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Metal−organic chemical vapor deposition (MOCVD) of thin films of two representative rare-earth nitrides is reported here for the first time. Four homoleptic, all-nitrogen-coordinated, rare-earth (RE) complexes were evaluated as precursors for the respective nitride thin film materials. Two guanidinato complexes [RE{(iPrN)2C(NMe2)}3] [RE = Gd (1), Dy (2)] and two amidinato complexes [RE{(iPrN)2CMe}3] [RE = Gd (3), Dy (4)] were compared and used either as single source precursors or together with ammonia for MOCVD of gadolinium nitride (GdN) and dysprosium nitride (DyN), respectively. The thermal properties of the precursors were studied and the fragmentation patterns were characterized by high-resolution electron impact−mass spectrometry (HR EI-MS). The obtained nitride films were investigated using a series of techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), nuclear reaction analysis (NRA), Rutherford backscattering (RBS), and X-ray photoelectron spectroscopy (XPS). The f...

Absorption spectroscopy is known to be a powerful tool to gain spatially and temporally resolved information on excited and reactive species in a plasma discharge. Furthermore, the interaction of the discharge with short intense laser pulses can trigger the ignition and the transition into other transient states of the plasma. In this context laser-assisted ‘pump-probe’ experiments involving simultaneously generated supercontinuum radiation yield highly temporally resolved and spatially well-defined information on the transient phenomena. In this paper we demonstrate the possibility for ‘pump–probe’ experiments by initiating breakdown on a picosecond time scale (‘pump’) with a high-power beam and measuring the broadband absorption with the simultaneously provided supercontinuum (‘probe’). Since both pulses are generated from the same mode-locked master oscillator, they have a strong level of synchronization.

International audience; Reactive RF plasmas are an excellent source for the production of nanoparticles. The field of application of nanoparticles is nowadays rapidly growing, as well as the request for investigations on the nanoparticle material itself. Thus, we deal with the emerging need for targeted sampling of nanoparticles from the plasma. We developed a sampling system based on the effect of thermophoresis on the transport of nanoparticles within the plasma bulk.

Axial emission profiles in a parallel plate dc micro discharge (feedgas: argon; discharge gap d=1mm; pressure p=10Torr) were studied by means of time resolved imaging with a fast ICCD camera. Additionally, volt-ampere (V-A) characteristics were recorded and Ar* metastable densities were measured by tunable diode laser absorption spectroscopy (TDLAS). Axial emission profiles in the steady state regime are similar to corresponding profiles in standard size discharges (d=1cm, p=1Torr). For some discharge conditions relaxation oscillations are present when the micro discharge switches periodically between low current Townsend-like mode and normal glow. At the same time the axial emission profile shows transient behavior, starting with peak distribution at the anode, which gradually moves towards the cathode during the normal glow. The development of argon metastable densities highly correlates with the oscillating discharge current. Gas temperatures in the low current Townsend-like mode (T= 320-400K) and the high current glow mode (T=469-526K) were determined by the broadening of the recorded spectral profiles as a function of the discharge current., Comment: submitted to Plasma Sources Sci. Technol

Space resolved concentrations of helium He metastable atoms in an atmospheric pressure radio-frequency micro-plasma jet were measured using tunable diode laser absorption spectroscopy. The spatial profile of metastable atoms in the volume between the electrodes was deduced for various electrode gap distances. Density profiles reveal the sheath structure and reflect the plasma excitation distribution, as well as the dominance of the α-mode discharge. Gap width variations show the transition from a normal glow plasma to a pure sheath discharge. In order to analyse and verify the experimentally observed profiles of the metastable atoms, a two-dimensional simulation model was set up. Applying an appropriate He/N2/O2 chemistry model, the correlation between the metastable profiles and the underlying excitation mechanisms was obtained.

Space- and time-resolved measurements of Ar (3P2) metastable atoms at the exit of an atmospheric pressure radio-frequency micro-plasma jet are performed using tunable diode laser absorption spectroscopy. The discharge features a coaxial geometry with a hollow capillary as the inner electrode and a ceramic tube with a metal ring as the outer electrode. Absorption profiles of metastable atoms and optical emission measurements reveal the dynamics and the filamentary structure of the discharge. Single filaments with a diameter of 125 µm and metastable densities of about 1013 cm−3 are observed. The average spatial distribution of Ar metastables is characterized with and without a target in front of the jet, showing that the target potential and, therewith, the electric field distribution substantially change the filaments' expansion. Together with a detailed analysis of the ignition phase and the discharge's behavior under pulsed operation, the results give an insight into the excitation and de-excitation mechanisms.

