Here we present for the first time a study of the photoresistive properties and dynamics of ordered, high-density arrays of germanium nanowire photoresistors. Germanium is a wellknown semiconducting material with an indirect bandgap, E g , of approximately 0.66 eV (temperature T = 300 K) [1] and has been widely used for the fabrication of photodetectors, [2][3][4][5] radiation detectors, [6][7][8] charged particle and photon tracking devices, [9] far-infrared photoresistors, [10] and numerous other devices. [11] During the last few years there has also been increasing interest in the use of nanostructures (quantum dots and wires) of both germanium and silicon as materials for potential applications in sensors, nanophotonics, and nanoelectronics. [12][13][14] However, in order to successfully integrate onedimensional semiconductors into useful devices, ordered architectures of aligned nanowires are required. Using templates such as anodized aluminium oxide (AAO) [15,16] or mesoporous materials [17,18] as hosts for nanowires offers a viable method for forming high-density arrays of ordered, crystalline nanowires. Significantly, AAO membranes with ordered and highly oriented pore structures have recently been synthesized on silicon substrates, [19,20] which is very promising for the integration of such materials into current complementary metal oxide semiconductor technologies. At University College Cork we have developed supercritical-fluid-inclusion phase methods for forming semiconductor [21][22][23] and metal/ semiconductor core/shell [24] nanowires and nanotubes within the pores of mesoporous matrices and AAO membranes.Supercritical-fluid-inclusion methods are ideal solvents for forming high-density arrays of nanowires within AAO templates as they do not suffer from the inherent problem of pore blocking associated with other methods, such as electrodeposition and incipient wetness techniques. The electrical conductivity and photoluminescence properties of semiconductor nanowire arrays have been investigated by several research groups. [25][26][27][28] However, photoconductivity measurements on ordered semiconducting nanowire arrayshave not yet been performed. An investigation into the photoconductivity of ordered arrays of nanowires is important in order to fully understand their potential in future photodetection devices, for example, as photoresistors or photodiodes. In this paper, we report the photoconductive properties of germanium nanowire photoresistors with mean diameters of 50 and 100 nm, incorporated within the pores of AAO membranes. A comparative study of the photoresistive properties of germanium nanowire photoresistor arrays with different optically transparent electrodes, namely ultrathin gold films and tin-doped indium tin oxide (ITO) layers, is described in this paper. ITO is a well known n-type semiconductor widely used in the fabrication of transparent electrodes in various optoelectronic devices. [29] To our knowledge, this study is the first analysis of photoconductivity in ordered semicond...

The kinetics of electrocatalytic oxidation of ascorbate was studied on a series of redox self-assembled monolayers (SAMs) of the general formula Fc(CH2)4COO(CH2)nSH as electron-transfer mediators, where Fc is the ferrocenyl group and n = 3, 6, 9, and 11. We show that the rate of electron transfer from ascorbate to the surface-confined Fc+ decreases with increasing n. The rationale for the dependence of the rate of electrocatalytic activity and n, in the presence of ClO4, is obtained from Fourier-transform surface-enhanced Raman spectroscopy (FT-SERS), cyclic voltammetry, and electrochemical quartz crystal microbalance (EQCM) data. In particular, FT-SERS shows decreasing amounts of surface-bound ClO4- upon oxidation of the ferrocene with decreasing n, while EQCM data show the effective electrode mass increase was consistently higher on the shorter chain SAMs. This mass increase is likely due to increasing ferricinium cation hydration. As n decreases, the SAMs become less ordered (FT-SERS data), as is widely known from previous literature. Disorder favors water penetration into the SAM, which, in turn, increases the hydration of the Fc+ (EQCM data). Increased hydration of the Fc+ impedes the formation of Fc+-ClO4- ion pairs (EQCM and FT-SERS data), which, consequently, accelerates the electrocatalytic electron transfer from the solution-dissolved ascorbate.

We present the experimental and theoretical study of correlation effects in epitaxial SrRuO 3 thin films. Experimentally, we have performed resonant ultraviolet photoemission spectroscopy (UPS) and angle-resolved hard x-ray photoemission spectroscopy (HAXPES) measurements. For resonant UPS, the two methods, Fanoprofile fitting of constant initial state spectra and the energy distribution curves equidistant difference spectra, were used to extract Ru 4d partial spectral weight (PSW) in the valence band. We find Ru 4d PSW possessing a clearly pronounced coherent peak at the Fermi level together with angle-resolved HAXPES spectra demonstrating no difference in surface and bulk electronic structure. From comparison of experimental data with theoretical calculations done at density functional theory level, we conclude that SrRuO 3 is a weakly correlated material and electronic structure of it can be consistently described employing first-principles approaches.

Thin LaNiO 3−δ films with pseudocubic (100) preferred orientation were prepared by reactive DC magnetron sputtering and in situ annealed in O2 and vacuum. X-ray photoelectron spectroscopy (XPS) was used to determine the variation in composition of the films under high temperature annealing. The experimental O 1s and La 3d -Ni 2p 3/2 spectra of LaNiO 3−δ films was analysed in terms of O 2− , O − /(OH) − , and weakly adsorbed oxygen species. It was shown that the change in the type of conductivity from metallic to semiconducting one is accompanied by a marked increase in the intensity of the lateral (∼531 eV) peak of oxygen. The quantitative analyses of La 3d -Ni 2p 3/2 spectra show that the Ni/La concentration ratio significantly decreases after heating above the dehydration temperature. These variations in conductivity and surface composition were attributed to the loss of lattice oxygen with subsequent adsorption of O − and (OH) − anions and weakly adsorbed oxygen species from ambient air.

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