Publikationen


Suche nach „[D.] [Liu]“ hat 39 Publikationen gefunden
Suchergebnis als PDF
    NachhaltigElektrotechnik und Medientechnik

    Zeitschriftenartikel

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

    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

    2019

    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 Medientechnik

    Zeitschriftenartikel

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

    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

    2018

    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.

    NachhaltigElektrotechnik und MedientechnikMaschinenbau und Mechatronik

    Beitrag (Sammelband oder Tagungsband)

    Alexander Hofer, D. Liu, Günther Benstetter, M. Lanza, Werner Frammelsberger

    Chapter 3: Fundamentals of CAFM Operation Modes

    Conductive Atomic Force Microscopy: Applications in Nanomaterials, Weinheim

    2017

    ISBN: 978-3-527-34091-0

    IQWSonstige

    Zeitschriftenartikel

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

    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

    2017

    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 Medientechnik

    Zeitschriftenartikel

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

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

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

    2016

    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 Medientechnik

    Zeitschriftenartikel

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

    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

    2016

    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 Medientechnik

    Zeitschriftenartikel

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

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

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

    2016

    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 Medientechnik

    Zeitschriftenartikel

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

    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

    2015

    DOI: 10.1038/srep10959

    NachhaltigElektrotechnik und Medientechnik

    Zeitschriftenartikel

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

    Ordered arrangement of irradiation-induced defects of polycrystalline tungsten irradiated with low-energy hydrogen ions

    Journal of Nuclear Materials, vol. 464, pp. 216-220

    2015

    NachhaltigElektrotechnik und Medientechnik

    Zeitschriftenartikel

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

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

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

    2015

    NachhaltigAngewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    S. Liu, J. Sun, C. Sang, Thomas Stirner, S. Dai, D. Wang

    Molecular dynamics simulation of the formation, growth and bursting of bubbles in tungsten exposed to high fluxes of low energy deuterium

    Journal of Nuclear Materials - PLASMA-SURFACE INTERACTIONS 21 — Proceedings of the 21st International Conference on Plasma-Surface Interactions in Controlled Fusion Devices Kanazawa, Japan, May 26-30, 2014, vol. 463, no. August, pp. 363-366

    2015

    DOI: 10.1016/j.jnucmat.2014.12.060

    Abstract anzeigen

    Molecular dynamics simulations are carried out to investigate the formation, growth and bursting of bubbles in tungsten exposed to the irradiation of an extremely high deuterium flux. It is found that the bubbles form in the region near the location of the implanted ion distribution peaks, and that the effect of the substrate temperature on the bubble formation depth is negligible; it is also found that the percentage of deuterium that is found in D2 molecules increases as the bubble grows, and that the evolution of the bubble’s internal pressure is strongly associated with the properties of its surrounding structure. The simulations display the development of a dome-shaped structure at the tungsten surface during the bubble growth. The merging of two deuterium bubbles is also observed. The present simulations also show that the bubble bursts by generating a partially opened lid, which has already been observed in previous independent experiments.

    Elektrotechnik und Medientechnik

    Zeitschriftenartikel

    J. Niu, J. Gu, D. Li, D. Liu, Z. Feng, Günther Benstetter

    Comparison of fluorocarbon film deposition by pulsed/continuous wave and downstream radio frequency plasmas

    Vacuum, vol. 85, no. 2, pp. 253-262

    2010

    Abstract anzeigen

    Fluorocarbon (FC) films have been deposited using pulsed and continuous wave (cw) radio frequency (rf) plasmas fed with hexafluoroethane (C2F6), octafluoropropane (C3F8), or octafluorocyclobutane (C4F8). The effects of feed gases used, discharge pressure, rf power, substrate positions and discharge modes (pulsed or cw) on the deposited films are examined. Film properties are determined using X-ray photoelectron spectroscopy, atomic force microscopy, and static contact angle measurements. The contact angles of FC films are well related to their compositions and structures. Feed gases used, discharge pressure, rf power, substrate positions and discharge modes strongly affect the morphology of the resulting film, as revealed by atomic force microscopy. Optical emission spectrometry measurements were performed to in-situ characterize the gas-phase compositions of the plasmas and radicals’ emission intensities during film deposition. Correlations between film properties, gas-phase plasma diagnostic data, and film growth processes were discussed. The film growth in pulsed or downstream plasmas was controlled by the surface migration of radicals, such as CF2 towards nucleation centers, which result in the deposition of FC films with less cross-linked nature and rougher surfaces. These results demonstrate that it is possible to control film compositions and surface structure by changing deposition parameters.

    Elektrotechnik und Medientechnik

    Zeitschriftenartikel

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

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

    Submitted Article

    Thin Solid Films

    2010

    Elektrotechnik und Medientechnik

    Zeitschriftenartikel

    D. Liu, Günther Benstetter, R. Biberger

    A Review of Advanced Scanning Probe Microscope Analysis of Functional Films and Semiconductor Devices

    Thin Solid Films, vol. 517, no. 17, pp. 5100-5105

    2009

    Abstract anzeigen

    This paper gives an overview of established methods and new developments in the field of Scanning Probe Microscopy (SPM) of functional films and semiconductor devices. It focuses on both, SPM analyses of passive structures and devices in operation. The contribution includes techniques such as Scanning Capacitance Microscopy (SCM) and Scanning Spreading Resistance Microscopy (SSRM) for implant mapping, Conductive AFM (C-AFM) for thin dielectrics analysis and Kelvin Probe Force Microscopy (KPFM) to study the potential distribution across active electronic devices. Finally combinations of different SPM-based techniques are described and future challenges for SPM-based techniques are discussed.

