Wei-Jhih Su

Field Emission Characteristics of the Structure of Vertically Aligned Carbon Nanotube Bundles

In this study, we performed thermal chemical vapor deposition for growing vertically aligned carbon nanotube (VACNT) bundles for a field emitter and applied photolithography for defining the arrangement pattern to simultaneously compare square and hexagonal arrangements by using two ratios of the interbundle distance to the bundle height (R) of field emitters. The hexagon arrangement with R = 2 had the lowest turn-on electric field (Eto) and highest enhancement factor, whereas the square arrangement with R = 3 had the most stable field emission (FE) characteristic. The number density can reveal the correlation to the lowest Eto and highest enhancement factor more effectively than can the R or L. The fluorescent images of the synthesized VACNT bundles manifested the uniformity of FE currents. The results of our study indicate the feasibility of applying the VACNT field emitter arrangement to achieve optimal FE performance.

Oxygen adsorption effect on nitrogen-doped graphene electrical properties

A simple method was found to observe the semiconducting behavior of graphene using the O2 gas adsorption property. Graphene was synthesized by thermal chemical vapor deposition with NH3 as the nitrogen doping source. The current response increased significantly when the p-type graphene was exposed to an O2 environment. The current response decreased gradually when the nitrogen content was increased. When the NH3 flow rate was increased to 80 sccm during graphene synthesis, the p-type graphene becomes n-type and the nitrogen-doped graphene current response clearly decreases during O2 gas adsorption measurements. We measured the graphene Dirac point using a field-effect transistor to define the graphene semiconducting properties. These results show that gas adsorption measurements can reveal the graphene semiconducting performance and also the n-type graphene synthesis conditions.

Mo1− x W x S2-based photodetector fabrication and photoconductive characteristics

We investigated the photoconductive characteristics of tungsten-substituted molybdenum disulfide (Mo1− x W x S2) series materials synthesized by the chemical vapor transport (CVT) method using different x values of W composition (x = 0–1, Δx = 0.1). We applied the Mo1− x W x S2 series materials to photoconductive detectors and then measured photocurrent at different laser source wavelengths: 405, 532, 633, and 808 nm. The band gap bowing effect and absorbance indicated the photoconduction mechanism in the Mo1− x W x S2 series materials. The proportion of x influenced the conductivity and absorbance, and induced the energy-gap bowing effect of Mo1− x W x S2.