In this work, boron-doped nanocrystalline diamond (BDND) films are grown on silicon substrates by hot-filament (HF)CVD in Ar/H 2 /CH 4 gas mixtures. In this study, the transition from ultra-nanocrystalline to nanocrystalline diamond films is clearly shown by the addition of boron dopant to the growth of the gas mixture. The doping process consists of an additional H 2 line passing through a bubbler containing B 2 O 3 dissolved in methanol with various B/C ratios. Five sample sets are obtained with doping in the methanol bubbler solution of 2 000, 5 000, 10 000, 20 000, and 30 000 ppm for a 16 h growth time. The morphology, roughness, and structure of these films have markedly different properties. The cross-section of the films is characterized by scanning electron microscopy (SEM) showing the transition from ultra-nanocrystalline growth (renucleation process) to a columnar structure of nanocrystalline films. The acceptor density values, evaluated by Raman spectra and by Mott-Schottky plot analysis, vary from 10 20 to 10 21 B cm À3 as the doping level increases. The grain size and the relative intensity of the (111)/ (220) peaks are obtained from X-ray diffraction (XRD) patterns of the films. The diamond average grain size increases from 10 to 35 nm for films with 2 000 and 30 000 ppm B/C, respectively, in the methanol bubbler solution. The preferential orientation also changes, from (220) to (111), as the boron doping level increases.