An ab initio study of cluster-assembled hydrogenated silicon nanotubes

The search or design of silicon cage-like or tube-like structures similar to their carbon analogues has attracted great interest recently. In this work, density functional calculations are performed to systematically study a series of finite and infinite hydrogenated cluster-assembled silicon nanotubes (H-SiNTs). It is found that stable one-dimensional H-SiNTs with formula Sim(3k+1)H2m(k+1) can be constructed by proper assembly of hydrogenated fullerene-like silicon clusters Si4mH4m. The stability is first demonstrated by the large cohesive energies and HOMO–LUMO gaps. Among all such silicon nanotubes, the ones built from Si20H20(m = 5) and Si24H24(m = 6) are the most stable due to the silicon bond angles that are most close to the bulk sp3 type in these structures. Thermostability analysis further verifies that such tubes may well exist at room temperature. Both finite nanotubes and infinite nanotubes show a large energy gap. A direct–indirect–direct band gap transition has been revealed with the increase of the tube radius. The existence of direct band gap may make them potential building blocks for electronic and optoelectronic devices.