Investigation of nanoscale strain and its relation to optoelectronic phenomena

Abstract

Strain engineering, which is a field to change electrical and optical properties using physical effects related to strain, has recently received great attention in nanostructures. It has recently been discovered that role of the strain in nanostructures is a important factor that can impart new functionality rather than for deterioration of the device performance. Specifically, band structure modulation in the semiconductor via strain changes the electronic and optical properties to develop new functional devices such as flexible light-emitting diodes, optical sensors, and transistors. In this regard, we studied the role of the strain and strain-related optoelectric phenomena in two-dimensional transition metal dichalcogenide and tapered zinc oxide nanorods, respectively. To investigate the role of strain on optical characteristics, Photoluminescence (PL) spectra of monolayer WSe2 and MoSe2, which are the two-dimensional transition metal dichalcogenide materials, were observed under mechanically bending. The application of shear strain induces PL energy redshift and variation of PL intensity due to spin-state mixing. In particular, it was observed that the W- and Mo-based materials were opposite to each other under the application of shear strain. Through a theoretical analysis Based on spin-specific effective Hamiltonian, we found out that the spin-state mixing via shear strain induces darkening (brightening) of bright (dark) exciton in monolayer WSe2 (MoSe2). For the tapered ZnO NR, the PL spectra were measured via a two-photon excitation that can be decomposed in nanoscale at the substrate-interface and the top of the NR. interface and surface strain were extracted from the obtained PL spectra at the substrate-interface and the top of the tapered ZnO NR, respectively. The surface strain at the top of the tapered ZnO NR occurs as the diameter of the NR decreases. The interface strain is caused by lattice mismatch at the interface between the ZnO and the sapphire substrate. The effect of these strains are expected to change the electrical and optical performance of ZnO-based nanodevices. These studies are expected to contribute to improve the performance and functionality of nanodevices by the developed high-resolution spectroscopy and optical analysis.