Search Results - (Author, Cooperation:C. Hoffman)

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  1. 1
    Staff View
    Publication Date:
    2018-10-17
    Publisher:
    American Physical Society (APS)
    Print ISSN:
    0556-2813
    Electronic ISSN:
    1089-490X
    Topics:
    Physics
    Keywords:
    Nuclear Structure
    Published by:
    http://www.aps.org/

    Latest Papers from Table of Contents or Articles in Press
  2. 2
    A. S. Morrissy ; L. Garzia ; D. J. Shih ; S. Zuyderduyn ; X. Huang ; P. Skowron ; M. Remke ; F. M. Cavalli ; V. Ramaswamy ; P. E. Lindsay ; S. Jelveh ; L. K. Donovan ; X. Wang ; B. Luu ; K. Zayne ; Y. Li ; C. Mayoh ; N. Thiessen ; E. Mercier ; K. L. Mungall ; Y. Ma ; K. Tse ; T. Zeng ; K. Shumansky ; A. J. Roth ; S. Shah ; H. Farooq ; N. Kijima ; B. L. Holgado ; J. J. Lee ; S. Matan-Lithwick ; J. Liu ; S. C. Mack ; A. Manno ; K. A. Michealraj ; C. Nor ; J. Peacock ; L. Qin ; J. Reimand ; A. Rolider ; Y. Y. Thompson ; X. Wu ; T. Pugh ; A. Ally ; M. Bilenky ; Y. S. Butterfield ; R. Carlsen ; Y. Cheng ; E. Chuah ; R. D. Corbett ; N. Dhalla ; A. He ; D. Lee ; H. I. Li ; W. Long ; M. Mayo ; P. Plettner ; J. Q. Qian ; J. E. Schein ; A. Tam ; T. Wong ; I. Birol ; Y. Zhao ; C. C. Faria ; J. Pimentel ; S. Nunes ; T. Shalaby ; M. Grotzer ; I. F. Pollack ; R. L. Hamilton ; X. N. Li ; A. E. Bendel ; D. W. Fults ; A. W. Walter ; T. Kumabe ; T. Tominaga ; V. P. Collins ; Y. J. Cho ; C. Hoffman ; D. Lyden ; J. H. Wisoff ; J. H. Garvin, Jr. ; D. S. Stearns ; L. Massimi ; U. Schuller ; J. Sterba ; K. Zitterbart ; S. Puget ; O. Ayrault ; S. E. Dunn ; D. P. Tirapelli ; C. G. Carlotti ; H. Wheeler ; A. R. Hallahan ; W. Ingram ; T. J. MacDonald ; J. J. Olson ; E. G. Van Meir ; J. Y. Lee ; K. C. Wang ; S. K. Kim ; B. K. Cho ; T. Pietsch ; G. Fleischhack ; S. Tippelt ; Y. S. Ra ; S. Bailey ; J. C. Lindsey ; S. C. Clifford ; C. G. Eberhart ; M. K. Cooper ; R. J. Packer ; M. Massimino ; M. L. Garre ; U. Bartels ; U. Tabori ; C. E. Hawkins ; P. Dirks ; E. Bouffet ; J. T. Rutka ; R. J. Wechsler-Reya ; W. A. Weiss ; L. S. Collier ; A. J. Dupuy ; A. Korshunov ; D. T. Jones ; M. Kool ; P. A. Northcott ; S. M. Pfister ; D. A. Largaespada ; A. J. Mungall ; R. A. Moore ; N. Jabado ; G. D. Bader ; S. J. Jones ; D. Malkin ; M. A. Marra ; M. D. Taylor
    Nature Publishing Group (NPG)
    Published 2016
    Staff View
    Publication Date:
    2016-01-14
    Publisher:
    Nature Publishing Group (NPG)
    Print ISSN:
    0028-0836
    Electronic ISSN:
    1476-4687
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Published by:
    http://www.nature.com/

    Latest Papers from Table of Contents or Articles in Press
  3. 3
    Staff View
    Publication Date:
    2018-05-05
    Publisher:
    American Physical Society (APS)
    Print ISSN:
    0031-9007
    Electronic ISSN:
    1079-7114
    Topics:
    Physics
    Keywords:
    Nuclear Physics
    Published by:
    http://www.aps.org/

    Latest Papers from Table of Contents or Articles in Press
  4. 4
    Staff View
    Publication Date:
    2018-05-09
    Publisher:
    American Physical Society (APS)
    Print ISSN:
    0556-2813
    Electronic ISSN:
    1089-490X
    Topics:
    Physics
    Keywords:
    Nuclear Astrophysics
    Published by:
    http://www.aps.org/

    Latest Papers from Table of Contents or Articles in Press
  5. 5
    Staff View
    Publication Date:
    2018-10-12
    Publisher:
    American Society of Hematology (ASH)
    Print ISSN:
    0006-4971
    Electronic ISSN:
    1528-0020
    Topics:
    Biology
    Medicine
    Keywords:
    Immunobiology and Immunotherapy, Lymphoid Neoplasia, Clinical Trials and Observations
    Published by:
    http://www.hematology.org/

    Latest Papers from Table of Contents or Articles in Press
  6. 6
    Xie, H. ; Wang, W. I. ; Meyer, J. R. ; Hoffman, C. A. ; Bartoli, F. J.

