Localized Charge Transfer Process and Surface Band Bending in Methane Sensing by GaN Nanowires

The physicochemical processes at the surfaces of semiconductor nanostructures involved in electrochemical and sensing devices are strongly influenced by the presence of intrinsic or extrinsic defects. To reveal the surface controlled sensing mechanism, intentional lattice oxygen defects are created on the surfaces of GaN nanowires for the elucidation of charge transfer process in methane (CH4) sensing. Experimental and simulation results of electron energy loss spectroscopy (EELS) studies on oxygen rich GaN nanowires confirmed the possible presence of 2(ON) and VGa-3ON defect complexes. A global resistive response for sensor devices of ensemble nanowires and a localized charge transfer process in single GaN nanowires are studied in situ scanning by Kelvin probe microscopy (SKPM). A localized charge transfer process, involving the VGa-3ON defect complex on nanowire surface is attributed in controlling the global gas sensing behavior of the oxygen rich ensemble GaN nanowires.Comment: 42 pages, 6 figures, Journa

触媒表面イオン種を活かした環状炭化水素の転換による水素製造

早大学位記番号:新8175早稲田大

Reversal of anomalous Hall effect and octahedral tilting in SrRuO₃ thin films via hydrogen spillover

The perovskite SrRuO3 (SRO) is a strongly correlated oxide whose physical and structural properties are strongly intertwined. Notably, SRO is an itinerant ferromagnet that exhibits a large anomalous Hall effect (AHE) whose sign can be readily modified. Here, a hydrogen spillover method is used to tailor the properties of SRO thin films via hydrogen incorporation. It is found that the magnetization and Curie temperature of the films are strongly reduced and, at the same time, the structure evolves from an orthorhombic to a tetragonal phase as the hydrogen content is increased up to ≈0.9 H per SRO formula unit. The structural phase transition is shown, via in situ crystal truncation rod measurements, to be related to tilting of the RuO6 octahedral units. The significant changes observed in magnetization are shown, via density functional theory (DFT), to be a consequence of shifts in the Fermi level. The reported findings provide new insights into the physical properties of SRO via tailoring its lattice symmetry and emergent physical phenomena via the hydrogen spillover technique

Temperature anomalies in transition-metal-oxides and their correlations with photocatalytic activity: structural, dielectric and electrical characterisation of titania systems

Annealing titania in vacuum while an external electrical field was applied resulted in the observation of structural, morphological and electrical anomalies. However, treating titania in vacuum leads to a redistribution of lattice defects. The diffusion of these lattice defects forms charge carrier trapping sites and permanent dipoles. The alignment of these dipoles leads to the formation of anisotropic conductive channels. Furthermore, the redistribution of lattice defects results in a new crystalline phase

Artificially steering electrocatalytic oxygen evolution reaction mechanism by regulating oxygen defect contents in perovskites.

The regulation of mechanism on the electrocatalysis process with multiple reaction pathways is more efficient and essential than conventional material engineering for the enhancement of catalyst performance. Here, by using oxygen evolution reaction (OER) as a model, which has an adsorbate evolution mechanism (AEM) and a lattice oxygen oxidation mechanism (LOM), we demonstrate a general strategy for steering the two mechanisms on various LaxSr1-xCoO3-δ. By delicately controlling the oxygen defect contents, the dominant OER mechanism on LaxSr1-xCoO3-δ can be arbitrarily transformed between AEM-LOM-AEM accompanied by a volcano-type activity variation trend. Experimental and computational evidence explicitly reveal that the phenomenon is due to the fact that the increased oxygen defects alter the lattice oxygen activity with a volcano-type trend and preserve the Co0 state for preferably OER. Therefore, we achieve the co-optimization between the activity and stability of catalysts by altering the mechanism rather than a specific design of catalysts.Min Lu, Yao Zheng, Yang Hu, Bolong Huang, Deguang Ji, Mingzi Sun, Jianyi Li, Yong Peng, Rui Si, Pinxian Xi, Chun-Hua Ya

Pseudo-piezoelectricity in calcium titanate and structural changes under electric field

Calcium titanate does not exhibit piezoelectric behaviour. However, in present study such behaviour is observed in calcium titanate prepared by sol-gel synthesis and densified by field assisted sintering. Presumably, the instability of regular TiO6 octahedra results in the off-centering of titanium positions in nanostructured bulk calcium titanate. As a consequence, piezoelectric behavior is observed in calcium titanate which is referred to "pseudo-piezoelectricity". This particular response is of great interest in biomedicine because it can improve osseointegration of implant materials.Die vorliegende Arbeit weist piezoelektrisches Verhalten von Calciumtitanat nach, das mittels Sol-Gel Synthese hergestellt und mittels Feld-Aktiviertem Sintern verdichtet wurde. Vermutlich verursacht die Instabilität regulärer TiO6 Oktaeder eine Verschiebung der Positionen von Titanatomen in Festkörpern aus nanostrukturiertem Calciumtitanat. Daher kann piezoelektrisches Verhalten, genannt "Pseudopiezoelektrizität", in Calciumtitanat beobachtet werden. Dieses Ergebnis ist von großem Interesse für biomedizinische Anwendungen zur Verbesserung der Osseointegration von Implantatmaterialien

A rapid and low-cost novel biosensor for the detection of early-stage chronic kidney disease

There is an unmet medical need for the effective detection of early-stage kidney disease as many current techniques lack the accuracy to detect it early on. Therefore, most patients are diagnosed at a later phase when irreversible kidney damage has already been done. Blood tests typically detect serum creatinine however this can be unreliable and require laboratory and trained personnel. Within this thesis a metal oxide gas sensor has been developed to detect the volatile organic compound (VOC) trimethylamine (TMA), known to be elevated in early disease stages, via patients expired breath. Aerosol assisted chemical vapour deposition (AACVD) was chosen for its simplicity and ability to produce thin reproducible films without vacuum. Consequently molybdenum oxide (MoO3) thin films were successfully deposited by AACVD and used for the sensing of TMA. Films were further modified with cerium and gold to increase the sensitivity and performance of the sensors, and a variety of characterisation techniques were used such as scanning electron microscopy with coupled energy dispersive spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy to explore the crystallinity and properties of the optimised sensor films. The sensor was then evaluated successfully using simulated kidney disease patient breath in order to test its feasibility in practice. Finally, initial studies into the use of silicon carbide-tungsten core fibres were investigated as a potential for a next generation self-heating integrated substrate for molybdenum oxide sensors and the detection of TMA gas