Focussing of a transient low energy Cs+ probe for improved NanoSIMS characterizations - Study of charged particle opticsM. Bernheim, T. D. Wu, J. L. Guerquin-Kern and A. CroisyEur. Phys. J. Appl. Phys., 42 3 (2008) 311-319DOI: https://doi.org/10.1051/epjap:2008062