A novel VHF plasma source using a method of superposing standing waves is proposed in this article. The characteristics of VHF plasma generated by this method were measured with the Langmuir probe and a digital camera. Here, the frequency was 80 MHz, and an electrode size and discharge gap of electrodes was 1 800 × 300 mm2 and 20 mm, respectively. The distributions of plasma light emission were uniform across the whole electrode in the pressure range from 0.1 to 0.3 Torr. The spatial profile of the ion saturation current density was flat in the direction of the electrode. In this case, the non‐uniformity of VHF plasma was less than ±10% at 0.3 Torr.

Weak spurious intensities arising from the n-beam interaction (the multiple diffraction) often obscure the existence of screw axes or glide planes. It is pointed out that the n-beam interaction may also introduce· significantly different intensities to a set of crystallographically equivalent reciprocal lattice points. These problems can be solved by making IJI scanning measurements and, more definitely, by a comparison with the simulation based on the Soejima-Okazaki-Matsumoto (1985) formalism; some examples are shown. Since the influence on the intensity reaches 10% for strong reftections and more for weaker ones, a careful examination is essential for the accurate determination of F values.