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Suche nach „[Y.] [Liu]“ hat 24 Publikationen gefunden
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    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    H. Fan, Y. Zhang, D. Liu, C. Niu, L. Liu, W. Ni, Y. Xia, Z. Bi, Günther Benstetter, G. Lei

    Tensile stress-driven cracking of W fuzz over W crystal under fusion-relevant He ion irradiations

    Nuclear Fusion, vol. 60, no. 4

    DOI: 10.1088/1741-4326/ab71bb

    Abstract anzeigen

    Although W fuzz is formed in the divertor region of the fusion reactor, no theory may clearly explain the W fuzz growth mechanism. In this study, we observe the growth process of W fuzz over W crystal under ITER-relevant He ion irradiations. We propose the tensile stress-driven cracking of nano-structured fuzz during the initial growth of W fuzz. We demonstrate that the existence of tensile stress is due to the swelling of He nano-bubbles in the fuzz. After this cracking, the W fuzz breaks away from the planar network and grows over the W surface, where the micro-stress in the W surface layer acts as the driving force.

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    Z. Bi, D. Liu, Y. Zhang, L. Liu, Y. Xia, Y. Hong, H. Fan, Günther Benstetter, G. Lei, L. Yan

    The evolution of He nanobubbles in tungsten under fusion-relevant He ion irradiation conditions

    Nuclear Fusion, vol. 59, no. 8

    DOI: 10.1088/1741-4326/ab2472

    Abstract anzeigen

    He-induced W nanofuzz growth over the W divertor target is one of the main limiting factors affecting the current design and development of fusion reactors. In this paper, based on He reaction rate model in W, we simulate the growth and evolution of He nanobubbles during W nanofuzz formation under fusion-relevant He+ irradiation conditions. Our modeling unveils the existence of He nanobubble-enriched W surface layer (<10 nm), formed due to the He diffusion in W crystal into defect sites. At an elevated temperature, the growth of He bubbles in the W surface layer prevents He atoms diffusing into the deep layer (>10 nm). The formation of W nanofuzz at the surface is attributed to surface bursting of high-density He bubbles with their radius of ~4 nm, and an increase in the surface area of irradiated W. Our findings have been well confirmed by the experimental measurements.

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    W. Ni, L. Liu, Y. Zhang, C. Niu, H. Fan, G. Song, D. Liu, Günther Benstetter, G. Lei

    Effect of intermittent He/D ion irradiations on W nano-fuzz growth over W targets

    Vacuum, vol. 173, no. March

    DOI: 10.1016/j.vacuum.2019.109146

    Abstract anzeigen

    The intermittent He/D ion irradiations of polycrystalline W have been performed at the ion energy of 50 eV by changing the time of the single irradiations and the irradiation temperature. All irradiated W specimens have been observed by scanning electron microscopy, and the effect of intermittent He/D ion irradiations on the W fuzz growth has been analyzed. The W fuzz growth over W targets does not show the clear dependence on the intermittent He/D ion irradiations, where the He/D ion fluence of the single irradiations typically varies from 5.0 × 1024 to 2.5 × 1025/m2. However, a slight change in the W surface temperature during the single He ion irradiations significantly affects the W fuzz growth rate. Analysis indicates that W fuzz growth is significantly affected by the total He ion fluence varying from 5.0 × 1024 to 5.0 × 1025/m2 and the irradiation temperature varying from 1100 to 1450 K. This current study will play a crucial role in understanding the W fuzz growth under the periodic He/D ion irradiations of W divertor in fusion reactors, such as ELMs.

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    W. Ni, L. Liu, Y. Zhang, H. Fan, G. Song, D. Liu, Günther Benstetter, G. Lei

    Mass loss of pure W, W-Re alloys, and oxide dispersed W under ITER-relevant He ion irradiations

    Journal of Nuclear Materials, vol. 527

    DOI: 10.1016/j.jnucmat.2019.151800

    Abstract anzeigen

    In this study, polycrystalline W, W-Re alloys, and La2O3 and Y2O3 dispersion-strengthened W have been irradiated by our large-power materials irradiation experimental system (LP-MIES) at the irradiation temperature of 1360–1460 K. Our measurements show that the W nano-fuzz layer which is < 5.2 μm thick has been formed over all the specimens exposed to the low-energy (50 or 100 eV) and high-flux (1.37 × 1022–1.62 × 1022 ions/m2⋅s) He+ irradiations. The mass loss of the fuzz layer almost linearly increases with the He+ fluence, which does not show any dependence on the thickness of fuzz layer varying from 1.1 to 5.2 μm La2O3 and Y2O3 dispersions into W significantly suppress the growth of W fuzz, indicating that He diffusion and the evolution of He nano-bubbles in the near-surface can be significantly influenced due to the dispersion. After He+ (100 eV) irradiation at He+ fluence of 5.83 × 1026/m2, the mass loss of 0.1 vol% - 1.0 vol% La2O3-dispersed W is about 20% lower than the one of the pure W, and the La2O3 dispersed W exhibits the best erosion resistance among various W material grades. Our analysis indicates that both the surface sputtering of W fuzz by energetic ions and surface bursting of He nano-bubbles can be responsible for the mass loss of W under ITER-relevant He+ irradiations.

