Elementary processes governing V₂AlC chemical etching in HF.

Area of Science:

• Materials Science
• Nanotechnology
• Chemistry

Background:

• MXenes are a significant class of 2D materials.
• Understanding MXene chemical exfoliation from MAX phases is crucial.
• Well-defined structures are needed to study exfoliation mechanisms.

Purpose of the Study:

• Investigate the chemical exfoliation of V2AlC to MXene.
• Determine the kinetics and spatial resolution of MXene conversion.
• Clarify the role of crystal orientation in exfoliation.

Main Methods:

• Utilized well-defined square pillars of V2AlC (7-500 μm).
• Employed Raman spectroscopy, scanning electron microscopy, and optical microscopy.
• Assessed MXene conversion kinetics with μm spatial resolution.

Main Results:

• HF penetration and Al loss occur primarily through the edges of V2AlC pillars.
• No significant etching observed through basal planes at room temperature.
• Etching rate is initially linear (2.2 ± 0.3 μm h⁻¹) and isotropic in defect-free pillars.
• Etching rate diminishes significantly beyond ~45 μm.

Conclusions:

• Chemical exfoliation of V2AlC to MXene is predominantly an edge-driven process.
• Basal plane etching by HF is negligible under studied conditions.
• The findings provide critical insights into controlling MXene synthesis and properties.