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Now showing items 1 - 16 of 41969

  • Ordered nanocrystal formation in Cu50Zr45Ti5 metallic glass

    Aitkaliyeva, A.   Shao, L.   Price, L.   Gigax, J.   Kim, H.   Lucca, D. A.   Zare, A.   Fu, E. G.   Xie, G.  

    The paper reports formation of ordered nanocrystals in amorphous Cu50Zr45Ti5 metallic glass (MG) when exposed to ions in focused ion beam (FIB) instrument. The specimen was subjected to 30 keV Ga ion beam during trenching, lift out of a lamella, and thinning to a thickness of about 100 nm. Transmission electron microscopy confirms formation of ordered nanocrystals 2-5 nm In size, aligned along lines, which have similar to 10 nm separation distance. It is hypothesized that solid flow induced by ion bombardment leads to ripple formation. The diffusible short-range order quasicrystals agglomerate in the crest regions under stress and the agglomeration is followed by local nanocrystal nucleation. The FIB process is unable to induce such an ordered nanocrystal matrix in MG Ti40Cu31Pd14Zr10Sn2Si3. The difference in radiation resistance is explained by the level of complexity in the correlated diffusion needed for crystal nucleation, which is reflected by the width of the supercooled liquid region.
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  • The electrical behavior of Cu thin film induced by carbon ion irradiation

    Wang, P. P.   Liang, Y. X.   Xu, C.   Wang, X. J.   Zhang, Y.   Yan, X. Q.   Wang, Y. G.   Fu, E. G.  

    This study systematically investigates the influence of carbon ion irradiation on the electrical resistivity of single layer Cu films. Carbon ion irradiations with the energy of 3 MeV and the fluences of 5 x 10(13) ions/cm(2) and 5 x 10(14) ions/cm(2) were performed on the Cu films. The change of the resistivity and the temperature coefficient of resistivity before and after irradiation largely depends on the grain boundary. The amended model was proposed to describe the resistivity of ion-irradiated Cu films by considering the surface scattering, grain boundary scattering and the defects induced by ion irradiation. (C) 2019 Elsevier B.V. All rights reserved.
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  • Erosion and deuterium retention of CLF-1 steel exposed to deuterium plasma

    Qiao, L.   Wang, P.   Hu, M.   Gao, L.   Jacob, W.   Fu, E. G.   Luo, G. N.  

    In recent years reduced activation ferritic martensitic steel has been proposed as the plasmafacing material in remote regions of the first wall. This study reports the erosion and deuterium retention behaviours in CLF-1 steel exposed to deuterium (D) plasma in a linear experimental plasma system as function of incident ion energy and fluence. The incident D ion energy ranges from 30 to 180 eV at a flux of 4 x 10(21) D m(-2) s(-1) up to a fluence of 10(25) D m(-2). SEM images revealed a clear change of the surface morphology as functions of incident fluence and impinging energy. The mass loss results showed a decrease of the total sputtering yield of CLF-1 steel with increasing incident fluence by up to one order of magnitude. The total sputtering yield of CLF-1 steel after 7.2 x 10(24) D m(-2) deuterium plasma exposure reduced by a factor of 4 compared with that of pure iron, which can be attributed to the enrichment of W at the surface due to preferential sputtering of iron and chromium. After D plasma exposure, the total deuterium retention in CLF-1 steel samples measured by TDS decreased with increasing incident fluence and energy, and a clear saturation tendency as function of incident fluence or energy was also observed.
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  • The structural behavior of SrTiO3 under 400 keV Ne2+ ion irradiation

    Su, X.   Liu, C. G.   Yang, D. Y.   Wen, J.   Fu, E. G.   Zhang, J.   Chen, L. J.   Xu, D. P.   Wang, Y. Q.   Li, Y. H.  

