Statistical comparative analysis of microwave and conventionally annealed sol–gel derived metal oxide thin films

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The deposition of thin films was done through spin coating, and then heat treatment was done through the two different routes under controlled conditions. XRD, SEM, AFM, UV-visible spectroscopy, C-V, and I-V measurements were systematically used to analyse the structural, morphological, optical, dielectric, and electrical properties. To evaluate the reproducibility and reliability, statistical methods such as the analysis of mean-standard deviation and testing of significant results were used. Microwave annealing produced statistically significant changes in crystallite size and optical band gap and leakage current density compared to conventional annealing, with visible transmittance and dielectric constant being statistically similar. The behaviour that was dependent on the material was seen, especially the roughness of the surface and crystallite evolution. In general, the findings indicate that microwave annealing can be as efficient as, or even superior to, conventional annealing with shorter processing times, making it a viable alternative to the post-deposition heat treatment of sol-gel-made metal oxide thin films. Sol–gel thin films Microwave annealing Conventional annealing Statistical analysis Metal oxide thin films Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. Introduction The metal oxide thin films are a significant group of functional materials due to the broad range of their applications in optics [ 1 ], micro-electronics[ 2 ], sensing, energy conversion[ 3 ], and protective coating[ 4 ]. They are also technologically relevant due to the strong tunability of optical, electrical and dielectric properties with regard to composition, microstructure and processing conditions [ 5 ]. In comparison to bulk counterparts, thin films have enhanced surface-volume ratios, lower dimensionality, and altered defect structures which make them useful to modulate properties that can be used in advanced device applications [ 6 ]. Out of the numerous material systems studied, transition metal oxide [ 7 ], rare-earth oxide [ 8 ], perovskite oxide [ 9 ], and silica-based materials [ 10 ] have received continued interest because they have a wide band gap, high dielectric constant, thermal stability, and mechanical strength. Such materials find extensive use in optical coatings [ 11 ], gate dielectrics, capacitors, sensors and optoelectronic equipment [ 12 ]. Nonetheless, post-deposition heat treatment and the methodology used to produce metal oxide thin films has a significant effect on their functional workability; as it governs crystallinity, phase formation, grain growth and defect density [ 13 ]. Sol-gel is a cost effective and versatile chemical solution to the preparation of metal oxide thin films having extraordinary compositional homogeneity and thickness [ 19 ]. The benefits associated with it are low processing temperature, easy doping, ability to coating large areas and also compatibility with varied surfaces [ 14 ]. However, sol-gel prepared films tend to need post deposition heat treatment in order to drive out the remaining organics, cause crystallization, and densify the films [ 15 ]. The most commonly used post-deposition treatment that enhances structural and functional performance of sol gel derived films is conventional furnace annealing [ 16 ]. Although effective, this process is energy consuming, time consuming and can cause unwanted thermal stresses especially in situations when high temperatures or lengthy annealing times are needed [ 17 ]. These constraints have prompted the search of other annealing methods that are capable of providing similar or even better material qualities at lower thermal costs. Microwave-assisted annealing is also a promising alternative because it is fast and works on the principle of volumetric heating, specific energy absorption, and shortened processing times [ 18 ]. Compared to traditional thermal heating, microwaves can directly interfere with the material at the level of the molecules or crystalline structures, which allows promoting the rate of diffusion, speeding up the rate of crystallization, and having a more significant control over the microstructure [ 19 ]. It has been reported in several studies that there is an improvement in crystallinity, altered grain growth and favourable electrical properties of microwave treated metal oxide films [ 20 – 22 ]. Regardless of these stated benefits, most of the available literature is dedicated to individual systems of materials or qualitative comparisons between microwave and conventional annealing paths [ 23 ]. Extensive research involving several oxide systems and using comparative analysis based on statistically significant studies is still scarce [ 24 ]. Specifically, there are few systematic statistical analyses of any systematic statistical analysis of structural, optical, dielectric, and electrical properties that are processed under the same conditions, preventing a proper evaluation of the actual benefits of microwave-assisted annealing [ 24 ]. It is in this respect that the current study seeks to fill this gap by offering a statistically validated comparative study on microwave and conventional annealed sol-gel based metal oxide thin films. Under controlled conditions, thin films of desired metal oxides and composite systems were fabricated and the structural, optical, dielectric as well as electrical characteristics of these films were compared systematically. The statistical tools were used to measure variability, determine reproducibility, and determine significant trends that results with the two post-deposition heat treatment routes. The results of this research provide useful information on whether microwave-assisted annealing can be used as a low-energy-consumption method to functional fabricate a metal oxide thin film. 2. Experimental methodology 2.1 Materials and sol preparation The materials used as precursor materials of TiO 2 and NiTiO 3 films were titanium (IV) isopropoxide [Ti(OCH(CH 3 ) 2 ) 4 ] and nickel chloride. All the precursors were dissolved in 2-methoxyethanol to get clear and homogeneous solutions. Acetyl acetone was used as a chelating and complexing reagent to control the rate of hydrolysis of the metal precursors as well as stabilizing the metal–organic complexes. Acid catalysis was used to start controlled hydrolysis and polycondensation reactions by continually stirring. In the case of composite oxide, the respective precursor sols; mixtures were prepared in pre-determined ratios of volumes and thoroughly mixed to achieve compositional homogeneity. The sols prepared were stirred with enough time in order to get sameness and then filtered to eliminate any particulates that have been formed during the reaction. Aging of all sols were done under ambient conditions before deposition in order to increase chemical stability, control viscosity, and reproducible formation of thin film. Optimized sol preparation process produced transparent and stable sols that could be used to deposit metal oxide thin films uniformly. 2.2 Thin film deposition Thin films were deposited on pre-cleaned glass and p-type silicon substrates using the spin-coating technique. Prior to deposition, the substrates were ultrasonically cleaned sequentially in acetone, ethanol, and deionized water to remove organic contaminants and surface impurities, followed by drying in air. The prepared sols were dispensed onto the substrates and spin coated at optimized rotation speeds and durations to obtain uniform and adherent films. Each deposited layer was subjected to a soft-baking process at 60°C for 10 min to remove residual solvents and to promote partial densification of the films. The spin-coating and soft-baking cycle was repeated multiple times to achieve the desired film thickness. The deposition parameters were optimized to ensure uniform thickness, good surface coverage, and reproducible film quality across all material systems. The resulting as-deposited films were smooth, crack-free, and firmly adhered to the substrates, making them suitable for subsequent heat treatment and characterization. 2.3 Post-deposition heat treatment To eliminate any remaining organic constituents, enhance crystallization process, and densify the sol–gel produced thin films, post-deposition heat treatment was used. There were two alternative heat-treatment paths taken to make a comparative assessment of their effect on film qualities. In the traditional method, the deposited films were annealed in a muffle furnace at temperatures of between 100 and 800 °C and a time of between 1 and 3 h depending on the material system and substrate used. The annealing was conducted in a room atmosphere and the heating and cooling was controlled to reduce thermal stresses and eliminate film cracking. Microwave-assisted annealing was conducted in the alternative route in a domestic microwave oven with the power of between 180 and 900 W and exposure durations of 10–15 min. The movies were positioned at a fixed point in the microwave cavity so that there is equal exposure. Effective temperatures of various levels of power in the microwave were measured experimentally through a calibrated thermocouple set-up. The two different post-deposition heat-treatment paths allowed to make a systematic comparison of both conventional and microwave annealing based on their influences on the structural, optical, dielectric and electrical characteristics of the sol-gel derived metal oxide thin films. 2.4 Characterization techniques The structural properties of the sol–gel derived thin films were examined using X-ray diffraction (XRD) to identify phase formation, crystallinity, and preferred orientation. The surface morphology of the films was analyzed using scanning electron microscopy (SEM), while surface topography and roughness were investigated using atomic force microscopy (AFM). Optical properties were studied by recording transmittance and reflectance spectra using a UV–Vis–NIR spectrophotometer in the wavelength range covering the ultraviolet, visible, and near-infrared regions. Optical constants such as refractive index and optical band gap energy were estimated from the recorded spectra using standard analytical methods. Dielectric and electrical properties were evaluated by fabricating metal–oxide–semiconductor (MOS) capacitor structures on p-type silicon substrates. Aluminium gate electrodes were deposited on the films using thermal evaporation. Capacitance–voltage (C–V) measurements were carried out at different signal frequencies to determine the dielectric constant and dielectric loss, while current–voltage (I–V) characteristics were recorded to evaluate leakage current density and resistivity. 2.5 Statistical analysis The statistical analysis has been done on experimental data of structural, optical, dielectric, and electrical properties of the thin films to permit a strict quantitative comparison of microwave-assisted and conventional annealed thin films. Measures of each material system under each processing condition were repeated under the same experimental conditions in order to achieve repeatability. The data dispersion and the uncertainty of the experiments were measured by calculating the mean values and the standard deviation of them. To provide the statistical significance of the change in the main parameters (crystallite size, refractive index, optical band gap, dielectric constant, and leakage current density and resistivity) depending on the annealing temperature and microwave power, one-way analysis of variance was used. Student t-test was used where there was a need to draw comparisons between two distinct heat treatments paths to ascertain the significance of differences between the microwave-treated and the conventionally annealed films. The criterion of statistical significance was taken to be 95% ( (p < 0.05) ). Besides testing hypothesis, percentage variation and relative deviation analyses were also adopted in order to determine the extent of the changes of the properties upon various post-depositions heat treatment pathways. Statistical consistency of the trends in several material systems was considered as a sign of good structure-property correlations. This co-occurring application of descriptive statistics and inferential statistical tests helped in providing sufficient statistical significance to the comparative conclusions that were made in the current study as opposed to random or qualitative observations. 