Vapor-liquid-solid growth, silicon

Westwater, J. Gosain, D.P. Tomiya, S. Usui, S. Ruda, H. Growth of silicon nanowires via gold/ silane vapor-liquid-solid reaction. J. Vac. Sci. Technol. B 1997, 15 (3), 554. 

Wagner, R.S. and Ellis, W.C. (1964) Vapor-liquid-solid mechanism of single crystal growth, Appl. Phys. Lett. 4, 89 (1965) Vapor-liquid-solid mechanism of crystal growth and its application to silicon, Trans. Met. Soc. AIME 233, 1053. The description of the VLS mechanism. Now used for more than Si. 

Almost all short fibers, which are derived from the vapor phase, grow by a vapor-liquid-solid (VLS) phase transformation, including single crystal silicon whiskers and carbon nanotubes. Only rarely does the growth of short fibers or whiskers occur by a vapor-solid (VS) phase transformation, and the evidence for this type of phase transformations is often difficult to obtain experimentally. 

A method combining laser ablation cluster formation and vapor-liquid-solid (VLS) growth was recently developed for the synthesis of single crystal semiconductor siiicon and germanium nanowhiskers [74], Specificaily, iaser abiation was used to prepare dusters of moiten metal catalyst particles with a nanometer diameter. The droplet diameter defines the diameter of the resulting nanowhiskers. Buik quantities of uniform silicon and germanium nanowhiskers with diameters from 6 to 20 and from 3 to 9 nanometers, respectiveiy, and lengths from 10 to 300 nanometers were obtained. 

Zhang JG et al (2010) Vapor-induced solid-liquid-solid process for silicon-based nanowire growth. J Power Sources 195 1691-1697... 

Epitaxial Layers. Epitaxial deposition produces a single crystal layer on a substrate for device fabrication or a layer for multilevel conductive interconnects which may be of much higher quality than the substrate. The epitaxial layer may have a different dopant concentration as a result of introducing the dopant during the epitaxial growth process or may have a different composition than the substrate as in silicon on sapphire. Methods used for epitaxial growth include chemical vapor deposition (CVD), vapor phase epitaxy (VPE), liquid phase epitaxy (LPE), molecular beam epitaxy (MBE) and solid phase epitaxy (SPE). 

Figure 9 illustrates the VLS whisker growth sequence. At 1400°C the solid catalyst melts and forms the liquid catalyst ball. Carbon and silicon from the gas phase dissolve into the liquid catalyst, which soon becomes supersaturated and solid SiC precipitates at the interface with the carbon substrate. Continued dissolution of gas species into the liquid catalyst allows the whisker to grow, lifting the catalyst ball from the substrate as additional SiC precipitates. These VLS whiskers are typically larger in diameter (4-6 jim) than those formed by the vapor ohd process (VS-whiskers). They frequently grow to length of tens of millimeters. 

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