The nucleation and growth of palladium clusters supported on anatase TiO 2 (101) surface has been studied using periodic supercell models and density functional theory. The most active site for single Pd adatom on the perfect TiO 2 (101) surface is the bridge site formed by two two-coordinated oxygen (2cO) atoms at the step edge with the highest adsorption energy of 2.18 eV. On the defective surface, the effect of oxygen vacancy on Pd nucleation is not as strong as that in the Pt or Au deposition case. The shift of active sites for the Pd dimer growing to trimer on the perfect anatase TiO 2 (101) surface is observed. On both perfect and defective anatase surfaces, the adsorbed Pd 3 clusters prefer to form planar triangles and the adsorbed Pd 4 and Pd 5 clusters tend to three-dimensional structures. The nucleation and growth of Pd clusters at the anatase TiO 2 (101) surface is mainly driven by the interaction between Pd and surface atoms when the cluster size is less than four. The strength of Pd-Pd interaction turns out to control dominantly the Pd deposition process as the Pd cluster gets larger.
In this study, we design and demonstrate a novel type of self-powered UV photodetectors (PDs) using single-crystalline ZnS nanotubes (NTs) as the photodetecting layer and Ag nanowires (NWs) network as transparent electrodes. The self-powered UV PDs with asymmetric metal-semiconductor-metal (MSM) structure exhibit attractive photovoltaic characteristic at 0 V bias. Device performance analysis reveals that the as-assembled PDs have a high on/off ratio of 19173 and a fast response speed (τr = 0.09 s, τf = 0.07 s) without any external bias. These values are even higher than that of ZnS nanostructures- and ZnS heterostructure-based PDs at a large bias voltage. Besides, its UV sensivity, responsivity and detectivity at self-powered mode can reach as high as 19172, 2.56 A/W and 1.67 × 1010 cm Hz1/2 W−1, respectively. In addition, the photosensing performance of the self-powered UV PDs is studied in different ambient conditions (e.g., in air and vacuum). Moreover, a physical model based on band energy theory is proposed to explain the origin of the self-driven photoresponse characteristic in our device. The totality of the above study signifies that the present self-powered ZnS NTs-based UV nano-photodetector may have promising application in future self-powered optoelectronic devices and integrated systems.
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