Heat treatment effects on the structural and optical properties of thin Bi2(Se1-xTex)3 films

Thin layers of Bi₂-chalcogenides, in the form of Bi₂(Se_1-xTe_x)₃ films, were evaporated on glass substrates by means of the vacuum thermal evaporation. Microstructure of the as prepared layers was investigated by x-ray diffraction (XRD) analysis. Identifications of the surface morphology and roughness were determined via scanning electron microscope (SEM). Optical transmissivity spectra proved that the as prepared films have low transparency with growing trend upon increasing the wavelength beyond the infra-red region. Low transmittance was observed for the as prepared films. Heat treatment, in the form of temperature annealing, was carried out aiming at boosting the structural features and the materials transmissivity. Structural properties and surface features of the annealed films were probed also via XRD and SEM analyses. It was found that the crystal size increases while the micro-strain and the dislocation density decrease obviously due to annealing. It was also observed that the annealing process significantly enhances the materials transmission especially in the range of higher wavelengths. Optical band gap was studied after annealing at various temperatures. Notable change in the band gap value was observed as a result of annealing. The band gap of the undoped (Bi₂Se₃) materials showed significant rise from 0.14 to 1.79 eV due to annealing. Similarly, the Te-doped samples exhibited notable increase in their band gap values after annealing. For example, the optical band gap of the sample doped at x = 0.20 increased from 0.03 to 0.41 eV by annealing. On the other hand, transmittance was also enhanced by annealing. For samples treated at 250 °C for 3 h, their optical transmissivity is enhanced to over 99% at the visible near-IR range. Such significant enhancement can be ascribed to structural enhancements. With such enhancement in the optical transmissivity, optoelectronic applications including transparent electrode can be met.     

Influence of post-annealing atmosphere on microstructure,optical and electrical properties of zinc cadmium oxide films deposited by DC and RF magnetron co-sputtering

Zinc cadmium oxide (Zn_1−xCd_xO) films were deposited on quartz substrates by direct current (DC) and radio frequency (RF) reactive magnetron co-sputtering and the influence of post-annealing atmosphere on their microstructure, optical and electrical properties were investigated by X-ray diffraction (XRD), optical absorbance, photoluminescence (PL) and Hall measurements. Results indicate that the band gap (E_g) of all Zn_1−xCd_xO films annealed in different atmospheres are smaller than that of the undoped ZnO, the observed shifts in E_g being 0.43, 0.37 and 0.32 eV for the Zn_1−xCd_xO films annealed in argon, oxygen and vacuum, respectively. Hall measurement results indicate that all Zn_1−xCd_xO films annealed in different atmospheres show the n-type conduction, but the Zn_1−xCd_xO film annealed in vacuum has low resistivity and high concentration, which has room-temperature resistivity of 1.59 Ω cm and carrier concentration of 2.07×10¹⁷ cm⁻³. Compared with Zn_1−xCd_xO films annealed in oxygen and argon, Zn_1−xCd_xO film annealed in vacuum has the best crystal quality, luminescence and electrical properties. The influencing mechanism of the post-annealing atmosphere on the electrical and optical properties of the Zn_1−xCd_xO film is discussed.     

Effect of substrate temperature on microstructure and optical properties of nanocrystalline alumina thin films

Aluminum oxide (Al₂O₃) thin films were deposited on silicon (100) and quartz substrates by pulsed laser deposition (PLD) at an optimized oxygen partial pressure of 3.0×10^?3 mbar in the substrate temperatures range 300–973 K. The films were characterized by X-ray diffraction, transmission electron microscopy, atomic force microscopy, spectroscopic ellipsometry, UV–visible spectroscopy and nanoindentation. The X-ray diffraction studies showed that the films deposited at low substrate temperatures (300–673 K) were amorphous Al₂O₃, whereas those deposited at higher temperatures (≥773 K) were polycrystalline cubic γ-Al₂O₃. The transmission electron microscopy studies of the film prepared at 673 K, showed diffuse ring pattern indicating the amorphous nature of Al₂O₃. The surface morphology of the films was examined by atomic force microscopy showing dense and uniform nanostructures with increased surface roughness from 0.3 to 2.3 nm with increasing substrate temperature. The optical studies were carried out by ellipsometry in the energy range 1.5–5.5 eV and revealed that the refractive index increased from 1.69 to 1.75 (λ=632.8 nm) with increasing substrate temperature. The UV–visible spectroscopy analysis indicated higher transmittance (>80%) for all the films. Nanoindentation studies revealed the hardness values of 20.8 and 24.7 GPa for the films prepared at 300 K and 973 K respectively.     

