Effect of [Zn]/[S] ratios on the properties of chemical bath deposited zinc sulfide thin films

ZnS thin films have been prepared by chemical bath deposition (CBD) technique onto glass substrates deposited at about 80 °C using aqueous solution of zinc sulfate hepta-hydrate, ammonium sulfate, thiourea, ammonia and hydrazine hydrate. Ammonia and hydrazine hydrate were used as complexing agents. The influence of the ratio of [Zn]/[S] on formation and properties of ZnS thin films has been investigated. The ratio of [Zn]/[S] was changed from 3:1 to 1:9 by varying volumes and/or concentrations of zinc sulfate hepta-hydrate and thiourea in the deposition solution. The structural and morphological characteristics of films have been investigated by X-ray diffraction (XRD), scanning electron microscope and UV-vis spectroscopic analysis. ZnS films were obtained with the [Zn]/[S] ratio ranged from1:1 to 1:6. In the cases of [Zn]/[S] ratio ≥ 3:1 or ≤1:9, no deposition was found. Transparent and polycrystalline ZnS film was obtained with pure-wurtzite structure at the [S]/[Zn] ratio of 1:6. The related formation mechanisms of CBD ZnS are discussed. The deposited ZnS films show good optical transmission (80-90%) in the visible region and the band gap is found to be in the range of 3.65-3.74 eV. The result is useful to further develop the CBD ZnS technology.     

Optical and electrical properties of aluminum zinc oxide (AZO) nanostructured thin film deposited on polycarbonate substrate

Transparent polymer materials, due to their unique properties, such as light weight, optical transparency, and electrical and mechanical properties, have become very attractive as a replacement for inorganic glass substrates in a wide range of optoelectronic applications. In this research, aluminum zinc oxide nanostructured thin film was deposited on polycarbonate polymer substrates using a magnetron sputtering technique. The structure, morphology, and surface composition of the thin film were investigated by X-ray diffraction and field emission scanning electron microscopy. The optical and electrical properties of the thin film were investigated by UV–VIS-NIR spectrophotometer, ellipsometer, and four point probe method. The X-ray diffraction pattern showed that the aluminum zinc oxide thin film had a polycrystalline structure. The optical and electrical results indicated that the refractive index, band gap, and sheet resistance of the aluminum zinc oxide thin film were 1.8, 3.2 eV, and 265 Ω/sq, respectively.     

Nanocrystalline formation and optical properties of germanium thin films prepared by physical vapor deposition

Amorphous and nanocrystalline germanium thin films were prepared on glass substrates by physical vapor deposition (PVD). The influence of thermal annealing on the characteristics of the Ge thin films has been investigated. X-ray diffraction (XRD) and SEM show amorphous structure of films deposited at room temperature. After thermal annealing, the crystallinity was improved when the annealing temperature increases. The Ge thin films annealed at different temperatures in air were nanocrystalline, having the face-centered cubic structure with preferred orientation along the 〈1 1 1〉 direction. The nanostructural parameters have been evaluated by using a single-order Voigt profile analysis. Moreover, the analysis of the optical transmission and reflection behavior was carried out. The values of direct and indirect band gap energies for amorphous and nanocrystalline phases are 0.86±0.02, 0.65±0.02 and 0.79±0.02, 0.61±0.02 eV, respectively. In addition, the complex optical functions for the wavelength range 600-2200 nm are reported. The refractive index of the nanocrystalline phase drops from 4.80±0.03 to 2.04±0.02, and amorphous phase changes from 5.18±0.03 to 2.42±0.02 for the whole wavelength range. The dielectric functions ε₁ and ε₂ of the deposited films were recorded as a function of wavelength within the range from 600 to 2200 nm.     

Synthesis and optical properties of coated nanoparticle composites

The synthesis of coated nanoparticles is a new direction in engineering, specifically in the study of physical properties of materials. We examine semiconductor coated semiconductor particles, CdS/PbS, and metal coated particles, Au₂S/Au, and the theoretical basis for their unique properties. Coated self-assembled nanoparticles are also studied and recent progress is reported.     