The applicability of Dynamic Light Scattering (DLS) on strongly coupled complex plasmas (plasma crystals) in a RF discharge is discussed. A ballistic particle movement is observed and the particle velocity can be measured in all phase states. The results are in very good agreement with video based measurements. Phase transitions were studied in detail. A theoretically predicted hysteresis loop in the phase transition were observed experimentally for the first time. The diffusive particle movement was studied by small angle light scattering. These measurements are also validated by video observations.

A time-resolved analysis of the emission of power impulse magnetron sputtering plasmas reveals inhomogeneities in the form of rotating spokes. The shape of these spokes depends on the target material in a characteristic manner; the peculiar shape of the emission profiles is explained by the localization of the sputtering process as being governed by Ar gas rarefaction and the local dynamics of secondary electrons generation. This general picture is able to explain the observed emission patterns for different target materials as presented.

International audience; Diode laser absorption at 772.38 nm is used to measure the time resolved density of Ar*(3 P 2) metastable atoms in a capacitively coupled radio-frequency (RF) discharge running in argon/acetylene mixture at 0.1 mbar. The RF power is pulsed at 100 Hz and the density of Ar*(3 P 2) atoms in the 5 ms ON time and in the afterglow are recorded. Different plasma conditions, namely: 1) pure argon, 2) argon + 7% acetylene before powder formation, 3) argon + 7% acetylene after dust particles have been formed and 4) argon with dust particles remained in the plasma volume but without acetylene are studied. The measured steady-state Ar*(3 P 2) density in the middle of the reactor is always about 10 times larger in dusty argon plasma than in pure argon discharge. This is mainly a consequence of the enhancement of electron temperature after dust formation. Both steady state densities and decay times in the afterglow indicate that the degree of dissociation of C 2 H 2 in the plasma volume can be as high as 99%. It is shown that in our plasma conditions on the surface of dust particles the loss of Ar*(3 P 2) atoms is negligible compared to their loss by diffusion to the electrodes.

International audience; The spatial dynamics of the optical emission from an array of 50 times 50 individual micro cavity plasma devices are investigated. The array is operated in argon and argon-neon mixtures close to atmospheric pressure with an AC voltage. The optical emission is analysed with phase and space resolution. It has been found that the emission is not continuous over the entire AC period, but occurs once per half period. Each of the observed emission phases shows a self-pulsing of the discharge, with several bursts of emission of fixed width and repetition rate. The number of emission bursts depends on applied voltage and frequency. Spatially resolved measurements prove that the emission bursts are formed by overlapping emission pulses from single discharge cavities. Intensity differences between positive and negative half-wave can be interpreted through spatially resolved measurements of single discharge cavities.

International audience; We present experimental and numerical studies of the properties of a capacitively coupled 13.56 MHz discharge in a mixture of Ar and C2H2 with growing nanosize particles. It is found that at the initial stage of the growth, nanoparticles are accumulated near the sheath-plasma boundaries, where the ionization by electrons is maximal. The nanoparticles suppress the ionization due to the absorbing fast electrons and stimulate a quick change of the plasma parameters followed by a transition between different modes of discharge operation. At that moment the peaked distribution of the dust particles transforms into a flat one.

Micro plasmas operated at ambient pressure with dimensions of the confining geometry in the order of a few ten micrometers to a millimeter are actually in the focus of interest due to the broad regime of applicability they offer and due to a similarly broad range of open physical questions. Here we present optical measurements within the discharge core and the effluent region of an especially developed micro discharge jet. To get an understanding of the complex system of this discharge it is important to analyse transport phenomena of energy and particles within both parts of the discharge by various highly sophisticated diagnostics. As a consequence of the limited access and the dimensions of the micro discharge most of these diagnostics are optical. Here we present diagnostics applied to determine spatially resolved absolute atomic oxygen densities as the most reactive constituent of the effluent, density maps of ozone as final reaction product of the gas chemical chain induced by the discharge and phase resolved optical emission spectroscopy yielding insight into the excitation dynamics of the discharge. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA. Weinheim.

