A theoretical study of silicon nanowire formation mechanism

Abstract

The formation mechanism of silicon nanowires is not completely understood. The commonly accepted models were the metal-assisted growth mechanism and the oxide-assisted growth mechanism. In this study, a charged-assisted growth mechanism was proposed and possibility of presence of charges at the nanowire tip was investigated. The excess pressure and the lowering in melting temperature at the nanowire tip were calculated, and the temperature profile of the nanowire was found. The central idea of the charge-assisted growth mechanism was that a strong electric field existed at the tip of the nanowires due to charge accumulation. The charges were generated during the phase separation because of the difference in electronegativity of Si and SiO2. SiO clusters in the vapor were attracted by the electric field and most of them would land on the tip. This mechanism did not require that the sidewall of the nanowires be totally non-adhesive. Analysis had shown that given a sufficiently strong electric field, all SiO vapor would land on the nanowire tip. Based on the charge-assisted model of nanowire growth, electrostatic charges originated from this electric field could produce a highly negative pressure. Since negative pressure favors the increase of surface area, it could be the key force in driving the silicon nanowire to grow in one direction only. Calculations of excess pressure and the corresponding lowering in melting temperature at the nanowire tip showed that surface tension alone could not produce sufficiently excess pressure or a significant lowering in melting temperature at the nanowire tip. The temperature difference at the silicon nanowire tip was found to be small. Therefore, difference in temperature could not be responsible for the difference in adhesive property of the silicon nanowire tip and the sidewall.

Date of Award	15 Jul 2005
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Ho Fai CHEUNG (Supervisor)