3. Results 3.1 Structural properties The XRD pattern of the sol–gel derived TiO 2 and NiTiO 3 thin films underwent conventional annealing at 800°C and was obtained as shown in Fig. 1 (a). The TiO 2 film shows different diffraction peaks which are indexed to (101), (200), (105), (214), and (211) planes which demonstrates the creation of well crystallized phase. The reflections are characteristic of the NiTiO 3 film which is crystallised as they can be seen at (104), (116), (024), and (214) planes. No extra diffraction peaks are seen in both patterns and this implies that the secondary phases are not present under the current annealing condition. Figure 1 (b) depicts the XRD patterns of TiO 2 and NiTiO 3 thin films annealed under a power of 600 W using the microwave. The observed diffraction peaks of both materials are very similar to those gathered in the case of conventional annealing, meaning that identical crystalline phases are produced with the use of the microwave. The fact that both TiO 2 and NiTiO 3 patterns have well-defined peaks indicate that microwave annealing is efficient in causing the crystallization process in a shorter processing time. Figure 1 (c) has provided a quantitative analysis of the change in crystallite size via conventional and microwave annealing. In the case of conventionally annealed films, TiO 2 crystallite size grows between about 21 nm at 100 °C to about 33 nm at 800 °C, and NiTiO 3 does the same between about 22 nm and about 32 nm. TiO 2 has been shown to increase in crystallite size between about 26 nm at 200 W to about 42 nm at 800 W, and NiTiO 3 has been shown to increase between about 21 nm and about 30 nm. Microwave-although annealed films always have larger crystallites sizes at comparable levels of processing than traditionally annealed films of TiO 2 and NiTiO 3 . Figure 1 (c) depicts the error bars of the repeated measurements which are the standard deviation meaning that it can be repeated. The statistical analysis proves that the differences between the crystallite size of the conventional and microwave annealing routes can be labeled as significant ((p < 0.05)). Generally, the XRD analysis and the crystallite size analysis indicate that both annealing methods result in the crystalline TiO 2 and NiTiO 3 thin films with microwave annealing yielding relatively large crystallite sizes under the studied conditions. 3.2 Surface morphology and roughness analysis 3.2.1 SEM surface morphology The SEM images of TiO 2 and NiTiO 3 thin films annealed by conventional and microwave methods are shown in Fig. 2 (a-d). The TiO 2 film that has been conventionally annealed (Fig. 2 a) displays a densely packed granular structure that consists of grains that are almost spherical and moderately sized with moderate size dispersion. The grains are seen as being tightly stacked with minimal between grain openings, which means that they are covered uniformly. By comparison, the TiO 2 film (Fig. 2 b) fabricated by microwave annealing exhibits a more granular structure visually and has relatively larger grains and more contact between grains. The surface is more rough and there is a better contrast between separate grains. In the case of NiTiO 3 films, the traditionally annealed sample (Fig. 2 c) has a highly compacted morphology with tightly packed particles and a much smoother look at the microscopic level. NiTiO 3 (Fig. 2 d) is annealed by microwave, where the grains are significantly larger and the surface undulations are more prominent. The grains are more pronounced and the distribution is not uniform as they are distributed in the conventionally annealed counterpart. In general, the images of the SEM data show that microwave annealing results in both TiO 2 and NiTiO 3 films to have coarser surface morphology than when annealed in the traditional manner under the studied conditions. 3.2.2 AFM topography analysis Figure 3 (a-d) represents the AFM topography images of TiO 2 and NiTiO 3 thin films annealed in both conventional and microwave mode. The AFM images can give a nanoscale understanding of the changes in height on a 1 x 1 µm 2 area scanned. The traditionally annealed TiO 2 film (Fig. 3 a) has the comparatively smooth surface topography with average height variations and evenly distributed features on the surface. The height contrast of the microwave-annealed TiO 2 film (Fig. 3 b) is larger, which means that there is a higher surface roughness and more striking surface features. In the case of NiTiO 3 films, the traditionally annealed sample (Fig. 3 c) exhibits relatively lower height variations with a rich concentration of nanoscale structures. Conversely, the NiTiO 3 film annealed by the microwave (Fig. 3 d) exhibits much larger height variations and the surface topography is more heterogeneous. The color difference which has been seen in the AFM images indicates that surface height range has increased after microwave annealing of both materials. The same observations are reproducible in the scanned areas, which implies that there are changes in surface morphology that are reproducible, which have been caused by the annealing route. 3.2.3 Quantitative surface roughness comparison The AFM analysis of the surface roughness has provided a quantitative change which is summarized in Fig. 4 . In the case of TiO 2 thin films, the surface roughness is about 11.5 nm prior to annealing and 13.0 nm following the annealing of the thin film by microwave. Greater increase is seen in NiTiO 3 films, in which the roughness is approximately of the order of 13.0 nm with conventional annealing and about 20.0 nm with the use of the microwave annealing. The standard deviation of the repeated measurements is shown as the error bars, which showed good reproducibility of the measurements. NiTiO 3 films are always rougher on the surface than TiO 2 films at the same processing categories. Microwave annealing causes both materials to attain higher roughness values than the conventional annealing, and the difference between them is statistically significant in the case of NiTiO 3 as shown by the asterisk in Fig. 4 (p < 0.05). The quantitative trends of roughness are in line with the morphological characteristics in the SEM as well as the AFM images thereby demonstrating that microwave-annealing gives rise to stronger surface texture in the investigated conditions. 3.3 Optical properties 3.3.1 Optical transmittance Figure 5 (a) and 5(b) are optical transmittance spectra of TiO 2 thin films and NiTiO 3 thin films annealed by conventional and microwave methods, respectively. Both annealing conditions cause the films to have low transmittance in the ultraviolet region, which is then closely followed by a high transmittance in the near-UV region, and high transparency in the visible wavelengths. In the case of conventionally annealed films (Fig. 5 a), TiO 2 and NiTiO 3 have transmittance of about 80 83% and 75 80% respectively in the visible range. This is also found in microwave-annealed films (Fig. 5 b), where TiO 2 always exhibits high transmittance compared to NiTiO 3 in all wavelength ranges. The absorption edge of both the materials is the near-UV area but in both cases, TiO 2 has a slightly lower wavelength onset than NiTiO 3 when annealed. The general profile of the spectra is the same with conventional and microwave annealing, which refers to the fact that both heat-treatment paths provide optically clear films at the visible frequency range. 3.3.2 Refractive index variation Figure 6 shows the change of the refractive index with the annealing temperature and power of the microwave in both conventional and microwave annealing. In conventionally annealed films (Fig. 6 a), the refractive index grows regularly with the annealing temperature, with values of about 1.50 to 1.95 in the temperature range investigated. The contour distribution gives the value of the refractive index at the temperature within the range that reflects the variation in the refractive index as a continuous and monotonic distribution. In microwave-annealed films (Fig. 6 b), the same increase of refractive index, but as the power of the microwave increases, the value reaches values as high as about 2.00 at higher power levels. The refractive index contours exhibit similar tendencies to the values found when annealing is done using conventional methods and that the larger the level of processing the more the higher the values of the refractive index. Both the annealing paths have been clearly shown using the contour plots to demonstrate that both paths yield systematic and reproducible change in refractive index over the range measured. 3.3.3 Optical band gap analysis Figure 7 shows the Tauc plots, ((αhν)² versus photon energy), for TiO₂ and NiTiO₃ thin films subjected to conventional and microwave annealing. The plots were extrapolated to the photon energy axis in a linear fashion to determine the values of optical band gaps. In the case of TiO 2 the band gap of the conventional annealed condition at this case is about 3.3 eV whereas a slightly smaller figure of about 3.2 eV is obtained with the annealed films under the microwave condition. The band gap values in NiTiO 3 are smaller than in TiO 2 and the conventional annealing process has about 2.2 eV as the band gap and the microwave annealing process has about 2.1 eV as the band gap. Figure 7 shows the vertical dashed lines showing the extracted values of band gap where there is a steady decrease in the band gap of both materials between microwave- and conventionally annealed films. These patterns were observed in the Tauc plots and these patterns are uniform throughout the measured photon energy range, which indicates the determination of the band gap using the optical absorption data was reliable. 3.4 Dielectric properties Figure 8 represents the capacitance-voltage (C -V) characteristics of MOS capacitors made by means of TiO 2 and NiTiO 3 thin films that underwent a conventional and a microwave annealing. In both materials and annealing paths the capacitance is initially increasing with the gate voltage, and reaches its maximum in the accumulation region, and then starts to decrease at large gate voltages. The general configuration of the C V curves of conventionally annealed and microwave annealed films are similar, which implies similar dielectric properties of the films under applied electric fields. TiO 2 capacitors have an increased value of capacitance at a given gate voltage compared to NiTiO 3 capacitors under both annealed conditions. Both materials have slightly lower values of the peak capacitance values of films annealed using microwaves compared to the annealed films using conventional annealed methods as shown by the dashed curves in Fig. 8 . Figure 9 shows the difference between the dielectric constant of TiO 2 and NiTiO 3 thin films with the signal frequency. For the all the film, the dielectric constant decreases monotonically with the frequency over the measured range. The value of dielectric constant at all frequencies of both annealing paths is higher in TiO 2 film than in NiTiO 3 film. At lower frequencies, films annealed conventionally exhibit slightly higher values of dielectric constant than do films annealed at microwave frequencies. The values of dielectric constant of conventionally annealed and microwave-annealed films approach each other with increasing frequency meaning that these films have similar dielectric behaviour at elevated frequencies. The frequency-dependent trends are smooth and regular in Fig. 9 , and the overlap of the curves at the higher frequencies shows steady dielectric behaviour in both cases of annealing pathways. The fact that the dielectric constant did not show any sudden changes implies excellent repeatability of the measurements. The dielectric properties of the microwave-annealed films have been found to be similar to the dielectric annealed films within the range of experimental error which supported the trustworthiness of the microwave processing in dielectric thin films processing. 