    The structural behavior of polycrystalline perovskite SrTiO3 under 400 keV Ne2+ ion irradiation at both liquid nitrogen (LN2) and room temperature (RT) has been investigated. The grazing incident X-ray diffraction technique was applied to examine the radiation-induced structural evolution. The radiation behavior of SrTiO3 depends strongly on the irradiation temperature. At LN2 temperature, the samples exhibit significant lattice swelling and amorphization, whereas at RT, the lattice swelling is much less conspicuous and no amorphization is detected even at the highest irradiation dose of 5.0 dpa. Nevertheless, Ne2+ irradiation induces peak splitting in XRD patterns at both temperatures. Furthermore, first-principle calculations have been performed with VASP, involving possible defect types, to identify which defect is responsible for the radiation effect of SrTiO3. The results reveal that the oxygen vacancy defect is the most likely to contribute to the radiation behavior of SrTiO3.
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  • A facile approach to direct growth of layer-tunable graphene on Ge substrates

    Zhao, Yunbiao   Han, Dong   Wang, Xu   Hu, Zhaoyi   Chen, Yi   Chen, Yuhan   Zhou, Danqing   Li, Yue   Fu, E. G.   Zhao, Ziqiang  

    Direct synthesis of graphene with tunable layer number on semiconductor has proven challenging. Synthesis of layer-tunable graphene on catalytic metal surfaces, in particular Cu and Ni, has shown great success. The growth methods on metal layers involve an inevitable transfer procedure, which degrades and contaminates the graphene. Thus, direct synthesis of graphene on semiconductor is necessary and profound. Here, a facile synthesis approach for direct growth of graphene on Ge(110) subtrate via ion implantation was reported. Interestingly, the graphene growth during annealing is not self-limiting and the thickness of graphene can be precisely controlled by the carbon ion implanted fluence. Moreover, a detailed growth process upon segregation was investigated, and the results show graphene nucleation tends to occur near the Ge atomic step edges. Furthermore, the facile approach involving the ion implantation can be adopted to investigate the growth process on semiconductor and to control the number of graphene layers, thus promoting the practical application of graphene in nanoelectronics. (C) 2019 Elsevier Ltd. All rights reserved.
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  • Brilliant GeV gamma-ray flash from inverse Compton scattering in the QED regime

    Gong, Z.   Hu, R. H.   Lu, H. Y.   Yu, J. Q.   Wang, D. H.   Fu, E. G.   Chen, C. E.   He, X. T.   Yan, X. Q.  

    An all-optical scheme is proposed for studying laser plasma based incoherent photon emission from inverse Compton scattering in the quantum electrodynamic regime. A theoretical model is presented to explain the coupling effects among radiation reaction trapping, the self-generated magnetic field and the spiral attractor in phase space, which guarantees the transfer of energy and angular momentum from electromagnetic fields to particles. Taking advantage of a prospective similar to 10(23) W cm(-2) laser facility, 3D particle-in-cell simulations show a gamma-ray flash with unprecedented multi-petawatt power and brightness of 1.7 x 10(23) photons s(-1) mm(-2) mrad(-2)/0.1% bandwidth (at 1 GeV). These results bode well for new research directions in particle physics and laboratory astrophysics exploring laser plasma interactions.
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  • Design of Radiation Tolerant Nanostructured Metallic Multilayers

    Zhang, X.   Fu, E. G.   Li, Nan   Misra, A.   Wang, Y. -Q.   Shao, L.   Wang, H.  

    We review He ion induced radiation damage in several metallic multilayer systems, including Cu/V, Cu/Mo, Fe/W, and Al/Nb up to a peak dose of several displacements per atom (dpa). Size dependent radiation damage is observed in all systems. Nanolayer composites can store a very high concentration of He. Layer interfaces promote the recombination of opposite type of point defects and hence reduce the accumulative defect density, swelling, and lattice distortion. Interfaces also alleviate radiation hardening substantially. The chemical stability of interfaces is an important issue when considering the design of radiation tolerant nanolayer composites. Immiscible and certain miscible systems possess superior stability against He ion irradiation. Challenge and future directions are briefly discussed.
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  • Effect of grain boundary character on sink efficiency

    Han, W. Z.   Demkowicz, M. J.   Fu, E. G.   Wang, Y. Q.   Misra, A.  

