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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 686-696 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The critical-voltage effect has been combined with the convergent-beam electron diffraction technique using a high-voltage electron microscope. The method allows the critical voltage Vc to be detected to within approximately ± 1 kV, compared with ± 5 kV in previous methods. This accuracy is achievable throughout the 100 to 1000 kV accelerating-voltage range of the high-voltage microscope used. Vc has also been determined by varying the specimen temperature at constant voltage, which has the advantage that all electron-optical parameters are kept constant: thus the 'transfer function' of the microscope is constant. The critical voltage is easily identified experimentally by the appearance of a characteristic 'dark band' in the Bragg-satisfied second-order convergent-beam disc. Changes in the asymmetry of the Kikuchi line within the dark band enable the precise localization of Vc to ± 1 kV to be made. The improved precision of this new method considerably increases its application to the determination of scattering factors in pure materials and to ordering and electron-transfer effects in certain alloys. The method is illustrated by applying it to Cu and Cu-Al alloys.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 27 (1971), S. 42-45 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: There are a number of different Bloch wave labelling systems currently in use in the theory of the diffraction of electrons by crystals. It is suggested that the Bloch wave labelling scheme for electron diffraction which is the simplest and the most logical is an ordered labelling scheme in which the top branch of the dispersion surface corresponds to wave 1, the second branch to wave 2, the third branch to wave 3, and so on. Such a scheme would be consistent with accepted notations in other forms of Bloch wave propagation. The essential mathematical unity of all forms of wave propagation in crystals is discussed, and the use of the proposed notation in describing the critical voltage effect is briefly considered.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 3143-3150 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ohmic contacts to AlGaN/GaN heterostructures which have low contact resistance and good surface morphology are required for the development of commercial high power, high frequency transistors in the GaN system. The development of such contacts would be helped by a better understanding of the effect of microstructure on electrical behavior, which is studied here. Au/Ni/Al/Ti/AlGaN/GaN ohmic contact structures were rapid thermal annealed in argon for 60 s at temperatures in the range 550–900 °C. The variation of contact resistance with anneal temperature was correlated with the phase distribution observed by transmission electron microscopy (TEM). A combination of TEM techniques was required to determine the resulting microstructure, including energy filtered TEM, high resolution electron microscopy and energy dispersive x-ray spectrum imaging. Contacts with the lowest resistance were formed after 700 °C annealing. Very little consumption of the 30 nm AlGaN layer was observed. An unidentified phase containing Al, Ti and Au is present at the interface in the samples with low specific contact resistance. The identification of the observed thin interfacial phases (including TiN and AlN) is discussed, along with the effects of oxidation and possible mechanisms of ohmic contact formation. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 222-224 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of strains on the local crystallographic symmetry and structure of a Si/GexSi1−x model heterostructure grown on a (100) silicon substate was studied using convergent beam electron diffraction techniques and a cross-sectional specimen geometry. The alloy layers are seen to distort into relaxed tetragonal and monoclinic structures which are dependent on position and/or alloy composition. These observations can be explained in terms of strain relaxation in a thin-film specimen and deviations of the substrate from a perfect (100) orientation. The results have implications not only for the use of cross-sectioned specimens in the characterization of strained-layer heterostructures, but also for the band engineering of Si/GexSi1−x strained-layer superlattices and other materials which are grown on vicinal (100) and other low-symmetry substrate orientations. In particular relaxed tetragonal and monoclinic structures may be quite relevant to the emerging science of strain-induced lateral confinement of carriers in quantum well semiconductors.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 2499-2504 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron beam-induced crystallization studies in amorphous FeF3 films using electron energy loss spectroscopy (EELS) are discussed in this letter. Time-resolved EELS studies show that the coordination polyhedra in amorphous FeF3 (a-FeF3) are randomly arranged FeF6 octahedra. They arrange themselves to give long range order during crystallization to FeF2 and FeF3 under the electron beam. Changes in the d-band occupancy by one electron as well as the sensitivity of the ratio of the Fe L3 and L2 edges to the electronic configuration of the iron ion are clearly seen during the crystallization process. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 2083-2085 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An x-ray topography study is presented of the coherency breakdown in GexSi1−x/Si(100) strained epilayers. Finite dislocation densities (in excess of 103 cm−2) are observed at compositions in the range 12–13 at. % Ge for an epilayer thickness of h≈180 nm. Above 13 at. % Ge the dislocation density starts to change rapidly and this composition is identified as critical for h≈180 nm, a thickness which is almost a factor of 4 lower than the accepted "critical'' thickness for this lattice mismatch. The result suggests that in low-mismatched GexSi1−x alloys the dislocation density will increase continuously at the "critical'' thickness, as opposed to exhibiting a sharp onset. The implications of these results to the various models of the critical thickness transition are discussed.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 457-459 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An electron diffraction and microscopy study is presented of a variety of phases in the Y:Ba:Cu:O system in which superconductivity occurs. The superconducting phase is demonstrated by convergent beam electron diffraction to be centrosymmetric with space group Pmmm, in contrast to a previous determination of Pmm2. This discrepancy arises from local symmetry-breaking defects. In addition to this phase and a cubic BaCuO2 phase, we characterize two other phases. One is the Y-rich orthorhombic phase: Pnma with a=13.5 A(ring), b=6.3 A(ring), and c=7.6 A(ring). The second occurs by a phase transition of the superconducting Pmmm phase to P4/mmm with a=3.85 A(ring), c=11.7 A(ring). The superconducting phase may now be described as either an ordered array of oxygen vacancies in the perovskite structure, or an ordered array of oxygen interstitials in the new tetragonal phase, which may explain how the material can lose oxygen reversibly.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2527-2529 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate that scanning transmission electron beam induced conductivity can be used to image the recombination activity of an orthogonal 〈110〉 misfit dislocation array within a relaxed Si/Si1−xGex/Si(001) heterostructure on the submicrometer scale. Correlation with structural images suggests that an array of bunched dissociated 60° misfit dislocations is primarily responsible for the electrical activity in this instance. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 170-172 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transmission electron microscopy is used to investigate electron-induced crystallization of thermally evaporated amorphous AlF3(a-AlF3). It is shown that this material undergoes a very complicated crystallization process with three crystalline substances (Al, AlF3, and Al2O3) formed as the dose increases. The sequence of the crystallization is highly sensitive to the presence of water, which inhibits radiolytic dissociation of a-AlF3 into Al and fluorine, reduces the dose required for the crystallization of a-AlF3, and causes the transformation of AlF3 into Al2O3. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 809-811 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The local Ge composition in undulating Si0.8Ge0.2 layers on Si has been studied in a scanning transmission electron microscope using electron energy-loss spectroscopy. We observe Ge enrichment of the SiGe layer near the free surface (vertical Ge segregation in the growth direction) as well as Ge depletion of the ripple troughs compared to the peaks (lateral segregation). These lateral compositional fluctuations are likely to retard the generation of misfit dislocations and might be relevant to the Stranski–Krastanov growth of strained epitaxial alloy layers as well as to the self-organized growth of quantum dot structures. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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