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Substrate temperature-dependent properties of sprayed cobalt oxide thin films
摘要： Cobalt oxide (Co3O4) thin films were deposited onto amorphous glass substrates using a home-made pneumatic spray pyrolysis system (SPT) from aqueous solution of cobalt chloride salt (CoCl2) as a source of cobalt. The films were deposited at different substrate temperatures ranging from 250 to 450?°C in steps of 50?°C. The effect of substrate temperature on structural, electrical and optical properties was studied. The characterization of samples was carried out by X-ray diffraction (XRD), UV–Vis spectroscopy, energy dispersive spectroscopy (EDS), scanning electron microscopy and four probe points measurements. The XRD study showed that all the films were polycrystalline consisting of Co3O4 spinel cubic phase. The preferred orientation of the crystallites changed from (311) to (111) when the substrate temperature increases. The average calculated grain size was about 40.38?nm. Morphological studies exposed that the films surface morphology is almost homogeneous and well-covered. Peaks associated with Co and O elements are present in EDS analysis witch confirm the composition of the films. The optical transmittance and the band gaps energy increase with the increase of substrate temperature. The measured electrical conductivity at room temperature was found in the order of 10?1 (??cm)?1.
关键词： Thin films,Substrate temperature,Cobalt oxide,Spray pyrolysis,Structural properties,Optical properties,Electrical properties
更新于2025-09-10 09:29:36
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Optical properties of p-type SnOx thin films deposited by DC reactive sputtering
摘要： Refractive index (n), extinction coefficient (k), effective complex dielectric function (ε) and band gap energy (Eg) of p-type SnOx thin films from 0.75 to 4 eV are studied. 25 nm thick films were deposited by direct current (DC) magnetron sputtering in reactive argon and oxygen atmosphere at different relative oxygen partial pressure (OPP) followed by a post annealing treatment at 250 °C in air atmosphere for 30 min. The relative high Hall effect mobility (μ) of the SnOx was attributed to the dominant SnO phase in films grown at 15% OPP. Films deposited at 5 and 11% OPP showed incomplete Sn oxidation resulting in a mixture of Sn and SnO phases with lower hole mobility. Optical transmittance (T) and reflectance (R) are described by assuming a model where the p-type SnOx films are defined by a dispersion formula based on a generalization of the Lorentz oscillator model. The roughness of the films (r) was modeled by a Bruggeman effective medium approximation (BEMA). From the optical analysis, k in the visible spectral region show high values for films with phase mixture, while films with single SnO phase presented negligible values. Films with single SnO phase have low n, this latter result from the lower compact microstructure of these films. Also, energies associated to direct and indirect transitions of the Brillouin zone of the SnOx films were identified from the evaluated ε. Finally, the increase in the values of Eg energy was related to the increase in the SnO phase.
关键词： p-type SnOx,optical properties,Hall effect mobility,thin films,DC reactive sputtering
更新于2025-09-10 09:29:36
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Study of the optical properties of amorphous As–Se–S thin films
摘要： This study investigates the effects of substitution of selenium by sulfur on the optical constants of amorphous (a-)As20Se80 ? xSx films (x = 0, 4, 8, 12, 16, and 20 at%), where the coordination number for both Se and S is the same. The absorption coefficient, α, and the index of refraction, n, were derived using the transmission spectra in a wide range of wavelengths from 400 to 2500 nm. This revealed that the index of refraction for the a-As20Se80 ? xSx system decreases with increase in sulfur content throughout the range under study. The effective coordination number of As has been determined based on the refractive index dispersion analysis. A decreasing in Nc from 4.022 to 3.752 with increase content of sulfur from 0 to 20 at% has been recorded. In addition, the optical bandgap, Eg, of the a-As20Se80 ? xSx thin films increases with increase in S content which can be explicated in terms of the chemical bond approach.
