Accurate low-order structure factors for copper metal have been measured by quantitative convergent beam electron diffraction (QCBED). The standard deviation of the measured structure factors is equal to or smaller than the most accurate measurement by any other method, including X-ray single crystal Pendellösung, Bragg γ-ray diffraction, and high-energy electron diffraction. The electron structure factor for the (440) reflection was used to determine the Debye-Waller (DW) factor. The local heating of the specimen by the electron beam is determined to be 5 K under the current illumination conditions. The low-order structure factors for copper measured by different methods are compared and discussed. The new data set is used to test band theory and to obtain a charge density map. The charge deformation map shows a charge surplus between the atoms and agrees fairly well with the simple model of copper 2+ ions at the atomic sites in a sea of free uniformly distributed electrons.

Current X-ray diffraction techniques intended for “ideally imperfect” specimens provide structure factors only on a relative scale and ever-present multiple scattering in strong low-angle Bragg reflections is difficult to correct. Multiple scattering is implicit in the quantitative convergent beam electron diffraction (QCBED) method, which provides absolutely scaled structure factors. Conventional single crystal X-ray diffraction has proved adequate in softer materials where crystal perfection is limited. In hard materials, the highly perfect nature of the crystals is often a difficulty, due to the inadequacy of the conventional corrections for multiple scattering (extinction corrections). The present study on α-Al2O3 exploits the complementarity of synchrotron X-ray measurements for weak and medium intensities and QCBED measurement of the strong low-angle reflections. Two-dimensional near zone axis QCBED data from different crystals at various accelerating voltages, thicknesses, and orientations have been matched using Bloch-wave and multislice methods. The reproducibility of QCBED data is better than 0.5%. The low-angle strong QCBED structure factors were combined with middle and high-angle extinction-free data from synchrotron X-ray diffraction measurements. Static deformation charge density maps for α-Al2O3 have been calculated from a multipole expansion model refined using the combined QCBED and X-ray data.

Of all the long-lived particles available as probes of condensed matter, and of all the signals available on a modern electron microscope, electron nanodiffraction patterns provide the strongest signal from the smallest volume. The technique is therefore perfectly suited to nanostructural investigations in inorganic chemistry and materials science. The Vacuum Generators HB501S, an ultrahigh vacuum (UHV) variant of the HB501 scanning transmission electron microscope (STEM), with side-entry double-tilt stage, specimen preparation and analysis chamber, three postspecimen lenses, and cold field-emission tip with integral magnetic gun lens, has therefore been modified to optimize nanodiffraction and quantitative convergent beam electron diffraction (QCBED) performance. A one-micrometer grain-size phosphor screen lying on a fiber-optic faceplate atop the instrument is fiber-optically coupled to a 2048 × 2048 charge-coupled device (CCD), 16-bit camera. This arrangement promises to provide much greater sensitivity, larger dynamic range, and a better modulation transfer function (MTF) than conventional single crystal scintillator (YAG) CCD systems, with noticeable absence of cross talk between pixels. The design of the nanodiffraction detector system is discussed, the gain of the detector is measured, the spherical aberration constant of the objective lens is measured by the Ronchigram method, and preliminary results from the modified instrument are shown.