Origin of unusual work function change upon forming Tl nanoclusters on Si(111)-7x7 surface

We report an unusual behavior of the work function that remains unchanged while increasing the coverage (theta) of thallium (Tl) nanoclusters regularly arranged on a Si(111)-7x7 surface. Such a constant work function with increasing theta is understood in terms of a theta-dependent inter-cluster interaction that cancels the change induced by dipoles due to Tl nanoclusters. The spectral changes of Si 2p and Tl 5d(5/2) core-levels as a function of theta strongly indicates the presence of such an inter-clusters interaction, which is further supported by our theoretical calculation revealing a significant charge redistributionclose3