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We propose and demonstrate a new principle for sensing. Impact of light, radiation, charge particle and gas molecular etc. can induce the change of the surface work function of a solid. This will result in a profound effect to a device’s output, such as current and voltage. Such an effect is in particular outstanding in a nanodevice using van der Waals stacked two-dimensional (2D) atomic crystals. In this paper, a study of a gas sensing device relying on such a principle is presented. Van der Waals bipolar junction transistors (V2D-BJT) based on vertically stacked MoS2/WSe2/MoS2 and WSe2/MoS2/WSe2 heterostructures are separately fabricated to detect NH3 and NO2 gas. Kelvin probe force microscope measurement shows that the work function change at the overlapped region of MoS2/WSe2/MoS2 heterostructure upon exposure to 50 ppm NH3 gas is 80 meV. In addition, the MoS2/WSe2/MoS2 V2D-BJT manifest superior sensing performances in detecting NH3, while the WSe2/MoS2/WSe2 V2D-BJT exhibited superior NO2 sensing properties in terms of high sensitivity (18), low power dissipation (12 nW), fast response (26 s) and recovery (14 s) time. We demonstrate that the NH3 and NO2 gas can be selectively detected by the V2D-BJT through changing the van der Waals heterostructure stacking sequences.

Self-heating effect can be applied to develop gas sensors avoiding use of external heaters. We report here a prototype self-heated hydrogen gas sensor based on Pt-coated W 18 O 49 nanowire networks. Such a sensor has been shown to have promising performance, e.g., high sensitivity (able to detect down to 50 ppm of H 2 ), good selectivity (poor response to ethanol, CH 4 , CO, and C 3 H 8 ), and low power consumption of 30–60 mW at 6 V compatible to a portable device. Coaxial cable model and percolation theory are applied to explain the gas sensing effect of the Pt-coated W 18 O 49 nanowire networks.

Being a typical Kondo topological insulator, samarium hexaboride (SmB6) attracts much interest in condensed physics and material sciences in recent years. In comparison with their bulk counterparts, SmB6 nanostructures have more abundant surface electron states due to larger specific surface area, which are believed as idea platforms for studying surface quantum properties and physic mechanism. Through chemical vapor deposition (CVD), SmB6 nanobelt and nanowire films were respectively prepared on Si substrate. Both SmB6 nanowires and nanobelts are proven as the cubic single crystals, and their growth directions are, along [100] and [110], respectively. Field emission (FE) results show that SmB6 nanobelts have a turn-on field of 3.24 V/μm and their maximum current density arrives at 466.16 µA/cm 2, which are better than SmB6 nanowires. Considering that SmB6 nanostructures have lower electron affinity, higher electron conductivity and more abundant surface states, they are regarded as excellent cold cathode nanomaterials if their FE performances can be further improved.

Interest in silicon field emitters for flat screen display and other applications has continued to grow very rapidly over the past several years. To obtain stable field emission from silicon emitters, diamond and DLC coatings are being considered widely. In this paper we report results from a series of experiments to assess the influence of a thin layer of amorphous diamond coating on ultra sharp single crystal silicon field emitter arrays.

We report the first observation of ultraviolet superfluorescence (SF) from oxygen vacancies in WO3−x nanowires at room temperature, and of picosecond-scale energy transfer between emission centers (oxygen vacancies) in a plane. A theoretical development from Dicke’s model leads to general formulation for a two-dimensional system, and is applied to explain the energy transfer process. The results demonstrate a possibility to generate ultrafast pulse of ultraviolet light through SF from a localized ensemble of defect states.

The photoluminescence spectra of WO3−x nanowire networks, WO3 nanowires networks, and the bulk phase WO3 powder have been investigated under the continuous wave excitation light at 320nm. Two broad band emissions in spectrum of WO3−x nanowire networks are observed including the ultraviolet-visible (UV-vis) emission centered at 395nm and the blue emission centered at 467nm. The authors demonstrate that the blue emission in WO3−x nanowire networks is due to band-band transition of the bulk phase WO3 and the UV-vis emission is attributed to the state of oxygen vacancies, which are characterized by using scanning electron microscopy and x-ray photoelectron spectroscopy. The UV-vis emission exhibits a strong dependence on the excitation wavelength, while the blue emission is independent of the excitation wavelength. The UV-vis emission is discussed in configuration-coordinate diagram of a localized state of oxygen vacancies. In particular, this state of defect is a high-lying resonant state in the conduction band of WO3.