SCIENTIFIC HIGHLIGHTS
Claudia Fasolato*, Marta De Luca, Doriane Djomani, Laetitia Vincent, Charles Renard, Giulia Di Iorio, Vincent Paillard, Michele Amato, Riccardo Rurali, and Ilaria Zardo* Nano Lett., Article ASAP
DOI: 10.1021/acs.nanolett.8b03073
Semiconducting nanowires (NWs) offer the unprecedented opportunity to host different crystal phases in a nanostructure, which enables the formation of polytypic heterostructures where the material composition is unchanged. This characteristic boosts the potential of polytypic heterostructured NWs for optoelectronic and phononic applications.
In this work, we investigate cubic Ge NWs where small (∼20 nm) hexagonal domains are formed due to a strain-induced phase transformation. By combining a nondestructive optical technique (Raman spectroscopy) with density-functional theory (DFT) calculations, we assess the phonon properties of hexagonal Ge, determine the crystal phase variations along the NW axis, and, quite remarkably, reconstruct the relative orientation of the two polytypes. Moreover, we provide information on the electronic band alignment of the heterostructure at points of the Brillouin zone different from the one (Γ) where the direct band gap recombination in hexagonal Ge takes place.
We demonstrate the versatility of Raman spectroscopy and show that it can be used to determine the main crystalline, phononic, and electronic properties of the most challenging type of heterostructure (a polytypic, nanoscale heterostructure with constant material composition). The general procedure that we establish can be applied to several types of heterostructures.
This publication made it to the COVER of the issue in Nano Letters!
Tuneable and low cost molecular electronics
Crystalline, Phononic, and Electronic Properties of Heterostructured Polytypic Ge Nanowires by Raman Spectroscopy

