Growth Mechanisms of Inductively-Coupled Plasma Torch Synthesized Silicon Nanowires and their associated photoluminescence properties

Abstract

Ultra-thin Silicon Nanowires (SiNWs) were produced by means of an industrial inductively-coupled plasma (ICP) based process. Two families of SiNWs have been identified, namely long SiNWs (up to 2–3 micron in length) and shorter ones (~100 nm). SiNWs were found to consist of a Si core (with diameter as thin as 2 nm) and a silica shell, of which the thickness varies from 5 to 20 nm. By combining advanced transmission electron microscopy (TEM) techniques, we demonstrate that the growth of the long SiNWs occurred via the Oxide Assisted Growth (OAG) mechanism, while the Vapor Liquid Solid (VLS) mechanism is responsible for the growth of shorter ones. Energy filtered TEM analyses revealed, in some cases, the existence of chapelet-like Si nanocrystals embedded in an otherwise silica nanowire. Such nanostructures are believed to result from the exposure of some OAG SiNWs to high temperatures prevailing inside the reactor. Finally, the intense photoluminescence (PL) of these ICP-grown SiNWs in the 620–950 nm spectral range is a clear indication of the occurrence of quantum confinement. Such a PL emission is in accordance with the TEM results which revealed that the size of nanostructures are indeed below the exciton Bohr radius of silicon.

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

“…By examining the structural and morphological characteristics of the as-grown ICP-Si nanopowder, we found that three main families of Si nanostructures can be distinguished [5], as shown in figure 1: (i) cylindrical SiNWs presenting a rod-shaped Si nanocore (mean diameter of 2.7 nm), as depicted in figure 1(a); (ii) chaplet-like SiNWs featuring a chain of almond-shaped SiNCs (mean diameter of 4.5 nm) connected by a very thin Si wire (diameter of 1-2 nm), as illustrated in figure 1(b); and (iii) SiNC chains consisting of a sequence of isolated spherical Si nanocrystals (mean diameter of 7 nm) embedded in a continuous SiO 2 cylinder, as those shown in figure 1(c). The nano-crystalline nature of all these three configurations was ascertained by high-resolution TEM (HRTEM) analyses, as shown in the figures 1(d)-(f).…”

“…Figures 4(a)-(c) show the statistical distributions of the occurrence of the three different SiNW morphologies for the as-grown as well as the annealed ICP-SiNWs at 800 and 1200°C, respectively. It was found that the cylindrical SiNWs constitute the major component (53% of the overall population) of the as-grown sample, while the percentages of the chaplet-like SiNWs and the SiNC chains represent respectively 35% and 12% of the total nanostructures constituting the as-grown ICP-SiNWs (see figure 4(a)) [5]. When the sample was annealed at 800°C, the percentages of both cylindrical and chaplet-like SiNWs decreased to ∼44% and 32%, respectively, while the proportion of SiNC chains increased to 24% (see figure 4(b)).…”

“…In particular, the system formed by Si nanocrystals (SiNCs) embedded in silica matrix has been designated as a suitable material for optical emission at room temperature [1][2][3]. On the other hand, ultrathin Si nanowires (SiNWs) have recently shown remarkable optoelectronic properties due to the occurrence of QC effects in these unidimensional nanostructures [4,5]. In the case of inductively coupled plasma (ICP) torch synthesized Si nanostructures, we have recently reported a new class of Si hybrid nanostructures consisting of a random mixture of SiNCs and SiNWs wrapped by a silica shell, which emit strong photoluminescence over the 600-900 nm range [5].…”

“…On the other hand, ultrathin Si nanowires (SiNWs) have recently shown remarkable optoelectronic properties due to the occurrence of QC effects in these unidimensional nanostructures [4,5]. In the case of inductively coupled plasma (ICP) torch synthesized Si nanostructures, we have recently reported a new class of Si hybrid nanostructures consisting of a random mixture of SiNCs and SiNWs wrapped by a silica shell, which emit strong photoluminescence over the 600-900 nm range [5]. The idea of modulating the size of 0D, 1D, and 2D materials and mixing them to form new nanohybrids has emerged as an original approach to access enhanced properties or even new functionalities [6][7][8][9][10].…”

“…In this paper, we report on the thermal-annealing-induced nanostructuring of ultrathin SiNWs synthesized by means of an ICP-based process [5]. The as-synthesized SiNWs consist of a mixture of ultrathin SiNWs (as thin as 2-3 nm) and SiNCs as small as 3 nm wrapped into a silica nanoshell.…”