Scanning ion microprobe (SIM) image using a gallium focused ion beam (FIB) is greatly improved in sensitivity by the in-situ implantation of cesium or oxygen ions with the dose of 10(15)-10(17) atoms/cm(2). When the cesium ions are implanted into the imaging area prior to gallium beam analysis, the brightness of the SIM images in negative ion mode is greatly enhanced. In the same way, the implantation of oxygen ions causes the remarkable enhancement of the brightness of SIM images in positive ion mode. A layered structured sample is beveled and polished mechanically with a slope angle of 0.5degrees, which magnifies the thickness of a layer at about 110 times on the slope. By implanting cesium ions into the beveled surface, an SiO2, layer of 30 nm thickness is clearly distinguished by the enhanced O- image.(C) 2002 Elsevier Science B.V. All rights reserved.