The electronic structure of TPD films grown by different methods

We present X-ray photoelectron spectra and X-ray emission spectra of N,N′-bis(3-methylphenyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (TPD) films excited with synchrotron radiation. The measurements are compared with density-functional theory calculations performed for a TPD monomer and the electronic structure of this material is discussed in detail. The TPD films studied in this work were prepared by ionized and neutral cluster beam deposition (ICBD and NCBD, respectively) as well as by thermal evaporation. X-ray fluorescence measurements show that the ICBD technique provides the most promising way of preparing high quality TPD films with strong electroluminescence. C–N bonds in the TPD structure are destroyed under NCBD as well as under thermal evaporation.