Pulsed laser atom 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... 

Voltage-pulsed AP analysis of resistive materials is difficult, since they do not transmit high-voltage pulses effectively. In the case of semiconducting materials there is the further problem of their brittleness, so that the mechanical shock due to the voltage pulse often causes specimen fracture. The pulsed laser atom probe (PLAP) is more effective for these materials. 

Fig. 3.4 (c) Penn State design tip exchange setup ffor an FIM or a pulsed-laser atom-probe with a vacuum lock. The tip can be heated by passing a current through the wire loop. The tip is mounted on an internal gimbal and is cooled through a copper braid by a refrigerator. 

The mechanical construction of the pulsed-laser atom-probe is greatly simplified without the need of properly terminating the ns HV pulses very close to the tip. There is also no need of a flight-time focusing lens. Very short duration laser pulses can be much more easily produced... 

In a preliminary pulsed-laser atom-probe measurement,158 the critical ion energy deficits of Rh and W atoms, field evaporated from kink sites, are measured at a rate of 1010 layers per second at a temperature around 100 K. Using the system constants, i.e. the flight path constant and the... 

Kellogg, G.L.,Tsong,T.T. (1980) Pulsed-laser atom-probe field-ion microscopy. Journal of Applied Physics, 51, 1184-1193. 

Kellogg, G.L. (1981) Determining the field emitter temperature during laser irradiation in the pulsed laser atom probe. Journal of Applied Physics, 52, 5320-5328. 

Liddle, I, Norman, A., Cerezo, A., Grovenor, C. (1988) Pulsed laser atom probe analysis of ternary and quaternary III-V epitaxial layers. Le Journal De Physique Colloques, 49,509-514. 

Bunton, J.H., Olson, ID., Lenz, D.R., Kelly, T.F. (2007) Advances in pulsed-laser atom probe instrument and specimen design for optimum performance. Microscopy and Microanalysis, 13,418-427. 

PLAP pulsed laser atom probe TMR tunnel magnetoresistance... 

A modern instrument using an energy-compensated TOF mass spectrometer is shown in Figure 94 from Miller [367]. Atoms may also be removed from a tip by focusing a pulsed laser onto it, as an alternative to field evaporation, leading to the variation of APFIM called the pulsed laser atom probe (FLAP). 

---