Tuning size and coverage of Pd nanoparticles using atomic layer deposition

Highlights: • Synchrotron-based in situ GISAXS and XRF are applied during Pd plasma-enhanced ALD. • The nucleation and the evolution in Pd nanoparticle morphology is investigated. • Pre-pulses with trimethylaluminum enhance the initial coverage of Pd nanoparticles. • The role of extra O₂ plasma pulse, with H₂ plasma as co-reactant, is investigated. • Precise control of the Pd nanoparticle dimensions and coverage is achieved. The morphology evolution of supported palladium nanoparticles (Pd NPs) during plasma-enhanced atomic layer deposition using palladium hexafluoroacetylacetonate (Pd(hfac)₂) as precursor was investigated using in situ and ex situ X-ray fluorescence (XRF) and grazing incidence small angle X-ray scattering (GISAXS), as well as ex situ scanning electron microscopy (SEM). The initial areal density of Pd NPs increases through adding cycles of the three-step process using Pd(hfac)₂, H₂ plasma and trimethylaluminum (TMA) prior to the standard Pd(hfac)₂ + H₂ plasma process. The participation of an O₂ plasma exposure as additional co-reactant before or after the H₂ plasma step also plays a role in the nucleation density and particle coalescence, affecting also the shape of the deposited particles. Based on the gathered knowledge, a synthetic approach that enables precise control of the Pd nanoparticle dimensions and coverage is developed.