Using different chemical methods for deposition of CdS on TiO2 surface and investigation of their influences on the dye-sensitized solar cell performance

Chalcogenide phase change materials based on germanium-antimony-tellurides (GST-PCMs) have shown outstanding properties in non-volatile memory (NVM) technologies due to their high write and read speeds, reversible phase transition, high degree of scalability, low power consumption, good data retention, and multi-level storage capability. However, GST-based PCMs have shown recent promise in other domains, such as in spatial light modulation, beam steering, and neuromorphic computing. This paper reviews the progress in GST-based PCMs and methods for improving the performance within the context of new applications that have come to light in recent years.

https://www.mdpi.com/2076-3417/9/3/530/pdf

A Review of Germanium-Antimony-Telluride Phase Change Materials for Non-Volatile Memories and Optical Modulators

Structural and optical characterization of ZnO thin films for optoelectronic device applications by RF sputtering technique

Polymer electrolyte system based on poly(vinyl alcohol) (PVA)-chitosan blend doped with ammonium bromide (NH4Br) has been prepared by solution cast method. Fourier transform infrared (FTIR) spectroscopy analysis confirms the complexation between salt and polymer host. The highest ionic conductivity obtained at room temperature is (7.68 ± 1.24) × 10−4 S cm−1 for the sample comprising of 30 wt% NH4Br. X-ray diffraction (XRD) patterns reveal that PVA-chitosan with 30 wt% NH4Br exhibits the most amorphous structure. Thermogravimetric analysis (TGA) reveals that the electrolytes are stable until ∼260 °C. The conductivity variation can also be explained by field emission scanning electron microscopy (FESEM) study. Dielectric properties of the electrolytes follow non-Debye behavior. The conduction mechanism of the highest conducting electrolyte can be represented by the correlated barrier hopping (CBH) model. From linear sweep voltammetry (LSV) result, the highest conducting electrolyte is electrochemically stable at 1.57 V.

Incorporation of NH4Br in PVA-chitosan blend-based polymer electrolyte and its effect on the conductivity and other electrical properties

N-doped TiO2 thin films have been prepared by reactive RF magnetron sputtering at different pressures and with different compositions using a dual reactive gas mixture of nitrogen and oxygen. The morphological, optical, photo-electrochemical and photocatalytic properties have been studied in order to investigate the white light and visible light photoactivities of the films. Significant control over the band gap energy in the films was achieved by varying the deposition parameters. Photoelectrochemical characterization revealed improved white light photocurrent generation in nitrogen doped films prepared at low pressures. However, the visible light photocurrent generation showed improvement for all deposition pressures, and changed accordingly with the nitrogen incorporation. Photocatalytic measurements of a common chemical pollutant NMP (N-methyl-2-pyrrolidone) under different irradiation conditions provided evidence of improved photoactivity for samples prepared at high pressure, due to the increased active surface area and optimal nitrogen doping levels. Overall, this study showed a simple method to produce highly controllable nitrogen doping in different sites within TiO2 showing improved visible light photoactivity and photo induced pollutant degradation. More interestingly, by investigating the effect of different nitrogen sites in nitrogen doped TiO2, we have shown that the optimized conditions for photocatalysis do not correspond to those for water splitting.

Control of the visible and UV light water splitting and photocatalysis of nitrogen doped TiO2 thin films deposited by reactive magnetron sputtering

Zinc telluride thin films with different thicknesses have been deposited by electron beam gun evaporation system onto glass substrates at room temperature. X-ray and electron diffraction techniques have been employed to determine the crystal structure and the particle size of the deposited films. The stoichiometry of the deposited films was confirmed by means of energy-dispersive X-ray spectrometry. The optical transmission and reflection spectrum of the deposited films have been recorded in the wavelength optical range 450–2500 nm. The variation of the optical parameters, i.e. refractive index, n , extinction coefficient, k , with thickness of the deposited films has been investigated. The refractive index dispersion in the transmission and low absorption region is adequately described by the single-oscillator model, whereby the values of the oscillator strength, oscillator position, dispersion parameter as well as the high-frequency dielectric constant were calculated for different film thickness. Graphical representations of the surface and volume energy loss function were also presented.