Research on the optical properties of collodion film

This paper centers on the deposition process and optical properties of collodion film. Collodion film was prepared on the double side polished silicon and k9 optical glass using the sol–gel method. The studying results have showed four characteristics of collodion film. First of all, the thickness of collodion film decreases with increasing the revolution speed. Secondly, the refractive index of collodion film changes from 1.529306 to 1.500128, which accords with the normal dispersion. Thirdly, the transmittance of collodion film is higher in the visible wavelength range 380–760 nm and its average transmittance is 91.9%. At last, the absorption property is very well in the infrared region. The infrared absorption coefficient is greater than 0.69/μm in range of 3–5 μm, and it is up to 1.433528/μm in 8–14 μm because of its many strong infrared absorption peaks. In addition, the absorption characteristics have been analyzed in detail.     

Effects of annealing temperature on shape transformation and optical properties of germanium quantum dots

The influences of thermal annealing on the structural and optical features of radio frequency(rf) magnetron sputtered self-assembled Ge quantum dots(QDs) on Si(100) are investigated.Preferentially oriented structures of Ge along the(220) and(111) directions together with peak shift and reduced strain(4.9%to 2.7%) due to post-annealing at 650 ℃ are discerned from x-ray differaction(XRD) measurement.Atomic force microscopy(AFM) images for both pre-annealed and post-annealed(650 ℃) samples reveal pyramidal-shaped QDs(density ~ 0.26×10~(11) cm~(-2)) and dome-shape morphologies with relatively high density ~ 0.92×10~(11) cm~(-2),respectively.This shape transformation is attributed to the mechanism of inter-diffusion of Si in Ge interfacial intermixing and strain non-uniformity.The annealing temperature assisted QDs structural evolution is explained using the theory of nucleation and growth kinetics where free energy minimization plays a pivotal role.The observed red-shift ~ 0.05 eV in addition to the narrowing of the photoluminescence peaks results from thermal annealing,and is related to the effect of quantum confinement.Furthermore,the appearance of a blue-violet emission peak is ascribed to the recombination of the localized electrons in the Ge-QDs/SiO_2 or GeO_x and holes in the ground state of Ge dots.Raman spectra of both samples exhibit an intense Ge-Ge optical phonon mode which shifts towards higher frequency compared with those of the bulk counterpart.An experimental Raman profile is fitted to the models of phonon confinement and size distribution combined with phonon confinement to estimate the mean dot sizes.A correlation between thermal annealing and modifications of the structural and optical behavior of Ge QDs is established.Tunable growth of Ge QDs with superior properties suitable for optoelectronic applications is demonstrated.     

Electronic and optical properties in ZnO:Ga thin films induced by substrate stress

The effects of biaxial stress in ZnO:Ga thin films on different substrates, e.g., sapphire(0001), quartz, Si(001), and glass have been investigated by X-ray diffraction, atomic force microscopy, and electrical transport and ellipsometric measurements. A strong dependence of orientation, crystallite size, transport, and electronic properties upon the substrate-induced stress has been found. The structural properties indicate that a tensile stress exists in epitaxial ZnO:Ga films grown on sapphire, Si, and quartz, while a compressive stress appears in films grown on glass. The resistivity of the films decreased with increasing biaxial stress, which is inversely proportional to the product of the carrier concentration and Hall mobility. The refractive index n was found to decrease with increasing biaxial stress, while the optical band gap E₀ increased with stress. These behaviors are attributed to lattice contraction and the increase in the carrier concentration that is induced by the stress. Our experimental data suggest that the mechanism of substrate-induced stress is important for understanding the properties of ZnO:Ga thin films and for the fabrication of devices which use these materials.     