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    L. Liu, S. Li, D. Liu, Günther Benstetter, O. Man, J. Michalicka, Y. Zhang, Y. Hong, H. Fan, W. Ni, Q. Yang, Y. Wu, Z. Bi

    The effect of O2 impurity on surface morphology of polycrystalline W during low-energy and high-flux He+ irradiation

    Fusion Engineering and Design, vol. 139, pp. 96-103

    DOI: 10.1016/j.fusengdes.2019.01.003

    Abstract anzeigen

    The interaction between the impurities (such as carbon, nitrogen, oxygen) and the plasma-facing materials (PFMs) can profoundly influence the performance and service of the PFMs. In this paper, we investigated the influence of oxygen (O2) impurity in the helium radio frequency (RF) plasma on the surface morphology of polycrystalline tungsten (W) irradiated at the surface temperature of 1450 ± 50 K and the ion energy of 100 eV. The pressure ratio of O2 to He (R) in RF source varied from 4.0 × 10−6 to 9.0 × 10-2. The total irradiation flux and fluence were ˜1.2 × 1022 ions·m-2·s-1 and ˜1.0 × 1026 ions·m-2, respectively. After He+ irradiation, the specimen surface morphology was observed by scanning electron microscopy. It was found that with increasing R from 4.0 × 10−6 to 9.0 × 10-2 the thickness of nano-fuzz layer at the W surface was thinner and thinner, accompanied by the formation of rod-like structures. The erosion yield increased from 5.2 × 10-4 to 2.3 × 10-2 W/ion when R varied from 4.0 × 10-6 to 9.0 × 10-2. The X-ray diffraction analysis shows that tungsten oxides were formed at the near surface of specimens when R exceeded 1.8 × 10-2. The erosion yield measurements revealed that in addition to surface physical sputtering process, the chemical erosion process could occur due to the interaction between oxygen-containing species and W at the surface. The results indicated that the presence of O2 impurity in He plasma can obviously affect the surface microstructure of W. The study suggested that O2 impurity can effectively reduce the growth of nano-fuzz structures.

    NachhaltigElektrotechnik und MedientechnikIQMA

    Vortrag

    D. Liu, H. Fan, L. Liu, Y. You, Günther Benstetter, F. Zhang

    Surface diffusion and growth of W self-interstitials during low-energy and large-flux H/He ion irridiations of polycrystalline W

    International Conference on Plasma Surface Interactions in Controlled Fusion Devices, Princeton University, NJ, USA

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    L. Liu, S. Li, D. Liu, Günther Benstetter, Y. Zhang, Y. Hong, H. Fan, W. Ni, Q. Yang, Y. Wu, Z. Bi

    Surface damages of polycrystalline W and La2O3-doped W induced by high-flux He plasma irradiation

    Journal of Nuclear Materials, vol. 501, no. April, pp. 275-281

    Abstract anzeigen

    In this study, polycrystalline tungsten (W) and three oxide dispersed strengthened W with 0.1 vol %, 1.0 vol % and 5.0 vol % lanthanum trioxide (La2O3) were irradiated with low-energy (200 eV) and high-flux (5.8 × 1021 or 1.4 × 1022 ions/m2⋅s) He+ ions at elevated temperature. After He+ irradiation at a fluence of 3.0 × 1025/m2, their surface damages were observed by scanning electron microscopy, energy dispersive spectroscopy, scanning electron microscopy-electron backscatter diffraction, and conductive atomic force microscopy. Micron-sized holes were formed on the surface of W alloys after He+ irradiation at 1100 K. Analysis shows that the La2O3 grains doped in W were sputtered preferentially by the high-flux He+ ions when compared with the W grains. For irradiation at 1550 K, W nano-fuzz was formed at the surfaces of both polycrystalline W and La2O3-doped W. The thickness of the fuzz layers formed at the surface of La2O3-doped W is 40% lower than the one of polycrystalline W. The presence of La2O3 could suppress the diffusion and coalescence of He atoms inside W, which plays an important role in the growth of nanostructures fuzz.

