Jun-Cheng Lin

Fast Photoresponse and Long Lifetime UV Photodetectors and Field Emitters Based on ZnO/Ultrananocrystalline Diamond Films

We have designed photodetectors and UV field emitters based on a combination of ZnO nanowires/nanorods (ZNRs) and bilayer diamond films in a metal-semiconductor-metal (MSM) structure. The ZNRs were fabricated on different diamond films and systematic investigations showed an ultra-high photoconductive response from ZNRs prepared on ultrananocrystalline diamond (UNCD) operating at a lower voltage of 2 V. We found that the ZNRs/UNCD photodetector (PD) has improved field emission properties and a reduced turn-on field of 2.9 V μm(-1) with the highest electron field emission (EFE) by simply illuminating the sample with ultraviolet (UV) light. The photoresponse (Iphoto /Idark ) behavior of the ZNRs/UNCD PD exhibits a much higher photoresponse (912) than bare ZNRs (229), ZNRs/nanocrystalline diamond (NCD; 518), and ZNRs/microcrystalline diamond (MCD; 325) under illumination at λ=365 nm. A photodetector with UNCD films offers superior stability and a longer lifetime compared with carbon materials and bare ZNRs. The lifetime stability of the ZNRs/UNCD-based device is about 410 min, which is markedly superior to devices that use bare ZNRs (92 min). The ZNRs/UNCD PD possesses excellent photoresponse properties with improved lifetime and stability; in addition, ZNRs/UNCD-based UV emitters have great potential for applications such as cathodes in flat-panel displays and microplasma display devices.

Low temperature synthesis of ZnO nanotubes based hydrogen sensors

A facile method has been developed to synthesize zinc oxide nanotubes (ZNTs) based hydrogen sensors at low temperature. ZnO nanorods (ZNRs) are first synthesized using the aqueous chemical process at 90 °C for 3 h, and then cooled down and maintained at 50 °C for a certain time (t = 6 h, 12 h and 18 h, respectively). ZNRs are transformed to ZNTs after the low temperature self-etching process. The ZNTs can provide a larger surface area than the pristine ZNRs for adsorbing additional gas ions, along with more oxygen vacancies to effectively sense gas ions with t increased from 6 h to 18 h. It is found that the hydrogen response of all ZNT hydrogen sensors, which is about 2 times higher than that of the pristine ZNR sensor (13.1%, at 500 ppm). It is noted that the ZNTs for t = 18 h possess the highest oxygen vacancies and the best response for hydrogen sensing (29.6%, at 500 ppm).