Structuring of Si into Multiple Scales by Metal‐Assisted Chemical Etching

Abstract

classified into two common approaches: bottom-up chemical synthesis, such as vapor-liquid-solid growth, [16][17][18][19][20] and topdown fabrication schemes. [21][22][23] This review will focus on the top-down fabrication of Si structures using a wet chemical etching technique aided with a metal catalyst, called metal-assisted chemical etching (MaCE). [24][25][26][27][28][29][30][31][32] In comparison with top down fabrication methods based on dry etching using a reactive plasma in vacuum, MaCE is less expensive and less complex. [33][34][35] MaCE is a nano-scale reductionoxidation (redox) process that usually occurs in aqueous solution where the sample to be etched is in contact with the etchant. MaCE is a simple, cost-effective, and versatile method to produce Si nanostructures; due to these attractive features, there have been many good review articles published on the process. [36][37][38][39][40][41][42] With two-decades of research of the MaCE and its innovative variations, recent studies have focused on the various applications of Si nanostructures prepared by MaCE, including photovoltaics, [43,44] thermoelectrics and piezoelectric nanogenerators, [45] energy storage, [46][47][48] nanophotonics and optoelectronics, [49] and biosensors and biomedical applications. [50][51][52] In this review, we provide an overview of the recent advances in MaCE processes and their novel applications. To differentiate this review from previous review articles, the main emphasis is on the recently developed novel MaCE processes and the macroscale structuring of Si by MaCE. We begin the review by describing new MaCE processes, particularly catalysts for MaCE. In contrast to well-known noble metal catalysts, such as Ag, Au, and Pt, carbon-based catalysts, such as graphene, graphene oxide, and carbon nanotubes, have been successfully applied as catalysts for MaCE. In addition, TiN has been found to be a catalyst for MaCE, making the whole process CMOS-compatible. Different types of etch additives, such as various alcohols and chlorides, have also been discussed, which enhance etch uniformity by increasing the wettability of etchants and suppressing the random diffusion of excessive (holes) h + by trapping them for better etch control. Recent novel variations of the MaCE process have been introduced, such as MaCE with externally applied electric or magnetic fields. The external field has a profound effect on the output of MaCE, by controlling the etch directionality and etch rate. In addition, MaCE can be combined with unconventional patterning techniques, StructuringSi, ranging from nanoscale to macroscale feature dimensions, is essential for many applications. Metal-assisted chemical etching (MaCE) has been developed as a simple, low-cost, and scalable method to produce structures across widely different dimensions. The process involves various parameters, such as catalyst, substrate doping type and level, crystallography, etchant formulation, and etch additives. Careful optimization of these parameters is the key to the succe...

Metal-Assisted Catalytic Etching (MACE) for Nanofabrication of Semiconductor Powders

“…These lithographic techniques can be implemented to machine single-crystal wafers of silicon [13,37,38] as well as other semiconductors [29,39,40]. The advantageous properties of MacEtched structures have made them ripe for exploitation in a wide variety of applications [40][41][42]. Surface-enhanced Raman spectroscopy (SERS) was performed with electric field enhancement being provided by the same metal nanoparticles used to catalyze MACE [43].…”

“…Silicon nanostructures, both por-Si and SiNWs, are of great interest in multiple energy applications. Nanostructures formed with MACE have been investigated for energy harvesting applications such as thermoelectric [51] and piezoelectric generators [40]. Extensive activity [40] has been directed toward high-performance Li-ion battery (LIB) anodes using either SiNWs [52][53][54] or por-Si [55,56].…”

“…Applications that require macroscale structures such as microfluidics, and microelectromechanical systems (MEMS) [40] have also been pursued. If metal rather than Si nanowires is desired, the metal nanoparticle at the bottom of the etch track pore can be used as a catalyst for metal deposition within the pores.…”

Metal Assisted Catalytic Etching (MACE) for Nanofabrication of Semiconductor Powders

“…Silicon nanostructures, both por-Si and SiNWs are of great interest in multiple energy applications. Nanostructures formed with MACE have been investigated for energy harvesting applications such as thermoelectric [49] and piezoelectric generators [40]. Extensive activity [40] has been directed toward high-performance Li-ion battery (LIB) anodes using either SiNWs [50][51][52] or por-Si [53,54].…”

“…These applications necessitate the use of powdered semiconductors rather than wafers. While the vast majority of MACE studies and reviews have concentrated on wafers [13,37,39,40,66,[71][72][73][74], the focus of this review will be on the etching of powders.…”