An atom-scale analysis of electron transfer from individual sodium atoms to the TiO_2(110) substrate by Kelvin probe force microscope

摘要

Alkali metals are often added to heterogeneous catalysts as a promoter. The electron transfer from the alkali atoms to the catalysts is received to enhance the dissociative adsorption of reactants. Atom-scale mapping of the work function should reveal how alkali additives promote catalytic activities. We observed the sodium-deposited TiO_2(110)-(1 X 1) surface by Kelvin probe force microscope (KPFM) -The sodium atoms were observed as protrusions on the titanium-atom rows of the surface in topographical images, and significantly affected the work function map simultaneously obtained. Extra sample bias voltage of-200 mV was required on the adatoms to cancel the contact potential difference between the tip and sample. The observed decrease of the local work function on the adatoms was attributed to permanent electric dipole moment created by the electron transfer from the adatoms to the surface. Perturbed work function extended to nanometer vicinity away from the adatoms.