Morphological and structural characterization of Pb:ZnS nanostructure films deposited by simple thermal evaporation

ZnS nanostructure films were deposited by a thermal evaporation method. Two films were prepared; the first was zinc sulfide (undoped ZnS) and the second was Pb-doped zinc sulfide (Pb:ZnS). X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) techniques were employed to investigate the element contents of the two films; they were found to be stoichiometric. Surface and growth evolution of films were explored by SEM images and found to have morphological development from spherical forms into nanostructure lookalike Taraxacum erythrospermum (Dandelion) with increasing the Pb from 0 wt.% to 12 wt.%. A structural study was performed using XRD patterns. The films have ZnS hexagonal structure (002) preferential orientation with various Pb percentages. In the doped sample, ZnS nanostructure and pores and nanowires (NWs) were formed with a mean diameter less than 50 nm; the undoped film had dense structure and was thin. This study illustrated the influence of Pb doped on the morphological modification of ZnS films.

New Comparative Study of High-Sensitivity H2Gas Sensors at Room Temperature Based on ZnO NWs Grown on Si and PS/Si Substrates without Catalyst by Wet Thermal Evaporation Method

A novel approach for growing high-quality ZnOnano-structures with no catalyst using an inexpensive technique that is called wet thermal evaporation has been investigated for gas sensor applications. For a novel comparative investigation of H2 gas sensors, large regions regarding the well-aligned coral reef-like ZnOnano-structures on the porous Si (PS) and flower-like nano-rods on Silicon were successfully utilized. In the presented study, a Pd/ZnO/Pd metal-semiconductor-metal was efficiently created for H2 gas sensor device employing high-quality ZnOnano-structures that are grown on a variety of the substrates. At room temperature, the sensitivity related to ZnO/PS and ZnO/Si is evaluated at various flow rate values (25sccm, 50sccm, 100sccm, and 150sccm) of 2% H2 gas. The I-V characteristics revealed that ZnO/Si has a larger hydrogen gas barrier height than ZnO/PS. At room temperature, the ZnO/Si sensitivity was about 105% and 190% for ZnO/PS at 150sccm flow rate. The sensors’ sensitivity and optimum operating temperature for ZnO/PS at 150sccm of H2 gas are 350% (at 100 Celsius), which is higher compared to double the maximal sensitivity with regard to ZnO/Si device at a temperature of 150 Celsius. This research concluded that because ZnO/PS has a large specific area, it has a greater possibility of reacting with gases and increasing sensitivity at the temperature of theroom.

The structural effects on silver nanoparticles plasma edges in optical reflectance spectra of Ag/Ag2O composites synthesized by oxygen plasma treatment of silver thin films

In this work, we present the results of a unique study that aims to detect the structural effects on the plasma edges in optical reflectance spectra of Ag/Ag2O composites synthesized by treating silver thin films manufactured by thermal evaporation method with oxygen plasma afterglow. The results showed that, each of the optical reflectance spectra contains two plasma edges, the first (λI) belongs to the surface plasmons of the individual silver nanoparticles, and the second (λL) belongs to the larger silver nanoparticles. In addition, we found that the positions of the plasma edges are linearly related to the positions of the optical absorption peaks, except for high and low oxidation rates cases. On the other hand, taking into account previous work, we obtained indications that, the ratio NI/NL may be a measure of the film's effectiveness in inhibiting bacteria.

Single Step Growth of Vertically Oriented Zinc Oxide Nanowire Using Thermal Evaporation

Commonly, the synthesis of ZnO nanowires involves the use of metal catalyst via a non-direct step growth which contribute to the contamination on the final product. Thus, in this work we synthesized catalyst-free ZnO nanowires using a direct or single step growth of nanowires. Thermal evaporation method is used to synthesize ZnO nanowires on bare glass substrates with different distances between Zn powder and the substrates; on-top (1.2 cm), 16 cm and 18 cm. Field Emission Scanning Electron Microscopy images showed a vertically well-aligned with high density of ZnO nanowires were successfully synthesized via self-seeding process and the longest nanowires were produced at the shortest distance. Energy Dispersive X-ray and X-Ray Diffraction analyses confirmed that high purity of ZnO nanowires were obtained and ZnO (002) strongest and sharp peak was observed, indicating preferentially grown ZnO nanowires along the c-axis perpendicular to the substrates and leading towards single crystal structure. Four peaks were observed in visible range from Photoluminescence spectra (PL) which related to fundamental defects with the highest peak at 3.04 eV. The on-top sample with distance 1.2 cm from Zn powder has the lowest transmittance due to the high thickness of ZnO nanowires. The range of energy band gap for ZnO nanowires obtained from the extrapolation graph is in agreement with PL highest peak approximately 3.00 eV. Therefore, this direct or single step deposition method is of great interest since it has successfully produced ZnO nanowires with significant characteristics without employing the non-direct step growth.

Optimization of Different Temperature Annealed Nanostructured CdSe Thin Film for Photodetector Applications

In this report, we have discussed the performance of highly sensitive CdSe based photodetector. The CdSe thin films were prepared by thermal evaporation method on the cleaned glass substrate at room temperature. The influence of post annealing on the optical, morphological, structural and photo-electrical properties at different temperatures were investigated. The formation of polycrystalline CdSe films was confirmed from X-ray diffraction (XRD) and Raman studies. The change in surface morphology along with the average grain size of films were observed by field emission scanning electron microscopy (FESEM). The stoichiometric ratio of Cd and Se elements in the deposited films was verified from Energy dispersive X-ray spectroscopy (EDS). The change in various optical parameters like absorption coefficient (α), extinction coefficient (k), optical band gap (Eg), refractive index (n) etc. of the studied films were calculated from the UV-Visible measurement. Importantly, the band gap values were decreased and increased with different annealing temperatures. The CdSe film annealed at 300 °C showed good photo-response and the corresponding optical properties which make them suitable for photodetector applications.

Enhanced Electrochromic Properties of Nanostructured WO3 Film by Combination of Chemical and Physical Methods

WO3 films are the most widely used electrochromic functional layers. It is known that WO3 films prepared by pure chemical method generally possess novel nanostructures, but the adhesion between WO3 films and substrates is weak. However, WO3 films prepared by pure physical method usually show relatively dense morphology, which limits their electrochromic properties. In order to break through these bottlenecks and further improve their electrochromic properties, this work first prepared nanostructured WO3 powder by chemical method, and then using this powder as the evaporation source, nanostructured WO3 films were fabricated by vacuum thermal evaporation method. Properties of nanostructured WO3 films were systematically compared with those of ordinary WO3 films. It turned out that the nanostructured WO3 film exhibited better cyclic stability and memory effect, and also the optical modulation rate was 14% higher than that of the ordinary WO3 film. More importantly, the nanostructured WO3 film showed better adhesion with the ITO substrates. These results demonstrate that a combination of chemical and physical methods is an effective preparation method to improve the electrochromic properties of WO3 films.