Addressing the unique properties of such individual nano-structures opens new ways to integrate structural investigation with other material properties. The researchers perform nano-focused X-ray diffraction (XRD) supported by finite element method (FEM) simulations to study the strain distribution inside single nanowires. They then connect the results to the µ-focused Raman spectroscopy results of the phonon modes in exactly the same part of the wire.

Band alignment

The aim of the project is to deepen the knowledge of single crystal germanium deformation potentials of nano-scaled objects. Ge wires are chosen to study their behaviour under an applied uniaxial tensile strain along the [111] growth axis. Theoretical band-gap calculations predict a transition from an indirect to direct gap for applied tensile strains in the order of 4%. In order to in-situ tune the band alignment by varying the strain state of the sample the researchers start with a static strain state, applied during sample growth and elaborate post-processing. The ambitious XRD measurements are accomplished at the experimental station ID01 of the European Synchrotron in France.

Combining individual studies

FEM simulations are of great value to disentangle lattice strain from lattice bending, both of which influence the measured diffraction patterns. Full strain tensors, calculated from the simulations are then compared with Raman studies of the very same nanowire. The successful combination of the individual studies reveals more detailed information and brings us one step closer to fully understanding the interplay between the crystalline structure and resulting material properties as well as their control in nano-fabrication. The "calibration" of the experiment enables measurement of the uniaxial tension using Raman in a lab rather than bringing every sample to the synchrotron, allowing for much faster device development.

More information about this research can be found in the journal Nanotechnology 27 055705.

Further reading

Inducing magnetism in phosphorene nanoribbons under strain (Jul 2015)
Titanium carbides: mechanical properties rival those of molybdenum disulphide (Jun 2015)
Taking the strain for more efficient solar cells (Nov 2014)