the sensitivity of GIXRD to thin-film diffraction features, the position of the (002) reflection alone does not allow for unambiguous discrimination between different WS₂ polymorphs. Therefore, the observed shift is interpreted here in terms of interlayer disorder and structural distortion rather than definitive phase identification. In contrast, the 10 nm thick WS₂ film (Figure 1b) displays a markedly simpler diffraction pattern, reflecting its ultrathin and nanocrystalline nature. The diffraction profile is dominated by a broadened basal-plane reflection at 2θ ≈ 12.6°, which can be assigned to the (002) reflection of layered WS₂ with a reduced interlayer spacing compared to the thicker film. Additional weak diffraction features are observed at approximately 26.7°, 32.5°, and 45.5°, which can be tentatively indexed to higher-order and non-basal reflections of WS₂, such as (004), (100)/ (101), and (006), respectively. Fig. 1. XRD pattern of ws 2 film for samples of different thickness, a) 100 nm and (b) 10 nm. Although the diffraction angles observed at 2θ ≈ 39.5°, 65°, 71°, and 79° do not exactly match the standard positions of bulk α-W reflections, previous studies on magnetron-sputtered tungsten films have shown that both α-W and metastable β-W phases can coexist and that film microstructure, crystallite size, and residual stress influence the diffraction peak positions and intensities. Such structural complexity in sputtered W thin films thus reasonably accounts for the observed diffraction features near the W-related angular ranges rather than layered WS₂ phases [23]. Considering the ultrathin nature of the film, the non-equilibrium sputtering process, and the absence of a sulfur-containing atmosphere during post-deposition annealing, the formation of tungsten-rich regions or partial sulfur depletion within the film cannot be excluded. Nevertheless, the assignment of these high-angle reflections remains tentative, as factors such as residual strain, nanoscale grain size effects, peak overlap, and instrumental broadening inherent to the grazing-incidence geometry may also influence their positions and intensities. Definitive identification of these features would require complementary chemical-state or high-resolution structural analyses, such as X-ray photoelectron spectroscopy or transmission electron microscopy. In addition to the diffraction features associated with layered WS₂, a group of strong reflections is observed in the range of 2θ ≈ 55–56.5°, particularly in the 10 nm thick film. The presence of multiple closely spaced peaks in this angular region cannot be satisfactorily explained by the hexagonal WS₂ structure, which typically exhibits only a single (110) reflection near this angle. Instead, the observed peak multiplicity is consistent with diffraction features reported for tungsten oxide phases (WOₓ), which often display several reflections in this range due to their lower symmetry crystal structures. Considering the ultrathin nature of the film, possible sulfur deficiency, and exposure to ambient conditions after deposition, partial oxidation of tungsten-rich regions or near-surface layers cannot be excluded. However, in the absence of direct chemical-state analysis, the assignment of these peaks to WOₓ remains tentative [24]. 3.2. Morphological Transformation: SEM Analysis The surface morphology of the WS₂ films, particularly the 10 nm sample, was examined by SEM before and after annealing, as shown in Figure 2. The as-deposited 10 nm film (Figure 2a) exhibits a continuous and relatively smooth surface composed of densely packed, nano-grained Fig. 2. SEM image of the WS 2 film 10 nm, (a) Before and (b) After annealing at 400C o . After annealing at 400°C (Figure 2b), a remarkable morphological transformation is observed. The film surface now displays well-defined, discrete triangular-shaped crystals with edge lengths ranging from 200 nm to 500 nm. The formation of such triangular domains is a well-known characteristic of monolayer and few-layer TMDs, including WS₂, synthesized under specific conditions [25,26]. This transformation is driven by the thermal energy provided during annealing, which enhances surface diffusion and allows atoms to rearrange into their thermodynamically most stable configurations [27]. The emergence of triangles is often associated with a sulfur-deficient (tungsten-rich) growth environment [28]. It is plausible that during annealing in an inert atmosphere, slight sulfur desorption occurs, creating a W-rich condition that favors the growth of 2H-WS₂ with triangular geometry and specific edge terminations [15]. This recrystallization process also suggests that the annealed film is not a continuous layer but may consist of isolated monolayer islands embedded within a thinner matrix, which has profound implications for its optical and electronic properties. 3.3. Raman Spectroscopy Raman spectroscopy is a powerful and non-destructive tool for identifying the phase and layer number of TMDs. The Raman spectra of both WS₂ films, before and after annealing, are displayed in Figure 3 Fig. 3. Raman spectroscopy of WS 2 films (10 and 100 nm) before and after annealing at 400 . Raman spectroscopy was employed to investigate the vibrational characteristics and structural order of the WS₂ thin films in the spectral range of 50–430 cm⁻¹. Figure X compares the Raman spectra of the 10 nm and 100 nm films in both the as-deposited and annealed states. The overall Raman response is strongly influenced by film thickness, deposition-induced disorder, and post-deposition thermal treatment. In crystalline 2H-WS₂, the first-order E 2g 1 (in-plane) and A₁g (out-of-plane) phonon modes are typically observed at approximately 350–356 cm⁻¹ and 417–422 cm⁻¹, respectively [29]. In the present sputter-deposited films, however, these modes are considerably broadened and, in some cases, appear only as weak shoulders rather than well-resolved peaks. Such behavior has been widely reported for nanocrystalline and highly disordered WS₂ thin films and is attributed to strong structural disorder, reduced crystallite size, sulfur vacancies, and the breakdown of Raman selection rules under non-equilibrium growth conditions [24]. A pronounced Raman feature is observed at approximately 267 cm⁻¹, particularly in the as-deposited 10 nm film. This band is assigned to the disorder-activated longitudinal acoustic phonon mode at the M point [LA(M)], which becomes Raman-active in the presence of lattice imperfections and sulfur deficiency. The intensity of this mode is significantly reduced after annealing and is much weaker in the 100 nm films, indicating partial recovery of structural order and a lower defect density in thicker layers. In addition, a broad Raman band centered around ~390–405 cm⁻¹, with a maximum near ~397 cm⁻¹, is detected in some samples. This feature does not correspond to a fundamental first-order Raman mode of WS₂ and is therefore attributed to defect-assisted or second-order phonon scattering processes, which commonly dominate the Raman spectra of sputtered and sulfur-deficient WS₂ films. The presence of this band further supports the high degree of structural disorder inferred from the XRD analysis. Minor shoulders appearing around ~150 and ~220 cm⁻¹, particularly in the as-deposited 100 nm film, are not characteristic of the first-order Raman modes of WS₂. These features are therefore assigned to defect-assisted or higher-order scattering processes that become detectable in thicker and more disordered films. Importantly, the absence of a complete set of characteristic J-modes excludes the presence of a dominant metallic 1T-WS₂ phase. Thermal annealing leads to a general reduction in background intensity, suppression of defect-related features, and partial sharpening of the Raman bands, indicating improved crystallinity and relaxation of deposition-induced disorder. The combined Raman results demonstrate that the films predominantly consist of disordered, nanocrystalline WS₂, with the vibrational response strongly governed by thickness-dependent defect density and post-deposition thermal treatment rather than by a distinct polymorphic phase transition. 