Low energy positron channeling in silicon

A low energy (1-60 keV variable) positron beam facility has been used to study positron channeling through a 0.26 μm Si(100) crystal. Along the LFAN100〉 axis, a strong reduction in the wide-angle (12°-15°) scattering yield was observed even at the lowest energy studied (15 keV). The angular widths were consistent with theoretical predictions. The minimum yields agreed with extrapolation from dechanneling measurements made with high energy protons. Measurements were also made at 50 keV along the 〈210〉 and 〈310〉 axes, as well as the (100), (110), and (210) planes. Again, the results were consistent with the classical theory, although the magnitude of the effect was less than that in the case of 〈100〉 channeling. Only slight evidence of a first order diffraction effect was seen in some of the data obtained; however, a rather large degree of positron-electron multiple scattering presumably masked out any detailed observation of diffractive features.