Vertically grown cadmium sulfide ͑CdS͒ nanowire ͑NW͒ arrays were prepared using two different processes: hydrothermal and physical vapor deposition ͑PVD͒. The NWs obtained from the hydrothermal process were composed of alternating hexagonal wurtzite ͑WZ͒ and cubic zinc blende ͑ZB͒ phases with growth direction along WZ ͗0001͘ and ZB ͓111͔. The NWs produced by PVD process are single crystalline WZ phase with growth direction along ͗0001͘. These vertically grown CdS NW arrays have been used to converting mechanical energy into electricity following a developed procedure ͓Z. L. Wang and J. Song Science 312, 242 ͑2006͔͒. The basic principle of the CdS NW nanogenerator relies on the coupled piezoelectric and semiconducting properties of CdS, and the data fully support the mechanism previously proposed for ZnO NW nanogenerators and nanopiezotronics.

Energy shortage and global warming are two grand challenges to human beings in the 21st century. The development of clean alternative energies and emission control of gases, such as CO 2 , have become most-urgent research fields. For the development of clean alternative energies, a wide range of approaches has been explored, including solar cells, [1] fuel cells, [2] and thermoelectric devices.[3] Solar cells, fuel cells, and thermoelectric devices convert optical, chemical, and thermal energies to electrical energy, respectively. Generation of electric energy from conversion of mechanical energy is of great interest owing to its abundance and unique fit for some applications. Recently, ZnO-nanowire (NW)-array-based piezoelectric nanogenerators have been demonstrated to convert mechanical energy to electricity by utilizing the coupling effect of the semiconducting and piezoelectric properties of ZnO. [4][5][6] Further exploration of this piezotronic concept [7] has led to the development of a wide variety of ZnO-NW-based piezotronic devices, such as piezoelectric field effect transistors, [8] nanoforce sensors, [8] and gate diodes.[9]More recently, CdS NWs were also successfully demonstrated for piezoelectric nanogenerators.[10] As another member in the wurtzite family, CdS is a piezoelectric, semiconducting, [11] and optoelectric [12] material with a direct energy band gap of about 2.5 eV [13] (corresponding to an on-set absorption of 500 nm). A wide range of 1D CdS nanostructures such as NWs, [14] NW arrays, [15] nanobelts, [16] nanotubes, [17] nanocombs, [18] and tetrapods, [19] have been synthesized by wet-chemistry or vapor-phase processes. The photon-induced conduction of 1D CdS nanostructures has also been demonstrated and studied. [20] A wide variety of 1D CdS nanostructure-based optoelectronic devices, such as photoconductors, [20] waveguides, [21] lasers, [22] logic gates, [23] field emitters, [24] and field-effect transistors (FETs) [25,26] have been developed.

The Schottky contact based photon detection was demonstrated using CdS ͑visible light responsive͒, silicon ͑indirect n-type oxygen-non-adsorbing͒, and CuO ͑indirect p-type oxygen-adsorbing͒ nanowire nanosensors. With changing one of the two nanowire-electrode contacts from ohmic to Schottky, detection sensitivities as high as 10 5 % were achieved by the CdS nanowire nanosensor operated at the reverse bias mode of Ϫ8 V, which was 58 times higher than that of the corresponding ohmic contact device. The reset time was also significantly reduced. In addition, originally light nonresponsive silicon and CuO nanowires became light responsive when fabricated as a Schottky contact device. These improvements in photon detection can be attributed to the Schottky gating effect realized in the present nanosensor system by introducing a Schottky contact.

Preparation of coaxial (core–shell) CdS–ZnS and Cd1–xZnxS–ZnS nanowires has been achieved via a one‐step metal–organic chemical vapor deposition (MOCVD) process with co‐fed single‐source precursors of CdS and ZnS. Single‐source precursors of CdS and ZnS of sufficient reactivity difference were prepared and paired up to form coaxial nanostructures in a one‐step process. The sequential growth of ZnS on CdS nanowires was also conducted to demonstrate the necessity and advantages of the precursor co‐feeding practice for the formation of well‐defined coaxial nanostructures. The coaxial nanostructure was characterized and confirmed by high‐resolution transmission electron microscopy and corresponding energy dispersive X‐ray spectrometry analyses. The photoluminescence efficiencies of the resulting coaxial CdS–ZnS and Cd1–xZnxS–ZnS nanowires were significantly enhanced compared to those of the plain CdS and plain Cd1–xZnxS nanowires, respectively, owing to the effective passivation of the surface electronic states of the core materials by the ZnS shell.

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A Tris-chelated diselenophosphato complex of bismuth, Bi[Se 2 P(OiPr) 2 ] 3 , was successfully prepared and used to obtain two separate, uniform deposits of nanostructured metal phosphate, BiPO 4 , and metal chalcogenide, Bi 2 Se 3 , in a one-step metal-organic chemical vapor deposition process. This work expands the applications of single-source precursors in a new dimension by producing two separate, uniform products from decomposition of a single-source precursor in one step. The inclusion of oxygen and phosphorus elements in the precursor molecule makes possible the simultaneous production of BiPO 4 nanowires and Bi 2 Se 3 nanoplates from the single-source precursor. The resulting BiPO 4 nanowires and Bi 2 Se 3 nanoplates show promising field emission properties, comparable to the more popular oxide semiconductor nanowires. The Bi 2 Se 3 nanoplates also exhibit a superior thermoelectric property over bulk Bi 2 Se 3 .

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In this work, thin films of pure Cu, and Cu with 0.02 or 2.98 wt % Ti were deposited on SiO 2 covered Si substrates. The samples were annealed at 500-800°C in vacuum to investigate their morphological evolution, interfacial reaction, and diffusion. X-ray diffraction reveals Cu͑111͒ and Cu͑200͒ peaks for pure Cu and Cu͑0.02 wt % Ti͒ films. However, the Cu͑2.98 wt % Ti͒ film exhibits a very weak Cu͑200͒ peak, indicating that this film is textured in ͗111͘ orientation. Concurrently, scanning electron microscopy shows that the grain size of the Cu͑2.98 wt % Ti͒ film is significantly smaller than those of pure Cu and Cu͑0.02 wt % Ti͒ films. In addition, Cu͑2.98 wt % Ti͒ film remains smooth after annealing up to 800°C, while the other two films become discontinuous. X-ray photoelectron spectroscopy indicates that a TiO x layer has formed at the Cu(0.02 wt % Ti)/SiO 2 and Cu(2.98 wt % Ti)/SiO 2 interfaces after 700°C annealing. Nevertheless, the TiO x layer is thicker in the Cu͑2.98 wt % Ti͒ system than in the Cu͑0.02 wt % Ti͒ system. Consequently, the Cu͑2.98 wt % Ti͒ film shows no diffusion of Cu into SiO 2 at temperatures up to 700°C. Connections between the segregation of Ti addition and the morphological/interfacial characteristics are discussed.