    [S.l.] : American Institute of Physics (AIP)
    Published 1993
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Theoretical investigations are presented of the electric-field dependence of normal-incidence interconduction subband absorption in Ga1−xAlxSb/AlSb L-valley quantum wells. Under an applied electric field of 50 kV/cm, a blue shift of the absorption peak from 4.94 to 4.82 μm was found in a Ga0.7Al0.3Sb/AlSb structure with well width of 25 A(ring). The ability to absorb normally incident light and to achieve significant Stark shifts with bias makes the Ga1−xAlxSb/AlSb L-valley system an attractive choice for the 3–5 μm vertical optical modulators.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.354630

    Articles: DFG German National Licenses
  7. 7
    Meyer, J. R. ; Bartoli, F. J. ; Youngdale, E. R. ; Hoffman, C. A.

    [S.l.] : American Institute of Physics (AIP)
    Published 1991
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Using dispersion relations from the Kane band model, we obtain limiting forms for the third-order nonlinear susceptibilities due to nonparabolicity, thermal-carrier generation, and nonequilibrium optical-carrier generation. We show that whereas χ(3)'s for all three processes increase with decreasing energy gap, there is no further benefit once Eg becomes smaller than either the Fermi or thermal energies. In fact, simultaneous optimization of both the magnitude of χ(3) and the saturation properties favors materials with a large direct gap and large effective mass, coupled with a smaller thermal gap which may be indirect in either real or momentum space.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.349110

    Articles: DFG German National Licenses
  8. 8
    Meyer, J. R. ; Arnold, D. J. ; Hoffman, C. A. ; Bartoli, F. J.

    [S.l.] : American Institute of Physics (AIP)
    Published 1993
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    We present a general theoretical treatment of ionized impurity scattering in semiconductor superlattices. Employing an extension of the quasi-two-dimensional calculations of Stern and Howard to multi-well structures, we explicitly account for nonuniformity of the wavefunction distribution function, arbitrary dispersion relations, scattering by impurities in neighboring periods, and screening by electrons in neighboring wells. Interperiod phenomena are found to be quite significant whenever the screening length is comparable to or longer than the distance between the quantum wells. Calculated results are compared with recent data for modulation-doped and setback-modulation-doped HgTe-CdTe superlattices. However, the discussion emphasizes general aspects of the problem rather than features specific to a particular system.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.355338

    Articles: DFG German National Licenses
  9. 9
    Xie, H. ; Wang, W. I. ; Meyer, J. R. ; Hoffman, C. A. ; Bartoli, F. J.

    [S.l.] : American Institute of Physics (AIP)
    Published 1993
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    We propose a new type of optical modulator employing two-step Ga1−xAlxSb/Ga1−yAlySb/Ga1−zAlzSb L-valley quantum wells to enhance the Stark shifts of the intersubband transition energy and therefore to achieve large absorption spectral changes with applied bias. Due to the effective-mass anisotropy of electrons in the L-valleys and the tilted growth direction with respect to the valleys, this novel structure can intrinsically absorb normal incidence light. Under an electric field of 50 kV/cm, a blue shift of the absorption peak from 10.9 to 9.8 μm was found from our calculations in a Ga0.7Al0.3Sb/Ga0.5Al0.5Sb/Ga0.4Al0.6Sb structure with a Ga0.7Al0.3Sb well width of 25 A(ring) and a Ga0.5Al0.5Sb step width of 25 A(ring). The ability to absorb normally incident light and to achieve significant Stark effects with bias makes this structure an attractive choice for such high-speed optoelectronic devices as vertical infrared light modulators and voltage tunable photodetectors.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.354920

    Articles: DFG German National Licenses
  10. 10
    Meyer, J. R. ; Bartoli, F. J. ; Hoffman, C. A.

