Growth and properties of coherent twinning superlattice nanowires

Abstract

Although coherent twin boundaries require little energy to form in nanoscale single crystals, their influence on properties can be dramatic. In recent years, some important steps forward have been made in understanding and controlling twinning processes at the nanoscale, making possible the fabrication of nanoengineered twinning superlattices in crystalline nanowires. These advances have opened new possibilities for properties and functionalities at the atomic and quantum scales by modulating twin densities. This article presents a brief overview of recent theoretical and experimental progress in growth mechanisms and promising properties of coherent twinning superlattice nanowires with special emphasis toward cubic systems in semiconductor and metallic materials. In particular, we show how nanoscale growth twins can considerably enhance bandgap engineering and mechanical behaviour in quasi-one-dimensional materials. Opportunities for future research in this emerging area are also discussed.

Mechanism of crack healing at room temperature revealed by atomistic simulations

“…Early much work focuses on the crack healing caused by the heating in ceramics [24,25], polymers [26,27] and metal materials [28], because the heating reduces the atomic diffusion activation energy which in turn makes crack close through the volume diffusion or through the dislocation diffusion. Crack also can be healed through oxidation reaction which forms oxide film to prevent surface oxidation and fill of crack space with an oxidation product [29,30].…”

Inducing imperfections in germanium nanowires

“…[18][19][20] In recent years, a remarkable degree of control of 4 twinning and polytype generation has been demonstrated in III-V nanowires with the formation of twinning superlattices. [21,22] However, the intentional induction and control of twin boundaries and polytypes in group IV semiconductor nanowires (Si and Ge) are an ongoing challenge, although for group IV semiconductors the influence of twin boundaries on the electronic band structure of Si and Ge is well documented.…”

Diameter-Controlled Germanium Nanowires with Lamellar Twinning and Polytypes

“…Additionally, nanowires with inhomogeneous heterostructures and periodic twin boundaries are attracting attention as components for optical, electrical and thermophysical applications. [27][28][29] The control of twin periodicity in group IV nanowires, especially Ge, offers the possibility of band structure engineering [30][31] and the modulation of thermoelectric properties through modulated side faceting. 29 Inhomogeneous stress fields caused by twinning and surface faceting can locally affect the conduction and valence band potential thus altering electronic band structure.…”

“…32 Periodic twinned planes in semiconductor nanowires can also generate polytype superstructures, where stacking faults in the abc stacking sequence, along the ˂111˃ direction, can produce local hexagonal ordering in a cubic crystal; for example aba packing, leading to polytypes with distinctly unique optical and electrical properties. 27,[33][34] The generation of controlled twinned and polytype defects within individual nanowires allows the realization of heterostructures from a single component semiconductor, with perfect lattice matching and preserved interface bonds.…”