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ENHANCEMENT OF MECHANICAL STABILITY OF SILICON MACROSPECIMENS CONTAINING HIERARCHICALLYSTRUCTURED POROUS SILICON K. V. Krukovskii,1 O. A. Kashin,1 S. I. Romanov,2 O. V. Bakina,1 A. I. Lotkov,1 and A. V. Luchin1

UDC 538.911

The paper presents the research findings in the field of mechanical stability of single-crystal silicon macrospecimens containing hierarchically-structured porous silicon. Macrospecimens are designed to produce a porous layer 170 µm thick, without cracking and fracture. Indentation tests show that the crack resistance of porous silicon is higher than that of single-crystal silicon. The parameters of porous silicon are determined herein. The adsorption and desorption properties of the porous silicon layer are examined. As a result, it is shown that the proposed silicon macrospecimens can be used, for example, for cancer drug delivery. Keywords: porous silicon, mechanical stability, crack resistance.

INTRODUCTION The unique properties of porous silicon determine its wide use in semiconductor devices, micro- and nanoelectronics, and solar energy. In medicine, porous silicon is used as biosensors, filtration membranes for the molecule separation, and containers for pharmaceutical drug delivery [1]. All this triggers the interest of researchers in the properties of porous silicon. Over 1000 articles in this field are published annually. A significant number of publications are devoted to the structure formation mechanisms of porous silicon. Based on these investigations, reliable methods are developed for the production of porous silicon with an adjustable structure. However, the use of porous silicon in specific products faces a number of difficulties, one of which is its high liability to brittle fracture. In this connection, porous silicon is mainly produced on silicon single-crystal substrates in the form of thin layers of the limited thickness. When the thickness of the porous silicon layer exceeds its critical value, it cracks, peels off the substrate and fractures. The main reason is that mechanical stresses that occur during the formation of the porous structure grow with increasing layer thickness. The mechanisms of this phenomenon are studied in many works, for example, in [2, 3]. Thus, a certain problem is the porous silicon layer resistant to mechanical loads. At the same time, many of applications require porous silicon specimens of a sufficiently large volume, in particular, to provide the adsorption capacity when using porous silicon as containers for drug delivery systems. One way to improve the mechanical stability of such specimens is their design, that can reduce the possibility of their stress-induced destruction during the formation of the silicon porous layer. The aim of this work is to investigate the design of silicon macrospecimens containing hierarchically-structured porous silicon influencing their mechanical stability. Based on the investigation of their adsorption/desorption

1

Institute of Strength Physics and Materials Science of the Siberian Branch of the Russian Ac