    IQWSonstige

    Zeitschriftenartikel

    A. Al Lily, J. Foland, D. Stoloff, A. Gogus, I. Erguvan, M. Awshar, J. Tondeur, M. Hammond, I. Venter, P. Jerry, A. Oni, Y. Liu, R. Badosek, López de la Madrid, M.C., E. Mazzoni, D. Vlachopoulos, H. Lee, K. Kinley, M. Kalz, U. Sambuu, T. Bushnaq, N. Pinkwart, N. Adedokun-Shittu, P.-O. Zander, K. Oliver, L. Teixeira Pombo, J. Balaban Sali, S. Gregory, S. Tobgay, M. Joy, J. Elen, Odeh Helal Jwaifell, M., M.N.H.M. Said, Y. Al-Saggaf, A. Naaji, J. White, K. Jordan, J. Gerstein, İ. Umit Yapici, C. Sanga, P. Nleya, B. Sbihi, M. Rocha Lucas, V. Mbarika, S. Schön, L. Sujo-Montes, M. Santally, P. Häkkinen, A. Al Saif, Andreas Gegenfurtner, S. Schatz, V. Padilla Vigil, C. Tannahill, S. Padilla Partida, Z. Zhang, K. Charalambous, A. Moreira, M. Coto, et al.

    Academic domains as political battlegrounds

    A global enquiry by 99 academics in the fields of education and technology

    Information Development, vol. 33, no. 3, pp. 270-288

    DOI: 10.1177/0266666916646415

    Abstract anzeigen

    This article theorizes the functional relationship between the human components (i.e., scholars) and non-human components (i.e., structural configurations) of academic domains. It is organized around the following question: in what ways have scholars formed and been formed by the structural configurations of their academic domain? The article uses as a case study the academic domain of education and technology to examine this question. Its authorship approach is innovative, with a worldwide collection of academics (99 authors) collaborating to address the proposed question based on their reflections on daily social and academic practices. This collaboration followed a three-round process of contributions via email. Analysis of these scholars’ reflective accounts was carried out, and a theoretical proposition was established from this analysis. The proposition is of a mutual (yet not necessarily balanced) power (and therefore political) relationship between the human and non-human constituents of an academic realm, with the two shaping one another. One implication of this proposition is that these non-human elements exist as political ‘actors’, just like their human counterparts, having ‘agency’ – which they exercise over humans. This turns academic domains into political (functional or dysfunctional) ‘battlefields’ wherein both humans and non-humans engage in political activities and actions that form the identity of the academic domain.

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    H. Fan, Y. You, W. Ni, Q. Yang, L. Liu, Günther Benstetter, D. Liu, C. Liu

    Surface degeneration of W crystal irradiated with low-energy hydrogen ions

    Scientific Reports (Nature Publishing Group), vol. 6, no. Article number: 23738

    DOI: 10.1038/srep23738

    Abstract anzeigen

    The damage layer of a W (100) crystal irradiated with 120 eV hydrogen ions at a fluence of up to 1.5 × 1025/m2 was investigated by scanning electron microscopy and conductive atomic force microscopy (CAFM). The periodic surface degeneration of the W crystal at a surface temperature of 373 K was formed at increasing hydrogen fluence. Observations by CCD camera and CAFM indicate the existence of ultrathin surface layers due to low-energy H irradiation. The W surface layer can contain a high density of nanometer-sized defects, resulting in the thermal instability of W atoms in the surface layer. Our findings suggest that the periodic surface degeneration of the W crystal can be ascribed to the lateral erosion of W surface layers falling off during the low-energy hydrogen irradiation. Our density functional theory calculations confirm the thermal instability of W atoms in the top layer, especially if H atoms are adsorbed on the surface.

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    L. Liu, D. Liu, Y. Hong, H. Fan, W. Ni, Q. Yang, Z. Bi, Günther Benstetter, S. Li

    High-flux He+ irradiation effects on surface damages of tungsten under ITER relevant conditions

    Journal of Nuclear Materials, vol. 471, no. April, pp. 1-7

    DOI: 10.1016/j.jnucmat.2016.01.001

    Abstract anzeigen

    A large-power inductively coupled plasma source was designed to perform the continuous helium ions (He+) irradiations of polycrystalline tungsten (W) under International Thermonuclear Experimental Reactor (ITER) relevant conditions. He+ irradiations were performed at He+ fluxes of 2.3 × 1021–1.6 × 1022/m2 s and He+ energies of 12–220 eV. Surface damages and microstructures of irradiated W were observed by scanning electron microscopy. This study showed the growth of nano-fuzzes with their lengths of 1.3–2.0 μm at He+ energies of >70 eV or He+ fluxes of >1.3 × 1022/m2 s. Nanometer-sized defects or columnar microstructures were formed in W surface layer due to low-energy He+ irradiations at an elevated temperature (>1300 K). The diffusion and coalescence of He atoms in W surface layers led to the growth and structures of nano-fuzzes. This study indicated that a reduction of He+ energy below 12–30 eV may greatly decrease the surface damage of tungsten diverter in the fusion reactor.

