Rui Zhu

Peking University, Peping, Beijing, China

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Publications (18)67.48 Total impact

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    ABSTRACT: Anisotropic polymetallic hollow nanostructures are highly desired for many applications because of their unique morphology, large specific surface areas and attractive electronic effects. Here, a simple method using gold nanorods as a self-sacrificed template has been developed for the fabrication of hollow dumbbell-like nanorods of Au@PtAg. The formation of the hollow structures involves the growth of another metallic shell first, and then the etching of gold nanorods, which is induced by oxygen and ascorbic acid. The lattice mismatch and cohesive energy of the shell, along with its surface passivation, greatly affect the subsequent etching and the resulting products, as has been demonstrated by a positive control in the case of Rh and a negative control in the case of Pd. Hollow dumbbell-like nanorods of Au@PtAg show great enhancement for the dehydrogenation pathway in the oxidation of formic acid, as compared to solid Au@PtAg nanorods, PtAu nanotubes and commercial Pt/C.
    Nanoscale 08/2014; · 6.73 Impact Factor
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    ABSTRACT: Controlled growth of hybrid metallic nanocomposites for a desirable structure in a combination of selected components is highly important for their applications. Herein, the controllable growth of RhAg on the gold nanorods is achieved from the dumbbell-like RhAg-tipped nanorods to the brushy RhAg-coated nanorods, or the rod-like Au@Ag-Rh nanorattles. These different growth modes of RhAg on the gold nanorods are correlated with the reducing kinetics of RhCl3 and AgNO3. In view of the promising catalytic properties of Rh, the gold nanorods modified by RhAg in different structures are examined as catalysts for the oxidation of o-phenylenediamine. It is found that brushy RhAg-coated nanorods present a higher catalytic efficiency than dumbbell-like RhAg-tipped nanorods and rod-like Au@Ag-Rh nanorattles. These results would benefit the overgrowth control on the one-dimensional metallic nanorods and the rational design of new generation heterogeneous catalysts and optical devices.
    Nanoscale 03/2014; · 6.73 Impact Factor
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    ABSTRACT: In purely bent ZnO microwires, the excitons can be effectively driven and concentrated by the elastic strain-gradient towards the tensile outer side of the purely bent wire. Experimental and theoretical approaches are combined to investigate the dynamics of excitons in inhomogeneous strain field with uniform elastic strain-gradient. Cathodoluminescence spectroscopy analysis on purely bent ZnO microwires verifies that excitons can be effectively driven and concentrated along the elastic strain-gradient.
    Advanced Materials 01/2014; · 14.83 Impact Factor
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    ABSTRACT: The formation mechanism of experimentally observed epitaxial morphologies on (000 ± 1) polar surfaces of ZnO microwire was studied by density functional theory simulation of atomic step models on both polar surfaces. In situ observations by environmental scanning electron microscopy were employed to control and detect the morphology evolutions during the epitaxial growth process. Edge formation energies for representative step models were calculated as a function of Zn chemical potential. The energetically favorable step structures were determined under different conditions, which could be related to certain surface morphologies regarding the aspects of crystallography and growth kinetics. Our experiments can be well explained by theoretical simulations.
    CrystEngComm 05/2013; 15(21):4249-4254. · 3.88 Impact Factor
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    ABSTRACT: The stability and surface evolution of solid-state nanopores in aqueous solutions are extremely important since they would get immersed in solutions during DNA translocation experiment for DNA analyses. In this work, we systematically studied the size evolution of SiN nanopores in ethanol, deionized water and potassium chloride (KCl) solutions by careful surface characterization and composition analyses using a transmission electron microscope. Surprisingly, we found that nanopores closed up completely in ethanol in an hour and showed a 30% and 20% size decrease in deionized water and KCl solutions, respectively. Strong evidence of surface oxidation was found by composition analyses in the nanopore area. Nanopore size evolution was strongly dependent on initial pore size and solution pH value. In pH = 13 KCl solution, SiN nanopores were observed to increase in size instead of decrease. The results not only provide useful information for DNA detection based on solid-state nanopores, but can also guide design and application of other nanodevices exposed to electrolyte-solvent systems such as cell-on-a-chip devices and biosensors.
    Nanoscale 03/2012; 4(5):1572-6. · 6.73 Impact Factor
  • Advanced Science Letters. 01/2012; 5(1):192.
