• PDF / 1,508,992 Bytes
• 6 Pages / 612 x 792 pts (letter) Page_size
• 96 Downloads / 195 Views

DOWNLOAD

REPORT

---

Growth Mechanism of Chains of Silicon Nanocrystallites Hideo Kohno1, Koji Tanaka2, and Seiji Takeda1 Department of Physics, Graduate School of Science, Osaka University 1-16 Machikaneyama, Toyonaka, Osaka 560-0043, JAPAN, [email protected] 2 Department of Material Physics, Osaka National Research Institute, 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, JAPAN 1

ABSTRACT The growth mechanism of chains of silicon nanocrystallites was investigated. Energy-filtered transmission electron microscopy observations provided strong evidence that the chains were formed as a result of surface oxidation of silicon nanowires. In addition, the periodic instability in the wetting property of molten catalysts was simulated numerically.

INTRODUCTION Authors have reported the fabrication and characterizations of the chains of silicon nanospheres [1-5]: silicon nanocrystallites of about 10 nm in diameter are covered with and connected by amorphous silicon oxide forming a self-standing chain-like nanostructure. The chains are of great interest because they have a self-organized periodic arrangement of semiconductor and insulator in nanometer scale, and have potential applications to photo-emitting and single-electron devices. The growth mechanism of the chains was unknown except that the chains were grown via an extension of the vapor-liquid-solid (VLS) process [6, 7] from gold catalysts. The growth mechanism was speculated by authors [1] as follows: (i) The diameter of a silicon nanowire changes periodically due to a periodic instability in the wetting property of a catalyst on the top of the growing wire. (ii) The surface of the silicon nanowire is oxidized during growth. At necks of the wire, the oxidation reaches the core, while only the surface of the wire is oxidized at knots. However, we had no strong evidence to support our speculation. In order to elucidate the growth mechanism of the chains, study of nanostructures in the chains is indispensable. Energy-filtered TEM, employed in this study, is a powerful means of studying nanostructures. Inner structures of the chains were investigated using the technique [3]. Regarding the periodic instability, Givargizov [8] reported a similar periodic instability in much thicker silicon whiskers. His whiskers were grown epitaxially on a silicon substrate implying that they were not chains of silicon nanocrystallites but single-crystalline rods. The structure of our chains is obviously different from that of Givargizov’s whiskers. However, we think that the periodic instability in the chain growth is identical with that in the growth of his whiskers. Givargizov proposed a basic idea on the mechanism of the periodic instability, but no theoretical and simulation studies have been performed. We refined his basic idea and performed numerical simulations of the periodic instability in order to clarify the growth mechanism of the chains [4].

F13.3.1 

GROWTH AND TEM OBSERVATIONS OF THE CHAINS P-doped Czochralski-silicon (001) was used as a substrate. Gold of about 10 nm thick was