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  • American Institute of Physics (AIP)  (54)
  • International Union of Crystallography (IUCr)  (35)
  • 1
    Electronic Resource
    Electronic Resource
    Contrast of 180° domains of PbTiO3 in an electron microscopic image (1975)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 31 (1975), S. 59-63 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The contrast of 180° domains of PbTiO3 depends on temperature and is caused by differences in the intensity of the diffuse background. The thickness extinction fringes of 180° domains taken at different temperatures between room temperature and near the Curie temperature are qualitatively explained with the use of many-beam dynamical theory, in which different anomalous absorption factors are assumed for each case. The origin of the contrast is interpreted and discussed in terms of the difference in thermal diffuse scattering between the 180° domains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739475000113
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  • 2
    Electronic Resource
    Electronic Resource
    Lattice-image interpretation of a relatively-small-unit-cell crystal (1984)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 143-151 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Many-beam lattice images obtained at 200 kV from V2O3 crystals are discussed in comparison with those calculated in the Bloch-wave approach. The technique of optical diffractogram and equal-thickness fringes is utilized, if possible, to determine the defocus value and the crystal thickness which are the essential parameters for objective interpretation at atomic resolution. Whereas images observed in a thin region (∼ 50 Å) of crystal have been reproduced fairly well by simulation, there are others from thicker regions which are not always explained for lack of knowledge of the parameters. As for the effect of the partial coherence, the validity of the envelope-function approximation is examined with the aid of the first principle involving image-intensity summation, and under the experimental conditions used it proved to be satisfactory for qualitatively reproducing the observed image even for relatively thick (∼ 450 Å) regions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767384000313
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  • 3
    Electronic Resource
    Electronic Resource
    Many-beam lattice images calculated at 100 kV and 1000 kV (1980)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1033-1041 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Lattice images of high-temperature-phase vanadium sesquioxide (V2O3) were calculated within the Bloch-wave approach. At an accelerating voltage of 1000 kV the structure image can be produced while at 100 kV it cannot be obtained because of the small number of reflections available in the image formation, which demonstrates clearly an advantage of high voltages which are produced by improvement in the transfer condition of the objective lens. On the other hand, if an ideal phase-contrast lens is assumed in order to obtain the structure image at 100 kV, lattice-image calculations can be carried out with modified unit-cell size. The results show that the maximum allowable thickness to obtain the structure image varies more rapidly than in a linear manner with the required resolution. The maximum allowable thickness increases either with higher voltages (from about 20 Å at 100 kV to about 35 Å at 1000 kV) or with larger unit cells (e.g. a dilatation of 25% in unit-cell size increases the maximum thickness from about 20 to about 35 Å). However, the evolution of the image details as a function of crystal thickness is different for these two factors, due to the different dynamical interactions of electron waves.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739480002094
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  • 4
    Electronic Resource
    Electronic Resource
    Space-group determination by dynamic extinction in convergent-beam electron diffraction (1983)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 825-837 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Tables of dynamic extinction lines which occur in convergent-beam electron diffraction patterns (GM lines) are given for all the space groups on the basis of the rules given by Gjønnes & Moodie [Acta Cryst. (1965), 19, 65-67]. It is found that 191 space groups can be identified by GM lines. A convenient experimental method which distinguishes a screw axis and a glide plane is demonstrated. Experimental results are shown in which the GM lines due to a screw axis and those due to a glide plane are separately observed. The GM lines appearing in a symmetrical four-beam pattern are demonstrated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767383001695
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  • 5
    Electronic Resource
    Electronic Resource
    Symmetry determination of the room-temperature form of LnNbO4 (Ln = La,Nd) by convergent-beam electron diffraction (1980)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 350-352 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Three different space groups, C2/c, C2 and Cc, have been reported for the room-temperature form of the rare-earth orthoniobates, LnNbO4 (Ln = La, Nd). They belong to different point groups: 2/m, 2 and m, respectively. By means of convergent-beam electron diffraction, the point group has been determined to be 2/m in the present study. Therefore the true space group must be C2/c.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739480000800
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  • 6
    Electronic Resource
    Electronic Resource
    Space-group determination by dynamic extinction in convergent-beam electron diffraction: errata (1984)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 721-721 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Tables 13 and 17 of the paper by Tanaka, Sekii & Nagasawa [Acta Cryst. (1983), A39, 825-837] are not perfect. The correct tables are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767384001495
