TiO<sub>2</sub> thin film photocatalysis has suffered from poor photocatalytic efficiency due to its low surface area-to-volume ratio. The efficiency can be enhanced by narrowing the bandgap, defect engineering or introducing surface plasmonic effect. However, the fabrication process is normally complicated and time consuming. This work offers a simple method to fabricate disordered defect-rich black TiO<sub>2</sub> ultrathin film by atomic layer deposition (ALD). Surface defects of TiO2 have been suggested to play a significant role in the process of photocatalysis. With ALD, the bandgap and surface defects of the material can be controlled effectively through the deposition parameters. Surface plasmonic effects could also be introduced by the deposition of Ag nanoclusters via simple thermal evaporation. Absorption at ~450 nm was significantly enhanced. The overall photocatalytic behavior of composite material is greatly boosted and we observed an excellent efficiency towards the degradation of organic pollutants such as bisphenol A. The mechanism of surface plasmonic enhanced black TiO<sub>2</sub> photocatalysis was studied by in-situ infrared atomic force microscope (IR-AFM) under the illumination of different wavelength. The reaction sites of the composite materials were determined accurately and the working mechanism was discussed.
Metal oxide materials for solid state gas sensors has attracted lots of attention in the past few decades due to its low fabrication cost, small device size and potential application in toxic gases detection. SnO<sub>2</sub> is one of the favorable materials since it has outstanding performance towards the detection of various gases. Its sensing mechanism in brief was based on the change in charge carrier density of the materials due to the presence of gas molecules and the change was determined by measuring the resistance or capacitance. Despite of its great success, researches has continue to further optimize the selectivity, sensitivity, response time and more importantly lowering the working temperature of the material. In this work, SnO<sub>2</sub> nanostructures with metal nanoclusters on the surface was prepared. The incorporation of different metal nanoclusters would offer feasibility on the selection of gas detection. The energy level alignment and the Schottky barriers at the metal-metal oxide interface would further improve the sensitivity and response time of the materials. The surface plasmon generated by the metal nanoclusters utilizing visible light could lower the operation temperature and enhance sensitivity by offering more charge carriers. The SnO<sub>2</sub> nanofiber in this work was prepared by a scalable electrospinning method and the Ag and Au nanoclusters were prepared by sputtering or thermal evaporation. Effect of the SnO<sub>2</sub> morphology, size and distribution of the metal nanoclusters and the illumination on the device performance will be investigated and the detail working mechanism will be discussed.