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  • 1
    Electronic Resource
    Electronic Resource
    Low-temperature scanning tunneling microscope for ballistic electron emission microscopy and spectroscopy (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 91-96 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Design details and initial results are presented for a low-temperature scanning tunneling microscope specifically intended for measurements of ballistic-carrier transmittance through heterostructures. The basic design is of the Besocke type, modified for ballistic electron emission microscopy and spectroscopy (BEEM). This instrument is the first to acquire BEEM spectra below 77 K. Salient features are (1) operation in a liquid-helium storage Dewar to below 6 K, (2) a lateral positioning range of 5 mm at low temperature, and (3) lateral drift rate less than 0.2 nm/h at the lowest temperatures. For BEEM spectroscopy, the microscope's high positional stability allows extended signal-averaging at a single location on the sample. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146206
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  • 2
    Electronic Resource
    Electronic Resource
    Adaptive silicon monochromators for high power insertion devices: Tests at CHESS, ESRF, and HASYLAB (abstract) : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 2190-2190 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: X-ray wigglers which produce tens of kilowatts of photon power within the white beam will soon become available as third-generation sources of synchrotron radiation. Insertion devices that produce several kilowatts already exist and we have used those at CHESS, ESRF, and HASYLAB to test and develop an adaptive 111 silicon water jet-cooled monochromator at up to 2 kW total incident beam power. This development of earlier work at the Brookhaven National Synchrotron Light Source uses the pressure in the water coolant to provide active compensation of the strain field in the thermal footprint, nulling its effect to within residual variations in the Bragg angle of only a few seconds of arc. The design is robust, vacuum compatible, and uses no moving mechanical parts. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145702
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  • 3
    Electronic Resource
    Electronic Resource
    Microstructure and composition in rapidly quenched NdFeB-based hard magnet alloys : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4848-4850 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A detailed study of the microstructure and composition in hot-pressed (MQ-2) and die-upset (MQ-3) magnet alloys based on the Nd2Fe14B composition, utilizing high resolution and analytical transmission electron microscopy, is reported. The initial magnetic properties of the two samples show different behaviors, which are attributed to the difference in the anisotropy of the grain structure and the grain boundaries. The hot-pressed sample shows faceted grains of the 2-14-1 phase, while die-upset sample shows plate-like grains, together with larger equiaxed grains that contain a speckling of precipitates in the grain interior. The grain structure and composition remain rather similar in the two samples. The grain boundary phase averages ∼1–(approximately-greater-than)10 nm in width. The thicker grain boundaries are Nd-rich, while the thinner grain boundaries in the hot-pressed sample exhibit an Fe-rich composition near that of the NdFe3 phase. Nd-rich phases are found at the grain boundary junctions of both samples, with the Nd:Fe ratio near 7:3 in the die-upset sample, and up to 3:2 in the hot-pressed sample. The significance of the microstructure and the grain boundary phases on the magnetic behavior in the two samples is discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361630
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  • 4
    Electronic Resource
    Electronic Resource
    Strain and crystallographic orientation effects on interband optical matrix elements and band gaps of [11l ]-oriented III-V epilayers (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 2447-2455 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a derivation of the 4×4 Luttinger valence band and Bir–Pikus strain Hamiltonians valid for any [11l]-oriented epilayers. It is shown that epitaxial layers grown on substrates oriented in certain of the [11l] directions exhibit anisotropic optical transition matrix elements. This anisotropy is predicted to have its maximum for the (110) surface. For pseudomorphic epitaxial layers, calculations indicate that the zone center band gap of these structures is changed due to the effects of strain, with the largest changes occurring for those structures grown on the (111) surface. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360098
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  • 5
    Electronic Resource
    Electronic Resource
    GaAs nanocrystals formed by sequential ion implantation (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 1876-1880 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Sequential ion implantation of As and Ga into SiO2 and α-Al2O3 followed by thermal annealing has been used to form zinc-blende GaAs nanocrystals in these two matrices. In SiO2, the nanocrystals are nearly spherical and randomly oriented, with diameters less than 15 nm. In Al2O3, the nanocrystals are three dimensionally aligned with respect to the crystal lattice. Infrared reflectance measurements show evidence for surface phonon modes in the GaAs nanocrystals in these matrices. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361088
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  • 6
    Electronic Resource
    Electronic Resource