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    ABSTRACT: Polarity-dependent homo-epitaxy on (0001)-Zn and (000)-O surfaces of cleaved ZnO microwires was investigated by in situ growth in ESEM and DFT simulations. ZnO monomers adsorption, adatoms desorption and chemisorption were simulated to understand the explicit mechanism.
    CrystEngComm 12/2011; 14(2):355-358. · 3.88 Impact Factor
  • Advance Science Letters. 11/2011; 4(11-12):3398.
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    ABSTRACT: Single-crystalline, high-quality branched ZnTe-core/ZnO-branch nanoheterostructures were synthesized by an in situ strategy in an environmental scanning electron microscope. Composition and structure characterization confirmed that ZnO nanowires were perfectly epitaxially grown on ZnTe nanowires as branches. Noticeably, growth temperature plays a crucial role in determining the density and diameter of the ZnO nanobranches on ZnTe nanowires: a higher growth temperature leads to ZnO nanowires with higher density and smaller diameter. It was demonstrated that ZnO nanobranches exhibited a selective nucleation behavior on distinct side facets of ZnTe nanowires. Highly ordered ZnO nanobranches were found epitaxially grown on {211} facet of ZnTe nanowires, while there was no ZnO nanowire growth on {110} facet of ZnTe nanowires. Using first-principles calculation, we found that surface energy of distinct side facets has a strong impact on ZnO nucleation, and confirm that {211} facet of ZnTe nanowires is energetically more favorable for ZnO nanowire growth than {110} facet, which is in good agreement with our experimental findings. Remarkably, such unique ZnTe/ZnO 3D branched nanowire heterostructures exhibited improved photocatalytic abilities, superior to ZnO nanowires and ZnTe nanowires, due to the much enhanced effective surface area of their unique architecture and effective electron-hole separation at the ZnTe/ZnO interfaces.
    Nanoscale 09/2011; 3(10):4418-26. · 6.73 Impact Factor
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    ABSTRACT: Using pre-existing ZnO nanowires as lattice-matched templates, we have systematically studied the catalyst-free regrowth of ZnO nanostructures in a chemical vapor deposition (CVD) system. Because the templates (or crystal seeds) provided nanoscale preferential nucleation sites for the subsequent growth, changing ZnO supersaturation and growth temperature led to distinct growth modes, from nonepitaxy to homoepitaxy and from axial to radial epitaxy. The perfect borderless homoepitaxial ZnO nanostructures demonstrate the inherent growth behaviors that were especially researched with the help of their position-dependent optical properties. Neither the self-catalyst vapor–liquid–solid (VLS) growth mechanism nor the defects-induced growth mechanism could explain most of these homoepitaxial growth modes. Instead, two-dimensional nucleation and step propagation model based on avapor–solid (VS) scenario was suggested and all these phenomena were well interpreted. In addition, our work presents a very convenient and well-controlled way of fabricating useful nanostructures in a CVD system.
    Crystal Growth & Design. 05/2011; 11(6).
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    ABSTRACT: 2D planar field emission devices based on individual ZnO nanowires were achieved on Si/SiO2 substrate via a standard e-beam lithography method. The anode, cathode and ZnO nanowires were on the same substrate; so the electron field emission is changed to 2D. Using e-beam lithography, the emitter (cathode) to anode distance could be precisely controlled. Real time, in situ observation of the planar field emission was realized in a scanning electron microscope. For individual ZnO nanowires, an onset voltage of 200 V was obtained at 1 nA. This innovative approach provides a viable and practical methodology to directly implement into the integrated field emission electrical devices for achieving “on-chip” fabrication.Highlights► Novel 2D planar field emission devices based on individual ZnO nanowires were achieved. ► Field emission current of individual ZnO nanowires was in situ acquired in a scanning electron microscope chamber. ► Tip to electrode distance could be precisely controlled by the standard e-beam lithography technique.
    Solid State Communications 01/2011; 151(22):1650-1653. · 1.53 Impact Factor
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    ABSTRACT: In situ epitaxial growth of high-oriented ZnOnanowires on annealed zinc film was realized in an environmental scanning electron microscope. Energy dispersive spectra, X-ray diffraction and photoluminescence measurements demonstrated that a thin layer of [001] ZnO was formed on the surface of zinc film after annealing. Formation of a ZnO layer on annealed zinc film caused dense [001] oriented nanowires compared to the sparse random nanowires grown on unannealed zinc film. Possible growth mechanism for the nanowires grown on annealed and unannealed film was discussed. This work offers a novel approach for effective epitaxial growth of high-oriented ZnOnanowires and helps to understand the growth mechanism of ZnOnanowires.
