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Chemical vapour deposition has been utilised for the fabrication of nickel–nitrogen defects in diamond. By introducing nickel, as well as nitrogen into the process gas, this approach offers the advantage, that a direct formation of nickel–nitrogen centres on the growing surface is possible. This could therefore make postannealing steps superfluous. Nanocrystalline diamond films, as well as single crystal layers were grown under addition of nickel and nitrogen using different doping sources, namely: gaseous nickelocene, nickel powder and nickel wire. The amount of nickel present in the gas phase was characterised by optical emission spectroscopy OES. In order to investigate the presence of nickel or nickel–nitrogenrelated defects, photoluminescence PL measurements at different temperatures have been applied. A strong fluorescence in the range between 800 and 900 nm, accompanied by a peak at around 817 nm, as well as a narrow peak at 788 nm has been observed at cryogenic temperatures 10 K. The peak at 788 nm indicates the presence of nickel and nickel–nitrogenrelated complexes in our samples. PL measurements at higher temperatures reveal, an initially rising intensity of a broad emission band at temperatures up to 200 K, while the emission is quenched at 300 K.

The photochemical attachment of 10-amino-dec-1-ene molecules protected with a trifluoroacetic acid group (TFAAD) on hydrogen-terminated single-crystalline chemical vapor deposited (CVD) diamond is characterized by total photoyield spectroscopy (TPYS), conductivity, Hall-effect, spectrally resolved photoconductivity (SPC), optical transmission experiments, and, for the first time, by in situ internal photoemission (IPE) spectroscopy applied in the spectral regime from 4 to 6 eV on the alkene/diamond (liquid/solid) heterostructures. These experiments are performed on undoped, (100) oriented, single-crystalline CVD diamond films, which contain no grain boundaries and have negligible bulk and surface defect densities. X-ray photoelectron spectroscopy (XPS) is used to investigate the chemical bonding of alkene molecules to diamond. The spectroscopic set of data shows that the photochemical reaction window of H-terminated diamond is shifted below the optical gap of diamond because of the negative electron affinity. In situ IPE experiments reveal electron emission between 4.5 and 5.2 eV. A model is introduced and discussed in which valence-band electrons are optically excited into empty hydrogen-induced surface states of diamond from where they tunnel into empty states of alkene molecules. We theoretically discuss the fastest attachment time to achieve a saturated TFAAD layer of about 2 × 1014cm-2on diamond, which is experimentally detected to be 7 h. In the case of direct optical electron excitations from diamond, the bonding efficiency will be one TFAAD molecule attachment arising from about 1600 emitted electrons.

Time-of-flight (TOF) experiments of a-Si: H, in which carrier transport proceeds via multiple trapping in, and re-emission from, a continuous distribution of localized states below the mobility edge, have been analysed using a computer simulation technique based on a numerical inversion of the Laplace transform. A detailed discussion of experimental (TOF) transit time, the moment when the centre of charge leaves the sample at the back contact, and the physical interpretation of activation energies calculated from log(μeff) against 1/T plots is presented. The activation energy is used to determine the trapping region of the tail-state distribution which dominates carrier transport and it is shown that the experimental transit time is approximately the free-carrier transit time plus the total resting time of carriers in traps visited at least once. TOF experiments have been carried out over a wide range of temperature and electric field. Experimental drift mobility data are evaluated to calculate the tail-state distribution at the conduction band for the case of strong and weak electron - multiphonon coupling (SEMPC and WEMPC). Calculations reveal a hybrid distribution of tail states g(E) (for example a linear decay close to the mobility edge followed by a steep exponential) for both SEMPC and WEMPC. It is shown that interpretations of drift mobility data with respect to parameters such as g(E), attempt-to-escape-frequency, and demarcation-energy movement depend strongly on the assumed electron - phonon interaction.

Measurements of steady-state photoconductivity with respect to light-induced defect generation in amorphous hydrogenated silicon (a-Si: H) show that the power index of the time evolution (long-term observation) of the photodegradation is determined by the exposure temperature and the material. [ABSTRACT FROM AUTHOR]