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Zenji Horita - One of the best experts on this subject based on the ideXlab platform.
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high pressure torsion of pure metals influence of Atomic Bond parameters and stacking fault energy on grain size and correlation with hardness
Acta Materialia, 2011Co-Authors: Kaveh Edalati, Zenji HoritaAbstract:Abstract The grain size in pure elements (magnesium, aluminum, silicon, titanium, vanadium, chromium, iron, nickel, copper, zinc, germanium, zirconium, niobium, molybdenum, palladium, silver, indium, tin, hafnium, tantalum, gold and lead) after processing by high-pressure torsion (HPT) reaches steady-state levels where the grain size remains unchanged with straining. The steady-state grain sizes decrease by Atomic Bond energy and related parameters such as specific heat capacity, activation energy for self-diffusion and homologous temperature and are reasonably independent of stacking fault energy. A good correlation exists between the hardness normalized by the shear modulus and grain size normalized by the Burgers vector, indicating that the important factor for strengthening HPT-processed pure metals is the average size of grains having high angles of misorientation.
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correlations between hardness and Atomic Bond parameters of pure metals and semi metals after processing by high pressure torsion
Scripta Materialia, 2011Co-Authors: Kaveh Edalati, Zenji HoritaAbstract:High-purity elements (magnesium, aluminum, silicon, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, germanium, zirconium, niobium, molybdenum, palladium, silver, indium, tin, tellurium, neodymium, hafnium, tantalum, tungsten, rhenium, platinum, gold and lead) were processed by high-pressure torsion and subsequently evaluated by Vickers microhardness measurements. The hardness at the steady state was expressed as a unique function of Atomic Bond energy, specific heat capacity, specific latent heat of fusion, linear thermal expansion coefficient and activation energy for self-diffusion.
Ki Hyun Yoon - One of the best experts on this subject based on the ideXlab platform.
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Defect density and Atomic Bond structure of tetrahedral amorphous carbon (ta-C) films prepared by filtered vacuum arc process
Journal of Applied Physics, 2004Co-Authors: Jin-koog Shin, Ki Hyun YoonAbstract:Defect density of tetrahedral amorphous carbon (ta-C) film prepared by filtered vacuum arc process was investigated in a wide range of fraction of sp3 hybridized Bond. We could observe a close relationship between unpaired spin density measured by electron spin resonance spectroscopy and their Atomic Bond structure: the defect density was proportional to the content of sp3 hybridized Bond in the film. Near edge x-ray absorption fine structure analysis further showed that the content of the surface C–H Bonds presumably due to the absorption of hydrocarbon to the surface dangling Bond also increased with increasing content of sp3 hybridized Bond. The observed dependence was discussed in terms of the degree of clustering or pairing of the isolated sp2 sites.
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structure and properties of si incorporated tetrahedral amorphous carbon films prepared by hybrid filtered vacuum arc process
Diamond and Related Materials, 2002Co-Authors: Churl Seung Lee, Ki Hyun Yoon, Kwangryeol Lee, Kwang Yong Eun, Jun Hee HanAbstract:The mechanical properties and Atomic Bond structure of Si incorporated into tetrahedral amorphous carbon (ta-C) films were investigated. The films were deposited by a filtered vacuum arc of graphite with simultaneous sputtering of Si. The Si concentration in the film could be controlled by changing the flow rate of the Ar sputtering gas. It was observed that the incorporated Si preferentially substituted sp Bonded carbon when the Si concentration was less than 2.5 at.%. Since the Si-C Bond generated by 3
Aiying Wang - One of the best experts on this subject based on the ideXlab platform.
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microstructure and electrochemical properties of nitrogen doped dlc films deposited by pecvd technique
Applied Surface Science, 2015Co-Authors: Yousheng Zou, Kai Zhou, Aiying WangAbstract:Abstract Nitrogen-doped diamond-like carbon (N-DLC) films were synthesized by glow discharge plasma enhanced chemical vapor deposition (PECVD) using a hybrid ion beam system. The influence of nitrogen incorporation on the microstructure and electrochemical properties of N-DLC films was investigated by scanning probe microscopy, Raman spectroscopy, X-ray photoemission spectroscopy and cycle voltammetry. Regardless of the deposition parameters, the surface of all the deposited films is very smooth. Raman spectra show that ID/IG increases from 0.6 to 1.04 with the substrate bias voltage increases. XPS results identify that carbon is Bonded with nitrogen and the substrate bias makes no distinct contribution to the N content in the films, even the N-DLC film at bias of −550 V has the lowest N–O Bonds concentration and the highest C–N Bonds concentration. The film electrodes show the wide potential windows range over 4 V, lower background currents in strong acid media. At the bias of −550 V, the N-DLC film electrode not only exhibits the ΔEp at 209 mV and I p o x / I p r e d at 0.8778 in K3Fe(CN)6 solution, respectively, but also illustrates a nearly reversible electrode reaction. The mechanism of electroproperties is discussed in terms of the Atomic Bond structures and diffusion process.
