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  • 1
    Digitale Medien
    Digitale Medien
    Pulsed-laser induced desorption and subsequent readsorption in ambient gas (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 2877-2879 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have investigated the phenomenon of readsorption after pulsed-laser induced thermal desorption during the presence of ambient gas. The temporal evolution of the readsorption of water has been measured as a function of the ambient gas pressure for helium and carbon-dioxide atmospheres. CO2 pressures above 10 mbar lead to a virtually complete readsorption of the desorbed material. A model based on a nearly one-dimensional diffusion scheme explains this remarkable result.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.109187
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  • 2
    Digitale Medien
    Digitale Medien
    Grain size control in polycrystalline colloidal solids (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 5082-5087 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Recent experiments on the static and dynamic properties of polycrystalline colloidal solids show a pronounced influence of morphological details. Here we investigate several possibilities to vary systematically one key morphological parameter, namely the average crystallite radius rc of polycrystalline solids. We report measurements of rc as observed by microscopy in well-characterized Yukawa model suspensions. The pair energy of interaction is systematically varied through precise experimental adjustment of the suspension parameters packing fraction Φ, number of ionic surface groups N, and concentration of screening ions c. The average size is found to systematically decrease with increasing interaction. At fixed suspension parameters we performed solidification under shear, i.e., in the presence of alternating electric fields. We report preliminary results in dependence on both the electric field strength and frequency. The grain size increases with increasing shear rates. It shows a complex behavior as a function of the frequency and the wave form of the applied field. Qualitative explanations are discussed and a first application is presented. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.469558
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  • 3
    Digitale Medien
    Digitale Medien
    Wetting studies of liquid 4He on various Cs surfaces (1998)
    Springer
    Journal of low temperature physics 113 (1998), S. 805-810 
    Details
    ISSN: 1573-7357
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Cesium is a surface not wetted by liquid 4 He below a certain temperature, T w ≈ 2K. However, one observes that a thick helium film remains on the Cs substrate even if the surface is cooled below T w from the wetted state. This leaves the question how the system will finally evolve from this metastable state to the thermodynamic equilibrium, represented by a microscopically thin film. We investigate the dynamic and static behavioar of dewetting 4 He films on cesiated surfaces. Space and time resolved measurements of the thickness of the helium film are performed using a surface plasmon microscope. We have measured the work function of pure and oxidized Cs via photo current spectroscopy.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1022586402420
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  • 4
    Digitale Medien
    Digitale Medien
    Possible correlation effects of surface state electrons on a solid hydrogen film (1992)
    Springer
    Journal of low temperature physics 89 (1992), S. 743-746 
    Details
    ISSN: 1573-7357
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We have investigated the transport properties of surface state electrons on thin quench-condensed hydrogen films for various electron densities. The surface state electron mobility showed a continuous dependence on the plasma parameter Γ in the range from 20 to 130, indicating a strong influence of correlation effects within the electron system for all measured values of Γ.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00694131
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  • 5
    Digitale Medien
    Digitale Medien
    Surface state electrons on a hydrogen film. 2. Influence of adsorbed helium films (1991)
    Springer
    Journal of low temperature physics 85 (1991), S. 423-444 
    Details
    ISSN: 1573-7357
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We have investigated the conductivity of surface state electrons on liquid4He films supported by a quench-condensed thin solid hydrogen substrate. A pronounced dip in the ac-conductivity was observed as the He film thickness reached about 10 layers. This phenomenon was studied at different temperatures (range between 1.6 and 2 K), electron densities from 0.9 to 19×108 cm−2, frequencies between 1 and 100 kHz, and for various amplitudes of the ac driving voltage. Ripplon scattering and a ripplonic polaron are discussed as sources for the conductivity dip.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00682195
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  • 6
    Digitale Medien
    Digitale Medien
    Surface-state electrons on a hydrogen film. 1. Annealing of the film (1991)
    Springer
    Journal of low temperature physics 82 (1991), S. 279-293 
    Details
    ISSN: 1573-7357
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We have investigated the surface of thin films (thickness ∼2 µm) of solid H2 between 1.5 and 4.2 K by measuring the ac conductivity of surface-state electrons (SSE). The films were prepared on a glass substrate by quench condensation at 1.5 K and were therefore initially strongly disordered. In fact the surface of the virgin films before any heat treatment was so rough that no current due to SSE could be observed. Annealing the films decreased the surface roughness and gave rise to a thermal-activation-type temperature dependence of the SSE conductivity. By proper heat treatment up to 8 K the activation energy could be reduced to 10k B.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00681420
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  • 7
    Digitale Medien
    Digitale Medien
    First dc Measurements of Electrons on Liquid Helium: the Helium-FET (2000)
    Springer
    Journal of low temperature physics 121 (2000), S. 603-608 
    Details
    ISSN: 1573-7357
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We present the first dc-measurements on a 2-dimensional (2D) electron system floating above a liquid 4 He-film which covers a structured metal surface. With our arrangement of a source-, gate-, and drain-electrode a 2-dimensional charge transport is realized in analogy to a field-effect-transistor. The electrons which are moving along the x-direction due to different dc potentials are directly measured. This dc current, of the order of pA, is strongly dependent on the applied split-gate voltage. So the electrons were laterally confined to a narrow channel between the two gate electrodes. The effective width of the channel is reduced by the gate potential, so that a quasi-1D configuration can be realized. The measured electron current through the split-gate is analyzed and discussed on grounds of reduced dimensionality and 1D electron transport behaviour.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1017567611934
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  • 8
    Digitale Medien
    Digitale Medien
    Ions at helium interfaces (1995)
    Springer
    The European physical journal 98 (1995), S. 303-308 
    Details
    ISSN: 1434-6036
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The boundaries between different phases of condensed helium provide an interesting testing ground for studying ions in a quantum matter matrix. Here we consider the simplest positive and negative ions in helium — snowballs and electron bubbles, respectively — being trapped at the liquid-liquid interface of phaseseparated3He−4He mixtures and at the liquid-solid interface of4He. A comparison of experimental results for the trapping with predictions of the snowball and the bubble models shows that the models are in qualitative accord with the observations, but disagree in detail. It is suggested to use such studies for refinements of the ion models. In addition multielectron bubbles (=mesoscopic ions) and electrons on helium films are briefly discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01338394
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  • 9
    Digitale Medien
    Digitale Medien
    Mapping EEG-potentials on the surface of the brain: A strategy for uncovering cortical sources (1997)
    Springer
    Brain topography 9 (1997), S. 203-217 
    Details
    ISSN: 1573-6792
    Schlagwort(e): High spatial sampling EEG ; Spatial deblurring ; Current source density ; Cortical Mapping ; Spherical spline interpolation ; Inverse problem
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary This paper describes a uniform method for calculating the interpolation of scalp EEG potential distribution, the current source density (CSD), the cortical potential distribution (cortical mapping) and the CSD of the cortical potential distribution. It will be shown that interpolation and deblurring methods such as CSD or cortical mapping are not independent of the inverse problem in potential theory. Not only the resolution but also the accuracy of these techniques, especially those of deblurring, depend greatly on the spatial sampling rate (i.e., the number of electrodes). Using examples from simulated and real (64 channels) data it can be shown that the application of more than 100 EEG channels is not only favourable but necessary to guarantee a reasonable accuracy in the calculations of CSD or cortical mapping. Likewise, it can be shown that using more than 250 electrodes does not improve the resolution.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01190389
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