Effects of laser energy and wavelength on the analysis of LiFePO4 using laser assisted atom probe tomography

Abstract

The effects of laser wavelength (355 nm and 532 nm) and laser pulse energy on the quantitative analysis of LiFePO₄ by atom probe tomography are considered. A systematic investigation of ultraviolet (UV, 355 nm) and green (532 nm) laser assisted field evaporation has revealed distinctly different behaviors. With the use of a UV laser, the major issue was identified as the preferential loss of oxygen (up to 10 at%) while other elements (Li, Fe and P) were observed to be close to nominal ratios. Lowering the laser energy per pulse to 1 pJ/pulse from 50 pJ/pulse increased the observed oxygen concentration to nearer its correct stoichiometry, which was also well correlated with systematically higher concentrations of (16)O₂(+) ions. Green laser assisted field evaporation led to the selective loss of Li (~33% deficiency) and a relatively minor O deficiency. The loss of Li is likely a result of selective dc evaporation of Li between or after laser pulses. Comparison of the UV and green laser data suggests that the green wavelength energy was absorbed less efficiently than the UV wavelength because of differences in absorption at 355 and 532 nm for LiFePO₄. Plotting of multihit events on Saxey plots also revealed a strong neutral O2 loss from molecular dissociation, but quantification of this loss was insufficient to account for the observed oxygen deficiency.

Three‐Dimensional Microstructural Characterization of Lithium Manganese Oxide with Atom Probe Tomography

“…Additionally,peaks for molecules of Mn andOwith different charge states are found, as typically observed for oxides. [18,19,[30][31][32][33] Theh ydrogen assigned to the peaks at m/z = 1, 2, and 3amu most likely stems from residual gas in the chamber, which is field ionized at the sample apex and does not originate from the analyzed material itself. [34,35] At m/z = 69 amu, as ignal from Ga is visible in the overall mass spectrum.…”

“…19 Co 0.04 Al 0.01 Mg 0.01 O 0. 49 , [17] LiFePO 4 , [18] and layered Li 1.2 Ni 0.2 Mn 0.6 O 2 ; [19] these studies have shown the ability and benefit of APT for characterizationo ft hese materials,b ut interpretation of the results in view of Li-ion batteries is limited.…”

A Brief Comment on Atom Probe Tomography Applications

“…Although high laser pulse energy generally results in high success yield, better MRP, and low background, extreme high energy leads to surface migration, complex ion generation, and nonuniform spatial evaporation behavior. The stoichiometry deficiency observed in APT analyses of nitrides and oxide at high laser pulse energy is well known (Devaraj et al, 2013;Kinno et al, 2014;Santhangopalan et al, 2015). For example, in the case of GaN, at the lowest laser energies, the apparent composition is nitrogen-rich, while higher laser energies results in gallium-rich (i.e., nitrogen-deficient) (Gu et al, 2013;Riley et al, 2014;Sanford et al, 2014).…”

Investigation of material property influenced stoichiometric deviations as evidenced during UV laser-assisted atom probe tomography in fluorite oxides

“…While this process is relatively well understood for most conducting materials, especially metallic systems [12], the field evaporation process is not always well controlled for insulating materials [13], leading to artifacts in the measured stoichiometry [14][15][16][17][18][19]. These can be exacerbated by the presence of a laser used to thermally assist evaporation for oxides and other materials with limited electrical conductivity.…”