We have characterized ultrananocrystalline diamond films with different surface terminations by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). The surface terminations were performed by plasma functionalization in atmospheres of hydrogen, fluorine, and oxygen. XPS proves the dense monolayer coverage of the surface functionalization. AFM and STM show low impact of the plasma treatment on the surface morphology. STS has been used to investigate the surface electronic properties, for H-terminated surfaces the electronic structure is dominated by the sp3 carbon phase of the grain surfaces; for O- and F-terminated surfaces, however, sp2 carbon from the grain boundaries seems to determine the surface band gap.