![]() ![]() Most SIMS instruments used for elemental and isotopic analyses function by accelerating ions produced in the source along a potential gradient, typically 10 KV, and then transferring these ions into the mass spectrometer. Ions generated by this process form the secondary beam and are subsequently transmitted within a continuous high vacuum environment to a mass spectrometer. Most of these instruments are characterized by a source region in which the intensity, energy, and orientation of the primary beam (relative to the sample) are controlled. There are several different designs of SIMS currently being manufactured commercially that have applications in the geosciences (e.g., Cameca's 1280, 7f, and NanoSIMS, ASI's SHRIMP and SHRIMP RG, EAG's ToF SIMS). Typical forward geometry SIMS/ion microprobe configuration (Cameca IM 6f) showing: 1) negative primary beam source, 2) positive primary beam source, 3) electrostatic lens for primary beam, 4) sample stage and sputtering, 5) electrostatic sector, 6) magnetic sector, 7) collectors, and 8) ion imaging detector. Secondary Ion Mass Spectrometer (SIMS) Instrumentation - How Does It Work? organic compounds see module on Time-of-Flight SIMS. This technique is typically used for analysis of atomic monolayers on material surfaces to obtain information about molecular species on material surfaces (e.g. Alternatively, "static SIMS" uses a much lower energy primary ion beam (usually Ga or Cs). This technique is used for "bulk" analysis of elements and isotopes, and is particularly well-suited for analysis of isotopes and trace elements in minerals (e.g. In "dynamic SIMS" mode the primary ion beam exceeds the "static limit" (~1E12 ions/cm 2) producing a high yield of secondary ions. These ions are then accelerated, focused, and analyzed by a mass spectrometer. Although most atoms and molecules removed from the sample by the interaction of the primary beam and the sample surface (referred to as sputtering) are neutral, a percentage of these are ionized. ![]() If the primary beam is composed of positively charged ions, the resultant ionization favors production of negative ions primary beams of negative ions favor generation of positive ions. The interaction of the primary ion beam with the sample (under vacuum) provides sufficient energy to ionize many elements. Schematic depiction of SIMS source region. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. Archives
January 2023
Categories |