Pt atoms adsorbed onTiO2(110)−(1×1)studied with noncontact atomic force microscopy and first-principles simulations

Abstract

We have studied the local properties of single Pt atoms adsorbed on hydroxylated TiO 2 (110)-(1 × 1) by combining noncontact atomic force microscopy (nc-AFM) and first-principles calculations. Room-temperature high-resolution nc-AFM images for the most frequently observed contrast modes reveal bright and elongated protrusions that can be traced back to the Pt atoms, and that are centered on the fivefold coordinated titanium rows, confined between two bridging oxygen rows. These observations are in line with the theoretical results, as the lowest energy sites for the Pt atom on the TiO 2 (110) surface are in the neighborhood of the titanium rows, and high energy barriers have to be overcome to displace the Pt atom over the bridging oxygen rows. Single Pt atoms can be distinguished from H adsorbates (OH defects) due to their characteristic shape and binding site and, because they appear as the brightest surface features in all of the contrast modes. Force spectroscopy data over the protrusion and hole imaging modes and the corresponding tip-sample forces, simulated with O and OH terminated TiO 2 nanoclusters, provide an explanation for this puzzling result in terms of the intrinsic strength of the interaction with the Pt adatom and the adatom and tip apex relaxations induced by the tip-sample interaction. These imaging mechanisms can be extended to other electropositive metal dopants and support the use of nc-AFM not only to characterize their adsorption structure but also to directly probe their chemical reactivity.

Photoinduced Charge Transfer and Trapping on Single Gold Metal Nanoparticles on TiO2

“…The Au/TiO 2 interface has been the subject of theoretical and experimental investigation. Theoretically, metal–semiconductor contact theory 14 and density functional theory 15 are most frequently employed. On the experimental side, ultrahigh vacuum studies using scanning tunneling microscopy and atomic force microscopy (AFM) have been used for atomic-scale characterization of TiO 2 sensitized with metal clusters 16 , 17 and with organic dyes used in solar cells, 18 which contributed to our current knowledge of charge transfer in model metal/TiO 2 (110) systems, 19 including Pt 20 and small Pt clusters.…”

Effect of reducible oxide–metal cluster charge transfer on the structure and reactivity of adsorbed Au and Pt atoms and clusters on anatase TiO2

“…13,20,[23][24][25] To improve the performance of existing catalysts and photocatalysts, a detailed understanding of all the factors that can affect their activity is crucial. To this end, numerous theoretical and experimental studies have examined the interaction between the metal NPs and oxide surfaces, 9,[26][27][28] as well as the mechanisms of nucleation, growth, and diffusion of supported metal NPs. [29][30][31] As a typical reducible oxide, TiO 2 usually contains "excess" electrons (i.e., electrons in excess of those that a) Author to whom correspondence should be addressed.…”

Noncontact Atomic Force Microscopy: An Emerging Tool for Fundamental Catalysis Research

“…47 Furthermore, well-known size and support effects in transition metal catalysis have motivated NC-AFM experiments on Pt atoms on TiO 2 (110). 46 Results have revealed that isolated Pt atoms exhibit the highest chemical interaction with the probing tip for all tip apexes under consideration, thereby illustrating the high chemical reactivity of metal atoms on metal oxide substrates compared with other sites (Figure 7). …”

“…42−45 Additionally, individual metal atoms have been recently imaged and characterized on supports such as TiO 2 (110). 46 The main advantage provided by NC-AFM over STM is the ability to clearly distinguish different adsorbates and surface atoms via force spectroscopy. Imaging and spectroscopy experiments performed on rutile TiO 2 (110) are particularly illustrative in this case, where it was demonstrated via a combination of site-specific force spectroscopy experiments and ab initio calculations that characteristic force−distance relationships for adsorbed OH groups and Ti as well as O atoms on the surface can be reliably determined for different tip apex models.…”