Cover Picture (Angew. Chem. Int. Ed. Engl. 10/1988)

The title picture shows the luminescence of a Ni(CO)₄ molecular beam after excitation with a xenon chloride UV laser. The pulsed molecular beam emerges from a nozzle (above in the picture, diameter ca. 50 μm) and expands conically. Interaction with the laser pulse leads to photolysis and formation of excited Ni(CO)₃, which is responsible for the luminescence. In the center of the picture is the cone of a skimmer, the function of which is to admit only the core of the molecular beam through an opening (diameter < 1 mm) and thus collimate the beam. Such molecular beam experiments make it possible to investigate the physical-chemical basis of laser-activated gas-phase deposition of solids. Further, high-purity nickel films can be deposited on substrates in this way. More details on gas-phase deposition of thin metal and semiconductor films, as well as on high-quality powders for ceramics and on etching reactions for surface microstructuring, are reported by K. L. Kompa in a review article on p. 1314ff.