In ToF-SIMS analysis, the sample is placed in an ultrahigh vacuum environment where primary ions bombard and sputter atoms, molecules, and molecular fragments from the sample surface. Due to the differences in velocities, smaller ions move through the analyzer more rapidly than the larger ions. The mass of the secondary ions are determined by their travel time through the analyzer. The high resolution of the ToF analyzer can distinguish species whose masses differ by only a few millimass units. Depth profile - During SIMS analysis, the sample surface is slowly sputtered away.
Continuous analysis obtains composition information as a function of depth.
High sensitivity mass spectra can be recorded or reconstructed at any depth of the depth profile. Secondary ion mapping - Measures the lateral distribution of elements and molecules on the surface. To obtain a SIMS map, a highly focused primary ion beam is rastered across the sample surface, and the secondary ions are collected at specific points. Image brightness at each point is a function of the relative concentration of the mapped element or molecule. Lateral resolution is less than 100 nm for elements and 0.5 for large molecules.