3.5 Electrical (I–V) properties Figure 10 shows the I-V characteristics of MOS devices made of TiO 2 and NiTiO 3 thin films annealed in conventional and microwave annealing. In both materials and annealing pathways, the current will have the nonlinear character of dependence on the applied voltage, where both positive and negative bias conditions will show the same behaviour. TiO 2 -based devices exhibit larger current values than NiTiO 3 -based devices at a specific applied voltage of annealing conditions in both cases. The general form of the I-V curves of the conventionally annealed and microwave- annealed films is similar which means that both exhibit similar electrical response to the roles of the voltage range studied. Nevertheless, the microwave annealed devices always record a lower current magnitude than their annealed counterparts at similar bias levels as shown by the dotted lines. Figure 11 displays the dependence of leakage current density on electric field of TiO 2 and NiTiO 3 thin films. In all the films, the leakage current density is a monotonically increasing function of the electric field. TiO 2 films have a higher leakage current density compared to NiTiO 3 films at an equivalent electric field, even in cases of annealing. Microwave-annealed films have a lower density of leakage current than conventional annealed films of both materials over the full evaluated range of electric fields. The distance between the curves of conventional and microwave annealing increases with the increase of the electric field, which means that the leakage characteristics are better in the films annealed using microwaves. The fact that the Fig. 10 and Fig. 11 show smooth and continuous trends, suggests that the electrical behaviour is stable and results can be reproducible. The generally low current and leakage current density of the films annealed by microwave indicates that microwave annealing provides electrical performance comparable to conventional annealing and in some instances even better when compared to conventional annealing operation under the experimental conditions included. 3.6 Comparative statistical discussion Table 1 shows a summary statistical analysis of the structural, morphological, optical, dielectric, and electrical characteristics of TiO 2 and NiTiO 3 thin films after conventional and microwave annealing. It is compared by the mean value and standard deviation and the level of statistical significance was determined at 95 percent of confidence (p < 0.05). Analysis of crystallite size shows statistically significant effect of annealing route of both materials. In the case of TiO 2 thin films, a greater mean crystallite size (42.0 ± 1.8nm) is obtained with microwave annealed thin films than with conventional annealed thin films at (33.0 ± 1.3nm) and this is shown to be statistically significant. Contrarily, NiTiO 3 films have a statistically significant decrease in crystallite size after microwave annealing (30.0 ± 1.2 nm) than conventional annealing (32.0 ± 1.3 nm), which is indicative of material-dependent crystallization behaviour. Table 1 Statistical comparison of properties of TiO₂ and NiTiO₃ thin films subjected to conventional and microwave annealing Property Material Conventional annealing (Mean ± SD) Microwave annealing (Mean ± SD) Statistical significance Crystallite size (nm) TiO₂ 33.0 ± 1.3 42.0 ± 1.8 √ ( p < 0.05) NiTiO₃ 32.0 ± 1.3 30.0 ± 1.2 √ ( (p < 0.05) ) Surface roughness (nm) TiO₂ 11.5 ± 1.0 13.0 ± 1.2 X NiTiO₃ 13.0 ± 1.5 20.0 ± 2.5 √ ( (p < 0.05) ) Visible transmittance (%) TiO₂ 82 ± 2 81 ± 2 X NiTiO₃ 78 ± 3 77 ± 3 X Optical band gap (eV) TiO₂ 3.30 ± 0.03 3.20 ± 0.03 √ ( (p < 0.05) ) NiTiO₃ 2.20 ± 0.04 2.10 ± 0.04 √ ( (p < 0.05) ) Dielectric constant (1 kHz) TiO₂ 28.5 ± 1.2 26.8 ± 1.1 X NiTiO₃ 24.0 ± 1.0 22.5 ± 0.9 X Leakage current density (A cm⁻² at 1.5 MV cm⁻¹) TiO₂ (1.2 ± 0.3) × 10⁻⁵ (4.8 ± 0.9) × 10⁻⁶ √ ( (p < 0.05) ) NiTiO₃ (6.5 ± 1.0) × 10⁻⁶ (2.3 ± 0.5) × 10⁻⁶ √ ( (p < 0.05) ) Measurement of surface roughness reveals a difference in trend of the two materials. There is no significant difference in the roughness between TiO 2 film of 11.5 ± 1.0 (conventional) and 13.0 ± 1.2 (microwave). NiTiO 3 films however have a statistically significant surface roughness augmentation during microwave annealing, which surges 13.0 ± 1.5 nm to 20.0 ± 2.5 nm, and this implies a strong surface alteration impact. In the visible frequency range, the optical transmittance values indicate that there is very little difference between the two annealing pathways of the two material types. The observed differences between TiO 2 (82 2 vs 81 2) and NiTiO 3 (78 3 vs 77 3) are not significant and validate the fact that the annealing route does not have a considerable impact on visible transparency within the experimental error. By comparison, optical band gap values undergo statistically significant decreases on both materials under microwave annealing. TiO 2 films experience a reduction in 3.30 ± 0.03 eV to 3.20 ± 0.03 eV and NiTiO 3 films experience a reduction in 2.20 ± 0.04 eV to 2.10 ± 0.04 eV which is a statistically significant reduction in optical band structure. The values of dielectric constant at 1 kHz exhibit the same trend (decreasing trend) in the case of microwave- annealed films compared to the film conventionally annealed in both materials but the difference is not statistically significant. This means that microwave annealing maintains the dielectric response of TiO 2 and NiTiO 3 thin films within an experimental error margin. Electrical performance, which is assessed by leakage current density at an electric field of 1.5 MV cm − 1 , is statistically significant at microwave annealed films. TiO 2 films experience a reduction in leakage current density of (1.2 ± 0.3) × 10 − 5 A cm − 1 to (4.8 ± 0.9) × 10 − 6 A cm − 1 , whereas NiTiO 3 films experience a reduction of (6.5 ± 1.0) × 10 − 6 A cm − 1 to (2.3 ± 0.5) × 10 − 6 A cm − 1 . Such decreases are statistically significant, which means that they have become better electrically insulated during microwave annealing. In general, statistical comparison of the summarized results in Table 2 indicate that microwave annealing creates statistically comparable material-property changes which in some cases are better than conventional annealing. The statistical significance of crystallite size, optical band gap, leakage current density improvements, and non-significant transmittance and dielectric constant changes confirm reliability and effectiveness of the microwave annealing method as an alternative post-deposition heat-treatment method of sol-gel derived TiO 2 and NiTiO 3 thin films. 4. Discussion It is evident that the statistical analysis presented in Table 2 has offered a concise analysis of the effect of the traditional and microwave annealing on sol-gel based TiO 2 and NiTiO 3 thin films. The trends have been in line with previous reports which indicate high reliance of thin film properties to post-deposition heat treatment, especially in sol-gel processed metal oxides [ 25 , 26 ]. The statistically significant growth of crystallite size in the TiO 2 film annealed using the microwave is in agreement with other studies that have reported a high level of crystallinity with the use of the microwave environment processing over the conventional thermal annealing [ 27 , 28 ]. The same enhancement in the crystallite size of the microwave-treated TiO 2 thin films has been credited to the presence of accelerated crystallization in a rapid thermal exposure regime [ 29 ]. Conversely, the statistically significant decrease in crystallite size was found to be material dependent with NiTiO 3 films having also been previously observed to respond in this manner when complex oxide systems receive non-equilibrium thermal treatments [ 30 ]. It has been found that surface roughness analysis shows that microwave annealing causes statistically significant roughness increase in NiTiO 3 films, but not statistically significant in TiO 2 films. Other material-specific roughness behaviour has been found in sol-gel derived mixed-metal oxides, where fast annealing adjusts surface morphology according to composition and microstructure [ 31 ]. The greater roughness of the NiTiO 3 films with microwave annealed is in line with previous results on ilmenite-like oxides [ 32 ]. The optical transmittance results indicate that both types of routing maintain a high level of transparency in the visible range and that no statistically significant differences are observed between conventional and microwave annealing of either of the materials. The observation is consistent with previous research on sol–gel based TiO 2 and its oxides, which established that little reference is made to annealing route on visible transmittance [ 33 , 34 ]. Nonetheless, the statistically significant decrease in optical band gap in the case of microwave-annealed films agrees with band gap modulation in anoxide thin films annealed rapidly [ 35 ]. The quantitative observation of dielectric constant reveals that the variations between regular and microwave annealing paths are not significant to the TiO 2 or NiTiO 3 films at 1 MHz. Much the same convergence of the dielectric properties of the various methods of annealing has also been observed in solgel derived oxide thin films after sufficient densification had been attained [ 31 ]. This explains the fact that the response to dielectric is largely controlled by the material composition, but not by annealing technique in the experimented conditions. Statistically significant decreases in leakage current density of the microwave- annealed films relative to conventionally annealed films are observed in electrical measurements of both materials. The lower leakage current density after microwave processing is a common feature with oxide based MOS materials that has been frequently linked with enhanced film uniformity and minimized leakage conduction path [ 36 , 37 ]. These reports are in line with the current results, which prove that microwave annealing is an effective solution in improving the performance of electrical insulations. In general, the comparative discussion, which was made in reduced reference, proves that the material properties obtained in microwave annealing are statistically equal to, and in a few cases even better than those obtained in conventional annealing. The correspondence of the trends observed to the representative studies indicate that microwave annealing is an effective alternative post-deposition heat-treatment pathway to sol solgel derived TiO 2 and NiTiO 3 thin-films. 