Novel Heterostructured Ge Nanowires Based on Polytype Transformation

Vincent, L., G. Patriarche, G. Hallais, C. Renard, C. Gardès, D. Troadec and D. Bouchier, 2014

Image courtesy of Nano Letters

Abstract

We report on a strain-induced phase transformation in Ge nanowires under external shear stresses. The resulted polytype heterostructure may have great potential for photonics and thermoelectric applications. ⟨111⟩-oriented Ge nanowires with standard diamond structure (3C) undergo a phase transformation toward the hexagonal diamond phase referred as the 2H-allotrope. The phase transformation occurs heterogeneously on shear bands along the length of the nanowire. The structure meets the common phenomenological criteria of a martensitic phase transformation. This point is discussed to initiate an on going debate on the transformation mechanisms. The process results in unprecedented quasiperiodic heterostructures 3C/2H along the Ge nanowire. The thermal stability of those 2H domains is also studied under annealing up to 650 °C by in situ TEM.

Impact Statement

The demonstration of a strain-induced phase transformation in (111)-oriented Ge nanowires under external shear stresses, in which the nanowires’ standard diamond structure developed toward a hexagonal diamond phase (2-H allotrope). In addition, the researchers examined the 2H domains’ thermal stability using in situ TEM for annealing up to 650° C.