An electrostatic beam rocking system on the Surrey nuclear microprobe

The use of two sets of magnetic dipoles, producing opposite fields, to rock a focused MeV ion beam over the surface of a crystalline sample is now wel l established in several nuclear microprobe laboratories. Such a 'beam rock ing' system allows ion channeling analysis from micron-size regions of the sample to be measured, with a beam displacement over the sample surface as small as a few microns, and no requirements for an automated goniometer. While magnetic beam rocking systems are ideal for many applications, they a re limited in the speed at which the beam can be rocked in angle owing to h ysteresis effects. This may also cause problems of non-reproducibility of t he beam displacement on a micron scale. Also, heavier ions are more difficu lt to rock through a given angle using a magnetic beam rocking system, wher eas an electrostatic beam rocking system gives a rocking angle which is ind ependent of the ion mass. This paper describes the construction and uses of a fast electrostatic beam rocking system, which uses two sets of high voltage plates driven in oppos ition at high frequencies. Ion optics simulations are used to model the per formance of the system. The optics of this beam rocking system, in which bo th sets of deflection plates are located before the quadruplet lens formati on are discussed. The uses of this system to rapidly image the location of crystal planes and axes, and to carry out rapid channeling analysis are pre sented. (C) 2001 Elsevier Science B.V. All rights reserved.