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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2524-2526 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Field ion-scanning tunneling microscopy has been used to study 6H–SiC(0001) surfaces with Si adlayers on the Si-terminated surface, formed by in situ Si molecular beam etching at 950 °C. The as-cleaned surface showed a ((square root of 3)×(square root of 3)) reconstruction. The (2×3), (2(square root of 3)×6(square root of)6), and (3×3) phases were formed by evaporating Si on this clean 6H–SiC(0001)-((square root of 3)×(square root of 3)) surface. A Si(111) film 6 monolayers thick was also epitaxially grown on the 6H–SiC(0001)-((square root of 3)×(square root of 3)) surface at 800 °C, and the surface exhibited the Si(111)–(7×7) reconstruction. A surface vacancy model for the ((square root of 3)×(square root of 3)) reconstruction is proposed, and a possible application of utilizing the various surface reconstructions to control the growth of different polytypes of SiC on the 6H–SiC substrate is discussed. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Charge-exchange (C–X) neutral particle measurements have been carried out in hot-ion-mode plasmas of the GAMMA 10 tandem mirror. In the present experiment, a microwave power of 40 kW in 28 GHz is injected toward a second harmonic ECR layer located in the vicinity of the ICR layer at the central region and the radial profiles of ion temperatures determined from the energy spectrum of the C–X neutrals by using a neutral particle energy analyzer (NPA) are investigated from the viewpoint of ion energy balance. At the onset of the ECRH pulse, a remarkable increase of C–X neutral flux with high energy (few keV to few tens keV) is observed with NPA and the resultant ion temperature on the plasma axis is found to increase from 2.5 to 5.0 keV at the electron line density of 3×1013 cm−2. Based on the measured plasma parameters, radial profiles of ion-energy losses due to classical processes are evaluated and ECRH in the central region is confirmed to reduce the energy loss due to electron drag significantly in the core-plasma region. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2995-2997 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have studied the rapid degradation of the AlGaAs/GaAs single quantum well laser diodes on Si substrates grown by metalorganic chemical vapor deposition. The dislocations propagate at velocities up to ∼75 μm/h along 〈100〉 and ∼20 μm/h along 〈110〉, which cause an increase in threshold current and a decrease in differential quantum efficiency. The degraded current–voltage characteristic resulted from the defect-assisted impurity diffusion. The degradation process occurs very rapidly due to the presence of a high density of defects and thermally induced strain. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 2265-2267 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The three-dimensional (3D) island structure was prepared by molecular beam epitaxy for the lattice mismatched InAs/GaAs(001) system and its images showing atomic structure on faceted planes were taken in situ by ultrahigh vacuum scanning tunneling microscopy (STM). The (113), (114), and (215) faceted planes are observed for the 3D islands. Based on the STM images, atomic structural models are proposed for the faceted surfaces. The surface structure of the (113) faceted planes we propose is different from those observed on the flat GaAs(113) surface. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 523-525 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report the preliminary results on self-formed GaAs islands grown on the GaAs/Si substrate by metalorganic chemical vapor deposition using droplet epitaxy. Atomic force microscope observation shows that the GaAs islands exhibit a conical shape with heights of 90–170 nm, diameters of 600–750 nm, and densities of 107 cm−2, which are controlled by the trimethylgallium flow rate. In addition, an AlGaAs/GaAs light-emitting diode (LED) on Si with a self-formed GaAs island active region was fabricated by the use of this technique. The LED was operated up to 27 μW at 190 mA under direct current conditions at room temperature. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 2468-2470 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A scratch-free and atomically flat 6H–SiC(0001) surface has been successfully prepared by a two-step method which combines atmospheric hydrogen treatment and ultrahigh vacuum Si etching. On this surface, a high-quality GaN(0001) thin film is obtained by radio frequency nitrogen plasma assisted molecular beam epitaxy. Its surface exhibits a typical terrace-plus-step morphology, which enables us to study various GaN(0001) surface superstructures and hollow-core defects with atomic resolution by scanning tunneling microscopy. