PREPARATION OF ULTRATHIN FREESTANDING TARGETS FOR (E,2E) SPECTROSCOPY

We describe in detail the procedures used for the preparation of ultra thin (similar to 10 nm) free-standing membranes for (e, 2e) spectrosco py. Such a thin target is needed to minimize electron multiple scatter ing before and after an (e, 2e) event. The development of a rf plasma source which allows in situ thinning and thickness monitoring is of ke y importance to the success of the target preparation. Materials (C, S i, Ni, Cu, Al2O3, SiO2, CuO) with different properties and structures are usually prepared in different ways. For insulating targets it is i mportant to have a conducting sublayer to avoid the charging problem. A well prepared target usually has a thin area larger than the (e, 2e) beam size (similar to 0.2 mm in diameter) and yields high quality (e, 2e) data from which the electron energy-momentum density in a chosen direction is determined. Efforts demonstrated in this article indicate that the preparation of ultrathin free-standing films is a challengin g area where significant technical development is needed. (C) 1997 Ame rican Institute of Physics.