    Photoluminescence spectroscopy and the effective mass theory of strained (In,Ga)As/GaAs heterostructures grown on (112)B GaAs substrates (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 843-848 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The photoluminescence characteristics of pseudomorphic In0.19Ga0.81As/GaAs quantum well structures grown on both the conventional (001) and the unconventional (112)B GaAs substrate are investigated. It is found that the emission spectra of the structures grown on the (112)B surface exhibit some spectral characteristics not observed on similar structures grown on the (001) surface. A spectral blue shift of the e→hh1 transition with increasing optical pump intensity is observed for the quantum wells on the (112) surface. This shift is interpreted to be evidence of a strain-induced piezoelectric field. A second spectral feature located within the band gap of the In0.19Ga0.81As layer is also observed for the (112) structure; this feature is thought to be an impurity-related emission. The expected transition energies of the quantum well structures are calculated using the effective mass theory based on the 4×4 Luttinger valence band Hamiltonian, and a related strain Hamiltonian. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359009
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  • 7
    Electronic Resource
    Electronic Resource
    Effective mass theory for III-V semiconductors on arbitrary (hkl) surfaces (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 2029-2037 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of arbitrary substrate orientation on the electronic and optical properties of III-V zinc-blende semiconductors are considered. A unitary transformation matrix is used to rotate the 4×4 Luttinger valence band Hamiltonian, and the Bir-Pikus strain Hamiltonian from the conventional (001) surface to any arbitrary (hkl) surface of interest. The effects of strain on several electronic and optical properties are examined. It is found that the strain-induced change in the forbidden gap is largest for the (111) plane and other equivalent planes. Furthermore, the strain is also found to induce both a longitudinal and a transverse piezoelectric field. The longitudinal field reaches a maximum for the (111) surface and its other equivalent planes, while the transverse field reaches a maximum for the (110) surface and its other equivalent planes. The orientation-dependence of the hole effective masses is also examined; it is found that the (111) surface, and other equivalent planes, exhibits the largest heavy-hole mass among all possible planes. Finally, this article examines the effects of orientation on the optical transition matrix elements. For incident light with in-plane polarization vectors, the matrix elements are, in general, anisotropic—with the largest anisotropies predicted for two new surfaces: the ((square root of)310) and the (1(square root of)30) surface. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361057
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  • 8
    Electronic Resource
    Electronic Resource
    On the lack of influence of disorder in Cr3+-doped LiSr0.8Ca0.2AlF6 (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 2232-2234 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optical and electron spin resonance spectroscopies have been used to investigate the thermal stability of lasers based on Cr3+:LiSr0.8Ca0.2AlF6, a material in which the onset of critically inhibiting nonradiative decay at temperatures below 300 K might be expected based on results from other Cr3+-activated disordered gain media. The influence of disorder on the Cr3+ environment is shown to be very small in LiSr0.8Ca0.2AlF6 so that the 4T2→4A2 fluorescence transition is not broadened relative to that in LiSrAlF6 and the onset of significant nonradiative decay is also held above room temperature. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121330
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  • 9
    Electronic Resource
    Electronic Resource
    Renormalized path integral in quantum mechanics (1997)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 38 (1997), S. 2171-2180 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: We obtain direct, finite, formulations of a renormalized quantum mechanical system with no reference to ultraviolet cutoffs and running coupling constants, in both the Hamiltonian and path integral pictures. The path integral description requires a modification to the Wiener measure on continuous paths that describes an unusual diffusion process wherein colliding particles occasionally stick together for a random interval of time before going their separate ways. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.531967
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  • 10
    Electronic Resource
    Electronic Resource
    Renormalized contact potential in two dimensions (1998)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 39 (1998), S. 749-759 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: We obtain for the attractive Dirac δ-function potential in two-dimensional quantum mechanics a renormalized formulation that avoids reference to a cutoff and running coupling constant. Dimensional transmutation is carried out before attempting to solve the system, and leads to an interesting eigenvalue problem in N−2 degrees of freedom (in the center of momentum frame) when there are N particles. The effective Hamiltonian for N−2 particles has a nonlocal attractive interaction, and the Schrodinger equation becomes an eigenvalue problem for the logarithm of this Hamiltonian. The three-body case is examined in detail, and in this case a variational estimate of the ground-state energy is given. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.532350
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