| AVS 64th International Symposium & Exhibition | |
| Thin Films Division | Thursday Sessions |
| Session TF+SE-ThM |
| Session: | Control, Characterization, and Modeling of Thin Films I |
| Presenter: | Eduardo Solano, Ghent University, Belgium |
| Authors: | J. Dendooven, Ghent University, Belgium E. Solano, Ghent University, Belgium R.K. Ramachandran, Ghent University, Belgium M.M. Minjauw, Ghent University, Belgium A. Coati, Synchrotron SOLEIL, France D. Hermida-Merino, ESRF, France C. Detavernier, Ghent University, Belgium |
| Correspondent: | Click to Email |
Supported noble metal nanoparticles (NPs) are widely used in heterogeneous catalysis because of their high resistance against chemical poisoning. Atomic Layer Deposition (ALD) can be used to synthesize noble metal NPs on different high surface area supports, and offers sub-monolayer control over the metal loading (atoms per cm2 of support) [1]. However, an improved understanding of how the deposition parameters influence the formation and growth of noble metal NPs is required to fully exploit the tuning potential of ALD.
We developed a synchrotron-compatible high-vacuum setup that enables in-situ monitoring during ALD [2]. Using this setup and focusing on ALD of Pt with the MeCpPtMe3 precursor at 300 °C [3], we present an in-situ investigation of Pt NP growth on planar SiO2 substrates by means of X-ray fluorescence (XRF) and grazing incidence small-angle X-ray scattering (GISAXS). The surface density of Pt atoms was determined by XRF. Analysis of the GISAXS patterns [4] yielded dynamic information on average real space parameters such as Pt cluster shape, size and spacing. The results indicate a diffusion-mediated particle growth regime for the standard O2-based Pt ALD process, marked by a decreasing average areal density and formation of laterally elongated Pt clusters. Growth of the Pt NPs is thus not only governed by the adsorption of Pt precursor molecules from the gas-phase and subsequent combustion of the ligands, but is largely determined by adsorption of migrating Pt species on the surface and diffusion-driven particle coalescence [5].
Next, we have studied the influence of the reactant type (O2 gas, O2 plasma, N2 plasma, NH3 plasma [6]) on the Pt NP growth. Surprisingly, a clear difference in island growth behavior was found for the oxygen- vs. nitrogen-based processes. The latter processes were marked by a constant average particle distance during the growth process. Particle dimension analysis furthermore revealed vertically elongated NPs for the N2 and NH3 plasma-based Pt ALD processes. Therefore, it is concluded that atom and cluster surface diffusion phenomena are suppressed during the nitrogen-based processes. Finally, this insight provided the ground for the development of a tuning strategy that is based on combining the O2-based and N2 plasma-based ALD processes and offers independent control over NP size and coverage.
[1] Lu et al., Surf. Sci. Rep. 71 (2016) 410. [2] Dendooven et al., Rev. Sci. Instrum. 87 (2016) 113905. [3] Aaltonen et al., Chem. Mater. 15 (2003) 1924. [4] Schwartzkopf et al., Nanoscale 5 (2013) 5053. [5] Mackus et al., Chem. Mater. 25 (2013) 1905. [6] Longrie et al., ECS J. Solid State Sci. Technol. 1 (2012) Q123.