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Zhong Lin Wang - One of the best experts on this subject based on the ideXlab platform.
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in situ transmission electron microscopy observation of zno Polar and non Polar Surfaces structure evolution under electron beam irradiation
Journal of Applied Physics, 2016Co-Authors: Yong Ding, Ken C Pradel, Zhong Lin WangAbstract:Using in situ transmission electron microscopy, we investigated the dynamic reconstruction and evolution of ZnO Polar and non-Polar Surfaces under high-energy electron beam irradiation. Electron beam radiolysis creates oxygen vacancies and a Zn rich (0001) Surface. Positive Polar charges at the (0001) Surface expel loosely bonded Zn ions to diffuse away from the (0001) Polar Surface. As a result, mass loss was observed around the (0001) Surface. Dehydration by the electron beam breaks the charge balance on the ( 0001¯) Polar Surface. The negative charges on the ( 0001¯) Surface suppress the radiolysis effect and further absorb Zn ions to the Surface to neutral the Polar charges. The ideal stacking sequences of Zn ions in hexagonal ZnO structure can be considered as ABAB… along its c axis, while the absorbed individual Zn ion on the ( 0001¯) Surface occupies the C site to form three bonds with Surface O ions beneath, instead of one bond in the ideal structure. With more Zn ion absorption and Surface oxidiz...
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growth of crossed zno nanorod networks induced by Polar substrate Surface
Crystal Growth & Design, 2009Co-Authors: C W Wang, Yong Ding, L J Chen, Zhong Lin WangAbstract:We show that by controlling the growth conditions, the crossed networks of ZnO nanorods were grown on an MgO (001) substrate. The [0001] ZnO nanorods grow along the ⟨111⟩ directions of MgO substrate and form aligned arrays. This growth is a result of Polar Surface induced growth from both the MgO {111} and ZnO ± (0001). The crossed ZnO nanorod networks are a potential candidate for field emission, optoelectronics, ultrasensitive sensing, catalysts and filtering.
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Profile imaging of reconstructed Polar and non-Polar Surfaces of ZnO
Surface Science, 2007Co-Authors: Yong Ding, Zhong Lin WangAbstract:Abstract The atomic scale Surface structures of ZnO ( 0 1 1 ¯ 0 ) non-Polar as well as ( 0 1 ¯ 1 1 ) and ±(0 0 0 1) Polar Surfaces have been directly imaged by high-resolution transmission electron microscopy (HRTEM). The observations were made on clean Surfaces created by irradiating a single ZnO nanobelt using 400 keV electron beam in TEM, under which ZnO dots were grown epitaxially and in situ on the Surface of the nanobelt. A technique is demonstrated for directly distinguishing the Surface Polarity of the ±(0 0 0 1) Polar Surfaces. For the ( 0 1 1 ¯ 0 ) non-Polar Surface, HRTEM images and simulation results indicate that the Zn ions in the first and second layer suffer from inward and outward relaxation, respectively; the oxygen ions in the first and second layer prefer shifting to vicinal Zn ions to shorten the bonding distance. For the oxygen-terminated ( 0 1 ¯ 1 1 ) Polar Surface, the oxygen ions at the outmost top layer were directly imaged. a × 2 reconstruction has also been observed at the ( 0 1 ¯ 1 1 ) Surface, and its atomic structure has been proposed based on image simulation. Oxygen-terminated ( 0 0 0 1 ¯ ) Polar Surface is flat and shows no detectable reconstruction. For the Zn-terminated (0 0 0 1) Polar Surface, HRTEM may indicate the existence of Zn vacancies and a possibly c-axis, random outward displacement of the top Zn ions. Our data tend to support the mechanism of removal of Surface atoms for maintaining the stability of (0 0 0 1) Polar Surfaces.
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formation of double side teethed nanocombs of zno and self catalysis of zn terminated Polar Surface
Chemical Physics Letters, 2006Co-Authors: Changshi Lao, Ying Dai, Puxian Gao, Rusen Yang, Yue Zhang, Zhong Lin WangAbstract:Polar Surface induced asymmetric growth of single-side teethed ZnO nanocombs was attributed to the self-catalysis of the Zn-terminated (0 0 0 1) Surface (Z.L. Wang, X.Y. Kong, J.M. Zuo, Phys. Rev. Lett. 91 (2003) 185502). In this Letter, nanocombs of ZnO with double-sided teeth have been observed. This symmetric growth of the fish-ribbon like teeth has been identified due to the existence of an inversion domain boundary along the ribbon, so that both side Surfaces of the ribbon are terminated with the chemically active Zn-(0 0 0 1) plane. A model is also given about the formation of � 110� double-sided nanocombs based on the nucleus composed of multiply twinned pyramids. The data show that the Zn-terminated (0 0 0 1) Surface is responsible for the formation of the teeth, while the oxygen-terminated (0 0 0 1) Surface is chemically inactive and does not grow teeth. � 2005 Elsevier B.V. All rights reserved.