Dependence of film thickness on the electrical and optical properties of ZnO-Cu-ZnO multilayers

ZnO-Cu-ZnO multilayers were prepared by simultaneous RF magnetron sputtering of ZnO and DC magnetron sputtering of Cu. Cu films with different thickness were used as the intermediate metal layer. The optical and electrical properties of the multilayers studied by UV-vis spectrophotometer and four point probe method, respectively, shows that transmittance increases with decrease of copper thickness up to an optimum thickness of 5 nm and sheet resistance decreases with increase of thickness. Low resistivity and high transmission were obtained when the film structure has a thickness of ZnO/Cu/ZnO: 50/5/50 nm. The performance of the multilayers as transparent conducting material was better than the single layer ZnO of equal thickness.     

Effect of ambient hydrogen sulfide on the physical properties of vacuum evaporated thin films of zinc sulfide

Evaporated thin films of zinc sulfide (ZnS) have been deposited in a low ambient atmosphere of hydrogen sulfide (H₂S ∼10⁻⁴ Torr). The H₂S atmosphere was obtained by a controlled thermal decomposition of thiourea [CS(NH₂)₂] inside the vacuum chamber. It has been observed that at elevated substrates temperature of about 200 °C helps eject any sulfur atoms deposited due to thermal decomposition of ZnS during evaporation. The zinc ions promptly recombine with H₂S to give better stoichiometry of the deposited films. Optical spectroscopy, X-ray diffraction patterns and scanning electron micrographs depict the better crystallites and uniformity of films deposited by this technique. These deposited films were found to be more adherent to the substrates and are pinhole free, which is a very vital factor in device fabrication.     

Effects of the substrate and oxygen partial pressure on the microstructures and optical properties of Ti-doped ZnO thin films

Ti-doped ZnO (ZnO:Ti) thin films were deposited on the glass and Si substrates using radio frequency reactive magnetron sputtering. The effects of substrate on the microstructures and optical properties of ZnO:Ti thin films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and a fluorescence spectrophotometer. The structural analyses of the films indicated that they were polycrystalline and had a hexagonal wurtzite structure on different substrates. When ZnO:Ti thin film was deposited on Si substrate, the film had a c-axis preferred orientation, while preferred orientation of ZnO:Ti thin film deposited on glass substrate changed towards (1 0 0). Finally, we discussed the influence of the oxygen partial pressures on the structural and optical properties of glass-substrate ZnO:Ti thin films. At a high ratio of O₂:Ar of 18:10 sccm, the intensity of (0 0 2) diffraction peak was stronger than that of (1 0 0) diffraction peak, which indicated that preferred orientation changed with the increase of O₂:Ar ratios. The average optical transmittance with over 93% in the visible range was obtained independent of the O₂:Ar ratio. The photoluminescence (PL) spectra measured at room temperature revealed four main emission peaks located at 428, 444, 476 and 527 nm. Intense blue-green luminescence was obtained from the sample deposited at a ratio of O₂:Ar of 14:10 sccm. The results showed that the oxygen partial pressures had an important influence for PL spectra and the origin of these emissions was discussed.     

Electrical and optical properties of thin film of amorphous silicon nanoparticles

Electrical and optical properties of thin film of amorphous silicon nanoparticles (a-Si) are studied. Thin film of silicon is synthesized on glass substrate under an ambient gas (Ar) atmosphere using physical vapour condensation system. We have employed Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) to study the morphology and microstructure of this film. It is observed that this silicon film contains almost spherical nanoparticles with size varying between 10 and 40 nm. The average surface roughness is about 140 nm as evident from the AFM image. X-ray diffraction analysis is also performed. The XRD spectrum does not show any significant peak which indicates the amorphous nature of the film. To understand the electrical transport phenomena, the temperature dependence of dc conductivity for this film is studied over a temperature range of (300-100 K). On the basis of temperature dependence of dc conductivity, it is suggested that the conduction takes place via variable range hopping (VRH). Three-dimensional Mott's variable range hopping (3D VRH) is applied to explain the conduction mechanism for the transport of charge carriers in this system. Various Mott's parameters such as density of states, degree of disorder, hopping distance, hopping energy are estimated. In optical properties, we have studied Fourier transform infra-red spectra and the photoluminescence of this amorphous silicon thin film. It is found that these amorphous silicon nanoparticles exhibits strong Si-O-Si stretching mode at 1060 cm⁻¹, which suggests that the large amount of oxygen is adsorbed on the surface of these a-Si nanoparticles. The photoluminescence observed from these amorphous silicon nanoparticles has been explained with the help of oxygen related surface state mechanism.     