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  • 7
    Electronic Resource
    Electronic Resource
    Point-group determination by convergent-beam electron diffraction (1983)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 357-368 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The method of point-group determination from convergent-beam electron diffraction patterns has been established by Buxton, Eades, Steeds & Rackham [Philos. Trans. R. Soc. London (1976), 281, 171-194]. However, Table 2 given by them is inconvenient for practical purposes, since many symmetries of the dark-field and ±G dark-field patterns are not given and are left for the reader's consideration. The table is improved and completed with the help of some new symmetry symbols and illustration of symmetries. The new table makes the point-group determination easy and quick. The symmetries of the symmetrical many- beam convergent-beam electron diffraction patterns have been studied by Tinnappel [PhD Thesis (1975), Tech. Univ. Berlin] using group theory. It is shown that the graphical method used by Buxton et al. can reveal the symmetries of these patterns. A method of point-group determination which uses three types of symmetrical many-beam patterns, the hexagonal six- beam, square four-beam and rectangular four-beam patterns, is described. This method requires only one photograph in determining most diffraction groups. This fact means that the method is more convenient and reliable than that of Buxton et al., since their method requires two or three photographs for most cases. Experimental results which verify the theoretical ones are given. The characteristic features of the symmetrical many-beam method are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S010876738300080X
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  • 8
    Electronic Resource
    Electronic Resource
    Anisotropic transport and nonparabolic miniband in a novel in-plane superlattice consisting of a grid-inserted selectively doped heterojunction (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 1214-1216 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transport properties of electrons in a novel in-plane superlattice structure are studied and the field-effect transistor action has been demonstrated. The structure consists of an n-AlGaAs/GaAs modulation-doped heterojunction in which an array of monolayer-thick AlAs grid is embedded with an average period of 162 A(ring) in the channel region of the heterojunction. This grid has been prepared with molecular beam epitaxy by depositing a half monolayer of AlAs on a GaAs (001) vicinal plane, where periodically spaced atomic terraces are formed. The electron mobilities μ(parallel),μ⊥ parallel and normal to the grid are measured as functions of electron concentration NS. While the mobility ratio (μ(parallel)/μ⊥) is nearly unity at low NS, the ratio is found to get as large as 2.2 as NS increases. This anisotropic behavior of μ is well accounted for by the calculated nonparabolicity in the miniband structure of in-plane superlattices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101658
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  • 9
    Electronic Resource
    Electronic Resource
    Epitaxial ferromagnetic MnAs thin films grown on Si (001): The effect of substrate annealing : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4957-4959 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied two different types of epitaxial ferromagnetic MnAs thin films on Si (001) substrates grown by molecular beam epitaxy. When the Si substrates were annealed at a relatively high temperature (∼900 °C) and then MnAs was grown, we obtained epitaxial MnAs films with twofold crystal symmetry (type I). In contrast, when the thermal cleaning of the Si substrate was done at a lower temperature (∼600 °C), epitaxial MnAs thin films had fourfold crystal symmetry (type II). The growth plane in both types of MnAs thin films was the (1¯101) of the hexagonal MnAs. The type I MnAs films are single domain with strong magnetic anisotropy, whereas the type II MnAs films are double domain with the lack of strong magnetic anisotropy. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361602
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  • 10
    Electronic Resource
    Electronic Resource
    Galvanomagnetic properties and magnetic domain structure of epitaxial MnAs films on GaAs(001) : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4967-4969 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial MnAs films on GaAs(001) in the thickness range 20–200 nm were studied. Using ordinary and extraordinary Hall effect data to determine the field required for perpendicular saturation and saturation magnetizations reported elsewhere, we determined the shape anisotropy constant in the basal plane of the hexagonal structure to be 3.7(0.6)×105 erg/cm3 and the surface anisotropy constant to be −1.3(0.4) erg/cm2. The negative sign indicates thin enough films will be perpendicularly magnetized. By magnetic force microscopy of a 100 nm film we found stripe domains with 180° Bloch walls, thereby avoiding the hard c axis. The widths of the domains and the walls are 4.0(0.3) μm and 95(6) nm, respectively. In magnetoresistance, we observed behavior similar to other ferromagnets, namely peaks centered around the positive and negative coercive fields, and at fields beyond the coercive field a linear dependence on magnetic field. The electrical resistance showed rapid increase with temperature beginning about 5° below the Curie temperature (40 °C) caused by the change in crystal structure from hexagonal to orthorhombic. The resistivities are, respectively, 300(24) and 375(30) μΩ cm. Comparison with bulk values indicates the large lower temperature value is partly due to the presence of some orthorhombic phase observed in x-ray studies. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361605
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