Atomic Layer Deposition of Platinum Nanoparticles on Titanium Oxide and Tungsten Oxide Using Platinum(II) Hexafluoroacetylacetonate and Formalin as the Reactants

Abstract

Pt nanoparticles were grown on titanium oxide and tungsten oxide at 200 °C by Pt atomic layer deposition (ALD) using platinum(II) hexafluoroacetylacetonate [Pt(hfac)2] and formalin as the reactants. The Pt ALD surface chemistry and Pt nanoparticles were examined using in situ Fourier transform infrared (FTIR) vibrational spectroscopy and ex situ transmission electron microscopy (TEM). The FTIR spectra identified the surface species after the Pt(hfac)2 and formalin exposures on TiO2. An infrared feature at ∼2100 cm–1 in the FTIR spectrum after Pt(hfac)2 and formalin exposures on TiO2 was consistent with CO on Pt, revealing that Pt(hfac)2 and formalin exposures led to the formation of Pt nanoparticles. The FTIR spectrum of Pt(hfac)2 on TiO2 was very similar to the FTIR spectrum of hexafluoroacetylacetone (hfacH) on TiO2. The FTIR spectra also revealed that hfacH blocked the adsorption of Pt(hfac)2 on TiO2. The coverage of the Pt nanoparticles could be reduced by preadsorbing hfacH on TiO2 prior to Pt(hfac)2 adsorption. Time-dependent FTIR spectra showed that the coverage of hfacH and its adsorption products were reduced versus time following hfacH exposure. Pt ALD on WOx at 200 °C led to the growth of Pt nanoparticles that were fairly similar to the Pt nanoparticles from Pt ALD on TiO2. The TEM images revealed that the size of the Pt nanoparticles on WOx could be adjusted by varying the number of Pt ALD cycles. Because of site-blocking by the hfac ligands, the Pt(hfac)2 and formalin reactants required many more ALD cycles for nucleation and growth compared with other Pt ALD surface chemistries.