Atomic probe

The atom probe field-ion microscope (APFIM) and its subsequent developments, the position-sensitive atom probe (POSAP) and the pulsed laser atom probe (PLAP), have the ultimate sensitivity in compositional analysis (i.e. single atoms). FIM is purely an imaging technique in which the specimen in the form of a needle with a very fine point (radius 10-100 nm) is at low temperature (liquid nitrogen or helium) and surrounded by a noble gas (He, Ne, or Ar) at 10 -10 Pa. A fluorescent screen or a... 

Just recently (Wilde et al. 2000), half a century after the indirect demonstration, it has at last become possible to see carbon atmospheres around dislocations in steel directly, by means of atom-probe imaging (see Section 6.2.4). The maximum carbon concentration in such atmospheres was estimated at 8 2 at.% of carbon. 

Various ion-optical tricks have to be used to compensate for the spread of energies of the extracted ions, which limit mass resolution unless corrected for. In the latest version of the atom probe (Cerezo et at. 1988), spatial as well as compositional information is gathered. The hole in the imaging screen is dispensed with and it is replaced by a position-sensitive screen that measures at each point on the screen the time of flight, and thus a compositional map with extremely high (virtually atomic) resolution is attained. Extremely sophisticated computer control is needed to obtain valid results. 

R. Jayaram, M.K.Miller, An atom probe study of grain boundary and matrix chemistry in microalloyed NiAl, Acta metall.mater. 42 1561 (1994)... 

J. Paul, L. Wallden, and A. Rosen, The reactivity of adsorbed Na atoms probed by coadsorbed CH3OH, Surf. Sci. 146, 43-60 (1984). 

Accelerator mass spectrometry Acousto-optical tuneable filter Acousto-optical tuneable spectrometer/scanning Atom probe... 

The atom probe (AP) consists of a modified field ion microscope (FIM), and we will first review the basic phenomena involved in the operation of the FIM. 

A schematic diagram of the conventional atom probe due to Hono (1999) is shown in Figure 1.4. 

Figure 1.4. Schematic diagram of the basic principles of the conventional (one-dimensional) atom probe, with a reflection energy compensator. (Reproduced by permission of Hono 1999.)...

Figure 1.9. FIM micrograph showing boron segregation to a grain boundary in austenitic 316L stainless steel, together with atom probe composition profiles for boron (Karlsson and Norden 1988).

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