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In this paper the low temperature deposition of nanocrystalline and ultrananocrystalline diamond (UNCD) films is compared and discussed. NCD films were prepared by hot filament chemical vapor deposition from a 1% CH4/H2 mixture, while microwave plasma chemical vapour deposition was used to deposit UNCD films from a mixture of 17% CH4/N2. The resulting films have been thoroughly characterized concerning their morphology and structure by scanning electron microscopy and concerning their crystalline properties by X‐ray diffraction. The composition was analyzed by X‐ray photoelectron spectroscopy (XPS), whereas XPS and Raman spectroscopy were applied to get information on the bonding structure of the films. The most important result of this study is that the composition, structure, morphology, and bonding environment of UNCD hardly change if the deposition temperature is lowered from 770 to 530 °C or even 450 °C. In contrast, there are drastic changes of the nature of NCD films if the temperature is reduced to 700 °C or even lower. Interestingly, the sp2/sp3 ratio of the NCD films remains low and constant in the temperature range investigated. Rather, the nature of the sp2 grain boundary material undergoes drastic changes if the temperature is lowered below 700 °C. In addition, the films become inhomogeneous on a micrometer (not nanometer) scale. Possible reasons for these observations will be discussed throughout the paper.

Thin boron-doped nanocrystalline diamond (NCD) films have been prepared by microwave plasma enhanced chemical vapour deposition (MPCVD) and used as platforms for grafting of photosensitizer (manganese phthalocyanine, Mn-Pc). The surface of the as-grown films is H-terminated; in order to modify it and study the influence of the termination on the attachment of Mn-Pc the NCD films were subjected to O 2 plasma or NH 3 /N 2 plasma treatments. Contact angle measurements and XPS results showed a successful exchange of the surface termination with OH-or NH 2 -groups. Manganese phthalocyanine molecules were grafted on the NCD surfaces with different terminations, after which each sample was subsequently characterized by XPS and Raman spectroscopy. Finally, the NCD/Mn-Pc samples were used for the preparation of electrodes which were tested in an electrochemical cell with a Pt counter electrode and an Ag/AgCl reference electrode; phosphate buffered saline was used as electrolyte. The characteristics of the electrodes were measured by cyclic voltammetry (CV) and open circuit potential (OCP) in dark and under illumination with a light-emitting diode (LED) operating at 770 nm (a wavelength close to the absorption maximum of Mn-Pc). The first results indicated that after plasma modifications NCD surfaces are suited for Mn-Pc grafting.

Boron doped diamond (BDD) shows high chemical stability in contact with a liquid phase even under extreme pH conditions, high electrochemical activity, and allows very stable covalent functionalization on O-or N-terminated surfaces. It is therefore an excellent electrode material for many applications such as analytics, biosensors, and purification. Furthermore, the electrodes can be covalently functionalized with photosensitive dyes to generate photo currents. However, the energetic conditions and charge transfer mechanisms are not fully known and therefore have been investigated in this work. The focus was set on the energy band diagrams of nanocrystalline diamond (NCD) layers, especially on the flat-band potential V F and the band-bending w B in the space charge layer, for both O-and N-terminated surfaces, and the charge transfer mechanisms at the semiconductor/electrolyte phase-boundary, with or without electro-active organic dyes, such as manganese phthalocyanine. For this study NCD samples were grown by hot filament chemical vapor deposition (HFCVD) with a boron doping density N A ranging between 5.8 and 9.6 Â 10 20 cm À3 .The pristine surface was then processed by oxygen or ammonia plasma to modify the termination to O and NH 2 , respectively. After that a series of Mott-Schottky plots was measured for both terminations at several frequencies spanning from 3 Hz to 10 kHz and in two different electrolytes, namely 0.1 M H 2 SO 4 and 0.1 M KCl. The results showed nearly the same flat-band potential for both surface terminations, but a remarkable difference in the band-bending. The latter is most probably responsible for the better photoelectrical conversion observed in N-terminated NCD samples. The open-circuit potential (OCP) and chronoamperometric measurements performed after covalent functionalization of the samples with the color dyes revealed that only the N-terminated material delivered a measurable photocurrent. Although the global efficiency of the photoelectric conversion was low, these initial results show that by optimized selection of materials and modification technologies providing a proper match of the energy levels at all charge transfer steps, a higher energy output could be achieved.