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

摘要

We use suspended graphene electromechanical resonators to study the variationof resonant frequency as a function of temperature. Measuring the change infrequency resulting from a change in tension, from 300 K to 30 K, allows us toextract information about the thermal expansion of monolayer graphene as afunction of temperature, which is critical for strain engineering applications.We find that thermal expansion of graphene is negative for all temperaturesbetween 300K and 30K. We also study the dispersion, the variation of resonantfrequency with DC gate voltage, of the electromechanical modes and findconsiderable tunability of resonant frequency, desirable for applications likemass sensing and RF signal processing at room temperature. With lowering oftemperature, we find that the positively dispersing electromechanical modesevolve to negatively dispersing ones. We quantitatively explain this crossoverand discuss optimal electromechanical properties that are desirable fortemperature compensated sensors.