Xiaohu Huang

Metal-insulator transition in SrTiO(3-x) thin films induced by frozen-out carriers.

Z. Q. Liu, D. P. Leusink, X. Wang, W. M. Lü, K. Gopinadhan, A. Annadi, Y. L. Zhao, X. H. Huang, S. W. Zeng, Z. Huang, A. Srivastava, S. Dhar, T. Venkatesan, and Ariando1,2∗ NUSNNI-Nanocore, Department of Physics, Department of Electrical and Computer Engineering, National University of Singapore, Singapore and Faculty of Science and Technology and MESA Institute for Nanotechnology, University of Twente, 7500 AE Enschede, The Netherlands (Dated: January 13, 2013)

Pulsed electrodeposition of single-crystalline Bi2Te3 nanowire arrays

Thermoelectric material Bi2Te3 nanowire arrays have been successfully prepared by pulsed electrochemical deposition into the nanochannels of porous anodic alumina membranes. X-ray diffraction analyses show that the as-synthesized nanowires have a highly preferential orientation. Scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy observations indicate that the high-filling-rate and uniform Bi2Te3 nanowires are single crystalline. Energy dispersive spectrometer analyses indicate that the compositions of the nanowires can be controlled by changing the potentials and the solution concentrations. The electrical resistance measurements indicate that the resistances increase with decreasing temperature and show a typical semiconductor characteristic. The growth mechanism is discussed together with the electrochemical deposition process studies.

Rayleigh-instability-driven simultaneous morphological and compositional transformation from Co nanowires to CoO octahedra

Arrays of regularly distributed CoO nano-octahedra are obtained by annealing Co nanowires at high temperatures. Both the size and the separation distance of the nano-octahedra can be controlled by tuning the annealing temperature. These self-assembled linear arrays of CoO nanocrystals result from the synergetic combination of the morphological transformation due to the intrinsic Rayleigh instability and the phase transformation due to the cobalt oxidation.

Green luminescence from Cu-doped ZnO nanorods: Role of Zn vacancies and negative thermal quenching

Bright and stable structured green luminescence (GL) is achieved from solution-grown Cu-doped ZnO nanorods. Dependence of photoluminescence on the annealing parameters reveals that GL is correlated with creation of Zn vacancies (VZn) and then formation of Cu dopants at Zn sites (CuZn). High internal quantum efficiency (43%) of the GL can be sustained up to 240 K due to negative thermal quenching. In contrast to the poor stability of defects-related visible emission, the structured GL shows good stability with respect to sample heating. Cu-doped ZnO nanorods with strong and stable GL have potential applications in visible light display and lighting.

Universal photoluminescence evolution of solution-grown ZnO nanorods with annealing: important role of hydrogen donor

Poor near-band-edge emission (NBE) prohibits the application of solution-grown ZnO nanorods in optoelectronics, thus their photoluminescence (PL) was studied with respect to post-annealing temperature and duration. A universal behavior was revealed: NBE was enhanced by one order (or two) of magnitude after annealing in air (or H2) at about 425 °C for 30 min, while the enhancement factor starts to decrease after annealing at higher temperatures. The evolution of PL was mainly ascribed to annealing-induced activation and dissociation of hydrogen donor, which was identified as HO by both PL and Raman analyses. Results from nanorods with different diameters and annealing gases further support this assignment. The results provide new insights to understand and optimize the properties of solution-grown ZnO.

Magnetic properties of single crystalline Co nanowire arrays with different diameters and orientations

Single crystalline Co nanowire arrays with different diameters and orientations were grown within porous anodic alumina membranes by a pulsed electrodeposition technique and the magnetic properties of the nanowire were systematically studied. It was found that the magnetization behavior of the Co nanowire arrays is anisotropic and their magnetic properties can be effectively modulated through tuning either the diameter or the orientation of the nanowires. The magnetic properties of the Co nanowires were discussed qualitatively by using the classical magnetization theory and single domain model.

Controlled Manipulation and in Situ Mechanical Measurement of Single Co Nanowire with a Laser-Induced Cavitation Bubble

The flow induced by a single laser-induced cavitation bubble is used to manipulate individual Co nanowires. The short-lived (<20 μs) bubble with a maximum size of 45 μm is created in an aqueous solution with a laser pulse. Translation, rotation, and radial motion of the nanowire can be selectively achieved by varying the initial distance and orientation of the bubble with respect to the nanowire. Depending on the initial distance, the nanowire can be either pushed away or pulled toward the laser focus. No translation is observed for a distance further than approximately 60 μm, while at closer distance, the nanowire can be bent as a result of the fast flow induced during the bubble collapse. Studying the dynamics of the shape recovery allows an estimation of the Youngs modulus of the nanowire. The low measured Youngs modulus (in a range from 9.6 to 13.0 GPa) of the Co nanowire is attributed to a softening effect due to structural defects and surface oxidation layer. Our study suggests that this bubble-based technique allows selectively transporting, orienting, and probing individual nanowires and may be exploited for constructing functional nanodevices.

Template Epitaxial Growth of Thermoelectric Bi/BiSb Superlattice Nanowires by Charge-Controlled Pulse Electrodeposition

Bi/BiSb superlattice nanowires SLNWs with a controllable and very small bilayer thickness and a sharp segment interface were grown by adopting a charge-controlled pulse electrodeposition. The deposition parameters were optimized to ensure an epitaxial growth of the SLNWs with a preferential orientation. The segment length and bilayer thickness of the SLNWs can be controlled simply by changing the modulating time, and the consistency of the segment length can be well maintained by our approach. The Bravais law in the electrodeposited nanowires is verified by the SLNW structure. The current‐voltage measurement shows that the SLNWs have good electrical conductance, particularly those with a smaller bilayer thickness. The Bi/BiSb SLNWs might have excellent thermoelectric performances.

Solution-Grown ZnO Films toward Transparent and Smart Dual-Color Light-Emitting Diode.

An individual light-emitting diode (LED) capable of emitting different colors of light under different bias conditions not only allows for compact device integration but also extends the functionality of the LED beyond traditional illumination and display. Herein, we report a color-switchable LED based on solution-grown n-type ZnO on p-GaN/n-GaN heterojunction. The LED emits red light with a peak centered at ∼692 nm and a full width at half-maximum of ∼90 nm under forward bias, while it emits green light under reverse bias. These two lighting colors can be switched repeatedly by reversing the bias polarity. The bias-polarity-switched dual-color LED enables independent control over the lighting color and brightness of each emission with two-terminal operation. The results offer a promising strategy toward transparent, miniaturized, and smart LEDs, which hold great potential in optoelectronics and optical communication.

Initial Growth of Single-Crystalline Nanowires:From 3D Nucleation to 2D Growth

The initial growth stage of the single-crystalline Sb and Co nanowires with preferential orientation was studied, which were synthesized in porous anodic alumina membranes by the pulsed electrodeposition technique. It was revealed that the initial growth of the nanowires is a three-dimensional nucleation process, and then gradually transforms to two-dimensional growth via progressive nucleation mechanism, which resulting in a structure transition from polycrystalline to single crystalline. The competition among the nuclei inside the nanoscaled-confined channel and the growth kinetics is responsible for the structure transition of the initial grown nanowires.