    The dependence of the width of void-denuded zones (VDZs) on grain boundary (GB) characters was investigated in Cu irradiated with He ions at elevated temperature. Dislocation loops and voids formed near GBs during irradiation were characterized by transmission electron microscopy, and GB misorientations and normal planes were determined by electron back-scatter diffraction. The VDZ widths at Sigma 3 < 1 1 0 > tilt GBs ranged from 0 to 24 nm and increased with the GB plane inclination angle. For non-Sigma 3 GBs, VDZ widths ranged from 40 to 70 nm and generally increased with misorientation angle. Nevertheless, there is considerable scatter about this general trend, indicating that the remaining crystallographic parameters also play a role in determining the sink efficiencies of these GBs. In addition, the VDZ widths at two sides of a GB show different values for certain asymmetrical GBs. Voids were also observed within GB planes and their density and radius also appeared to depend on GB character. We conclude that GB sink efficiencies depend on the overall GB character, including both misorientation and GB plane orientation. Published by Elsevier Ltd. on behalf of Acta Materialia Inc.
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  • Surface effects on the radiation response of nanoporous Au foams

    Fu, E. G.   Caro, M.   Zepeda-Ruiz, L. A.   Wang, Y. Q.   Baldwin, K.   Bringa, E.   Nastasi, M.   Caro, A.  

    We report on an experimental and simulation campaign aimed at exploring the radiation response of nanoporous Au (np-Au) foams. We find different defect accumulation behavior by varying radiation dose-rate in ion-irradiated np-Au foams. Stacking fault tetrahedra are formed when np-Au foams are irradiated at high dose-rate, but they do not seem to be formed in np-Au at low dose-rate irradiation. A model is proposed to explain the dose-rate dependent defect accumulation based on these results.
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  • Surface effects on the radiation response of nanoporous Au foams

    Fu, E. G.   Caro, M.   Zepeda-Ruiz, L. A.   Wang, Y. Q.   Baldwin, K.   Bringa, E.   Nastasi, M.   Caro, A.  

    We report on an experimental and simulation campaign aimed at exploring the radiation response of nanoporous Au (np-Au) foams. We find different defect accumulation behavior by varying radiation dose-rate in ion-irradiated np-Au foams. Stacking fault tetrahedra are formed when np-Au foams are irradiated at high dose-rate, but they do not seem to be formed in np-Au at low dose-rate irradiation. A model is proposed to explain the dose-rate dependent defect accumulation based on these results. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4764528]
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  • Radiation damage in helium ion irradiated nanocrystalline Fe

    Yu, K. Y.   Liu, Y.   Sun, C.   Wang, H.   Shao, L.   Fu, E. G.   Zhang, X.  

    Fe films with an average columnar grain size varying from 49 to 96 nm are deposited by magnetron sputtering technique. Sputtered films have predominant body centered cubic structure together with a small fraction of face centered cubic phase. Bulk Fe with an average grain size of 700 nm is also irradiated at the same condition for comparison. Helium bubbles are observed in Fe films and bulk Fe irradiated by 100 keV helium ions to a fluence of 6 x 10(20) ions/m(2) at room temperature. Smaller grains lead to lower density of He bubbles. Radiation hardening in Fe films is much less than that of bulk Fe, and is a combined consequence of He bubble induced hardening and radiation induced compressive stress in Fe films. (c) 2011 Elsevier B.V. All rights reserved.
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  • Effects of ion irradiation in metallic glasses RID A-8619-2011

    Carter, Jesse   Fu, E. G.   Bassiri, G.   Dvorak, B. M.   Theodore, N. David   Xie, Guoqiang   Lucca, D. A.   Martin, Michael   Hollander, Mark   Zhang, Xinghang   Shao, Lin  

