Electron Diffraction Photographs Research Articles

Sir Clifford Charles Butler. 20 May 1922 – 30 June 1999

Clifford Butler was born in Earley, Reading, on 20 May 1922 to Charles and Olive Butler. An only child, he went to Reading School in 1932, having won a Berkshire County Council Educational Scholarship worth £15 per year. In addition to his academic work he was active in the Scouts and was a House Prefect (East House). Leaving school he went to Reading University to take physics, as did Kathleen Collins, whom he was to marry in 1947. Graduating in 1942 with a first–class BSc (Special) he stayed on as a demonstrator, his National Service taking the form of teaching radio as part of the State scheme to produce radar physicists, and acted part–time as a physicist at the Royal Berkshire Hospital. Kathleen went to work at the Road Research Laboratory. Butler found time, largely in the evenings, to undertake research for a PhD in electronic diffraction in the laboratory of Professor J.A. Crowther. He worked very closely with his thesis supervisor Dr Tom Rymer and it was there that he started to demonstrate his considerable skills in technical matters. His thesis, ‘some factors affecting precise measurement in electron diffraction’, was presented in April 1946 and was a detailed study, covering both technical and theoretical aspects, of how to improve the use of Debye–Scherrer electron–diffraction photographs to investigate crystal structure. The research on which it was based initiated four very different papers and led Crowther to predict, immediately after Butler's PhD examination, the latter's Fellowship of The Royal Society.

Crystal Growth and Structure of AlSr2YCu2O7

Millimeter-size crystals of AlSr2YCu2O7 were synthesized by the flux method in alumina crucibles. Different mixtures of SrO:CuO (ranging from 25:75 to 12:88 mol ratio) were used as flux. No aluminum was added to the reagents. Depending on the flux composition and cooling rate, crystals different in morphology and size were obtained. The crystals appear to be tetragonal, space group P4/mmm. However, electron diffraction photographs, in agreement with Ramı́rez-Castellanos et al. (1), reveal that the symmetry is othorhombic with a cell a=2at, b=4at, and c=2ct (the subscript t refers to the YBCO tetragonal cell). The structural refinement was based on X-ray data collected with a KCCD Nonius diffractometer equipped with a graphite monochromator and AgKα radiation. One hundred and ninety-seven independent reflections with respect to the space symmetry quoted above, with I>3σ, were used. The arrangement is that of a YBCO structure in which the chain Cu cations have been replaced by Al. This substitution induces the movement of the oxygen atoms in the basal layer in such a way as to form, together with the apical oxygen atoms, corner-sharing zig-zag chains of oxygen tetrahedra centered around the Al cations and running parallel to the a-axis either tetragonally or orthorhombically. The b- and c-axes are quadrupled and doubled, respectively, because the zig-zag chains are out of phase perpendicularly to these directions. The additional distortion results in the shift of Al to xx0 (x≈0.056) from 000, O1 to xxz (x≈0.073) from 00z, and O3 to (0.5, y, 0) (y≈0.116) from (0.5, 0, 0).

Initial stages in the formation of epitaxial films of II–VI compounds on a muscovite mica substrate under highly nonequilibrium conditions

A discussion is presented regarding the results obtained from investigations of the initial stages of the epitaxial growth of CdTe and CdS films on substrates cooled to negative temperatures Celsius. Electron diffraction patterns and photographs of the surface are shown, corresponding to the early stages of growth. The features that are revealed (island size 20–25 nm, a δ-function size distribution of the islands, and a monotonic orientation process of the islands) are explained in the framework of a phenomenological theory of heterophase fluctuations and nucleation with the use of a model of the motion of misfit dislocations.

Sector growth and symmetry of (F,OH) apatite from the Asio mine, Japan

AbstractA study of apatite crystals from the Asio mine, Japan, showed sectoral texture related to the growth of the crystal, and with optically biaxial properties within the sectors. Wet chemical analysis gave a composition Ca5(PO4)3(F0.64,OH0.38,Cl0.01)1.03 for the specimen.Additional diffraction spots were not observed in precession and oscillation X-ray photographs and electron diffraction photographs. Since the internal textures correlate with the surface growth features, it is suggested that the internal textures and the unusual optical properties were produced during nonequilibrium crystal growth. The fluorine/hydroxyl sites in hexagonal apatite are symmetrically equivalent in the solid crystal but, at a growth surface, this equivalence may be lost, resulting in a reduction of crystal symmetry. Heating of the apatite to about 850°C results in the almost complete disappearance of the optical anomalies due to disordering, which may be related to the loss of hydroxyl from the crystal.

