Local magnification effects in the atom probe

Investigation of new aspects in the initial stages of decomposition of Cu2at.%Co with the tomographic atom probe and the field ion microscope

“…5(a-c) each box represents a volume of 10 ð 10 ð 20 nm 3 . The slightly elliptical shape is caused by the local magnification effect due to the difference in evaporation fields of Cu and Co. 7,8 Fewer precipitates can be observed after 30 min annealing at 853 K (Fig. 5(b)).…”

“…5(c)), the precipitates have not only grown in size but also appear to be slightly elliptical in shape. The slightly elliptical shape is caused by the local magnification effect due to the difference in the evaporation fields of Cu and Co. 7 The course of the distribution of the particle size has been characterised with a cluster search. As shown in Fig.…”

C12/C13Lewis1, Isheim2, Floss3 et al. 2015Ultramicroscopy310120View full textAdd to dashboardCite

“…There are, however, at least three other factors that may contribute to the low measured density of C. One is that we may be measuring amorphous C associated with the nanodiamonds, which is less dense than diamond; however, the difference should only be a few percent. Another factor is that the high evaporation field of diamond can lead to preferential evaporation and trajectory aberrations [30], resulting in a local magnification effect, an overestimation of the volume of the nanodiamonds, and thus an underestimation of their density: The evaporation field of carbon is not well known, but may be estimated to be 103 V nm À 1 [21], 2.6 times our estimation of the overall field. Trajectory aberration could therefore cause a 2.6 Â overestimation of the x and y dimensions of a nanodiamond, yielding a ∼7 Â overestimation of volume and underestimation of density.…”

An analytical model accounting for tip shape evolution during atom probe analysis of heterogeneous materials

“…It results in a nonhemispherical complex surface shape, which in turns gives rise to local magnification [15]. These effects have been first postulated [16] and then demonstrated by numerical simulations [17], and they are now directly demonstrated experimentally by APT and TEM complementary analysis [18,19]. However, if great efforts have been made to model the imaging process in APT [20][21][22][23], at the moment there is no theoretical framework describing the tip shape evolution when made up of materials with different evaporation behavior.…”