Theoretical Study on Structures and Stability of SiC2S Isomers

THEORETICAL STUDY ON THE POTENTIAL ENERGY SURFACE OF Si2NS

New species with molecular formula Si 2 NS , not yet observed experimentally, are described theoretically for the first time. Various levels of calculations are applied to obtain the structures, energies, dipole moments, vibrational spectra, rotational constants, and isomerization of Si 2 NS species. A total of 15 minima which are connected by 21 interconversion transition states on the potential energy surface are located at the DFT/B3LYP/6-311G(d) level of theory. And at the higher (single point) CCSD(T)/6-311+G(2d)//QCISD/6-311G(2d)+ZPVE level of theory, the global state of 1 (at 0.0 kcal/mol) corresponds to a nonlinear SiNSiS with a 2A′ electronic state. The next most stable isomer of 2 (only 3.7 kcal/mol higher 1) possesses a rhomboidal-type structure similar to the global state of Si 2 NO . This is followed by another local minimum of 6 (at 43.8 kcal/mol above 1) which is a nonlinear SiNSSi form with a 2A′ electronic state. Note that both 1 and 6 have the important Si ≡ N triple bonding. Too, the analog of (NCCS) NSiSiS is unstable due to the higher energy of its own. The bonding natures of the relevant species are also discussed. An analysis of the bonding properties and structural similarities and differences between C 2 NO , C 2 NS , SiCNO , and Si 2 NO is also carried out.

Direct synthesis of single-walled carbon nanotubes selectively suspended on tips of vertically aligned silicon nanostructures fabricated by hydrogen plasma etching

Here we present a method to synthesize single-walled carbon nanotubes (SWNTs) selectively suspended on tips of silicon-based nanostructure (Si-ns) templates. The Si-ns templates vertically aligned to the substrates are fabricated via an anisotropic etch process using reactive hydrogen plasmas, in which the etch-resistive nanomasks are the nanosized particles formed by thermal annealing of multi-layered catalytic thin films. After plasma etching, the nanosized self-masks remaining at the tips of the Si-ns directly serve as the catalysts for SWNT growth by thermal chemical vapour deposition. Consequently, the synthesized SWNTs are selectively suspended on the tips of the Si-ns, as revealed by characterizations using scanning electron microscopy and resonance Raman spectroscopy. This methodology provides a simple and straightforward approach to assemble two different nanomaterials, i.e., Si-ns and suspended SWNTs, together as a building block for constructing nanodevices for possible applications.