Normandie Université, UNIROUEN, INSA Rouen, CNRS, Groupe de Physique des Matériaux, 76000, Rouen, France
Terahertz assisted Atom Probe Tomography: Effect of single-cycle THz pulses on ion dynamic
The Atom Probe Tomography (APT) is an analytical microscope that allows the three-dimensional mapping of chemical heterogeneities in a material at the atomic scale as a result of the controlled evaporation of surface atoms by the combined action of a strong static electric field and a laser pulse. When a positive electric field of several volts per angstrom is applied to the surface of a metal, the surface atoms evaporate as ions even at cryogenic temperatures. To generalise this mechanism to non-metallic surfaces, a laser field, focused on the tip, was added to the electric field. In this case, the evaporation results from the optical and thermal response of the tip to the laser illumination. However, the interaction of these pulses with the material induces a thermal heating which causes a low spatial and chemical resolutions.
We recently proposed to use a monocycle THz pulse in order to reduce the thermal effects and we proved that the high-amplitude THz monocycle (20MV/m) is enhanced at the vicinity of the apex of nanometric needle up to <1GV/m. Therefore, the THz field is able to trigger the field emission of atoms from the surface of the nano-needle and positively ionize them.
In this presentation, results obtained with THz-assisted APT on metallic and non-metallic samples (silicon and LaB6) will be presented to show that the emission process is athermal and that both positive and negative THz pulses can be used to trigger the evaporation of positive ions. Furthermore, we study the dynamic of the emitted ions and their energy as a function of the characteristics of the THz pulse, in terms of amplitude and phase.