Unusual ultralow frequency fluctuations in freestanding graphene

TL;DR

This paper introduces a novel STM-based method to track ultralow frequency fluctuations in freestanding graphene, revealing dynamic ripple behavior and unexpected colossal jumps, advancing understanding of graphene's intrinsic properties.

Contribution

It presents a new technique for measuring out-of-plane fluctuations in graphene over long periods, combining experimental tracking with elasticity theory modeling.

Findings

Detection of ultralow frequency oscillations in graphene

Observation of sudden colossal jumps interpreted as mirror buckling

Development of a low-frequency nano-resonator using thermal load

Abstract

Intrinsic ripples in freestanding graphene have been exceedingly difficult to study. Individual ripple geometry was recently imaged using scanning tunneling microscopy, but these measurements are limited to static configurations. Thermally-activated flexural phonon modes should generate dynamic changes in curvature. Here we show how to track the vertical movement of a one-square-angstrom region of freestanding graphene using scanning tunneling microscopy, thereby allowing measurement of the out-of-plane time trajectory and fluctuations over long time periods. We also present a model from elasticity theory to explain the very-low-frequency oscillations. Unexpectedly, we sometimes detect a sudden colossal jump, which we interpret as due to mirror buckling. This innovative technique provides a much needed atomic-scale probe for the time-dependent behavior of intrinsic ripples. The discovery of this novel progenitor represents a fundamental advance in the use of scanning tunneling microscopy, which together with the application of a thermal load provides a low-frequency nano-resonator.