Smart Oxygen Injection for Selective Milling 

Limitations of Standard Plasma Milling in MXene–Polymer Systems

MXene/polymer nanocomposites pose a challenge in FIB-SEM workflows. The carbon-rich composition of both matrix and filler leads to poor intrinsic contrast. Standard plasma FIB milling, while effective for bulk materials, introduces curtaining artifacts and terracing, obscuring structural relationships. Differentiating MXene sheets within the polymer is particularly difficult without selective contrast enhancement.

Gas-Enhanced Plasma FIB Workflow for Contrast Improvement

The study analyzed 10:90 wt:wt Ti₃C₂Tₓ MXene/polyDADMAC nanocomposites using a Tescan AMBER X plasma FIB-SEM equipped with the OptiGIS O2module. A 30 kV, 10 nA Xe⁺ beam was used for trenching, followed by a 30 kV, 1 nA polish with flowing oxygen at 2×10⁻³ Pa.

Some regions were protected with a FIBID Pt layer to evaluate curtaining behavior. Additional conditions tested included lower voltages and beam currents, with and without oxygen, to optimize conditions for surface clarity and material contrast.

Contrast and Curtaining Improve with Targeted Gas Injection

Initial Xe⁺ milling alone resulted in heavy terracing and low contrast. When oxygen was introduced during the polishing step, surface quality improved significantly — especially under the Pt protective layer. MXene sheets became distinguishable from the surrounding polymer, even at depths greater than 10 µm.

Samples polished without a Pt layer still benefited from gas injection, though to a lesser degree. Lower-voltage experiments (20–10 kV) showed diminishing returns in milling depth but confirmed that oxygen-assisted milling consistently enhanced contrast and reduced curtaining.

These results demonstrate that the introduction of oxygen gas selectively interacts with carbon-based phases, allowing more precise material differentiation in FIB-SEM cross-sectioning.