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  • 1
    Electronic Resource
    Electronic Resource
    Surface and domain structures of ferroelectric crystals studied with scanning force microscopy (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 7461-7471 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The understanding of the phenomena of ferroelectricity requires profound knowledge of the ferroelectric domain structure. In this paper we report on the progress of studying ferroelectric domains and domain walls with scanning force microscopy (SFM). Domains and domain walls of ferroelectric crystals of guanidinium aluminum sulfate hexahydrate (GASH) are imaged with SFM. Two sets of complementary results are obtained depending on the operation mode of the instrument. In the non-contact imaging mode (attractive force regime), domain walls are imaged. In the contact imaging mode (repulsive force regime) in addition to the domain wall structure, information about the polarity of the domains is obtained. In these latter images, the opposing contrast of the ferroelectric positive and negative domains is superimposed on the GASH cleavage structure. The imaging mechanism of the contact and noncontact modes are discussed. Corroborating scanning electron microscopy images are presented as well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354969
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  • 2
    Electronic Resource
    Electronic Resource
    Normal-incidence electroabsorption in Ga1−xAlxSb/AlSb L-valley quantum wells for 3–5 μm optical modulation (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2810-2812 
    Details
    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
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  • 3
    Electronic Resource
    Electronic Resource
    Anisotropic screening and ionized impurity scattering in semiconductor superlattices and multiple quantum wells (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6676-6685 
    Details
    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
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  • 4
    Electronic Resource
    Electronic Resource
    Enhancement of intersubband Stark effects in L-valley step quantum wells for infrared modulation and voltage tunable detection (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 1195-1198 
    Details
    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
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  • 5
    Electronic Resource
    Electronic Resource
    Optimization of modulation-doped Ga1−xInxAs/InP heterostructures towards extremely high mobilities (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 4489-4493 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper presents a study of the electrical and structural properties of inverted modulation-doped GaInAs/InP heterostructures grown by low-pressure metalorganic vapor phase epitaxy. First, the thickness of the GaInAs layer was optimized in lattice-matched samples to find the smallest thickness in which high Hall mobility is observed. Next, in a section closest to the InP the In content was varied. A steady increase of mobility with indium composition was observed. A maximum of 450 000 and 15 500 cm2/V s was obtained for a 10-nm-thick Ga1−xInxAs layer with x=0.77 at 6 and 300 K, respectively. Channels with higher indium content exceed the critical thickness and mobility drops off sharply. The decreasing mobility correlates with the formation of misfit dislocations at the interface indicating increasing scattering processes of the GaInAs layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352789
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  • 6
    Electronic Resource
    Electronic Resource
    Application of microwave detection of the Shubnikov–de Haas effect in two-dimensional systems (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 7533-7542 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Microwave detection of the Shubnikov–de Haas (SdH) effect as a contact-free characterization technique for different types of two-dimensional semiconductor structures is explored in the low magnetic field region. The detection technique and the data analysis are described. The character and relevance of the single-particle relaxation time that can be detected by this technique are distinguished from the usual transport scattering time. The measured values of the carrier concentration and single-particle relaxation time agree with electrical measurements, while the problem of making contacts on the structure is avoided. Uncertainties in the analysis for the single-particle relaxation time are discussed. Cyclotron resonance, optically detected cyclotron resonance, and magneto-photoluminescence are applied as other contact-free techniques on the same samples. The results and suitability of these techniques are compared with the microwave detection of the SdH effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354001
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  • 7
    Electronic Resource
    Electronic Resource
    The vacuum ultraviolet photodissociation of silane at 125.1 nm (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 5944-5950 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We observe the photodissociation of SiH4 in a pulsed molecular beam after excitation with 125.1 nm vacuum ultraviolet light generated via resonant four-wave mixing in mercury vapor. Ultraviolet radiation from a Nd:YAG/dye laser combination ionizes the neutral photodissociation fragments and a time-of-flight mass spectrometer detects the ions. The photodissociation signal consists entirely of silicon atoms and silylidyne (SiH) in its first electronically excited state. We see no silylene (SiH2) or silyl radicals (SiH3). Thus, the photodissociation cleaves almost all of the silicon–hydrogen bonds, but the energetics of the dissociation require the production of at least one hydrogen molecule per dissociation event. These results imply that the high energy content of the initially excited Rydberg state prevents formation of the silylene and silyl radicals in stable vibronic states and that dissociation pathways exist that connect the Rydberg state directly to the corresponding silicon atom and silylidyne asymptotes. These pathways are likely to exist because of Jahn–Teller distortion from the initial Td symmetry. Very little of the available energy appears as kinetic energy of the fragments but rather as electronic excitation of the products. Our results differ from those of earlier studies that concluded silylene and silyl are the principle products.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465893
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  • 8
    Electronic Resource
    Electronic Resource
    Correlated static–exchange interaction calculation for e−+N2 scattering using the coupled cluster techniquea) (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 945-949 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The correlation contribution to the static–exchange interaction potential (ΔVSE) appears as an important quantity in the electron molecule scattering calculations. We have shown that the single and double excitation configuration interaction (CISD) method does not give reliable results for ΔVSE. Only properly chosen multireference CISD calculation or Green's function based calculations were found to be reliable. In this paper we carry out the coupled cluster (CC) calculations to test whether good results are obtained or not. The CC method will also help us to identify the important contributions to ΔVSE and to understand why a low order CI performs poorly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465359
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  • 9
    Electronic Resource
    Electronic Resource
    Dynamic multipole polarizabilities and long range interaction coefficients for the systems H, Li, Na, K, He, H−, H2, Li2, Na2, and K2 (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 7845-7858 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Different approaches to the calculation of dynamic polarizabilities are briefly discussed and compared. Using a perturbational approach dynamic multipole polarizabilities are calculated from full valence configuration interaction wave functions. The polarizabilities are expressed in terms of reduced spectra which, in turn, are used to compute the dispersion and induction coefficients for all combinations of the systems listed, including anisotropic contributions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465663
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  • 10
    Electronic Resource
    Electronic Resource
    Long-range interaction coefficients for the metastable states of He (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 8351-8352 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Following the lines presented in a recent paper [J. Chem. Phys. (unpublished)] reduced spectra representing the dynamic polarizabilities are reported with special emphasis on accurate values for the metastable states of the He atom. Together with the reduced spectra taken from Ref. 1, long range interaction coefficients are computed for all combinations between the three lowest He states and the atoms H, Li, Na, K, and H−.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465610
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