ToF-SIMS

Applications

ToF SIMS allows the characterisation of the elementary chemical and molecular composition of extrem surfaces of solid samples, without any special preparation. All compatible materials with ultra-high vacuum can be analysed : metals, alloys, semiconductors, polymeres, vernish, paint, adhesives, additives, surfactants, ceramics, glass, wood, papers, textiles, ultra thin deposits, mono molecular layers, biological samples (nails, hair, etc…).
 

Principle

A pulsed source of primary ions, mono or multi-atomic (Ga+, Bin+, Au+, C60+, …) which have an energy of a few keV bombs the surface of the sample and create secondary ions emitted from the first layer in surface. They are focused and accelerated with the same cinetic energy. The time of flight of secondary ions in the analyser is proportional to their mass square root. The mass spectrum obtained represent the intensity of secondary ions according to their mass. The use of a ‘time of flight’ analyser allows to get a really high resolution in mass (ΔM/M > 10 000 to the mass 28). Thanks to a scanning device of the primary ions beam, we can get a cartography of the different elements and molecular species on the sample surface, with a submicronic resolution . We also can, alternating acquisition and abrasion phases, trace a profile of composition with a resolution in nanometric depth.

• Mass spectrums give the intensity (number of secondary ions detected) in function of the ratio of mass on charge (m/z). Secondary ions, positive and negative, are mainly mono-charged (z = ±1). They only appear in monoatomic samples spectrums. They are calibrated in mass and analysed qualitatively on the basis of atomic elements and their molecular combinations.
• Ionic images are obtained on a microprobe mode : the primary ions beam reduced at a low diameter spot (> 100 nm) scan the surface to image. The secondary optic of extraction and analysis in mass is fixed. The image is made throught the synchronisation of secondary signal with the primary beam scan. The lateral resolution of images depends on the micro beam size (from 5 µm to 100 nm).
• Profiles in depth are obtained alterning analysis phases and abrasion phases. The speed of abrasion changes according to the density and chemical nature of abraded layers ; it has to be measured for each crossed environment. So we need to calibrate the instrument using deposits of known thickness or measuring the depth of craters throught optical or mechanical methods (Talystep).