What is the Ground-State Structure of the Thinnest Si Nanowires?

Abstract

Pristine silicon whiskers are compared through energy analysis by separating the surface, edge, and bulk contributions, and by energy computation for a variety of structures and diameters d. It is shown that for d<6 nm a polycrystalline wire of five-fold symmetry, rather than single-crystal types, represents the ground state. It remains stable in molecular dynamics tests up to approximately 1000 K. Its specific surface reconstruction also stands out in that it favors kinetics of whisker growth and thus appears potentially realizable.

Electronic transport through Si nanowires: Role of bulk and surface disorder

“…The SiNW structures used in this paper have rounded, rather than perfectly square angles. It has been proposed in the literature [47][48][49] that smooth angles would be favored during the growth process with respect to the sharp angles that naturally arise from the square symmetry of the ͓100͔ cleavage plane. The topic has been discussed at some details elsewhere 49 for surface-reconstructed wires, concluding that at nanometric diameters no clear difference emerges.…”

Structural and tunneling properties of Si nanowires

“…We do not consider surface reconstructions and apply the Wulff's law for minimal free energy equilibrium shapes 11 generalized to NWs, where a cylindrical shape with a core that retains the diamond structure is favored. 12 Figure 1(b) shows the configurations used in the transport calculations: On the left-hand side a pristine long Si NW is presented, where the outermost units are used as electrodes, while on the right-hand side the Si NW is placed between two Au 111 electrodes. All structures are fully relaxed by density functional theory, using the localized orbitals basis set of the SIESTA package, 30,31 until the forces on all atoms are less than 0.04 eV/Å.…”

“…7 It has been demonstrated that Si NWs are rodlike structures with a bulk Si single crystalline core 8 and thus grow along well-defined crystalline directions 9,10 and follow the Si surface reconstruction criteria according to Wulff's minimum energy law, 11 thereby having a well defined shape in their cross section. 12 Due to the sp 3 nature of the Si bonding, the atoms at the surface have dangling bonds, 13 which need to be passivated in order to ensure chemical stability. To this aim, the synthesized Si NWs are coated with an oxide layer (amorphous oxide formed by exposure to the environment), which is then removed by hydrofluoric acid, resulting in hydrogenated (H-terminated) Si NWs.…”

Structures and energetics of silicon nanotubes from molecular dynamics and density functional theory

“…4͒ and hollow NTs. 5,6 The several hollow and nonhollow structures proposed and theoretically characterized in recent years include fullerene-based structures 5 and hexagonal wires, 7 polycrystals with fivefold symmetry, 8 carbon NT structure, 9 and square, pentagonal, and hexagonal single-walled NTs. 10 These structures were proposed based on intuition or the behavior of similar materials, and some are high-energy configurations unlikely to be observed experimentally.…”