Distinct nonequilibrium plasma chemistry of C2 affecting the synthesis of nanodiamond thin films from C2H2 (1%)/H2/Ar-rich plasmas

6 pages, 5 figures, 6 tables.We show that the concentrations of the species C2 (X 1Σg+), C2 (a 3Πu), and C2H exhibit a significant increase when the argon content grows up to 95% in medium pressure (0.75 Torr) radio frequency (rf) (13.56 MHz) produced C2H2 (1%)/H2/Ar plasmas of interest for the synthesis of nanodiamond thin films within plasma enhanced chemical vapor deposition devices. In contrast, the concentrations of CH3 and C2H2 remain practically constant. The latter results have been obtained with an improved quasianalytic space–time-averaged kinetic model that, in addition, has allowed us to identify and quantify the relative importance of the different underlying mechanisms driving the nonequilibrium plasma chemistry of C2. The results presented here are in agreement with recent experimental results from rf CH4/H2/Ar-rich plasmas and suggest that the growth of nanodiamond thin films from hydrocarbon/Ar-rich plasmas is very sensitive to the contribution of C2 and C2H species from the plasma.This work was partially funded by CICYT (Spain) under a Ramón y Cajal project and under Project No. TIC2002- 03235. One of the authors (F.J.G.V.) acknowledges a Ramón y Cajal contract from the Spanish Ministry of Science and Technology (MCYT). One of the authors (J.M.A.) acknowledges partial support from CICYT (Spain) under Project No. MAT 2002-04085-C02-02.Peer reviewe

Bestimmung und Bewertung des elektrischen Widerstands von Beton mit geophysikalischen Verfahren

The electrical resistivity of concrete correlates with various durability related properties and thus allows an assessment of the condition of a structure. The reliability of the condition assessment depends on the accuracy of the determination of concrete resistivity as well as on the correlation of the resistivity with material properties. Reinforced concrete is a heterogeneous composite material for which the integral consideration to determine the resistivity may lead to misinterpretations. In particular conductive reinforcement bars can significantly influence the measurement results considering the methods typically used in condition surveys. Taking this into account, the distribution of the resistivity within the concrete is determined using the electrical resistivity tomography known from geophysics. Evaluating the applicability of this method, electrode probes are developed for adopting the measurement procedure on concrete structures which allows an application on parametrically varied specimens. The studies focus on the influence of reinforcement bars and near-surface conductive layers on the results. Furthermore the influence of relevant material properties on the impedance spectra are studied by means of spectral induced polarisation measurements. The influences of the material properties are assigned to different frequency ranges. The applicability of Archie’s law on concrete is studied in order to correlate resistivity values with saturation degrees and pore structure parameters. In comparison with the logarithmic approach typically used in civil engineering, the advantages are demonstrated and the significance of the parameters with pore structure properties is discussed. Furthermore a modification of Archie’s second law is introduced leading to conclusions about the critical saturation degree. This parameter can be understood as a threshold level, below which no charge is transferred

Bestimmung und Bewertung des elektrischen Widerstands von Beton mit geophysikalischen Verfahren

The electrical resistivity of concrete correlates with various durability related properties and thus allows an assessment of the condition of a structure. The reliability of the condition assessment depends on the accuracy of the determination of concrete resistivity as well as on the correlation of the resistivity with material properties. Reinforced concrete is a heterogeneous composite material for which the integral consideration to determine the resistivity may lead to misinterpretations. In particular conductive reinforcement bars can significantly influence the measurement results considering the methods typically used in condition surveys. Taking this into account, the distribution of the resistivity within the concrete is determined using the electrical resistivity tomography known from geophysics. Evaluating the applicability of this method, electrode probes are developed for adopting the measurement procedure on concrete structures which allows an application on parametrically varied specimens. The studies focus on the influence of reinforcement bars and near-surface conductive layers on the results. Furthermore the influence of relevant material properties on the impedance spectra are studied by means of spectral induced polarisation measurements. The influences of the material properties are assigned to different frequency ranges. The applicability of Archie’s law on concrete is studied in order to correlate resistivity values with saturation degrees and pore structure parameters. In comparison with the logarithmic approach typically used in civil engineering, the advantages are demonstrated and the significance of the parameters with pore structure properties is discussed. Furthermore a modification of Archie’s second law is introduced leading to conclusions about the critical saturation degree. This parameter can be understood as a threshold level, below which no charge is transferred