An orbital-overlap model for minimal work functions of cesiated metal surfaces

• Published in: Journal of physics. Condensed matter Vol. 24; no. 44; pp. 445007 - 7
• Main Authors: Chou, Sharon H, Voss, Johannes, Bargatin, Igor, Vojvodic, Aleksandra, Howe, Roger T, Abild-Pedersen, Frank
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 07.11.2012; Institute of Physics
• Subjects: Adsorbates; Cesium; Condensed matter; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Construction; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Impurity and defect levels; energy states of adsorbed species; Mathematical models; Metal surfaces; Physics; Surface and interface electron states; Surface double layers, schottky barriers, and work functions; Transition metals; Work functions; Ultrathin films; Work functions; Alkali metals; Electrostatic interaction; Surface electron state; Cesium; Coverage rate; Interfaces; Transition elements; Adsorbed state; Chemical bonds; Density functional method; Dipole moments
• ISSN: 0953-8984; 1361-648X; 1361-648X
• DOI: 10.1088/0953-8984/24/44/445007

We introduce a model for the effect of cesium adsorbates on the work function of transition metal surfaces. The model builds on the classical point-dipole equation by adding exponential terms that characterize the degree of orbital overlap between the 6s states of neighboring cesium adsorbates and its effect on the strength and orientation of electric dipoles along the adsorbate-substrate interface. The new model improves upon earlier models in terms of agreement with the work function-coverage curves obtained via first-principles calculations based on density functional theory. All the cesiated metal surfaces have optimal coverages between 0.6 and 0.8 monolayers, in accordance with experimental data. Of all the cesiated metal surfaces that we have considered, tungsten has the lowest minimum work function, also in accordance with experiments.