1,720,975 research outputs found
Phase diagram of Si nanowire growth by disproportionation of SiO
No full textSilicon nanowires have been grown in a horizontal tube furnace by disproportionation of silicon monoxide in combination with the vapor-liquid-solid mechanism. We present a phase diagram of the nanowire growth, indicating different morphologies for varying growth pressure and temperature. The morphology was characterized by scanning electron microscopy and detailed structural analysis was performed by transmission electron microscopy. A variety of morphologies is found and the optimum parameter range for the growth of straight and uniform nanowires consisting of crystalline silicon cores and amorphous SiO(2) shells is identified and discussed. (C) 2010 Elsevier B.V. All rights reserved.German Research Foundation (DFG) [Ro1198/7
Catalyst-nanostructure interaction and growth of ZnS nanobelts
No full textDetails of the vapour-liquid-solid Au droplet catalysed growth of ZnS nanobelts are elucidated in this work. The inclination of the Au droplet after solidification shows that it is indeed in the liquid state during nanobelt growth. Numerous stacking faults are observed when (0001) wurtzite is the side surface of the nanobelt. Compressive stress at the droplet-nanobelt-atmosphere triple interface is the cause of the stacking faults. Sawteeth-like structures are observed on the Zn-terminated polar (0001) side surface only. These surfaces are chemically active, while S-terminated (000 (1) over bar) surfaces and non-polar surfaces are not. Oil these active surfaces, autocatalysed vapour-solid growth leads to the formation of the observed sawteeth
Optical activation of implanted impurities in ZnS nanowires
No full textNanostructures of zinc sulfide (ZnS), a II-VI compound semiconductor with a direct band gap of 3.66 eV in the cubic phase and 3.74 eV in the wurtzite phase, show interesting optical properties, making it a promising candidate for optoelectronic devices. Single-crystalline nanobelts and nanowires were synthesized in a computer-controlled process according to the vapor-liquid-solid-mechanism. We investigated the morphology, structure, and composition by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. The optical properties were studied by low-temperature photoluminescence (PL) and cathodoluminescence. The synthesized ZnS nanowires were implanted with nitrogen and boron as potential donor and acceptor, respectively. The implanted nanowires were investigated directly after ion implantation and showed a high quantity of defects resulting in nonluminescent material. Annealing procedures recovered the crystal structure and the luminescence, and we found emerging and varying PL lines indicating the activation of the implanted impurities. (c) 2006 American Vacuum Society
Catalyst-nanostructure interaction in the growth of 1-D ZnO nanostructures
No full textVapor-liquid-solid is a well-established process in catalyst guided growth of 1-D nanostructures, i.e., nanobelts and nanowires. The catalyst particle is generally believed to be in the liquid state during growth, and is the site for impinging molecules. The crystalline structure of the catalyst may not have any influence on the structure of the grown nanostructures. In this work, using An guided growth of ZnO, we show that the interfaces between the catalyst droplet and the nanostructure grow in well-defined mutual crystallographic relationships. The nanostructure defines the crystallographic orientation of the solidifying An droplet. Possible alloy, intermetallic, or eutectic phase formation during catalysis are elucidated with the help of a proposed ternary Au-Zn-O phase diagram
Characterization of the donor-acceptor-pair transition in Nitrogen-implanted zinc oxide
No full textZinc oxide bulk crystals were doped with nitrogen by ion beam implantation. After postimplantation annealing, a luminescent transition appears at 3.230 eV. Power-dependent photoluminescence studies and time-resolved measurements at several spectral positions within this band can be described by a model for donor-acceptor-pair (DAP) transitions. By tracing the luminescence in a temperature-dependent study, a connection to phonon replicas could be excluded. Based on these results, this luminescence line could be clearly assigned to a DAP transition. In order to increase the doping efficiency, various approaches are considered and discussed. A slight increase could be obtained by high-temperature implantation without postimplantation annealing. (c) 2008 American Institute of Physics
Scalable Fabrication of Nanowire Photonic and Electronic Circuits Using Spin-on Glass
