Showing papers by "Guanxiong Liu published in 2015"

Selective Gas Sensing With $h$ -BN Capped MoS 2 Heterostructure Thin-Film Transistors

Abstract: Owing to their ultimate surface-to-volume ratio two-dimensional (2D) van der Waals materials are candidates for flexible gas sensor applications. However, all demonstrated devices had relied on direct exposure of the active 2D channel to gases, which presents problems for their reliability and stability. We demonstrated, for the first time, selective gas sensing with molybdenum disulfide (MoS2) thin films transistors capped with a thin layer of hexagonal boron nitride ( $h$ -BN). The resistance change, $\Delta R/R$ , was used as a sensing parameter to detect chemical vapors. It was found that $h$ -BN dielectric passivation layer does not prevent gas detection via changes in the current in the MoS2 channel. The detection without direct contacting the channel with analyte molecules was achieved with $\Delta R/R$ ratio as high as $10^{\mathrm { {3}}}$ . In addition, we show that the use of $h$ -BN cap layers (thickness $H \sim 10$ nm) improves sensor stability and prevents degradation due to environmental and chemical exposure.

Gas Sensing with h-BN Capped MoS2 Heterostructure Thin Film Transistors

Abstract: We have demonstrated selective gas sensing with molybdenum disulfide (MoS2) thin films transistors capped with a thin layer of hexagonal boron nitride (h-BN). The resistance change was used as a sensing parameter to detect chemical vapors such as ethanol, acetonitrile, toluene, chloroform and methanol. It was found that h-BN dielectric passivation layer does not prevent gas detection via changes in the source-drain current in the active MoS2 thin film channel. The use of h-BN cap layers (thickness H=10 nm) in the design of MoS2 thin film gas sensors improves device stability and prevents device degradation due to environmental and chemical exposure. The obtained results are important for applications of van der Waals materials in chemical and biological sensing.

Reduced 1/f noise in high-mobility BN-graphene-BN heterostructure transistors

Abstract: Raman spectroscopy was used to determine the number of atomic planes in the exfoliated graphene samples and verify the quality of the selected flakes (see Figure 2 (a)). The optical microscopy images of the exfoliated BN and graphene flakes, and the resulting heterostructure are shown in Figure 2 (b-c). The current-voltage (I–V) characteristics of a representative BN-graphene-BN HFET are shown in Figure 3 (a). Both the effective and field-effect mobility extractions gave consistent results and the room-temperature (RT) mobility was determined to be ∼30,000 cm2/Vs at 7·1011 cm−2. The normalized 1/f noise spectral density of the graphene encapsulated device is presented in Figure 3 (b). We found that the channel-area normalized noise spectral density in BN-graphene-BN HFET is factor of ×5 – ×10 smaller than that in typical reference graphene FETs without channel encapsulation. The observed strong noise reduction can be related to screening of the traps in SiO 2 by the BN barrier. Other possible physical mechanisms and prospects of further noise suppression will be discussed at the presentation.