    [S.l.] : American Institute of Physics (AIP)
    Published 1985
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    A more rigorous numerical method for determining bulk semiconductor transport properties from photo-Hall data is presented and is used to determine compensation densities in narrow-gap HgCdTe. Previous studies have treated carrier density inhomogeneities by means of a two-layer approach, assuming a photoexcitation layer of constant thickness associated with either the absorption depth or the ambipolar diffusion length. Here, we show that this approximation can lead to significant error. For arbitrary optical intensities a more detailed integration over depth is required, properly accounting for the variation in the optical and transport of the material with carrier density and optical intensity. In the present technique, the spatial profile of the carrier density, n(z), is calculated as a function of optical intensity Φ0. The electron mobility μ is expanded in known functions of the carrier density. By using this n(Φ0,z) and μ(n), integral expressions for the net conductivity and Hall coefficient are then evaluated. The unknown coefficients in the mobility expansion are varied parametrically to obtain the best fits to the measured Hall coefficient and conductivity as a function of optical flux. From this fit, the electron mobility is determined as a function of carrier density. Detailed sample calculations are performed for the case of narrow-gap, n-type Hg1−xCdxTe at low temperatures assuming 10.6 μm CO2 laser excitation. Analysis of the photo-Hall data using the improved method leads to a reliable determination of compensation densities in this material.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.335374

    Articles: DFG German National Licenses
  11. 11
    Meyer, J. R. ; Vurgaftman, I. ; Hoffman, C. A.

    [S.l.] : American Institute of Physics (AIP)
    Published 1997
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    We propose an all-optical limiter based on the thermally induced intervalley transfer of electrons from Γ-valley states with forbidden normal-incidence intersubband interactions to L-valley states which absorb strongly. Detailed modeling of the device performance in the short-pulse regime (≤100 ns) yields that the output intensity for a limiter with only 10% insertion loss at low excitation levels will remain clamped over a dynamic range of 25–40.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.365344

    Articles: DFG German National Licenses
  12. 12
    Meyer, J. R. ; Arnold, D. J. ; Hoffman, C. A. ; Bartoli, F. J.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1991
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    We demonstrate that interface roughness is the dominant low-temperature scattering mechanism for electrons in HgTe-CdTe superlattices with thin wells. Not only do the experimental mobilities follow the expected d6W dependence, but the observed temperature dependence is accurately reproduced by theory when the treatment of interface roughness scattering is generalized for narrow-gap superlattices. The fits to data yield roughness correlation lengths in the range 60–200 A(ring).
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.104840

    Articles: DFG German National Licenses
  13. 13
    Youngdale, E. R. ; Meyer, J. R. ; Hoffman, C. A. ; Bartoli, F. J. ; Partin, D. L. ; Thrush, C. M. ; Heremans, J. P.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1990
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    We discuss the first investigation of Bi1−xSbx as an infrared nonlinear optical material. Nondegenerate four-wave mixing experiments at CO2 laser wavelengths yield a large nonlinearity (χ(3)≈3×10−4 esu) which does not saturate at power densities up to 0.5 MW/cm2. Both the ambient and substrate interfaces of the film are highly reflective and the étalon they form is found to have a large effect on the transmission and reflectivity spectra of the as-grown films. This suggests the possibility that constructive interference of the film's internal optical fields could be used to considerably enhance the nonlinear signal.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.103683

    Articles: DFG German National Licenses
  14. 14
    Meyer, J. R. ; Felix, C. L. ; Bewley, W. W. ; Vurgaftman, I. ; Aifer, E. H. ; Olafsen, L. J. ; Lindle, J. R. ; Hoffman, C. A. ; Yang, M.-J. ; Bennett, B. R. ; Shanabrook, B. V.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1998
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Two different approaches, a photoconductive response technique and a correlation of lasing thresholds with theoretical threshold carrier concentrations have been used to determine Auger lifetimes in InAs/GaInSb quantum wells. For energy gaps corresponding to 3.1–4.8 μm, the room-temperature Auger coefficients for seven different samples are found to be nearly an order-of-magnitude lower than typical type-I results for the same wavelength. The data imply that at this temperature, the Auger rate is relatively insensitive to details of the band structure. © 1998 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.122609

    Articles: DFG German National Licenses
  15. 15
    Shirk, James S. ; Lindle, J. R. ; Bartoli, F. J. ; Hoffman, C. A. ; Kafafi, Zakya H. ; Snow, Arthur W.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1989
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The third-order optical susceptibility of the Pt, Pb, and metal-free tetrakis(cumylphenoxy)phthalocyanines was measured by degenerate four-wave mixing at 1.064 μm, far from strong absorption bands. Metal substitution strongly enhances the off-resonant χ(3). The χ(3)xxxx for Pt-phthalocyanine (2×10−10 esu) and Pb phthalocyanine (2×10−11esu) is about 45 times and 5 times that of the metal-free form (4×10−12 esu), respectively.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.101634

