Work Function Measurements of Thin Oxide Films on Metals-MgO on Ag(001)

The metal work function is a suggested key parameter for charging adsorbates with high electron affinity on thin oxide films grown on metal single crystal surfaces. Here, the first experimental data for the work function shift of Ag(001) induced by 1, 3, and 8 monolayers of MgO is measured in situ by three independent scanning probe techniques on the same surface area, making the different approaches comparable. Furthermore, the results are compared to density functional theory calculations. The measurements are performed using a dual-mode dynamic force microscope and scanning tunneling microscope working in ultrahigh vacuum at low temperature (5 K). The methods to detect the work function shift are based on Kelvin probe force microscopy measuring the contact potential difference, I(z) curves and field emission resonances.