3.4. Optical Properties and Bandgap Engineering 3.4.1. Photoluminescence (PL) Spectroscopy The PL response of a material is a direct probe of its electronic band structure and is highly sensitive to its dimensionality and phase. The PL spectra of our WS₂ films, acquired under 420 nm excitation, are presented in Figure 4. Fig. 4. The Photoluminescence of WS 2 thin films (10 and 100 nm) before and after annealing at 400 C under 420 nm excitation wavelength. Photoluminescence (PL) spectroscopy was employed to investigate the optical transitions and excitonic properties of WS₂ thin films with thicknesses of 10 and 100 nm in both as-deposited and annealed states. All samples exhibit a near-band-edge emission centered in the wavelength range of approximately 630–634 nm, corresponding to photon energies of ~1.95–1.97 eV [30]. This emission is attributed to the A-exciton of WS₂, originating from direct optical transitions at the K point of the Brillouin zone. It is emphasized that the PL energy represents excitonic recombination rather than the intrinsic quasiparticle bandgap due to the finite exciton binding energy. A systematic thickness-dependent red-shift of the A-excitonic emission is observed. The 10 nm film shows its PL maximum at ~630 nm in the as-deposited state, which slightly shifts to ~631 nm after annealing. In contrast, the annealed 100 nm film exhibits a further red-shift to ~634 nm. This trend is attributed to reduced quantum confinement, enhanced interlayer coupling, and increased dielectric screening in thicker WS₂ layers [31]. The as-deposited 100 nm film displays a broadened emission feature, indicating electronic and structural inhomogeneity rather than a distinct shift in emission energy. In addition to the A-excitonic transition, a weak higher-energy PL peak is detected at approximately 465 nm (∼2.67 eV) exclusively in the annealed 100 nm film. This emission is assigned to the B-exciton of WS₂, which arises from spin–orbit splitting of the valence band at the K point. The energy separation between the A- and B-excitonic transitions (~0.7 eV) is consistent with reported values for WS₂. The emergence of the B-excitonic feature only after annealing suggests that thermal treatment significantly improves the structural and electronic homogeneity of the thicker film, thereby suppressing defect-assisted non-radiative recombination and enabling the observation of higher-energy excitonic transitions. The absence of additional emission bands outside the characteristic excitonic energy range of WS₂ indicates that the PL response is governed primarily by intrinsic excitonic processes rather than by secondary phases or chemical degradation. These optical results are fully consistent with the thickness-dependent structural evolution observed in XRD and the defect-related vibrational features revealed by Raman spectroscopy. 3.4.2. Diffuse Reflectance Spectroscopy (DRS) and Bandgap Analysis To further quantify the optical properties and bandgap, DRS measurements were performed. The Kubelka-Munk function, F(R) = (1-R)²/2R, was used to convert the reflectance data into a equivalent absorption spectrum. The Tauc plot method was then applied, and for direct bandgap semiconductors like 2H-WS₂, a plot of [F(R)hν]² versus photon energy (hν) was constructed, as shown in Figures 5c and 5d. Fig. 5. DRS of WS 2 films a) 100 nm, b) 10 nm, and their band gaps c) 100 nm and d) 10 nm The absorption spectra of both samples (Figures 5a and 5b) display characteristic excitonic features associated with WS₂. After annealing, these excitonic features become more defined, indicating an improvement in structural ordering and a reduction in defect-related optical scattering. The absorption edge also becomes sharper, reflecting enhanced optical homogeneity of the films after thermal treatment . Optical bandgap values were extracted by extrapolating the linear region of the Tauc plots to the energy axis. For the 10 nm film, the estimated bandgap decreases slightly from 1.70 eV in the as-deposited state to 1.62 eV after annealing. This bandgap narrowing is attributed to partial relaxation of intrinsic strain and an increase in effective crystallite size, which reduce confinement-induced energy widening. In contrast, the 100 nm film exhibits nearly unchanged bandgap values, decreasing marginally from 1.465 eV to 1.448 eV after annealing, indicating its more bulk-like optical response. The higher bandgap of the 10 nm film compared to the thicker sample confirms the thickness-dependent modification of the electronic structure. Although the extracted bandgap values remain larger than that of bulk WS₂ (~1.3 eV), the gradual reduction of the bandgap with increasing thickness reflects the weakening of quantum confinement and enhanced interlayer electronic coupling. It is noted that the obtained bandgap values represent effective optical gaps influenced by excitonic effects rather than the intrinsic quasiparticle bandgap. 3.5. Electronic Transport Properties: Hall Effect Measurements The electronic transport properties of the WS₂ films, which are paramount for assessing their potential in nano electronic and optoelectronic devices, were investigated using Hall effect measurements at room temperature. The results, summarized in Table 1, reveal a significant dependence of the electrical parameters on film thickness. Table 1 . Electrical properties of WS₂ thin films obtained from Hall effect measurements. Sample Thickness Resistivity (Ω·cm) Conductivity (Ω·cm) ⁻¹ Mobility (cm²/V·s) Conductivity Type 10 nm 7.72 × 10³ 1.31 × 10⁻⁴ 20.1 n-type 100 nm 4.57 × 10⁴ 2.39 × 10⁻⁵ 17.1 n-type Both films exhibit n-type conductivity, which is commonly observed in undoped WS₂ thin films grown by sputtering methods. This behavior is generally attributed to donor-like intrinsic defects, particularly sulfur vacancies, which act as effective electron donors. Compared to the 100 nm film, the 10 nm sample shows lower resistivity and higher conductivity, indicating improved charge transport in the thinner layer. The Hall mobility of the 10 nm film (20.1 cm²/V·s) is slightly higher than that of the 100 nm film (17.1 cm²/V·s), revealing a moderate but systematic thickness dependence. Although the difference in mobility between the two samples is not large, it reflects the influence of microstructural quality and defect density on carrier transport. The thinner film likely benefits from a more uniform crystallographic structure and reduced grain-boundary scattering, whereas the thicker film, grown over a longer deposition time, may incorporate a higher density of point defects, extended dislocations, and grain boundaries that limit carrier mobility. The significantly higher resistivity of the 100 nm film further supports the presence of enhanced carrier scattering and potential barrier formation across microstructural features. In addition, thickness-induced strain accumulation and local electronic inhomogeneity may also contribute to the reduced conductivity of the thicker layer. It is noted that Hall mobility values in polycrystalline WS₂ thin films represent effective mobilities influenced by multi-channel conduction and microstructural disorder. Nevertheless, the consistent trend observed here confirms that reducing film thickness improves the electronic transport characteristics of sputter-deposited WS₂ films. 