Growth of SiC Nanorods on Si Substrate
Abstract
Silicon carbide (SiC) is a ™-™ compound miconductor material with a wide band gap. Semiconductor electronic devices and circuits made from SiC are prently being developed for high-temperature, high-power, and high-radiation conditions in which conventional miconductors cannot adequately perform. One-dimensional SiC, such as nanowires and nanorods, is of great interests for many applications due to their excellent properties, such as high mechanical strength, high thermal stability, high thermal conductivity. Especially SiC nanorods are widely considered as reinforcement materials for ceramic composites providing very high strength and toughness due to their very high elastic modulus and strength over their bulk-counterpart. In this study, the SiC nanorods were fabricated by vapor-liquid-solid (VLS) mechanism on Si substrate. The SiC nanaorods were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD)and energy diffraction spectrometer (EDS).The factors which influenced the formation of SiC nanorods were studied.
Keywords: SiC nanorods, VLS mechanism, CVD
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Introduction
新婚燕尔是什么意思Silicon carbide (SiC) is a wide band gap miconductor with many super properties, such as high breakdown field，high thermal conductivity, high saturation drift velocity, low relative dielectric constant and excellent resistance to oxidation and corrosion[1-2]. The outstanding properties make SiC a very attractive miconductor material. For example, SiC is commercially applied for optoelectronic devices [3], such as photodiodes and light-emitting diodes which emit throughout the visible spectrum into the ultraviolet. The applications of SiC also cover the area of high-temperature nsors, high-power devices, and microwave devices (both avalanche diodes and field effect transistors).
In the meantime, since carbon nanotubes emerged into the scientific world in 1991 and their exceptional excellent properties were introduced, one-dimensional nanomaterials such as SiC, GaN, have attracted much interest from rearchers becau the extreme geometry of the nanomaterials is of importance to investigate the physical and chemical properties of the materials such as their quantum size effect. The nanosized materials are important for ceramic nanocomposite materials [4, 5]. They are also claimed to be promising raw materials for engineering ceramic devices offering superplasticity and high strength at high temperatures. Furthermore nanoscale filters or support for a
catalytic surface might be interesting application of SiC nanopowders.
A lot of methods have been developed to synthesize SiC nanorods [6]. SiC nanorods can be fabricated without the metallic catalysts. For instance, Zhou [7] fabricated SiC nanowires by the hot filament chemical vapor deposition (CVD) method. B.-C. Kang synthesized SiC nanorods by CVD method.Li [8] synthesized SiC nanowires by using a SiC rod as the anode to arc-discharge. And Hyung Suk Ahn [9] synthesized SiC nanorods by using LPCVD. SiC nanorods can be also fabricated with the metallic catalysts. For example, B.-C. Kang fabricated SiC nanorods by using nickel as a catalyst. And Zhang [10] et al. synthesized SiC nanorods using Fe powders as the catalyst. Among the methods, carbothermal reduction of silica-containing materials and the CVD method are the most commonly employed.
In carbonthermal reduction process, three mechanisms are involved to form SiC nanorods. They are called vapor-solid (VS) mechanism, two-stage growth (TS) mechanism and vapor-liquid-solid (VLS) mechanism. [11] By the VS mechanism, the nanorods are grown by direct accommodation of silicon and carbon atoms to the growth plane from the silicon- and carbon-carrying vapors. The nanorods are formed in the raw materials containing metal impurities such as rice-hulls by the TS mechanism. The impurities form discrete liquid droplets on the growth plane. The droplets are quickly covered wit
h vapor species becau of their high accommodation coefficient and act as nucleation sites for the
nanorods growth. It results in axial growth of nanaorods (first stage), and, then in lateral thickening (cond stage) [11, 12]. The esntial features of VLS mechanism can be expresd as the growth of nanorods via the assistance of liquid solution containing the desired ingredient of the nanorods to be grown. The process are complex and the fundamental issues remain to be ascertained. The growth of nanorods involves the dissolution of solute at the vapor/liquid interface and its subquent precipitate at the liquid/solid interface during the VLS growth process. In this paper, nickel was ud as a metallic catalyst to deposit SiC nanorods on Si substrate via the VLS mechanism.
鸳鸯瓦冷霜华重Experiment
科员级别>元宵节小故事SiC nanorods were fabricated in metalorganic chemical vapor deposition (MOCVD) system. The water-cooled reactor, as shown in
Fig. 1 schematic configuration of MOCVD reactor
Fig.1, was a horizontal quartz tube. First, nickel thin film with thickness of 400∗500 nm, which acted as a catalyst in growing SiC nanorods, was deposited on Si substrate by DC sputtering. The Si subst
15英尺rates covered with nickel thin flim were t on a SiC-coated graphite susceptor, which was heated by ratio frequency (RF) induction. According to Ni-Si and Ni-C phadiagram [13-15], the growth temperature was lected between 1250ε and 1380ε . Silane (SiH4) and acetylene (C2H2) were ud as source gas. Hydrogen (H2) gas purified by a Pd purifier was ud as the carrier gas. The flow rate of H2 was fixed to be 500 sccm (standard cubic centimeter per minute). And the growth pressure of SiC nanorods was fixed to be 60 Torr.
Two process were carried out to synthesize SiC nanorods. One was called two-step process, in which only C2H2 was first introduced into the reactor to fabricate carbon nanotubes on the Si substrates covered nickel thin film at 1150ε for veral minutes. Then the growth temperature incread to 1150ε∗1350ε , and C2H2 and SiH4 were reacted as the source gas to synthesize SiC nanorods. Another process was called one-step process, in which C2H2 and SiH4 as the source gas were introduced into the reactor at the same time.
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The crystal structure of SiC nanorods was characterized by X-ray diffraction (XRD). The morphology of SiC nanorods was characterized by scanning electron microscopy (SEM). Energy dispersive spectrometer
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