Tim Booth

Effective surface conductivity approach for graphene metamaterials based terahertz devices

Functional terahertz (THz) devices such as tunable polarizers, modulators, filters and absorbers are on demand. Graphene, a monolayer of carbon atoms, allows for tuning its THz conductivity through the Fermi level change. Graphene layers structured at the subwavelength scale form metamaterial which can have very unusual electromagnetic properties and thus expanding the range of its application for THz devices [1]. Usually graphene metamaterial based devices are designed straight through numerical simulations [2-4] and that requires time-consuming multiple variables analysis.

In Situ Tuning of Focused-Ion-Beam Defined Nanomechanical Resonators Using Joule Heating

Nanomechanical resonators have a huge potential for a variety of applications, including high-resolution mass sensing. In this paper, we demonstrate a novel rapid prototyping method for fabricating nanoelectromechanical systems using focused-ion-beam milling as well as in situ electromechanical characterization using a transmission electron microscope. Nanomechanical resonators were cut out of thin membrane chips, which have been prefabricated using standard cleanroom processing. We have demonstrated the fabrication of double-clamped beams with feature sizes down to 200 nm using a fabrication time of 30 min per device. Afterwards, the dynamic and structural properties of a double-clamped beam were measured after subsequent Joule heating events in order to ascertain the dependence of the internal structure on the Q-factor and resonant frequency of the device. It was observed that a change from amorphous to polycrystalline silicon structure significantly increased the resonant frequency as well as the Q-factor of the nanomechanical resonator. Aside from allowing detailed studies of the correlation between internal structure and nanomechanical behavior on an individual rather than a statistical basis, the combination of a short turnaround time and in situ nonlithographic tuning of the properties provide a flexible approach to the development and prototyping of nanomechanical devices.