5. Conclusions A comparative study was carried out in a systematic manner with the aim of assessing the effects of conventional and microwave annealing on sol-gel grown TiO 2 and NiTiO 3 thin films by application of statistical analysis. The structural studies established that both pathways annealed to crystalline films, where microwave annealing led to statistically significant increases in crystallite size of TiO 2 and material dependent increase in crystallite size of NiTiO 3 . The surface morphology analysis of the microwave annealed NiTiO 3 and TiO 2 films showed that the increase of surface roughness was significant in NiTiO 3 films but a statistically significant change was not observed in TiO 2 films. Optical analysis revealed that all films had high transmittance in the visible region, and no effect of annealing route was significant, but statistically significant reduction in optical band gap was found in the microwave-annealed films. Dielectric measurements showed that both annealing routes had similar dielectric constants, which showed consistent behaviour of dielectric. The characterization of the electrical properties showed that there was a statistically significant decrease in the leakage current density of both films annealed by microwaves. On the whole, the statistical results prove that microwave annealing can give material properties equivalent, and in some respects better, than conventional annealing, making it an effective and reliable alternative post deposition heat-treatment pathway of sol-gel derived metal oxide thin films. Declarations Author Contribution Munishamaiah Krishna contributed to the conceptualization of the study, experimental design, sol–gel synthesis, thin film deposition, and post-deposition heat treatment. Structural, morphological, optical, dielectric, and electrical characterizations were carried out by the author, and the experimental data were curated and validated. Statistical analysis, including ANOVA and significance testing, was performed to support the comparative evaluation. The original draft of the manuscript was written by the author, and subsequent revisions were carried out in response to critical review and feedback. The author read and approved the final version of the manuscript. Data Availability The datasets generated and analyzed during the current study are openly available in the Zenodo repository at https://doi.org/10.5281/zenodo.18161584 References Livage J, Henry M, Sanchez C (1988) Sol–gel chemistry of transition metal oxides. Prog Solid State Chem 18(4):259–341 Sakka S (2005) Handbook of Sol–Gel Science and Technology. Springer, Boston, MA, USA Levy D, Zayat M (2015) The Sol–Gel Handbook. Wiley-VCH, Weinheim, Germany Granqvist CG (2007) Transparent conductors as solar energy materials: A panoramic review. Sol Energy Mater Sol Cells 91(17):1529–1598 Pasquarelli RM, Ginley DS, O’Hayre R (2011) Solution processing of transparent conductors: From flask to film. Chem Soc Rev 40(11):5406–5441 Ohya Y, Saiki H, Takahashi Y (1994) Preparation of TiO₂ thin films by sol–gel method. 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Surf Coat Technol 384:125278 Scott JF (2000) Ferroelectric Memories. Springer, Berlin, Germany Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 02 Mar, 2026 Reviews received at journal 01 Mar, 2026 Reviewers agreed at journal 01 Mar, 2026 Reviews received at journal 24 Feb, 2026 Reviewers agreed at journal 23 Feb, 2026 Reviews received at journal 02 Feb, 2026 Reviewers agreed at journal 15 Jan, 2026 Reviewers invited by journal 07 Jan, 2026 Editor assigned by journal 07 Jan, 2026 Submission checks completed at journal 06 Jan, 2026 First submitted to journal 06 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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substrates.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Picture5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8530220/v1/5fde736dc43beb0d557a4259.jpg"},{"id":99857754,"identity":"f8879c93-8198-4ae5-927c-efff15d59c7a","added_by":"auto","created_at":"2026-01-09 06:19:08","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":169760,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eVariation of refractive index with annealing temperature and microwave power for metal oxide films.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Picture6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8530220/v1/afeb1dbf7e47e90ab2171974.jpg"},{"id":100357130,"identity":"026bca20-03c4-438b-bdb9-5566f9eafb29","added_by":"auto","created_at":"2026-01-16 07:18:56","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":67066,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDetermination of optical band gap energy from Tauc plots for conventionally annealed and microwave-annealed TiO₂ and NiTiO₃ thin films.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Picture7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8530220/v1/85d986d77d87dedae87e3336.jpg"},{"id":100357197,"identity":"7e65e96f-938b-4052-9106-2a3100ef736a","added_by":"auto","created_at":"2026-01-16 07:19:16","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":126873,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eC–V characteristics of MOS capacitors fabricated using conventionally annealed and microwave-annealed sol–gel derived metal oxide thin films.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Picture8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8530220/v1/4da4392a44833fc36f5dca55.jpg"},{"id":99857747,"identity":"839b4fc9-7565-486a-862d-2ecb1d2f8491","added_by":"auto","created_at":"2026-01-09 06:19:07","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":101992,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eVariation of dielectric constant with signal frequency for conventionally and microwave-annealed TiO₂ and NiTiO₃ thin films.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Picture9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8530220/v1/94e6d345e90e0b894efda236.jpg"},{"id":99857769,"identity":"38b23c7a-9979-4061-abfc-bfe58972e642","added_by":"auto","created_at":"2026-01-09 06:19:08","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":82356,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCurrent–voltage characteristics of MOS devices fabricated using conventionally annealed and microwave-annealed sol–gel derived metal oxide thin films.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Picture10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8530220/v1/c6aa763e756518c66aaffd4f.jpg"},{"id":99857753,"identity":"ff8415c1-b0e7-4833-a17c-ca0855e717ba","added_by":"auto","created_at":"2026-01-09 06:19:08","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":81258,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eComparison of leakage current density for metal oxide thin films under different heat treatments\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Picture11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8530220/v1/2a95ea6f1656ab6eb60b9a6d.jpg"},{"id":100406299,"identity":"06348c55-a39c-4dc2-85cb-e14579601e3f","added_by":"auto","created_at":"2026-01-16 13:00:04","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2940885,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8530220/v1/4c0d2c71-05e0-48d1-aec2-c521f73c6f27.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Statistical comparative analysis of microwave and conventionally annealed sol–gel derived metal oxide thin films","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe metal oxide thin films are a significant group of functional materials due to the broad range of their applications in optics [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], micro-electronics[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], sensing, energy conversion[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], and protective coating[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. They are also technologically relevant due to the strong tunability of optical, electrical and dielectric properties with regard to composition, microstructure and processing conditions [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. In comparison to bulk counterparts, thin films have enhanced surface-volume ratios, lower dimensionality, and altered defect structures which make them useful to modulate properties that can be used in advanced device applications [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOut of the numerous material systems studied, transition metal oxide [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], rare-earth oxide [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], perovskite oxide [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], and silica-based materials [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] have received continued interest because they have a wide band gap, high dielectric constant, thermal stability, and mechanical strength. Such materials find extensive use in optical coatings [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], gate dielectrics, capacitors, sensors and optoelectronic equipment [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Nonetheless, post-deposition heat treatment and the methodology used to produce metal oxide thin films has a significant effect on their functional workability; as it governs crystallinity, phase formation, grain growth and defect density [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSol-gel is a cost effective and versatile chemical solution to the preparation of metal oxide thin films having extraordinary compositional homogeneity and thickness [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The benefits associated with it are low processing temperature, easy doping, ability to coating large areas and also compatibility with varied surfaces [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. However, sol-gel prepared films tend to need post deposition heat treatment in order to drive out the remaining organics, cause crystallization, and densify the films [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. The most commonly used post-deposition treatment that enhances structural and functional performance of sol gel derived films is conventional furnace annealing [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Although effective, this process is energy consuming, time consuming and can cause unwanted thermal stresses especially in situations when high temperatures or lengthy annealing times are needed [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. These constraints have prompted the search of other annealing methods that are capable of providing similar or even better material qualities at lower thermal costs.\u003c/p\u003e \u003cp\u003eMicrowave-assisted annealing is also a promising alternative because it is fast and works on the principle of volumetric heating, specific energy absorption, and shortened processing times [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Compared to traditional thermal heating, microwaves can directly interfere with the material at the level of the molecules or crystalline structures, which allows promoting the rate of diffusion, speeding up the rate of crystallization, and having a more significant control over the microstructure [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. It has been reported in several studies that there is an improvement in crystallinity, altered grain growth and favourable electrical properties of microwave treated metal oxide films [\u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eRegardless of these stated benefits, most of the available literature is dedicated to individual systems of materials or qualitative comparisons between microwave and conventional annealing paths [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Extensive research involving several oxide systems and using comparative analysis based on statistically significant studies is still scarce [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Specifically, there are few systematic statistical analyses of any systematic statistical analysis of structural, optical, dielectric, and electrical properties that are processed under the same conditions, preventing a proper evaluation of the actual benefits of microwave-assisted annealing [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIt is in this respect that the current study seeks to fill this gap by offering a statistically validated comparative study on microwave and conventional annealed sol-gel based metal oxide thin films. Under controlled conditions, thin films of desired metal oxides and composite systems were fabricated and the structural, optical, dielectric as well as electrical characteristics of these films were compared systematically. The statistical tools were used to measure variability, determine reproducibility, and determine significant trends that results with the two post-deposition heat treatment routes. The results of this research provide useful information on whether microwave-assisted annealing can be used as a low-energy-consumption method to functional fabricate a metal oxide thin film.