Effect of gas-timing technique on structure and optical properties of sputtered zinc oxide films

Zinc oxide thin films were prepared by the RF magnetron sputtering using a gas-timing technique whereby the flow of argon into the sputtering chamber was controlled by an on–off sequence. With this technique, polycrystalline ZnO thin films on glass substrates have been achieved without any thermal treatment of the substrate. In addition, the RF power and the gas-timing sequence can be fine-tuned to produce the hexagonal structure of ZnO thin films. X-ray diffraction (XRD) measurements confirm a (0 0 2) plane oriented wurtzite structure ZnO thin films. The optimized conditions for this hexagonal structure are an RF power of 30 W and an on–off gas-timing sequence of 50:2 s. The root mean square surface roughness of ZnO thin films measured by atomic force microscopy are in the range of 6.4–11.5 nm. The optical transmittance of ZnO thin films is over 85% in the visible range.     

Effect of precursor concentration on structural,morphological and opto-electric properties of ZnO thin films prepared by spray pyrolysis

Sprayed ZnO films were grown on glass substrate at 400 °C using zinc chloride as precursor with different molar concentrations varying from 0.05 to 0.2 M. X-ray diffraction patterns reveal that ZnO films are polycrystalline with hexagonal wurtzite structure with preferred orientation in (002) plane. Optical measurements show that transmittance reaches a maximum value of 95% in the visible region for ZnO films prepared from precursor with 0.05 M concentration. The films obtained from the precursor with 0.1 M concentration have the highest electrical conductivity and photocurrent values.     

Impacts of thickness reduction and heat treatment on the optical properties of thin chalcogenide films

Bi-based chalcogenides, in the form of thin crystalline films, were deposited at different thicknesses onto highly cleaned glass slides with the aid of vacuum thermal evaporation technique. The influence of thermal annealing on the optical properties of Bi₂Te₃-Bi₂Se₃ films at different thicknesses is investigated in this work. Wavelength dependence of the optical transmittance and reflectance was recorded, for the as-prepared and the annealed films, in the wavelength range from 350 to 2700 nm using a double beam spectrophotometer. Fundamental optical properties such as absorption coefficient and energy band gap were derived based on the measured spectra and film's thickness. We demonstrate in the present work that the synergy of annealing and thickness reduction can be exploited for light transmittance enhancements, and consequently for optoelectronic applications including transparent conductive electrodes.     

Effect of annealing temperature on the evolution of structural,microstructural, and optical properties of spin coated ZnO thin films

Zinc oxide (ZnO) thin films were sol-gel spin coated on glass substrates and annealed at various temperatures from 300–500 °C. Zinc acetate dihydrate (ZAD), monoethanolamine (MEA), and 2-methoxyethanol were used as the starting materials, stabilizer and solvent, respectively. The effect of annealing temperature on the structural and optical properties of the ZnO thin films was investigated by X-ray diffractometer (XRD), atomic force microscope (AFM), UV–VIS spectrophotometry and ellipsometry. The XRD results showed the films to have a preferential c-axis orientation, whereas the AFM results confirmed a columnar structure. The surface roughness increased with the increase in annealing temperature. Parameters such as ratio of free charge carrier concentration to effective mass (N/m*) and plasma frequency (ω_p) were determined from the transmittance graph using the Wemple di Domenico model. Both N/m* and ω_p were noticed to reduce with the increase in annealing temperature. Band gap decreased with the increase in the annealing temperature indicating absorption edge shift towards the red region.     

Structures,morphological control,and antibacterial performance of tungsten oxide thin films