4. Conclusion In this work, the thickness-dependent structural, vibrational, optical, and electrical properties of sputter-deposited WS₂ thin films were systematically investigated. XRD analysis revealed a clear evolution in interlayer ordering and crystallographic coherence with increasing film thickness, while Raman spectroscopy confirmed the presence of characteristic WS₂ vibrational modes accompanied by defect-related features, reflecting the polycrystalline nature of the films. Photoluminescence measurements demonstrated that the optical response is dominated by excitonic recombination. The A-excitonic emission exhibited a thickness-dependent red-shift from the 10 nm to the 100 nm films, which was attributed to enhanced interlayer coupling and dielectric screening. The observation of the B-excitonic transition in the annealed 100 nm film further indicated improved electronic homogeneity after thermal treatment and confirmed the intrinsic excitonic nature of the optical transitions in WS₂. Diffuse reflectance spectroscopy provided complementary insight into the optical band structure. The extracted effective optical bandgap values showed a systematic decrease with increasing thickness, consistent with the weakening of confinement effects and enhanced interlayer electronic interaction. The DRS results were fully consistent with the PL observations, confirming that the optical behavior of the films is governed by excitonic and thickness-dependent band structure modulation rather than by changes in chemical composition. Hall effect measurements revealed n-type conductivity for all samples, which was attributed to intrinsic donor-like defects such as sulfur vacancies. The thinner WS₂ film exhibited lower resistivity, higher conductivity, and slightly enhanced carrier mobility compared to the thicker film, highlighting the beneficial role of reduced defect density and improved microstructural uniformity on electronic transport. Overall, this study demonstrates that film thickness and post-deposition annealing play critical roles in controlling the structural order, excitonic landscape, optical band structure, and charge transport properties of sputter-deposited WS₂ thin films. The combined results indicate that ultra-thin WS₂ layers with optimized microstructural quality provide a more favorable platform for future electronic and optoelectronic applications than thicker, structurally heterogeneous films. These findings offer valuable guidance for engineering high-performance WS₂-based devices through precise thickness control and thermal processing strategies. Declarations Author Contribution All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Samira Bahadivand Chegini, Mohammad Reza Khanlary, Zahra Pasalari, and Milad Parhizkari. The first draft of the manuscript was written by Mohammad Reza khanlary and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Data Availability The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request. References Shahbazi, M., Khanlary, M.R., Taherkhani, A.: Enhancement of optical, morphological and electronic properties of MoS2 thin film by annealing to improve the performance of silicon solar cells. J. Mater. Sci. Mater. Electron. 34 , 57 (2023) Gutiérrez, H.R., Perea-López, N., Elías, A.L., Berkdemir, A., Wang, B., Lv, R., López-Urías, F., Crespi, V.H., Terrones, H., Terrones, M.: Extraordinary Room-Temperature Photoluminescence in Triangular WS2 Monolayers. 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Res. 13 , 2412–2417 (1998) Somweer, D.S., Ahlawat, B., Singh, B., Gangwar, J.: Insights into phase engineering and morphological tailoring of WS2 nanostructures via temperature controlled hydrothermal synthesis. Nano Express. 6 , 025010 (2025) Piao, M., Li, C., Joo, M.K., Chu, J., Wang, X., Chi, Y., Zhang, H., Shi, H.: Hydrothermal Synthesis of Stable 1T-WS2 and Single-Walled Carbon Nanotube Hybrid Flexible Thin Films with Enhanced Thermoelectric Performance. Energy Technol. 6 , 230–236 (2018) Kaidatzis, A., Psycharis, V., Mergia, K., Niarchos, D.: Annealing effects on the structural and electrical properties of sputtered tungsten thin films. Thin Solid Films. 619 , 61–67 (2016) Berkdemir, A., Gutiérrez, H.R., Botello-Méndez, A.R., Perea-López, N., Elías, A.L., Chia, C.I., Wang, B., Crespi, V.H., López-Urías, F., Charlier, J.C., Terrones, H., Terrones, M.: Identification of individual and few layers of WS 2 using Raman Spectroscopy. Sci Rep. ; 3:1755. (2013). 10.1038/srep01755 . PMCID: PMC3639451 Wang, Y., Sohier, T., Watanabe, K., Taniguchi, T., Verstraete, M.J., Tutuc, E.: Electron mobility in monolayer WS2 encapsulated in hexagonal boron-nitride. Appl. Phys. Lett. 118 , 123104 (2021) Jafari, M., Shahidi, M.M., Ehsani, M.H.: Optimization of WS2 layer thickness for enhanced performance in self-powered gas sensors. Results Phys. 66 , 107852 (2025) Kumar, A., Villarreal, E., Zhang, X., Ringe, E.: Micro-Extinction Spectroscopy (MECXS): a versatile optical characterization technique. Adv. Struct. Chem. Imaging. 4 , 1 (2018) Ahmad, R., Ahmad, Z., Khan, A.U., Mastoi, N.R., Aslam, M., Kim, J.: Photocatalytic systems as an advanced environmental remediation: Recent developments, limitations and new avenues for applications. J. Environ. Chem. Eng. 4 , 4143–4164 (2016) He, J.-M., Gao, J., Huo, C.-G., Qi, M.-R., Li, X.-D., Hu, S.-H., Shi, Y.-J., Wang, S.: Xiao-Peng Fane and Cheng-Bing Qin, Temperature-dependent Raman spectroscopy in double spiral WS2 nanostructures. RSC Adv. 15 , 38522–38531 (2025) Zhao, W., Ghorannevis, Z., Chu, L., Toh, M., Kloc, C., Tan, P.H., Eda, G.: Evolution of electronic structure in atomically thin sheets of WS2 and WSe2. ACS Nano. 7 (1), 791–797 (2013). 10.1021/nn305275h Epub 2012 Dec 28. PMID: 23256505 Ashwin, Ramasubramaniam: Large excitonic effects in monolayers of molybdenum and tungsten dichalcogenides. Phys. Rev. B. 86 , 115409 (2012) Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Revision Version 1 posted Editorial decision: Revision requested 30 Jan, 2026 Editor assigned by journal 29 Jan, 2026 Submission checks completed at journal 29 Jan, 2026 First submitted to journal 29 Jan, 2026 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. 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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-8731932","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":582841594,"identity":"735c5a7f-09ba-4e2b-807e-060a37278328","order_by":0,"name":"samira Bahadivand Chegini1","email":"","orcid":"","institution":"Imam Khomeini International University","correspondingAuthor":false,"prefix":"","firstName":"samira","middleName":"Bahadivand","lastName":"Chegini1","suffix":""},{"id":582841595,"identity":"86775ca4-7da8-40bf-a7d7-0c307a29ba35","order_by":1,"name":"mohammad reza khanlary","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzUlEQVRIiWNgGAWjYBACCQkg8QCI+RkY2EjQkgDEkg0kazE4QKwWydnNzx4k1NxL3Hwj+dmDDxUM8vxiB/BrkZY5Zm6QcKw4cduNNHPDGWcYDGfOTsCvRU4iwUwigS0BqCXBTJq3jSHB4DZBLenfJBL+JSRunpH+jTgt0hI5ZhKJbQmJG4AM4rRIzsgpk0jsSzCeceZNmeSMMxKE/SJxI32bxIdvCbL97SBGhY08vzQBLTDg2CAAVilBnHIQsGfgP0C86lEwCkbBKBhZAAAxA0LFQUICrQAAAABJRU5ErkJggg==","orcid":"","institution":"Imam Khomeini International University","correspondingAuthor":true,"prefix":"","firstName":"mohammad","middleName":"reza","lastName":"khanlary","suffix":""},{"id":582841596,"identity":"fb43d82e-0fc6-4f33-adea-215245b869ca","order_by":2,"name":"zahra pasalari","email":"","orcid":"","institution":"Imam Khomeini International University","correspondingAuthor":false,"prefix":"","firstName":"zahra","middleName":"","lastName":"pasalari","suffix":""},{"id":582841597,"identity":"8eee4744-cba4-450f-b032-be646510a8f0","order_by":3,"name":"Saeid Baghshahi","email":"","orcid":"","institution":"Imam Khomeini International University","correspondingAuthor":false,"prefix":"","firstName":"Saeid","middleName":"","lastName":"Baghshahi","suffix":""},{"id":582841598,"identity":"91fe3263-a79e-43e8-bf36-aec141f45156","order_by":4,"name":"Seyedeh Zahra Mortazavi","email":"","orcid":"","institution":"Imam Khomeini International University","correspondingAuthor":false,"prefix":"","firstName":"Seyedeh","middleName":"Zahra","lastName":"Mortazavi","suffix":""},{"id":582841599,"identity":"dd8bdefb-3ea1-4621-acb5-c47f35d252f4","order_by":5,"name":"milad Parhizkari","email":"","orcid":"","institution":"Imam Khomeini International University","correspondingAuthor":false,"prefix":"","firstName":"milad","middleName":"","lastName":"Parhizkari","suffix":""}],"badges":[],"createdAt":"2026-01-29 13:09:35","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8731932/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8731932/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104018719,"identity":"d06b5202-c276-4771-9434-cbddd683a8ec","added_by":"auto","created_at":"2026-03-05 17:51:11","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":136022,"visible":true,"origin":"","legend":"\u003cp\u003eXRD pattern of ws\u003csub\u003e2\u003c/sub\u003e film for samples of different thickness, a) 100 nm and (b) 10 nm.