    CrystEngComm 12/2010; 13(2):606-610. · 3.88 Impact Factor
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    ABSTRACT: High-quality straight and multiply kinked CdTe nanowires (NWs) were synthesized by the facile chemical vapor deposition method at 600 °C. The as-synthesized NWs were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive x-ray spectroscopy, and photoluminescence (PL) spectroscopy. The straight CdTe NWs have single crystalline zinc blende structure with growth direction along the 〈111〉 direction. Their PL spectra consist only sharp near band edge emission around 824.3 nm. The multiply kinked CdTe NWs contain one or more fixed ( ∼ 125.2°) angle joints; each arm of the kinked NWs is single crystalline with similar selected area electron diffraction pattern as that of the straight CdTe NWs. The two growth directions in the multiply kinked CdTe NWs are 〈200〉 and 〈111〉. Single straight and kinked CdTe NW photoresponse devices were fabricated and testified to have high photocurrent decay ratio, high responsivity, fast response time, and no decay tail under 633 nm He–Ne laser illumination. These straight and multiply kinked CdTe NWs may open up potential applications in the bottom-up integrated nanoelectronic and nanophotonic systems, such as photovoltaic and multiterminal nanodevices etc.
    Journal of Applied Physics 08/2010; 108(4):044301-044301-4. · 2.21 Impact Factor
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    ABSTRACT: An ultrahigh field emission current density of 10.3 mA cm(-2) was obtained from nitrogen-implanted ZnO nanowires. The sample was characterized and clearly showed a nitrogen doping signal. Field emission properties of the ZnO nanowires were considerably improved after N-implantation with lower turn-on field and a much higher current density. Removal of an amorphous layer, the presence of nanoscale protuberances, and surface-related defects were found to be responsible for the significantly enhanced field emission. Our work is important for the possible applications of ZnO nanowires in flat panel displays and high brightness electron sources.
    Nanotechnology 03/2010; 21(9):095701. · 3.84 Impact Factor
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    ABSTRACT: In situ uniform growth of ZnO nanowires was realized and monitored at real time by heating zinc film in an environmental scanning electron microscope. Better controllability and repeatability were obtained by using zinc film as source material compared to traditionally used zinc powder. Morphology of the as-grown ZnO nanowires was found to depend on both the growth temperature and holding time. Low temperature (500 degrees C) and short growth time (approximately 20 min) favor one-dimensional nanowire growth, whereas longer holding time (>40 min) or higher temperature (700 degrees C) lead to nanosheet growth. The results suggest that the zinc vapor partial pressure is vital in determining the final morphology. These results help to give more insights into the mechanism of ZnO nanowire synthesis.
    The Journal of Chemical Physics 03/2010; 132(12):124705. · 3.12 Impact Factor
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    ABSTRACT: Near-band-edge emission in photoluminescence of ZnO nanowires was found to be significantly improved after plasma treatment. The ratio of ultraviolet emission peak intensity before and after plasma treatment is as high as 3.5. Field emission properties were considerably enhanced after plasma treatment as well. Current emission density has been increased two orders of magnitude under the same electric field. Passivation of surface states and surface morphology change were found to be responsible for such an effective improvement. Our results suggest that the plasma treatment method is effective in enhancing both the near-band-edge emission in photoluminescence and field electron emission performance from ZnO nanowires.
    Applied Physics A 01/2010; 100(1):165-170. · 1.69 Impact Factor
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    ABSTRACT: Surface coating effect on field emission performance of ZnO nanowires was studied by zinc surface coating. Coating time was found to play an important role in determining the field emission properties. 3 s and 5 s coating enhanced the field emission properties considerably, with lower turn-on field and larger electron emission current density. Prolonging the coating time to 10 s deteriorated the field emission properties of ZnO nanowires. Surface morphology change and green emission in photoluminescence related surface state were found to be responsible for such improvement. Our results provide an innovative approach to improve the field emission properties of ZnO nanowires for development of vacuum nanoelectronic devices.
    Applied Physics A 106(3). · 1.69 Impact Factor