Detecção de H2 em dispositivos de monocamada de MoS2 e estudo de suas propriedades elétricas em altas temperaturas

Abstract

Among the 2D materials, molybdenum disulfide (MoS2) has attracted scientific interest due to its electronic, optical and structural properties. Several studies demonstrate that MoS2 can be applied in phototransistors, photodetectors, sensors, among others. This material also presents controllable spin polarization, allowing the application in valleytronic. The transition of the 1.2 eV indirect gap from bulk to direct gap of 1.8 eV in the monolayer is fundamental for the fabrication of semiconductor nanodevices. In addition, MoS2 has high mechanical strength values and Young's modulus around 270 ± 100 GPa. Especially, MoS2 is promising for detection of gases due to its large surface area. The adsorption and diffusion of molecules on the MoS2 surface cause drastic changes in its electrical conductivity, which makes it very sensitive to various gases. MoS2 transistors have been used to monitor gases such as NO, NO2, NH3, and O2. However, the hydrogen detection by monolayer MoS2, has not yet been fully explored experimentally. In this work, we produce monolayer MoS2 field effect transistors (MoS2 FET) to study both electrical properties and the application in hydrogen gas detection. The MoS2 FET exhibit a response to H2 that covers a broad range of concentration (0.1-90%) at a relatively low operating temperature range (25-200 °C). Most important, H2 sensors based on MoS2 FETs show desirable properties such as full reversibility and absence of catalytic metal dopants (Pt or Pd). We proposed that such process involves dissociative H2 adsorption driven by interaction with sulfur vacancies in the MoS2 surface. Later, we present our study about the hysteresis in the source-drain current versus gate voltage as a function of the temperature in two different devices: MoS2 supported on silicon oxide (MoS2/SiO2), and MoS2 supported on boron nitride (MoS2/BN). For MoS2/BN devices, we observe an anomalous behavior of the transconductance (dISD/dVG) as a function of the temperature, which makes it impossible to obtain real mobility values for this device.