Chemical Modification of Si Nanowires for Bioconjugation

Abstract

One-dimensional nanomaterials, such as nanotubes and nanowires, have been investigated in detail for numerous applications due to their extraordinary optical, mechanical, and electrical properties. In the context of both processing and properties of nanowires (NWs), a detailed understanding of their surface chemistry is required to meet the technological applications of NWs. For example, the chemical and electronic stability of the surface of NWs is particularly important for applications including nanowire-based logic elements and chemical and biological sensors, which require direct interfacing with their surrounding environment. While there have been many efforts to chemical modifications of carbon nanotubes, there have been a few reports on chemical modifications of NWs. Silicon nanowires (SiNWs) have recently attracted a great deal of attention because silicon (Si) is of technological importance in microelectronics. Many successful synthetic strategies have now been developed to obtain bulk quantities of SiNWs using both gas-phase and condensed-phase techniques with or without metal catalysts. The chemical nature of the Si surface has also been studied in detail. Si forms a very stable oxide and can be chemically passivated with a number of organic species. The reaction mechanisms have extensively been investigated for solution-phase and vapor-phase oxidation, metallization, nitridation, and organic monolayer-based passivation of both Si surfaces of singlecrystal substrates and surfaces of porous Si. Therefore, SiNWs are a very good candidate for studying chemical modifications of NW surfaces, and in this Note we report the chemical modification of SiNWs by a combination of the formation of covalently bonded, organic monolayers on the surface of SiNWs and successive surface organic reactions. Boron-doped, single-crystal SiNWs were synthesized by gold nanocluster-catalyzed chemical vapor deposition with SiH4/B2H6 (1000 : 1 or 4000 : 1) as a vapor-phase reactant by following the reported procedure. The average diameter of SiNWs was ~40 nm and the length of SiNWs was 3-6 μm (Figure 1). The gradual bending of SiNWs may be due to elastic strains on the very small diameter of the wires. Figure 1. FE-SEM image of synthesized boron-doped Si nanowires.