Formation of a Ti-Cu(111) single atom alloy: Structure and CO binding

Junjie Shi; Cameron J Owen; Hio Tong Ngan; Siyu Qin; Vikram Mehar; Philippe Sautet; Jason F Weaver

doi:10.1063/5.0050800

Formation of a Ti-Cu(111) single atom alloy: Structure and CO binding

J Chem Phys. 2021 Jun 21;154(23):234703. doi: 10.1063/5.0050800.

Authors

Junjie Shi¹, Cameron J Owen², Hio Tong Ngan³, Siyu Qin¹, Vikram Mehar¹, Philippe Sautet³, Jason F Weaver¹

Affiliations

¹ Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611, USA.
² Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
³ Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, California 90095, USA.

PMID: 34241242
DOI: 10.1063/5.0050800

Abstract

A single atom Ti-Cu(111) surface alloy can be generated by depositing small amounts of Ti onto Cu(111) at slightly elevated surface temperatures (∼500 to 600 K). Scanning tunneling microscopy shows that small Ti-rich islands covered by a Cu single layer form preferentially on ascending step edges of Cu(111) during Ti deposition below about 400 K but that a Ti-Cu(111) alloy replaces these small islands during deposition between 500 and 600 K, producing an alloy in the brims of the steps. Larger partially Cu-covered Ti-containing islands also form on the Cu(111) terraces at temperatures between 300 and 700 K. After surface exposure to CO at low temperatures, reflection absorption infrared spectroscopy (RAIRS) reveals distinct C-O stretch bands at 2102 and 2050 cm^-1 attributed to CO adsorbed on Cu-covered Ti-containing domains vs sites in the Ti-Cu(111) surface alloy. Calculations using density functional theory (DFT) suggest that the lower frequency C-O stretch band originates specifically from CO adsorbed on isolated Ti atoms in the Ti-Cu(111) surface alloy and predicts a higher C-O stretch frequency for CO adsorbed on Cu above subsurface Ti ensembles. DFT further predicts that CO preferentially adsorbs in flat-lying configurations on contiguous Ti surface structures with more than one Ti atom and thus that CO adsorbed on such structures should not be observed with RAIRS. The ability to generate a single atom Ti-Cu(111) alloy will provide future opportunities to investigate the surface chemistry promoted by a representative early transition metal dopant on a Cu(111) host surface.