Broadband microwave and time-domain terahertz spectroscopy of CVD grown graphene

TL;DR

This study uses broadband microwave and terahertz spectroscopy to analyze the complex impedance of CVD-grown graphene, revealing frequency-independent behavior and technical measurement insights.

Contribution

It introduces a method to measure the intrinsic impedance of graphene across a broad frequency range, overcoming technical challenges related to substrate effects.

Findings

Impedance shows little temperature dependence down to helium temperatures.

Imaginary impedance contributions are minimal, mainly from substrate effects.

Frequency dependence of conductance is negligible within measurement accuracy.

Abstract

We report a study of the complex AC impedance of CVD grown graphene. We measure the explicit frequency dependence of the complex impedance and conductance over the microwave and terahertz range of frequencies using our recently developed broadband microwave Corbino and time domain terahertz spectrometers (TDTS). We demonstrate how one may resolve a number of technical difficulties in measuring the intrinsic impedance of the graphene layer that this frequency range presents, such as distinguishing contributions to the impedance from the substrate. From our microwave measurements, the AC impedance has little dependance on temperature and frequency down to liquid helium temperatures. The small contribution to the imaginary impedance comes from either a remaining residual contribution from the substrate or a small deviation of the conductance from the Drude form.