POSAP

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... 

POSAP is the only technique available for identifying and locating precipitates, second phases, particles, and interfaces on an atomic scale, and has therefore found considerable application in metallurgical and semiconductor problems. 

Fig. 5.20 (a) and (b) are POSAP composition maps of Ga and As at an interface of a GalnAs/InP quantum-well heterostructurc. (c) is a composition profile showing Ga and As concentrations across the interface. The approximate position of the interface is shown by arrows in these figures. Data are from Liddle et a/.130 (Courtesy of G. D. W. Smith.)... 

Atom Probe Field-Ion Microscopy (APFIM, POSAP, PLAP)... 

POSAP has also been applied to the phase chemistry of AlNiCo 2 magnet alloys the precipitation of copper in iron-based alloys surface segregation in ceramic oxide superconductors hetero-... 

Figure 95. Sequence of images A - F obtained in POSAP by Cerezo 1370] from the ferrite phase of an aged duplex stainless steel CF3...

POSAP (high field) M all elemental 1-100 monolayers (profile) 2-20 nm (1 atom) very good no yes yes... 

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