关键词： optical bandgap,refractive index,amorphous As–Se–S thin films,chalcogenide glasses,optical properties
更新于2025-09-10 09:29:36
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Reusable surface-enhanced Raman substrates using microwave annealing
摘要： In this work, we report the fabrication of large-scale homogeneous surface-enhanced Raman scattering (SERS) substrates using a microwave annealing (MWA) process on Ag thin films on silicon, using a typical low-cost domestic microwave oven, avoiding the use of chemicals and stabilizing agents, or time-consuming and expensive approaches. We provide evidence that in 5–15 s, uniform and reproducible SERS substrates of several centimeter squares can be grown, providing a Raman signal enhancement of five orders of magnitude, for an incident Raman laser with an intensity as low as ~ 0.035 mW, against the characterization of Rhodamine 6G, which is a standard test molecule for SERS. Moreover, we tested the reusability of the fabricated MWA SERS substrates under conditions as tough as ultrasonic sonication in isopropyl alcohol and acetone for 15 min, respectively, and we demonstrate that our SERS substrates can be efficiently reused for more than six times after sonication, which is quite critical since it minimizes the cost of the procedure to minimum.
关键词： Surface-enhanced Raman scattering (SERS),Ag thin films,Rhodamine 6G (R6G),Reusable substrates,Microwave annealing (MWA)
更新于2025-09-10 09:29:36
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Synthesis of uniform silver nanowires from AgCl seeds for transparent conductive films via spin-coating at variable spin-speed
摘要： Uniform silver nanowires (AgNWs) with high aspect ratio are significant to fabricate high-performance transparent conductive films (TCFs). In this work, AgNWs were synthesized through polyol method using AgCl as seeds. The growth mechanism of AgNWs upon AgCl particles was demonstrated, which provided a clear understanding of heterogeneous nucleation for synthesizing crystal. The amounts and the reaction time of AgCl were discussed to probe the effect on morphology of final AgNWs. Apart from that, the temperature was also tuned to provide appropriate thermal energy for synthesis of AgNWs. Uniform AgNWs with thin diameter about 52 nm and aspect ratio above 1000 were synthesized by optimizing the amounts, reaction time of AgCl and the temperature. These AgNWs were utilized to fabricate TCFs firstly through spin-coating at a variable speed. The resulting films coated at variable spin-speed largely improved the performance of films compared with those of films coated at constant spin-speed, exhibiting a low sheet resistance of 54Ω sq-1 and high transmittance of 92% at 550 nm with haze of 5.4%.
关键词： growth,AgCl,Silver nanowires,transparent conductive films,spin-coating
更新于2025-09-10 09:29:36
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Synthesis and characterization of Ni incorporated titanium dioxide thin films
摘要： Thin ?lms of insulating Ti1(cid:1)xNixO2 (x 5 0.00, 0.05, 0.10, and 0.15) are synthesized by the spray pyrolysis technique. All the ?lms are seen to crystallize into polycrystalline anatase phase of TiO2. However, weak signature of the NiTiO3 phase is also observed for the ?lms having higher Ni ion concentration. Optical absorption analysis suggests nonmonotonous band gap decrease from 3.67 to 3.59 eV with respect to added concentration of Ni ions unto ‘x’ 5 0.10 in the TiO2 matrix. The presence of ferromagnetic ordering at room temperature in Ni incorporated TiO2 ?lms is revealed by M–H measurements. Calculated values of saturation magnetization indicate that the observed ferromagnetism is not due to the presence of Ni clusters or segregation of other ferromagnetic phase. Electrically insulating nature of the ?lms suggests that the observed FM ordering is most probably due to the ferromagnetic interaction between bound magnetic polarons which formed due to the creation of oxygen vacancies or defects.
关键词： ferromagnetism,Ni incorporated titanium dioxide,spray pyrolysis,optical properties,thin films
更新于2025-09-10 09:29:36
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Large anomalous Nernst effect in thin films of the Weyl semimetal Co <sub/>2</sub> MnGa
摘要： The magneto-thermoelectric properties of Heusler compound thin films are very diverse. Here, we discuss the anomalous Nernst response of Co2MnGa thin films. We systematically study the anomalous Nernst coefficient as a function of temperature, and we show that unlike the anomalous Hall effect, the anomalous Nernst effect in Co2MnGa strongly varies with temperature. We exploit the on-chip thermometry technique to quantify the thermal gradient, which enables us to directly evaluate the anomalous Nernst coefficient. We compare these results to a reference CoFeB thin film. We show that the 50-nm-thick Co2MnGa films exhibit a large anomalous Nernst effect of (cid:2)2 lV/K at 300 K, whereas the 10-nm-thick Co2MnGa film exhibits a significantly smaller anomalous Nernst coefficient despite having similar volume magnetizations. These findings suggest that the microscopic origin of the anomalous Nernst effect in Co2MnGa is complex and may contain contributions from skew-scattering, side-jump, or intrinsic Berry phase. In any case, the observed anomalous Nernst coefficient of (cid:2)2 lV/K at 300 K is large compared to the values measured in other thin films and makes this material system a very promising candidate for efficient spin-caloritronic devices.
