65 research outputs found
Si nanowires produced by very high frequency plasma enhanced chemical vapor deposition (PECVD) via VLS mechanism
No full textSilicon nanowires (SiNWs) with diameter of about a few nanometers and length of 3 ?m on silicon wafers were synthesized by very high frequency plasma enhanced chemical vapor deposition. Scanning electron microscopy (SEM) observations showed that the silicon nanowires were grown randomly and energy-dispersive X-ray spectroscopy analysis indicates that the nanowires have the composition of Si, Au and O elements. The SiNWs were characterized by high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. SEM micrographs displayed SiNWs that are needle-like with a diameter ranged from 30 nm at the top to 100 nm at the bottom of the wire and have length a few of micrometers. In addition, HRTEM showed that SiNWs consist of crystalline silicon core and amorphous silica layer
The role of catalyst metals to the growth of SI nanowire
No full textThe metal catalyst plays an important role on the catalytic growth. The growth mechanism of silicon nanowires synthesized with several metal catalysts via chemical-vapordeposition (CVD) is discussed by using vapor–liquid–solid (VLS) mechanism. However, the growth of silicon nanowires is chiefly affected by the compound decomposition, gas stream, and temperature difference. Silicon nanowires were fabricated on single crystalline silicon wafer. VLS growth of needle-like silicon nanocones via atmospheric pressure chemical vapor deposition from SiCl4 and using Ga, Al, Pt, Au, and Pb catalysts are reported. Scanning electron microscopy and transmission electron microscopy reveal different shapes due to differences of metals catalyst. For all of catalysts the nanocones are composed of an oxide shell with a Si core. In this growth mechanism, the gradual etching of the Ga, Al catalyst leads to a gradual decrease of the catalyst volume, and hence the tapered Si nanowire morphology. The growth rates were higher with Pt than with Au under all processing conditions. Also the rate determining step is the incorporation of Si atoms in the lattice at the liquid/solid interfaces and, furthermore, the metal catalysts affect this step, resulting in different activation energy. Using Pb resulting the flower-like SiO2 nanostructures were formed. Unlike any previously observed results using Ga, Al, Pt, and Au as catalyst, the molten Pb-catalyzed VLS growth exhibits many amazing growth phenomena. The silicon oxide nanowires grow out perpendicularly from the surface of the metal Pb balls. For each ball, numerous nanowires simultaneously nucleate, grow at nearly the same rate and direction, and simultaneously stop growing. Hence the type of metals play an important role to the shape of Si nanowire formed
Ultra-sharp pointed tip Si nanowires produced by very high frequency plasma enhanced chemical vapor deposition via VLS mechanism
No full textNeedle-like silicon nanowires have been grown using gold colloid as the catalyst and silane (SiH4) as the precursor by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). Si nanowires produced by this method were unique with sharpness below 3 nm. High resolution transmission electron microscopy (HRTEM) and X-ray diffraction technique (XRD) confirmed the single crystalline growth of the Si nanowires with (111) crystalline structure. Raman spectroscopy also has revealed the presence of crystalline Si in the grown Si nanowire body. In this research, presence of a gold nanoparticle on tip of the nanowires proved vapor–liquid–solid growth mechanism
Effect of plasma power and flow rate of silane gas on diameter of silicon nanowires grown by plasma enhanced chemical vapor deposition
No full textSilicon nanowires (SiNWs) have been synthesized by plasma enhanced chemical vapor deposition (PECVD) at different power for generation of plasma and different flow rate of silane gas. Silane (10% SiH4 in Ar) gas with flow rate ranging between 6-15 standard cubic centimeter per minute(sccm) were employed as the source and gold colloid as the catalyst. A p-type Si (100) wafer was used as substrate in this experiment and the substrate’s temperature was 370°C.The plasma power range was 12-17 watts. The grown silicon nanowires were analyzed using field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX). FESEM results show that some silicon nanowires are cone like and some of them are cylindrical. The EDX result revealed that the existence of silicon and oxygen elements in the nanowires. The silicon nanowires obtained have different diameters and lengths and the SiNWs consist of silicon core which are surrounded by oxide sheath. It has been found that the plasma power and flow rate of the silane gas influence the size of silicon nananowires growth by PECVD. The diameter of wires decreased from 140 nm to 80 nm averagely when plasma power was increased from 12 to 17 watts. The diameter also increased about 90 nm to 150 nm when the flow rate of silane gas is increased from 6 to 15 scc