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 2776-2778 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have performed the first scanning tunneling microscopy (STM) study of gallium adsorption on both the Si-terminated 6H-SiC(0001) ((square root of 3)×(square root of 3)) and C-terminated 6H-SiC(0001¯) (2(square root of 3)×2(square root of 3)) surfaces. The structure of the Ga terminated 6H-SiC surface showed strong polarity dependence. On the Si-terminated (square root of 3)×(square root of 3) surface, parallel rows of Ga atoms arranged in three different domains oriented at 120° with respect to each other at 1 ML coverage were observed. On the C-terminated 2(square root of 3)×2(square root of 3) surface, sets of two concentric rings formed an overall 4(square root of 3)×4(square root of 3) reconstruction at 1 ML coverage. We propose a structural model for the 4(square root of 3)×4(square root of 3) structure which explains the STM image. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 3668-3670 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report that local modification and its erasing with a nanometer-scale size can be performed at a Au/Si(111) interface using ballistic electron emission microscopy (BEEM). By applying a negative voltage on the tip, a region was created where no BEEM current flows at the interface and was imaged with BEEM. The modified area can be erased by applying a voltage with the opposite polarity. It is found that the minimum size of writing and erasing corresponds to Au grains, suggesting a method of rewritable memory on a nanometer-scale dimension. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Skeletal radiology 26 (1997), S. 354-359 
    ISSN: 1432-2161
    Schlagwort(e): Key words MRI ; Dysbaric osteonecrosis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  Objective. To assess the diagnostic value of magnetic resonance imaging (MRI) as compared with radiographic findings in osteonecrosis in divers. Design and patients. MRI scans and conventional radiographs of the shoulder, hip and knee joints of 23 professional male scuba divers were reviewed together with their clinical findings and personal histories. Correlations between the MRI findings and the radiographic evaluation, clinical symptoms, and personal history were then investigated. Results and conclusions. Lesions found on MRI in 23 divers included 27 in 39 proximal humeri, 17 in 36 proximal femora, 13 in 32 distal femora, and 12 in 32 proximal tibiae. Diffuse, marginated, or irregular patterns were observed. No lesions were seen in epiphyses of the distal femur or proximal tibia. We tried to classify these MRI findings by location and appearance. MRI showed no patients with only one affected bone. A close correlation between the MRI findings and maximum diving depth was observed in the proximal humerus. MRI depicted bone lesions that could not be detected on the radiographs. A routine MRI investigation of the hip joints should be performed in every diver in whom osteonecrosis is diagnosed at another site, for early detection of femoral head osteonecrosis. MRI of the shoulder joint is also the best surveillance in divers who dive deeper than 15 m.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Osteoporosis international 7 (1997), S. 195-199 
    ISSN: 1433-2965
    Schlagwort(e): Bone mineral density ; Osteoporosis ; Quantitative computed tomography ; Radius
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The present study evaluated a commercial device for peripheral quantitative computed tomography (pQCT) and examined the age-related changes in normal Japanese women. The volumetric bone mineral density (vBMD) of the distal radius [integral bone mineral density (BMDI), trabecular bone mineral density (BMDT) and cortical with subcortical bone mineral density (BMDSC)] was measured using pQCT (Norland-Stratec XCT960) in 617 healthy women aged 20–79 years and 75 subjects with osteoporosis aged 60–89 years who exhibited at least one vertebral fracture. The short-term precision errors in vivo (CV, %) were 1.1% for BMDI 1.1% for BMDT and 1.2% for BMDSC. The correlations between pQCT and dual-energy X-ray absorptiometry measurements (Lunar DPX) of the lumbar spine werer∼0.8 (BMDI, BMDT and BMDSC). The maximal mean vBMD values were observed between 20 and 49 years; BMDI BMDT and BMDSC all showed a linear postmenopausal decline averaging 1.1% per year. The overall decreases in vBMD from the peak values in those 70–79 years were 34%, 32% and 33% in BMDI, BMDT and BMDSC, respectively. The diagnostic sensitivity of osteoporosis was expressed as aT-score.T-scores using pQCT were −3.0 (BMDI), −2.4 (BMDT) and −2.9 (BMDSC). Bone mineral measurement of the distal radius may be useful in the evaluation of age-related bone loss and for the diagnosis of osteoporosis.
    Materialart: Digitale Medien
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