No full textWe present a method which can be used for the mass-fabrication of nanowire photonic and electronic devices based on spin-on glass technology and on the photolithographic definition of independent electrical contacts to the top and the bottom of a nanowire. This method allows for the fabrication of nanowire devices in a reliable, fast, and low cost way, and it can be applied to nanowires with arbitrary cross section and doping type (p and n). We demonstrate this technique by fabricating single-nanowire p-Si(substrate)−n-ZnO(nanowire) heterojunction diodes, which show good rectification properties and, furthermore, which function as ultraviolet light-emitting diodes
Nanomaterial electronic structure investigation by valence electron energy loss spectroscopy - An example of doped ZnO nanowires
No full textThe effects of doping (by ion implantation) on the electronic structure of ZnO nanowires, particularly on the defect states generation in the band gap of ZnO, are investigated using valence electron energy loss spectroscopy (VEELS) performed in a transmission electron microscope (TEM). The improved spectrum energy resolution via the introduction of a gun monochromator, together with the reduced intensity in the zero loss peak tail as realized by spectrum acquisition at non-zero momentum transfer, enable us to extract such electronic structure information from the very low loss region of the EEL spectra. We have compared the doping effects of several dopant elements, i.e., Er, Yb, and Co, and found that generation of the band tail states (similar to 2-3.3 eV) is a common consequence of the ion implantation process. On the other hand, specific mid-gap state(s) in the lower energy range are created only in the rare earth element doped ZnO nanowires, suggesting the dopant-sensitive nature of such state. (C) 2007 Elsevier Ltd. All rights reserved
Energy Transfer and Dynamics of the Mn 3d(5) Luminescence in Low Dimensional (Zn,Mn)S Nanostructures
No full textZnS:Mn nanostructures with different morphology, i.e. wires and belts, have been studied by time resolved photoluminescence. The temporal evolution of the internal Mn2+(3d(5)) luminescence is measured over 4 orders of magnitude in intensity. The decay behavior shows a clear dependence on the morphology of the nanostructure, in particular, on the ratio between the average Mn ion killer center distance and the characteristic lateral size of the nanostructure. The non-exponential transients observed can be well described in the framework of a Forster-transfer at reduced dimensionality. We present an important step in resolving a longstanding controversy in the literature regarding the lifetime of the internal Mn2+ emission in ZnS nanoparticles
Energy Transfer and Dynamics of the Mn 3d(5) Luminescence in Low Dimensional (Zn,Mn)S Nanostructures
No full textZnS:Mn nanostructures with different morphology, i.e. wires and belts, have been studied by time resolved photoluminescence. The temporal evolution of the internal Mn2+(3d(5)) luminescence is measured over 4 orders of magnitude in intensity. The decay behavior shows a clear dependence on the morphology of the nanostructure, in particular, on the ratio between the average Mn ion killer center distance and the characteristic lateral size of the nanostructure. The non-exponential transients observed can be well described in the framework of a Forster-transfer at reduced dimensionality. We present an important step in resolving a longstanding controversy in the literature regarding the lifetime of the internal Mn2+ emission in ZnS nanoparticles
Dimensional dependence of the dynamics of the Mn 3d(5) luminescence in (Zn, Mn)S nanowires and nanobelts
No full textZnS nanostructures of different morphologies, i.e., nanowires and nanobelts, have been ion implanted with Mn and subsequently annealed to obtain Zn1-xMnxS nanostructures. The Mn content x was adjusted to lie in the range from 4x10(-6)% to 4% corresponding to a variation of the mean Mn-Mn distance between about 200 and 2 nm, respectively. The Zn1-xMnxS nanowires have been studied by photoluminescence spectroscopy. The yellow Mn luminescence band indicates that the Mn2+ ions are incorporated on cation lattice sites replacing Zn. The temporal evolution of this internal Mn2+(3d(5)) luminescence is measured over 4 orders of magnitude in intensity. The decay behavior shows a clear dependence on the morphology of the nanostructure, in particular, on the ratio between the average Mn ion-killer center distance and the characteristic lateral size of the nanostructure. If the mean Mn-Mn distance is comparable to or smaller than the average Mn ion-killer center distance in the nanostructures, then concentration quenching of the Mn luminescence occurs similar to bulk. The nonexponential transients observed can be well described in the framework of a modified Forster model at reduced dimensionality. The photoluminescence (PL) behavior of the nanowires loses its one-dimensional character when the mean Mn ion-killer center distance becomes much smaller than the wire diameter. In contrast, the temporal PL behavior of the nanobelts is only purely two dimensional in this case and is of intermediate character between one dimensional and two dimensional otherwise
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