Under the ion bombardment, fragment ions or even intact molecular ions are emitted from the top monolayer. One important point is that after each ion impact, all molecules within a 5-10 nm diameter are damaged and no further molecular information can be obtained from this zone. Thus, the number of molecule available on a given top surface area is finite and limited. If the primary ion dose is limited to a level at which every primary ion should (statistically) always hit a fresh area, the (static) SIMS spectrum reveals molecular information through its peaks and its peak pattern (relative peak intensities). Progressively, as the ion dose increases, the molecular signal decreases then vanishes when the whole area has been damaged. To stay in static SIMS mode, the primary ion dose must be kept below 1E12 Primary Ions per cm2.


As only a limited small amount of matter is to be sputtered, and the Secondary Ion yield is low (1E-3 to 1E-8), specific analyzers should be used to collect nearly all the secondary ions. The Time of Flight (TOF) analyzer is the mass analyzer of choice for this molecular application. Parallel detection, high transmission together with reasonable mass resolution, and high mass range are among its major advantages. The main drawback of such a pulsing analyzer is a very low Duty Cycle (1E-3/1E-4): most of the time is lost waiting for the ions to reach the detector, without any sample sputtering. When it comes to dynamic SIMS, this results in dramatically longer acquisition times than a DC mass analyzer, for a given signal intensity (or statistics). Depth profiling with an independent second sputter gun can improve the sputtering speed but reduces by the same amount the ratio analyzed volume/ sputtered volume (most of the matter is then sputtered away and lost for the analysis): the faster you profile, the less sensitive you become compared with a DC mass analyzer. Hence TOF depth profiles are restricted to ultra shallow profiles or relatively high concentrations.  

Analysis of bulk sample surface in static SIMS gives rise to a fingerprint mass spectrum that contains "low mass" (< 500 amu) ion fragments and thus helps identifying organic surface composition. Due to the complexity of the static SIMS mass spectrum, this technique is mostly used as a qualitative characterization of the molecular composition of the top surface. Access to the oligomeric distribution and "intact" molecular ions is possible by preparing samples as a monolayer on noble metal substrate, at the cost of the loss of the lateral spatial distribution information. Cationization by such metal substrate allows access to mass range of up to a few thousands amu. 

By focusing and scanning the primary ion beam, molecular information can be obtained with lateral resolution of half to one micrometer diameter (limited by the physics, not the instrumentation), and molecular surface distribution can be imaged.