A focused ion beam (FIB) is one of the few tools with which it is possible to directly fabricate structures on the nanometer scale. The FIB produces a tiny beam of gallium ions which is steered electrostatically and can be programmed to either raster uniformly across an area or to dwell at specific locations for pre-determined intervals. The gallium ion beam rapidly erodes most materials by sputtering, a process aptly described as atomic-scale sand blasting. Thus, structures with feature sizes approaching the resolution of the beam - about 10 nm - can be fabricated. In addition, by collecting secondary electrons from the gallium ion impacts, images analogous to those obtained by a scanning electron microscope can be generated. Thus, it is possible with the FIB to both create nanoscale structures and image them in real time. Taken alone, or in conjunction with additional processing steps the FIB is a powerful and flexible tool for engineering and analyzing nanostructures.
As a demonstration of the flexibility of the FIB to create arbitrary structures, we have reproduced a well-known portrait in an area smaller than a human red blood cell. The image of George Washington in the attached figure is approximately 6 micrometers wide and 8 micrometers high and was itself produced in the FIB following the etching of the portrait. The letters in the word "WASHINGTON" are approximately 100 nm with detail in the face, eyes, hair and clothes approaching the FIB's nominal resolution. Contrast in this image is produced by beam-induced variations in secondary electron emission created during the etching, although similar structures analyzed by atomic force microscopy show corresponding vertical relief.