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  • 1
    Electronic Resource
    Electronic Resource
    Carrier recombination at single dislocations in GaN measured by cathodoluminescence in a transmission electron microscope (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 92 (2002), S. 2000-2005 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study radiative and nonradiative recombination at individual dislocations in GaN by cathodoluminescence performed in a transmission electron microscope. The dislocations are produced by indentation of dislocation free single crystals and have a-type Burgers vectors (b=1/3〈112¯0〉). They are aligned along 〈112¯0〉 directions in the basal plane. Our direct correlation between structural and optical properties on a microscopic scale yields two main results: (i) 60°-basal plane dislocations show radiative recombination at 2.9 eV; (ii) screw-type basal plane dislocations act as nonradiative recombination centers. We explain the nonradiative recombination by splitting this dislocation into 30° partials that have dangling bonds in the core. The dissociation width of these dislocations is 〈2 nm. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1490618
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  • 2
    Electronic Resource
    Electronic Resource
    Simultaneous experimental evaluation of In and N concentrations in InGaAsN quantum wells (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 3792-3798 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We propose a method that solves the problem of the independent determination of the indium and nitrogen concentrations in a strained quaternary InGaAsN superlattice. The method is experimentally based on the simultaneous measurement: (i) of the tetragonal lattice distortion of the unit cell from high resolution micrographs and (ii) of the intensity of the chemically sensitive (002) reflection from dark field images. As an example, we evaluate InGaAsN quantum wells with a nominal N concentration of 1.7% and with In concentrations of 10%, 20%, or 35%. We reveal local fluctuations of the In and N concentrations over distances down to 4 nm with a sensitivity of 0.1% for N and 1% for In fluctuations in this distance range. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1402139
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  • 3
    Electronic Resource
    Electronic Resource
    Six-circle diffractometer for surface diffraction using an in-vacuum x-ray detector (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 3239-3243 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report on the design of a diffractometer, which offers improved capabilities for x-ray experiments in ultrahigh vacuum. Its main features are (i) the possibility to follow the evolution of diffraction spots in situ during adsorption or film deposition; (ii) the measurement of reflections at high exit angles, i.e., large perpendicular momentum transfer. This goal is achieved by placing a movable x-ray detector inside the vacuum chamber. (iii) Other surface analysis equipment, e.g., a low-energy electron diffraction or an electron energy analyzer can be moved in front of the sample and operated simultaneously with x-ray diffraction. (iv) A load lock system—currently in preparation—will allow the quick exchange of samples without breaking system vacuum. In addition, a new design of the chi circle used for sample alignment provides a compact, space-saving design of the diffractometer. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149899
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  • 4
    Electronic Resource
    Electronic Resource
    Surface ripples, crosshatch pattern, and dislocation formation: Cooperating mechanisms in lattice mismatch relaxation (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1232-1234 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study the interplay of elastic and plastic strain relaxation of SiGe/Si(001). We show that the formation of crosshatch patterns is the result of a strain relaxation process that essentially consists of four subsequent stages: (i) elastic strain relaxation by surface ripple formation; (ii) nucleation of dislocations at the rim of the substrate followed by dislocation glide and deposition of a misfit dislocation at the interface; (iii) a locally enhanced growth rate at the strain relaxed surface above the misfit dislocations that results in ridge formation. These ridges then form a crosshatch pattern that relax strain elastically. (iv) Preferred nucleation and multiplication of dislocations in the troughs of the crosshatch pattern due to strain concentration. The preferred formation of dislocations again results in locally enhanced growth rates in the trough and thus leads to smoothing of the growth surface. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115017
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  • 5
    Electronic Resource
    Electronic Resource
    Ultrafast broadband frequency modulation of a continuous wave reflectometry system to measure density profiles on ASDEX Upgrade (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 4138-4145 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A reflectometry system has been developed for ASDEX Upgrade to measure the plasma profile from the scrape-off layer until the bulk plasma, simultaneously at the high and low field sides. Unique features of the system are the ultrafast broadband frequency modulation of a continuous wave using solid state stable hyper abrupt tuned oscillators (down to 10 μs), high and low field side channels and fully remote control operation, via optical fiber links. Due to the special design of the transmission line, with decoupled in going and out going lines and one-antenna configuration, the system is optimized for reception and spurious reflections are eliminated. The ultrafast operation guarantees that the effect of plasma turbulence is greatly reduced. Both features determine the high performance of the diagnostic. A dedicated data acquisition system handles the large amounts of data generated by the broadband operation. Recent developments include the operation of new channels and an automatic and accurate frequency calibration circuit. Also, advanced digital signal processing techniques were applied to obtain density profiles with high spatial and temporal (20 μs) resolutions under turbulent plasma regions, e.g., the scrape-off layer. Experimental results are presented showing the great sensitivity of the diagnostic to plasma radial movements and its tolerance to vertical movements of the plasma. Density profiles measured in ELMy regimes illustrate the capabilities of the diagnostic to detect fast profile changes. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147517
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  • 6
    Electronic Resource
    Electronic Resource
