Spectroscopic characterization of Ag catalyzed silicon carbide nanowires deposited via CVD reactor (original) (raw)
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Electronic structure and optical vibrational modes of 3C-SiC nanowires
International Journal of Nanotechnology, 2015
The electronic structure and vibrational optical modes of silicon carbide nanowires (SiCNWs) were studied using the first principles density functional theory. The nanowires were modelled along the [111] direction using the supercell technique passivating all the surface dangling bonds with H atoms, OH radicals and a combination of both. Results show that the full OH passivation lowers the band gap energy compared to the full H passivation owing to C-OH surface states. A shift of the highest optical vibrational modes of Si and C to lower frequency values compared to their bulk counterparts was observed in accordance with phonon confinement scheme.
Chemistry of Materials, 2007
SiC nanowires are grown by a novel catalyst-assisted sublimation-sandwich method. This involves microwave heating-assisted physical vapor transport from a "source" 4H-SiC wafer to a closely positioned "substrate" 4H-SiC wafer. The "substrate wafer" is coated with a group VIII (Fe, Ni, Pd, Pt) metal catalyst film about 5 nm thick. The nanowire growth is performed in a nitrogen atmosphere, in the temperature range of 1650-1750°C for 40 s durations. The nanowires grow by the vapor-liquid-solid (VLS) mechanism facilitated by metal catalyst islands that form on the substrate wafer surface at the growth temperatures used in this work. The nanowires are 10-30 µm long. Electron backscatter diffraction (EBSD) and selected area electron diffraction analyses confirm the nanowires to crystallize with a cubic 3C structure of 3C-SiC. EBSD from the nanowire caps are indexed as Fe 2 Si, Ni 3 Si, Pd 2 Si, and PtSi phases for the nanowires grown using Fe, Ni, Pd, and Pt as the metal catalysts, respectively. The nanowires are found to grow along the 〈112〉 directions, as opposed to the commonly observed 〈111〉 directions. The micro-Raman spectra from single nanowires indicate regions with varying compressive strain in the nanowires and also show modes not arising from the Brillouin zone center, which may indicate the presence of defects in the nanowire.
Catalyst-Free Chemical Vapor Deposition for Synthesis of SiC Nanowires with Controlled Morphology
Springer Series in Materials Science, 2013
SiC wires of different morphology were grown using methyltrichlorosilane (MTS) and hydrogen by chemical vapor deposition under ambient pressure. Taguchi method has been used to design experiments to get the optimum parameters for growing SiC wires of diameter in nanometer range. Results from XRD and SEM analyses showed the growth of -SiC wires having different morphology. At higher temperature (1500 °C), the growth of SiC grains was observed rather than wires. The optimum deposition conditions for uniform diameter growth of SiC nano wires, smoothness of the surface and homogeneous growth of SiC on the surface have been obtained. The hydrogen to MTS flow rate ratio should be above 20 for the growth of SiC wires of nanometer diameter. The deposition temperature for the growth of crystalline SiC wires should be 1100-1300 °C. The total flow rate of carrier gas comprising of argon and hydrogen for a particular H2/MTS flow rate ratio is critical for morphological outcome of SiC. In the present study it was 2 lpm for H2/MTS flow rate ratio 14 to obtain wire morphology. When the total gas flow rate was increased to 6 lpm for the same H2/MTS flow rate ratio 14, the wire morphology of SiC disappeared and the formation of grains occurred. The optimum deposition temperature i.e. 1300 °C was kept constant and further experiments were conducted by changing H2/MTS mole ratio to verify morphological outcome of SiC. A plausible mechanism has been suggested for the above observations using vapor-solid mechanism. . TEM images of the SiC nanowires grown at H2/MTS = 70 and T = 1300 °C.
Silicon carbide nanowires synthesis and preliminary investigations
Acta Physica Polonica Series a
As the field of biotechnology expands and the semiconductor industry approaches the limit of size reduction with conventional materials, these and other fields will increasingly rely on nanomaterials with novel properties. Silicon carbide (SiC) possesses many properties that make it appealing to research and industry: a large band gap, high hardness, high strength, low thermal expansion, chemical inertness, etc. It is known that silicon carbide nanowires can be synthesized through a reaction between silicon vapor and multiwalled carbon nanotubes. This process was refined to produce smaller, straighter nanowires. This was done by analyzing the dependence of the reaction rate on the partial vapor pressure of silicon. The reaction rate was studied by comparison of SiC and multiwalled carbon nanotubes peak intensities in X-ray diffractograms, which produced an estimate of the respective reactions' SiC yields. The particle morphologies were then analyzed with transmission electron mi...
