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

Abstract

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 × 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 ± 0.6 nm at 575 K and increased to 1.7 ± 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 Å 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.

A Comparative Discussion of the Catalytic Activity and CO2-Selectivity of Cu-Zr and Pd-Zr (Intermetallic) Compounds in Methanol Steam Reforming

“…The adsorbate coverage is determined from XP models as outlined in Ref. [32][33][34][35]. In order to validate the CVD-based catalytic results and to obtain a broader experimental basis of the Pd-Zr 0 system with respect to methanol steam reforming performance, also an intermetallic bulk phase of …”

Atomic Layer Deposition of FeO on Pt(111) by Ferrocene Adsorption and Oxidation

“…A detailed understanding of ferrocene adsorption and oxidation, as well as the formation of monolayer thick FeO islands on Pt(111), is developed here using a suite of Ultra High Vacuum (UHV) surface sensitive techniques, whose efficacy has been established in previous studies of vacuum ALD. [38][39][40][41][42] …”

Deposition of copper from Cu(i) and Cu(ii) precursors onto HOPG surface: Role of surface defects and choice of a precursor

“…First, the position of this peak is consistent with the fluorine still being attached to carbon rather than with the formation of Cu− −F species. 22,52 Thus, it is likely that the source of the remaining fluorine is the − −CF 3 groups of the hfac. Second, the Cu/F ratio is calculated to be 1:1 again for Cu(hfac) 2 while that for Cu(hfac)VTMS is found to be approximately 4:1.…”