Formation of silicon nanocrystal chains induced via Rayleigh instability in ultrathin Si/SiO2 core/shell nanowires synthesized by an inductively coupled plasma torch process

Abstract

A new class of silicon (Si) nanohybrids is formed exploiting the Rayleigh instability experienced by Si nanowires (SiNWs) synthesized via inductively coupled plasma. These nanohybrids consist of three main categories of Si nanostructures: (i) core/shell silicon/silicon oxide nanowires (where the inner Si cores have diameters as small as 2-3 nm), (ii) sequences of almond-shaped silicon nanocrystals (SiNCs), having diameters in the range of 4-5 nm, connected by an ultrathin silicon nanowire (diameter of 1-2 nm) and embedded in a silica nanowire, and (iii) sequences of isolated spherical SiNCs (having diameters in the range of 4-7 nm) embedded in an otherwise continuous silica nanowire. The predominance of one morphology over the others can be tuned via post-synthesis thermal treatments, with a clear predominance of the spherical SiNC chain configuration after high-temperature annealing (1200 °C). It is demonstrated that the Rayleigh model describes very well the morphological transformations undergone by the Si core of the nanostructures when subject to the capillarity-related instability induced by the thermal annealing. More interestingly, we have been able, for the first time to our knowledge, to follow in situ the occurrence of Rayleigh instability in SiNWs leading to the breakage of their inner core and formation of smaller SiNCs. Finally, the optoelectronic properties of the Si nanohybrids, studied via photoluminescence measurements, have confirmed the occurrence of quantum confinement effects in the ultra-small SiNCs present in these new nanohybrids.