Ordered arrays of nanoporous silicon nanopillars and silicon nanopillars with nanoporous shells

Dong Wang,Song Du,Arne Albrecht,Peter Schaaf,Ran Ji

doi:10.1186/1556-276x-8-42

Dong Wang, Song Du + Show 3 more

Open Access

https://doi.org/10.1186/1556-276x-8-42

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Abstract

The fabrication of ordered arrays of nanoporous Si nanopillars with and without nanoporous base and ordered arrays of Si nanopillars with nanoporous shells are presented. The fabrication route is using a combination of substrate conformal imprint lithography and metal-assisted chemical etching. The metal-assisted chemical etching is performed in solutions with different [HF]/[H2O2 + HF] ratios. Both pore formation and polishing (marked by the vertical etching of the nanopillars) are observed in highly doped and lightly doped Si during metal-assisted chemical etching. Pore formation is more active in the highly doped Si, while the transition from polishing to pore formation is more obvious in the lightly doped Si. The etching rate is clearly higher in the highly doped Si. Oxidation occurs on the sidewalls of the pillars by etching in solutions with small [HF]/[H2O2 + HF] ratios, leading to thinning, bending, and bonding of pillars.

Highlights

Nanostructured Si is drawing a great deal of interest due to its potential applications in nanoscale electronics [1,2], optoelectronics [3], thermoelectrics [4], photovoltaics [5], biosensors [6], nanocapacitor arrays [7], and as electrodes in Li-ion batteries [8]
Two-level nanoscaled porous Si nanowires were even synthesized with highly doped Si using metal-assisted chemical etching (MaCE), and Ag nanoparticles acted as catalyst [15,16,17]
After 3-min etching, the nanoporous Si nanopillars had a vertical length of 1.6 μm, accompanied by the formation of a nanoporous base with a homogenous thickness of 1.2 μm below the Au film and the nanopillars (Figure 2a)

Summary

Introduction

Nanostructured Si is drawing a great deal of interest due to its potential applications in nanoscale electronics [1,2], optoelectronics [3], thermoelectrics [4], photovoltaics [5], biosensors [6], nanocapacitor arrays [7], and as electrodes in Li-ion batteries [8]. Metal-assisted chemical etching (MaCE) as a simple and low-cost method to fabricate Si nanowires and nanoporous Si has attracted increasing attention [11,12,13,14]. In this process, Si wafer coated with a noble metal is etched in a solution consisting of HF and an oxidant (e.g., H2O2 or AgNO3) to form the nanostructures. Two-level nanoscaled porous Si nanowires were even synthesized with highly doped Si using MaCE, and Ag nanoparticles acted as catalyst [15,16,17]. These zigzag Si nanowires were even fabricated with (100)-oriented Si by a two-step

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