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  • 2000-2004  (23)
  • 1995-1999  (70)
  • 1990-1994  (70)
  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 5905-5911 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of β-FeSi2 on Si(111) have been studied by low energy electron diffraction (LEED) and high resolution electron energy loss spectroscopy (HREELS). The observed LEED pattern is consistent with two possible epitaxial orientations. HREELS measurements demonstrate the semiconducting character of the films. The energy gap is determined to Eg(approximately-equal-to)0.92 eV–0.33 meV/K T(K). Additionally a number of optical phonons is found in the range between 200 and 500 cm−1. Theoretical spectra are calculated with optical phonon parameters obtained from infrared data and are compared with the measured spectra.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The lattice parameters and the saturation magnetization are measured for the series of intermetallic compounds A(Fe,B)2, A=Zr, Hf and B=Si and Al, with concentrations less than 15%. The magnetization measurements and the lattice parameter behavior are qualitatively discussed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5497-5499 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article, the power spectra of the Barkhausen noise of Ni1−xMnx is presented. The measurements were made in the ferromagnetic phase at several temperatures and manganese concentrations in order to map the effects of the degree of disorder and of the temperature on domain wall dynamics. Measurements in standard ferromagnetic materials were also made to compare the dynamics in both cases.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 99-109 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Optically-detected electron–nuclear double resonance was employed to measure the entire hyperfine and quadrupole tensors of the two nitrogen nuclei and the hyperfine tensors of the four hydrogen nuclei in the lowest triplet state T0 of pyrimidine-h4 as a guest in a single crystal of benzene-d6. The electron-spin-density distribution and the molecular geometry in the lowest triplet state have been determined as well as the orientation of the molecule in the benzene crystal. It is found that upon excitation into T0, pyrimidine remains a planar molecule of approximately C2v symmetry; the C–N–C angles, which are 115.5° in the ground state, and the angle between the directions of the nonbonding nitrogen orbitals both become 〉120°. Nearly 60% of the total electron-spin density is located at the two nitrogen atoms, the two nonbonding orbitals each carrying a spin density of 0.21, and the π orbitals a spin density of 0.08. We conclude that the lowest triplet state of pyrimidine is appropriately described in terms of an nπ* excitation; we find no evidence for vibronic coupling of this state with higher lying 3ππ* states.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 110-117 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The hyperfine and quadrupole tensors of the two nitrogen atoms and the hyperfine tensors of the four hydrogen atoms of pyrazine in the lowest triplet state T0 are obtained from optically-detected electron–nuclear double resonance (ENDOR) experiments on pyrazine-h4 in a single crystal of benzene-d6 at 1.2 K. Analysis of these tensors shows that pyrazine is in good approximation a planar molecule of D2h symmetry in the lowest triplet state. The in-plane structure changes significantly upon excitation into T0. An increase of the C–N–C angles is observed and a reduction of the C–N bond lengths. From the hyperfine tensors the distribution of the electron-spin density is derived. The nitrogen nonbonding orbitals together carry 36% of the total spin density and it is shown that the lowest triplet state of pyrazine is appropriately described in terms of a 3nπ* excitation. The results of the optically-detected ENDOR experiments give no indication of vibronic coupling of the lowest 3nπ* state with nearby 3ππ* states.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 7094-7099 
    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
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  • 7
    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
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 582-589 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We measured the thicknesses of the vapor–liquid interfaces near the critical points of carbon dioxide (CO2), sulfur hexafluoride (SF6), and trifluoromethane (CHF3) using ellipsometry. The data (when scaled by the refractive index difference Δn and the correlation length ξ) are in agreement with other ellipticity data for binary and pseudobinary mixtures at low pressures. Fully constrained theories of the interface correctly predict the temperature dependence and scaling of the thickness but systematically overestimate the thickness itself by 15%–20%. The theory can be brought into agreement with experiment when an intrinsic interfacial stiffness is added to the theory. A novel feature of the present measurements is that the effects from pressure-induced window strain were measured and mitigated by using a cylindrically-symmetric pressure cell with floating seals.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 451-455 
    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
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 4601-4603 
    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
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