Electronic Band Structure of Cubic Silicon Carbide Nanowires
In this work, the effects of the diameter and morphology on the electronic band structure of hydrogenated cubic silicon carbide (β-SiC) nanowires is studied by using a semiempirical sp 3 s* tight-binding (TB) approach applied to the supercell model, where the Si-and C-dangling bonds on the surface are passivated by hydrogen atoms. Moreover, TB results (for the bulk) are compared with density functional calculations in the local density approximation. The results show that though surface morphology modifies the band gap, the change is more systematic with the thickness variation. As expected, hydrogen saturation induces a broadening of the band gap energy because of the quantum confinement effect. Introduction Bulk silicon carbide (SiC), one of the third-generation wide band-gap semiconductor materials, has been extensively researched on its electrical, physical, and chemical properties. There is significant interest in the synthesis of SiC nanostructures [1–3] as novel functional materials for nanoscale engineering. Using laser ablation technique Shi et al. [4] have synthesized SiC nanowires growth in the [001] direction, the growth mechanism was discussed based on the vapor-liquid-solid reaction. The red shift, broadening peak, and asymmetry of the Raman peak were explained by the size confinement effect in the radial and growth directions. SiC nanostructures have been shown to exhibit more superior properties (greater elasticity and strength) than bulk SiC. In addition, the electron field-emission properties of SiC nanowires have a threshold field comparable to that of a carbon nanotube based material with stable emission. SiC has also attracted much interest due to its potential application in blue–green light-emitting diodes and UV photodetectors, since intense visible photoluminescence has been observed in SiC nanostructures [5]. In contrast to the extensive experimental research, very few theoretical studies have involved in the electronic properties of the β-SiC Nanowires [6]. The TB approach provides a bridge between accuracy and numerical efficiency or, in other words, between empirical and ab-initio total energy functionals. Furthermore, TB is based on a simplified, but quite effective description of interatomic bonding; this is an essential feature when dealing with a material characterized by directional and covalent bonding. As a matter of fact, any fundamental process involved in the physics of surface defects can be traduced into a sequence of dangling bonds and rebonding phenomena. TB is accurately designed to provide a sharp description of both. Despite of these recent developments and studies, a detailed understanding of the electronic properties of hydrogenated β-SiC nanowires is required for their future developments and applications in nanotechnology. As ab-initio calculations become computationally demanding with increasing wire diameter, and for examination of larger diameter nanowire structures at lower computational cost, we have applied the semiempirical TB approach.
Extended Vapor–Liquid–Solid Growth of Silicon Carbide Nanowires
We developed an alloy catalytic method to explain extended vapor-liquid-solid (VLS) growth of silicon carbide nanowires (SiC NWs) by a simple thermal evaporation of silicon and activated carbon mixture using lanthanum nickel (LaNi 5 ) alloy as catalyst in a chemical vapor deposition process. The LaNi 5 alloy binary phase diagram and the phase relationships in the La-Ni-Si ternary system were play a key role to determine the growth parameters in this VLS mechanism. Different reaction temperatures (1300, 1350 and 1400 C) were applied to prove the established growth process by experimentally. Scanning electron microscopy and transmission electron microscopy studies show that the crystalline quality of the SiC NWs increases with the temperature at which they have been synthesized. La-Ni alloyed catalyst particles observed on the top of the SiC NWs confirms that the growth process follows this extended VLS mechanism. The X-ray diffraction and confocal Raman spectroscopy analyses demonstrate that the crystalline structure of the SiC NWs was zinc blende 3C-SiC. Optical property of the SiC NWs was investigated by photoluminescence technique at room temperature. Such a new alloy catalytic method may be extended to synthesis other onedimensional nanostructures.
First principles band gap engineering of [1 1 0] oriented 3C-SiC nanowires
Computational Materials Science, 2018
Silicon carbide nanowires offer excellent opportunities for technological applications under harsh environmental conditions, however, the 3C-SiC polytype nanowires, grown along the [1 1 0] crystallographic direction, have been rarely studied, as well as the effects of the surface passivation on their physical properties. This work addresses the effects of hydrogen passivation on the electronic band gap of silicon carbide nanowires (SiCNWs) grown along the [1 1 0] direction by means of Density Functional Theory. We compare the electronic properties of fully hydrogen-passivated SiCNWs in comparison to those of SiCNWs with a mixed passivation of oxygen and hydrogen by changing some of the surface dihydrides with SiAOASi or CAOAC bonds. The results show that regardless of the diameter and passivation, most of the nanowires have a direct band gap which suggests an increased optical activity. The surface CAOAC bonds reduce the electronic band gap energy compared to that of the fully H-terminated phase, while the nanowires with SiAOASi bonds have a larger band gap. The calculation of formation energies shows that the oxygen increases the chemical stability of the SiCNWs. These results indicate the possibility of band gap engineering on SiC nanostructures through surface passivation.
β-SiC nanowires were successfully fabricated on pare Si (100) substrate using simple carbo-thermal evaporation of graphite at 1200˚C. The obtained β-SiC nanowires were aligned with diameters ranged between 40 to 500 nm. The majority of crystal planes were β-SiC (111) with other less intensity of (200), (220) and (311). The silicon substrate location inside the furnace found to be critical in the formation of the β-SiC nanowires. Also, FTIR absorption peaks for β-SiC nanowires found at higher frequency side of 1110 cm-1 which is pointed to Si–O asymmetric stretching mode.