ABSTRACT
The history of silicon nanowire (SiNW) arrays started almost 60 years ago when Treuting and Arnold (1957) reported on the formation of “silicon whiskers” in the vapor deposition process. Further progress was achieved in 1964 when Wagner and Ellis employed the vapor–liquid–solid (VLS) technique to produce silicon nanowires of about 100 nm in diameter. However, the SiNW arrays have not become merely a brilliant manifestation of technological abilities but have undergone further developments. New approaches for their formation have been developed and are widely used. Nowadays, SiNW arrays attract more and more researchers’ interest in various fields of study because of the possible practical applications of the SiNW-based devices. Indeed, silicon is one of the fundamental materials of modern microelectronics, and silicon technologies are well developed, which makes integration of the SiNW arrays with the present electronics easy. It is worth noting the broad spectrum of possible practical applications. For example, SiNW arrays allow the control of wetting from superhydrophobicity to complete wetting of the nanostructure by the applied voltage (Krupenkin et al. 2004). They look to be promising as anodes in batteries, in particular due to incorporation of huge amount of lithium into silicon (Chan et al. 2008; Baek et al. 2016), low-threshold field emitters (Huang et al. 2007; Kumar et al. 2014). In comparison with crystalline silicon (c-Si), SiNW arrays demonstrate lower thermal conductivity and practically the same electric conductivity and Seebeck coefficient, which makes them good thermal-isolating and thermoelectric materials (Boukai et al. 2008; Hochbaum et al. 2008; Calaza et al. 2015). Single SiNWs seem to be very promising for their employment in sensorics, for example, as a basis for molecular or, with additional functionalization, biological sensitive resistors or field-effect transistors (Cao et al. 2014; Williams et al. 2014). They use the generation of the carriers and, as a result, variation of the conductivity in the SiNWs covered with molecules (e.g., gas or lipids). Employment of the SiNW arrays allows researchers to consider more sophisticated sensors. For example, an array of the vertical SiNWs with palladium tops between two electrodes can serve as a hydrogen detector because of palladium expansion in hydrogen atmosphere resulting in their connection and a current flowing through the device. Low gas ionization voltage in SiNW arrays could be useful for gas detection (Sadeghian and Islam 2011). Adsorption of molecules at SiNWs will result in variation of the mass and, as a result, change in mechanical resonance frequency.
