QDev Seminar: Lincoln Lauhon – University of Copenhagen

QDev Seminar: Lincoln Lauhon

Optomechanical studies of VO2 nanowires and MoS2 membranes

Prof. Lincoln J. Lauhon
Department of Materials Science and Engineering, Northwestern University, Evanston, IL

Nanomechanical resonators fabricated additively from 1-D and 2-D nanomaterials present a wealth of scientific opportunities beyond those of conventional resonators fabricated in a subtractive manner from dielectric thin films. Our research group is using methods from the nanomechanical systems community to investigate the properties of new low dimensional materials and explore phenomena that emerge in extremely high aspect ratio nanostructures. For example, nanoscale resonators provide a compelling platform to investigate and exploit phase transitions coupled to mechanical degrees of freedom because resonator frequencies and quality factors are exquisitely sensitive to changes in state, particularly for discontinuous changes accompanying a first-order phase transition. We used correlated scanning fiber-optic interferometry and dual-beam Raman spectroscopy to investigate mechanical fluctuations of vanadium dioxide (VO2) nanowires across the first order insulator to metal transition (Nano Lett. 14, 1898 (2014). Unusually large and controllable changes in resonator frequency were observed due to the influences of domain wall motion and anomalous phonon softening on the effective modulus. In addition, extraordinary static and dynamic displacements were generated by local strain gradients, suggesting new classes of sensors and nanoelectromechanical devices with programmable discrete outputs as a function of continuous inputs. We have recently extended the same interferometric measurement method to study thermally driven displacements in square few-layer MoS2 membranes. By exploiting above-gap optical excitation and sub-gap optical detection, we show that such membranes can reach the strong coupling regime and demonstrate related phenomena such as normal mode splitting.