In our work we are focused on study of powder formation in C2H2/Ar plasmas. In this scope we used a combination of FTIR and mass spectroscopy, which are the mostly used experimental techniques for plasma powder formation diagnostics. To test the proposed mechanism for particle nucleation delay we measured the particle nucleation under different plasma conditions: firstly we increased the gas temperature and secondly we changed the background gas from argon to helium., Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France)

The axial light distributions in parallel-plate dc microdischarges in argon show similar behavior to large scale discharges. Between the low-current Townsend mode and the high current glow mode exists a large region of currents where different oscillations appear and the dynamic Volt-Ampere characteristic shows hysteresis behavior. During the oscillations the maximum peak intensity moves closer to the cathode, which is characteristic for the abnormal glow regime even though the average current is considerably smaller., Comment: submitted to: IEEE Trans. Plasma Sci., Spec. Issue on Images in Plasma Sci

We report for the first time on instabilities of High Power Impulse Magnetron Sputtering Plasmas (HIPIMS) which are likely to be of the generalised drift wave type. They are characterized by well defined regions of high and low plasma emissivity along the racetrack of the magnetron and causes periodic shifts in floating potential. The azimuthal mode number m depends on plasma current, plasma density, and gas pressure. The structures rotate in

Two different oscillation modes in microdischarge with parallel-plate geometry has been observed: relaxation oscillations with frequency range between 1.23 and 2.1 kHz and free-running oscillations with 7 kHz frequency. The oscillation modes are induced by increasing power supply voltage or discharge current. For a given power supply voltage, there is a spontaneous transition from one to other oscillation mode and vice versa. Before the transition from relaxation to free-running oscillations, the spontaneous increase of oscillation frequency of relaxation oscillations form 1.3 kHz to 2.1 kHz is measured. Fourier Transform Spectra of relaxation oscillations reveal chaotic behaviour of microdischarge. Volt-Ampere characteristics associated with relaxation oscillations describes periodical transition between low current, diffuse discharge and normal glow. However, free-running oscillations appear in subnormal glow only.

Inside a miniaturized capacitively coupled cold atmospheric pressure plasma jet operated at a helium base gas flow with a minor molecular oxygen admixture atomic oxygen is created. The build up of atomic oxygen along the discharge channel and its further decay in the effluent is investigated by means of xenon calibrated two photon laser induced fluorescence spectroscopy (TALIF). The longitudinal and the transversal atomic oxygen distribution is measured from the discharge core through the transition area into the effluent. A particular emphasis is set on the influence of collisional quenching at elevated pressures.

The 19th International Symposium on Plasma Chemistry (ISPC-19) was held at Ruhr-University Bochum, Germany, from 26 to 31 July 2009 under the sponsorship of the International Union of Pure and Applied Chemistry (IUPAC) and the International Plasma Chemistry Society (IPCS), and under the patronage of the Ministry of Innovation, Science, Research and Technology of North-Rhine Westphalia, Germany. Bochum also served as the host venue for ISPC-10 in 1991, and this return occasion of ISPC-19 was co-sponsored by the German Science Foundation, the Ruhr-University Bochum, and the town of Bochum.ISPC is a bi-annual international conference with topics encompassing the complete areas of plasma chemistry and plasma processing science. Almost 650 participants from over 40 countries presented 682 papers. Six plenary speakers and 22 topical invited speakers covered a broad range of topics. These keynote lectures were complemented by 105 oral contributions and about 530 poster presentations in 16 categorized scientific topics. The large number of papers reflects that the current field of plasma chemistry is lively and evolving, and crosses the borders between many disciplines ranging from natural to engineering sciences.This issue of Pure and Applied Chemistry contains 13 papers based on plenary lectures and topical invited talks presented at ISPC-19. This compilation illustrates very well that the traditional distinction between low-pressure and thermal high-pressure plasmas almost disappears; the current research topics on microplasmas and microplasma jets exhibit many similarities if compared to research on conventional arcs used for thermal spraying. We sincerely hope that this issue provides readers an overview of current and future scientific developments.Achim von KeudellConference ChairJörg WinterConference Co-Chair

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The spatial dynamics of the optical emission from an array of 50x50 individual microplasma devices is reported. The array is operated in noble gas at atmospheric pressure with an ac voltage. The optical emission is analyzed with phase and space resolution. It has been found that the emission is not continuous over the entire ac period, it occurs only twice in each cycle. Each of the observed emission phases shows a self-pulsing of the discharge, with several bursts of emission of a fixed width and repetition rate. Cross-talk between the individual devices can be observed through spatially resolved measurements. (C) 2008 American Institute of Physics.

Plasma polymerisation and growth of the dust particles are still in the scope of the plasma community. We analyze the morphology and constitution of plasma polymerized carbonaceous dust particles. The dust particles were grown under different discharge conditions with the different background gas constituents and different monomers. The strong non-equilibrium between electron and ion transport properties causes the charging of the dust in plasma. This, on the other hand, produces changes in the discharge properties, such as: mean electron energy, plasma potential, excitation profiles and sheath dynamics. We report here some of our most relevant results on the properties of complex plasmas.

