Atomic and electronic structure of CsBr film grown on LiF and KBr(0 0 1)

Atomic and electronic structures of CsBr films grown on LiF(0 0 1) and KBr(0 0 1) were studied by reflection high energy electron diffraction, electron energy loss spectroscopy (EELS) and ultraviolet photoelectron spectroscopy (UPS). On a LiF(0 0 1) substrate, an α-CsBr film with a cesium chloride structure grew heteroepitaxially at 300 K, while a β-CsBr film with a rock salt structure grew heteroepitaxially at substrate temperatures higher than 400 K. On a KBr(0 0 1) substrate, a single crystalline β-CsBr film grew heteroepitaxially in a layer-by-layer fashion independently of the substrate temperature from 300 to 500 K. The EELS results showed that the band gap energy of α-CsBr was smaller than that of β-CsBr, and the UPS results showed that the binding energy of Br− 4p of α-CsBr was smaller than that of β-CsBr. The difference in the band gap energy and the difference in the binding energy of Br− 4p between α-CsBr and β-CsBr were explained, in terms of Madelung potential.