Fabrication of large area silicon nanothickness membranes for channeling experiments

Membranes of micrometer lateral sizes and nanometer thickness are nowadays routinely fabricated through silicon micromachining processes, while more difficult is the fabrication of large areas mem- branes. In this paper we describe a method for fabrication of large area nanothickness silicon crystalline membranes starting from a SIMOX wafer. The realized structures have been characterized by means of high resolution X-ray diffraction and planar channeling of a 2 MeV proton beam. This last analyses dem- onstrates a very interesting phenomenon: As the beam direction is inclined by less than the planar chan- nelling critical angle with respect to the crystal planes, channeled particles undergo half a ‘‘channeling oscillation’’ and exit the crystal with reversed transverse momenta, i.e., the protons trajectories are ‘‘mir- rored’’ by the crystal planes. Over-barrier particles are deflected of a minor extent in the opposite direc- tion with respect to the ‘‘mirroring’’ direction. Observation of such effects not only proves the high crystalline quality of the Si membrane, but open new ways to manipulate high energy charged particle beams through crystals.