Influence of the substrate optical properties on the backscattering of contaminated microstructures

The presence of small defects in micron-sized structured surfaces introduces small changes in the backscattering that can be assessed by means of an integrated parameter. In this work the influence of the optical properties of the substrate on this technique is analyzed for two different configurations: defect on the microstructure and defect on the substrate beside the microstructure.     

Effect of substrate temperature and oxygen partial pressure on microstructure and optical properties of pulsed laser deposited yttrium oxide thin films

Yttrium oxide thin films were deposited on Si (1 1 1) and quartz substrates by pulsed laser deposition technique at different substrate temperature and oxygen partial pressure. XRD analysis shows that crystallite size of the yttrium oxide thin films increases as the substrate temperature increases from 300 to 873 K. However the films deposited at constant substrate temperature with variable oxygen partial pressure show opposite effect on the crystallite size. Band gap energies determined from UV-visible spectroscopy indicated higher values than that of the reported bulk value.     

The influence of oxygen on the optical properties of RF-sputtered zinc oxide thin films

In this article, we investigate the effects of oxygen partial pressure in the deposition chamber on the optical properties of zinc oxide (ZnO) thin films; in particular, we examine the variation of the refractive index with oxygen flux.ZnO thin films were deposited by radio-frequency (RF) magnetron sputtering and studied by means of X-ray diffraction (XRD) and spectroscopic ellipsometry (SE). We have found a preferential c-axis growth of ZnO films, with slightly variable deposition rates from 2.6 to 3.8 Å/s. Conversely, the refractive index exhibits, from ultraviolet (UV) to near infrared (IR), a considerable and almost linear variation when the oxygen flux value in the deposition chamber varies from 0 to 10 sccm.     

Consequence of oxidant to monomer ratio on optical and structural properties of Polypyrrole thin film deposited by oxidation polymerization technique

This paper reports the effect of oxidant to monomer (O/M) ratio on optical and structural properties of Polypyrrole (PPy) thin film deposited by chemical oxidation polymerization technique. Noticeable changes have observed in the properties of PPy thin films with O/M ratio. Cauliflower structure have been observed in FE-SEM images, wherein grain size is observed to decrease with increase in O/M ratio. AFM results are in good agreement with FE-SEM results. From FTIR spectra it is found that, PPy is in highly oxidized form at low O/M ratio but oxidation decreased with increase in O/M ratio. Also C–C stretching vibrations of PPy ring is decreased whereas C=C stretching is increased with ratio. Absorption peak around 450 nm corresponds to π–π^⁎ transition and around 800 nm for polarons and bipolarons. The intensity of such peaks confirms the conductivity of PPy, which is observed maximum at low O/M ratio and found to decrease with increase in ratio. Optical band gap (BG) is found to increase from 2.07 eV to 2.11 eV with increase in the O/M ratio.     

Electrical conductivity and optical properties of ZnO nanostructured thin film

The electrical conductivity, structural and optical properties of ZnO nanostructured semiconductor thin film prepared by sol-gel spin coating method have been investigated. The X-ray diffraction result indicates that the ZnO film has the polycrystalline nature with average grain size of 28 nm. The optical transmittance spectrum indicates the average transmittance higher than 90% in visible region. The optical band gap, Urbach energy and optical constants (refractive index, extinction coefficient, real and imaginary parts of the dielectric constant) of the film were determined. The electrical conductivity of the film dependence of temperature was measured to identify the dominant conductivity mechanism. The conductivity mechanism of the film is the thermally activated band conduction. The electrical conductivity and optical results revealed that the ZnO film is an n-type nanostructured semiconductor with a direct band gap of about 3.30 eV at room temperature.     

