MICROSCOPIC CHEMICAL IMAGING WITH LASER-DESORPTION MASS-SPECTROMETRY

Mass spectrometric chemical images of surfaces were obtained using a l aser desorption/laser postionization time-of-flight mass spectrometer. Using a single laser to both desorb and ionize surface species result s in a large variability in the ion signal as the laser is rastered fr om spot to spot on the surface. The variation is greatly reduced when the detected species are photoionized desorbed neutrals rather than io ns produced directly by the desorption laser. A Schwarzschild microsco pe mounted outside of the vacuum chamber is used to focus the desorpti on laser on the sample. Ion dispersion and defection are accomplished by a simple time-of-flight mass analyzer. The spatial resolution of th e system is on the order of 1 mu m. The design and use of the imaging laser microprobe mass spectrometer are presented, along with images of organic and inorganic surfaces.