A set of hydrogenated nanocrystalline silicon (nc-Si:H) films prepared in a home-built plasma enhanced chemical vapour deposition (PECVD) system using the layer-by-layer (LBL) deposition technique have been studied. The 13.56 MHz rf power was varied from 20 W to 100 W to study the influence of rf power on the structural properties of the nc-Si:H films. The structure of the films was studied by X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. Appearance of XRD peaks at 2q angles of 28o and 56o which correspond to silicon orientation of (111) and (311) respectively were observed in all films deposited on c-Si substrate indicating evidence of crystallinity in the films. The crystallite sizes were in the range of 8 to 100 nm as determined using the Scherrer technique. The integrated intensities of absorption bands at 630 cm-1, 780 - 880 cm-1 and 2000 – 2090 cm-1 from FTIR spectrum which corresponds to various Si-H bonding configurations in the films were studied and were related to the presence of small clusters of nanocrystallites embedded in an amorphous matrix. Based on the dependence of amplitudes of Si-H vibrational modes on crystallite size and rf power, the properties and the role of hydrogen in nc-Si:H films prepared using the LBL technique were discussed.
Optical constants derived from optical transmission (T) and reflectance (R) spectra in the wavelength range of 220 to 2200 nm are presented in this paper for hydrogenated silicon (Si:H) thin films deposited by plasma enhanced chemical vapor deposition (PECVD) using the layer-by-layer (LBL) deposition technique. The films were deposited on quartz substrate by decomposition of SiH4 and H2 gases at flow-rate of 5 sccm and 20 sccm, respectively. The substrate temperature, deposition pressure and deposition rate are 100°C, 0.8 mbar and 2.8 nm/s, respectively. The as-prepared films were annealed in nitrogen for one hour at annealing temperatures of 400°C, 600°C, 800°C and 1000°C. The as-prepared film thickness of 301 nm decreased to 260 nm when samples were annealed at 1000°C. The refractive indices (~ 3.0 to 3.4) of annealed films were determined from the interference fringes of transmission spectrum following Manifacier and Davies methods. The electronic transition from valence band to conduction band in these films are characterized from the optical energy gap; EG (~1.64 to 2.41 eV), the dispersion energy; Ed (~26.4 to 34.0 eV) and the oscillator strength; Eo (~2.8 to 3.2 eV). It is interesting to note that EG is lowest for the films annealed at temperature of 600°C which has the lowest hydrogen content, CH in the film. Evidence of the presence of nanocrystallites formed in amorphous matrix is also observed for the films annealed at temperatures above 600°C.
The effects of rf power on the structural properties of hydrogenated nanocrystalline silicon (nc-Si:H) thin films deposited using layer-by-layer (LbL) deposition technique in a home-built plasma enhanced chemical vapor deposition (PECVD) system were investigated. The properties of the films were characterized by X-ray diffraction (XRD), microRaman scattering spectroscopy, high resolution transmission electron microscope (HRTEM) and Fourier transform infrared (FTIR) spectroscopy. The results showed that the films consisted of different size of Si crystallites embedded within an amorphous matrix and the growth of these crystallites was suppressed at higher rf powers. The crystalline volume fraction of the films was optimum at the rf power of 60 W and contained both small and big crystallites
with diameters of 3.7 nm and 120 nm, respectively. The hydrogen content increased with increasing rf power and enhanced the structural disorder of the amorphous matrix thus decreasing the crystalline volume fraction of the films. Correlation of crystalline volume fraction, hydrogen content and structure disorder of the films under the effect of rf
power is discussed.
The influence of pH of the electrolyte used during anodization of Titanium substrate has been
investigated in order to determine the optimum pH condition to form self-organized Titanium dioxide
(TiO2) nanotubes (NTs) structure. The TiO2 NTs was formed by anodizing Titanium substrate in an
electrolyte containing 1M of sodium sulfate (Na2SO4) with 0.7 g of ammonium fluoride (NH4F) for 180
minutes with potential 20 V. The optimum conditions were determined by characterization using FESEM
and XRD analysis. As shown in the result, it can be summarized that pH of the anodization electrolyte can
affect the length and diameter of the NTs as confirmed by FESEM images. FESEM result shows that, the
length of nanotubes increased as the pH increased which are from 50 nm to 424 nm for pH 5 and pH 7,
respectively. However, at higher pH more than 7, the nanotube structure was collapsed and only form
bulk oxide film. The FESEM result also supported by the XRD result as the peak at 24°
increased up from
pH 3 to pH 7 and drop at pH 9.