Flexible room-temperature NO2 gas sensors based on carbon nanotubes/reduced graphene hybrid films

We present a flexible room temperature NO2 gas sensor consisting of vertical carbon nanotubes (CNTs)/reduced graphene hybrid film supported by a polyimide substrate. The reduced graphene film alone showed a negligible sensor response, exhibiting abnormal N-P transitions during the initial NO2 injection. A hybrid film, formed by the growth of a vertically aligned CNT array (with CNTs 20 ??m in length) on the reduced graphene film surface, exhibited remarkably enhanced sensitivities with weak N-P transitions. The increase in sensitivity was mainly attributed to the high sensitivity of the CNT arrays. The outstanding flexibility of the reduced graphene films ensured stable sensing performances in devices submitted to extreme bending stress.open786

Layer number identification of CVD-grown multilayer graphene using Si peak analysis

Abstract Since the successful exfoliation of graphene, various methodologies have been developed to identify the number of layers of exfoliated graphene. The optical contrast, Raman G-peak intensity, and 2D-peak line-shape are currently widely used as the first level of inspection for graphene samples. Although the combination analysis of G- and 2D-peaks is powerful for exfoliated graphene samples, its use is limited in chemical vapor deposition (CVD)-grown graphene because CVD-grown graphene consists of various domains with randomly rotated crystallographic axes between layers, which makes the G- and 2D-peaks analysis difficult for use in number identification. We report herein that the Raman Si-peak intensity can be a universal measure for the number identification of multilayered graphene. We synthesized a few-layered graphene via the CVD method and performed Raman spectroscopy. Moreover, we measured the Si-peak intensities from various individual graphene domains and correlated them with the corresponding layer numbers. We then compared the normalized Si-peak intensity of the CVD-grown multilayer graphene with the exfoliated multilayer graphene as a reference and successfully identified the layer number of the CVD-grown graphene. We believe that this Si-peak analysis can be further applied to various 2-dimensional (2D) materials prepared by both exfoliation and chemical growth

Gas molecule sensing of van der Waals tunnel field effect transistors

van der Waals (vdW) heterostructures with two-dimensional (2D) crystals such as graphene, hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMDCs) allow us to demonstrate atomically thin field-effect transistors (FETs), photodetectors (PDs) and photovoltaic devices capable of higher performance and greater stability levels than conventional devices. Although there have been studies of gas molecule sensing with 2D crystal channels, vdW heterostructures based on 2D crystals have not been employed thus far. Here, utilizing graphene/WS2/graphene (G/WS2/G) vdW heterostructure tunnel FETs, we demonstrate the rectification behavior of the sensitivity signal by tuning the WS2 potential barriers as a function of the gas molecule concentration and devise a fingerprint map of the sensitivity variation corresponding to an individual ratio of two different molecules in a gas mixture. Because the separation of different gas molecule concentrations from gas mixtures is in high demand in the gas-sensing research field, this result will greatly assist in the progress on selective gas sensing. This journal is © The Royal Society of Chemistry 201711sciescopu