    Elektrotechnik und Medientechnik

    Zeitschriftenartikel

    H. Du, D. Liu, Günther Benstetter, S. Zhang, S.-E. Ong

    Surface and electron emission properties of hydrogen-free diamond-like carbon films investigated by atomic force microscopy

    Materials Science & Engineering A, vol. 426, no. 1-2, pp. 114-120

    2006

    Abstract anzeigen

    In this study, we have deposited hydrogen-free diamond-like carbon (DLC) films by using DC magnetron sputtering of graphite target at various r.f. bias voltages. Surface and nanoscale emission properties of these DLC films have been investigated using a combination of atomic force microscopy (AFM)-based nanowear tests and conducting-AFM, by simultaneously measuring the topography and the conductivity of the samples. Nanowear tests show that these DLC films are covered with the thin (1.5–2.0 nm) graphite-like layers at surfaces. Compared to the film bulk structure, the graphite-like surface layers are more conductive. The graphite-like surface layers significantly influence the electron emission properties of these films. Low-energy carbon species can be responsible for the formation of graphite-like surface layers. Nanoscale electron emission measurements have revealed the inhomogeneous emission nature of these films. The low-field emission from these films can be attributed to the existence of sp2-configured nanoclusters inside the films.

    Elektrotechnik und Medientechnik

    Zeitschriftenartikel

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

    Properties and deposition processes of a-C: H films from CH4/Ar dielectric barrier discharge plasmas

    Surface & Coatings Technology, vol. 200, no. 20-21, pp. 5819-5822

    2006

    Abstract anzeigen

    Hydrogenated amorphous carbon (a-C: H) films were deposited from CH4+ Ar gas with low-pressure dielectric barrier discharge (DBD) plasmas. The deposition rate, film hardness and surface roughness were examined as a function of Ar concentration in CH4+ Ar. The experimental results revealed that both film hardness and surface roughness increase with increasing Ar concentration from 20% to 67%, and then decrease for Ar concentration exceeding 67%. Also, the deposition rate decreases monotonously with increasing Ar concentration. The high ratio of Ar+ flux per hydrocarbon species for the cases of Ar concentration exceeding 67% leaded to the decrease in growth rate and in surface roughness. CH4+ and Ar+ kinetic energies during the film deposition process were also analyzed theoretically based on ion drift-diffuse model. The theoretical analysis on ion kinetic energy indicated that the deposition of dense a-C: H film is proportional to an increase in kinetic energy of the hydrocarbon ion and the sputter of energetic Ar+ ions.

    Elektrotechnik und MedientechnikMaschinenbau und Mechatronik

    Zeitschriftenartikel

    D. Liu, Günther Benstetter, Werner Frammelsberger

    Nanoscale electron field emissions from the bare, hydrogenated and graphite-like layer covered tetrahedral amorphous carbon films

    Journal of Applied Physics, vol. 99, no. 4

    2006

    DOI: 10.1063/1.2171806

    Abstract anzeigen

    We have compared nanoscale electron field emissions from the bare, hydrogenated, and graphitelike-layer-covered tetrahedral amorphous carbon (ta-C) films. The electron field emission is investigated using a combination of atomic force microscopy (AFM)-based nanowear tests and conducting AFM, by simultaneously measuring the topography and the conductivity of the samples. The analysis of Fowler-Nordheim tunneling currents indicates the formation of filamentlike emission channels within ta-C films. The low-field emission from carbon films is primarily due to a field enhancement arising from conducting nanostructures inside the films. The implications of surface structures for electron field emission are discussed. Electrons are easily delocalized within sp2-bonded rings/chains at a film surface, which leads to an increase in the nanotip emission area. At identical emission currents of 60–80 pA, hydrogenated films are much more easily destroyed due to a relatively insulating surface structure. The results suggest that a very high emission site density, required for field-emission display applications, may be produced by locally modifying a film surface layer.

    Elektrotechnik und Medientechnik

    Zeitschriftenartikel

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

    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

    2005

    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 Medientechnik

    Zeitschriftenartikel

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

    Growth processes and surface properties of diamondlike carbon films

    Journal of Applied Physics, vol. 97

    2005

    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 Medientechnik

    Zeitschriftenartikel

    D. Liu, Günther Benstetter

    Conducting atomic force microscopy for nanoscale electron emissions from various diamond-like carbon films

    Applied Surface Science, vol. 249, no. 1-4, pp. 315-321

    2005

    DOI: 10.1016/j.apsusc.2004.12.029

    Abstract anzeigen

    Conducting atomic force microscopy (C-AFM) has been used to compare the nanoscale electron emissions from hydrogen-free (a-C), hydrogenated (a-C:H), and tetrahedral (ta-C) diamond-like carbon films. The current measurements are performed on the locations where the low-resistant surface layers are removed. The measurements show the uniform electron emissions from a-C:H and ta-C films. The inhomogeneous electron emission from the a-C film is primarily due to the conducting graphite clusters inside the film. The analysis of Fowler–Nordheim tunnelling currents indicates the formation of filament-like emission channels inside these films. The implications of film structures for electron field emissions are discussed.