Estimating Evaporation Fields and Specific Heats Through Atom Probe Tomography

Abstract

Estimations of evaporation field values in atom probe tomography (APT) literature are sparse despite their importance in the reconstruction and data analysis process. This work describes a straightforward method for estimating the zero-barrier evaporation field ($F_E$) that uses the measured voltage vs. laser pulse energy for a constant evaporation rate. This estimate depends on the sample radius of curvature and its specific heat ($C_p$). If a similar measurement is made of the measured voltage vs. base temperature for a fixed evaporation rate, direct extraction of the material's $C_p$ can be made, leaving only the sample radius of curvature as an input parameter. The method is applied to extract $F_E$ from a previously published voltage vs. laser pulse energy dataset for CdTe ($18.07 \pm 0.87~\mathrm{V~nm^{-1}}$); furthermore, using the published voltage vs. base-temperature sweep of CdTe permits extraction of a specific heat ($11.27 \pm 2.54~\mathrm{J~K^{-1}mol^{-1}}$ at $23.1~\mathrm{K}$) in good agreement with the literature ($11.14~\mathrm{J~K^{-1}mol^{-1}}$ at $22.17~\mathrm{K}$). The method is then applied to the previously uncharacterized material tris[2-phenylpyridinato-C2,N]iridium(III) ($\mathrm{Ir(ppy)_3}$), yielding $F_E = 7.49 \pm 0.96~\mathrm{V~nm^{-1}}$ and $C_p = 173 \pm 27~\mathrm{J~K^{-1} mol^{-1}}$; this $F_E$ is much lower than most materials characterized with APT to date.