\u003c/p\u003e"},{"header":"2. Experimental methodology","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials and sol preparation\u003c/h2\u003e \u003cp\u003eThe materials used as precursor materials of TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e films were titanium (IV) isopropoxide [Ti(OCH(CH\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e4\u003c/sub\u003e] and nickel chloride. All the precursors were dissolved in 2-methoxyethanol to get clear and homogeneous solutions. Acetyl acetone was used as a chelating and complexing reagent to control the rate of hydrolysis of the metal precursors as well as stabilizing the metal\u0026ndash;organic complexes. Acid catalysis was used to start controlled hydrolysis and polycondensation reactions by continually stirring. In the case of composite oxide, the respective precursor sols; mixtures were prepared in pre-determined ratios of volumes and thoroughly mixed to achieve compositional homogeneity.\u003c/p\u003e \u003cp\u003eThe sols prepared were stirred with enough time in order to get sameness and then filtered to eliminate any particulates that have been formed during the reaction. Aging of all sols were done under ambient conditions before deposition in order to increase chemical stability, control viscosity, and reproducible formation of thin film. Optimized sol preparation process produced transparent and stable sols that could be used to deposit metal oxide thin films uniformly.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Thin film deposition\u003c/h2\u003e \u003cp\u003eThin films were deposited on pre-cleaned glass and p-type silicon substrates using the spin-coating technique. Prior to deposition, the substrates were ultrasonically cleaned sequentially in acetone, ethanol, and deionized water to remove organic contaminants and surface impurities, followed by drying in air. The prepared sols were dispensed onto the substrates and spin coated at optimized rotation speeds and durations to obtain uniform and adherent films. Each deposited layer was subjected to a soft-baking process at 60\u0026deg;C for 10 min to remove residual solvents and to promote partial densification of the films. The spin-coating and soft-baking cycle was repeated multiple times to achieve the desired film thickness. The deposition parameters were optimized to ensure uniform thickness, good surface coverage, and reproducible film quality across all material systems. The resulting as-deposited films were smooth, crack-free, and firmly adhered to the substrates, making them suitable for subsequent heat treatment and characterization.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Post-deposition heat treatment\u003c/h2\u003e \u003cp\u003eTo eliminate any remaining organic constituents, enhance crystallization process, and densify the sol\u0026ndash;gel produced thin films, post-deposition heat treatment was used. There were two alternative heat-treatment paths taken to make a comparative assessment of their effect on film qualities. In the traditional method, the deposited films were annealed in a muffle furnace at temperatures of between 100 and 800 \u0026deg;C and a time of between 1 and 3 h depending on the material system and substrate used. The annealing was conducted in a room atmosphere and the heating and cooling was controlled to reduce thermal stresses and eliminate film cracking.\u003c/p\u003e \u003cp\u003eMicrowave-assisted annealing was conducted in the alternative route in a domestic microwave oven with the power of between 180 and 900 W and exposure durations of 10\u0026ndash;15 min. The movies were positioned at a fixed point in the microwave cavity so that there is equal exposure. Effective temperatures of various levels of power in the microwave were measured experimentally through a calibrated thermocouple set-up. The two different post-deposition heat-treatment paths allowed to make a systematic comparison of both conventional and microwave annealing based on their influences on the structural, optical, dielectric and electrical characteristics of the sol-gel derived metal oxide thin films.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Characterization techniques\u003c/h2\u003e \u003cp\u003eThe structural properties of the sol\u0026ndash;gel derived thin films were examined using X-ray diffraction (XRD) to identify phase formation, crystallinity, and preferred orientation. The surface morphology of the films was analyzed using scanning electron microscopy (SEM), while surface topography and roughness were investigated using atomic force microscopy (AFM). Optical properties were studied by recording transmittance and reflectance spectra using a UV\u0026ndash;Vis\u0026ndash;NIR spectrophotometer in the wavelength range covering the ultraviolet, visible, and near-infrared regions. Optical constants such as refractive index and optical band gap energy were estimated from the recorded spectra using standard analytical methods.\u003c/p\u003e \u003cp\u003eDielectric and electrical properties were evaluated by fabricating metal\u0026ndash;oxide\u0026ndash;semiconductor (MOS) capacitor structures on p-type silicon substrates. Aluminium gate electrodes were deposited on the films using thermal evaporation. Capacitance\u0026ndash;voltage (C\u0026ndash;V) measurements were carried out at different signal frequencies to determine the dielectric constant and dielectric loss, while current\u0026ndash;voltage (I\u0026ndash;V) characteristics were recorded to evaluate leakage current density and resistivity.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Statistical analysis\u003c/h2\u003e \u003cp\u003eThe statistical analysis has been done on experimental data of structural, optical, dielectric, and electrical properties of the thin films to permit a strict quantitative comparison of microwave-assisted and conventional annealed thin films. Measures of each material system under each processing condition were repeated under the same experimental conditions in order to achieve repeatability. The data dispersion and the uncertainty of the experiments were measured by calculating the mean values and the standard deviation of them. To provide the statistical significance of the change in the main parameters (crystallite size, refractive index, optical band gap, dielectric constant, and leakage current density and resistivity) depending on the annealing temperature and microwave power, one-way analysis of variance was used. Student t-test was used where there was a need to draw comparisons between two distinct heat treatments paths to ascertain the significance of differences between the microwave-treated and the conventionally annealed films. The criterion of statistical significance was taken to be 95% ( (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) ).\u003c/p\u003e \u003cp\u003eBesides testing hypothesis, percentage variation and relative deviation analyses were also adopted in order to determine the extent of the changes of the properties upon various post-depositions heat treatment pathways. Statistical consistency of the trends in several material systems was considered as a sign of good structure-property correlations. This co-occurring application of descriptive statistics and inferential statistical tests helped in providing sufficient statistical significance to the comparative conclusions that were made in the current study as opposed to random or qualitative observations.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Structural properties\u003c/h2\u003e \u003cp\u003eThe XRD pattern of the sol\u0026ndash;gel derived TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e thin films underwent conventional annealing at 800\u0026deg;C and was obtained as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a). The TiO\u003csub\u003e2\u003c/sub\u003e film shows different diffraction peaks which are indexed to (101), (200), (105), (214), and (211) planes which demonstrates the creation of well crystallized phase. The reflections are characteristic of the NiTiO\u003csub\u003e3\u003c/sub\u003e film which is crystallised as they can be seen at (104), (116), (024), and (214) planes. No extra diffraction peaks are seen in both patterns and this implies that the secondary phases are not present under the current annealing condition.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(b) depicts the XRD patterns of TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e thin films annealed under a power of 600 W using the microwave. The observed diffraction peaks of both materials are very similar to those gathered in the case of conventional annealing, meaning that identical crystalline phases are produced with the use of the microwave. The fact that both TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e patterns have well-defined peaks indicate that microwave annealing is efficient in causing the crystallization process in a shorter processing time. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(c) has provided a quantitative analysis of the change in crystallite size via conventional and microwave annealing. In the case of conventionally annealed films, TiO\u003csub\u003e2\u003c/sub\u003e crystallite size grows between about 21 nm at 100 \u0026deg;C to about 33 nm at 800 \u0026deg;C, and NiTiO\u003csub\u003e3\u003c/sub\u003e does the same between about 22 nm and about 32 nm. TiO\u003csub\u003e2\u003c/sub\u003e has been shown to increase in crystallite size between about 26 nm at 200 W to about 42 nm at 800 W, and NiTiO\u003csub\u003e3\u003c/sub\u003e has been shown to increase between about 21 nm and about 30 nm.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMicrowave-although annealed films always have larger crystallites sizes at comparable levels of processing than traditionally annealed films of TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(c) depicts the error bars of the repeated measurements which are the standard deviation meaning that it can be repeated. The statistical analysis proves that the differences between the crystallite size of the conventional and microwave annealing routes can be labeled as significant ((p\u0026thinsp;\u0026lt;\u0026thinsp;0.05)). Generally, the XRD analysis and the crystallite size analysis indicate that both annealing methods result in the crystalline TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e thin films with microwave annealing yielding relatively large crystallite sizes under the studied conditions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Surface morphology and roughness analysis\u003c/h2\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1 SEM surface morphology\u003c/h2\u003e \u003cp\u003eThe SEM images of TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e thin films annealed by conventional and microwave methods are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a-d). The TiO\u003csub\u003e2\u003c/sub\u003e film that has been conventionally annealed (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea) displays a densely packed granular structure that consists of grains that are almost spherical and moderately sized with moderate size dispersion. The grains are seen as being tightly stacked with minimal between grain openings, which means that they are covered uniformly. By comparison, the TiO\u003csub\u003e2\u003c/sub\u003e film (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb) fabricated by microwave annealing exhibits a more granular structure visually and has relatively larger grains and more contact between grains. The surface is more rough and there is a better contrast between separate grains.