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deposition and properties of al containing diamond like carbon films by a hybrid ion beam sources
Journal of Alloys and Compounds, 2011Co-Authors: Wei Dai, Aiying WangAbstract:Metal incorporation is one of the most effective methods for relaxing internal stress in diamond-like carbon (DLC) films. It was reported that the chemical state of the incorporated metal atoms has a significant influence on the film internal stress. The doped atoms embedding in the DLC matrix without Bonding with C atoms can reduce the structure disorder of the DLC films through Bond angle distortion and thus relax the internal stress of the films. In present paper, Al atoms, which are inert to carbon, were incorporated into the DLC films deposited by a hybrid ion beams system comprising an anode-layer ion source and a magnetron sputtering unit. The film composition, microstructure and Atomic Bond structure were characterized using X-ray photoelectron spectroscopy, transmission electron microscopy and Raman spectroscopy. The internal stress, mechanical properties and tribogoical behavior were studied as a function of Al concentration using a stress-tester, nanoindentation and ball-on-disc tribo-tester, respectively. The results indicated that the incorporated Al atoms were dissolved in the DLC matrix without Bonding with C atoms and the films exhibited the feature of amorphous carbon. The structure disorder of the films tended to decrease with Al atoms incorporation. This resulted in the distinct reduction of the internal stress in the films. All Al-DLC films exhibited a lower friction coefficient compared with pure DLC film. The formation of the transfer layer and the graphitization induced by friction were expected to contribute to the excellent friction performance.
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effect of bias voltage on growth property of cr dlc film prepared by linear ion beam deposition technique
Vacuum, 2010Co-Authors: Wei Dai, He Zheng, Guosong Wu, Aiying WangAbstract:Cr-containing diamond-like carbon films were deposited on silicon wafers by a combined linear ion beam and DC magnetron sputtering. The influence of the bias voltage on the growth rate, Atomic Bond structure, surface topography and mechanical properties of the films were investigated by SEM, XPS, Raman spectroscopy, AFM, and nano-indentation. It was shown that the chromium concentration of the films increased with negative bias voltage and that a carbide phase was detected in the as-deposited films. The surface topography of the films evolved from a rough surface with larger hillocks reducing to form a smoother flat surface as the bias voltage increased from 0 to � 200 V. The highest hardness and elastic modulus were obtained at a bias voltage of about � 50 V, while the maximum sp 3 Bonding fraction was acquired at � 100 V. It was suggested that the mechanical properties of the films not only depended on the sp 3 Bonding fraction in the films but also correlated with the influence of Cr doping and ion bombardment.
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structure and mechanical properties of w incorporated diamond like carbon films prepared by a hybrid ion beam deposition technique
Carbon, 2006Co-Authors: Aiying Wang, Kwangryeol Lee, Jaepyoung Ahn, Jun Hee HanAbstract:Abstract W incorporated diamond-like carbon films were prepared on silicon(1 0 0) wafers using a hybrid deposition system composed of an end-Hall-type hydrocarbon ion gun and a tungsten DC magnetron sputter source. The W concentration in the films was controlled by changing the fraction of Ar in the Ar and C6H6 reaction gas. The chemical composition, Atomic Bond structure, and mechanical properties were investigated for W concentrations ranging from 0 to 8.6 at.%. When the W concentration was 2.8 and >3.6 at.%, respectively. It was found that the hardness and elastic modulus were not sensitive to the W concentration in this concentration range. On the other hand, the residual compressive stress was strongly dependent on the chemical state of the incorporated W atoms. The change in mechanical properties is discussed in terms of the microstructural changes induced by W incorporation.
Kwangryeol Lee - One of the best experts on this subject based on the ideXlab platform.
