Comparing sub-gap and above-gap pulsed radiation sources for measuring oxygen concentration in MgO using atom probe...

Area of Science:

• Materials Science
• Surface Science
• Analytical Chemistry

Background:

• Atom probe tomography (APT) is a powerful technique for nanoscale chemical analysis.
• Accurate stoichiometric composition measurement in materials like MgO can be challenging due to material-specific interactions with laser pulsing.
• Understanding experimental parameters is crucial for reliable APT data.

Purpose of the Study:

• To investigate the experimental conditions for achieving stoichiometric composition measurements in MgO using atom probe tomography.
• To compare the effects of near-ultraviolet (NUV) and extreme ultraviolet (EUV) laser pulsing on MgO composition.
• To identify the primary experimental parameters influencing composition accuracy in MgO APT analysis.

Main Methods:

• Utilized atom probe tomography with both NUV (355 nm) and EUV (≈29 nm) pulsed laser sources.
• Conducted experiments varying laser pulse energy, pulse frequency, and detection rates.
• Analyzed Mg++ and O+ ionic fractions to determine composition bias and identify stoichiometric conditions.

Main Results:

• MgO exhibits significant composition bias under both NUV and EUV laser pulsing.
• Stoichiometric 1:1 bulk composition in MgO is achievable at high average nanoscale fields (low laser pulse energy) for both NUV and EUV.
• Reported the first instance of oxygen-rich composition measurements in MgO.
• A single calibration curve for oxygen concentration versus Mg++ fraction was observed across various conditions, except at high NUV laser pulse energy.

Conclusions:

• The average nanoscale field is the critical parameter for achieving stoichiometric composition in MgO via APT, overriding laser wavelength effects.
• Higher photon energy (EUV) does not inherently improve composition measurement accuracy for materials with sub-gap absorption mechanisms like MgO.
• High NUV laser pulse energy can lead to significant deviations from stoichiometric measurements, necessitating careful experimental control.