Fabrication of porous silicon by metal-assisted etching using highly ordered gold nanoparticle arrays

Sebastian P Scheeler,Claudia Pacholski,Simon Ullrich,Stefan Kudera

doi:10.1186/1556-276x-7-450

Sebastian P Scheeler, Claudia Pacholski + Show 2 more

Open Access

https://doi.org/10.1186/1556-276x-7-450

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Abstract

A simple method for the fabrication of porous silicon (Si) by metal-assisted etching was developed using gold nanoparticles as catalytic sites. The etching masks were prepared by spin-coating of colloidal gold nanoparticles onto Si. An appropriate functionalization of the gold nanoparticle surface prior to the deposition step enabled the formation of quasi-hexagonally ordered arrays by self-assembly which were translated into an array of pores by subsequent etching in HF solution containing H2O2. The quality of the pattern transfer depended on the chosen preparation conditions for the gold nanoparticle etching mask. The influence of the Si surface properties was investigated by using either hydrophilic or hydrophobic Si substrates resulting from piranha solution or HF treatment, respectively. The polymer-coated gold nanoparticles had to be thermally treated in order to provide a direct contact at the metal/Si interface which is required for the following metal-assisted etching. Plasma treatment as well as flame annealing was successfully applied. The best results were obtained for Si substrates which were flame annealed in order to remove the polymer matrix - independent of the substrate surface properties prior to spin-coating (hydrophilic or hydrophobic). The presented method opens up new resources for the fabrication of porous silicon by metal-assisted etching. Here, a vast variety of metal nanoparticles accessible by well-established wet-chemical synthesis can be employed for the fabrication of the etching masks.

Highlights

Porous silicon has been extensively studied in the last 30 years due to its high potential for a variety of applications such as in optoelectronic devices [1], sensors [2], and solar cells [3,4]
The key parameter of the fabricated gold nanoparticle arrays are presented in Table 1, and representative Scanning electron microscope (SEM) images are shown in the Additional file 1
In summary for metalassisted etching, three differently prepared gold nanoparticle arrays on Si were used which vary in the cleaning procedure of the Si substrates prior to spin-coating and/ or in the thermal treatment method employed for the removal of the polymer matrix of the gold nanoparticles: (1) piranha treatment + plasma treatment, (2) piranha treatment + flame annealing, and (3) HF immersion + flame annealing

Summary

Introduction

Porous silicon has been extensively studied in the last 30 years due to its high potential for a variety of applications such as in optoelectronic devices [1], sensors [2], and solar cells [3,4]. The chemical reactions involved are extremely complex and, advantages of this method [10,11] It is simple and low-cost, and allows for controlling the properties of the resulting nanostructure including cross-sectional shape, diameter, depth, and orientation of the pores. From this perspective it is surprising that metal deposition was almost exclusively achieved by techniques such as sputtering, electroless deposition, and thermal evaporation, leading to the formation of metal nanostructures with undefined shape, broad size distribution, and undefined interparticle spacing [12]. The self-assembled gold nanoparticle arrays were thermally treated in order to remove the polystyrene shell and subsequently etched in a solution composed of HF and H2O2

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