Jerry Yu

Reverse biased Pt/nanostructured MoO3/SiC Schottky diode based hydrogen gas sensors

Pt/nanostructured molybdenum oxide (MoO3)/SiC Schottky diode based gas sensors were fabricated for hydrogen (H2) gas sensing. Due to the enhanced performance, which is ascribed to the application of MoO3 nanostructures, these devices were used in reversed bias. MoO3 characterization by scanning electron microscopy showed morphology of randomly orientated nanoplatelets with thicknesses between 50 and 500 nm. An α-β mixed phase crystallographic structure of MoO3 was characterized by x-ray diffraction. At 180u2009°C, 1.343 V voltage shift in the reverse I-V curve and a Pt/MoO3 barrier height change of 20 meV were obtained after exposure to 1% H2 gas in synthetic air.

Enhancement of electric field properties of Pt/nanoplatelet MoO3/SiC Schottky diode

A comprehensive investigation of the electric field enhancement on a novel reverse biased Schottky contact induced by nanoplateleted morphology is presented. The phenomenon that causes the enhancement of the electric field in nanoplatelets is discussed and the equations describing it are derived. Pt/nanoplatelet MoO3/SiC Schottky diode based devices are fabricated to show the dependence of the current voltage (I – V) characteristics to the enhanced electric field at different temperatures. The devices are used as sensors as they were exposed to 1% hydrogen (H2) gas to show the effect of free carrier density change. (Some figures in this article are in colour only in the electronic version)

Hydrothermally formed functional niobium oxide doped tungsten nanorods.

Nanorod forms of metal oxides are recognized as one of the most remarkable morphologies. Their structure and functionality have driven important advancements in a vast range of electronic devices and applications. In this work, we postulate a novel concept to explain how numerous localized surface states can be engineered into the bandgap of niobium oxide nanorods using tungsten. We discuss their contributions as local state surface charges for the modulation of a Schottky barrier height, the relative dielectric constant and their respective conduction mechanisms. Their effects on hydrogen gas molecule interaction mechanisms are also examined herein. We synthesized niobium tungsten oxide (Nb17W2O25) nanorods via a hydrothermal growth method and evaluated the Schottky barrier height, ideality factor, dielectric constant and trap energy level from the measured I-V versus temperature characteristics in the presence of air and hydrogen to show the validity of our postulations.

A comparison study on hydrogen sensing performance of Pt/MoO 3 nanoplatelets coated with a thin layer of Ta 2 O 5 or La 2 O 3

In this work, we investigate how hydrogen sensing performance of thermally evaporated MoO₃ nano-platelets can be further improved by RF sputtering a thin layer of tantalum oxide (Ta₂O₅) or lanthanum oxide (La₂O₃). We show that dissociated hydrogen atoms cause the thin film layer to be polarised, inducing a measurable potential difference greater than that as reported previously. We attribute these observations to the presence of numerous traps in the thin layer; their states allow a stronger trapping of charge at the Pt-thin film oxide interface as compared to the MoO₃ sensors without the coating. Under exposure to H₂ (10 000 ppm), the maximum change in dielectric constant is 45.6 (at 260 °C) for the Ta₂O₅/MoO₃ nanoplatelets and 31.6 (at 220 °C) for the La₂O₃/MoO₃ nano-platelets. Subsequently, the maximum sensitivity for the Ta₂O₅/MoO₃ and La₂O₃/MoO₃ based sensors is 16.8 and 7.5, respectively.

ZnO nanostructured arrays grown from aqueous solutions on different substrates

ZnO nanostructures were grown from a solution of zinc nitrate hexahydrate and hexamethylenetetramine onto different substrates that were pretreated with an RF sputter coated ZnO seed layer. The choice of substrate was observed to have a direct effect on the morphology, orientation and surface coverage of the nanostructured arrays. Substrates that were covered in a 1.2 mum sputter coated ZnO seed layer, include; 6H-SiC, LiNbO3, gold, LiTaO3, ITO (indium tin oxide) glass and plate glass. The ZnO seed layer facilitates the uniform growth of nanostructured arrays of ZnO, without such a layer nanostructure growth was found to be sporadic and unaligned. Under identical reaction conditions, a range of different ZnO nanostructured arrays were observed.

Reverse biased Schottky contact hydrogen sensors based on Pt/nanostructured ZnO/SiC

Pt/nanostructured ZnO/SiC Schottky contact devices were fabricated and characterized for hydrogen gas sensing. These devices were investigated in reverse bias due to greater sensitivity, which attributes to the application of nanostructured ZnO. The current‐voltage (I‐V) characteristics of these devices were measured in different hydrogen concentrations. Effective change in the barrier height for 1% hydrogen was calculated as 27.06 meV at 620°u2009C. The dynamic response of the sensors was also investigated and a voltage shift of 325 mV was recorded at 620°u2009C during exposure to 1% hydrogen in synthetic air.

Pt/TiO 2 nanotubes/SiC schottky diodes for hydrogen gas sensing applications

Titanium oxide nanotubes Schottky diodes were fabricated for hydrogen gas sensing applications. The TiO2 nanotubes were synthesized via anodization of RF sputtered titanium films on SiC substrates. Two anodization potentials of 5 V and 20 V were used. Scanning electron microscopy of the synthesized films revealed nanotubes with avarage diameters of 20 nm and 75 nm. X-ray diffraction analysis revealed that the composition of the oxide varied with the anodization potential. TiO2 (anatase) being formed preferentially at 5 V and TiO (no anatase) at 20 V. Current-voltage characteristics of the diodes were studied towards hydrogen at temperatures from 25°C to 250°C. At constant current bias of −500 μA and 250°C, the lateral voltage shifts of 800 mV and 520 mV were recorded towards 1% hydrogen for the 5 V and 20 V anodized nanotubes, respectively.