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In nanoscience and nanotechnology, it is very attractive to develop self-powered nanodevices with the use of nanogenerators replacing batteries. In this way, one could realize independent and continuous operations of implantable biosensors, microelectromechanical systems, nanorobots and even portable personal electronics.[1] Moreover, due to the current energy crisis, it would be even more alluring if the generators can harvest the wasted energy in the environment, such as body-movement, light wind and vibration of acoustic waves.[2] By focusing on these applications, great progress has been made in developing piezoelectric nanogenerators using ZnO nanowires, [3] CdS nanowires, [4] ZnS nanowires, [5] PZT nanofibers, [6] and GaN nanorods, [7] which give great promise for the integration of piezotronics and nanoelectronics.Group-III nitride semiconductors, highlighted for their tunable, direct band gap and good chemical stability, [8] also have a pronounced piezoelectric property owing to their wurtzite crystal structures. In terms of the coupling between their piezoelectric and semiconducting properties, an output power should be generated by scanning an atomic force microscope (AFM) tip in contact mode across 1D group-III nitride nanomaterials. In this study, a family of 1D group-III nitrides, including AlN and AlGaN nanocones, GaN nanorods and InN nanocones, are synthesized through a facile chemicalvapor-deposition (CVD) route based on previous work. [9] Increasing electricity generation is demonstrated following the sequence: AlN, AlGaN, GaN and InN, which can be attributed to the increasing piezoelectric potential and carrier density. These results not only extend piezotronics to a new domain of group-III nitrides, but also deepen the understanding of the underlying physics of piezoelectric nanogenerators. Figure 1 shows scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of the quasialigned arrays of AlN nanocones, AlGaN nanocones, GaN nanorods and InN nanocones, with diameters at the middle of around 100, 70, 500, and 700 nm, and the lengths of about 2, 1, 3.5, and 4 mm, respectively. The nanostructures preferentially stand perpendicularly on the Si substrates. Due to the relatively large sizes of the GaN nanorods and InN nanocones, their hexagonal intersections are obvious, and are determined by their common family crystal structure.[10] The corresponding highresolution transmission electron microscopy (HRTEM) images and selected-area electron-diffraction (SAED) patterns (insets of Fig. 1b, 1d [11] GaN, and InN, respectively. X-ray diffraction (XRD) profiles of these samples are shown in Figure 2, and could be indexed to hexagonal wurtzite AlN, Al 0.33 Ga 0.67 N (based on Vegard's law [12] ), GaN and InN (JCPDS card No 65-0832, 50-0792, 50-1239). The much-stronger intensity of the (002) peak relative to the corresponding standard diffraction pattern indicates preferential growth along the c-axis, [9] in agreement with the SAED patterns.In the demonstration of piezoelectric ...

Good understanding of the reaction mechanism in the electrochemical reduction of water to hydrogen is crucial to renewable energy technologies. Although previous studies have revealed that the surface properties of materials affect the catalytic reactivity, the effects of a catalytic surface on the hydrogen evolution reaction (HER) on the molecular level are still not well understood. Contrary to general belief, water molecules do not adsorb onto the surfaces of 3C-SiC nanocrystals (NCs), but rather spontaneously dissociate via a surface autocatalytic process forming a complex consisting of -H and -OH fragments. In this study, we show that ultrathin 3C-SiC NCs possess superior electrocatalytic activity in the HER. This arises from the large reduction in the activation barrier on the NC surface enabling efficient dissociation of H(2)O molecules. Furthermore, the ultrathin 3C-SiC NCs show enhanced HER activity in photoelectrochemical cells and are very promising to the water splitting based on the synergistic electrocatalytic and photoelectrochemical actions. This study provides a molecular-level understanding of the HER mechanism and reveals that NCs with surface autocatalytic effects can be used to split water with high efficiency thereby enabling renewable and economical production of hydrogen.

Hydrogen generated by water splitting provides a renewable energy source, but development of materials with efficient electrocatalytic water splitting capability is challenging. Thin-film electrocatalytic material (H 2 −NiCat) with robust water reduction properties, which can be readily prepared by a reduction-induced electrodeposition method from nickel salts in a borate-buffered electrolyte (pH 9.2), is reported. The material consists of nanoparticles with nickel oxide or hydroxide species located at the surface and metallic nickel in the bulk. The catalyst mediates H 2 evolution in a near-neutral aqueous buffer at low overpotential. The catalyst requires a subsequent oxidative pretreatment in order to attain a well-defined hydrogen evolution reaction (HER) activity, and the 1.5 h anodized catalyst film exhibits a HER current density of about 1.50 mA cm −2 at 0.452 V overpotential over a period of 24 h with no observable corrosion. In addition, it can be converted by anodic equilibration into an amorphous Ni-based oxide film (O 2 −NiCat) to catalyze O 2 evolution, and the switch between the two catalytic forms is fully reversible. The robust, bifunctional, switchable, and noble-metal-free catalytic material has immense potential in artificial solar water-splitting devices.

AlGaN ternary alloys have unique properties suitable for numerous applications due to their tunable direct band gap from 3.4 to 6.2 eV by changing the composition. Herein we report a convenient chemical vapor deposition growth of the quasi-aligned Al(x)Ga(1-x)N alloy nanocones over the entire composition range. The nanocones were grown on Si substrates in large area by the reactions between GaCl(3), AlCl(3) vapors, and NH(3) gas under moderate temperature around 700 °C. The as-prepared wurtzite Al(x)Ga(1-x)N nanocones have single-crystalline structure preferentially growing along the c-axis, with homogeneous composition distribution, as revealed by the characterizations of electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and selected area electron diffraction. The continuous composition tunability is also demonstrated by the progressive evolutions of the band edge emission in cathodoluminescence and the turn-on and threshold fields in field emission measurements. The successful preparation of Al(x)Ga(1-x)N nanocones provides the new possibility for the further development of advanced nano- and opto-electronic devices.

Highly oriented SiC porous nanowire (NW) arrays on Si substrate have been achieved via in situ carbonizing aligned Si NW arrays standing on Si substrate. The resultant SiC NW arrays inherit the diameter and length of the mother Si NW arrays. Field emission measurements show that these oriented SiC porous NW arrays are excellent field emitter with large field emission current denstity at very low electric field. The in situ conversion method reported here might be exploited to fabricate NW arrays of other materials containing silicon.

Uniformly cut In2O3 truncated octahedrons are fabricated on a large scale by a simple chemical vapor deposition (CVD) technique. This theoretical analysis predicts that the emergence of {100} facets on the In2O3 truncated octahedrons enhances oxygen evolution significantly in photocatalysis and experimental photoelectrochemical measurements are consistent.

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