Surface Chemistry of Trimethylaluminum on Pd(111) and Pt(111)

Abstract

The behavior of trimethylaluminium (TMA) was investigated on the surfaces of Pt(111) andPd(111) single crystals. TMA was found to dissociatively adsorb on both surfaces between 300 -473 K. Surfaces species observed by high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS) after TMA adsorption at 300 K included Al-CH 3 and CH x,ads (x = 1, 2, or 3) on Pt(111), and ethylidyne (CCH 3 ), CH x,ads (x = 1, 2, or 3), and metallic Al on Pd(111). Density functional theory (DFT) calculations predicted methylaluminum (MA, Al-CH 3 ) to be the most kinetically favorable TMA decomposition product on (111) terraces of both surfaces, however, HREELS signatures for Al-CH 3 were detected only on Pt(111), whereas ethylidyne was observed on Pd(111). XPS demonstrated higher amount of carbonaceous species on Pt(111) than on Pd (111) DFT calculations showed that further dissociation of MA to metallic aluminum and methyl groups to be more kinetically favorable on step sites of both metals. In our proposed reaction mechanism, MA migrates to and dissociates at Pd(111) steps at 300 K forming adsorbed methyl groups and metallic Al. Some methyl groups dehydrogenate and recombine forming ethylidyne. Metallic Al or ejected Pd atoms from steps diffuse across Pd(111) terraces until coalescing into irregularly shaped islands on terraces or steps, as observed by scanning tunneling microscopy (STM). Upon heating above 300 K, the Pd-Al alloy diffuses into the Pd bulk. On Pt(111), a high coverage of carboncontaining species following TMA adsorption at 300 K prevented MA diffusion and dissociation at steps, as evidenced by isolated clusters of MA in STM images. Heating above 300 K resulted in MA dissociation, but no Pt-Al alloy formation was observed. We conclude that the differing abilities of Pd and Pt to hydrogenate carbonaceous species plays a key role in MA dissociation and alloy formation, and, therefore, the adsorption and dissociation chemistry of TMA depends on properties of the metal substrate surface and determines thin film morphology and composition.

Trimethylaluminum and Oxygen Atomic Layer Deposition on Hydroxyl-Free Cu(111)

“…HREELS did not detect any characteristic vibrations of TMA or its fragments. 42 The absence of TMA adsorption on clean Cu(111) is in agreement with the findings of Lu et al 17 …”

Reaction of Trimethylaluminum with Water on Pt(111) and Pd(111) from 10–5 to 10–1 Millibar

“…The carbon chemistry on Pt and Pd is not straightforward and shows dependence on the metal substrate; therefore, this chemistry will be the focus of a future publication. 57 A final interesting phenomenon is aluminum oxidation by H 2 O. In the case of Pd(111), the Al−Pd alloy is reversed, and all Pd was reverted to the monometallic phase.…”

Mechanism for Al2O3 Atomic Layer Deposition on LiMn2O4 from In Situ Measurements and Ab Initio Calculations

“…C-H deformation modes in FTIR (Figure 2A) suggest surface-bound CH 3 , as was previously shown on metal and oxide substrates. [41][42][43][44] Demethylated surface intermediates may therefore include Al( Thermodynamics for intermediates in Equations 1, 2, 3, and 4 are shown in Figure 5A, with coadsorbed CH 3 * fragments assumed to be widely separated from one another (closer proximity of the methyl groups does not change any trends). Adsorption configurations are considered at the lattice oxygen top, two-fold, and three-fold sites, as labeled in Figure 5C.…”