| AVS 58th Annual International Symposium and Exhibition | |
| Surface Science Division | Wednesday Sessions |
| Session SS-WeA |
| Session: | Adsorption & Reactions on Oxide Surfaces |
| Presenter: | Shail Sanghavi, Pacific Northwest National Laboratory |
| Authors: | S.P. Sanghavi, Pacific Northwest National Laboratory A.S. Karakoti, Pacific Northwest National Laboratory M.I. Nandasiri, Pacific Northwest National Laboratory W. Wang, Pacific Northwest National Laboratory P. Nachimuthu, Pacific Northwest National Laboratory P. Yang, Pacific Northwest National Laboratory S.V.N.T. Kuchibhatla, Pacific Northwest National Laboratory S. Thevuthasan, Pacific Northwest National Laboratory |
| Correspondent: | Click to Email |
The use of nanoparticles in energy, environmental and medical applications has been growing significantly in recent years. In most of these applications, the nanoparticles are being used in as-synthesized form and/or functionalized through ligand conjugation. When particle size decreases to nanometer scale, a large percentage of the atoms are at or near the surface which makes the surface highly dynamic and reactive in nature. Consequently, these particles exhibit unique properties that make their characterization more difficult by conventional spectroscopic methods. Furthermore, knowledge on how the ligand molecules bind to the surface of nanoparticles is very limited. To better understand the interactions between ligand molecules and the surface of nanoparticles, we used a model system approach to study the interaction between the carboxylate anchoring group from trimethylacetic acid (TMAA) and CeO2(111) surfaces as a function of oxygen stoichiometry. The epitaxial CeO2(111) thin films 50nm in thickness were grown on YSZ(111) by oxygen plasma-assisted molecular beam epitaxy at 650°C under 2.5x10-5 Torr of oxygen plasma. The sample films from MBE system were transferred to X-ray photoelectron spectroscopy (XPS) system and sputter cleaned to remove any surface contamination during the transfer. Following sputtering, stoichiometric CeO2(111) surface was obtained by annealing the thin film under 2.0x10-5 Torr of oxygen at ~550°C for 30 min. In order to reduce the CeO2(111) surface, the thin film was annealed in ~5.0x10-10 Torr vacuum at 550°C, 650°C, 750°C and 850°C for 30 min to progressively increase the oxygen defect concentration on the surface. XPS was used to characterize these surfaces prior to and following dissociative adsorption of TMAA on these surfaces using a molecular doser. The saturated TMAA coverage and the oxygen defect concentration were determined from XPS elemental composition. The saturated TMAA coverage on CeO2(111) surface is found to increase with increasing oxygen defect concentration. This is attributed to increase in under coordinated cerium sites on the surface with increase in the oxygen defect concentrations. In parallel, we studied the interactions of TMAA adsorbed at various sites on the stoichiometric CeO2(111) surface using periodic density functional theory (DFT) calculations. Both energetics and electronic properties of the surface and TMAA will be presented and correlated with experimental observations.