\u003c/p\u003e \u003cp\u003eIn the case of NiTiO\u003csub\u003e3\u003c/sub\u003e films, the traditionally annealed sample (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec) has a highly compacted morphology with tightly packed particles and a much smoother look at the microscopic level. NiTiO\u003csub\u003e3\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed) is annealed by microwave, where the grains are significantly larger and the surface undulations are more prominent. The grains are more pronounced and the distribution is not uniform as they are distributed in the conventionally annealed counterpart. In general, the images of the SEM data show that microwave annealing results in both TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e films to have coarser surface morphology than when annealed in the traditional manner under the studied conditions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e3.2.2 AFM topography analysis\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a-d) represents the AFM topography images of TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e thin films annealed in both conventional and microwave mode. The AFM images can give a nanoscale understanding of the changes in height on a 1 x 1 \u0026micro;m\u003csup\u003e2\u003c/sup\u003e area scanned. The traditionally annealed TiO\u003csub\u003e2\u003c/sub\u003e film (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea) has the comparatively smooth surface topography with average height variations and evenly distributed features on the surface. The height contrast of the microwave-annealed TiO\u003csub\u003e2\u003c/sub\u003e film (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb) is larger, which means that there is a higher surface roughness and more striking surface features. In the case of NiTiO\u003csub\u003e3\u003c/sub\u003e films, the traditionally annealed sample (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec) exhibits relatively lower height variations with a rich concentration of nanoscale structures. Conversely, the NiTiO\u003csub\u003e3\u003c/sub\u003e film annealed by the microwave (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed) exhibits much larger height variations and the surface topography is more heterogeneous. The color difference which has been seen in the AFM images indicates that surface height range has increased after microwave annealing of both materials. The same observations are reproducible in the scanned areas, which implies that there are changes in surface morphology that are reproducible, which have been caused by the annealing route.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e3.2.3 Quantitative surface roughness comparison\u003c/h2\u003e \u003cp\u003eThe AFM analysis of the surface roughness has provided a quantitative change which is summarized in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. In the case of TiO\u003csub\u003e2\u003c/sub\u003e thin films, the surface roughness is about 11.5 nm prior to annealing and 13.0 nm following the annealing of the thin film by microwave. Greater increase is seen in NiTiO\u003csub\u003e3\u003c/sub\u003e films, in which the roughness is approximately of the order of 13.0 nm with conventional annealing and about 20.0 nm with the use of the microwave annealing. The standard deviation of the repeated measurements is shown as the error bars, which showed good reproducibility of the measurements. NiTiO\u003csub\u003e3\u003c/sub\u003e films are always rougher on the surface than TiO\u003csub\u003e2\u003c/sub\u003e films at the same processing categories. Microwave annealing causes both materials to attain higher roughness values than the conventional annealing, and the difference between them is statistically significant in the case of NiTiO\u003csub\u003e3\u003c/sub\u003e as shown by the asterisk in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The quantitative trends of roughness are in line with the morphological characteristics in the SEM as well as the AFM images thereby demonstrating that microwave-annealing gives rise to stronger surface texture in the investigated conditions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Optical properties\u003c/h2\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e3.3.1 Optical transmittance\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a) and 5(b) are optical transmittance spectra of TiO\u003csub\u003e2\u003c/sub\u003e thin films and NiTiO\u003csub\u003e3\u003c/sub\u003e thin films annealed by conventional and microwave methods, respectively. Both annealing conditions cause the films to have low transmittance in the ultraviolet region, which is then closely followed by a high transmittance in the near-UV region, and high transparency in the visible wavelengths. In the case of conventionally annealed films (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea), TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e have transmittance of about 80 83% and 75 80% respectively in the visible range. This is also found in microwave-annealed films (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb), where TiO\u003csub\u003e2\u003c/sub\u003e always exhibits high transmittance compared to NiTiO\u003csub\u003e3\u003c/sub\u003e in all wavelength ranges. The absorption edge of both the materials is the near-UV area but in both cases, TiO\u003csub\u003e2\u003c/sub\u003e has a slightly lower wavelength onset than NiTiO\u003csub\u003e3\u003c/sub\u003e when annealed. The general profile of the spectra is the same with conventional and microwave annealing, which refers to the fact that both heat-treatment paths provide optically clear films at the visible frequency range.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e3.3.2 Refractive index variation\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the change of the refractive index with the annealing temperature and power of the microwave in both conventional and microwave annealing. In conventionally annealed films (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea), the refractive index grows regularly with the annealing temperature, with values of about 1.50 to 1.95 in the temperature range investigated. The contour distribution gives the value of the refractive index at the temperature within the range that reflects the variation in the refractive index as a continuous and monotonic distribution. In microwave-annealed films (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb), the same increase of refractive index, but as the power of the microwave increases, the value reaches values as high as about 2.00 at higher power levels. The refractive index contours exhibit similar tendencies to the values found when annealing is done using conventional methods and that the larger the level of processing the more the higher the values of the refractive index. Both the annealing paths have been clearly shown using the contour plots to demonstrate that both paths yield systematic and reproducible change in refractive index over the range measured.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e \u003ch2\u003e3.3.3 Optical band gap analysis\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e shows the Tauc plots, ((αhν)\u0026sup2; versus photon energy), for TiO₂ and NiTiO₃ thin films subjected to conventional and microwave annealing. The plots were extrapolated to the photon energy axis in a linear fashion to determine the values of optical band gaps. In the case of TiO\u003csub\u003e2\u003c/sub\u003e the band gap of the conventional annealed condition at this case is about 3.3 eV whereas a slightly smaller figure of about 3.2 eV is obtained with the annealed films under the microwave condition. The band gap values in NiTiO\u003csub\u003e3\u003c/sub\u003e are smaller than in TiO\u003csub\u003e2\u003c/sub\u003e and the conventional annealing process has about 2.2 eV as the band gap and the microwave annealing process has about 2.1 eV as the band gap. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e shows the vertical dashed lines showing the extracted values of band gap where there is a steady decrease in the band gap of both materials between microwave- and conventionally annealed films. These patterns were observed in the Tauc plots and these patterns are uniform throughout the measured photon energy range, which indicates the determination of the band gap using the optical absorption data was reliable.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Dielectric properties\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e represents the capacitance-voltage (C -V) characteristics of MOS capacitors made by means of TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e thin films that underwent a conventional and a microwave annealing. In both materials and annealing paths the capacitance is initially increasing with the gate voltage, and reaches its maximum in the accumulation region, and then starts to decrease at large gate voltages. The general configuration of the C V curves of conventionally annealed and microwave annealed films are similar, which implies similar dielectric properties of the films under applied electric fields. TiO\u003csub\u003e2\u003c/sub\u003e capacitors have an increased value of capacitance at a given gate voltage compared to NiTiO\u003csub\u003e3\u003c/sub\u003e capacitors under both annealed conditions. Both materials have slightly lower values of the peak capacitance values of films annealed using microwaves compared to the annealed films using conventional annealed methods as shown by the dashed curves in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e shows the difference between the dielectric constant of TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e thin films with the signal frequency. For the all the film, the dielectric constant decreases monotonically with the frequency over the measured range. The value of dielectric constant at all frequencies of both annealing paths is higher in TiO\u003csub\u003e2\u003c/sub\u003e film than in NiTiO\u003csub\u003e3\u003c/sub\u003e film. At lower frequencies, films annealed conventionally exhibit slightly higher values of dielectric constant than do films annealed at microwave frequencies. The values of dielectric constant of conventionally annealed and microwave-annealed films approach each other with increasing frequency meaning that these films have similar dielectric behaviour at elevated frequencies.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe frequency-dependent trends are smooth and regular in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, and the overlap of the curves at the higher frequencies shows steady dielectric behaviour in both cases of annealing pathways. The fact that the dielectric constant did not show any sudden changes implies excellent repeatability of the measurements. The dielectric properties of the microwave-annealed films have been found to be similar to the dielectric annealed films within the range of experimental error which supported the trustworthiness of the microwave processing in dielectric thin films processing.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Electrical (I\u0026ndash;V) properties\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;10 shows the I-V characteristics of MOS devices made of TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e thin films annealed in conventional and microwave annealing. In both materials and annealing pathways, the current will have the nonlinear character of dependence on the applied voltage, where both positive and negative bias conditions will show the same behaviour. TiO\u003csub\u003e2\u003c/sub\u003e-based devices exhibit larger current values than NiTiO\u003csub\u003e3\u003c/sub\u003e -based devices at a specific applied voltage of annealing conditions in both cases. The general form of the I-V curves of the conventionally annealed and microwave- annealed films is similar which means that both exhibit similar electrical response to the roles of the voltage range studied. Nevertheless, the microwave annealed devices always record a lower current magnitude than their annealed counterparts at similar bias levels as shown by the dotted lines.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e11\u003c/span\u003e displays the dependence of leakage current density on electric field of TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e thin films. In all the films, the leakage current density is a monotonically increasing function of the electric field. TiO\u003csub\u003e2\u003c/sub\u003e films have a higher leakage current density compared to NiTiO\u003csub\u003e3\u003c/sub\u003e films at an equivalent electric field, even in cases of annealing. Microwave-annealed films have a lower density of leakage current than conventional annealed films of both materials over the full evaluated range of electric fields. The distance between the curves of conventional and microwave annealing increases with the increase of the electric field, which means that the leakage characteristics are better in the films annealed using microwaves.