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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4273-4281 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Roughness and general surface topography of polished Si wafers were systematically studied on an angstrom to nanometer scale by scanning tunneling microscopy (STM). Evaluation of a large number of STM images by using a simple classification scheme assures statistically relevant results without the disadvantages and loss of information connected with averaging the rms roughness or similar methods. For the flat parts of the surface, a rms roughness of 1.2–1.8 A(ring) is found, comparable to that derived from light scattering and diffraction measurements on similar surfaces. Significant amounts of the surfaces were found to exhibit more pronounced structures, contrasting results of other techniques. The reliability and applicability of STM measurements on technical surfaces, on an angstrom to nanometer scale, is discussed in the light of these results.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 2253-2255 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Under conditions of increased tunnel current and voltage, with the electron flow directed towards the sample, nanometer-scale structures have been written into ultrathin (∼20 nm) light-emitting porous silicon (PS) films using scanning tunneling microscopy in a high-vacuum environment. For the writing process, a threshold voltage of ∼4.5 V is observed and the resulting dimensions range between 20 and 50 nm. Depending on the writing parameters, the modified regions relax or remain stable during the observation time of several days at room temperature. These results can be assigned, in the first case, to a disruption of a small number of bonds, followed by reconfiguration, and a charging of dangling bond sites, followed by carrier release, in near surface regions. In the latter case, the creation of time-stable defect states within the PS layer is proposed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 1365-1367 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The evolution of visible photoluminescence is demonstrated by measuring the surface morphology of thin (∼20 nm) electrochemically etched porous silicon (PS) films with scanning tunneling microscopy (STM). Using low current densities, three sorts of samples were prepared under different conditions: In the dark (A), under illumination with ultraviolet (UV) light (B), and in the dark followed by a postphotochemical treatment (C). Upon UV light excitation, type A samples do not emit visible light, while samples of type B and C show weak and efficient photoluminescence in the visible range, respectively. STM imaging of these PS layers reveals a considerable decrease in the lateral dimensions of the surface features from approximately 10 nm (type A) to roughly 2 nm (type C), in accordance with the quantum confinement approach in describing the luminescence properties.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 2136-2138 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A scanning tunneling microscope (STM) is used to locally modify p-n junctions on a scale of a few tens of nanometers. The p-n junction is composed of a phosphorus-doped, hydrogenated amorphous Si [a-Si:H(P)] layer deposited on heavily doped p-type crystalline Si(111). Under conditions of high current densities, with the p-n junction biased in forward direction, the a-Si:H layer is structurally changed leading to a decrease of the junction barrier height. The resulting exponential increase of hole injection into the modified amorphous layer leads to electronically active structures. They are detected by STM owing to their differing electronic properties.
    Type of Medium: Electronic Resource
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  • 5
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    Unknown
    London, etc. : Periodicals Archive Online (PAO)
    Slavonic and East European review. 69:3 (1991:July) 559 
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 162 (1994), S. 430-432 
    ISSN: 1432-072X
    Keywords: Key words     Methanogens ; Archaea ; Methanobacterium thermoautotrophicum ; Cell walls ; Peptide biosynthesis ; Pseudomurein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract      The peptide subunits of the pseudomurein, the cell-wall peptidoglycan of some methanogens, are usually composed of glutamic acid, alanine and lysine. In order to get a more detailed picture of the biosynthetic pathway of the peptide subunit, we performed in vitro assays. Starting from glutamic acid a pentapeptide was obtained in seven steps: Nα-UDP-Gluγ→Ala→εLys→Ala ↑γ Glu The pentapeptide structure was identical to that of the peptide subunit of the intact pseudomurein except one additional alanine residue, which is split off during further processing. The pentapeptide synthesis starts with glutamic acid, which is phosphorylated at the Nα-amino group. Nα-phosphoryl-glutamic acid is transferred to a nucleotide-carrier, forming Nα-UDP-glutamic acid. The further pentapeptide biosynthesis is achieved via a di-, tri- and tetrapeptide by stepwise addition of the corresponding amino acids.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Naturwissenschaften 77 (1990), S. 472-475 
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 78 (1990), S. 69-80 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We use the Gutzwiller variational method to study the ground state phase diagram of the infinite dimensional Hubbard model, paying special attention to features associated with the Gaussian form of the tight binding band density of states. We only consider trial states for which the validity of the Gutzwiller approximation has been proven, i.e., the paramagnetic, ferromagnetic, and two-sublattice antiferromagnetic states. We map out the phase diagram numerically, and give approximate analytic arguments to explain the behaviour in the small-U, and large-U limits. We give two versions of the phase diagram: one restricted to homogeneous phases, and another when phase separation is allowed. In the latter case, a homogeneous antiferromagnetic state is found only at exact half-filling, where the state is also insulating. Off half-filling, four different regions are found: pure paramagnetic, and ferromagnetic states, as well as antiferromagnetic-paramagnetic, and antiferromagnetic-ferromagnetic mixed phases.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 79 (1990), S. 91-99 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The level statistics and the localization of a particle in a one-dimensional random potential are investigated numerically. First, we study the level spacing distributionP(S) as a function of the system lengthN and of the disorderw of the system. We show that in addition to the localized and delocalized regimes a third regime can be distinguished: For large disorder a resonance appears inP(S), which is caused by a local level repulsion effect. Second, we investigate the distribution of the localization lengths within the Anderson chain as a function ofN andw. Here, we identify the localization length with the rms spread of the wave functions and we show that this measure for the localization of the eigenstates is not a self-averaging quantity.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 90 (1993), S. 47-50 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The tensor of optical activity of TeO2 was derived with the aid of measurements of the Faraday effect. This technique allows the separation of gyrative effects in crystals having a large birefringence. The natural activity of TeO2 perpendicular to the fourfold axis is by about a factor two larger than along this axis. The sign of the tensorial components is related to structural details.
    Type of Medium: Electronic Resource
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