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8731932/v1/85dea407e4c5d7e005ad60bd.png"},{"id":104402981,"identity":"50485f12-6059-42cc-8bcc-4a7949104076","added_by":"auto","created_at":"2026-03-11 12:17:05","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":87937,"visible":true,"origin":"","legend":"\u003cp\u003eSEM image of the WS\u003csub\u003e2 \u003c/sub\u003efilm\u003csub\u003e \u003c/sub\u003e10 nm, (a) Before and (b) After annealing at 400C\u003csup\u003eo\u003c/sup\u003e .\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8731932/v1/2ae7fe96c927d0484e41da46.jpg"},{"id":104018717,"identity":"bdddd8ca-9d7c-4af0-98a6-fa436e227d81","added_by":"auto","created_at":"2026-03-05 17:51:11","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":48899,"visible":true,"origin":"","legend":"\u003cp\u003eRaman spectroscopy of WS\u003csub\u003e2\u003c/sub\u003e films (10 and 100 nm) before and after annealing at 400.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8731932/v1/f169c4d7edf12f6931ff52e1.jpg"},{"id":104018722,"identity":"c4bd6a44-cd34-4b36-b477-f9cb250f957c","added_by":"auto","created_at":"2026-03-05 17:51:12","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":47606,"visible":true,"origin":"","legend":"\u003cp\u003eThe Photoluminescence of WS\u003csub\u003e2\u003c/sub\u003e thin films (10 and 100 nm) before and after annealing at 400 C\u0026nbsp;under 420 nm\u0026nbsp;excitation wavelength.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8731932/v1/b22f8b6201ecc38f6f5478de.jpg"},{"id":104018720,"identity":"8c394643-49d0-4f6f-9a2f-5c8be543da3c","added_by":"auto","created_at":"2026-03-05 17:51:12","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":82836,"visible":true,"origin":"","legend":"\u003cp\u003eDRS of WS\u003csub\u003e2\u003c/sub\u003e films a) 100 nm, b) 10 nm, and their band gaps c) 100 nm and d) 10 nm\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8731932/v1/f6d3154f43d90b63d001591c.jpg"},{"id":104408591,"identity":"b568c25a-a020-42bf-a739-92509e4f8418","added_by":"auto","created_at":"2026-03-11 12:42:51","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1049069,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8731932/v1/c6b9c12c-2f2c-4b07-9e9d-af5b5776a451.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Thickness-Dependent Structural and Optical Properties of WS₂ Thin Films Prepared by RF Magnetron Sputtering","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe discovery of graphene ignited a research revolution in two-dimensional (2D) materials, leading to the exploration of a wider family of compounds, notably transition metal dichalcogenides (TMDs) [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. While graphene boasts exceptional electronic properties, its lack of a natural bandgap limits its application in digital electronics and photonics. TMDs, with the general formula MX₂ (where M is a transition metal such as Mo or W, and X is a chalcogen such as S, Se, or Te), overcome this limitation by possessing layer-number-dependent bandgaps [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Among the TMDs, tungsten disulfide (WS₂) has emerged as a particularly compelling material due to its unique combination of properties: a crossover from an indirect bandgap of approximately 1.3 eV in the bulk to a direct bandgap approaching 2.1 eV in the monolayer limit [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], strong spin-orbit coupling, and high quantum efficiency [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. These characteristics make WS₂ an ideal candidate for a wide array of applications, including field-effect transistors [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], photodetectors [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], catalysts for the hydrogen evolution reaction (HER) [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], and components in advanced optoelectronic devices [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. A critical aspect of WS₂ is its polymorphism. The most common phases are the trigonal prismatic (2H, semiconducting) and the octahedral (1T, metallic) phases. The 1T phase is typically metastable but can be stabilized during specific synthesis routes. The ability to control the phase is paramount, as it dictates the electronic and catalytic properties of the material [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. While chemical vapor deposition (CVD) is widely used for synthesizing high-quality 2D TMDs, it often faces challenges in achieving uniform large-area coverage, precise thickness control, and phase purity [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. In this context, RF magnetron sputtering presents a highly attractive alternative. It is an industry-proven, scalable technique capable of depositing uniform, pinhole-free films over large areas with excellent control over thickness and composition, all at relatively low substrate temperatures [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. However, sputter-deposited TMD films are often amorphous or nanocrystalline and may contain a high density of defects and mixed phases. Post-deposition thermal annealing is a crucial processing step to enhance crystallinity, reduce defects, and induce phase transformations [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. The response to annealing is not universal and can be strongly influenced by initial film properties, with thickness being a key parameter. A systematic study elucidating how the thickness of sputter-deposited WS₂ films governs their structural evolution and optoelectronic response upon annealing is still lacking.\u003c/p\u003e \u003cp\u003eDespite the growing interest in WS₂ as a promising two-dimensional semiconductor for electronic and optoelectronic applications, a comprehensive understanding of how film thickness and post-deposition thermal treatment influence its excitonic behavior, optical band structure, and charge transport properties in sputter-deposited thin films remains limited. Most previous studies have focused on either exfoliated or CVD-grown WS₂, while systematic investigations on sputtered WS₂ layers with controlled thickness are still scarce. In this work, we address this gap by systematically investigating the structural, vibrational, optical, and electrical properties of WS₂ thin films with thicknesses of 10 and 100 nm, both in as-deposited and annealed states. By combining XRD, Raman spectroscopy, photoluminescence, diffuse reflectance spectroscopy, and Hall effect measurements, we provide a comprehensive thickness-dependent analysis that elucidates the interplay between microstructural order, excitonic transitions, optical bandgap modulation, and charge transport in WS₂ thin films. The insights gained from this study offer valuable guidance for the rational design and optimization of WS₂-based thin-film devices.