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    Y. Ji, H. Fei, Y. Shi, V. Igelsias, D. Lewis, N. Jiebin, S. Long, M. Liu, Alexander Hofer, Werner Frammelsberger, Günther Benstetter, A. Scheuermann, P. McIntyre, M. Lanza

    Characterization of the photocurrents generated by the laser of atomic force microscopes

    Review of Scientific Instruments, vol. 87, no. 8

    DOI: 10.1063/1.4960597

    Abstract anzeigen

    The conductive atomic force microscope (CAFM) has become an essential tool for the nanoscale electronic characterization of many materials and devices. When studying photoactive samples, the laser used by the CAFM to detect the deflection of the cantilever can generate photocurrents that perturb the current signals collected, leading to unreliable characterization. In metal-coated semiconductor samples, this problem is further aggravated, and large currents above the nanometer range can be observed even without the application of any bias. Here we present the first characterization of the photocurrents introduced by the laser of the CAFM, and we quantify the amount of light arriving to the surface of the sample. The mechanisms for current collection when placing the CAFM tip on metal-coated photoactive samples are also analyzed in-depth. Finally, we successfully avoided the laser-induced perturbations using a two pass technique: the first scan collects the topography (laser ON) and the second collects the current (laser OFF). We also demonstrate that CAFMs without a laser (using a tuning fork for detecting the deflection of the tip) do not have this problem.

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    Q. Yang, Y.-W. You, L. Liu, H. Fan, W. Ni, D. Liu, C. Liu, Günther Benstetter, Y. Wang

    Nanostructured fuzz growth on tungsten under low-energy and high-flux He irradiation

    Scientific Reports (Nature Publishing Group), vol. 5, no. Article number: 10959, pp. 1-9

    DOI: 10.1038/srep10959

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    Q. Yang, H. Fan, W. Ni, L. Liu, Tobias Berthold, Günther Benstetter, D. Liu, Y. Wang

    Observation of interstitial loops in He+ irradiated W by conductive atomic force microscopy

    Acta Materialia, vol. 92, pp. 178-188

    Elektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    J. Niu, H.-X. Ding, Y. Cong, N. Yu, Günther Benstetter, D. Liu

    Plasma-assisted chemical vapor deposition of titanium oxide films by dielectric barrier discharge

    Submitted Article

    Thin Solid Films

    Elektrotechnik und MedientechnikIQMA

    Vortrag

    D. Liu, Günther Benstetter, Y. Liu, T. Ma

    Surface Roughness and Mechanical Properties of a-C:H Films Prepared by Low-pressure Dielectric Barrier Discharge

    International Conference on Plasma Surface Engineering (PSE2002), Garmisch-Partenkirchen

    Elektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    Y. Liu, J. Zhang, D. Liu, T. Ma, Günther Benstetter

    A triangular section magnetic solenoid filter for removal of macro- and nano-particles from pulsed graphite cathodic vacuum arc plasmas

    Surface & Coatings Technology, vol. 200, no. 7, pp. 2243-2248

    DOI: 10.1016/j.surfcoat.2004.09.032

    Abstract anzeigen

    A novel magnetic filter with the triangular section has been designed to remove the macro- and nano-particles from the pulsed cathodic arc plasmas utilized to prepare the tetrahedral amorphous carbon (ta-C) films. The macro- and nano-particles at the surfaces of ta-C films were observed using an optical microscope and an atomic force microscope. The filter was found to be very effective in removing the macro- and nano-particles due to its zigzag-type inner surface structure. Particles that collided with the inner surface of the filter were reflected along the direction opposite to the plasma beam, and therefore separated from the arc plasma. The effect of arc current on the filter efficiency has also been investigated.

    Elektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    D. Liu, J. Zhang, Y. Liu, J. Xu, Günther Benstetter

    Growth processes and surface properties of diamondlike carbon films

    Journal of Applied Physics, vol. 97

    DOI: 10.1063/1.1890446

    Abstract anzeigen

    In this study, we compare the deposition processes and surface properties of tetrahedral amorphous carbon (ta-C) films from filtered pulsed cathodic arc discharge (PCAD) and hydrogenated amorphous carbon (a-C:H) films from electron cyclotron resonance (ECR)-plasma source ion implantation. The ion energy distributions (IEDs) of filtered-PCAD at various filter inductances and Ar gas pressures were measured using an ion energy analyzer. The IEDs of the carbon species in the absence of background gas and at low gas pressures are well fitted by shifted Maxwellian distributions. Film hardness and surface properties show a clear dependence on the IEDs. ta-C films with surface roughness at an atomic level and thin (0.3–0.9 nm) graphitelike layers at the filmsurfaces were deposited at various filter inductances in the highly ionized plasmas with the full width at half maximum ion energy distributions of 9–16 eV. The a-C:H filmsdeposited at higher H/C ratios of reactive gases were covered with hydrogen and sp3 bonded carbon-enriched layers due to the simultaneous interaction of hydrocarbon species and atomic hydrogen. The effects of deposited species and ion energies on filmsurface properties were analyzed. Some carbon species have insufficient energies to break the delocalized π(nC)bonds at the graphitelike filmsurface, and they can govern filmformation via surface diffusion and coalescence of nuclei. Dangling bonds created by atomic hydrogen lead to uniform chemisorption of hydrocarbon species from the ECR plasmas. The deposition processes of ta-C and a-C:H films are discussed on the basis of the experimental results.

    Elektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    D. Liu, Günther Benstetter, Edgar Lodermeier, J. Zhang, Y. Liu, J. Vancea

    Filtered pulsed carbon cathodic arc: plasma and amorphous carbon properties

    Journal of Applied Physics, vol. 95, pp. 7624-7631

    DOI: 10.1063/1.1753081

    Abstract anzeigen

    The carbonplasma ion energies produced by the filtered pulsed cathodic arc discharge method were measured as a function of filter inductance. The energy determination is based on the electro-optical time-of-flight method. The average ion energies of the pulsed ion beams were found to depend upon the rise time and duration of pulsed arc currents, which suggests that a gain of ion kinetic energy mainly arises from the electric plasma field from the ambipolar expansion of both electrons and ions, and an electron drag force because of the high expansion velocity of the electrons. The tetrahedral amorphous carbon (ta-C) films with a sp3 fraction of ∼70% were deposited on silicon substrates at the average ion energies of >6 eV in the highly ionized plasmas. The ta-C films were found to be covered with a few graphitelike atomic layers. The surfaceproperties of ultrathin carbonfilms, such as nanoscale friction coefficients, surface layer thickness, and silicon contents were strongly dependent on the ion energies. The growth of amorphous carbonfilms was explained in terms of the thermal spike migration of surfacecarbon atoms. In terms of this model, the thermal spike provides the energy required to release surface atoms from their metastable positions and leads to the formation of the sp3 bonded carbon on a sp3 bonded matrix. The experimental results indicate that the low-energy (<3 eV)carbon ions have insufficient energies to cause the rearrangement reaction within the film and they form graphitelike structures at filmsurface.

    Elektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    D. Liu, Günther Benstetter, Y. Liu, X. Xang, S. Yu, T. Ma

    Medium- to high-pressure plasma deposition of a-C:H films by dielectric barrier discharge

    New Diamond and Frontier Carbon Technology, vol. 13, no. 4, pp. 191-206

    Elektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    D. Li, Günther Benstetter, Edgar Lodermeier, I. Akula, I. Dudarchyk, Y. Liu, T. Ma

    SPM investigation of diamond-like carbon and carbon nitride films

    Surface & Coatings Technology, vol. 172, no. 2-3, pp. 194-203

    DOI: 10.1016/S0257-8972(03)00338-4

    Abstract anzeigen

    Scanning probe microscopy was used to evaluate and compare the surface roughness, mechanical and tribological properties of hydrogenated (a-C:H) and tetrahedral (ta-C) diamond-like carbon (DLC) and amorphous carbon nitride (a-C:N) films. Compared to the a-C:H and a-C:N films, the ta-C films exhibit the lowest surface roughness. The soft surface layers of DLC and a-C:N films were revealed by nanowear tests and their thickness varies over the range of 0.2 to 4.1 nm. The nanoscale friction coefficient measurements from lateral force microscopy shows that these films have obviously different friction coefficients. The lower friction coefficients of ta-C and a-C:N films can be attributed to the existence of soft graphite-like surface structure. We proposed the deposition processes of DLC and a-C:N films, where their surface roughness, structure and mechanical properties were associated with the vapor plasma particle energy distribution.