Papers by Keyword: Thermal Evaporation

Abstract: Nanoparticles Cu₂SnSe₃ alloys were synthesized by mechanical alloying from mixtures of pure crystalline Cu, Sn and Se powders using a low cost planetary ball milling process optimizing the milling duration and the rotational speed. The properties of Cu₂SnSe₃ (CTSe) thin films deposited by thermal evaporation from this powder on glass substrate at T_s = 400°C were investigated. Powders and films were analyzed by X-ray diffraction (XRD), scanning electron microscopy(SEM), energy dispersive X-ray analysis (EDX), atomic force microscopy (AFM), to determine their microstructure, morphology, chemical compositions and root-mean-square (RMS) roughness. XRD analysis revealed that all samples crystallize in polycrystalline nature with cubic structure and lattice parameter a = 5.68 Å. The optical measurements were carried out in the [500-2500nm] wavelength range and were determined from spectral transmission data. Optical measurements showed that the deposited layers had a relatively high absorption coefficient of 10⁴ cm^-1 and the direct energy band gap was found to be around Eg =1.29eV. The suitable p-type conductivity of CTSe thin films was confirmed by hot probe method. Other electrical parameters (carrier concentration n_p = 10.04x10¹⁸ cm^-3, electrical resistivity ρ = 30.49x10^-2 Ω cm and mobility μ_H = 94.33 cm²/V s) were measured at room temperature.

Abstract: 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.

Abstract: Zinc oxide (ZnO) is a metal oxide material that is interested in research due to its possibility of bandgap tailoring, doping with various types of materials as well as being able to form many structures from zero-dimensional to three-dimensional structures. All these properties allow ZnO to be used in broad applications. Several research studies have been reported on the synthesis of ZnO nanostructures by the physical vapour deposition (PVD) technique. One of the potential PVD technique is thermal evaporation process. Generally, the technique is used to grow thin-film but researchers have found a potential to be used in the growth of nanostructures due to the ability to provide high crystallinity with homogeneous and uniform nanostructures. This analysis will therefore explore more about the thermal evaporation synthesized ZnO nanostructures and the application as photocatalyst material in wastewater treatment.

Abstract: The present article reports the growth mechanism of zinc oxide (ZnO) nanowires grown on silicon substrate pre-coated with ZnO buffer layer by thermal evaporation method. ZnO nanowires are grown for different growth time of 0, 30, 90 and 120 mins with controlled supply of Ar and O₂ gas at 650 °C. The structural, morphological and crystallinity properties of ZnO nanowires are analyzed by field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) spectroscopy, high resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD). FESEM images infers that, the nanowires growth is driven by self-catalysed vapor-liquid-solid mechanism, where the buffer layer serve as nucleation site. EDX spectra show the uniform composition and purity of ZnO nanowires. A strong (002) peak is detected in XRD spectra which indicates that the preferred growth orientation of the nanowires is toward the c-axis with a hexagonal wurtzite structure. The HRTEM microscopic graphs confirm the growth of nanowire along the preferred [0001] axis. Based on the analysis of grown ZnO nanowires, the probable growth mechanism is schematically presented.

Abstract: Pb doped ZnS nanotubes films have been deposited on glass and Si (100) substrates by a thermal evaporation technique. Energy dispersive spectroscopy (EDX) analysis has been used to identify the element’s compositions. Pb concentration in the prepared films was increased from 0 to about ~6 wt. %. The X- Ray Diffraction (XRD) pattern exhibited the wurtzite structure of ZnS with (002) preferred orientation. It shows that the calculated grain size increased with increase in Pb concentration. XRD analysis was also used to determine the strain in the films. Morphology and thickness of the films were obtained from surface and cross section of the films, using scanning electron microscopy (SEM) images. SEM images have confirmed the ZnS nanotubes and modifications of the morphology when adding Pb. Atomic force microscope (AFM) and SEM characterization have been shown dense structure and demonstrated the growth of spherical forms with nanostructure (nanotubes not created) for a film deposited without doping (0 wt. %). The transparency of the films has been deduced from UV-Vis spectra, where the band gap increased with increase in Pb concentration

