Electronic Structure of Pd Multilayers on Re(0001): The Role of Charge Transfer

Abstract

Understanding the origin of the properties of metal-supported metal thin films is important for the rational design of bimetallic catalysts and other applications, but it is generally difficult to separate effects related to strain from those arising from interface interactions. Here we use density functional (DFT) theory to examine the structure and electronic behavior of fewlayer palladium films on the rhenium (0001) surface, where there is negligible interfacial strain and therefore other effects can be isolated. Our DFT calculations predict stacking sequences and interlayer separations in excellent agreement with quantitative low-energy electron diffraction experiments. By theoretically simulating the Pd core-level X-ray photoemission spectra (XPS) of the films, we are able to interpret and assign the basic features of both low-resolution and highresolution XPS measurements. The core levels at the interface shift to more negative energies, rigidly following the shifts in the same direction of the valence d-band center. We demonstrate 2 that the valence band shift at the interface is caused by charge transfer from Re to Pd, which occurs mainly to valence states of hybridized s-p character rather than to the Pd d-band. Since the d-band filling is roughly constant, there is a correlation between the d-band center shift and its bandwidth. The resulting effect of this charge transfer on the valence d-band is thus analogous to the application of a lateral compressive strain on the adlayers. Our analysis suggests that charge transfer should be considered when describing the origin of core and valence band shifts in other metal / metal adlayer systems.

Transition‐Metal Nitride Core@Noble‐Metal Shell Nanoparticles as Highly CO Tolerant Catalysts

“…[22a, [23][24][25] Thed irection of the CLSs appear to indicate ac harge transfer from the Pt shell to Wi nt he core,w hich would result in am ore attractive force on Pt electrons and more repulsive force on Welectrons.H owever,e xamination of the work functions suggest an et transfer in the opposite direction, indicating that asimple interatomic charge transfer is inadequate in describing the CLSs for metal overlayer systems,a schanges in the local potential around the core electrons arising from bonding and rehybridization can have astronger effect on the binding energy than an et difference in charge on the overall atom. [23][24][25] Although the exact cause is uncertain, these CLSs do demonstrate that the electronic and chemical properties of Pt are significantly altered by the presence of the TMC or TMN core and can also provide am easure of potential changes in the reactivity of Pt. Weinert and Watson showed that CLSs for metal overlayers are accompanied by similar shifts in the valence d-band center, [23] and Ontaneda et al determined an ear 1:1c orrelation for core level and d-band shifts of Pd overlayers on Re.…”

In Situ Induction of Strain in Iron Phosphide (FeP2) Catalyst for Enhanced Hydroxide Adsorption and Water Oxidation

“…On the contrary, a tensile strain will lead to a decrease in the d‐bandwidth if no charge transfer occurs. This results in the upshifting of the d‐band center toward the Fermi level and stronger interactions with surface adsorbates …”

“…This results in the upshifting of the d-band center toward the Fermi level and stronger interactions with surface adsorbates. [6] Strains are generally created based on the lattice mismatch effect, which can occur after depositing the desired material onto a substrate with a different lattice parameter ( Figure 1b). [7] This creates either a compressive or tensile strain localized at the interface between the desired material and the substrate.…”

Transition‐Metal Nitride Core@Noble‐Metal Shell Nanoparticles as Highly CO Tolerant Catalysts

“…[23][24][25] Although the exact cause is uncertain, these CLSs do demonstrate that the electronic and chemical properties of Pt are significantly altered by the presence of the TMC or TMN core and can also provide am easure of potential changes in the reactivity of Pt. [25] Thus,t he observed lower energy core electrons (higher XPS binding energy) of Pt in these coreshell materials should translate to ad own-shifted d-band center compared to that of apure Pt surface and consequently weaker adsorbate binding energies. [25] Thus,t he observed lower energy core electrons (higher XPS binding energy) of Pt in these coreshell materials should translate to ad own-shifted d-band center compared to that of apure Pt surface and consequently weaker adsorbate binding energies.…”

“…[22a, [23][24][25] Thed irection of the CLSs appear to indicate ac harge transfer from the Pt shell to Wi nt he core,w hich would result in am ore attractive force on Pt electrons and more repulsive force on Welectrons.H owever,e xamination of the work functions suggest an et transfer in the opposite direction, indicating that asimple interatomic charge transfer is inadequate in describing the CLSs for metal overlayer systems,a schanges in the local potential around the core electrons arising from bonding and rehybridization can have astronger effect on the binding energy than an et difference in charge on the overall atom. [22a, [23][24][25] Thed irection of the CLSs appear to indicate ac harge transfer from the Pt shell to Wi nt he core,w hich would result in am ore attractive force on Pt electrons and more repulsive force on Welectrons.H owever,e xamination of the work functions suggest an et transfer in the opposite direction, indicating that asimple interatomic charge transfer is inadequate in describing the CLSs for metal overlayer systems,a schanges in the local potential around the core electrons arising from bonding and rehybridization can have astronger effect on the binding energy than an et difference in charge on the overall atom.…”