Probing thermal expansion of graphene and modal dispersion at low-temperature using graphene NEMS resonators

TL;DR

This study uses suspended graphene resonators to investigate how temperature affects their resonant frequency and dispersion, revealing negative thermal expansion and mode tunability crucial for sensor applications.

Contribution

It provides the first detailed measurement of graphene's negative thermal expansion from 300K to 30K and analyzes the temperature-dependent dispersion crossover in electromechanical modes.

Findings

Graphene exhibits negative thermal expansion between 300K and 30K.

Resonant frequency shows significant tunability with gate voltage.

Electromechanical modes transition from positive to negative dispersion at low temperatures.

Abstract

We use suspended graphene electromechanical resonators to study the variation of resonant frequency as a function of temperature. Measuring the change in frequency resulting from a change in tension, from 300 K to 30 K, allows us to extract information about the thermal expansion of monolayer graphene as a function of temperature, which is critical for strain engineering applications. We find that thermal expansion of graphene is negative for all temperatures between 300K and 30K. We also study the dispersion, the variation of resonant frequency with DC gate voltage, of the electromechanical modes and find considerable tunability of resonant frequency, desirable for applications like mass sensing and RF signal processing at room temperature. With lowering of temperature, we find that the positively dispersing electromechanical modes evolve to negatively dispersing ones. We quantitatively explain this crossover and discuss optimal electromechanical properties that are desirable for temperature compensated sensors.