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Substrate Preparation and Film Deposition\u003c/h2\u003e \u003cp\u003eP-type silicon substrates with (100) crystallographic orientation and a thermally grown SiO₂ layer were used as the supporting substrates. They were meticulously cleaned through a sequential ultrasonic process in analytical-grade acetone for 15 minutes, followed by ethanol for 15 minutes, and finally deionized water for 10 minutes to remove organic and particulate contaminants. The substrates were then dried in a clean ambient environment using a nitrogen gun and subsequently baked on a hotplate at 100\u0026deg;C for 5 minutes to ensure complete removal of moisture.\u003c/p\u003e \u003cp\u003eThe WS₂ thin films were deposited using a high-vacuum RF magnetron sputtering system (DST\u003csub\u003e3\u003c/sub\u003e-A). A 2-inch diameter WS₂ target with a high purity of 99.99% was used as the source material. The chamber was first evacuated to a base pressure of 1 \u0026times; 10⁻\u003csup\u003e5\u003c/sup\u003e Torr to minimize impurities. High-purity argon (99.9%) was introduced as the sputtering gas at a constant flow rate of 15 sccm, maintained by a mass flow controller. Prior to each deposition, the target was pre-sputtered for 5 minutes with a shutter shielding the substrates to remove any native oxide or surface contamination. The depositions were carried out at room temperature with a constant RF power of 32 W, resulting in a deposition pressure of 8 mTorr. The distance between the target and the substrate holder was fixed at 70 mm. Film thicknesses of 10 nm and 100 nm were precisely controlled using an in-situ quartz crystal thickness monitor.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Post Deposition Annealing\u003c/h2\u003e \u003cp\u003eThe as-deposited samples were subjected to post-deposition annealing in a horizontal tube furnace. The annealing was performed at 400\u0026deg;C (673 K) for a duration of 30 minutes. The samples were placed in a quartz boat at the center of the hot zone. A continuous flow of high-purity argon gas (100 sccm) was maintained throughout the heating, soaking, and cooling cycles to prevent any oxidation of the films. The heating process were programmed so that the target temperature of 400\u0026deg;C was reached within 20 minutes, ensuring minimal thermal stress during annealing.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Characterization\u003c/h2\u003e \u003cp\u003eThe structural characterization of the films was performed using X-ray diffraction (XRD) on a diffractometer with Cu Kα radiation (λ\u0026thinsp;=\u0026thinsp;1.5406 \u0026Aring;), operating in the θ\u0026ndash;2θ scan mode over a range of 10\u0026deg; to 80\u0026deg;. Micro-Raman spectroscopy was conducted using a spectrometer equipped with a 532 nm Nd:YAG laser as the excitation source. The laser spot size was kept below 1 \u0026micro;m, and the power was maintained below 1 mW to avoid laser-induced heating. Photoluminescence (PL) spectra were acquired using a spectrophotometer with excitations at 420 nm and 532 nm. Diffuse Reflectance Spectroscopy (DRS) was carried out using a UV-Vis-NIR spectrophotometer equipped with an integrating sphere, with BaSO₄ used as a 100% reflectance standard. The optical bandgap was estimated from the DRS data using the Kubelka-Munk transformation. The surface morphology and microstructure of the films were examined by Field Emission Scanning Electron Microscopy (FESEM) using a microscope operating at 15 kV. The electrical properties, including resistivity (ρ), carrier concentration (n), and Hall mobility (\u0026micro;), were determined at room temperature using the van der Pauw configuration for Hall effect measurements under a magnetic field of 0.5 T.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cp\u003e\u003cstrong\u003e3.1. Grazing-incidence X-ray diffraction (GIXRD)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe structural characteristics of the WS₂ thin films with thicknesses of 10 nm and 100 nm were investigated using grazing-incidence X-ray diffraction (GIXRD), which is particularly suitable for thin and ultrathin films due to its enhanced surface sensitivity and reduced contribution from the silicon substrate. Consequently, the diffraction features discussed below predominantly originate from the deposited layers.\u003cspan dir=\"RTL\"\u003e\u0026nbsp;\u003c/span\u003eFor the 100 nm thick WS₂ film (Figure 1a), the GIXRD pattern exhibits multiple well-resolved diffraction peaks, indicating the development of a comparatively higher degree of crystallographic ordering. The most intense reflection appears at 2\u0026theta; \u0026asymp; 11.2\u0026deg;, which can be indexed to the (002) basal-plane reflection of layered WS₂. In addition, several reflections are observed at approximately 24.1\u0026deg;, 28.4\u0026deg;, 34.1\u0026deg;, 49.3\u0026deg;, 55.3\u0026deg;, and 61.1\u0026deg;, corresponding to the (004), (101), (103), (105), (110), and (114) planes, respectively [18,19]. The positions of the non-basal reflections at 49.3\u0026deg;, 55.3\u0026deg;, and 61.1\u0026deg; are consistent with reported diffraction data for layered WS₂ and primarily reflect the in-plane W\u0026ndash;S atomic arrangement. Compared with bulk crystalline 2H-WS₂, for which the (002) reflection is typically located at 2\u0026theta; \u0026asymp; 14.2\u0026deg;\u0026ndash;14.4\u0026deg; [20], the pronounced shift of the (002) peak toward lower angles indicates an expanded interlayer spacing in the 100 nm film. Such expansion is frequently observed in sputter-deposited WS₂ thin films and is commonly attributed to stacking disorder, residual strain, point defects, and non-equilibrium growth effects [21,22]. It should be emphasized that, despite the sensitivity of GIXRD to thin-film diffraction features, the position of the (002) reflection alone does not allow for unambiguous discrimination between different WS₂ polymorphs. Therefore, the observed shift is interpreted here in terms of interlayer disorder and structural distortion rather than definitive phase identification. In contrast, the 10 nm thick WS₂ film (Figure 1b) displays a markedly simpler diffraction pattern, reflecting its ultrathin and nanocrystalline nature. The diffraction profile is dominated by a broadened basal-plane reflection at 2\u0026theta; \u0026asymp; 12.6\u0026deg;, which can be assigned to the (002) reflection of layered WS₂ with a reduced interlayer spacing compared to the thicker film. Additional weak diffraction features are observed at approximately 26.7\u0026deg;, 32.5\u0026deg;, and 45.5\u0026deg;, which can be tentatively indexed to higher-order and non-basal reflections of WS₂, such as (004), (100)/ (101), and (006), respectively.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig. 1.\u003c/strong\u003e XRD pattern of ws\u003csub\u003e2\u003c/sub\u003e film for samples of different thickness, a) 100 nm and (b) 10 nm.\u003c/p\u003e\n\u003cp\u003eAlthough the diffraction angles observed at 2\u0026theta; \u0026asymp; 39.5\u0026deg;, 65\u0026deg;, 71\u0026deg;, and 79\u0026deg; do not exactly match the standard positions of bulk \u0026alpha;-W reflections, previous studies on magnetron-sputtered tungsten films have shown that both \u0026alpha;-W and metastable \u0026beta;-W phases can coexist and that film microstructure, crystallite size, and residual stress influence the diffraction peak positions and intensities. Such structural complexity in sputtered W thin films thus reasonably accounts for the observed diffraction features near the W-related angular ranges rather than layered WS₂ phases [23]. Considering the ultrathin nature of the film, the non-equilibrium sputtering process, and the absence of a sulfur-containing atmosphere during post-deposition annealing, the formation of tungsten-rich regions or partial sulfur depletion within the film cannot be excluded. Nevertheless, the assignment of these high-angle reflections remains tentative, as factors such as residual strain, nanoscale grain size effects, peak overlap, and instrumental broadening inherent to the grazing-incidence geometry may also influence their positions and intensities. Definitive identification of these features would require complementary chemical-state or high-resolution structural analyses, such as X-ray photoelectron spectroscopy or transmission electron microscopy.