Scan Distortion Research Articles

Method for Measuring the Incident-Beam Energy in Scanning Electron Microscopy Using Electron Channelling Patterns

Based on recently developed electron channelling pattern techniques, a method is presented for determining directly the incident-beam energy in scanning electron microscopy. A ``standard'' crystal is oriented to give a high-resolution pair of electron channelling lines (hkl) and (h̄k̄l̄) from a known set of Bragg planes, and from the width of the pair, the Bragg angle is determined using a simple conversion procedure. The De Broglie wavelength of the incident electrons, and hence their energy, can then be calculated. The method is demonstrated experimentally and shown to be accurate to about ±1.5%. This accuracy is possible provided a goniometer tilt stage is available with a tilt accuracy of about ±1% (for example, ±0.02° in 2° tilts), and the effect of scan distortions on the final image is negligible. It is pointed out that the accuracy of lattice parameter measurements using the electron channelling pattern technique could be limited by the accuracy of the incident wavelength. An appendix is given discussing the curvature of channelling lines and the effect of curvature on pair-width measurements.

Television Sweep Generation with Resonant Networks and Lines

The synthesis of a current sawtooth from a limited number of first harmonics has been studied. It was found that good linearity is easier to obtain than a fast retrace. Scan distortion may be held below 5 per cent over 80 per cent of scan, by adding only 4 harmonics in a least square proportion. Fast flyback, on the other hand, requires 8 harmonics to be usable for commercial television. Several practical systems for resonant sweep have been tested. All circuits used shock excitation of multiresonant networks by pulses of current. Both pentodes and small hydrogen thyratrons were used successfully. The best multiresonator for synthetic sweep is a delay-line, 3 per cent shorter than a halfwave long and shorted at the far end. To minimize dispersion, a slanting wafer type of construction has been developed which permits control of mutual without effect on self-inductance.