In the present work, one-dimensional nanostructures of silicon oxide (SiOx) have been synthesized by thermal annealing method with and without chromium thin film on silicon substrate. The synthesis was carried out at different process temperatures ranging from 1000°C to 1100°C by using gold/chromium (Au/Cr) catalysts stack layer on the Si substrate in nitrogen (N2) ambience. The as-synthesized SiOx nanostructures have tetragonal rutile structure and show polycrystalline nature. The SEM images reveal wire-like nanostructures on the substrate with and without chromium thin film. Under the catalytic reaction of the gold/chromium metal, the density of SiOx nanowires is enhanced, since the Cr layer serves as a diffusion barrier for the diffusion of the gold downwards into the Si substrate. The vapor-liquid solid (VLS) growth mechanism is found to be dominant in the growth of SiOx nanowires. Furthermore, X-Ray diffraction microscopy (XRD) and Photoluminescence spectroscopy (PL) analysis conclude the defect free growth of the SiOx nanowires on gold/chrome/silicon substrate.
Amorphous silicon oxide (SiOx) nanowires have many potential applications in blue light emitters, optical sensors [
In present work, we have synthesized SiOx nanostructures by thermal evaporation method with and without chromium thin film as a catalyst on Si substrate. During the growth of SiOx nanowires, the diffusion of the gold into the Si substrate is retarded by inserting a thin layer of chromium (Cr) metal in the Au/Si substrate. The growth of nanowires was carried out with the gold/chromium/silicon (Au/Cr/Si) substrate at different temperatures ranging from 1000˚C to 1100˚C. To investigate the effect of the Cr layer, the nanowire growth was also carried out in the Cr/Si sample at 1100˚C and 1150˚C.
The as-synthesized products were analyzed with Scanning Electron Microscopy (SEM), X-Ray diffraction microscopy (XRD), Energy Dispersive X-ray Spectroscopy (EDX), Transmission Electron Microscopy (TEM) and Photoluminescence spectroscopy (PL) for observing the effect of chromium thin film on the structural morphology, crystal structure, composition and optical properties of silicon oxide (SiOx) nanostructures.
N-type (100) Si wafer was used as a substrate for the growth of SiOx nanowires. Before depositing the catalyst films of Au and Cr, the Si substrate was atomically cleaned by using Isopropyl alcohol (IPA) with ultrasonic vibrations, a mixture solution of H2SO4 and H2O2, and 10% HF solution for removing the native SiO2. The gold (Au) and chromium (Cr) thin films were deposited on the Si surface in radio-frequency (RF) sputtering chamber at the pressure of 1 × 10−6 mbar and 100 watt power. The as-deposited thin layer of the Au and the Cr acts as catalyst for the growth of SiOx nanowires. Two types of samples were fabricated which consists of Au/Si and Au/Cr/Si substrates. Successively, these samples were loaded into the maximum temperature zone of horizontal tubular furnace. The furnace temperature was maintained at various temperatures ranging from 1000˚C to 1100˚C. The nanowires were grown by thermal annealing of Au (20 nm)/Si and the Au (10 nm)/Cr (10 nm)/Si substrates in nitrogen (N2) ambience. The synthesis was carried out at atmospheric pressure. The as-synthesized products were characterized by Scanning Electron Microscopy (SEM), X-Ray diffraction microscopy (XRD), Energy Dispersive X-ray Spectroscopy (EDX), Transmission Electron Microscope (TEM) and photoluminescence spectroscopy (PL) for observing the effect of chromium thin film on the structural morphology, crystal structure and composition and optical properties.
formation of higher density of the Au nanoparticles on the Au/Cr/Si substrate. The typical length of the SiOx nanowires is several tens of micrometers while the width is in the nanometer range.
Further, to investigate the role of the Cr layer, the Si substrate with 10 nm thick Cr layer were annealed in N2 ambience at 1100˚C and 1150˚C for 40 min. At these temperatures, the Cr thin film agglomerates into nanoparticles on Si substrate but the samples do not show any sign of the nanowire growth. Thus, it can be concluded that the Cr layer does not act as a catalyst and only the Au metal layer serves as catalyst in the growth of nanowires.
The XRD pattern (
From above experiments, the nanowires growth mechanism is concluded in the following way: For the Au/Si as well as Au/Cr/Si substrate, no nanowires growth was observed at process temperatures of 1000˚C, shown in
In this growth process, the Au film agglomerates into the nanoparticles at relatively lower temperature than the Cr layer. This is due to the lower melting point of the Au film (melting point ≈ 1064˚C) in comparison to the Cr film (melting point ≈ 1857˚C) [
We have synthesized the silicon oxide (SiOx) nanowires on gold coated and gold/chrome coated Si substrate by
thermal annealing process. The higher density of the SiOx nanowires is attained at process temperature of 1100˚C by using the thin layer of the Cr metal on the Au/Si substrate. This is due to the fact that the Cr layers stop the inward diffusion of the Au into the Si and cause the higher density of the Au nanoparticles which catalyze the nanowire growth. The surface morphology study concludes the growth of nanowires. The synthesized nanostructures have orthorhombic structure and polycrystalline in nature. In the PL spectra of SiOx nanowires, we have not observed any peak corresponding to oxygen deficiency on the Au/Cr/Si substrate whereas oxygen deficiency peaks exist on the Au/Si substrate. This confirms that we have synthesized defect free silicon oxide (SiOx) nanowires by using chromium as an intermediate layer.