\u003c/p\u003e\n\u003cp\u003eIn addition to the diffraction features associated with layered WS₂, a group of strong reflections is observed in the range of 2\u0026theta; \u0026asymp; 55\u0026ndash;56.5\u0026deg;, particularly in the 10 nm thick film. The presence of multiple closely spaced peaks in this angular region cannot be satisfactorily explained by the hexagonal WS₂ structure, which typically exhibits only a single (110) reflection near this angle. Instead, the observed peak multiplicity is consistent with diffraction features reported for tungsten oxide phases (WOₓ), which often display several reflections in this range due to their lower symmetry crystal structures. Considering the ultrathin nature of the film, possible sulfur deficiency, and exposure to ambient conditions after deposition, partial oxidation of tungsten-rich regions or near-surface layers cannot be excluded. However, in the absence of direct chemical-state analysis, the assignment of these peaks to WOₓ remains tentative [24].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2. Morphological Transformation: SEM Analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe surface morphology of the WS₂ films, particularly the 10 nm sample, was examined by SEM\u003cspan dir=\"RTL\"\u003e\u0026nbsp;\u003c/span\u003ebefore and after annealing, as shown in Figure 2. The as-deposited 10 nm film (Figure 2a) exhibits a continuous and relatively smooth surface composed of densely packed, nano-grained\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig. 2.\u003c/strong\u003e SEM image of the WS\u003csub\u003e2\u0026nbsp;\u003c/sub\u003efilm\u003csub\u003e\u0026nbsp;\u003c/sub\u003e10 nm, (a) Before and (b) After annealing at 400C\u003csup\u003eo\u003c/sup\u003e .\u003c/p\u003e\n\u003cp\u003eAfter annealing at 400\u0026deg;C (Figure 2b), a remarkable morphological transformation is observed. The film surface now displays well-defined, discrete triangular-shaped crystals with edge lengths ranging from 200 nm to 500 nm. The formation of such triangular domains is a well-known characteristic of monolayer and few-layer TMDs, including WS₂, synthesized under specific conditions [25,26]. This transformation is driven by the thermal energy provided during annealing, which enhances surface diffusion and allows atoms to rearrange into their thermodynamically most stable configurations [27]. The emergence of triangles is often associated with a sulfur-deficient (tungsten-rich) growth environment [28]. It is plausible that during annealing in an inert atmosphere, slight sulfur desorption occurs, creating a W-rich condition that favors the growth of 2H-WS₂ with triangular geometry and specific edge terminations [15]. This recrystallization process also suggests that the annealed film is not a continuous layer but may consist of isolated monolayer islands embedded within a thinner matrix, which has profound implications for its optical and electronic properties.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.3. Raman Spectroscopy\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eRaman spectroscopy is a powerful and non-destructive tool for identifying the phase and layer number of TMDs. The Raman spectra of both WS₂ films, before and after annealing, are displayed in Figure 3\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig.\u003cspan dir=\"RTL\"\u003e\u0026nbsp;\u003c/span\u003e3.\u003c/strong\u003e Raman spectroscopy of WS\u003csub\u003e2\u003c/sub\u003e films (10 and 100 nm) before and after annealing at 400 .\u003c/p\u003e\n\u003cp\u003eRaman spectroscopy was employed to investigate the vibrational characteristics and structural order of the WS₂ thin films in the spectral range of 50\u0026ndash;430 cm⁻\u0026sup1;. Figure X compares the Raman spectra of the 10 nm and 100 nm films in both the as-deposited and annealed states. The overall Raman response is strongly influenced by film thickness, deposition-induced disorder, and post-deposition thermal treatment. In crystalline 2H-WS₂, the first-order E\u003csub\u003e2g\u003c/sub\u003e\u003csup\u003e1\u003c/sup\u003e (in-plane) and A₁g (out-of-plane) phonon modes are typically observed at approximately 350\u0026ndash;356 cm⁻\u0026sup1; and 417\u0026ndash;422 cm⁻\u0026sup1;, respectively [29]. In the present sputter-deposited films, however, these modes are considerably broadened and, in some cases, appear only as weak shoulders rather than well-resolved peaks. Such behavior has been widely reported for nanocrystalline and highly disordered WS₂ thin films and is attributed to strong structural disorder, reduced crystallite size, sulfur vacancies, and the breakdown of Raman selection rules under non-equilibrium growth conditions [24]. A pronounced Raman feature is observed at approximately 267 cm⁻\u0026sup1;, particularly in the as-deposited 10 nm film. This band is assigned to the disorder-activated longitudinal acoustic phonon mode at the M point [LA(M)], which becomes Raman-active in the presence of lattice imperfections and sulfur deficiency. The intensity of this mode is significantly reduced after annealing and is much weaker in the 100 nm films, indicating partial recovery of structural order and a lower defect density in thicker layers. In addition, a broad Raman band centered around ~390\u0026ndash;405 cm⁻\u0026sup1;, with a maximum near ~397 cm⁻\u0026sup1;, is detected in some samples. This feature does not correspond to a fundamental first-order Raman mode of WS₂ and is therefore attributed to defect-assisted or second-order phonon scattering processes, which commonly dominate the Raman spectra of sputtered and sulfur-deficient WS₂ films. The presence of this band further supports the high degree of structural disorder inferred from the XRD analysis. Minor shoulders appearing around ~150 and ~220 cm⁻\u0026sup1;, particularly in the as-deposited 100 nm film, are not characteristic of the first-order Raman modes of WS₂. These features are therefore assigned to defect-assisted or higher-order scattering processes that become detectable in thicker and more disordered films. Importantly, the absence of a complete set of characteristic J-modes excludes the presence of a dominant metallic 1T-WS₂ phase. Thermal annealing leads to a general reduction in background intensity, suppression of defect-related features, and partial sharpening of the Raman bands, indicating improved crystallinity and relaxation of deposition-induced disorder. The combined Raman results demonstrate that the films predominantly consist of disordered, nanocrystalline WS₂, with the vibrational response strongly governed by thickness-dependent defect density and post-deposition thermal treatment rather than by a distinct polymorphic phase transition.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.4. Optical Properties and Bandgap Engineering\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.4.1. Photoluminescence (PL) Spectroscopy\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe PL response of a material is a direct probe of its electronic band structure and is highly sensitive to its dimensionality and phase. The PL spectra of our WS₂ films, acquired under 420 nm excitation, are presented in Figure 4.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig.\u003c/strong\u003e\u003cstrong\u003e\u003cspan dir=\"RTL\"\u003e \u003c/span\u003e\u003c/strong\u003e\u003cstrong\u003e4.