Abstract: Novel multipods-branched Cd-Se-S micro-/nanostructures (MNSs) were successfully prepared in a tube furnace by thermal evaporation under atmospheric pressure through using high-purity CdS and CdSe mixture powder with a molar ratio of 1:1 as evaporation source, high-purity Ar gas as carrier and protective gas, and mica wafer as substrate. Under the optimum condition, the evaporation temperature was 1100 °C, Ar gas flow rate was 200 sccm, and the distance between the evaporation source and substrate was 22 cm. The microstructure examination revealed that the length of the obtained branches was up to tens of microns and the diameter of the branches was of a few microns. The composition and crystal structure analyses indicated that, the chemical composition of the multipods-branched Cd-Se-S MNSs was CdSe_0.86S_0.14, which had a hexagonal structure and good crystallinity. The photoluminescence spectrum at room temperature displays an intrinsic emission peak around 620 nm. In addition, their growth might be controlled by a vapor-solid mechanism.

Abstract: The growth of zinc oxide nanowires is further investigated by thermal evaporation method and is discussed with respect to vapour-solid (V-S) growth mechanism. In this paper, ZnO nanowires were synthesized on glass substrate without the use of any catalyst with a constant flow of argon gas 1.36 psig and oxygen gas of 0.34 psig. Zinc powder of 99.99% purity is placed in a horizontal furnace and exposed to temperature of 600°C for 90 minutes. The surface morphology of the deposited zinc oxide is investigated by the atomic force microscopy (AFM) images and it was found that the deposited ZnO has a rough surface while field-emission scanning electron microscopy (FESEM) confirms the morphology of the ZnO nanowires. Photoluminescence (PL) spectra indicate that the optical quality of the deposited structure is potentially excellent with high energy excitonic emission close to the band edge which is assigned to the surface exciton in ZnO at 3.4eV.

Abstract: SnS thin films were deposited by thermal evaporation in vacuum on glass slide substrate. The as-deposited films were thermally annealed in a controlled N₂ atmosphere with annealing temperature in the range 100-500°C for 30 min. XRD, AFM, UV-VIS transmittance, FTIR and Hall effect measurements were used for characterization the as-deposited and annealed films. Based on the XRD patterns, the as-deposited and annealed films were indentified as the orthrombic structure. The band gap was found to increase from 1.15 to 1.42 eV when the annealing temperature increased from 100 to 500°C. The lowest resistivity and highest carrier concentration values were observed to be 12.95 Ω.cm and 1.98×10¹⁶ cm^-3 on the films annealed at 100 and 200°C, respectively.

Abstract: Amorphous SnSe thin films were deposited by thermal evaporation technique on glass substrates kept at room temperature in a vacuum better than 10^-5Torr. A detailed study of structural and optical properties of 150 nm thin film was carried out. The selected area diffraction patterns obtained by TEM for this thin film were analyzed by a new method that involves accurate determination of lattice parameters by image processing software. The obtained results are in good agreement with the JCPDS data. Optical transmission spectra obtained at room temperature were analyzed to study optical properties of deposited thin films. It has been found that indirect carrier transition is responsible for optical absorption process in the deposited thin films.

Abstract: MoO₂ has been widely used in many fields such as catalyst, gas-senor, super capacitor and Li-ion battery electrode. In this paper, MoO₂ nanoplates were synthesized in high density and large scale on silicon substrates via simple thermal evaporation of MoO₃ and S powders at 950 °C in a tube furnace. The morphology, composition and structure of the nanoplates were characterized by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The results indicate that the as-synthesized nanoplates are of well crystalline structure, and the thickness of these nanoplates is in the range of 100-300 nm. The growth mechanism of the nanoparticles was proposed as a vapor-solid process.