Indexed Powder Data for Incommensurate Bi2Sr2Ca2Cu3Oz

AbstractThe X-ray powder pattern of the Pb-free 110 K superconductor phase Bi2Sr2Ca2Cu3Oz has many lines which belong to an incommensurate supercell. Using electron diffraction photographs as a guide, an indexing scheme for the powder pattern has been obtained. The unit cell has a geometrically orthorhombic subcell a = 5.411 (2), b = 5.420(2), c = 37.29(2) Å. Supercell reflections have indices that are derived from the subcell k, l indices by addition of ± q, where q = nδb + nεc: n = 1,2 …; ε = 0.211(2); ε = −0.78(1).

Icosahedral and decagonal quasicrystals of intermetallic compounds are multiple twins of cubic or orthorhombic crystals composed of very large atomic complexes with icosahedral point-group symmetry in cubic close packing or body-centered packing: Structure of decagonal Al 6 Pd

A doubly icosahedral complex involves roughly spherical clusters of atoms with icosahedral point-group symmetry, which are themselves, in parallel orientation, icosahedrally packed. These complexes may form cubic crystallites; three structures of this sort have been identified. Analysis of electron diffraction photographs of the decagonal quasicrystal Al(6)Pd has led to its description as involving pentagonal twinning of an orthorhombic crystal with a = 51.6 A, b = 37.6 A, and c = 33.24 A, with about 4202 atoms in the unit, comprising two 1980-atom doubly icosahedral complexes, each involving icosahedral packing of 45 44-atom icosahedral complexes (at 0 0 0 and 1/2 1/2 1/2) and 242 interstitial atoms. The complexes and clusters are oriented with one of their fivefold axes in the c-axis direction.

Icosahedral quasicrystals of intermetallic compounds are icosahedral twins of cubic crystals of three kinds, consisting of large (about 5000 atoms) icosahedral complexes in either a cubic body-centered or a cubic face-centered arrangement or smaller (about 1350 atoms) icosahedral complexes in the β-tungsten arrangement

The twofold-axis electron-diffraction photographs of icosahedral quasicrystals are of three kinds, reflecting three different structures of the cubic crystals that by icosahedral twinning form the quasicrystals. The first kind, represented by Al(13)Cu(4)Fe(3), contains two very large icosahedral complexes, each of about 4680 atoms, in the body-centered arrangement, with six smaller icosahedral complexes (104 atoms each) in the principal interstices. The second kind, represented by Al(5)Mn, contains four of the very large complexes in the face-centered arrangement (cubic close packing), with four of the smaller clusters in the interstices. The third kind, represented by Al(6)CuLi(3), contains eight icosahedral complexes, each of about 1350 atoms, in the beta-W arrangement. The supporting evidence for these cubic structures is discussed as well as other evidence showing that the simple quasicrystal theory, which states that quasicrystals do not involve any translational identity operations, has to be modified.

Scattering of light in TiO 2 layers of broad band mirrors

It is shown by measurements of the scattered light of TiO 2/SiO 2 broad band mirrors, that the scattered light must have been generated from the bulk of the TiO 2 layers. By the application of two different technological procedures (water and oxygen technology) the structure of these layers can be altered, and this is demonstrated by the electron diffraction photographs. The reason for this scattered light is supposed to be the birefringence of TiO 2.

Reinvestigation of the carbon films prepared by ArF excimer laser-induced chemical vapor deposition

It has already been reported by the authors [K. Kitahama, K. Hirata, H. Nakamatsu, S. Kawai, N. Fujimori, T. Imai, H. Yoshino, and A. Doi, Appl. Phys. Lett. 49, 634 (1986)] that the formation of diamond was confirmed in an ArF excimer laser-induced chemical vapor deposition experiment using acetylene as a carbon source. However, a careful reexamination of the reflection electron diffraction photographs afterward reveals that the deposit is something other than diamond. Raman spectra of the deposit were compared with those of other homologous substances. It is concluded that the structure of the deposit consists of individual graphite layers which are randomly translated parallel to the layers and rotated about the normal of the layers, although separations between individual graphite layers are kept constant. The structure is identical with that of the material known as a ‘‘heat-treated carbon black.’’

