Strategies for Preparing and Analyzing Thin Passive Films With Atom Probe Tomography

Area of Science:

• Materials Science
• Surface Science
• Analytical Chemistry

Background:

• Atom probe tomography (APT) offers high-resolution 3D elemental and isotopic mapping, excelling at buried interfaces.
• Analyzing thin nanoscale surface films, like passive films on alloys, presents significant challenges for APT due to sample preparation and data collection complexities.

Purpose of the Study:

• To develop and validate sample preparation strategies for reliable APT characterization of thin passive films (∼2-5 nm thick) on alloys.
• To overcome the limitations of applying APT to nanoscale surface films formed during alloy passivation.

Main Methods:

• Investigated sample preparation involving deposition of a <100 nm capping layer prior to APT analysis.
• Compared different capping layer materials (Pt, Ti, Ni/Cr bilayer) and deposition methods.
• Utilized APT to analyze passive films on binary and multiprincipal element alloys.

Main Results:

• A sputtered Ni/Cr bilayer capping layer enabled complete characterization of the entire passive film.
• Concentration profiles clearly distinguished base alloy/passive film/capping layer interfaces.
• Demonstrated reliable APT analysis of thin passive films previously difficult to study.

Conclusions:

• A novel capping layer strategy significantly enhances APT's capability for analyzing thin passive films on alloys.
• The sputtered Ni/Cr bilayer is identified as an effective capping material for detailed interface and composition analysis.
• This approach opens new avenues for understanding alloy passivation mechanisms at the nanoscale.