First steps in ultrafast laser assisted atom probe tomography

Abstract

Summary form only given. With the development of on-table ultrafast lasers delivering high energy pulses with a duration of a few hundreds of femtoseconds, a new generation of laser assisted tomographic atom probes (TAP) is born in the last two years. The use of ultrafast laser pulses seems to be the most promising way to overcome all the classically admitted shortcomings of the atom probe technique. The mass resolving power is greatly enhanced due to the decrease of the pulse length. This gives the opportunity to decrease the flight length to increase the field of view of the TAP. Moreover, atom probe techniques are not really adapted for semiconductors or insulators analysis, because of problems caused by the high voltage pulses propagation in non-good conductive material. The opportunity to generate the pulsed electric field directly at the apex of the specimen by using ultrafast laser pulses should theoretically open the technique to this kind of materials. The feasibility of ultrafast laser TAP analysis on both metallic and semiconductor materials was demonstrated. But the physical phenomenon involved the ultrafast laser assisted field evaporation had to be well understood and characterised. The tip dimensions with respect to the wavelength of the laser give rise to intrinsic laser electric field enhancement at the tip apex. We demonstrated that this effect was pregnant in the case of TAP specimen. An original field evaporation process based on a non-linear second order optical effect was also proposed and demonstrated. The thermal effects due to laser absorption by the material are not supposed to generate field evaporation. In this contribution, the field enhancement phenomenon will be presented, the field evaporation process will be evoked, and finally, advantages brought by the use of ultrafast laser pulses for atom probe analysis will be discussed