Bernard Deconihout

The current work investigates numerically and experimentally the three-dimensional (3D) thermal response of a subwavelength tip illuminated by an ultrashort laser pulse. A model is developed on the nanometric scale to predict the 3D tip temperature evolution from the initial laser irradiation through the thermal equilibrium (several nanoseconds). The evolution of the ion temperature is experimentally monitored by atom probe tomography. The anisotropic ion emission observed on steel specimens illuminated with an ultrashort laser and the evaporation behavior of amorphous glasses is predicted by our 3D thermal model.

A laser assisted tomographic atom probe has recently been designed. The use of femtosecond laser evaporation pulses rather than of high-voltage pulses has opened the field of application of the technique to new materials such as semi-conductors and oxides. These classes of materials are of utmost importance in microelectronics for the design of nano-chips and nano-transistors in integrated devices. This type of instrument is the only 3D analytical microscope capable of mapping out the distribution of elements in a small volume (50 × 50 × 100 nm³) on a nearly atomic scale. In addition, the tomographic atom probe enables us to get quantitative composition measurements. This review illustrates the potential of this new instrument (laser assisted wide angle tomographic atom probe LaWaTAP) when applied to study scientific topics in nano-sciences. As an example, both the distribution of addition elements (Pt) during inter-diffusive reaction in NiSi contacts of nano-transistors and the investigation of interfaces in MgO/Fe tunnel junctions are presented and discussed.

A wide angle tomographic atom probe has been designed in which the field evaporation of atoms is assisted by subpicosecond laser pulses. It has been shown that the field evaporation is due to the generation of a THz pulse due to the rectification of the optical field at the specimen surface. The very short duration of the pulsed field (a few hundred fs) offers several advantages as compared to conventional pulsing method. First, it makes possible to bring intense electric field at the surface of resistive specimens opening the field of application of the atom probe tomography to new materials such as oxydes or semiconductors. Second, a high mass resolution can be achieved in a straight type configuration allowing to fully open the field of view in order to collect the whole amount of data available from field emitter specimens. Third, because the pulse duration is below the phonon vibration time, no cycling stress in applied on the specimen during the analysis. As a result, very fragile materials can be investigated by APT. In addition, this makes possible to investigate materials at very low temperature making the spatial resolution better. In this contribution, the design of the LaWaTAP will be presented and the performance of the instrument discussed through some applications to metals, oxydes and semiconductors

A tomographic atom probe (TAP) in which the atoms are field evaporated by means of femtosecond laser pulses has been designed. It is shown that the field evaporation is assisted by the laser field enhanced by the subwavelength dimensions of the specimen without any significant heating of the specimen. In addition, as compared with the conventional TAP, due to the very short duration of laser pulses, no spread in the energy of emitted ions is observed, leading to a very high mass resolution in a straight TAP in a wide angle configuration. At last, laser pulses can be used to bring the intense electric field required for the field evaporation on poor conductive materials such as intrinsic Si at low temperature. In this article, the performance of the laser TAP is described and illustrated through the investigation of metals, oxides, and silicon materials.