On the optical properties of amorphous Ge-Ga-Se-KBr films prepared by pulsed laser deposition

Amorphous thin films (1 − x)(4GeSe₂-Ga₂Se₃)-xKBr (x = 0, 0.1, 0.2, 0.3) were prepared by the pulsed laser deposition (PLD) technique. The optical parameters were calculated using the Swanepoel method from the optical transmission spectra. The optical band gap () of the studied films increased while the index of refraction decreased when increased the content of KBr. The Tauc slopes were discussed as an indicator of the degree of structural randomness of amorphous semiconductors. The index of refraction decreased and increased after annealing of as-deposited films below the glass transition temperature. The thermal-bleaching and thermal- contraction effects were observed, which are discussed in relation to the reduction in the density of homopolar bonds confirmed by the Raman spectra analysis and the decreased amount of fragments of the as-deposited films, respectively.     

Effect of gamma irradiation on the optical properties of nano-crystalline InP thin films

Thin films of InP were prepared onto glass and quartz substrates using laser ablation technique. Some of the prepared films were irradiated using a ⁶⁰Co γ -ray source irradiation with a total dose of 100 kGy at room temperature. The as deposited and irradiated films were identified by scanning electron microscopy, SEM and X-ray diffraction, XRD. The SEM images have shown a nano-flower like structure for the as deposited films and influenced by the irradiation dose. The Optical characterizations of the as deposited and irradiated InP films were studied using spectrophotometric measurements of transmittance T(λ) and reflectance, R(λ) at normal incidence of light in the spectral range from 200 nm to 2500 nm. The refractive index, n, and the absorption index, k values were calculated using a modified computer program based on minimizing (ΔT)² and (ΔR)² simultaneously, within the desired accuracy. Analysis of the dispersion of the refractive index in the range 900 ≤ λ ≤ 2500 was discussed in terms of the single oscillator model. The optical parameters, such as the dispersion energy, E_d, the oscillator energy, E_o, the high frequency dielectric constant, _∞ and the lattice dielectric constant, _L were evaluated for the as deposited and irradiated films. The allowed optical transitions were found to be direct for the as deposited and irradiated films with energy gaps of 1.35 eV and 1.54 eV, respectively.     

Improvement in mechanical and optical properties of vapour chopped vacuum evaporated PANI/PMMA composite thin film

PANI/PMMA composite was synthesized by emulsion polymerization pathway and the composite thin film was obtained by vacuum evaporation. The effect of vapour chopping and varying PMMA concentration was also studied. The FTIR spectra showed that the PANI/PMMA composite thin film deposited as a short chain oligomers. Increase in transmittance and decrease in refractive index was obtained with increasing concentration of PMMA, which further increased the adhesion and decreased intrinsic stress. The vapour chopping improved its optical as well as mechanical properties and produced smoother surface morphology. Increase of PMMA made the film more amorphous and does not change its band gap.     

Vacancy-defect effect on the electronic and optical properties of Pmm2 BC2N: A first-principles study

Orthorhombic-Pmm2-BC₂N as a superhard photocatalyst simulates great interests in the researches of materials-design and application. To promote the studies of Pmm2 BC₂N as a multifunctional material with both great hardness and good optical properties, we investigated the electronic and optical properties of Pmm2 BC₂N with various vacancy-defects by the systematic first-principles density functional theory (DFT) calculations in this work. The absorption, refractivity, reflectivity, and photoconductivity of considered structures were calculated and explored. The various characteristics of the optical properties were analyzed based on relative computed density of states (DOS).