We have investigated interfacial charge transfers and hole injection characteristics between oxygen-terminated boron-doped homoepitaxial (1 0 0) 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) mainly using X-ray photoelectron spectroscopy (XPS), Hall effect measurements and current-voltage (J-V) characteristic measurements. On one hand, no chemical shift was observed for C 1s and N 1s XPS spectra taken from the alpha-NPD overlayer-CVD diamond substrate system. On the, other hand, the low-temperature hole concentration of the diamond substrate decreased by approximate to10-17% after the alpha-NPD depositions, verifying that small but substantial amounts of holes were transferred from the diamond substrates to the alpha-NPD films. However, compared with those obtained from the specimens before the a-NPD depositions, the sheet electrical conductivities of the specimens after the alpha-NPD depositions increased at T greater than or equal to 230 K while decreasing at T less than or equal to 200 K. In addition, J-V data measured from layered alpha-NPD-diamond hetero-structures show evidence that the junction worked as a diode. These facts suggest that the alpha-NPD-CVD diamond system may be useful for a transparent anode electrode with a hole transport layer appropriate for organic light emitting diodes. 2004 Elsevier B.V. All rights reserved.