Atom probe tomography is a single-atom sensitive near-atomic resolution microscopy method based on field evaporation, with equal sensitivity throughout the periodic table. However, thus far, hydrogen was a special case in the analysis, as it is usually the most prevalent the residual contaminant in the vacuum system [1]. As a result, it adsorbs onto the specimen and is field evaporated with it. This made it largely impossible to distinguish the hydrogen stemming from the vacuum system from any hydrogen in the specimen, except for some cases where hydride formation occurs [2].  

The issue of hydrogen from the specimen and hydrogen from the stainless-steel vacuum system being indistinguishable can be somewhat circumvented by using deuterium as a tracer. Due to the atom probe’s time-of-flight principle, the deuterium can then be separated from the hydrogen present in the vacuum chamber through its mass [3]. This however has its limitation, as in many circumstances the formation of molecular hydrogen ions (H₂, H₃) occurs, once again rendering distinction between hydrogen from the specimen and hydrogen from the material difficult to impossible. One very important case where molecular hydrogen ion formation is heavily occurring is laser assisted field evaporation. The reason this is so important is that many specimens, such as non-conductive materials or brittle materials can only be analysed using pulsed laser atom probe in a meaningful way.  

In this talk, we will show reaults from a novel atom probe system with a titanium vacuum system, resulting in a drastically reduced hydrogen background [4]. In fact, this system has shown hydrogen backgrounds consistently more that two orders of magnitude lower than it’s stainless steel counterparts. In many materials, such as steels or superalloys, this results in no noticible hydrogen background originating from the vacuum chamber. Only in low-field materials such as Al, small hydrogen residuals are present (see fig.1a). We will also show first results from pulsed laser experiments in this system, indicating that the introduction of the thermal influence of the laser did not introduce hydrogen back into the measurement via thermally induced field gradient driven diffusion (see fig. 1b). This now opens up atom probe tomography to be used to analyse hydrogen in materials at the atomic scale, and image its distribution in 3D.