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A systematic study of various, nominally undoped ZnO single crystals, either hydrothermally grown ͑HTG͒ or melt grown ͑MG͒, has been performed. The crystal quality has been assessed by x-ray diffraction, and a comprehensive estimation of the detailed impurity and hydrogen contents by inductively coupled plasma mass spectrometry and nuclear reaction analysis, respectively, has been made also. High precision positron lifetime experiments show that a single positron lifetime is observed in all crystals investigated, which clusters at 180-182 ps and 165-167 ps for HTG and MG crystals, respectively. Furthermore, hydrogen is detected in all crystals in a bound state with a high concentration ͑at least 0.3 at. %͒, whereas the concentrations of other impurities are very small. From ab initio calculations it is suggested that the existence of Zn-vacancyhydrogen complexes is the most natural explanation for the given experimental facts at present. Furthermore, the distribution of H at a metal/ZnO interface of a MG crystal, and the H content of a HTG crystal upon annealing and time afterward has been monitored, as this is most probably related to the properties of electrical contacts made at ZnO and the instability in p-type conductivity observed at ZnO nanorods in literature. All experimental findings and presented theoretical considerations support the conclusion that various types of Zn-vacancy-hydrogen complexes exist in ZnO and need to be taken into account in future studies, especially for HTG materials.

The plasma enhanced chemical vapor deposition of a-C:H films using methane and acetylene as precursors was studied. Noninvasive in situ techniques were used to analyze the plasma processes with respect to the self-bias voltage, the displacement currents to the grounded electrode, the neutral gas composition, the optical sheath thickness as well as current and energy of the ions hitting the powered electrode. The a-C:H films were characterized for their deposition rate, surface roughness, hardness, mass density, and hydrogen content. Ion mean free paths, suitable for low-pressure rf sheaths, have been quantified for both precursors. The film with the highest hardness of 25GPa was formed in the C2H2 discharge when the mean energy per deposited carbon atom was approximately 50eV. The hardness obtained with the CH4 discharge was lower at 17GPa and less sensitive to changes in the process parameters. It was found that the creation of hard (hardness >15GPa) a-C:H films from both precursors is possible if the mean energy per deposited carbon atom exceeds only ∼15eV. Further film characteristics such as surface roughness and hydrogen content show the interplay of ion flux and deposition from radicals to form the a-C:H structure and properties.

Channeling implantation of Ga into Ge is performed at two very different ion fluxes (1012 and 1019cm−2s−1), at two temperatures (room temperature and 250°C), and at five different fluences. The fluence dependence of the range profiles and of the implantation damage is strongly influenced by defect accumulation and dynamic annealing. At 250°C, the maximum lifetime of the defects is less than 10s. On the other hand, at room temperature no significant annealing is found within the first 10s after ion impact. The measured Ga depth profiles are reproduced very well by atomistic computer simulations.

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