Staff at the Physics Department of Moscow State University have developed a method of synthesis of silicon nanowires using metal-stimulated etching, where instead of hydrofluoric acid (HF) used a safer and more environmentally friendly ammonium fluoride (NH 4 F). Results of the study, scientistspublished in the journal Nanoscale Research Letters.
Scientists from the Physics Department of MSU come up with new eco-friendly method of producing silicon nanowires, in which instead of hydrofluoric acid (HF) used ammonium fluoride (NH 4 F). Silicon nanowires – is elongated along a direction substantially parallel to each other nanostructures like filaments, wires or poles, grown on a silicon substrate. The diameter of the nanowires, metal-stimulated obtained by chemical etching, usually varies from 50 to 200 nm, the distance between the nanowires may be from 100 to 500 nm. The length of the nanowires according to the etching time may range from 100 nm to tens of microns. Interest in silicon nanowires connected to their promising applications in micro- and optoelectronics, photonics, photovoltaics, sensing and even in biomedicine because silicon nanostructures are not only biocompatible, but also biodegradable (can be completely dissolved in the body after some time). However, the standard method used in making silicon nanowires hydrofluoric acid is highly toxic.
Preparation of metal-silicon nanowires stimulated etching is chemical etching of the silicon wafer where etched initiator metallic nanoparticles serve, for example, silver.
“We have a two-step etching method was used. In the first stage silver nanoparticles deposited on the surface of the silicon substrate. But not deposited a uniform layer, and islands. In the second step of the silicon substrate is etched in areas covered by silver. Therefore, unsecured silver portions of the silicon wafer turned into nanowires. Silver nanoparticles are “sinking” into the silicon wafer, and lasted longer than the etching, the more long nanowires were obtained. At the end of the silver was removed with nitric acid “- explains the general scheme of creating nanowires junior researcher of the Department of low temperature physics and superconductivity of the Physics Department of Moscow State University Kirill Gonchar.
Researchers from the State University replaced the hazardous and toxic hydrofluoric acid to ammonium fluoride at all stages of chemical etching, and also studied the optical properties of silicon nanowires prepared in this manner, and compared them with the nanowires obtained by the standard method using hydrofluoric acid.
Cyril Potter explains how the idea arose to use in the synthesis of nanowires ammonium fluoride: “The idea of using ammonium fluoride for electrochemical etching of silicon has been known for more than 20 years ago, but have not found wide acceptance. However, we are the first who went to the so-called “green chemistry”, using ammonium fluoride at all stages of the method of the metal-stimulated chemical etching. At the same time, it has also been shown in our work, structural and optical properties of the samples are virtually identical to those of nanowires obtained by the standard method (using hydrofluoric acid). Our work is promising as part of large-scale industrial production of non-toxic silicon nanowires. ”
Nanowires produced by the method presented by us, have a number of advantages: data structures there is a strong scattering and localization of light in a broad spectral range, so that the samples have a very low total reflection of light (a few percent) in both the UV and visible region of the spectrum; in such nanostructures observed increase in the interband photoluminescence intensity of silicon (1.12 eV) and Raman scattering in comparison with the original substrates of crystalline silicon; among other things, have also received the nanowire efficient photoluminescence in the range 500-1100 nm.
“Thus, – says Kirill Gonchar – we are in their work, scientists have discovered enormous possibilities of applications of silicon nanostructures obtained using” green chemistry “: this is the use of photovoltaics as an antireflection coating to improve the efficiency of solar cells; and sensorics as sensitive elements of optical sensors for various substances (due to the intensity of the Raman amplification of the signal light, which is the “fingerprints” of molecules); in photonics and biomedicine (luminescent properties). “