The present work describes structural, morphological, and antibacterial properties of thin film coatings based on tungsten oxide material on stainless-steel substrates. Thin films were prepared by RF magnetron sputtering of W targets in the oxygen/argon plasma environment in 60 W sputtering power. The characterization of the specimens was made on the basis of microstructure and antibacterial properties of the thin films surface. The effect of O₂/Ar ratio on the structure, morphology, and antibacterial properties of the tungsten oxide thin films was studied. Methods such as X-ray diffraction (XRD), scanning electron microscope (SEM), and Fourier Transform Infrared Spectroscopy (FTIR) were used to assess the properties of deposited thin films. XRD peak analysis indicates (100) and (200) of WO₃ phase with hexagonal structure. Moreover, the micro-strain, grain size, and dislocation density were obtained. It is noteworthy that by increasing the oxygen percentage from 10% to 20%, the grain size decreases from 81 to 23 nm while the film micro-strain and dislocation density increases. The SEM results illustrates that tungsten oxide thin films are made of interconnected nano-points in a chain shape with sphere-shaped grains with diameter variation from 10 to 100 nm. The FTIR spectra displays four distinct bands corresponds to O–W–O bending modes of vibrations and W–O–W stretching modes of the WO₃ films. The antibacterial effects of tungsten oxide thin films on steel stainless substrate against Escherichia coli bacteria are also examined for the first time and our observation shows that the number of bacteria on all tungsten oxide samples decreases after 24 h. The samples exhibit an excellent antibacterial performance. This paper renders a strategy through which the tungsten oxide thin films for antibacterial purpose and proposes that WO₃ thin films are ideal for various medical applications including stainless steel medical tools, optical coatings, and antibacterial coatings.     

Spray deposited titanium oxide thin films as passive counter electrodes

Titanium dioxide (TiO₂) thin films were deposited from methanolic solution onto fluorine doped tin oxide coated conducting glass substrates by spray pyrolysis technique. The electrochemical properties of TiO₂ thin films were investigated using cyclic voltammetry, chronoamperometry, chronocoulometry and iono-optical studies, in 0.1N H₂SO₄ electrolyte. Performance of the films deposited at three different substrate temperatures, viz. 350, 400 and 450 °C is discussed in view of their utilization in electrochromic devices, as counter electrode. The magnitude of charge storage capacity, Q/t (4.75-6.13 × 10⁻³ mC/(cm² nm)) and colouration efficiency (3.2-4.3 cm²/mC) of TiO₂ rank these films among the promising counter electrodes in electrochromic devices.     

Structural,electrical, and linear/nonlinear optical characteristics of thermally evaporated molybdenum oxide thin films

Homogeneous thin films of Molybdenum oxide (MoO₃) were grown on quartz and glass substrates using the thermal evaporation method. XRD results showed that the MoO₃ powder has a polycrystalline structure with an orthorhombic crystal system whereas the MoO₃ thin films have amorphous nature. SEM images showed that the MoO₃ thin films have a nearly uniform surfaces with worm-like shape grains. The film thickness influences on the linear and nonlinear optical characteristics of MoO₃ thin films that were examined using spectrophotometric measurements and from which, the linear optical constants of the MoO₃ thin films were estimated. The electronic transition type was determined as a direct allowed one. The values of the optical band gap were obtained to be in the range of 3.88–3.72 eV. The dispersion parameters, third-order nonlinear optical susceptibility, and the nonlinear refractive index of the MoO₃ thin films were determined and interpreted in the light of the single oscillator model. The temperature dependence of the DC electrical conductivity and the corresponding conduction mechanism for the MoO₃ films were investigated at temperatures ranging from 303 to 463 K.     

Effects of annealing on wettability and physical properties of SnO thin films deposited at low RF power densities

The SnO thin films were deposited at low RF power densities by RF magnetron sputtering. According to XRD and XPS analyses, the SnO thin film comprised nanocrystalline orthorhombic SnO with a (110) orientation. Reducing RF power density resulted in better nanocrystallinity, changing hydrophobicity to hydrophilicity, and increasing the optical transmission in the UV–vis–NIR region. After annealing, the SnO thin film favored p-type conductivity and hydrophilicity. As the annealing temperature increased, the coexistence of nanocrystalline orthorhombic SnO and tetragonal SnO₂ in the film clearly increased the optical transmission in the ultraviolet region. The SnO thin films after annealing at 500 ℃ in vacuum and N₂ (200 sccm) exhibited a higher hole mobility and a better optical selection in the ultraviolet region, respectively.     

Influence of ZnO buffer layer thickness on the electrical and optical properties of indium zinc oxide thin films deposited on PET substrates

The influence of the ZnO buffer layer thickness on the electrical and optical properties of In₂O₃–10 wt.% ZnO and ZnO bilayers deposited on polyethylene terephthalate (PET) substrates by RF magnetron sputtering were investigated. The optimum ZnO buffer layer thickness was found to be 90 nm which gives the lowest electrical resistivity of the bilayer of IZO and ZnO deposited on the PET substrate. The surface roughness decreases and diffusion of moisture and gas is more efficiently restrained, which contributes to lower the resistivity of the bilayer as the ZnO buffer layer thickness is increased. On the other hand, the total resistivity of the bilayer increases as the ZnO buffer layer thickness is increased because the resistivity of ZnO is higher than that of IZO. Introduction of a ZnO buffer layer does not nearly affect the IZO/ZnO/PET sample.     

