Controlling the Nature of Etched Si Nanostructures: High- versus Low-Load Metal-Assisted Catalytic Etching (MACE) of Si Powders

Konstantin Tamarov; Joseph D Swanson; Bret A Unger; Kurt W Kolasinski; Alexis T Ernst; Mark Aindow; Vesa-Pekka Lehto; Joakim Riikonen

doi:10.1021/acsami.9b20514

Controlling the Nature of Etched Si Nanostructures: High- versus Low-Load Metal-Assisted Catalytic Etching (MACE) of Si Powders

ACS Appl Mater Interfaces. 2020 Jan 29;12(4):4787-4796. doi: 10.1021/acsami.9b20514. Epub 2020 Jan 13.

Authors

Konstantin Tamarov¹, Joseph D Swanson², Bret A Unger², Kurt W Kolasinski², Alexis T Ernst³, Mark Aindow³, Vesa-Pekka Lehto¹, Joakim Riikonen¹

Affiliations

¹ Department of Applied Physics , University of Eastern Finland , Kuopio FI-70211 , Finland.
² Department of Chemistry , West Chester University , West Chester , Pennsylvania 19383 , United States.
³ Department of Materials Science and Engineering, Institute of Materials Science , University of Connecticut , Storrs , Connecticut 06269 , United States.

PMID: 31888334
DOI: 10.1021/acsami.9b20514

Abstract

Metal-assisted catalytic etching (MACE) involving Ag deposited on Si particles has been reported as a facile method for the production of Si nanowires (Si NWs). We show that the structure of Si particles subjected to MACE changes dramatically in response to changing the loading of the Ag catalyst. The use of acetic acid as a surfactant and controlled injection of AgNO₃(aq) enhanced Ag deposition. The use of acetic acid and controlled injection of H₂O₂ not only facilitated optimization of the etching step but also allowed us to identify a previously unobserved etching regime that we denote as low-load MACE (LL-MACE). Material produced by LL-MACE exhibits dramatically different yield and structural characteristics as compared to conventionally produced material. We demonstrate the production of Si NWs as well as mesoporous Si nanoparticles from an inexpensive metallurgical-grade Si powder. High loading of Ag (HL-MACE) generates parallel etch track pores created by the correlated motion of Ag nanoparticles. The uniform size distribution (predominantly 70-100 nm) of the Ag nanoparticles is generated dynamically during etching. The walls of these etch track pores are cleaved readily by ultrasonic agitation to form Si NWs. Low loading of Ag (LL-MACE) creates 10-50 nm Ag nanoparticles that etch in an uncorrelated (randomly directed) fashion to generate a bimodal distribution of mesoporosity peaking at ∼4 and 13-21 nm. The use of a syringe pump to deliver the oxidant (H₂O₂) and Ag⁺ is essential for increased product uniformity and yield. Different process temperatures and grades of Si produced significantly different pore size distributions. These results facilitate the production of Si NWs and mesoporous nanoparticles with high yield, low cost, and controlled properties that are suitable for applications in, e.g., lithium-ion batteries, drug delivery, as well as biomedical imaging and contrast enhancement.

Keywords: metal-assisted catalytic etching (MACE); porous nanoparticles; porous silicon; silicon nanowires; silicon powders.