Nonresonant Laser–SNMS and TOF–SIMS analysis of sub-μm structures

We determined and compared the capabilities of TOF–SIMS and Laser–SNMS for chemical mapping of sub-μm structures by investigating different inorganic and organic samples. For our investigations we used a combined TOF–SIMS/Laser–SNMS instrument, equipped with a focused (<80 nm) Ga+-LMIS and an excimer laser for nonresonant postionization of sputtered neutrals. For 16 monoelemental metal samples we determined useful yields up to 10−2 (Laser–SNMS) and 10−3 (TOF–SIMS), respectively. The high yields allow chemical characterization of metal oxide particles, such as Al2O3, Fe3O4 and CeO2 with diameters well below the spot size of the primary ion beam, as well as the detection and identification of metal loads on nanotips and semiquantitative elemental mapping of catalysts. Compared with TOF–SIMS, Laser–SNMS features a number of advantages for elemental analysis: higher and more uniform yields, i.e. sensitivities, ease of quantification because of a drastically reduced matrix effect, and compatibility with extreme surface topographies, since sputtered neutrals are not affected by distortions of the extraction field. Laser–SNMS and TOF–SIMS results for phase separated phospholipid/protein LB monolayers on Au substrates demonstrate the capabilities of these techniques for molecular surface mapping.