SURFACE CHARACTERIZATION WITH ION-INDUCED DESORPTION AND MULTIPHOTON RESONANCE IONIZATION

It is known that high-molecular-weight, thermally labile molecules can be desorbed intact using keV ion beams. This knowledge has led to num erous applications of fast atom bombardment and secondary ion mass spe ctrometry (SIMS) by mass spectrometric detection of the desorbed ions. Here we show that these measurements can be enhanced significantly by using resonance-enhanced laser ionization to softly ionize the neutra l component of the desorbed flux. This experimental configuration can produce sensitivity improvements of several orders of magnitude over S IMS while adding a certain degree of selectivity to the ionization pro cess itself. Examples of this performance will be presented using a wi de variety of molecules, including polycyclic aromatic hydrocarbons, o rganic polymers, molecular salts and biologically important molecules. Results from model systems to complex samples are discussed, along wi th their implications for submicron molecular imaging using this techn ique.