Study of Si nanowires produced by very high frequency plasma enhanced chemical vapor deposition via VLS mechanism
No full textInvestigation on the properties of SnxSb10Se90-x chalcogenide semiconductor
No full textStudies on tin-antimony-selenium (TAS) system of SnxSb10Se90-x (x= 0, 5, 10, 12.5, 15, 20 and 30) have been carried out using XRD, XGT and DTA and density measurement, so as to elucidate the structural states and thermal properties. XRD analysis for x= 0, 5, 10 and 12.5 gave an indicative amorphous phase, while that of the samples with x= 15, 20 and 30 maintain the crystalline structures. These were further confirmed by XGT results, which measured the weight percentages and elemental mapping of the samples. It was also observed that x plays important roles in determining the thermal quantities and density of the samples
Effect of excess silicon concentration on the structural and optical characteristics of silicon nanocrystals embedded in silicon oxide
No full textSilicon (Si) nanocrystals embedded in Si oxide matrix have been formed by rapid thermal annealing of sub-stoichiometric Si oxide films (SiOx with x < 2). The SiOx films were deposited by co-sputtering of Si oxide and Si target using magnetron RF sputtering technique. The Si-to-SiO2 ratio was controlled by varying the number of Si chips being placed on the pure SiO2 target during sputtering. Rapid thermal anneal in nitrogen gas at 1100°C lead to the decomposition of SiOx into Si nanocrystals and SiO2. The structural (size of nanocrystals) and optical properties (absorption and luminescence) of Si nanocrystals embedded in oxide matrix, were found, strongly depend on the initial excess Si concentration in SiOx films
The formation of nanoscale clusters-nanofilms/quantum dots predicted using a capillary model of nucleation
No full textThis paper describes the theoretical and simulation studies of both homogenous and heterogeneous nucleation, the
phenomena that refers to the formation of stable nuclei prior to the growth of nanoclusters including nanofilms and
quantum dots. Essentially, a single cluster may contain few thousand of atoms, and interaction with the surface may be
preceded via processes, such as diffusion, hopping, sorption and coalescences. These complicated physical-chemical phenomena require in-depth theoretical understanding on how the various interacting quantities can be formulated and then resolved using specific mathematical approximation. In the case of a capillary model for heterogeneous nucleation, the nuclei are assumed to be in spherical shapes, which increase in both energies and diameters, and finally reach their critical points and settled to oval shapes prior to dome-like wetting on the substrate, essentially just like water droplet resting on a surface. The net change of energy, ∆G for the formation of cluster is found to be the functions of nucleus volume, surface area of atomic-nucleus interface, surface area of nucleus-surface interface and energy lost at substrate-atomic interface. The results for ∆G, ∆G*, r* and Ω and their respective changes with r, s and T were obtained and experimentally verified using existing data
Morphological of Yttrium Stabilized Zirconia (YSZ) Thin Film of Electrolyte in Solid Oxide Fuel Cell Application
No full textRecently, the performance of solid oxide fuel cell is focused on lowering operating temperature (400°C-650°C). To achieve the goal, the thickness of commonly used electrolyte, YSZ was reduced. The dip-coating technique was used for preparing dense YSZ electrolyte thin films on glass substrate. The suspensions were prepared by sol-gel method. Polyvinyl alcohol (PVA) and polyethylene glycol (PEG) was used as a ceramic binder and plasticizer, respectively. Crystalline structure and morphology of thin films were analyze by X-ray diffraction (XRD) and Atomic Force Microscope (AFM). The XRD reveals that crystallization of YSZ phase does not occur at any sintering temperature but can only have a small peak at 2θ = 30° as the thickness of layer increase. The roughness and morphology of the film with different thickness were observed. The roughness increased as the thickness increased. </jats:p
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