Scanning Microscopy


Progress towards the quantification of high-resolution electron microscopy and electron holograms has been achieved using digital acquisition with a slow-scan charge-coupled device (CCD) camera. Two applications are described: the precise measurement of lattice-fringe spacings and the determination of the mean inner potential. Lattice images can be characterized by a finite sum of two-dimensional sinusoids. A new method for measurement of the frequency, amplitude and phase of each sinusoid, based on an interpolation technique in reciprocal space, is presented. The method offers considerably higher precision for measurement of lattice fringes than the optical bench and is applicable to images recorded with an electron dose of less than 1 el / Å2 and specimen areas as small as 8 Å across. The attainable precision is dependent on specimen characteristics, electron dose and the size of the measured area, and ranges from 0.001 Å to 0.05 Å. An improved method has also been developed for measurement of mean inner potential using digital off-axis electron holograms from 90° crystal wedges. The value of (-14.21 ± 0.16) V obtained for GaAs represents the most accurate measurement yet reported for the mean inner potential.

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