We present the results of time resolved spectroscopy measurements of the Hα line of atomic hydrogen in an Ar-C2H2 radiofrequency plasma. The presence of the fast (high-energy) and slow (low-energy) components of the hydrogen atoms can be deduced from the Doppler broadening of the Hα line. With the appearance of the dust particles, the Hα profile became narrower, indicating reduction of the fast component. We discuss several mechanisms for the formation of the fast hydrogen atoms in our plasma. The main cause for the reduction of the hydrogen atom fast component is the plasma change from electropositive to electronegative, decreasing the sheath's width and voltage. The change of plasma conditions coincides with the end of the dust coagulation/agglomeration when the dust particles become multiply negatively charged. We propose here a new experimental technique for detection of the dust coagulation/agglomeration phase.

In synchronized Euglena gracilis (light-dark regime of 14:10 hours) the successive formation of the photosynthetic apparatus during cell ontogeny is correlated with large changes in photosynthetic efficiency (P Brandt, B von Kessel 1983 Plant Physiol 72: 616-619; B Kohnke, P Brandt 1984 Biochim Biophys Acta 766: 156-160). This observation led us to investigate the functional association of the chlorophyll a/b light-harvesting protein complex (LHCP) with photosystem I or II, because changes in energy flow to photosystem I or II and in energy transfer between the two photosystems can be a reason for these alterations. As criterion for the association of the LHCP with photosystem I or II, state transitions were determined after 15 minutes preillumination using wave-lengths of 725 or 620 nanometers. The state transitions were determined from measurements of fluorescence induction at room temperature, and fluorescence kinetics at 77 K. According to the obtained data (a) mobile LHCP is present only between the 6th and the 10th hour of the light-time of the cell cycle and (b) this functional relation of the LHCP to photosystem I only at this stage of Euglena chloroplast development is not accompanied by a decrease in stacking. A model for the organization of the newly inserted LHCP within the photosynthetic apparatus of E. gracilis is discussed.

Despite enormous potential for technological applications, fundamentals of stable non-equilibrium micro-plasmas at ambient pressure are still only partly understood. Micro-plasma jets are one sub-group of these plasma sources. For an understanding it is particularly important to analyse transport phenomena of energy and particles within and between the core and effluent of the discharge. The complexity of the problem requires the combination and correlation of various highly sophisticated diagnostics yielding different information with an extremely high temporal and spatial resolution. A specially designed rf microscale atmospheric pressure plasma jet (µ-APPJ) provides excellent access for optical diagnostics to the discharge volume and the effluent region. This allows detailed investigations of the discharge dynamics and energy transport mechanisms from the discharge to the effluent. Here we present examples for diagnostics applicable to different regions and combine the results. The diagnostics applied are optical emission spectroscopy (OES) in the visible and ultraviolet and two-photon absorption laser-induced fluorescence spectroscopy. By the latter spatially resolved absolutely calibrated density maps of atomic oxygen have been determined for the effluent. OES yields an insight into energy transport mechanisms from the core into the effluent. The first results of spatially and phase-resolved OES measurements of the discharge dynamics of the core are presented.

This thesis studies the formation mechanisms and the composition of Titan's aerosols analogs, so called tholins. The study of the gas phase allowed identifying several aerosols precursors, especially nitrogen-bearing species such as imines and nitriles. These species may be a first step on the gas to solid transition. The study of the infrared absorbance properties of tholins allowed providing for the first time the wavelength dependence of their linear absorption coefficient from far- to mid-infrared. The investigation on tholins chemical composition allowed to infer their polymeric structure and to detect a large amount of nitrogen in this structure. The last part of the thesis is dedicated to a comparison of the tholins chemistry induced by different energy sources. On a general way, this thesis proposes, when possible, the comparison between data obtained in the lab and actual observations of Titan's atmosphere., Cette thèse traite de l'étude des mécanismes de formation et de la composition d'équivalents d'aérosols de Titan, appelés tholins. L'étude de la phase gazeuse a permis d'identifier différents précurseurs d'aérosols, en particulier des espèces azotées telles que les imines et les nitriles, qui pourraient être un premier pas dans la transition gaz-solide. L'étude des propriétés infrarouge des tholins permet de fournir la dépendance en fonction de la longueur d'onde (du lointain au moyen infrarouge) de l'absorption des tholins. L'étude de la composition chimique des aérosols a permis de remonter à leur structure polymérique des tholins et de détecter la présence d'azote en grande quantité dans leur structure. La dernière partie de cette thèse comporte également une comparaison entre la chimie induite par différentes sources d'énergie De manière générale, cette thèse propose lorsqu'elle est possible une comparaison entre les données obtenues en laboratoire et les observations de Titan.