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characteristic of silver doped dlc films on surface properties and protein adsorption
Diamond and Related Materials, 2008Co-Authors: Heon Woong Choi, Kwangryeol Lee, Reinhold H Dauskardt, Seungcheol Lee, Kyu Hwan OhAbstract:Ag-incorporated diamond-like carbon (DLC) films were prepared on Si substrate using a hybrid deposition system composed of an end-Hall-type hydrocarbon ion gun and a silver DC magnetron sputter source. Ag was selected due to their potential values of biomaterial. The concentration of Ag in the films was varied from 0.1 to 9.7 at.% by controlling the fraction of Ar in the reaction gas mixture with benzene. In order to understand the influence of incorporated Ag on wettability, the surface energy and the protein adsorption as an indirect haemo-compatibility were measured. The surface energy of the Ag-incorporated DLC film decreased gradually with the increase of the Ag concentration. The haemo-compatibility was examined by the adsorption ratio of albumin/fibrinogen as an indirect method and improved with the increase of Ag concentration. The surface and biological behaviors of the films will be discussed in terms of the Atomic Bond characteristic and microstructure induced by Ag incorporation. Our results demonstrate that the Ag-incorporated DLC films are potentially useful as biomedical devices having good haemo-compatibility and hydrophobic characteristics.
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structure and mechanical properties of ag incorporated dlc films prepared by a hybrid ion beam deposition system
Thin Solid Films, 2007Co-Authors: Kwangryeol Lee, Heon Woong Choi, Junghae Choi, Jaepyoung Ahn, Kyu Hwan OhAbstract:Ag-incorporated diamond-like carbon films were prepared on Si(100) wafers using a hybrid deposition system composed of an end-Hall-type hydrocarbon ion gun and a silver DC magnetron sputter source. The Ag concentration in the films was controlled by changing the fraction of Ar in the Ar and benzene reaction gas. The chemical composition, microstructure, Atomic Bond structure, and mechanical properties were investigated for Ag concentrations ranging from 0 to 9.7at.%. When the Ag concentration was 0.1at.%, the Ag atoms were fully dissolved in the amorphous carbon matrix without forming any second phase. Amorphous and crystalline silver particles appeared when the Ag concentration was 1.7 and N6.8at.%, respectively. It was found that the hardness was not sensitive to the Ag concentration in this concentration range. On the other hand, the residual compressive stress was strongly dependent on the chemical state of the incorporated Ag atoms. The mechanical properties are discussed in terms of the changes in the microstructure and Atomic Bond structure induced by Ag incorporation. © 2007 Elsevier B.V. All rights reserved.
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structure and mechanical properties of w incorporated diamond like carbon films prepared by a hybrid ion beam deposition technique
Carbon, 2006Co-Authors: Aiying Wang, Kwangryeol Lee, Jaepyoung Ahn, Jun Hee HanAbstract:Abstract W incorporated diamond-like carbon films were prepared on silicon(1 0 0) wafers using a hybrid deposition system composed of an end-Hall-type hydrocarbon ion gun and a tungsten DC magnetron sputter source. The W concentration in the films was controlled by changing the fraction of Ar in the Ar and C6H6 reaction gas. The chemical composition, Atomic Bond structure, and mechanical properties were investigated for W concentrations ranging from 0 to 8.6 at.%. When the W concentration was 2.8 and >3.6 at.%, respectively. It was found that the hardness and elastic modulus were not sensitive to the W concentration in this concentration range. On the other hand, the residual compressive stress was strongly dependent on the chemical state of the incorporated W atoms. The change in mechanical properties is discussed in terms of the microstructural changes induced by W incorporation.
