Low temperature (<80 °C) neutral beam deposition (LTNBD) was investigated as a new approach to the fabrication and development of nano-crystalline silicon (nc-Si), which has better properties than that of amorphous silicon (α-Si). The difference between LTNBD and conventional PECVD is that the film formation energy of the nc-Si in LTNBD is supplied by controlled neutral beam energies at a low temperature rather than by heating. Especially, in this study, the characteristics of the nc-Si thin film were investigated by adding 10% of an inert gas such as Ne, Ar or Xe to SiH4/H2. Increasing the beam energy resulted in an increase in the deposition rate, but the crystallinity was decreased, due to the increased damage to the substrate. However, the addition of a higher mass inert gas to the gas mixture at a fixed beam energy resulted not only in a higher deposition rate but also in a higher crystallization volume fraction. The high resolution transmission electron microscopy image showed that the grown film is composed of about 10 nm-size grains.
[Show abstract][Hide abstract] ABSTRACT: Thin films of Se 35 Te 65 - x Ge x ( x = 0 , 3 , 6 , 9 , 12 ) nanoparticles were synthesized using thermal evaporation method. They were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and absorption and transmission spectra. XRD results show that these films are of amorphous nature, while SEM images show nanoparticles with average particle size around 30 nm. No significant changes are observed in morphology of the deposited films by changing concentrations of Te and Ge. The optical behaviors of these films have been studied using the absorption and transmission spectra in the spectral region 400–1100 nm. The absorption, extinction coefficients and refractive index were obtained and investigated in more detail. The optical band gap ( E g ) values were also determined and are found to decrease from 0.83 to 0.69 eV by increasing the concentration of Ge from 0 to 12. The transmission spectra for the thin films of Se 35 Te 65 - x Ge x nanoparticles show strong absorption at wavelength less than 500 nm and become highly transparent at wavelength above 800 nm. No significant changes in the transmission spectra are observed by increasing concentration of Ge. These results might be useful for development of optical disks and other semiconducting devices based on these nanochalcogenides.
Journal of Nanomaterials 01/2012; 2012. DOI:10.1155/2012/393084 · 1.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Thin films of Te94Se6 nanoparticles were synthesized using the physical vapor condensation technique at different argon (Ar) pressures. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy, absorption spectrum, photoluminescence (PL) and Raman spectroscopy. XRD results show that the as-grown films have a polycrystalline structure. SEM images display uniform nanoparticles in these films where the size increases from ~ 12 to about 60 nm by decreasing Ar pressure from 667 to 267 Pa. These as-grown thin films were found to have direct band gaps, whose value decreases with increasing particle size. The absorption and extinction coefficients for these films were also investigated. PL emission spectra exhibit three bands peaking at 666, 718 and 760 nm, while Raman spectra displayed three bands located at 123, 143 and 169 cm− 1. No significant changes are observed in positions or intensities of these bands by decreasing the Ar pressure, except that of the last band of PL; where the intensity increases. The obtained results on this Te94Se6 nanomaterial especially its controlled direct bandgap might be useful for development of optical disks and other semiconducting devices.
Thin Solid Films 03/2013; 531:70–75. DOI:10.1016/j.tsf.2012.12.021 · 1.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The nanostructure formation has been revealed in different types of materials and therefore an increasing interest has been witnessed in recent years to study the amorphous materials. Nano-structured materials show dramatic changes in their structural, optical and electrical characteristics due to the decrease in size below excitonic limit and provide new physical and chemical properties. In the present research work amorphous Se80Te20−xBix (x = 3 and 6) was prepared by melt quenching techniques. Nano-structured thin films of amorphous Se80Te20−xBix have been obtained using physical vapor condensation process on glass/Si wafer substrate. The morphology of amorphous Se80Te20−xBix films was scanned by employing field emission scanning electron microscope (FESEM). The optical absorption and reflection spectra of nano-structured films were inspected by UV/VIS/NIR spectrophotometer. The optical absorption analysis indicates the non-direct transitions predominate in nano-structured Se80Te20−xBix films. The extinction coefficient and absorption coefficient are found to decrease while optical energy band gap and the refractive index increase with Bi contents in Se–Te system.
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