An electron diffraction and lattice-dynamical study of the diffuse scattering in β-cristobalite, SiO2

Strong diffuse scattering has been observed on electron diffraction photographs of β-cristobalite. This is observed to be in the form of diffuse planes normal to the six (110) directions. A simple Born–von Karman force model including nearest-neighbour Si–O, O–O and Si–Si interactions has been used to calculate lattice-dynamical properties for β-cristobalite assuming the structure to be the simple Wyckoff [Z. Kristallogr. (1925), 62, 189–200] C9 structure. The force-model parameters used were obtained by fitting to the infrared and Raman frequencies of α-cristobalite and are very similar to those obtained by Barron, Huang & Pasternak [J. Phys. C (1976), 9, 3925–3940] for quartz. Calculated thermal diffuse scattering patterns obtained are in good agreement with the observed patterns, and may be interpreted in terms of low-lying relatively dispersionless branches of the phonon dispersion curve diagrams. These branches correspond to motions of the structure involving coupled rotations of the tetrahedra in columns along the (110) directions, the motion in neighbouring columns being virtually uncoupled.

Diffuse scattering in nickel arsenide, NiAs

The characteristic diffuse scattering distribution that is observed on electron diffraction photographs of nickel arsenide, NiAs, has been interpreted in terms of a force-constant model of the structure. Thermal diffuse scattering intensities for the system have been obtained, both by direct calculation from a force-constant model and also with the use of Monte Carlo simulation in combination with optical transform techniques. The diffuse scattering can largely be explained in terms of simple nearest-neighbour central-force constants between Ni-Ni (in the c direction and in the basal ab plane), Ni-As and As-As, and does not appear to be closely associated with the formation of the recently reported orthorhombic displacive superlattice, which has been attributed to the condensation of a q=1/3(11-20) Sigma 6 phonon. From the derived force model it is shown that the main driving force required to obtain the superlattice must be a force tending to make the Ni atoms form zigzag chains along c (i.e. alternative Ni atoms are displaced in opposite directions in the basal plane). Additional, albeit small, second-nearest-neighbour forces must also be invoked for the Sigma 6 phonon to condense at 1/3(11-20) rather than at 1/2(11-20), which would correspond to the MnP superlattice distortion.

Sigma-phase packing of icosahedral clusters in 780-atom tetragonal crystals of Cr 5 Ni 3 Si 2 and V 15 Ni 10 Si that by twinning achieve 8-fold rotational point-group symmetry

A 780-atom primitive tetragonal unit with edges 27.3, 27.3, and 12.6 A is assigned to rapidly solidified Cu(5)Ni(3)Si(2) and V(15)Ni(10)Si by analysis of electron diffraction photographs with the assumption that the crystals contain icosahedral clusters. There are thirty 26-atom clusters at the sigma-phase positions. Apparent 8-fold symmetry results from 45 degrees twinning on the basal plane.

Structure of the orthorhombic form of Mn 2 Al 7 , Fe 2 Al 7 , and (Mn 0.7 Fe 0.3 ) 2 Al 7 that by twinning produces grains with decagonal point-group symmetry

Analysis of electron diffraction photographs of grains of Mn(2)Al(7), Fe(2)Al(7), and (Mn(0.7)Fe(0.3))(2)Al(7) leads to the conclusion that they are 5-fold twins of a 1664-atom orthorhombic crystal with a = 32.86 A, b = 31.23 A, and c = 24.80 A and with 16 icosahedral clusters of 104 atoms in positions shifted by small amounts from those of the cubic beta-tungsten structure.

Oxygen vacancy ordering in Ba2YCu3O7−x around x= 0.5

Electron diffraction photographs of the title samples show extra diffuse scattering in the reciprocal a*b* plane, which can be attributed to the partial ordering of the oxygen vacancies. A unit cell 2ac x ac x 3ac (ac being the basic perovskite subcell parameter; ac≅3.8Å is proposed together with a structural model.

Oxygen-vacancy ordering in the Ba2YCu

Diffuse scattering streaks or bands have been observed in electron diffraction photographs for samples belonging to the superconducting system ${\mathrm{Ba}}_{2}\mathrm{Y}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$ ($0\ensuremath{\le}x\ensuremath{\le}1$). In situ experiments show that this diffuse scattering can be associated with short-range ordering of oxygen vacancies. The same vacancy ordering occurs in previously reduced samples. Three types of diffuse scattering are observed, each corresponding to a short-range-order scheme.

So-called icosahedral and decagonal quasicrystals are twins of an 820-atom cubic crystal.

