Local Measurement of Janus Particle Cap Thickness

Area of Science:

• Materials Science
• Nanotechnology
• Surface Chemistry

Background:

• Janus particles possess surface anisotropy affecting their dynamics and interactions.
• Metal-capped Janus particles, often prepared via glancing angle deposition, have a cap thickness critical for their properties.
• Nonuniform cap thickness, arising from particle curvature during fabrication, may significantly impact Janus particle behavior.

Purpose of the Study:

• To experimentally measure the local cap thickness of metal-capped Janus particles.
• To investigate the impact of fabrication parameters on cap thickness uniformity.
• To validate the hypothesis of variable cap thickness across the particle surface.

Main Methods:

• Utilized focused ion beam slicing for precise sectioning of Janus particles.
• Employed advanced image analysis to quantify local cap thickness.
• Fabricated 5 μm polystyrene spheres with gold caps (10 or 20 nm nominal thickness).

Main Results:

• Demonstrated that gold cap thickness varies continuously along the perimeter of the Janus particles.
• Found that deposition rates (0.5–2.0 Å/s) did not significantly alter the pattern of thickness variation.
• Confirmed that cap thickness is not uniform, deviating from typical modeling assumptions.

Conclusions:

• The fabrication process inherently leads to non-uniform cap thickness in metal-capped Janus particles.
• Direct measurement techniques are essential for accurate characterization of Janus particle anisotropy.
• Understanding cap thickness variation is vital for predicting and controlling Janus particle dynamics.