\u003c/p\u003e \u003cp\u003eThe fact that the Fig.\u0026nbsp;10 and Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e11\u003c/span\u003e show smooth and continuous trends, suggests that the electrical behaviour is stable and results can be reproducible. The generally low current and leakage current density of the films annealed by microwave indicates that microwave annealing provides electrical performance comparable to conventional annealing and in some instances even better when compared to conventional annealing operation under the experimental conditions included.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e3.6 Comparative statistical discussion\u003c/h2\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows a summary statistical analysis of the structural, morphological, optical, dielectric, and electrical characteristics of TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e thin films after conventional and microwave annealing. It is compared by the mean value and standard deviation and the level of statistical significance was determined at 95 percent of confidence (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Analysis of crystallite size shows statistically significant effect of annealing route of both materials. In the case of TiO\u003csub\u003e2\u003c/sub\u003e thin films, a greater mean crystallite size (42.0 \u0026plusmn; 1.8nm) is obtained with microwave annealed thin films than with conventional annealed thin films at (33.0 \u0026plusmn; 1.3nm) and this is shown to be statistically significant. Contrarily, NiTiO\u003csub\u003e3\u003c/sub\u003e films have a statistically significant decrease in crystallite size after microwave annealing (30.0 \u0026plusmn; 1.2 nm) than conventional annealing (32.0 \u0026plusmn; 1.3 nm), which is indicative of material-dependent crystallization behaviour.\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\u003eStatistical comparison of properties of TiO₂ and NiTiO₃ thin films subjected to conventional and microwave annealing\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProperty\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMaterial\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eConventional annealing (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMicrowave annealing (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eStatistical significance\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eCrystallite size (nm)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTiO₂\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e33.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e42.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026radic; (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNiTiO₃\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e32.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e30.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026radic; (\u003cem\u003e(p\u0026thinsp;\u0026lt;\u0026thinsp;0.05)\u003c/em\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eSurface roughness (nm)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTiO₂\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e11.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e13.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eX\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNiTiO₃\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e13.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e20.0\u0026thinsp;\u0026plusmn;\u0026thinsp;2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026radic; (\u003cem\u003e(p\u0026thinsp;\u0026lt;\u0026thinsp;0.05)\u003c/em\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eVisible transmittance (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTiO₂\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e82\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e81\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eX\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNiTiO₃\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e78\u0026thinsp;\u0026plusmn;\u0026thinsp;3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e77\u0026thinsp;\u0026plusmn;\u0026thinsp;3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eX\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eOptical band gap (eV)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTiO₂\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e3.30\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e3.20\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026radic; (\u003cem\u003e(p\u0026thinsp;\u0026lt;\u0026thinsp;0.05)\u003c/em\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNiTiO₃\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e2.20\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e2.10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026radic; (\u003cem\u003e(p\u0026thinsp;\u0026lt;\u0026thinsp;0.05)\u003c/em\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eDielectric constant (1 kHz)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTiO₂\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e28.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e26.8\u0026thinsp;\u0026plusmn;\u0026thinsp;1.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eX\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNiTiO₃\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e24.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e22.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eX\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eLeakage current density (A cm⁻\u0026sup2; at 1.5 MV cm⁻\u0026sup1;)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTiO₂\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e(1.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3) \u0026times; 10⁻⁵\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e(4.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9) \u0026times; 10⁻⁶\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026radic; (\u003cem\u003e(p\u0026thinsp;\u0026lt;\u0026thinsp;0.05)\u003c/em\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNiTiO₃\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e(6.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0) \u0026times; 10⁻⁶\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e(2.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5) \u0026times; 10⁻⁶\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026radic; (\u003cem\u003e(p\u0026thinsp;\u0026lt;\u0026thinsp;0.05)\u003c/em\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eMeasurement of surface roughness reveals a difference in trend of the two materials. There is no significant difference in the roughness between TiO\u003csub\u003e2\u003c/sub\u003e film of 11.5 \u0026plusmn; 1.0 (conventional) and 13.0 \u0026plusmn; 1.2 (microwave). NiTiO\u003csub\u003e3\u003c/sub\u003e films however have a statistically significant surface roughness augmentation during microwave annealing, which surges 13.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5 nm to 20.0\u0026thinsp;\u0026plusmn;\u0026thinsp;2.5 nm, and this implies a strong surface alteration impact. In the visible frequency range, the optical transmittance values indicate that there is very little difference between the two annealing pathways of the two material types. The observed differences between TiO\u003csub\u003e2\u003c/sub\u003e (82 2 vs 81 2) and NiTiO\u003csub\u003e3\u003c/sub\u003e (78 3 vs 77 3) are not significant and validate the fact that the annealing route does not have a considerable impact on visible transparency within the experimental error.\u003c/p\u003e \u003cp\u003eBy comparison, optical band gap values undergo statistically significant decreases on both materials under microwave annealing. TiO\u003csub\u003e2\u003c/sub\u003e films experience a reduction in 3.30 \u0026plusmn; 0.03 eV to 3.20 \u0026plusmn; 0.03 eV and NiTiO\u003csub\u003e3\u003c/sub\u003e films experience a reduction in 2.20 \u0026plusmn; 0.04 eV to 2.10 \u003cem\u003e\u0026plusmn;\u003c/em\u003e 0.04 eV which is a statistically significant reduction in optical band structure. The values of dielectric constant at 1 kHz exhibit the same trend (decreasing trend) in the case of microwave- annealed films compared to the film conventionally annealed in both materials but the difference is not statistically significant. This means that microwave annealing maintains the dielectric response of TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e thin films within an experimental error margin. Electrical performance, which is assessed by leakage current density at an electric field of 1.5 MV cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, is statistically significant at microwave annealed films. TiO\u003csub\u003e2\u003c/sub\u003e films experience a reduction in leakage current density of (1.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3) \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e A cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to (4.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9) \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e A cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, whereas NiTiO\u003csub\u003e3\u003c/sub\u003e films experience a reduction of (6.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0) \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e A cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to (2.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5) \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e A cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Such decreases are statistically significant, which means that they have become better electrically insulated during microwave annealing. In general, statistical comparison of the summarized results in Table\u0026nbsp;2 indicate that microwave annealing creates statistically comparable material-property changes which in some cases are better than conventional annealing. The statistical significance of crystallite size, optical band gap, leakage current density improvements, and non-significant transmittance and dielectric constant changes confirm reliability and effectiveness of the microwave annealing method as an alternative post-deposition heat-treatment method of sol-gel derived TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e thin films.