Selective surface modification of silicon nanowires by using nanoscale joule heating and its sensor application

Abstract

Since the last decade, one-dimensional nanostructures such as nanowires, nanotubes, and nanobelts have been investigated for sensor applications. Silicon nanowire based sensors have been developed by many groups and it was found that pristine silicon nanowires have sensitivities to some chemicals (pH and NO2 gas) but low selectivities. However, surface modification of silicon nanowires have shown to enhance both the sensitivities and selectivities to the bio molecules (DNA, protein, virus and etc.) or chemicals (hydrogen and ozone). In this thesis, two novel methods for selective surface modification of silicon nanowires are proposed. One method for selective surface modification of silicon nanowires is based on the selective and localized PMMA thermal decomposition by using Joule heating of silicon nanowire, metal layer deposition, and lift-off process. Another method is based on the direct hydrothermal synthesis of metal nanoparticles selectively and locally on silicon nanowires by using Joule heating of silicon nanowires. According to simulation results, it was observed that silicon nanowires could be locally heated with high temperature (Tmax=363 K by applying electrical bias of 30 V across 4 um long silicon nanowire in air environment) by Joule heating of the nanowires. Feasibility of the developed methods for selective surface modification was confirmed by decoration of palladium (Pd) nanoparticles on silicon nanowires. The silicon nanowires decorated with Pd nanoparticles were used as hydrogen sensors. The sensor showed sensitivity of ΔR/R0=70% and response time of τ10-90%=750 seconds to 0.5% of hydrogen gas. Also, it was found that the self-heating of the silicon nanowires can enhance the response time. (38.3 times faster than without self-heating) In addition, multiplexed silicon nanowire array decorated with different metal nanoparticles (Au and Pd) was fabricated by a repeated process of PMMA decomposition, metal layer deposition, and lift-off proc...