\u003c/strong\u003e The Photoluminescence of WS\u003csub\u003e2\u003c/sub\u003e thin films (10 and 100 nm) before and after annealing at 400 C \u0026nbsp;under 420 nm excitation wavelength.\u003c/p\u003e\n\u003cp\u003ePhotoluminescence (PL) spectroscopy was employed to investigate the optical transitions and excitonic properties of WS₂ thin films with thicknesses of 10 and 100 nm in both as-deposited and annealed states. All samples exhibit a near-band-edge emission centered in the wavelength range of approximately 630\u0026ndash;634 nm, corresponding to photon energies of ~1.95\u0026ndash;1.97 eV [30]. This emission is attributed to the A-exciton of WS₂, originating from direct optical transitions at the K point of the Brillouin zone. It is emphasized that the PL energy represents excitonic recombination rather than the intrinsic quasiparticle bandgap due to the finite exciton binding energy. A systematic thickness-dependent red-shift of the A-excitonic emission is observed. The 10 nm film shows its PL maximum at ~630 nm in the as-deposited state, which slightly shifts to ~631 nm after annealing. In contrast, the annealed 100 nm film exhibits a further red-shift to ~634 nm. This trend is attributed to reduced quantum confinement, enhanced interlayer coupling, and increased dielectric screening in thicker WS₂ layers [31]. The as-deposited 100 nm film displays a broadened emission feature, indicating electronic and structural inhomogeneity rather than a distinct shift in emission energy. In addition to the A-excitonic transition, a weak higher-energy PL peak is detected at approximately 465 nm (\u0026sim;2.67 eV) exclusively in the annealed 100 nm film. This emission is assigned to the B-exciton of WS₂, which arises from spin\u0026ndash;orbit splitting of the valence band at the K point. The energy separation between the A- and B-excitonic transitions (~0.7 eV) is consistent with reported values for WS₂. The emergence of the B-excitonic feature only after annealing suggests that thermal treatment significantly improves the structural and electronic homogeneity of the thicker film, thereby suppressing defect-assisted non-radiative recombination and enabling the observation of higher-energy excitonic transitions. The absence of additional emission bands outside the characteristic excitonic energy range of WS₂ indicates that the PL response is governed primarily by intrinsic excitonic processes rather than by secondary phases or chemical degradation. These optical results are fully consistent with the thickness-dependent structural evolution observed in XRD and the defect-related vibrational features revealed by Raman spectroscopy.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.4.2. Diffuse Reflectance Spectroscopy (DRS) and Bandgap Analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo further quantify the optical properties and bandgap, DRS measurements were performed. The Kubelka-Munk function, F(R) = (1-R)\u0026sup2;/2R, was used to convert the reflectance data into a equivalent absorption spectrum. The Tauc plot method was then applied, and for direct bandgap semiconductors like 2H-WS₂, a plot of [F(R)h\u0026nu;]\u0026sup2; versus photon energy (h\u0026nu;) was constructed, as shown in Figures 5c and 5d. \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig. 5.\u003c/strong\u003e DRS of WS\u003csub\u003e2\u003c/sub\u003e films a) 100 nm, b) 10 nm, and their band gaps c) 100 nm and d) 10 nm \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe absorption spectra of both samples (Figures 5a and 5b) display characteristic excitonic features associated with WS₂. After annealing, these excitonic features become more defined, indicating an improvement in structural ordering and a reduction in defect-related optical scattering. The absorption edge also becomes sharper, reflecting enhanced optical homogeneity of the films after thermal treatment\u003cspan dir=\"RTL\"\u003e.\u003c/span\u003e Optical bandgap values were extracted by extrapolating the linear region of the Tauc plots to the energy axis. For the 10 nm film, the estimated bandgap decreases slightly from 1.70 eV in the as-deposited state to 1.62 eV after annealing. This bandgap narrowing is attributed to partial relaxation of intrinsic strain and an increase in effective crystallite size, which reduce confinement-induced energy widening. In contrast, the 100 nm film exhibits nearly unchanged bandgap values, decreasing marginally from 1.465 eV to 1.448 eV after annealing, indicating its more bulk-like optical response.\u003cspan dir=\"RTL\"\u003e\u0026nbsp;\u003c/span\u003eThe higher bandgap of the 10 nm film compared to the thicker sample confirms the thickness-dependent modification of the electronic structure. Although the extracted bandgap values remain larger than that of bulk WS₂ (~1.3 eV), the gradual reduction of the bandgap with increasing thickness reflects the weakening of quantum confinement and enhanced interlayer electronic coupling. It is noted that the obtained bandgap values represent effective optical gaps influenced by excitonic effects rather than the intrinsic quasiparticle bandgap.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.5. Electronic Transport Properties: Hall Effect Measurements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe electronic transport properties of the WS₂ films, which are paramount for assessing their potential in nano electronic and optoelectronic devices, were investigated using Hall effect measurements at room temperature. The results, summarized in Table 1, reveal a significant dependence of the electrical parameters on film thickness.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1\u003c/strong\u003e. Electrical properties of WS₂ thin films obtained from Hall effect measurements.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eSample Thickness\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eResistivity (\u0026Omega;\u0026middot;cm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eConductivity (\u0026Omega;\u0026middot;cm) ⁻\u0026sup1;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eMobility (cm\u0026sup2;/V\u0026middot;s)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eConductivity Type\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e10 nm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e7.72 \u0026times; 10\u0026sup3;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.31 \u0026times; 10⁻⁴\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e20.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003en-type\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e100 nm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e4.57 \u0026times; 10⁴\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2.39 \u0026times; 10⁻⁵\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e17.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003en-type\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eBoth films exhibit n-type conductivity, which is commonly observed in undoped WS₂ thin films grown by sputtering methods. This behavior is generally attributed to donor-like intrinsic defects, particularly sulfur vacancies, which act as effective electron donors. Compared to the 100 nm film, the 10 nm sample shows lower resistivity and higher conductivity, indicating improved charge transport in the thinner layer. The Hall mobility of the 10 nm film (20.1 cm\u0026sup2;/V\u0026middot;s) is slightly higher than that of the 100 nm film (17.1 cm\u0026sup2;/V\u0026middot;s), revealing a moderate but systematic thickness dependence. Although the difference in mobility between the two samples is not large, it reflects the influence of microstructural quality and defect density on carrier transport. The thinner film likely benefits from a more uniform crystallographic structure and reduced grain-boundary scattering, whereas the thicker film, grown over a longer deposition time, may incorporate a higher density of point defects, extended dislocations, and grain boundaries that limit carrier mobility. The significantly higher resistivity of the 100 nm film further supports the presence of enhanced carrier scattering and potential barrier formation across microstructural features. In addition, thickness-induced strain accumulation and local electronic inhomogeneity may also contribute to the reduced conductivity of the thicker layer. It is noted that Hall mobility values in polycrystalline WS₂ thin films represent effective mobilities influenced by multi-channel conduction and microstructural disorder. Nevertheless, the consistent trend observed here confirms that reducing film thickness improves the electronic transport characteristics of sputter-deposited WS₂ films.