Surface conductance of graphene from non-contact resonant cavity

Abstract

A method is established to reliably determine surface conductance of single-layer or multi-layer atomically thin nano-carbon graphene structures. The measurements are made in an air filled standard R100 rectangular waveguide configuration at one of the resonant frequency modes, typically at TE103 mode of 7.4543 GHz. Surface conductance measurement involves monitoring a change in the quality factor of the cavity as the specimen is progressively inserted into the cavity in quantitative correlation with the specimen surface area. The specimen consists of a nano-carbon-layer supported on a low loss dielectric substrate. The thickness of the conducting nano-carbon layer does not need to be explicitly known, but it is assumed that the lateral dimension is uniform over the specimen area. The non-contact surface conductance measurements are illustrated for a typical graphene grown by chemical vapor deposition process, and for a high quality monolayer epitaxial graphene grown on silicon carbide wafers for which we performed non-gated quantum Hall resistance measurements. The sequence of quantized transverse Hall resistance at the Landau filling factors ν = ±6 and ±2, and the absence of the Hall plateau at ν = 4 indicate that the epitaxially grown graphene is a high quality mono-layer. The resonant microwave cavity measurement is sensitive to the surface and bulk conductivity, and since no additional processing is required, it preserves the integrity of the conductive graphene layer. It allows characterization with high speed, precision and efficiency, compared to transport measurements where sample contacts must be defined and applied in multiple processing steps.

Dielectric Characterization of Confined Water in Chiral Cellulose Nanocrystal Films

“…The complex relative permittivity ( ${\epsilon }_{\mathrm{normalr}}={\epsilon }_{\mathrm{normalr}}^{\prime }-j{\epsilon }_{\mathrm{normalr}}^{″}$) of the CNC films was measured at a frequency of 7.435 GHz using a noncontact cavity perturbation method, 23,24 which allows precise measurement of the dielectric permittivity in quantitative correlation with the moisture content. This method is nondestructive and experimentally simple, and it does not require any electrical contacts that would otherwise obscure the water absorption and its effect on the dielectric properties of CNCs.…”

“…In our earlier work 23,24 we showed that for a small specimen inside a rectangular cavity operating in the TE 10n , the classical perturbation equation 25 can be simplified to linear analytic expressions: $$y^{\prime }=({\epsilon }_{\mathrm{normalr}}^{\prime }-1)2x-b^{\prime }$$ $$y^{″}={\epsilon }_{\mathrm{normalr}}^{″}4x-2b^{″}$$…”

Contactless Microwave Characterization of Encapsulated Graphene p−n Junctions

“…An important example of this is graphene spintronics [8], where device performance is often limited by the contacts, which cause spin relaxation and decrease of the spin lifetime [9][10][11][12]. Therefore, contactless characterization such as microwave absorption [13] and microwave-impedance microscopy [14] can open up new ways to probe inherent properties of the studied system. In the past, other contactless schemes such as terahertz spectroscopy [15,16] and dielectric force microscopy [17] have been employed to study the carrier dynamics in graphene.…”

A $Q$ -Band Free-Space Characterization of Carbon Nanotube Composites

“…There is a strong need for an accurate nondestructive evaluation (NDE) technique for the online monitoring of the dispersion of CNTs in a composite, as they are being fabricated, with minimal disturbance to the fabrication process. Cavity measurements can provide high accuracy in retrieving the dielectric properties of the composite, but they are limited to materials with moderate resonance damping (conductivity) characteristics [5]–[6]. Also, resonant techniques operating on evanescent near-fields are highly non-linear with respect to the location of the specimen.…”