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Polar-Surface dominated ZnO nanobelts and the electrostatic energy induced nanohelixes, nanosprings, and nanospirals
Applied Physics Letters, 2004Co-Authors: Xiangyang Kong, Zhong Lin WangAbstract:We report the controlled synthesis of free-standing ZnO nanobelts whose Surfaces are dominated by the large Polar Surfaces. The nanobelts grow along the a axis, their large top/bottom Surfaces are the ±(0001) Polar planes, and the side Surfaces are (0110). Owing to the positive and negative ionic charges on the zinc- and oxygen-terminated ±(0001) Surfaces, respectively, the nanobelts form multiloops of nanohelixes/nanosprings/nanospirals for the sake of reducing electrostatic energy introduced by the Polar Surfaces as well as balancing the difference in Surface tension. The Polar Surface dominated ZnO nanobelts are likely to be an ideal system for understanding piezoelectricity and Polarization induced phenomena at nanoscale.
Yang Liu - One of the best experts on this subject based on the ideXlab platform.
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High Reactivity of the ZnO(0001) Polar Surface: The Role of Oxygen Adatoms
The Journal of Physical Chemistry C, 2017Co-Authors: Yang Liu, Yueyue ShanAbstract:Understanding the mechanism of water dissociation on metal oxide Surfaces is of particular interest in catalytic reactions. In this work, the interaction of water with the ZnO(0001) Polar Surface is investigated, and the role of oxygen adatoms in water splitting is uncovered. The individual Surface energies and electronic properties of ZnO Polar Surfaces are investigated on the basis of density functional theory calculations. The oxygen adatoms on the ZnO(0001) Surface introduce in-gap Surface states, resulting in a direct-to-indirect band gap transition. Water strongly interacts with oxygen adatoms to spontaneously form hydroxyl groups, recovering the direct band-gap characteristics of ZnO Polar Surfaces. Furthermore, water prefers to adsorb at the step edges of cavities after all of the oxygen adatoms are consumed, and the hydrogen-bonded network among water molecules triggers the dissociation of water at the edge sites, which is also confirmed by molecular dynamics calculations. Our results provide ato...
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Observation and Analysis of Ordered and Disordered Structures on the ZnO(0001) Polar Surface
The Journal of Physical Chemistry C, 2016Co-Authors: Lei Dong, Xingqiang Shi, Yang Liu, Michel A. Van Hove, Nian Lin, S. Y. TongAbstract:Using low temperature scanning tunneling microscopy (STM), we discovered locally ordered patches of O adatoms and single Zn vacancies on the Zn-terminated ZnO(0001) Polar Surface. Such patches are determined to be metastable ordered structures on the Surface. Density functional theory (DFT) calculations show that Zn atoms bonded to an O adatom encounter a larger reaction barrier for leaving lattice sites, explaining the observed general disordered nature of the Zn-terminated Surface that is populated by cavities of different shapes and sizes and disordered distribution of adatoms. The interplay among different driving mechanisms provides valuable insight as to how a Polar Surface of an ionic crystal achieves its lowest energy reconstructed Surface structure. Comparisons between the charge on Surface vs bulk layers for a relaxed (1 × 1) slab and a slab bounded on two ends by reconstructed Surfaces with stoichiometric changes reveal that in a neutral environment, the Polar Surface of an ionic crystal tends ...
Timon Rabczuk - One of the best experts on this subject based on the ideXlab platform.
