GHz nanomechanical resonator in an ultraclean suspended graphene p-n junction

TL;DR

This paper reports the development of GHz-range nanomechanical resonators using suspended graphene p-n junctions, demonstrating high resonance frequencies, enhanced signals in bipolar regimes, and insights into the mechanical properties of graphene.

Contribution

It introduces a method to achieve and analyze high-frequency graphene resonators with detailed characterization of their mechanical properties and resonance behavior in different electronic regimes.

Findings

Record resonance frequency of 1.17 GHz in graphene membrane.

Resonant signals are significantly enhanced in the bipolar regime.

Mechanical properties such as mass density and tension are quantitatively determined.

Abstract

We demonstrate high-frequency mechanical resonators in ballistic graphene p-n junctions. Fully suspended graphene devices with two bottom gates exhibit ballistic bipolar behavior after current annealing. We determine the graphene mass density and built-in tension for different current annealing steps by comparing the measured mechanical resonant response to a simplified membrane model. We consistently find that after the last annealing step the mass density compares well with the expected density of pure graphene. In a graphene membrane with high built-in tension, but still of macroscopic size with dimensions 3 $\times$ 1 $\mu m^{2}$, a record resonance frequency of 1.17 GHz is observed after the final current annealing step. We further compare the resonance response measured in the unipolar with the one in the bipolar regime. Remarkably, the resonant signals are strongly enhanced in the bipolar regime. This enhancement is caused in part by the Fabry-Perot resonances that appear in the bipolar regime and possibly also by the photothermoelectric effect that can be very pronounced in graphene p-n junctions under microwave irradiation.