Strain-induced generation of silicon nanopillars

Abstract

Silicon metal-assisted chemical etching (MACE) is a nanostructuring technique exploiting the enhancement of the silicon etch rate at some metal-silicon interfaces. Compared to more traditional approaches, MACE is a high-throughput technique, and it is one of the few that enables the growth of vertical 1D structures of virtually unlimited length. As such, it has already found relevant technological applications in fields ranging from energy conversion to biosensing. Yet, its implementation has always required metal patterning to obtain nanopillars. Here, we report how MACE may lead to the formation of porous silicon nanopillars even in the absence of gold patterning. We show how the use of inhomogeneous yet continuous gold layers leads to the generation of a stress field causing spontaneous local delamination of the metal-and to the formation of silicon nanopillars where the metal disruption occurs. We observed the spontaneous formation of nanopillars with diameters ranging from 40 to 65 nm and heights up to 1 μm. Strain-controlled generation of nanopillars is consistent with a mechanism of silicon oxidation by hole injection through the metal layer. Spontaneous nanopillar formation could enable applications of this method to contexts where ordered distributions of nanopillars are not required, while patterning by high-resolution techniques is either impractical or unaffordable.

Effect of isopropanol on gold assisted chemical etching of silicon microstructures

“…We observed the formation of micro-pits (cavities with radius > 100 nm) on the top of the etched gratings and up to an average depth of 2-3 µm from the top surface. In addition to micro-pits [38], nanoporosity (pore size  10 nm) has been reported [3,39]. By HR-SEM we detected the presence of a continuous layer of nanoporous Si, with thickness ranging between 250 -150 nm for = 0.37 and =0.8, respectively.…”

Silicon Nanowires: A Breakthrough for Thermoelectric Applications

“…The reasonable configuration for large-area nanostructured silicon thermoelectric devices consists of nanowires/nanostructures placed perpendicularly to the silicon substrate, which can be fabricated by means of maskless (no lithography), highly selective etching processes, such as metal assisted chemical etching (MACE) [ 72 , 73 ]. Very shortly, it consists in depositing metal nanoparticles, which can be gold, silver [ 74 , 75 , 76 ] and also ruthenium [ 77 ] (investigated very recently), on the top of a standard (and hence low-cost) silicon wafer. Soaking the wafer in an acqueous solution containing an oxidizing agent and HF, the silicon is locally oxidized very close to the nanoparticles (catalyzing agent) and then removed by HF.…”

Review of nanostructured devices for thermoelectric applications

“…Therefore, vertical trenches with high aspect ratio [117–119] (Fig. 13) and in particular silicon nanowires narrower than 100 nm and with a length of several micrometers [120–126] can be obtained by using metal masks with suitable patterning. However, if the generation of holes through the reducing reaction (Eq.…”