    Application of metallic glasses as structural materials has been limited by their poor ductility. To overcome brittle failure, nanocrystals are intentionally introduced to stabilize the glasses. In this study, we report on the application of ion irradiation to induce nanocrystalization in a Cu(50)Zr(45)Ti(5) (CZT) alloy. Transmission electron microcopy, microindentation and nanoindentation have been used to characterize the CZT alloy irradiated with 140 keV He ions at room temperature. Hardness enhancement was observed near the projected range of the He ions, coinciding with the formation of nanocrystals. Such microstructural changes, however, were not observed in the near surface region, where the electronic stopping process is dominant. (C) 2009 Elsevier B.V. All rights reserved.
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  • Interface-enabled Defect Reduction in He Ion Irradiated Metallic Multilayers

    Zhang, X.   Fu, E. G.   Misra, A.   Demkowicz, M. J.  

    Metallic multilayers are good model systems to explore the effects of heterophase interfaces in reducing radiation damage in structural materials We summarize recent studies on radiation damage in immiscible face centered cubic/body-centered cubic metallic multilayers in particular Cu/V and Cu/Nb These multilayers have shown unique characteristics compared to bulk metals under irradiation, including several orders of magnitude higher He solid solubility dramatic reduction of bubble density interface confined growth of He bubbles and much lower radiation hardening The mechanisms for interface enhanced radiation tolerance are briefly discussed
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  • Interface enabled defects reduction in helium ion irradiated Cu/V nanolayers

    Fu, E. G.   Misra, A.   Wang, H.   Shao, Lin   Zhang, X.  

    Sputter-deposited Cu/V nanolayer films with individual layer thickness, h, varying from 1 to 200 nm were subjected to helium (He) ion irradiation at room temperature. At a peak dose level of 6 displacements per atom (dpa), the average helium bubble density and lattice expansion decrease significantly with decreasing h. The magnitude of radiation hardening decreases with decreasing individual layer thickness, and becomes negligible when h is 2.5 nm or less. This study indicates that nearly immiscible Cu/V interfaces spaced a few nm apart can effectively reduce the concentration of radiation induced point defects. Consequently, Cu/V nanolayers possess enhanced radiation tolerance, i.e., reduction of swelling and suppression of radiation hardening, compared to monolithic Cu or V. (C) 2010 Elsevier B.V. All rights reserved.
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  • The temperature and size effect on the electrical resistivity of Cu/V multilayer films

    Wang, P. P.   Wang, X. J.   Du, J. L.   Ren, F.   Zhang, Y.   Zhang, X.   Fu, E. G.  

    The electrical resistivity of sputter-deposited Cu/V multilayer films with different individual layer thicknesses varying from 2.5 to 100 nm was evaluated in the temperature range of 150-300 K. The temperature coefficient of resistivity (TCR) of Cu/V multilayer was compared based on the semi-classical theory of Dimmich model. A new model has been proposed to describe the relationship between the resistivity and the individual layer thickness of metallic multilayer film by considering both interface scattering and grain boundary scattering based on Fuchs-Sondheimer method and Mayadas-Shatzkes method. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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  • Irradiation induced changes in small angle grain boundaries in mosaic Cu thin films

    Fu, E. G.   Wang, Y. Q.   Zou, G. F.   Xiong, J.   Zhuo, M. J.   Wei, Q. M.   Baldwin, J. K.   Jia, Q. X.   Shao, L.   Misra, A.   Nastasi, M.  

    We studied the effect of irradiation on small angle grain boundaries in mosaic structured Cu thin films. The films showed a decrease in mosaic spread via a narrowing of the full width at half maximum in XRD rocking curves and a smaller minimum yield of RBS channeling after irradiation. These data indicate the irradiation decreased the misorientation angles between mosaic blocks separated by small angle grain boundaries. Mechanisms involving interactions between grain boundary dislocations and irradiation induced defects are discussed.
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