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Ammonia gas sensors are very essential in many industries and everyday life. However, their complicated fabrication process, severe environmental fabrication requirements and desorption of residual ammonia molecules result in high cost and hinder their market acceptance. Here, laser direct writing is used to fabricate three parallel porous 3D graphene lines on a polyimide (PI) tape to simply construct an ammonia gas sensor. The middle one works as an ammonia sensing element and the other two on both sides work as heaters to improve the desorption performance of the sensing element to ammonia gas molecules. The graphene lines were characterized by scanning electron microscopy and Raman spectroscopy. The response and recovery time of the sensor without heating are 214 s and 222 s with a sensitivity of 0.087% ppm-1 for sensing 75 ppm ammonia gas, respectively. The experimental results prove that under the optimized heating temperature of about 70 °C the heaters successfully help implement complete desorption of residual NH₃ showing a good sensitivity and cyclic stability.

For the manufacture of graphene based electronic devices, graphene growth directly on SiO2/Si substrates is a prerequisite. However, the problem of metal contamination is a key issue that cannot be avoided when synthesizing graphene on SiO2/Si substrates. Additionally, the direct fabrication of patterned graphene still suffers from inefficient and low repeatable problems. In this article, an approach based on a germanium (Ge)-assisted chemical vapor deposition (CVD) is proposed. It can produce graphene directly on any dielectric substrates. Graphene is grown directly on Ge-covered SiO2/Si substrates due to the catalysis of Ge. By depositing the second Ge layer with a pattern by a designed hard mask onto the as-grown centimeter-scale and continuous graphene on SiO2/Si substrates followed by etching the graphene and removing the Ge, the monolayer graphene pattern was acquired. This process has the advantages of no metal pollution and high repeatability. Subsequently, the patterned and highly conductive graphene prepared on SiO2/Si substrates was used for gas sensor. The gas sensor exhibited well NO2 gas sensing properties because of large charge transferred from graphene to NO2 molecules. [ABSTRACT FROM AUTHOR]

Synthesis of graphene on Ni/Cu bilayer substrate by ion implantation is sensitive to the quality of the Ni/Cu substrate. In this work, different pretreatments of Cu foils were implemented to elucidate the role of Cu pretreatment on graphene synthesis. Four types of pretreatments including polishing, annealing at 950 °C, annealing at 1000 °C, and annealing at 1050 °C were conducted prior to the growth of the Ni coating layer. Four different Ni/Cu substrates were implanted by carbon ions and annealed to obtain monolayer graphene. It shows that the impurity particles emerging on the Cu foils annealed at 1000 °C and 1050 °C affect the crystalline quality of the synthesized graphene. In addition, the increase in roughness due to the polishing process induces non-uniformity of the obtained graphene. Overall, annealing at 950 °C is proven to be the proper pretreatment for Cu foil, and the corresponding graphene film has excellent crystalline quality and uniformity compared to those obtained on the substrates with other pretreatments. [ABSTRACT FROM AUTHOR]

We propose an approach to improve the performance of graphene-based gas sensors by the integration of defective graphene with pristine graphene. The defect density of defective graphene is controlled by the fluence of Si+ implantation, and an H2 etching process is utilized to tune defect size. As defects are able to adsorb target gas efficiently, the response of graphene-based sensors was improved remarkably with the controllable defect density. The response sensitivity of a defective-graphene-based sensor to concentrations of NO2 at 100 ppm can be as high as 248%, 13 times higher than that of a sensor built using pristine graphene. In addition, defective-graphene-based sensors exhibit high response and recovery rates at room temperature, which is comparable to those of pristine graphene-based sensors and faster than conventional defect-decorated graphene sensors. Most importantly, defective-graphene-based gas sensors exhibit excellent reproducibility, stability, and selectivity. Our study suggests a simple and effective strategy for the mass production of high-performance graphene-based gas sensors for NO2 gas detection. [ABSTRACT FROM AUTHOR]

To solve electrical contact problem of horizontal multilayer graphene nanoribbon (GNR), a vertical GNR (VGNR) interconnect scheme is proposed. Performance of the VGNR interconnect is theoretically evaluated and compared with those of conventional interconnect technologies. It is shown that the performance of VGNR is comparable (and even superior) to that of the horizontal GNR (HGNR). Moreover, VGNRs may provide a promising solution to the thermal challenges faced by HGNRs in nanoscale ICs. [ABSTRACT FROM AUTHOR]

Two dimensional electron systems (2DES) usually show the weak localization behavior in consequence of electron interaction in the limited dimension. Distinct from other 2DES, the monolayer graphene, due to the chirality, exhibits unique weak localization behavior sensitive to not only inelastic but also elastic carrier scattering. Grain boundaries, which usually exist in monolayer graphene, are apparently related to the elastic carrier scattering process, thus affecting the weak localization behavior. However, their effect is scarcely studied due to the lack of an ideal platform. Here, a complementary system consisting of both single-crystalline graphene grown on Ge (110) and poly-crystalline graphene grown on Ge (111) is constructed. From the comparison of magnetoresistivity measurements, the weak localization effect is found to be greatly enhanced for the poly-crystalline graphene on Ge(111) compared to the single-crystalline graphene on Ge(110). The degraded transport performance in graphene/Ge(111) is due to the presence of grain boundary in poly-crystalline graphene, which results in the enhanced elastic intervalley scattering. In addition, the inelastic scattering originating from the strong electron-electron interaction at low temperature also contributes to weak localization of poly-crystalline graphene/Ge(111). [ABSTRACT FROM AUTHOR]

We propose an approach to improve the performance of graphene-based gas sensors by the integration of defective graphene with pristine graphene. The defect density of defective graphene is controlled by the fluence of Si+ implantation, and an H2 etching process is utilized to tune defect size. As defects are able to adsorb target gas efficiently, the response of graphene-based sensors was improved remarkably with the controllable defect density. The response sensitivity of a defective-graphene-based sensor to concentrations of NO2 at 100 ppm can be as high as 248%, 13 times higher than that of a sensor built using pristine graphene. In addition, defective-graphene-based sensors exhibit high response and recovery rates at room temperature, which is comparable to those of pristine graphene-based sensors and faster than conventional defect-decorated graphene sensors. Most importantly, defective-graphene-based gas sensors exhibit excellent reproducibility, stability, and selectivity. Our study suggests a simple and effective strategy for the mass production of high-performance graphene-based gas sensors for NO2 gas detection. [ABSTRACT FROM AUTHOR]