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Particle‐Induced X‐Ray Emission

2002; Linguagem: Inglês

10.1002/0471266965.com094

J.L. Campbell,

Ion-surface interactions and analysis

Abstract Particle‐induced x‐ray emission (PIXE) is an elemental analysis technique that employs a mega‐electron‐volt energy beam of charged particles from a small electrostatic accelerator to induce characteristic x‐ray emission from the inner shells of atoms in the specimen. The accelerator can be single ended or tandem. Most PIXE work is done with 2‐ to 4‐MeV proton beams containing currents of a few nanoamperes within a beam whose diameter is typically a few millimeters; a small amount of work with deuteron and helium beams has been reported, and use of heavier ion beams has been explored. The emitted x rays are nearly always detected in the energy‐dispersive mode using a Si(Li) spectrometer. Although wavelength‐dispersive x‐ray spectrometry would provide superior energy resolution, its low geometric efficiency is a significant disadvantage for PIXE, in which potential specimen damage by heating limits the beam current and therefore the emitted x‐ray intensity. In the proton microprobe, magnetic or electrostatic quadrupole lenses are employed to focus the beam to micrometer spot size; this makes it possible to perform micro‐PIXE analysis of very small features and, also, by sweeping this microbeam along a preselected line or over an area of the specimen, to determine element distributions in one or two dimensions in a fully quantitative manner. Most proton microprobes realize a beam spot size smaller than a few micrometers at a beam current of at least 0.1 nA. In trace element analysis or imaging by micro‐PIXE, the high efficiency of a Si(Li) detector, placed as close to the specimen as possible, is again mandatory for x‐ray collection. To date, PIXE and micro‐PIXE have most often been used to conduct trace element analysis in specimens whose major element composition is already known or has been measured by other means, such as electron microprobe analysis. However, both variants are capable of providing major element analysis for elements of atomic number down to .