Characterization of α-NPD thermally deposited on hydrogen-terminated single-crystal chemical-vapor-deposited diamond films

We have investigated the interface formation between hydrogen-terminated homoepitaxial (100) chemical-vapor-deposited (CVD) diamond films and thermally deposited N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'biphenyl-4,4"diamine (alpha-NPD). The deposited alpha-NPD was found to form islands at the earliest initial stage, and to subsequently become a continuous film. It turned out that both X-ray photoemission peak positions of C1s and N1s electrons shifted to lower binding energies after the interface formation between sufficiently thin alpha-NPD films (< 10 nm) and the H-terminated p-type diamond, indicating that a substantial interaction between the H-terminated CVD diamond and the deposited alpha-NPD occurred. The possible origin of the interaction is discussed in relation to charge transfer and a relative change in the energy levels between alpha-NPD and the H-terminated diamond. Photoluminescence spectra taken from the deposited alpha-NPD films showed a broad emission peak at 435 nm with an excitation peak at 350 nm, differing from those taken from alpha-NPD in a chloroform solvent.