关键词： spin-caloritronic devices,thin films,anomalous Nernst effect,Co2MnGa
更新于2025-09-10 09:29:36
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Optical characterization of SiC films grown on Si(111)
摘要： Thin SiC films, grown on Si by substitution of C into Si on Si substrates with and without a SiGe buffer layer, have been investigated with optical techniques. The formation of SiC domains leads to strong green and blue photoluminescence from stacking faults and surface oxides. Introduction of a 10-nm-thick SiGe buffer layer leads to improved crystallinity as evidenced by X-ray diffraction and optical second-harmonic generation (SHG). Nonlinear optical azimuthal rotational spectra demonstrate the presence of cubic SiC in the film. Furthermore, angle-of-incidence scans are consistent with simulations based on a film with cubic symmetry which demonstrates that the cubic phase dominates the SiC film. Growth on vicinal Si(111) leads to a SiC film with the same c1v symmetry as the substrate, demonstrating that the lattice planes of the SiC film follow those of the Si substrate. Spatially resolved SHG scans show structures that are related to the underlying structure of the Si interface resulting from the growth process.
关键词： second-harmonic generation,optical characterization,SiC films,photoluminescence,crystallinity
更新于2025-09-10 09:29:36
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Ferroelectricity mediated by ferroelastic domain switching in HfO <sub/>2</sub> -based epitaxial thin films
摘要： Herein, ferroelastic domain switching from the nonpolar b-axis to the polar c-axis oriented domain in ferroelectric ?lms is demonstrated. Scanning 7%-YO1.5-substituted HfO2 (YHO-7) epitaxial transmission electron microscopy (STEM) indicates that the polarization of a pristine ?lm deposited on a Sn-doped In2O3/(001)YSZ substrate by the pulsed laser deposition method tends to be along the in-plane direction to avoid a strong depolarization ?eld with respect to the out-of-plane direction. Applying an electric ?eld aids in ferroelastic domain switching in YHO-7 ?lms. Such ?lms exhibit ferroelectric characteristics with a relatively large saturated polarization around 30 lC/cm2 by polarization reorientation from the in-plane to the out-of-plane directions and an increased dielectric constant. The synchrotron X-ray diffraction measurements with a focused beam for the pristine and poled area indicate ferroelastic 90(cid:2) domain switching as the odd number re?ection disappears, which is only allowed in the nonpolar b-axis orientation. STEM observations also show a signi?cant increase in the c-axis oriented domain. This observation of ferroelastic domain switching strongly supports the conclusion that the ferroelectricity of HfO2 originates from the non-centrosymmetric orthorhombic phase.
关键词： ferroelectricity,ferroelastic domain switching,epitaxial thin films,HfO2
更新于2025-09-10 09:29:36
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Annealing effects on properties of Ga2O3 films deposited by plasma-enhanced atomic layer deposition
摘要： We investigated annealing effects on the Ga2O3 thin films deposited on c-sapphire by plasma-enhanced atomic layer deposition. A metastable Ga2O3 films was deposited on c-sapphire substrate by PEALD with high plasma power at 250 °C. The (2?0?1) preferred orientation b-Ga2O3 films were obtained after annealing in oxygen atmosphere. Structure and surface analysis revealed that the annealed films had more fine-grained surface features. The film annealed for 2 h exhibited the best crystallinity. The bandgap of the as-deposited and annealed films for 2 h were 4.56 and 4.97 eV, respectively. The process of high-temperature annealing contributed gallium, oxygen atoms to obtain enough energy to migrate to the suitable location and increased the vigilance of crystallinity.
关键词： Thin films,Ga2O3,Epitaxial growth,XRD,Annealing
更新于2025-09-10 09:29:36