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  • Articles: DFG German National Licenses  (38)
  • 1995-1999  (36)
  • 1955-1959  (1)
  • 1890-1899  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Vacuum near-field scanning optical microscope for variable cryogenic temperatures (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 3458-3463 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the design of a novel near-field scanning optical microscope for cryogenic temperatures and operation in vacuum. A helium flow cryostat is used for active temperature control of the sample in the range between 8 and 330 K, while all components of the near-field microscope are kept at room temperature. This design greatly simplifies near-field microscopy at variable sample temperatures and permits large piezoelectric scan ranges of up to 100×100×10 μm 3, the implementation of hardware-linearized piezoelectric scan stages, as well as flexible coarse positioning. First experiments with single GaAs quantum wires demonstrate the excellent performance of this new instrument. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148308
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Dislocation generation and crack growth under monotonic loading (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6249-6264 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The processes of crack growth and dislocation emission induced by the crack tip are investigated. A crystal with cubic lattice of atoms under plane strain conditions is considered. The main principles of the nanofracture mechanics approach employed in this study are outlined. Both ductile and brittle mechanisms of crack growth in the crystal are examined in nano- or interatomic scale. Only the fundamental constants of the classical theory of dislocations are used which include the interatomic spacing, elastic constants, the Schmid friction constant, and the true surface energy of crystal lattice. The efficient solution of the elastic problem for an arbitrary number of dislocations near the crack tip is obtained in terms of complex potential functions. The equilibrium of dislocation pairs near the crack tip during monotonic loading is investigated. It is shown that dislocation generation at the crack tip occurs at certain quantum levels of external load. The magnitude of external load corresponding to crack growth initiation and emission of the first pair of dislocations is calculated. The mathematical problem for an arbitrary N number of dislocation pairs near the crack tip is reduced to a parametric system of N nonlinear equations, where the stress intensity factor of external load KI plays the role of parameter and N the role of discrete time. The minimum value of KI at which the solution of this system of equations exists corresponds to the stress intensity factor at which the Nth pair of dislocations is generated. The numerical method is presented to determine the minimum value of KI. The approximate method of self-consistent field is employed to reduce the order of the system of nonlinear equations. The approximate method is used to calculate the fracture curve KI(lc) relating the value of KI which maintains the crack growth to the crack length increment lc. The exact solution is also studied, and numerical results are given for a crack in an aluminum specimen and involve the quantum levels of external load corresponding to the moments of dislocation generation and the values of the superfine stress intensity factor up to 150 dislocations. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360572
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  • 3
    Electronic Resource
    Electronic Resource
    Lineshape, linewidth and spectral density of parametric x-radiation at low electron energy in diamond (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 267-269 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Applying an absorber technique, the experimental shape and width of a parametric x-radiation line has been determined. The 9 keV radiation was produced by bombarding a diamond crystal of 55 μm thickness with electrons of 6.8 MeV. The variance of the spectral line distribution was found to depend on the tilt angle of the crystal and to have a magnitude of σ=51 eV. Simulations based on a Monte Carlo method exhibit that the observed variance is mainly influenced by multiple scattering of electrons passing through the crystal ((approximate)43 eV) and the finite detector opening ((approximate)18 eV), leaving for the intrinsic linewidth a value of the order of 1 eV. The spectral density of the line was found to be J(approximate)10−7 photons/(electron×sr×eV). © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118359
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  • 4
    Electronic Resource
    Electronic Resource
    Exciton transport into a single GaAs quantum wire studied by picosecond near-field optical spectroscopy (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2176-2178 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a time-resolved near-field luminescence study of excitonic real-space transfer into single GaAs quantum wires. Excitons generated by local optical excitation in a 250 nm spot undergo diffusive transport over a length of several microns and are subsequently trapped into the quantum wire by optical phonon emission. Local energy barriers in the vicinity of the quantum wire, originating from the epitaxial growth mechanism of the nanostructure, directly influence the real-space transfer dynamics and trapping efficiency. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122414
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  • 5
    Electronic Resource
    Electronic Resource
    Light-induced expansion of fiber tips in near-field scanning optical microscopy (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 325-327 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The emission profiles of laser diodes working at 780 nm and 1300 nm are studied by near-field scanning optical microscopy. As the near-field probe is scanned across the laser mirror facet, the laser emission induces a transient expansion of the probe tip which is monitored using shear force microscopy. The thermal expansion of the tips reaches absolute values of up to 100 nm per mW of emitted laser power. A fully metallized near-field probe tip is shown to serve as a local bolometer with a spatial resolution of better than 1 μm. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118048
