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  • Articles: DFG German National Licenses  (93)
  • 2000-2004  (23)
  • 1995-1999  (70)
  • 1
    Electronic Resource
    Electronic Resource
    Microwave-mixing scanning capacitance microscopy of pn junctions (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 7094-7099 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe an approach to scanning capacitance microscopy. A mixing technique is employed for imaging local capacitance variations simultaneously with the sample topography using an atomic force microscope (AFM) with a conductive tip. A SiO2/Si sample with lateral pn junctions formed by ion implantation has been investigated. Microwave signals incident on the metal–oxide–semiconductor (MOS) structure formed by the AFM tip and the sample give rise to mixing signals due to the nonlinear voltage dependence of the space charge capacitance in the Si. In our experiments two microwave input signals with frequencies f1 and f2 and a variable dc bias voltage were applied to the tip-sample MOS structure. The dependence of the generated sum frequency and third harmonic signals on the dc sample voltage shows that the f1+f2 and 3 f signals are proportional to dC/dV and d2C/dV2, respectively. Images of the sum frequency and third harmonic signals delineating the pn junctions on our model sample are presented and the dc bias voltage dependence of the images is discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371797
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  • 2
    Electronic Resource
    Electronic Resource
    Physics issues in the design of high-beta, low-aspect-ratio stellarator experiments : The 41st annual meeting of the division of plasma physics of the american physical society (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1911-1918 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-beta, low-aspect-ratio ("compact") stellarators are promising solutions to the problem of developing a magnetic plasma configuration for magnetic fusion power plants that can be sustained in steady state without disrupting. These concepts combine features of stellarators and advanced tokamaks and have aspect ratios similar to those of tokamaks (2–4). They are based on computed plasma configurations that are shaped in three dimensions to provide desired stability and transport properties. Experiments are planned as part of a program to develop this concept. A β=4% quasi-axisymmetric plasma configuration has been evaluated for the National Compact Stellarator Experiment (NCSX). It has a substantial bootstrap current and is shaped to stabilize ballooning, external kink, vertical, and neoclassical tearing modes without feedback or close-fitting conductors. Quasi-omnigeneous plasma configurations stable to ballooning modes at β=4% have been evaluated for the Quasi-Omnigeneous Stellarator (QOS) experiment. These equilibria have relatively low bootstrap currents and are insensitive to changes in beta. Coil configurations have been calculated that reconstruct these plasma configurations, preserving their important physics properties. Theory- and experiment-based confinement analyses are used to evaluate the technical capabilities needed to reach target plasma conditions. The physics basis for these complementary experiments is described. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874015
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  • 3
    Electronic Resource
    Electronic Resource
    Molecular beam epitaxially grown n type Hg0.80Cd0.20Te(112)B using iodine (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 451-455 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The molecular beam epitaxial growth and n type doping of Hg0.80Cd0.20Te(112)B have been investigated. The surface morphology has been determined via atomic force microscopy and is appreciably different from that of the (001) orientation; long ridges and trenches are observed whose height difference is considerably less than that of the nearly elliptically shaped mounds found in (001) alloys. The mobility has been optimized with regard to growth parameters such as the Hg/Te flux ratio resulting in a maximum value of 4.0±0.6×105 cm2/(V s) for an undoped sample at low temperatures. n type Hg0.80Cd0.20Te(112)B has been grown using iodine in the form of CdI2 as a dopant. The maximum electron concentration due to iodine doping has been determined after an Hg vacancy anneal to be 4.2±0.7×1018 cm−3. Typical mobilities at low temperatures are 4.0×104 and 1.0×105 cm2/(V s) for electron concentration levels of 1.0×1017 and 5.0×1016 cm−3, respectively. By means of secondary ion mass spectroscopy the iodine concentration has been determined and hence the degree of activation. The electron concentration is proportional to that of iodine with a 100% electrical activation for concentrations up to (approximate)1018 cm−3. At higher concentrations compensation is observed. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1423770
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetic reversal of tapered permalloy bars with holes in the center (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 4601-4603 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic reversal mechanism of tapered permalloy bars with holes in the center was studied using a Magnetic Force Microscope with in situ magnetic field capability. The samples studied were lithographically patterned from a 20-nm-thick NiFe film using a subtractive process to create tapered bars 18 wide×348 μm long. The easy axis of the permalloy is parallel to the long axis of the bar. In the center of the tapered bar was either a 10, 5, or 3 μm diameter hole. The remnant state after saturation parallel to the long axis of the bar is a large domain magnetized along the saturating field direction except near the hole. The magnetization at the edge of the hole can be explained by considering edge pinning and the last direction of a saturating magnetic field. An inplane magnetic field parallel to the long axis of the bar reverses the magnetization by domain nucleation at the edge of the hole. After the bar has reversed, the same type of wall structure is seen as in the remnant state. As the magnetic field is increased further, the magnetization rotates away from parallel to the edge of the hole, as seen by the emergence of surface poles along the hole edge. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370421
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  • 5
    Electronic Resource
    Electronic Resource