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Polar Surface effects on the thermal conductivity of ZnO nanowires: a shell-like Surface reconstruction-induced preserving mechanism
Nanoscale, 2013Co-Authors: Jin-wu Jiang, Harold S. Park, Timon RabczukAbstract:We perform molecular dynamics (MD) simulations to investigate the effect of Polar Surfaces on the thermal transport in zinc oxide (ZnO) nanowires. We find that the thermal conductivity of nanowires with free Polar (0001) Surfaces is much higher than that of nanowires that have been stabilized with reduced charges on the Polar (0001) Surfaces, and also hexagonal nanowires without any transverse Polar Surface, where the reduced charge model has been proposed as a promising stabilization mechanism for the (0001) Polar Surfaces of ZnO nanowires. From normal mode analysis, we show that the higher thermal conductivity is due to the shell-like reconstruction that occurs for the free Polar Surfaces. This shell-like reconstruction suppresses twisting motion in the nanowires such that the bending phonon modes are not scattered by the other phonon modes, and this leads to substantially higher thermal conductivity of the ZnO nanowires with free Polar Surfaces. Furthermore, the auto-correlation function of the normal mode coordinate is utilized to extract the phonon lifetime, which leads to a concise explanation for the higher thermal conductivity of ZnO nanowires with free Polar Surfaces. Our work demonstrates that ZnO nanowires without Polar Surfaces, which exhibit low thermal conductivity, are more promising candidates for thermoelectric applications than nanowires with Polar Surfaces (and also high thermal conductivity).
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Preserving the Q-factors of ZnO nanoresonators via Polar Surface reconstruction.
Nanotechnology, 2013Co-Authors: Jin-wu Jiang, Harold S. Park, Timon RabczukAbstract:We perform molecular dynamics simulations to investigate the effect of Polar Surfaces on the quality (Q)-factors of zinc oxide (ZnO) nanowire-based nanoresonators. We find that the Q-factors in ZnO nanoresonators with free Polar (0001) Surfaces are about one order of magnitude higher than in nanoresonators that have been stabilized with reduced charges on the Polar (0001) Surfaces. From normal mode analysis, we show that the higher Q-factor is due to a shell-like reconstruction that occurs for the free Polar Surfaces. This shell-like reconstruction suppresses twisting motion in the nanowires such that the mixing of other modes with the resonant mode of oscillation is minimized, and leads to substantially higher Q-factors in ZnO nanoresonators with free Polar Surfaces.
Yueyue Shan - One of the best experts on this subject based on the ideXlab platform.
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High Reactivity of the ZnO(0001) Polar Surface: The Role of Oxygen Adatoms
The Journal of Physical Chemistry C, 2017Co-Authors: Yang Liu, Yueyue ShanAbstract:Understanding the mechanism of water dissociation on metal oxide Surfaces is of particular interest in catalytic reactions. In this work, the interaction of water with the ZnO(0001) Polar Surface is investigated, and the role of oxygen adatoms in water splitting is uncovered. The individual Surface energies and electronic properties of ZnO Polar Surfaces are investigated on the basis of density functional theory calculations. The oxygen adatoms on the ZnO(0001) Surface introduce in-gap Surface states, resulting in a direct-to-indirect band gap transition. Water strongly interacts with oxygen adatoms to spontaneously form hydroxyl groups, recovering the direct band-gap characteristics of ZnO Polar Surfaces. Furthermore, water prefers to adsorb at the step edges of cavities after all of the oxygen adatoms are consumed, and the hydrogen-bonded network among water molecules triggers the dissociation of water at the edge sites, which is also confirmed by molecular dynamics calculations. Our results provide ato...
S. Y. Tong - One of the best experts on this subject based on the ideXlab platform.
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Observation and Analysis of Ordered and Disordered Structures on the ZnO(0001) Polar Surface
The Journal of Physical Chemistry C, 2016Co-Authors: Lei Dong, Xingqiang Shi, Yang Liu, Michel A. Van Hove, Nian Lin, S. Y. TongAbstract:Using low temperature scanning tunneling microscopy (STM), we discovered locally ordered patches of O adatoms and single Zn vacancies on the Zn-terminated ZnO(0001) Polar Surface. Such patches are determined to be metastable ordered structures on the Surface. Density functional theory (DFT) calculations show that Zn atoms bonded to an O adatom encounter a larger reaction barrier for leaving lattice sites, explaining the observed general disordered nature of the Zn-terminated Surface that is populated by cavities of different shapes and sizes and disordered distribution of adatoms. The interplay among different driving mechanisms provides valuable insight as to how a Polar Surface of an ionic crystal achieves its lowest energy reconstructed Surface structure. Comparisons between the charge on Surface vs bulk layers for a relaxed (1 × 1) slab and a slab bounded on two ends by reconstructed Surfaces with stoichiometric changes reveal that in a neutral environment, the Polar Surface of an ionic crystal tends ...
