ISSN 8756-6990, Optoelectronics, Instrumentation and Data Processing, 2009, Vol. 45, No. 4, pp. 342–347. c  Allerton Press, Inc., 2009. Original Russian Text c  A. G. Nastovjak, I. G. Neizvestny, N. L. Swartz, E. S. Sheremet, 2009, published in Avtometriya, 2009, Vol. 45, No. 4, pp. 72–79. MATERIALS AND TECHNOLOGIES FOR NANO- AND OPTOELECTRONICS Mechanisms of Nanowhisker Formation: Monte Carlo Simulation A. G. Nastovjak a , I. G. Neizvestny a , N. L. Shwartz a , and E. S. Sheremet b a Rzhanov Institute of Semiconductor Physics, Siberian Branch, Russian Academy of Sciences, pr. Akademika Lavrent’eva 13, Novosibirsk, 630090 Russia E-mail: alla@isp.nsc.ru b Novosibirsk State Technical University, pr. Karla Marksa 20, Novosibirsk, 630092 Russia Received May 19, 2009 Abstract—Nanowhisker formation on substrates activated by catalyst drops is studied by Monte Carlo simulation. Dependences of the whisker growth rate on diameter are investigated for various growth modes. The influence of deposition conditions on whisker morphology is examined. It is shown that straight thin whiskers of uniform thickness can be obtained only using a catalyst having a large contact angle with the whisker material. In such a physicochemical system, variation of growth conditions can result in nanotube formation. An atomic mechanism for the formation of a hollow whisker is proposed. Ranges of model growth conditions suitable for the growth of nanowhiskers and nanotubes are determined. DOI: 10.3103/S8756699009040104 Key words: Monte Carlo method, simulation, nanowhisker, nanotube. INTRODUCTION In recent years, there has been increasing interest in semiconductor nanowhiskers (NWs)—filamentary crystals—because of the quantum confinement of charge carriers and, hence, their possible use in modern electronics. Chemical and biological sensors based on nanowhiskers and nanotubes which have higher sensi- tivity than sensors based on bulk materials [1, 2]. Ordered arrays of Si nanowhiskers are used to produce field emission displays, and single Si nanowhiskers serve as tips for atomic-force and chemical-force microscopy [3]. Of special interest are NW based heterostructures [4–6]. Radial heterostructures are candidates for use in high-speed field-effect transistors and effective emitters, and axial heterostructures in tunnel devices. Traditionally, NWs are grown from catalytic seed drops by the vapor–liquid–solid (VLS) mechanism [7]. A semiconductor material is deposited on a substrate activated by catalyst drops. Growth occurs by su- persaturation of the drops with the flux material, followed by crystallization at the interface. An analysis of the dependence of the whisker growth rate on diameter allows one to differentiate between adsorption- and diffusion-induced growth modes [8]. For catalyst drops of small diameter, the Gibbs–Thomson effect becomes significant, implying that in drops with a small curvature radius, the supersaturation is reduced. The supersaturation value determines the type of crystallization at the drop–whisker interface: mononuclear or polynuclear [7, 8]. NWs have different morphologies, depending on the growth conditions and materials used: they can be straight, curved, hollow, or branched [9–11]. Because the morphology can influence the electron-optical and mechanical properties of NWs, their growth processes have been extensively studied both experimentally and theoretically. The electron-optical and structural properties have been calculated by ab initio methods [12, 13], and the growth kinetics has been studied analytically [8]. Monte Carlo simulation allows one to study both the kinetics and morphology of growing whiskers. The purpose of this work was to study the effect of deposition conditions and growth mechanisms on the NW morphology by Monte Carlo simulation. Dependences of the NW growth rate on diameter were examined for various growth modes. 342