    Dependence of the magnetization and remanence of single-domain particles on the second cubic anisotropy constant (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 6243-6250 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization and remanent magnetization curves for noninteracting single-domain particles with cubic magnetocrystalline anisotropy have been calculated, taking into account the first two anisotropy constants. The dependencies of the saturation remanence, coercivity, remanence coercivity, and δM plots on the anisotropy constants ratio have been discussed. It has been found that the calculated saturation remanence shows maxima in the vicinity of the spin-reorientation transition points for both negative and positive first cubic anisotropy constants. The remanent magnetization for the case when the face diagonals 〈110〉 are the easiest magnetization orientations has been analytically determined as well. It has been shown that when more than one type of easiest directions coexist, the remanence of the system can only be obtained numerically because of the history dependence of the remanent magnetization for some particles' configurations. The predicted remanence behavior for systems representing spin-reorientation has been compared with that of a Tb0.6Ho0.4Fe2 powder sample, and an excellent agreement between numerical and experimental data has been found. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1415062
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  • 6
    Electronic Resource
    Electronic Resource
    Shear force interaction in the viscous damping regime studied at 100 pN force resolution (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 3108-3112 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a very good force resolution for tuning fork based shear force microscopy as used for feedback regulation in scanning near-field optical microcopy (NSOM). The sensitivity and dynamics of fiber tips attached to 100 kHz tuning forks are investigated both experimentally and theoretically applying a finite element analysis. Operating the tuning fork at vibration amplitudes smaller than 10 nm allows to discriminate between viscous damping due to capillary wetting, and fiber bending upon tip-sample approach to hydrophilic sample surfaces indicating the direct transition from "noncontact operation" (pure viscous damping due to contamination layer) down to tip-sample contact. Viscous damping manifests in frequency shifts of less than 50 mHz, as deduced from resonance curves recorded under feedback control. For relative amplitude changes of less than 0.5% the viscous damping force acting lateral on the fiber tip is calculated to ∼100 pN using the finite element method. This detection limit proves that tuning fork based shear force control is superior to other feedback mechanisms employed in NSOM. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372306
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  • 7
    Electronic Resource
    Electronic Resource
    Microwave-frequency alternating current scanning tunneling microscopy by difference frequency detection: Atomic resolution imaging on graphite (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 3377-3380 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present a detailed description of an experimental setup for alternating current scanning tunneling microscopy, in which two slightly detuned high frequency signals are mixed at the tunneling junction and the resulting difference frequency signal is amplified using conventional scanning tunneling microscope electronics. This signal is used to control the distance between the microscope tip and the sample. With graphite as a model surface atomic resolution images have been obtained. It is demonstrated that the origin of the generated signal on graphite is the nonlinearity of the static current–voltage characteristics. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149922
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  • 8
    Electronic Resource
    Electronic Resource
    An insert for single-molecule magnetic-resonance spectroscopy in an external magnetic field (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 4853-4856 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe an insert for optical and magnetic-resonance experiments on single molecules in a solid matrix at liquid-helium temperatures. The experimental arrangement allows in situ adjustment of the focusing lens and of the sample. A parabolic mirror serves to collect the fluorescence emission and to direct the light onto a photodetector. Microwaves can be irradiated through a coil around the sample while a superconducting magnet provides the possibility of a stationary magnetic field. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146164
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  • 9
    Electronic Resource
    Electronic Resource
    Compact ultrahigh vacuum sample exchange device with wide temperature range (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 313-314 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the design and performance of a compact ultrahigh vacuum sample holder, which allows (1) sample transfer, (2) liquid-nitrogen cooling, (3) heating by electron bombardment, and (4) temperature measurement in direct proximity to the sample. The device operates from close to liquid-nitrogen temperatures up to temperatures of 800–900 K in the steady-state regime with peak temperatures in excess of 1700 K and allows easy and reliable sample transfer. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148526
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  • 10
    Electronic Resource
    Electronic Resource
    Annealing-induced effects on the stability of hydrogenated amorphous silicon (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 5959-5964 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We performed isothermal annealing on a hydrogenated amorphous silicon (a-Si:H) sample deposited at low temperature in a glow discharge reactor. In order to change the hydrogen bonding configuration without affecting the silicon structure we choose a relatively low annealing temperature. We studied the dependence on the annealing time of the dark conductivity, photoconductivity, light-induced degradation of the photoconductivity, optical gap, vibrational spectra, and subgap defect density. As the annealing time increased we found an increase in the dark conductivity activation energy. This shift of the dark Fermi level toward the valence band was correlated with the growth of a peak in the density of states below midgap. From the vibrational spectra we obtained the microstructure parameter, which is indicative of the amount of hydrogen bonded as polihydrides and/or to some sort of internal surface. We used the bond-breaking model to fit photoconductivity decay as a function of illumination time, and we found a correlation between the Staebler–Wronski susceptibility and the microstructure parameter. This would mean that the stability of the material concerning light-induced degradation is related to the way hydrogen is attached in the amorphous network. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360598
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