Papers by Keyword: Oxide Semiconductor

Abstract: It is necessary to develop NO₂ gas sensors as NO₂ is a pollutant. While, different from the reducing gases, oxidizing gas NO₂ will put up a complicated sensing process. Density functional theory (DFT) calculations are necessary to be performed to understand NO₂-sensing mechanisms at the atomic level. In this study we introduce NO₂ to SnO₂ (110) surface with oxygen species pre-adsorbed. The results show that NO₂ sensing mechanism of SnO₂ surface strongly depends on the concentration of oxygen in the ambient atmosphere (usually, no effects of temperature and pressure are considered). The direct interactions between NO₂ molecule and SnO₂ sub-reduced surface (with two rows of fold-coordinated bridging oxygens removed) for very low oxygen concentrations show that, NO₂ gas molecules interact directly with Sn instead of reacting with oxygen species, resulting in an increase in resistance of SnO₂. We investigate gas-sensing processes of interaction between NO₂ molecule and SnO₂ surface with pre-adsorbed oxygen species for the case of considerable high oxygen concentrations. Adsorbed molecular oxygen ions compete with adsorbing NO₂ molecules for available surface sites and electrons from the SnO₂. As the availability of oxygen ions on the SnO₂ surface increasing, the interaction between NO₂ and adsorbed oxygen species give rise to a reducing interaction, which brings a decrease in resistance of SnO₂.

Abstract: The purpose of this work is to consider the basic concepts on the present state of understanding of photocatalytic energy conversion using oxide semiconductors. This work also considers the approaches in derivation of theoretical models that allow explanation of the effect of properties on the performance of oxide-based photocatalysts in photocatalytic water oxidation. In this work we show that the performance of photocatalytic systems must be considered in terms of a range of the key performance-related properties (KPPs) that, in addition to the band gap, include the concentration of surface active sites, charge transport and Fermi level. Taking into account that all these KPPs are related to defect disorder, defect engineering may be applied in processing oxide semiconductors with optimal properties that are required to exhibit maximised performance in solar-to-chemical energy conversion.

Abstract: Volatile Organic Compounds (VOCs) are highly reactive, often mixed with interfering gases and more importantly, their vapours in the gaseous form respond to the gas sensor devices. Oxide semiconductor based thin film gas sensors play vital role in detecting, monitoring and controlling the presence of hazardous and harmful gases in the environment at very low concentration and hence are tested for the detection of harmful or industrially important VOCs. The demand of sensitive as well stable gas/vapour sensors for direct sensing application has increased the importance of In₂O₃:SnO₂ based semiconductor materials. The paper presents the fabrication aspects of thin film gas sensors based on x1In₂O₃:x2SnO₂ compound and also their application for the detection of some important volatile organic compounds. Thin films of x1In₂O₃:x2SnO₂ were deposited using Thermal Evaporation technique and under the optimized fabrication conditions, the vapour sensors were prepared and mounted on the proper contact jig. Their response to the presence of Volatile Organic Compounds like CCl₄ was examined. The stability, the sensitivity and the response time of the sensors were studied for the different concentrations of test vapours.

Abstract: To minimize interfacial power losses, thin layers of NiO, a p-type oxide semiconductor, are inserted between the active organic layer, poly(3-hexylthiophene) (P3HT) [6,6]-phenyl-C61 butyric acid methyl ester (PCBM), and the ITO (tin-doped indium oxide) anode of bulk-heterojunction ITO/P3HT:PCBM/Al solar cells. The interfacial NiO layer is deposited by radio frequency (RF) magnetron sputtering deposition directly onto cleaned ITO, and the active layer is subsequently deposited by spin-coating. Insertion of the NiO layer affords cell power conversion efficiencies as high as 2.5% and enhances the fill factor to 56% and the open-circuit voltage (Voc) to 605 mV versus ones without NiO buffering layer control device. The value of such hole-transporting/electron-blocking interfacial layers is clearly demonstrated and should be applicable to other organic photovoltaics.

Abstract: Semiconductor gas sensors utilize porous polycrystalline resistors made of semiconducting oxides.The working principle involves the receptor function played by the surface of each oxide grain and the transducer function played by each grain boundary. In addition, the utility factor of the sensing body also takes part in determining the gas response. Therefore, the concepts of sensor design are determined by considering each of these three key factors.ZrO2 is one of the most commonly used sensitive material, The performances of the different components Y2O3-ZrO2 are studied in this paper.The performances of YSZ Prepared with different Y2O3 powder(untreated and 1300°C preburned) and the Mechanism are explored in this paper.

Abstract: The transport properties of Zn0.88-xMgxMn0.12O/ZnO modulation-doped heterostructures (x≤0.15) were investigated. The heterostructures were fabricated on ZnO single-crystal substrates by a pulsed laser deposition system. Atomic force microscope observation and X-ray diffraction analysis suggested that Zn0.88-xMgxMn0.12O layers have atomically flat surface and excellent crystallinity. The results of Hall measurement for Zn0.88-xMgxMn0.12O/ZnO modulation-doped heterostructure with x=0.075 revealed that the carrier concentration and the electron mobility were 5.1×1012cm-2 and 800 cm2/Vs at 10 K, respectively, suggesting that the carrier confinement effect exits at the heterointerface between Zn0.88-xMgxMn0.12O barrier layer and ZnO channel layer. In the magnetoresistance (MR) measurement at 1.85 K, a positive MR behavior was observed below 0.5 T, while a negative MR behavior was recognized above 0.5 T. The slope of the positive MR decreased with increasing the temperature and was well fitted to the Brillouin function with S=5/2. The electrical and magneto-transport properties were very similar to those of Zn0.88Mn0.12O/ZnO heterostructures without doping Mg.