Synthesis and application of millimeter-long silicon nanowires

Abstract

Ultralong nanowires whose lengths go over macroscopic length scales and reach the size of integrated systems, can be exploited as the basis for complex electronic circuits and functional nanosystems by the direct integration of a large number of device elements into a single wire. For example, the electronic sensor arrays based on nanometer-diameter but millimeter-length scale wires would provide the potential for the real-time monitoring of molecule-protein interactions at a single particle level along the millimeter-scale region simultaneously. To this end we report the controlled synthesis of millimeter-long silicon nanowires (SiNWs) by accelerating the rate-limiting step in vapor-liquid-solid (VLS). Quantitative analysis showed that the average length of 1-hour grown SiNWs is ~1.8 mm, and that the longest ones reach 3.5 mm while the diameters are uniform along the wires. TEM study revealed that millimeter-long SiNWs grow along the ＜110＞ direction without exhibiting diameter-dependent preference, in contrast to the general SiNW growth behavior of a preference for growth along the ＜110＞ direction in the smaller diameter SiNWs and along the ＜111＞ direction in larger SiNWs with a crossover diameter of ~20 nm. In addition, p-type SiNWs were synthesized by introducing diborane (B2H6) as a doping source, and transport measurements demonstrated uniform electrical properties along the entire length of wires. Electronic uniformity of millimeter-long SiNWs was further exploited to show multiplexed electrical sensing of cancer marker proteins. The detailed growth mechanism for the millimeter-long SiNWs will also be discussed.