    Reduced effective misfit in laterally limited structures such as epitaxial islands (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 574-576 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerical finite element calculations have been reported to determine a correction function Φ that describes the reduction of the misfit that occurs when laterally limited structures such as faceted islands or mesa structures are grown on a substrate. The reduction of the average strain energy density is calculated in these three-dimensional islands and compared to the constant strain energy density in a continuous layer. Ratios Φ are obtained from the calculation of different island geometries, i.e., different facet angles γ and different aspect ratios island width l to island height h. These discrete values are fitted by a function which can easily be applied to the full range of aspect ratios (l/h(approximately-greater-than)0) and facet angles (0°〈γ〈90°). Faceted Ge(Si) islands on Si(001) substrate, grown from the solution in the Stranski–Krastanov growth mode, serve as an example for the calculation. Experimental and theoretical values for the critical thickness of these islands agree well. This result demonstrates the drastic influence of islanding on misfit strain distribution in island and substrate as well and, consequently, on the strong increase of the critical thickness as determined by the mechanical equilibrium theory of Matthews and Blakeslee. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114017
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  • 7
    Electronic Resource
    Electronic Resource
    Misfit grainlets: Point strain sources compensating misfit during epitaxial growth (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 952-954 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We propose a misfit relaxation mechanism that may occur during growth in highly misfitting layers. It is based on a misfit compensating distribution of physical point strain sources at the interface between layer and substrate instead of misfit dislocations. These point strain sources are realized by interfacial islands (misfit grainlets) that have a lattice misfit opposite in sign to that of the surrounding epitaxial layer, in most cases brought about by an orientation relationship different from that of the surrounding layer to the substrate. We demonstrate the effectiveness in strain relaxation of misfit grainlets with an analysis of the interface structure of GaN on sapphire and discuss the formation of misfit grainlets in terms of a self-organized island growth process. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118451
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  • 8
    Electronic Resource
    Electronic Resource
    Writing of high-density patterned perpendicular media with a conventional longitudinal recording head (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 3409-3411 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated arrays of magnetic islands in perpendicular CoCrPt media with ∼100 nm lateral dimension using a focused ion beam. A quasistatic write/read tester was used to study aspects of the recording physics of these patterned media. We present results on the variation of the readback signal as the phase of the written square wave changes with respect to the patterned array as a function of island size and write current. Using an analytic near-field expression for head field we are able to model how the observed dependence between phase shift and readback signal as a function of write current arises. This analysis allows us to gain an insight into the role of the island switching field distribution and the write head magnetic field gradient in the patterned media writing process. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1476062
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  • 9
    Electronic Resource
    Electronic Resource
    Plasticity of hematopoietic stem cells and cellular memory (2002)
    Oxford, UK : Munksgaard International Publishers
    Immunological reviews 187 (2002), S. 0 
    Details
    ISSN: 1600-065X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Summary: Stem cell systems represent an effective and powerful approach for tissue development and regeneration of diverse tissue types. Common and defining features of these exceptional cells are the capacity for self-renewal and the potential for differentiation into multiple mature cell types. Recently, surprising new observations have indicated that stem cells isolated from one adult tissue can also give rise to mature cells of other cell lineages, irrespective of classical germ layer designations. This discovery has resulted in quantum leaps in both scientific knowledge and the potential applications of stem cells. The new findings contradict central dogmas of commitment and differentiation of stem and progenitor cells. However, the true potential of somatic stem cells is just emerging and the new findings have to be defined more fully and integrated into a unifying model of stem cell potential and behavior. Here we analyze the developmental potential of hematopoietic stem cells of mouse and man following their injection into the murine preimplantation blastocyst, an environment that allows the development of all cell lineages. In addition, we discuss the emerging lines of evidence of the developmental plasticity of hematopoietic and other somatic stem cells and consider how cellular memory of transcriptional states is established and may be potentially involved in this phenomenon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1600-065X.2002.18702.x
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  • 10
    Electronic Resource
    Electronic Resource
    Anatomical features and histology of the digestive tract of two related neotropical omnivorous fishes (Characiformes; Anostomidae) (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 58 (2001), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The estimated mean intestinal coefficients of Leporinus friderici Bloch, 1794 and L. taeniofasciatus Britski, 1997, from the Upper Tocantins River, central-western Brazil, were 1·25±0·15 and 1·14±0·07, respectively. The external surfaces of the lips have taste buds. The histological structure is composed of four layers: mucosa, submucosa, muscular, and serosa. No muscularis mucosa is detected. The oesophageal epithelium is stratified in L. friderici and pseudostratified in L. taeniofasciatus, the latter with PAS+ basal cells and eosinophilic apical cells. A thick layer of adipose tissue was found within the submucosa. Leporinus taeniofasciatus has a sphincter separating the cardiac and fundic portions of the stomach. In both species, gastric glands are present in the stomach, except in its pyloric portion. The pyloric caeca possess a simple columnar epithelium with brush border and three types of goblet cells. Rodlet cells were found in L. friderici. The three portions of the intestine showed no histological differences. Anatomical and histological features of the digestive tract are consistent with the omnivorous habit of both these species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.2001.tb02261.x
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