Bimetallic Interfaces
We are currently studying W(110)-based bimetallic interfaces using core-level photoemission from the near-surface W atoms. These interfaces are formed by growing a thin metallic film on top of the W(110) surface.
We have recently published results for bimetallic interfaces formed by adsorption of a group-10 metal (Ni, Pd, or Pt) on W(110): these systems are particularly interesting because a group-10 metal adsorbed on an early transition metal such as W behaves much like a noble metal.
A number of results are common among the three group-10/W(110) systems: (i) a separate substrate (W) core-level shift can be identified with each overlayer phase (1D chain, pseudomorphic, or commensurate); (ii) commensurate overlayers produce only one substrate core-level shift, even though not all substrate atoms are equivalently coordinated; (iii) the difference in substrate shifts induced by pseudomorphic and commensurate overlayers contains a large structural contribution; (iv) for a pseudomorphic overlayer the ratio of adlayer to substrate core-level shifts (when referenced to binding energies at the respective clean surfaces) is ~4 for all three systems; and (v) a partial-shift Born-Haber-cycle analysis semiquantitatively describes the substrate shifts induced by both the pseudomorphic and commensurate layers.
The Pd system also shows anomalous behavior at low coverages: Pd islands have a long range (~ 1nm = 3 lattice constants) lateral effect upon the substrate core-level atoms.
These results are discussed in the following three papers:
"Core
Level Spectroscopy of the Ni/W(110) Interface: Correlation of W
Interfacial Core Level Shifts with First-Layer Ni Phases," D. M.
Riffe, R. T. Franckowiak, N. D. Shinn, B. Kim, . J. Kim, and T.-H. Kang, Surface
Science 602, 2039 (2008) (
doi:10.1016/j.susc.2008.04.022 ).
"Core-Level Spectroscopy of the Pd/W(110) Interface: Evidence of Long-Range Pd-Island—W Interactions at Submonolayer Coverages," D. M. Riffe, N. D. Shinn, B. Kim, K. J. Kim, and T.-H. Kang, Surface Science 603, 1070 (2009) (doi:10.1016/j.susc.2009.02.026).
"Core-Level Shifts at the Pt/W(110) Monolayer Bimetallic Interface," D. M. Riffe, N. D. Shinn, B. Kim, K. J. Kim, and T.-H. Kang, Surface Science 603, 3431 (2009). (doi:10.1016/j.susc.2009.10.006).
We are also analyzing data from other M/W(110) interfaces, where M is one of the noble metals Au, Ag, or Cu.