Radio‐frequency transport Electromagnetic Properties of chemical vapour deposition graphene from direct current to 110 MHz

Abstract

We report measurement of the radio-frequency (RF) transport electromagnetic properties of chemical vapour deposition (CVD) graphene over the DC to 110 MHz frequency range at room temperature. Graphene on Si/SiO 2 substrate was mounted in a shielded four terminalpair (4TP) adaptor which enabled direct connection to a calibrated precision impedance analyser for measurements. Good agreement is observed for the DC four-probe resistance and the 4TP resistance at 40 Hz, both yielding R ≈ 104 Ω. In general the apparent graphene channel electromagnetic properties are found to be strongly influenced by the substrate parasitic capacitance and resistance, particularly for high-frequencies f > 1 MHz. A phenomenological lumped-parameter equivalent circuit model is presented which matches the frequency response of the graphene 4TP impedance device over approximately seven decades of the frequency range of the applied transport alternating current. Based on this model, it is shown for the first time, that the intrinsic graphene channel resistance of the 4TP device is frequency-independent (i.e. dissipationless) with R G ≈ 105 Ω or sheet resistance of approximately 182 Ω / □. The parasitic substrate impedance of the device is found shunt R G with R P ≈ 2.2 Ω in series with C P ≈ 600 pF. These results suggest that our new RF 4TP method is in good agreement with the conventional DC four-probe method for measuring the intrinsic sheet resistance of single-atom thick materials and could potentially open up new applications in RF electronics, AC quantum Hall effect metrology and sensors based on graphene 4TP devices operating over broad range of frequencies.

Sensitivity Comparison of Macro- and Micro-Electrochemical Biosensors for Human Chorionic Gonadotropin (hCG) Biomarker Detection

“…The macroelectrode showed typical voltammogram peaks for the fabricated sensor and acceptable detection limit (100pg/mL), whereas the micro-electrodes showed higher sensitivity (1 pg/mL) which may be attributed to better structural properties due to the nearest-neighbour distance as confirmed by Raman spectroscopy, and the more favorable electrochemical properties of the micro-electrode relative to the macro-electrode due to the lowered electronic resistance, as evidenced by CV characterization. Future work will aim to modify the proposed sensors by using different carbon materials such as graphene and two-dimensional materials [33] to investigate the electrochemical behavior of different matrices based on the surface area, to enhance the sensitivity and to target different sample types as well as impedance spectroscopy detection techniques [34]. Indeed, the principles of the presented assay can be exploited to fabricate a variety of diagnostic sensors by using different antibodies or aptamers to recognize wide range of biomarkers.…”