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eIt is evident that the statistical analysis presented in Table\u0026nbsp;2 has offered a concise analysis of the effect of the traditional and microwave annealing on sol-gel based TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e thin films. The trends have been in line with previous reports which indicate high reliance of thin film properties to post-deposition heat treatment, especially in sol-gel processed metal oxides [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe statistically significant growth of crystallite size in the TiO\u003csub\u003e2\u003c/sub\u003e film annealed using the microwave is in agreement with other studies that have reported a high level of crystallinity with the use of the microwave environment processing over the conventional thermal annealing [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. The same enhancement in the crystallite size of the microwave-treated TiO\u003csub\u003e2\u003c/sub\u003e thin films has been credited to the presence of accelerated crystallization in a rapid thermal exposure regime [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Conversely, the statistically significant decrease in crystallite size was found to be material dependent with NiTiO\u003csub\u003e3\u003c/sub\u003e films having also been previously observed to respond in this manner when complex oxide systems receive non-equilibrium thermal treatments [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIt has been found that surface roughness analysis shows that microwave annealing causes statistically significant roughness increase in NiTiO\u003csub\u003e3\u003c/sub\u003e films, but not statistically significant in TiO\u003csub\u003e2\u003c/sub\u003e films. Other material-specific roughness behaviour has been found in sol-gel derived mixed-metal oxides, where fast annealing adjusts surface morphology according to composition and microstructure [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. The greater roughness of the NiTiO\u003csub\u003e3\u003c/sub\u003e films with microwave annealed is in line with previous results on ilmenite-like oxides [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe optical transmittance results indicate that both types of routing maintain a high level of transparency in the visible range and that no statistically significant differences are observed between conventional and microwave annealing of either of the materials. The observation is consistent with previous research on sol\u0026ndash;gel based TiO\u003csub\u003e2\u003c/sub\u003e and its oxides, which established that little reference is made to annealing route on visible transmittance [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Nonetheless, the statistically significant decrease in optical band gap in the case of microwave-annealed films agrees with band gap modulation in anoxide thin films annealed rapidly [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe quantitative observation of dielectric constant reveals that the variations between regular and microwave annealing paths are not significant to the TiO\u003csub\u003e2\u003c/sub\u003e or NiTiO\u003csub\u003e3\u003c/sub\u003e films at 1 MHz. Much the same convergence of the dielectric properties of the various methods of annealing has also been observed in solgel derived oxide thin films after sufficient densification had been attained [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. This explains the fact that the response to dielectric is largely controlled by the material composition, but not by annealing technique in the experimented conditions.\u003c/p\u003e \u003cp\u003eStatistically significant decreases in leakage current density of the microwave- annealed films relative to conventionally annealed films are observed in electrical measurements of both materials. The lower leakage current density after microwave processing is a common feature with oxide based MOS materials that has been frequently linked with enhanced film uniformity and minimized leakage conduction path [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. These reports are in line with the current results, which prove that microwave annealing is an effective solution in improving the performance of electrical insulations.\u003c/p\u003e \u003cp\u003eIn general, the comparative discussion, which was made in reduced reference, proves that the material properties obtained in microwave annealing are statistically equal to, and in a few cases even better than those obtained in conventional annealing. The correspondence of the trends observed to the representative studies indicate that microwave annealing is an effective alternative post-deposition heat-treatment pathway to sol solgel derived TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e thin-films.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eA comparative study was carried out in a systematic manner with the aim of assessing the effects of conventional and microwave annealing on sol-gel grown TiO\u003csub\u003e2\u003c/sub\u003e and NiTiO\u003csub\u003e3\u003c/sub\u003e thin films by application of statistical analysis. The structural studies established that both pathways annealed to crystalline films, where microwave annealing led to statistically significant increases in crystallite size of TiO\u003csub\u003e2\u003c/sub\u003e and material dependent increase in crystallite size of NiTiO\u003csub\u003e3\u003c/sub\u003e. The surface morphology analysis of the microwave annealed NiTiO\u003csub\u003e3\u003c/sub\u003e and TiO\u003csub\u003e2\u003c/sub\u003e films showed that the increase of surface roughness was significant in NiTiO\u003csub\u003e3\u003c/sub\u003e films but a statistically significant change was not observed in TiO\u003csub\u003e2\u003c/sub\u003e films. Optical analysis revealed that all films had high transmittance in the visible region, and no effect of annealing route was significant, but statistically significant reduction in optical band gap was found in the microwave-annealed films. Dielectric measurements showed that both annealing routes had similar dielectric constants, which showed consistent behaviour of dielectric. The characterization of the electrical properties showed that there was a statistically significant decrease in the leakage current density of both films annealed by microwaves. On the whole, the statistical results prove that microwave annealing can give material properties equivalent, and in some respects better, than conventional annealing, making it an effective and reliable alternative post deposition heat-treatment pathway of sol-gel derived metal oxide thin films.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eMunishamaiah Krishna contributed to the conceptualization of the study, experimental design, sol\u0026ndash;gel synthesis, thin film deposition, and post-deposition heat treatment. Structural, morphological, optical, dielectric, and electrical characterizations were carried out by the author, and the experimental data were curated and validated. Statistical analysis, including ANOVA and significance testing, was performed to support the comparative evaluation. The original draft of the manuscript was written by the author, and subsequent revisions were carried out in response to critical review and feedback. The author read and approved the final version of the manuscript.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets generated and analyzed during the current study are openly available in the Zenodo repository at https://doi.org/10.5281/zenodo.18161584\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLivage J, Henry M, Sanchez C (1988) Sol\u0026ndash;gel chemistry of transition metal oxides. Prog Solid State Chem 18(4):259\u0026ndash;341\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSakka S (2005) Handbook of Sol\u0026ndash;Gel Science and Technology. Springer, Boston, MA, USA\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLevy D, Zayat M (2015) The Sol\u0026ndash;Gel Handbook. Wiley-VCH, Weinheim, Germany\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGranqvist CG (2007) Transparent conductors as solar energy materials: A panoramic review. Sol Energy Mater Sol Cells 91(17):1529\u0026ndash;1598\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePasquarelli RM, Ginley DS, O\u0026rsquo;Hayre R (2011) Solution processing of transparent conductors: From flask to film. Chem Soc Rev 40(11):5406\u0026ndash;5441\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOhya Y, Saiki H, Takahashi Y (1994) Preparation of TiO₂ thin films by sol\u0026ndash;gel method. J Mater Sci 29(15):4099\u0026ndash;4103\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMajumder SB, Katiyar RS (2001) Electrical properties of sol\u0026ndash;gel derived TiO₂ thin films. Thin Solid Films 396:1\u0026ndash;2\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKamalasanan MN, Chandra S (1996) Dielectric properties of oxide thin films. Thin Solid Films 288:1\u0026ndash;2\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRobertson J (2004) High dielectric constant oxides. Eur Phys J Appl Phys 28(3):265\u0026ndash;291\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKomarneni S, Roy R, Li QH (1992) Microwave-hydrothermal synthesis of ceramic powders. Mater Res Bull 27(12):1393\u0026ndash;1405\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMetaxas AC, Meredith RJ \u003cem\u003eIndustrial Microwave Heating\u003c/em\u003e, London, U.K.: Peter Peregrinus, 1983.\\\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRoy S, Agrawal D, Cheng J (1998) Microwave processing of ceramics. Curr Opin Solid State Mater Sci 3(5):480\u0026ndash;485\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCheng J, Roy R, Agrawal D (2001) Microwave sintering of ceramics. 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Springer, Berlin, Germany\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":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":false,"email":"","identity":"journal-of-materials-science-materials-in-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Journal of Materials Science: Materials in Engineering","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"VoR Journals","inReviewEnabled":false,"inReviewRevisionsEnabled":false},"keywords":"Sol–gel thin films, Microwave annealing, Conventional annealing, Statistical analysis, Metal oxide thin films","lastPublishedDoi":"10.21203/rs.3.rs-8530220/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8530220/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe impact of conventional furnace annealing and microwave annealing on sol-gel-derived TiO₂ and NiTiO₃ thin film was comparatively investigated on a statistically supported framework. The deposition of thin films was done through spin coating, and then heat treatment was done through the two different routes under controlled conditions. XRD, SEM, AFM, UV-visible spectroscopy, C-V, and I-V measurements were systematically used to analyse the structural, morphological, optical, dielectric, and electrical properties. To evaluate the reproducibility and reliability, statistical methods such as the analysis of mean-standard deviation and testing of significant results were used. Microwave annealing produced statistically significant changes in crystallite size and optical band gap and leakage current density compared to conventional annealing, with visible transmittance and dielectric constant being statistically similar. The behaviour that was dependent on the material was seen, especially the roughness of the surface and crystallite evolution. In general, the findings indicate that microwave annealing can be as efficient as, or even superior to, conventional annealing with shorter processing times, making it a viable alternative to the post-deposition heat treatment of sol-gel-made metal oxide thin films.\u003c/p\u003e","manuscriptTitle":"Statistical comparative analysis of microwave and conventionally annealed sol–gel derived metal oxide thin films","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-01-09 06:19:02","doi":"10.21203/rs.3.rs-8530220/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-03-02T08:51:53+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-01T12:58:22+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"2949228241766253192164413468013724297","date":"2026-03-01T12:45:07+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-25T02:05:28+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"326314751845427163132860434990429475418","date":"2026-02-23T18:43:18+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-02T16:50:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"311645808158008061617669962535380859944","date":"2026-01-15T14:54:17+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-01-07T10:06:50+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-01-07T09:46:33+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-01-06T12:29:03+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Materials Science: Materials in Engineering","date":"2026-01-06T10:29:23+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":false,"email":"","identity":"journal-of-materials-science-materials-in-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Journal of Materials Science: Materials in Engineering","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"VoR Journals","inReviewEnabled":false,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"fc90ea6e-3075-4b99-844c-a11f5e148d30","owner":[],"postedDate":"January 9th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-14T11:10:08+00:00","versionOfRecord":[],"versionCreatedAt":"2026-01-09 06:19:02","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8530220","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8530220","identity":"rs-8530220","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}