\u003c/p\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn this work, the thickness-dependent structural, vibrational, optical, and electrical properties of sputter-deposited WS₂ thin films were systematically investigated. XRD analysis revealed a clear evolution in interlayer ordering and crystallographic coherence with increasing film thickness, while Raman spectroscopy confirmed the presence of characteristic WS₂ vibrational modes accompanied by defect-related features, reflecting the polycrystalline nature of the films. Photoluminescence measurements demonstrated that the optical response is dominated by excitonic recombination. The A-excitonic emission exhibited a thickness-dependent red-shift from the 10 nm to the 100 nm films, which was attributed to enhanced interlayer coupling and dielectric screening. The observation of the B-excitonic transition in the annealed 100 nm film further indicated improved electronic homogeneity after thermal treatment and confirmed the intrinsic excitonic nature of the optical transitions in WS₂. Diffuse reflectance spectroscopy provided complementary insight into the optical band structure. The extracted effective optical bandgap values showed a systematic decrease with increasing thickness, consistent with the weakening of confinement effects and enhanced interlayer electronic interaction. The DRS results were fully consistent with the PL observations, confirming that the optical behavior of the films is governed by excitonic and thickness-dependent band structure modulation rather than by changes in chemical composition. Hall effect measurements revealed n-type conductivity for all samples, which was attributed to intrinsic donor-like defects such as sulfur vacancies. The thinner WS₂ film exhibited lower resistivity, higher conductivity, and slightly enhanced carrier mobility compared to the thicker film, highlighting the beneficial role of reduced defect density and improved microstructural uniformity on electronic transport. Overall, this study demonstrates that film thickness and post-deposition annealing play critical roles in controlling the structural order, excitonic landscape, optical band structure, and charge transport properties of sputter-deposited WS₂ thin films. The combined results indicate that ultra-thin WS₂ layers with optimized microstructural quality provide a more favorable platform for future electronic and optoelectronic applications than thicker, structurally heterogeneous films. These findings offer valuable guidance for engineering high-performance WS₂-based devices through precise thickness control and thermal processing strategies.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAll authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Samira Bahadivand Chegini, Mohammad Reza Khanlary, Zahra Pasalari, and Milad Parhizkari. The first draft of the manuscript was written by Mohammad Reza khanlary and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eShahbazi, M., Khanlary, M.R., Taherkhani, A.: Enhancement of optical, morphological and electronic properties of MoS2 thin film by annealing to improve the performance of silicon solar cells. J. Mater. Sci. Mater. 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PMID: 23256505\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAshwin, Ramasubramaniam: Large excitonic effects in monolayers of molybdenum and tungsten dichalcogenides. Phys. Rev. B. \u003cb\u003e86\u003c/b\u003e, 115409 (2012)\u003c/span\u003e\u003c/li\u003e \u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"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":"WS₂ thin films, Sputtering deposition, Thickness dependence, Excitonic transitions, Photoluminescence, Diffuse reflectance spectroscopy, Optical bandgap, Hall effect, Carrier mobility, Annealing effect, Two-dimensional materials","lastPublishedDoi":"10.21203/rs.3.rs-8731932/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8731932/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn this study, the thickness-dependent structural, vibrational, optical, and electrical properties of sputter-deposited WS₂ thin films were systematically investigated. Two film thicknesses, 10 nm and 100 nm, were deposited and subsequently annealed to evaluate the influence of thickness and post-deposition thermal treatment on material performance. X-ray diffraction analysis revealed thickness-dependent variations in interlayer ordering and crystallographic coherence. Raman spectroscopy confirmed the characteristic vibrational modes of WS₂ along with defect-related features, indicating the polycrystalline nature of the films. Photoluminescence spectroscopy showed that the optical response of the films is dominated by excitonic recombination. A thickness-dependent red-shift of the A-excitonic emission was observed, while the appearance of the B-excitonic transition in the annealed 100 nm film indicated improved electronic homogeneity after annealing. Diffuse reflectance spectroscopy further supported these findings, revealing a gradual decrease in the effective optical bandgap with increasing film thickness due to reduced confinement effects and enhanced interlayer electronic coupling. Hall effect measurements demonstrated n-type conductivity for both samples, attributed to intrinsic donor-like defects such as sulfur vacancies. The 10 nm film exhibited lower resistivity, higher conductivity, and slightly higher carrier mobility compared to the 100 nm film, highlighting the importance of thickness control for optimizing charge transport in WS₂ thin films. Overall, this work provides a comprehensive understanding of how thickness and thermal treatment govern the excitonic behavior, band structure, and electronic transport properties of sputter-deposited WS₂ thin films. The results offer valuable insights for the design and optimization of WS₂-based electronic and optoelectronic devices.\u003c/p\u003e","manuscriptTitle":"Thickness-Dependent Structural and Optical Properties of WS₂ Thin Films Prepared by RF Magnetron Sputtering","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-05 17:51:07","doi":"10.21203/rs.3.rs-8731932/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-01-30T06:09:04+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-01-30T03:55:27+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-01-30T03:52:59+00:00","index":"","fulltext":""},{"type":"submitted","content":"Optical and Quantum Electronics","date":"2026-01-29T12:39:23+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":"642bf4ae-694c-4f55-89fb-4f45e43c8283","owner":[],"postedDate":"March 5th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[],"tags":[],"updatedAt":"2026-03-31T10:25:03+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-05 17:51:07","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8731932","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8731932","identity":"rs-8731932","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}