Oxide semiconductors are conventionally used as sensing materials in gas sensors, however, there are limitations on the detection of gases at room temperature (RT). In this work, a hybrid of copper oxide (CuO) with functionalized graphene (rGO) is proposed to achieve gas sensing at RT. The combination of a high surface area and the presence of many functional groups in the CuO/rGO hybrid material makes it highly sensitive for gas absorption and desorption. To prepare the hybrid material, a copper oxide suspension synthesized using a copper acetate precursor is added to a graphene oxide solution during its reduction using ascorbic acid. Material properties of the CuO/rGO hybrid and its drop-casted thin-films are investigated using Raman, FTIR, SEM, TEM, and four-point probe measurement systems. We found that the hybrid material was enriched with oxygen functional groups (OFGs) and defective sites, along with good electrical conductivity (Sheet resistance~1.5 kΩ/□). The fabricated QCM (quartz crystal microbalance) sensor with a thin layer of the CuO/rGO hybrid demonstrated a high sensing response which was twice the response of the rGO-based sensor for CO₂ gas at RT. We believe that the CuO/rGO hybrid is highly suitable for existing and future gas sensors used for domestic and industrial safety.

The demand for carbon dioxide (CO₂) gas detection is increasing nowadays. However, its fast detection at room temperature (RT) is a major challenge. Graphene is found to be the most promising sensing material for RT detection, owing to its high surface area and electrical conductivity. In this work, we report a highly edge functionalized chemically synthesized reduced graphene oxide (rGO) thin films to achieve fast sensing response for CO₂ gas at room temperature. The high amount of edge functional groups is prominent for the sorption of CO₂ molecules. Initially, rGO is synthesized by reduction of GO using ascorbic acid (AA) as a reducing agent. Three different concentrations of rGO are prepared using three AA concentrations (25, 50, and 100 mg) to optimize the material properties such as functional groups and conductivity. Thin films of three different AA reduced rGO suspensions (AArGO25, AArGO50, AArGO100) are developed and later analyzed using standard FTIR, XRD, Raman, XPS, TEM, SEM, and four-point probe measurement techniques. We find that the highest edge functionality is achieved by the AArGO25 sample with a conductivity of ~1389 S/cm. The functionalized AArGO25 gas sensor shows recordable high sensing properties (response and recovery time) with good repeatability for CO₂ at room temperature at 500 ppm and 50 ppm. Short response and recovery time of ~26 s and ~10 s, respectively, are achieved for 500 ppm CO₂ gas with the sensitivity of ~50 Hz/µg. We believe that a highly functionalized AArGO CO₂ gas sensor could be applicable for enhanced oil recovery, industrial and domestic safety applications.

Ionization gas sensors using vertically aligned multi-wall carbon nanotubes (MWCNT) are demonstrated. The sharp tips of the nanotubes generate large non-uniform electric fields at relatively low applied voltage. The enhancement of the electric field results in field emission of electrons that dominates the breakdown mechanism in gas sensor with gap spacing below 14 μm. More than 90% reduction in breakdown voltage is observed for sensors with MWCNT and 7 μm gap spacing. Transition of breakdown mechanism, dominated by avalanche electrons to field emission electrons, as decreasing gap spacing is also observed and discussed.

Graphene has been extensively investigated in the context of electronic components due to its attractive properties, such as high carrier mobility and saturation velocity. In the past decade, the graphene field-effect transistor (GFET) has been considered one of the potential devices to be used in future radio frequency (RF) applications and can help usher in the Internet of Things and the 5G communication network. This review presents recent developments of GFETs in RF applications with a focus on components such as amplifiers, frequency multipliers, phase shifters, mixers, and oscillators. Initially, the figures of merit (FoMs) for the GFET are briefly described to understand how they affect these RF components. Subsequently, the FoMs of GFET-based RF components are compared with other non-GFET-based RF components. It is found that, due to its zero-band gap and ambipolar characteristics, GFETs are more suitable for use in frequency multiplier and phase shifter applications, outperforming non-GFET-based RF components. Finally, future research on GFETs themselves as well as GFET-based RF components is recommended. This review provides valuable insights into such components that could give rise to innovative applications in industry.

Transparent conductive electrodes (TCE) made of carbon nanotube (CNT) and graphene composite for GaN-based light emitting diodes (LED) are presented. The TCE with 533-Ω/□ sheet resistance and 88% transmittance were obtained when chemical-vapor-deposition grown graphene was fused across CNT networks. With an additional 2-nm thin NiO_x interlayer between the TCE and top p-GaN layer of the LED, the forward voltage was reduced to 5.12 V at 20-mA injection current. Four-fold improvement in terms of light output power was observed. The improvement can be ascribed to the enhanced lateral current spreading across the hybrid CNT-graphene TCE before injection into the p-GaN layer.