Synthesis and structural control of silicon and silicide nanowires/microrods using metal chloride sources

Abstract

Si and silicide nanowires/microrods were synthesized using metal-chloride-based sources by the CVD technique. In the case of Si nanowire synthesis, the morphological structures of the products depended on the distance from the source material. The distance dependence of the morphological and structural properties of the nanostructures was investigated to systemically clarify the shape modification phenomena in Si nanowire synthesis. The modification of the cross-sectional shape of the Si nanowires/microrods was successfully demonstrated. The triangular nanowire has a sawtooth faceting structure on its sidewall. In addition, the synthesis of Mn-silicide phases over the entire range of the Mn-Si system was examined. The effect of adding an impurity to the source materials on the structural modifications of the resulting nanowires/microrods was also investigated. It is expected that the morphological and structural control of the nanowires/microrods will be improved by a simple thermal treatment using a metal chloride as the source material.

Synthesis of Si nanowire/nanosheet complexes from CaSi2 crystals by thermal annealing under MnCl2/NH4Cl vapors

“…17) In contrast, the nanowire formation process is dominantly governed by the thermal annealing in the MnCl 2 vapor. [19][20][21][22] The simultaneous thermal annealing of the two source materials resulted in the successful synthesis of the nanowire/nanosheet complexes.…”

“…On the other hand, the synthesis of Si nanowires from a Si wafer with the catalysts of MnSi or Mn chloride compounds, and the growth of Si nanowires with MnSi 1.7 particles on the top of the nanowires using Au catalysts were previously reported. [19][20][21][22] It is considered that Si chlorides are formed by the reaction of MnCl 2 and Si, and they are transported to the nanowire formation sites. SiCl 4 would be one of most likely species produced considering that the enthalpy of formation for MnCl 2 (−38.4 kcal/g-atom) is similar to that of SiCl 4 (−31.7 kcal/g-atom).…”

“…For each case, Si was immediately damaged and oxidized by the higher-pressure treatment to form silicon oxide nanotubes and nanowires. Three types of Mn-related catalysts are considered; one is Mn-silicide, 20) and the other is a Mn-related compound, 21,22) and possibly liquid phase MnCl 2 above the annealing temperature, which is resolved by ethanol washing after the thermal annealing, and cannot be observed by SEM and TEM with EDS. The bottom-up synthesis of Si-oxides nanotubes without templates has been rarely reported.…”

“…17) On the other hand, the synthesis of Si nanowires from a Si wafer with the catalysts of MnSi or Mn chlorides compounds, and the growth of Si nanowires with MnSi 1.7 particles on the top of the nanowires using Au catalysts were previously reported. [19][20][21][22] In the former, the Si nanowires were synthesized using MnCl 2 /Si mixed powders. [19][20][21] It is expected that the construction of 3D architectures of nano-scaled size would be possible using the bottom up technique with MnCl 2 /NH 4 Cl mixed powders and CaSi 2 by the simultaneous synthesis process previously mentioned.…”

“…[19][20][21][22] In the former, the Si nanowires were synthesized using MnCl 2 /Si mixed powders. [19][20][21] It is expected that the construction of 3D architectures of nano-scaled size would be possible using the bottom up technique with MnCl 2 /NH 4 Cl mixed powders and CaSi 2 by the simultaneous synthesis process previously mentioned. In addition, the aggregation of the 2D nanosheets should be avoided by using the bundle structures with nanowires between the nanosheets.…”