Estimating Evaporation Fields and Specific Heats Through Atom Probe Tomography

TL;DR

This paper introduces a simple method to estimate evaporation fields and specific heats in atom probe tomography using voltage measurements, validated on known materials and applied to a new compound.

Contribution

The work presents a novel, straightforward approach to determine evaporation fields and specific heats from APT data, including for previously uncharacterized materials.

Findings

Estimated evaporation field for CdTe: 18.07 V/nm

Extracted specific heat for CdTe: 11.27 J/K/mol, matching literature

Determined evaporation field for Ir(ppy)3: 7.49 V/nm

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.