Graphene gas sensing using a non-contact microwave method.

We report a non-contact CVD graphene gas sensing method that utilises a high Q microwave dielectric resonator perturbation technique. A graphene sample is coupled to the evanescent field of a dielectric resonator whereupon nitrogen dioxide (NO2), a p-doping gas, is detected by monitoring the change in the linewidth and frequency of the resonant mode. The resonant peak shape is dependent on the number of carriers in the graphene sheet. Therefore, the linewidth perturbation can be converted to a measurement of the graphene sheet resistance. To demonstrate the strength of this technique, sensor response curves for NO2 at different concentrations and temperatures are measured showing sub ppm sensitivity. This technique eliminates interactions between the trace gas and metal contacts that otherwise effect the sensor response of the graphene device.

Towards a metrological determination of the performance of SERS media.

Enhancement factors under SERS conditions are characterised for two SERS active substrates with different geometries using a combination of optical pumping and photobleaching. A rigorous mathematical method of the photobleaching dynamics under SERS conditions is developed to allow the average enhancement factor to be investigated whilst maximal enhancement factors are studied using optical pumping. We show that both average and maximal enhancements are correlated for the surfaces with average enhancements of approximately 10(8).

Temperature-dependent anti-stokes/stokes ratios under surface-enhanced Raman scattering conditions.

We make systematic measurements of Raman anti-Stokes/Stokes (aS/S) ratios using two different laser excitations (514 and 633 nm) of rhodamine 6G (RH6G) on dried Ag colloids over a wide range of temperatures (100 to 350 K). We show that a temperature scan allows the separation of the contributions to the aS/S ratios from resonance effects and heating/pumping, thus decoupling the two main aspects of the problem. The temperature rise is found to be larger when employing the 633 nm laser. In addition, we find evidence for mode specific vibrational pumping at higher laser power densities. We analyze our results in the framework of ongoing discussion on laser heating/pumping under surface-enhanced Raman scattering (SERS) conditions.

Real-time scanning tunnelling microscopy imaging of protein motion at electrode surfaces.

A mutant (K27C) of the blue copper protein azurin [Eur. J. Biochem. 194 (1990) 109; J. Mol. Biol. 221 (1991) 765] for orientated immobilisation on gold surfaces was analysed by scanning tunnelling microscopy (STM) both in a resting state and following the application of a short potential pulse between the tip and sample.