Gold nanoparticles decorated WS2 microflakes (Au/WS2) have been synthesized by an in situ chemical reducing process. A chemiresistive-type sensor using as-synthesized Au/WS2 heterostructures as sensing materials shows an improved response to different concentrations of ammonia compared to pure WS2 at room temperature. As the concentrations of gold nanoparticles increased in heterostructures, response/recovery speeds of the sensors became faster although the sensitivity of the sensor was compromised compared to the sensitivity of the sensor with lower concentrations of Au. In addition, the Au/WS2-based sensor indicated excellent selectivity to formaldehyde, ethanol, benzene and acetone at room temperature. The improved performance of the sensors was attributed to the synergistic effect of electronic sensitization and chemical sensitization between WS2 and Au.

Simultaneous growth of different kinds of aligned GaN nanostructures (i.e., nanowires, needles, pyramids and micro-rods) on a single substrate was firstly realized at a low temperature of 790 C by naturally changing the III/V ratio across the substrate via a coaxial pipeline configuration. The effects of substrate distance and growth pressure on nanostructure growth were investigated. The morphology variation from nanowires to micros-rods would be explained in terms of Ga species changing from the Ga element to GaN molecule in a hot-wall reactor. This work is helpful for on chip integration of different kinds of nanodevices on unusual substrates of low melting temperature.

Tungsten sulfide decorated with indium oxide nanoparticles (In2O3/WS2) was studied for a chemiresistive-type NH3 sensor at room temperature. It was found that the responses of the developed In2O3/WS2 heterostructure nanocomposite-based sensors are significantly improved to 3.81 from 1.45 for WS2. The response and recovery time of the heterostructure-based sensor was found to significantly decrease to 88 s/116 s (10 ppm) from 112 s/192 s for the WS2-based one. The sensor also exhibits excellent selectivity and signal reproducibility. In comparison to WS2 decorated with both ZnO and SnO2 in similar ways, the In2O3-decorated WS2 has overall better sensing performance in terms of sensitivity, selectivity and response/recovery speeds for NH3 from 1 ppm to 10 ppm at room temperature. The improved sensing properties of WS2 incorporating In2O3 could be attributed to the joint enhancement mechanisms of the “electronic and catalytic” sensitizations.