T. Gries

Theoretical background of optical emission spectroscopy for analysis of atmospheric pressure plasmas

This review contains a theoretical background of optical emission spectroscopy and some selected examples of issues in the field of atmospheric plasmas. It includes elements like line broadening, emission of continua and molecules, radiation models, etc. Modernized expressions figuring the terms hidden in global constants where cgs units prevail are given together with restrictions of use. Easy-to-use formulas are provided to give access to essential plasma parameters.

Plasma-surface interaction in heptane

The main processes related to discharges between pin and plate electrodes in hydrocarbon liquid (heptane) are modelled for micro-gap (from 10 to 100 μm) conditions. When a plasma channel hits the surface, a micro-crater is created. The different phenomena controlling the geometry (shape and dimension) of a single crater are described and included in a theoretical model developed for the specific case of pure aluminium. The influence of the most important parameters affecting the geometry of the crater is discussed. Among them, one finds the pressure exerted by the plasma on the liquid metal. It is found that the distribution of the pressure applied on the liquid pool changes significantly the way the plasma shapes the pool. It is assumed that at high charges, the pressure profile is tilted from the channel axis, leading to the formation of a central protrusion. On the other hand, we demonstrate that Thomson-Marangoni forces play an important role for crater diameters smaller than 5 μm. Then, the choice of...

Diagnostics and modeling of CH4–CO2 plasmas for nanosmooth diamond deposition: Comparison to experimental data

Microwave plasma-assisted chemical vapor deposition of very smooth diamond coatings is an important process for various applications including mechanical and micromechanical systems and acoustic wave devices. Nanosmooth coatings have been deposited from CH4–CO2 gas mixtures at moderate temperature, the order of 600 °C. In order to increase the knowledge of the process and the control of the final characteristics of the films, a modeling of these plasmas is necessary. This has been carried out here from the prior determination of the plasma parameters. Optical emission spectroscopy was used in order to determine the gas kinetic temperature. Microwave interferometry and Langmuir double probe were used to determine the electron density and the electron temperature, respectively. All these experimental data have been obtained for a wide range of external parameters, such as the inlet composition, the pressure, the gas flow rate, and the power injected in the plasma. Then modeling of CH4–CO2 plasmas was develo...

Anisotropic biaxial stresses in diamond films by polarized Raman spectroscopy of cubic polycrystals

The anisotropic stresses in diamond films induced by permanent deformations of titanium tensile substrates are studied by polarized Raman spectroscopy. The influence of the in-plane orientation of each grain relative to the stress directions is shown experimentally and theoretically. Considering the dynamical equations under small strains, the solutions of the secular equation permit the determination of the triply degenerate phonon frequency of polycrystalline diamond, which splits into three singlets for each crystallite. The calculation is carried out here for six growth directions, along [001], [110], [111], [112], [113], and [331], and for all in-plane orientations normal to these textures. In the case of anisotropic stresses, it is shown how the relative values of the two stresses induce different shapes in the Raman spectra. For an isotropic polycrystalline diamond film, this Raman spectroscopy of strained cubic polycrystals approximates the complete solution for all crystallite orientations relati...

Fast synthesis of ultrathin ZnO nanowires by oxidation of Cu/Zn stacks in low-pressure afterglow

The synthesis of ultrathin, single-crystalline zinc oxide nanowires was achieved by treating in a flowing microwave plasma oxidation process, zinc films coated beforehand by a sputtered thin buffer layer of copper. The aspect ratio of the nanowires can be controlled by the following experimental parameters: treatment duration, furnace temperature, oxygen concentration. An average diameter of 6 nm correlated with a mean length of 750 nm can be reached with a fairly high surface number density for very short treatments, typically less than 1 min. The oxidized samples are characterized by means of SEM, XRD, SIMS, HRTEM and EDX techniques. Structural characterization reveals that these nanowires are single-crystalline, with the wurtzite phase of ZnO. Nanowires are only composed of ZnO without copper particles inside or at the end of the nanowires. Temperature-dependent photoluminescence measurements confirm that ZnO nanowires are of high crystalline quality and thin enough to produce quantum confinement.

Interaction of (3-Aminopropyl)triethoxysilane with Pulsed Ar–O2 Afterglow: Application to Nanoparticles Synthesis

The interaction of (3-Aminopropyl)triethoxysilane (APTES) with pulsed late Ar–O2 afterglow is characterized by the synthesis of OH, CO and CO2 in the gas phase as main by-products. Other minor species like CH, CN and C2H are also produced. We suggest that OH radicals are produced in a first step by dehydrogenation of APTES after interaction with oxygen atoms. In a second step, the molecule is oxidized by any O2 state, to form peroxides that transform into by-products, break thus the precursor C–C bonds. If oxidation is limited, i.e. a low duty cycle, fragmentation of the precursor is limited and produced nanoparticles keep the backbone structure of the precursor, but contain amide groups produced from the amine groups initially available in APTES. At high duty cycle, silicon-containing fragments contain some carbon and react together and produce nanoparticles with a non-silica-like structure.