Aliovalent Ho3+ ion doped BaZrO3 thin films; Structural,optical and photoluminescence properties

Ho doped BaZrO3 thin film phosphors with varying Ho content (1, 2, 3 and 4?at%) were prepared via pulsed laser deposition technique. To understand the effect of doping on structural, morphological, optical and emission properties of thin films, X-ray Diffractrometer (XRD), Scanning Electron Microscopy (SEM), Spectroscopic Ellipsometry (SE) and Photoluminescence (PL) Spectroscopy have been used, respectively. Polycrystalline nature with single phase cubic crystalline structure of the films has been obtained. The optical band gap energy, as estimated by SE, has been found to increase with increase in the Ho content. The PL spectra of the synthesized phosphor exhibit green and yellow-orange as prominent emission bands in response to 328?nm as excitation wavelength.     

Highly conducting and transparent antimony doped tin oxide thin films: the role of sputtering power density

Sb doped SnO₂ thin films were deposited on quartz substrates by magnetron sputtering at 600 °C and the effects of sputtering power density on the preferential orientation, structural, surface morphological, optical and electrical properties had been studied. The XRD analyses confirm the formation of cassiterite tetragonal structure and the presence of preferential orientation in (2 1 1) direction for tin oxygen thin films. The dislocation density analyses reveal that the generated defects can be suppressed by the appropriate sputtering power density in the SnO₂ lattice. The studies of surface morphologies show that grain sizes and surface roughness are remarkably affected by the sputtering power density. The resistivity of Sb doped SnO₂ thin films gradually decreases as increasing the sputtering power density, reaches a minimum value of 8.23×10⁻⁴ Ω cm at 7.65/cm² and starts increasing thereafter. The possible mechanisms for the change in resistivity are proposed. The average transmittances are more than 83% in the visible region (380–780 nm) for all the thin films, the optical band gaps are above 4.1 eV. And the mechanisms of the variation of optical properties at different sputtering power densities are addressed.     

Dispersive optical constants and electrical properties of nanocrystalline CuInS2 thin films prepared by chemical spray pyrolysis

Nanocrystalline CuInS₂ thin films were deposited on borosilicate glass substrates via chemical spray pyrolysis method. The structural, morphological, optical, and electrical properties were studied as a function of increasing annealing temperature from 250 to 350 ̊C. XRD analysis showed mixed phases at lower temperatures with the preferred orientation shifting towards the (112) chalcopyrite CuInS₂ plane at higher substrate temperature. The crystallite size increased slightly between 13 and 18 nm with increase in annealing temperature. The optical band gap was determined on basis of Tauc extrapolation method and the Wemple–Di-Domenico single oscillator model. Possible structural and quantum confinement effect may have resulted in relatively larger band gaps of 1.67–2.04 eV, relative to the bulk value of 1.5 eV. The presence of Cu_xS in the as-deposited and wurtzite peaks after annealing at 350 ^̊C play a role in influencing the optical and electrical properties of CuInS₂ thin films.     

Sol-gel preparation of Zn-V-Mn-O thin films for low voltage varistor applications

ZnO-based thin films in the Zn-V-Mn-O system have been synthesised by a sol-gel process and characterised for use in low voltage varistor applications. The films were prepared through multi-layer deposition of a precursor solution onto indium tin oxide-coated borosilicate glass substrates by spin-coating and subsequent annealing. Current-voltage characteristics measured for the films annealed at 700 °C showed varistor action with nonlinear coefficients (α) above 4.     

Electrochromism in spray deposited iridium oxide thin films

Electrochromic iridium oxide thin films were deposited onto fluorine doped tin oxide coated glass substrates from an aqueous iridium chloride solution by pneumatic spray pyrolysis technique. The as-deposited samples were X-ray amorphous. The electrochromic properties of thin films were studied in an aqueous electrolyte (0.5N H₂SO₄) using cyclic voltammetry (CV), chronoamperometry (CA) and spectrophotometry. Iridium oxide films show pronounced anodic electrochromism owing to Ir⁺⁴ ↔ Ir⁺³ intervalency charge transition. The reversibility of cyclic process in Ir oxide films is found to be higher, which increases with increasing number of colour-bleach cycles.