A study of local density of states of atom clusters on the W(110) surface

The kinetic energy distributions of field desorbed He ions from tungsten clusters of one to five atoms on a W(110) surface are measured using a high resolution pulsed-laser time-of-flight atom probe. The He field ion energy distribution from the single W adatom shows an extra peak-like feature centered at 2.7 eV above the Fermi level. It has a full width at half maximum (fwhm) of 2.3 eV. The data from two tungsten adatoms separated by two lattice constants have nearly the same feature with the extra peak located at 2.5 eV above the Fermi level. These peaks arise from resonance tunneling with the adatom local density of states (LDOS). The He ion energy distribution of a tungsten dimer has an extra peak centered at 1.5 eV above the Fermi level. The fwhm is about 4 eV. The spectra from four and five tungsten adatom clusters show only one peak each, similar to that from a flat plane.