Showing papers on "Electron backscatter diffraction published in 1972"

First X-Ray Diffraction Evidence for a Phase Transition during Shock-Wave Compression

Abstract: The x-ray diffraction pattern of a shock-compressed material which is in the process of undergoing a crystal structure transformation has been observed for the first time. Pyrolytic BN, explosively shocked to 245 kbar, exhibits a diffraction pattern which indicates that the crystal structure during compression is like that of wurtzite.

Order in amorphous polystyrenes as revealed by electron diffraction and diffraction microscopy

Abstract: Ordered regions ranging in size between 15 and 45 A have been established in several atactic polystyrenes of various molecular weights (4800; 51,000; and 1,800,000) as well as in an amorphous isotactic polystyrene by means of electron diffraction and high-resolution diffraction microscopy. The order is due to long-chain polymer molecules which tend to align more-or-less parallel to one another with a constant average spacing. The orderly chain packing can be disturbed upon cross-linking by electron irradiation, the disturbance being manifested in the irreversible changes in the d spacing and broadening of one of the diffuse rings which is inter-molecular in origin. From the results obtained, the high-resolution diffraction microscopy technique appears to have the potential for resolving the question regarding the presence of order in unoriented amorphous polymers. The technique can also differentiate between a broadened diffuse ring due to small crystallites and another due to paracrystals contai...

Determination of the Electron Density Matrix from X-Ray Diffraction Data

Abstract: We present a method for the conversion of x-ray diffraction data into an electron density which reflects the antisymmetry of the $N$-electron wave function.

Si(111) surface structures by glancing-incidence high-energy electron diffraction

Abstract: The structures which form on the (111) surface of a silicon single crystal have been examined by glancing incidence high-energy electron diffraction under ultra-high vacuum conditions. A quantitative measurement of the intensities of the hhh systematic set of Bragg reflections from the 2nd to the 7th order was observed as a function of azimuthal angle, rocking angle and temperature. In particular, the intensity of the hhh reflections was measured at crystal azimuths which minimize the non-systematic n-beam interference. These `azimuth-independent' rocking curves for the 1 × 1, 7 and √19 structures are compared and discussed, to explore the possibilities of obtaining structural information for both the surface and the bulk by the glancing incidence high energy technique. The data are suitable for comparison with the calculations of an n-beam dynamical theory as it is developed and adapted to the Bragg case. The refractive shift of the Bragg peaks yielded a value of 12.0 ± 0.4 volts for the mean inner potential of silicon.

The reciprocity of electron diffraction and electron channeling

Abstract: The reciprocity in electron diffraction is demonstrated in thin and thick crystals by using an electron microscope with scanning system. It is concluded that the experiment of electron channeling is identical with that of Kikuchi patterns. The diffraction patterns from thin and thick films of silicon, copper and gold are observed with a 1 MV electron microscope and the relations between the channeling and diffraction are studied along various crystal axes. The diffraction can be classified into flower and geometrical patterns. The former is observed for gold and for the axes in silicon and copper. In this case, the classical theory may be applicable, and the ratios between Lindhard's critical angle and the observed one are about 0.65. The relation between channeling and various well known phenomena in electron diffraction is discussed.

Comparison of experimental and n‐beam calculated intensities for glancing incidence high‐energy electron diffraction

Abstract: Rocking curves for the 2nd to 7th order reflections of the systematic set from the (111) planes of a highly perfect silicon single crystal have been obtained in an ultra-high-vacuum reflection electron diffraction camera operated at 40 keV. These have been compared with the profiles computed with an n-beam dynamic high-energy electron diffraction theory adapted to the Bragg case at glancing incidence. It is shown that, for the 333 reflection, six nodes of the hhh row from {\bar 111} up to 444 are adequate to take into account the systematic multiple beam interference effects. The calculated widths are found to agree with the observed widths within the experimental error for all reflections. The peak reflectivities computed initially for a perfect semi-infinite crystal are systematically higher than the experimental values, by a factor of 7 for the 222 node, decreasing to near agreement for the 777 node. Possible reasons for such discrepancies are discussed. Neither inelastic scattering effects nor reasonable changes in the silicon lattice potential near the surface can bring the observed and calculated intensities into agreement. The discrepancy can be considerably reduced for all orders of reflection, however, when the non-flat nature of the surface is considered.

Calculated X-Ray Diffraction Profiles for Interstratified Kaolinite-Montmorillonite

Abstract: Calculated diffraction profiles for interstratified kaolinite and montmorillonite have been used to determine the composition of clays reported from Poland, Japan and Mexico. The predicted layer proportions determined from the curves and by other methods are in close agreement for the first two but a higher kaolinite content than that originally proposed is obtained for the Mexican clays.

The Optical Potential in Electron Diffraction

Abstract: Abstract Expressions are derived for the optical potential and related mean free path as a function of energy in the range 20 eV to 100 keV for electrons and estimates are made of the contributions from the electronic excitations, thermal diffuse scattering and disorder scattering in Al, Cu and Au.

Crystallite Features of Valonia cellulose by Electron Diffraction and Dark-Field Electron Microscopy

Abstract: Individual cellulose crystallites from the cell wall of Valonia ventricosa have been studied by electron diffraction and observed by dark-field electron microscopy. These two techniques reveal that the crystalline zones which run along the fibrils are above 1000 A in length without any longitudinal periodicity. The width of the crystallites covers the width of the microfibrils and ranges from 140 to 180A without persistent 35 A subunits. In several instances, the crystalline zones terminate in the manner of a fork with two arms of 30 to 40 A in width.

The Spherical Sample Method in Neutron Diffraction Texture Determination

Abstract: Neutron diffraction proves advantageous as compared to X-ray diffraction in texture analysis because of the lower absorption coefficient for a broad variety of materials especially metals. The spherical sample method is recommended because it yields the most reliable results and it does not require great preparational efforts. The fundamental difference between the spherical sample method in X-ray and in neutron diffraction is discussed.