ban04

SIMS

pic48ION-TOF SIMS-5 system

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is a surface analysis technique that can produce high resolution chemical images in three dimensions. Coupled with a recently introduced Argon cluster sputtering ion source technology, SIMS is now capable of analysing soft materials and biological materials.75 In this technique, a focused high energy primary ion beam (1–40 keV) is used to bombard the sample surface, which causes emission of secondary ions. An ion image based on the time-of-flight of the secondary ions is then produced by rastering the primary ion beam across the sample surface. The TOF detection scheme also offers parallel detection of multiple species, ideal for the analysis of complex biological samples. In the ION-TOF SIMS-5 system (Figure 2.6), the Bi3+ analysis or primary ion source positioned at 45° to the sample was operated at 30 keV beam energy with a 0.4 pA beam current and a 100 μs pulse width. Secondary ions were electrostatically directed to the TOF analyser by biasing the sample stage at 2.5 kV with the extraction lens set at 4.5 kV at an opposite polarity. Appropriate secondary ions were collected over a rastered sampling area of 100×100 μm2 to obtain a 2D map. The sample could also be sputtered with a O2+ ion beam or an Argon cluster ion beam (each generated from a separate sputtering ion source) alternating with the Bi3+ primary ion beam to remove the sample layer by layer at a well-defined sputtering rate. The 2D maps were collected as a function of sputtering depth to obtain the depth profiles and construct the corresponding 3D images of the components.