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  • 6
    Electronic Resource
    Electronic Resource
    Optical near-field photocurrent spectroscopy: A new technique for analyzing microscopic aging processes in optoelectronic devices (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3981-3983 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The potential of optical near-field photocurrent spectroscopy for analyzing microscopic aging processes in optoelectronic devices is demonstrated. The technique combines the subwavelength spatial resolution of near-field optics with tunable laser excitation, allowing for selective investigation of specific parts of the device structure. Experiments on GaAs/(AlGa)As high power laser diodes before and after accelerated aging provide direct visualization of defect growth within the p-i-n junction and information on aging-enhanced recombination processes close to the laser facet. The effect of wave guiding of the exciting light on the image formation is discussed. The nondestructiveness makes this technique a particularly attractive method for in situ analysis in high power laser diodes. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117844
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  • 7
    Electronic Resource
    Electronic Resource
    Near-field scanning optical microscopy of polarization bistable laser diodes (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 2471-2473 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: TE/TM polarization bistability in a λ=1.3 μm ridge-waveguide InGaAsP/InP bulk laser is studied by near-field scanning optical microscopy with an optical resolution of better than λ/8. The near-field mode profiles of TE and TM emission show different lateral widths and distinctly different mode center positions. This lateral shift is related to a nonuniform strain distribution along the active layer. Based on this strain gradient, we present a model that accounts for the hysteresislike current dependence of the polarization resolved laser output. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117501
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  • 8
    Electronic Resource
    Electronic Resource
    Transitions to a new chiral phase in a Langmuir monolayer (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 8216-8220 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Isotherms and x-ray diffraction studies of eicosanoic acid Langmuir monolayers show a phase in which the molecular tilt is intermediate between nearest-neighbor (NN) and next-nearest-neighbor (NNN) directions. The transition from this "I" phase to an NN-tilted structure is first order, with a ∼60° change in the tilt direction, while the transition to an NNN-tilted structure is apparently continuous. These results can be explained using a Landau-type theory for uniaxially distorted lattices, which is a modification of an existing theory for hexagonal lattices [J. V. Selinger and D. R. Nelson, Phys. Rev. Lett. 61, 416 (1988)]. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473825
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  • 9
    Electronic Resource
    Electronic Resource
    Imaging with an atomic beam (1995)
    [s.l.] : Nature Publishing Group
    Nature 375 (1995), S. 214-216 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] In our experiment, a caesium atomic beam is laser-slowed, cooled, and polarized by the light chirp technique11'12 in a vacuum chamber of 1,285 mm length before it arrives at the imaging zone (Fig. 1). At the end of the laser cooling cycle, 95% of the atoms are ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/375214a0
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  • 10
    Electronic Resource
    Electronic Resource
    Großes Brunner-Adenom im Bulbus duodeni – ein Fallbeispiel (1998)
    Springer
    Der Chirurg 69 (1998), S. 1388-1390 
    Details
    ISSN: 1433-0385
    Keywords: Key words: Brunner's gland adenoma ; Duodenum ; Diagnosis ; Surgical treatment. ; Schlüsselwörter: Brunner-Adenom ; Duodenum ; Diagnose ; chirurgische Therapie.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung. Benigne proliferative Veränderungen der Brunner-Drüsen machen bis zu 10 % der gutartigen Tumoren des Duodenums aus. Große Polypen bzw. Adenome der Brunner-Drüsen sind jedoch sehr selten. Es wird der Fall eines ungewöhnlich großen Adenoms der Brunner-Drüsen (Größe: 12 × 5 × 2,5 cm) vorgestellt. Die klinische Symptomatik bestand aus isolierten, epigastrischen Beschwerden und postprandialem Völlegefühl. In der bildgebenden Diagnostik wurde der Verdacht auf einen Duodenalwandtumor oder Pankreaskopftumor geäußert. Das Adenom wurde durch eine Duodenotomie und Polypektomie operativ entfernt. Proliferative Veränderungen der Brunner-Drüsen des Duodenums manifestieren sich entweder als diffuse oder als lokalisierte noduläre Hyperplasie oder als Brunner-Adenom. Aufgrund ihrer submucösen Lage entgehen sie häufig der Diagnostik durch endoskopische Biopsien. In der Literatur sind bisher nur 14 Fälle maligner Entartung der Brunner-Drüsen beschrieben worden. Da es sich in der Regel um sehr kleine Tumoren handelt, können die meisten Fälle durch eine endoskopische Polypektomie sowohl diagnostiziert als auch behandelt werden. Größere Tumoren können, wie in diesem Fallbeispiel, eine chirurgische Excision erforderlich machen.
    Notes: Summary. Benign, proliferative changes of the Brunner's gland are very rare and account for about 10 % of duodenal bulb neoplasias. The authors present a case of Brunner's gland adenoma of unusual dimensions (12 × 5 × 2.5 cm). The patient presented with vague epigastric discomfort as isolated symptoms. In this case we performed surgical treatment, including a duodenotomy and polypectomy. Because they are localized in the submucosa small, superficial endoscopic biopsies may fail to confirm the diagnosis. Malignancy seems to occur only very rarely, with only 14 cases reported in the literature. As the majority of Brunner's adenomas are quite small, endoscopic polypectomy will confirm the diagnosis and cure the condition in most cases. Large symptomatic adenomas may require surgical resection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001040050591
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