It is proposed that a molten alloy may contain a 104-atom cluster with icosahedral symmetry and largely icosahedral packing. The cluster may be described as involving twenty interpenetrating Friauf polyhedra. On rapid freezing these clusters form cubic crystals related to the \ensuremath{\beta}-W structure. The structure is compatible with x-ray and neutron powder diffraction patterns, the single-crystal precession x-ray patterns of ${\mathrm{CuLi}}_{3}$${\mathrm{Al}}_{6}$, the electron diffraction photographs, and the high-resolution electron micrographs.

Synthesis of diamond by laser-induced chemical vapor deposition

Diamond has been obtained by ArF excimer laser-induced chemical vapor deposition. The reaction was carried out by use of C2H2 diluted with H2 as a source gas and at the pressure range of 8–75 Torr. The products were characterized by scanning electron microscopy and reflection electron diffraction. Deposits prepared in the temperature range of 40–800 °C, which were measured by the thermocouple attached to the substrate, show several lines of diamond in the reflection electron diffraction photographs. The fact that the laser beam must be concentrated for the diamond formation to occur strongly suggests that the reaction proceeds through a multiple photon process.

Synthesis of Diamond by Laser-Induced CVD

AbstractSynthesis of diamond thin-films has been tried by an ArF excimer laser-induced chemical vapor deposition (LCVD) technique, using acetylene diluted with hydrogen as a source gas and a silicon wafer as a substrate. In these experiments, irradiation geometry, substrate temperature and laser power density were varied. Upon irradiation by a focused laser beam, deposition of diamond on substrates heated above 400°Cwas observed, and was confirmed by reflection electron diffraction (RED) photographs. Homogeneity of the diamond films was improved by irradiation parallel to the substrate. These facts suggest that the formation of diamond proceeds through multiple photon decomposition of the reactant gas, and that electronic excitation of gas phase rather than that of substrate or adsorbate layer is essential to form diamond.

Structural comparison of native and deoxycholate-treated purple membrane

Lipid-depleted purple membrane prepared by extraction with deoxycholate has been compared with the native structure. X-ray and electron diffraction photographs show a reduction in cell dimension from 62.4 to 57.3 A, and a substantial change in the distribution of diffraction intensity compared with the native specimens. Low-dose electron microscopy has been used to obtain a projected density map of lipid-depleted membranes. The projected structure shows that the deoxycholate treatment removes a boundary layer of lipid, which in the native form separates adjacent trimers of bacteriorhodopsin. The map also provides an improved estimate of the molecular envelope of the protein. A plausible arrangement for the lipid molecules in both the native and the lipid-depleted membranes is proposed, but the precise positions of individual molecules cannot yet be specified.

Dehydration of Synthetic Hydrated Kaolinites: A Model for the Dehydration of Halloysite(10Å)

AbstractSeveral hydrates can be synthesized from well-crystallized kaolinites; of importance to the present work are a 10-Å hydrate (called the QS-10 hydrate), an 8.6-Å hydrate, and two kinds of partially dehydrated mixed-layer hydrates. One kind is a series of unstable materials with d(001) varying continuously between 10 and 8.6 Å, and the other kind is stable with d(001) approximately centered at 7.9 Å. The 10- and 7.9-Å phases have been observed in halloysites by many workers using X-ray powder diffraction, and the 8.6-Å phase has been seen by others in selected area electron diffraction photographs. Infrared spectra reveal additional similarities between the synthetic hydrates and both halloysite(10Å) and partially dehydrated halloysites. Because of these similarities, the synthetic hydrates can be used to develop a model for the dehydration of halloysite(10Å).Previous work on the 10- and 8.6-Å hydrates identified two structural environments for the interlayer water. In one, the water is keyed into the ditrigonal holes of the silicate layer (hole water), and in the other, the water is more mobile (associated water). Both types are found in the QS-10 hydrate and halloysite(10Å), whereas only hole water occurs in the 8.6-Å hydrate. In the QS-10 hydrate, stronger hydrogen bonding between hole water and the clay makes the hole water more stable than the associated water. This difference in stability is responsible for a two-step dehydration process. The first step is the loss of associated water which results in a material with d(001) = 8.6 Å. This stable hydrate must be heated to temperatures near 200°C to drive off the remaining hole water. The less perfect structure of halloysite and its common curvilinear morphology reduce the difference in stability between hole and associated water molecules, so that when halloysite(10Å) dehydrates, loss of hole water and associated water overlaps, and the d-spacing goes directly to 7.2–7.9 Å.