Initially, the 3D atom probe did not have energy compensator, so the mass
resolution was limited to be less than 200 due to the energy deficit of
ions during the field evaporation process. To improve the mass resolution,
a reflectron enegy compensator that have been widely used for conventional
atom probe was demonstrated to be effective for the 3D atom probe by Cerezo
et al. (A. Cerezo et a. Rev. Sci. Instrum. 69, 49-58 (1998).)
The following figure shows the principle of energy compensation by a reflectron
energy compensator. Since atoms were ionized by voltage pulses in those
days, ions inevitably had energy deficit as not all atoms are ionized at
the peak voltage of the pulses. When an ion has an higher energy, the flight
length becomes longer as it is reflected at alonger distance in the reflectron.
On the other hand, an ion with a lower energy will be reflected at a shorter
distance in the reflectron. As a result, the ions with slightly differenct
energy will arrive to the detector as long as the mass to charge ratios
are the same. Hence, the mass resolution can be substantially improved
as shown in the figure compare to that obtained with the straight type
atom probe.