Aqueous synthesis of silicon nanowire arrays and core-shell structures via electroless nanoelectrochemical process

Abstract

A solution growth of silicon nanowires (NWs) and core-shell structures is highly desirable due to low growth temperature and large-area synthesis capability. Silicon demonstrates novel electrochemical properties in aqueous solutions containing hydrofluoric acid which have raised significant research interests due to the complex electrochemical etching behavior involved. In the present study, we have demonstrated the synthesis of large-area vertically aligned silicon nanowire (SiNW) arrays (Fig. 1 and 2) in an aqueous solution containing AgNO3 and HF on p-type (001) Si substrate by self-selective electroless etching process [1]. The fabrication process was rather simple and rapid compared to the well-known Vapor-Liquid-Solid (VLS) growth [2] via chemical-vapor deposition (CVD) and other high-vacuum techniques. In this work, the temperature of electrolyte and etching duration were varied in order to achieve different stages of nanowire formation. Diameters of the SiNWs obtained varied from 50 nm to 200 nm and their lengths ranged from several to approximately a few tens of µm, depending on the reaction time and the electrolyte conditions used. Te-Si and Bi <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Te <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> -Si core-shell structures (Fig. 3) were subsequently obtained via galvanic displacement of SiNWs in acidic HF electrolytes containing Bi3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> and Bi3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> /HTeO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ions respectively. The reactions were basically a nanoelectrochemical process due to the difference in redox potentials between the materials. The modified SiNWs of the core-shell structures exhibit roughened surface morphologies and, therefore, have higher surface-to-bulk ratios compared to the unmodified SiNWs, which should have potential applications in sensor, photovoltaic and thermoelectric nanodevices. Growth study on the SiNWs and core-shell structures produced is presented using various microscopy, diffraction and probe-based techniques for structural, morphological and chemical characterizations.