Controlling Pt nanoparticle sintering by sub-monolayer MgO ALD thin films

Area of Science:

• Materials Science
• Catalysis
• Nanotechnology

Background:

• Metal nanoparticle (NP) sintering diminishes catalyst surface area and performance.
• Current protective overcoat methods lack structural control and precise surface atom management.
• Annealing to create porosity can compromise overlayer integrity.

Purpose of the Study:

• To investigate atomic layer deposition (ALD) for controlled MgO overcoats on Pt NPs.
• To compare two ALD processes for MgO growth characteristics and their impact on Pt accessibility.
• To develop a sintering prevention strategy that maintains catalyst activity and structural integrity.

Main Methods:

• Atomic layer deposition (ALD) of MgO using two different precursor/oxidant systems (Mg(EtCp)2/H2O and Mg(TMHD)2/O3).
• Characterization using spectroscopic ellipsometry, X-ray photoelectron spectroscopy, and low energy ion scattering.
• In situ monitoring of sintering behavior during O2 annealing using grazing incidence small angle X-ray scattering (GISAXS).

Main Results:

• The Mg(TMHD)2-O3 ALD process showed selective Pt growth with lower growth per cycle compared to Mg(EtCp)2/H2O.
• ALD process differences impacted the availability of uncoated Pt surface atoms.
• The Mg(TMHD)2-O3 process effectively controlled MgO coverage, preventing sintering during annealing without post-treatment.

Conclusions:

• ALD offers precise control over MgO overcoat thickness and coverage on Pt NPs.
• The Mg(TMHD)2-O3 ALD process provides a method to prevent NP sintering while maintaining catalytic activity.
• This approach eliminates the need for post-annealing, preserving overcoat integrity.