| AVS 63rd International Symposium & Exhibition | |
| Surface Science | Monday Sessions |
| Session SS+AS+HC-MoA |
| Session: | Metals, Alloys, and Oxides: Reactivity and Catalysis |
| Presenter: | Wei Zhang, University of Washington |
| Authors: | W. Zhang, University of Washington J. Lownsbury, University of Washington R. Uppuluri, The Pennsylvania State University T.E. Mallouk, The Pennsylvania State University C.T. Campbell, University of Washington |
| Correspondent: | Click to Email |
The metal/oxide interface is essential to many current and prospective technologies, including oxide-supported metal catalysts, fuel cells, photocatalysis, and nanoscale electronic contacts, so understanding the strength of metal – oxide bonding at such interfaces is of great interest. These strengths have been measured on single crystal oxide surfaces by single crystal adsorption calorimetry (SCAC) of metal atom adsorption in ultrahigh vacuum (UHV)1 and on niobate and tantalate nanosheets by solution-based isothermal titration calorimetry during the deposition of transition metal oxide (or hydroxide) nanoparticles from their aqueous salt solutions2,3. These niobate nanosheets are very interesting since they are highly ordered and essentially like single crystal surfaces in that the ratio of terrace sites to defect and edge sites is huge. Furthermore, when used as supports for transition metal oxide nanoparticles, they have been shown to display unusual stability against sintering.2,3 Here, we directly measure the adsorption energies of metal vapor on such niobate nanosheets using SCAC in UHV. Specifically, we study the adsorption of Ca and Ag vapor onto calcium niobate films that are 4 nanosheets thick (~4 nm total). Calcium atoms show a sticking probability near unity and an initial heat of adsorption of ~660 kJ/mol, much higher than the heat of bulk Ca(s) sublimation (178 kJ/mol). Low-energy ion scattering spectroscopy (LEIS), which is element-specific and probes only the topmost atomic layer, is used to investigate the resulting metal particle/film morphology. The possible chemical reactions between the metal vapor and the calcium niobate during adsorption are elucidated using X-ray photoelectron spectroscopy (XPS).
[1] Campbell, C. T.; Sellers, J. R. V. Faraday Discussions 2013, 162, 9.
[2] Strayer, M. E.; Binz, J. M.; Tanase, M.; Shahri, S. M. K.; Sharma, R.; Rioux, R. M.; Mallouk, T. E. J. Am. Chem. Soc. 2014, 136, 5687.
[3] Strayer, M. E.; Senftle, T. P.; Winterstein, J. P.; Vargas-Barbosa, N. M.; Sharma,R.; Rioux, R. M.; Janik, M. J.; Mallouk, T. E. J. Am. Chem. Soc. 2015, 137, 16216.