Thickness dependence of optical parameters for ZnTe thin films deposited by electron beam gun evaporation technique

Cu2HgI4 powder has been prepared by precipitation from reactive chemical solutions. An electron beam gun evaporation system was used to deposit the prepared powder in a thin film form onto a Corning 7059 glass substrate. The x-ray diffraction study reveals that the as-deposited films are polycrystalline in nature and have a composition corresponding to the Cu2HgI4 single phase. The differential thermal analysis curve exhibits a strange endothermic peak located at a temperature of 355.5 K, corresponding to the phase change from the first-order phase to the fast ion-conducting phase. The phase change is accompanied by a colour change from bright-red (β-phase) to dark-brown (α-phase). The optical properties of as-deposited films have been calculated from the recorded transmission and reflection data in the spectral range 600–2500 nm. The refractive index of the as-deposited films was found to follow the two-term Cauchy dispersion relation and is adequately described by the effective-single-oscillator model. The refractive index–wavelength variation leads to the determination of the oscillator parameters Eo and Ed to be 3.113 and 9.883, respectively. The static refractive index, no(0), and static dielectric constant, es, were also calculated as a result of the latter data and were found to be 2.043 and 4.175, respectively. The analysis of the optical absorption coefficient confirmed the presence of a direct optical transition with a band gap energy of 1.96 eV.

https://iopscience.iop.org/article/10.1088/0022-3727/41/2/025311/pdf

Optical properties of thermochromic Cu2HgI4 thin films

Nearly stoichiometric thin films of In 49 Se 48 Sn 3 were deposited at room temperature, by conventional thermal evaporation of the presynthesized materials, onto precleaned glass substrates. The microstructural studies on the as-deposited and annealed films, using transmission electron microscopy and diffraction (TEMD), revealed that the as-deposited films are amorphous in nature, while those annealed at 498 K are crystalline. The optical properties of the investigated films were determined from the transmittance and reflectance data, in the spectral range 650–2500 nm. An analysis of the optical absorption spectra revealed a non-direct energy gap characterizing the amorphous films, while both allowed and forbidden direct energy gaps characterized the crystalline films. The electrical resistance of the deposited films was carried out during heating and cooling cycles in the temperature range 300–600 K. The results show an irreproducible behavior, while after crystallization the results become reproducible. The analysis of the temperature dependence of the resistance (ln( R ) vs. 1000/ T ) for crystalline films shows two straight lines corresponding to both extrinsic and intrinsic conduction. The room temperature I – V characteristics of the as-deposited films sandwiched between similar Ag metal electrodes shows an ohmic behavior, while non-ohmic behavior attributed to space charge limited conduction has been observed when the films are sandwiched between dissimilar Ag/Al metal electrodes.

Optical and electrical properties of thermally evaporated In49Se48Sn3 films

AC Conductivity and Dielectric Properties of Cu2HgI4

Nearly stoichiometric thin films of the ternary AgSbSe2 compound have been deposited at room temperature by conventional thermal evaporation of the presynthesized material onto glass substrate. The X-ray and electron diffraction studies revealed that the as-deposited films are amorphous in nature, while an amorphous-to-crystalline phase transition could be obtained by thermal annealing at 373 K. The elemental chemical composition of as-deposited films was confirmed using the energy dispersive X-ray analysis. The transmission and reflection spectra of as-deposited and annealed films at annealing different temperatures were recorded at normal light incidence in the wavelength range 600-2500 nm. The refractive index and optical band gap have been calculated for the investigated films. The dispersion parameters, (Eo, Ed) static refractive index ns (0), static dielectric constant, ϵs and the carrier concentration to the effective mass ratio, N/m* have been calculated. An analysis of the optical absorption spectra revealed a non direct optical transition characterizing the as-deposited films and those annealed at 343 and 374 K while; direct and indirect optical transitions characterized the films annealed at 398 K. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A. M. Salem

Papers

Thickness dependence of optical parameters for ZnTe thin films deposited by electron beam gun evaporation technique

Optical properties of thermochromic Cu2HgI4 thin films

Optical and electrical properties of thermally evaporated In49Se48Sn3 films

AC Conductivity and Dielectric Properties of Cu2HgI4

Structure and optical properties in the amorphous to crystalline transition in AgSbSe2 thin films