Graphene Decorated with Silver Nanoparticles as a Low-Temperature Methane Gas Sensor.

This paper is devoted to an investigation on the methane sensing properties of graphene (G), decorated with silver nanoparticles (AgNPs), under ambient conditions. To do so, we first present an effective modification in the standard manner of decorating graphene by AgNPs. From structural analysis of the product (AgNPs/G), it is concluded that graphene is indeed decorated by AgNPs of a mean size 29.3 nm, free of aggregation, with a uniform distribution. The so-produced material is then used, as a resistivity-based sensor, to examine its response to the presence of methane gas. Our measurements are performed at relatively low temperatures, for various silver-to-graphene mass ratios (SGMRs) and methane concentrations. To account for the effects of humidity, we have made the measurements, at room temperature, for different levels of humidity. Our results demonstrate that an increase in the SGMR enhances the response of AgNPs/G to methane with an optimum value of SGMR ≅ 12%. It is also illustrated that for methane concentrations less than 2000 ppm, the maximal response increases linearly and rapidly, even at room temperature. Moreover, we demonstrate that AgNPs/G is of low limit of detection, highly stable, selective, reversible, repeatable, and sensor-to-sensor reproducible, for methane sensing. The results thus promise a low-cost and simple-to-fabricate methane sensing device.

Tunable graphene plasmonic Y-branch switch in the terahertz region using hexagonal boron nitride with electric and magnetic biasing.

A tunable graphene plasmonic Y-branch switch at THz wavelengths is proposed. The effects of magnetic and electric biasing are studied to harness the transmission of the transverse electric and magnetic guided mode resonances. In the structure, hexagonal boron nitride is utilized as a substrate for graphene. The application of hexagonal boron nitride, with the advantages of high mobility and ultralow ohmic loss, introduces a promising alternative substrate for graphene. Analytical and numerical results show that, by slight variation of the doping level in graphene through magnetic and electric biasing, the characteristics of the propagation of the guided mode resonances can be manipulated. A large extinction ratio of 40 dB at a wavelength of 60 µm is obtained. Besides, the proposed switch shows a low insertion loss of about 1 dB and a relatively large optical bandwidth of 1 µm. The electric biasing is of the order of 0.1 mV. Additionally, with the presence of magnetic biasing, a compact switch with a size of 25 µm is achieved. Showing a high extinction ratio, low insertion loss, and compact size, the proposed switch can find potential applications in graphene plasmonics integrated devices.