Palladium Nanoparticle Formation on TiO2(110) by Thermal Decomposition of Palladium(II) Hexafluoroacetylacetonate

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• 作者：Amir Gharachorlou ; Michael D. Detwiler ; Anna V. Nartova ; Yu Lei ; Junling Lu ; Jeffrey W. Elam ; W. Nicholas Delgass ; Fabio H. Ribeiro ; Dmitry Y. Zemlyanov
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2014
• 出版时间：August 27, 2014
• 年：2014
• 卷：6
• 期：16
• 页码：14702-14711
• 全文大小：506K
• ISSN：1944-8252

文摘

Palladium nanoparticles were synthesized by thermal decomposition of palladium(II) hexafluoroacetylacetonate (Pd(hfac)₂), an atomic layer deposition (ALD) precursor, on a TiO₂(110) surface. According to X-ray photoelectron spectroscopy (XPS), Pd(hfac)₂ adsorbs on TiO₂(110) dissociatively yielding Pd(hfac)_ads, hfac_ads, and adsorbed fragments of the hfac ligand at 300 K. A (2 脳 1) surface overlayer was observed by scanning tunneling microscopy (STM), indicating that hfac adsorbs in a bidentate bridging fashion across two Ti 5-fold atoms and Pd(hfac) adsorbs between two bridging oxygen atoms on the surface. Annealing of the Pd(hfac)_ads and hfac_ads species at 525 K decomposed the adsorbed hfac ligands, leaving PdO-like species and/or Pd atoms or clusters. Above 575 K, the XPS Pd 3d peaks shift toward lower binding energies and Pd nanoparticles are observed by STM. These observations point to the sintering of Pd atoms and clusters to Pd nanoparticles. The average height of the Pd nanoparticles was 1.2 卤 0.6 nm at 575 K and increased to 1.7 卤 0.5 nm following annealing at 875 K. The Pd coverage was estimated from XPS and STM data to be 0.05 and 0.03 monolayers (ML), respectively, after the first adsorption/decomposition cycle. The amount of palladium deposited on the TiO₂(110) surface increased linearly with the number of adsorption/decomposition cycles with a growth rate of 0.05 ML or 0.6 脜 per cycle. We suggest that the removal of the hfac ligand and fragments eliminates the nucleation inhibition of Pd nanoparticles previously observed for the Pd(hfac)₂ precursor on TiO₂.
<h4>Keywords: h4> X-ray photoelectron spectroscopy; scanning tunneling microscopy; atomic layer deposition; Pd(hfac)₂; TiO₂(110); nucleation delay; surface science; heterogeneous catalysis