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structure and properties of si incorporated tetrahedral amorphous carbon films prepared by hybrid filtered vacuum arc process
Diamond and Related Materials, 2002Co-Authors: Churl Seung Lee, Ki Hyun Yoon, Kwangryeol Lee, Kwang Yong Eun, Jun Hee HanAbstract:The mechanical properties and Atomic Bond structure of Si incorporated into tetrahedral amorphous carbon (ta-C) films were investigated. The films were deposited by a filtered vacuum arc of graphite with simultaneous sputtering of Si. The Si concentration in the film could be controlled by changing the flow rate of the Ar sputtering gas. It was observed that the incorporated Si preferentially substituted sp Bonded carbon when the Si concentration was less than 2.5 at.%. Since the Si-C Bond generated by 3
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effect of residual stress on the raman spectrum analysis of tetrahedral amorphous carbon films
Applied Physics Letters, 2001Co-Authors: Jin-koog Shin, Churl Seung Lee, Kwangryeol Lee, Kwang Yong EunAbstract:Tetrahedral amorphous carbon (ta-C) films deposited by the filtered vacuum arc process have large compressive residual growth stresses that depend on the Atomic-Bond structure. We observed that the G peak of the Raman spectrum shifts to higher frequency by 4.1±0.5 cm−1/GPa due to the residual compressive stress. This value agrees well with the calculated Raman-peak shift of the graphite plane due to applied stress. By considering the effect of residual stress on the G-peak position, we also observe a similar dependence between the G-peak position and the Atomic-Bond structure in both ta-C and hydrogenated amorphous carbon (a-C:H) films; namely, that a higher sp2 Bond content shifts the G-peak position to higher frequency.
Gang Ouyang - One of the best experts on this subject based on the ideXlab platform.
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thickness dependent photoelectric properties of mos 2 si heterostructure solar cells
Scientific Reports, 2019Co-Authors: Yipeng Zhao, Gang OuyangAbstract:In order to obtain the optimal photoelectric properties of vertical stacked MoS2/Si heterostructure solar cells, we propose a theoretical model to address the relationship among film thickness, Atomic Bond identities and related physical quantities in terms of Bond relaxation mechanism and detailed balance principle. We find that the vertical stacked MoS2/Si can form type II band alignment, and its photoelectric conversion efficiency (PCE) enhances with increasing MoS2 thickness. Moreover, the optimal PCE in MoS2/Si can reach 24.76%, inferring that a possible design way can be achieved based on the layered transition metal dichalcogenides and silicon.
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Geometry-Dependent Auger Recombination Process in Semiconductor Nanostructures
The Journal of Physical Chemistry C, 2017Co-Authors: Gang OuyangAbstract:The geometry-dependent Auger recombination (AR) rate of semiconductor nanostructures has been investigated based on Atomic-Bond-relaxation correlation mechanism. We found that the increase in dimension is of great benefit to suppress the AR process due to reduction of the Coulomb interaction between electron and hole. The AR lifetime increases as the size decreases with a Eg7/2D7 dependence. Moreover, the AR rate of nanostructures can be achieved though modulating the related geometry parameters. Our results are consistent with the available evidence, implying that the proposed model could be expected to be a general approach to deal with AR process in semiconductor nanostructures.
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lattice strain effect on the band offset in single layer mos2 an Atomic Bond relaxation approach
Journal of Physical Chemistry C, 2017Co-Authors: Yipeng Zhao, Zhe Zhang, Gang OuyangAbstract:Two-dimensional molybdenum disulfide (MoS2) attracts a great deal of interest owing to its potential application in the next generation of electronic devices in recent years. However, the physical mechanism on the strain engineering for the band offset in single-layer MoS2 from the atomistic origin is still a challenge. Herein, we propose an analytical model to address the band offset in single-layer MoS2 modulated by the uniaxial tensile strain based on Atomic-Bond-relaxation consideration. It was found that the bandgap of single-layer MoS2 shows an approximately linearly red shift with a rate of ∼53.4 meV/% strain under uniaxial tensile strain. The underlying mechanism can be attributed to the variation of crystal potential induced by the changes of Bond identities such as Bond length, strength, and angle. The results were validated by comparing them with the available evidence, suggesting that the proposed model can be an effective method to clarify the modulation mechanism of relevant electronic prope...
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Structure stabilities and transitions in polyhedral metal nanocrystals: An Atomic-Bond-relaxation approach
Applied Physics Letters, 2012Co-Authors: Ai Zhang, Ziming Zhu, Gang OuyangAbstract:We present an Atomic-Bond-relaxation (ABR) method to illustrate a deeper insight on structure stabilities and transitions of metal nanocrystals with polyhedral structure based on the thermodynamic consideration. It has been found that the end effects in polyhedral nanocrystals induced by the atoms located at edges, side facets, and vertexes play the dominant roles for their structure performances. The theoretical predictions are well consistent with the experimental measurements and simulations, which suggest the ABR model can be an effective method to understand solid-solid phase transition of polyhedral metal nanocrystals.