    Articles: DFG German National Licenses
  16. 16
    Lindle, J. R. ; Bartoli, F. J. ; Hoffman, C. A. ; Kim, O.-K. ; Lee, Y. S. ; Shirk, J. S. ; Kafafi, Z. H.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1990
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Third-order optical susceptibilities (χ(3)) of poly{(7-oxo-7, 10H-benz[de]imidazo[4',5':5,6]benzimidazo [2,1-a]isoquinoline-3,4:10,11-tetrayl)-carbonyl}, referred to as BBL, and poly(6,9-dihydro-6,9-dioxobisbenzimidazo[2,1b:1',2'j] benzo[1mn]-[3,8]phenanthroline-3,12-diyl), known as BBB, have been determined using the technique of degenerate four-wave mixing (DFWM) at 1.064 μm. BBL has a χ(3)xxxx=(1.5±0.4)×10−11 esu, three times as large as that of BBB and 38 times as large as that of CS2. Electrochemical doping led to a small (〈30%) increase in the third-order susceptibility of BBL.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.102689

    Articles: DFG German National Licenses
  17. 17
    Hoffman, C. A. ; Bartoli, F. J. ; Meyer, J. R.

    [S.l.] : American Institute of Physics (AIP)
    Published 1987
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    A comprehensive photo-Hall investigation of compensation densities in n-type Hg1−xCdxTe (0.224〈x〈0.235) is reported. The technique consists of measuring the low-temperature electron mobility as a function of optically excited carrier density. Pulses of 25-μs duration from a CO2 laser yield excess electron-hole plasma densities of between 1013 and 1016 cm−3. At low excitation levels the mobility increases due to the neutralization of ionized acceptors by photoexcited holes, while at higher excitation levels the mobility slowly decreases due to electron-hole scattering. By comparing to a detailed theory for electron transport in photoexcited narrow-gap semiconductors, the density of compensating acceptors NA can be accurately determined. The theory is generalized to account for multi-ion scattering, carrier heating, surface conduction, and inhomogeneous excitation. Experimental refinements significantly extending the range of narrow-gap n-type samples for which compensation densities may be determined are discussed. The present study demonstrates the broad applicability of the technique by determining NA for samples with compensation ratios between 0.09 and 0.96 and with both single and double acceptors.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.338196

    Articles: DFG German National Licenses
  18. 18
    Golding, T. D. ; Dura, J. A. ; Wang, W. C. ; Vigliante, A. ; Moss, S. C. ; Chen, H. C. ; Miller, J. H. ; Hoffman, C. A. ; Meyer, J. R.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1993
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    We have successfully synthesized heterojunctions and elementary multilayered structures of the semimetal-semiconductor system Sb/GaSb using molecular beam and migration enhanced epitaxies. The study is motivated in part by the potential for producing an indirect narrow-gap semiconductor, in which a confinement-induced positive energy gap in the Sb layers will lead to highly attractive properties for nonlinear optical switches operating in the infrared. One may also be able to exploit the long mean free path in Sb (up to 2 μm) in studying quantum transport phenomena. X-ray diffraction confirms the ordered growth of GaSb/Sb/GaSb multilayers, and field-dependent magnetotransport measurements yield electron and hole mobilities ≥3×104 cm2/V s in Sb thin films.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.109792

    Articles: DFG German National Licenses
  19. 19
    Eddy, C. R. ; Dobisz, E. A. ; Hoffman, C. A. ; Meyer, J. R.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1993
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The fabrication of nanometer scale features in the narrow gap, compound semiconductor mercury cadmium telluride has been demonstrated through the application of e-beam lithography and reactive ion etching with an electron cyclotron resonance (ECR) microwave generated methane/hydrogen plasma. The effects of methane concentration, substrate bias, total pressure, and substrate position with respect to the ECR condition on etch rate, anisotropy, and overall etch performance have been examined. The optimized process resulting from these studies has produced the first mercury-based nanostructures consisting of 30–60 nm features with sidewall angles of 88°.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.109390

    Articles: DFG German National Licenses
  20. 20
    Reisinger, A. R. ; Harris, K. A. ; Myers, T. H. ; Yanka, R. W. ; Mohnkern, L. M. ; Hoffman, C. A.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1992
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    We report excess carrier lifetimes of several hundred nanoseconds in HgTe/CdTe superlattices grown by photoassisted molecular beam epitaxy. The structures were doped either n-type in the low 1015 cm−3 range or p-type in the low 1016 cm−3 range, and were designed for peak response in the long-wave infrared regime. The measured lifetimes, recorded by the transient photoconductivity technique, approach values calculated for alloys of equivalent band-gap energy. They indicate that recombination at the superlattice interfaces has been substantially reduced and underscore the recent progress achieved in superlattice growth technology.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.107826

    Articles: DFG German National Licenses