Chee Lap Chow

Sensing Mechanisms for Carbon Nanotube Based NH3 Gas Detection

There has been an argument on carbon nanotube (CNT) based gas detectors with a field-effect transistor (FET) geometry: do the response signals result from charge transfer between adsorbed gas molecules and the CNT channel and/or from the gas species induced Schottky barrier modulation at the CNT/metal contacts? To differentiate the sensing mechanisms, we employed three CNTFET structures, i.e., (1) the entire CNT channel and CNT/electrode contacts are accessible to NH(3) gas; (2) the CNT/electrode contacts are passivated with a Si(3)N(4) thin film, leaving the CNT channel open to the gas and, in contrast, (3) the CNT channel is covered with the film, while the contacts are open to the gas. We suggest that the Schottky barrier modulation at the contacts is the dominant mechanism from room temperature to 150 degrees C. At higher temperatures, the charge transfer process contributes to the response signals. There is a clear evidence that the adsorption of NH(3) on the CNT channel is facilitated by environmental oxygen.

Bottom-Up Preparation of Porous Metal-Oxide Ultrathin Sheets with Adjustable Composition/Phases and Their Applications

A facile bottom-up synthesis approach is developed to prepare porous metal-oxide ultrathin sheets, e.g., SnO(2), Fe(2)O(3), and SnO(2)-Fe(2)O(3), with thicknesses of ∼5 nm. Graphene sheets are used as the sacrificing template. Such a process can be extended to the synthesis of multiphased porous metal-oxide thin sheets. These porous thin sheets show interesting applications as gas sensors, effective platforms for matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry, and supercapacitors.

Self-organization of a hybrid nanostructure consisting of a nanoneedle and nanodot

A special materials system that allows the self-organization of a unique hybrid nanonipple structure is developed. The system consists of a nanoneedle with a small nanodot sitting on top. Such hybrid nanonipples provide building blocks to assemble functional devices with significantly improved performance. The application of the system to high-sensitivity gas sensors is also demonstrated.

P1.0.20 N-P Transition Sensing Response of Strontium Titanate Ferrite Sol-Gel Thin Films

Perovskite oxide has been reported as a potential gas sensing material in addition to commonly used binary oxide. Strontium titanate ferrite (SrTi0.6Fe0.4O3) thin film sensors were fabricated using modified sol-gel spin coating technique and annealed at different annealing temperatures. An anomalous n- to p-type transition of oxygen sensing response was observed as annealing temperature increased. A typical p-type sensing response was observed for sensors annealed at temperature of 500 °C and higher. On the other hand, sensors annealed below 450 °C showed an unusual n-type sensing response, which has never been reported. The n-type sensing response was caused by the amorphous phases in the thin film annealed at low annealing temperature, as revealed by X-ray diffraction (XRD), tunneling electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS).