Modelling of laser ablation and reactive oxygen plasmas for pulsed laser deposition of zinc oxide

Pulsed laser deposition (PLD) in a low-pressure oxygen atmosphere is commonly used for the production of high-quality, stoichiometric zinc oxide thin films. An alternative approach that has the potential benefit of increased process control is plasma-enhanced PLD, i.e. the use of a low-temperature oxygen plasma instead of a neutral gas. So far, the development of PE-PLD, and PLD in general, has been hampered by a lack of detailed understanding of the underpinning physics and chemistry. In this paper, we present modelling investigations aimed at further developing such understanding. Two-dimensional modelling of an inductively-coupled radio-frequency oxygen plasma showed that densities of 1014–1015 cm− 3 of reactive oxygen species O and O2* can be produced for operating pressures between 3 and 100 Pa. Together with the absolute densities of species, also the ratio between different reactive species, e.g. O and O2*, can be controlled by changing the operating pressure. Both can be used to find the optimum conditions for stoichiometric zinc oxide thin film deposition. Additionally, we investigated laser ablation of zinc using a different two-dimensional hydrodynamic code (POLLUX). This showed that the amount of material that is ablated increases from 2.9 to 4.7 μg per pulse for laser fluences from 2 to 10 J/cm2. However, the increased laser fluence also results in an increased average ionisation of the plasma plume, from 3.4 to 5.6 over the same fluence range, which is likely to influence the chemistry near the deposition substrate and consequently the film quality

Изотопный состав подземных вод водосборного бассейна озера Поянху (Китай)

В статье приведены данные об изотопном составе ([delta]D, [delta]18O) подземных вод водосборного бассейна оз. Поянху. По соотношению изотопов [delta]D и [delta]18O определен генезис исследуемых вод, а также проанализировано возможное влияние испарительного концентрирования на формирование их состава. In the article data about isotopic composition ([delta]D, [delta]18O) of the Poyang Lake catchment groundwater is presented. Based on [delta]D and [delta]18O isotopes correlation genesis of the investigated groundwater and influence of evaporation to the groundwater composition are identified

The spatial density distribution of H2O2 in the effluent of the COST-Jet and the kINPen-sci operated with a humidified helium feed gas

Cold atmospheric plasma jets operated with a helium feed gas containing small admixtures of water vapour are excellent sources of H2O2 for direct biomedical applications. However, H2O2 is typically distributed non-uniformly throughout the effluent region, meaning the dosage received by a patient or substrate is dependent on their positioning relative to the plasma source. This study presents the spatial distribution of absolute H2O2 number densities in the effluent of two popular plasma jets, the COST-Jet and the kINPen-sci plasma jet, when operated with a humidified helium feed gas. The measurements were performed using continuous wave cavity ring-down spectroscopy with a tunable, mid-infrared laser. The H2O2 number density measured close to the jet nozzle is 2.3 × 1014 cm−3 for the kINPen-sci plasma jet and 1.4 × 1014 cm−3 for the COST-Jet. The average number density of H2O2 in the effluent of the kINPen-sci plasma jet is a factor of two higher than in the effluent of the COST-Jet. The distribution of H2O2 in the COST-Jet effluent is initially highly uniform and suggests negligible mixing of H2O2 with the ambient air up to 15 mm from the jet nozzle, although it is rapidly diluted at further distances. In the case of the kINPen-sci plasma jet, the number density of H2O2 has a more pronounced radial distribution close to the nozzle, while the mixing with the ambient air is more gradual at further distances from the nozzle. It is evident that a detailed understanding of the H2O2 production in the plasma source, as well as of the transport of H2O2 to the substrate through the effluent, is required in order to optimise the intended effects. This work serves to highlight the difference of the distinct spatial distribution of H2O2 in the effluent of both types of plasma jets when considering their direct application in biomedicine

Concepts and characteristics of the 'COST Reference Microplasma Jet'

Biomedical applications of non-equilibrium atmospheric pressure plasmas have attracted intense interest in the past few years. Many plasma sources of diverse design have been proposed for these applications, but the relationship between source characteristics and application performance is not well-understood, and indeed many sources are poorly characterized. This circumstance is an impediment to progress in application development. A reference source with well-understood and highly reproducible characteristics may be an important tool in this context. Researchers around the world should be able to compare the characteristics of their own sources and also their results with this device. In this paper, we describe such a reference source, developed from the simple and robust micro-scaled atmospheric pressure plasma jet (μ-APPJ) concept. This development occurred under the auspices of COST Action MP1101 'Biomedical Applications of Atmospheric Pressure Plasmas'. Gas contamination and power measurement are shown to be major causes of irreproducible results in earlier source designs. These problems are resolved in the reference source by refinement of the mechanical and electrical design and by specifying an operating protocol. These measures are shown to be absolutely necessary for reproducible operation. They include the integration of current and voltage probes into the jet. The usual combination of matching unit and power supply is replaced by an integrated LC power coupling circuit and a 5 W single frequency generator. The design specification and operating protocol for the reference source are being made freely available

Controlled production of atomic oxygen and nitrogen in a pulsed radio-frequency atmospheric-pressure plasma

International audienceRadio-frequency driven atmospheric pressure plasmas are efficient sources for the production of reactive species at ambient pressure and close to room temperature. Pulsing the radio-frequency power input provides additional control over species production and gas temperature. Here, we demonstrate the controlled production of highly reactive atomic oxygen and nitrogen in a pulsed radio-frequency ( ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn001.gif] 13.56 MHz) atmospheric-pressure plasma, operated with a small ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn002.gif] 0.1 % air-like admixture ( ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn003.gif] \rm N_2 / ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn004.gif] \rm O_2 at ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn005.gif] 4:1 ) through variations in the duty cycle. Absolute densities of atomic oxygen and nitrogen are determined through vacuum-ultraviolet absorption spectroscopy using the DESIRS beamline at the SOLEIL synchrotron coupled with a high resolution Fourier-transform spectrometer. The neutral-gas temperature is measured using nitrogen molecular optical emission spectroscopy. For a fixed applied-voltage amplitude (234?V), varying the pulse duty cycle from 10% to 100% at a fixed 10?kHz pulse frequency enables us to regulate the densities of atomic oxygen and nitrogen over the ranges of ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn006.gif] (0.18±0.03) ? ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn007.gif] (3.7±0.1)× 10^20 ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn008.gif] \rm m^-3 and ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn009.gif] (0.2±0.06) ? ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn010.gif] (4.4±0.8) × 10^19 ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn011.gif] \rm m^-3 , respectively. The corresponding 11?K increase in the neutral-gas temperature with increased duty cycle, up to a maximum of ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn012.gif] (314±4) K, is relatively small. This additional degree of control, achieved through regulation of the pulse duty cycle and time-averaged power, could be of particular interest for prospective biomedical applications

Comparative study on the dynamics and the composition between a pulsed laser deposition (PLD) and a plasma enhanced PLD (PE-PLD)

We report the effect of single and dual radio frequency (RF) plasma discharge on the composition and dynamics of a titanium plasma plume produced in a plasma-enhanced pulsed laser deposition (PE-PLD) system. The study was carried out in a nitrogen environment at different pressures. Time-resolved images, optical emission spectroscopy, and interferometry were employed to analyze the plasma. We were able to fit time-resolved images using different expansion models, obtained an expansion velocity between 6 and 30 x 103 m/s. Emission lines from N II, Ti II, were observed by changing the pressure and RF conditions. An increase in emission line intensity from N II was observed by increasing the pressure and RF power. We used Ti II lines to estimate the plasma temperature by using the Boltzmann equation, and we obtained the density from the Ti II line (454.9 nm) through Stark broadening. In addition, a Mach-Zehnder interferometer was employed to make a two-dimensional map of the electron density at early times. The estimated temperatures and densities are between 0.8 - 2.0 eV and 1017 – 1018 cm-3, respectively. The results suggest that increasing RF power enhanced the Ti-N atoms interaction, which is crucial in titanium nitride film applications

NDUFS4 deletion triggers loss of NDUFA12 in Ndufs4−/− mice and Leigh syndrome patients: A stabilizing role for NDUFAF2

Mutations in NDUFS4, which encodes an accessory subunit of mitochondrial oxidative phosphorylation (OXPHOS) complex I (CI), induce Leigh syndrome (LS). LS is a poorly understood pediatric disorder featuring brain-specific anomalies and early death. To study the LS pathomechanism, we here compared OXPHOS proteomes between various Ndufs4−/− mouse tissues. Ndufs4−/− animals displayed significantly lower CI subunit levels in brain/diaphragm relative to other tissues (liver/heart/kidney/skeletal muscle), whereas other OXPHOS subunit levels were not reduced. Absence of NDUFS4 induced near complete absence of the NDUFA12 accessory subunit, a 50% reduction in other CI subunit levels, and an increase in specific CI assembly factors. Among the latter, NDUFAF2 was most highly increased. Regarding NDUFS4, NDUFA12 and NDUFAF2, identical results were obtained in Ndufs4−/− mouse embryonic fibroblasts (MEFs) and NDUFS4-mutated LS patient cells. Ndufs4−/− MEFs contained active CI in situ but blue-native-PAGE highlighted that NDUFAF2 attached to an inactive CI subcomplex (CI-830) and inactive assemblies of higher MW. In NDUFA12-mutated LS patient cells, NDUFA12 absence did not reduce NDUFS4 levels but triggered NDUFAF2 association to active CI. BN-PAGE revealed no such association in LS patient fibroblasts with mutations in other CI subunit-encoding genes where NDUFAF2 was attached to CI-830 (NDUFS1, NDUFV1 mutation) or not detected (NDUFS7 mutation). Supported by enzymological and CI in silico structural analysis, we conclude that absence of NDUFS4 induces near complete absence of NDUFA12 but not vice versa, and that NDUFAF2 stabilizes active CI in Ndufs4−/− mice and LS patient cells, perhaps in concert with mitochondrial inner membrane lipids

Laboratory measurements of resistivity in warm dense plasmas relevant to the microphysics of brown dwarfs

Since the observation of the first brown dwarf in 1995, numerous studies have led to a better understanding of the structures of these objects. Here we present a method for studying material resistivity in warm dense plasmas in the laboratory, which we relate to the microphysics of brown dwarfs through viscosity and electron collisions. Here we use X-ray polarimetry to determine the resistivity of a sulphur-doped plastic target heated to Brown Dwarf conditions by an ultra-intense laser. The resistivity is determined by matching the plasma physics model to the atomic physics calculations of the measured large, positive, polarization. The inferred resistivity is larger than predicted using standard resistivity models, suggesting that these commonly used models will not adequately describe the resistivity of warm dense plasma related to the viscosity of brown dwarfs

Exotic dense-matter states pumped by a relativistic laser plasma in the radiation-dominated regime

In high-spectral resolution experiments with the petawatt Vulcan laser, strong x-ray radiation of KK hollow atoms (atoms without n = 1 electrons) from thin Al foils was observed at pulse intensities of 3 x 10(20) W/cm(2). The observations of spectra from these exotic states of matter are supported by detailed kinetics calculations, and are consistent with a picture in which an intense polychromatic x-ray field, formed from Thomson scattering and bremsstrahlung in the electrostatic fields at the target surface, drives the KK hollow atom production. We estimate that this x-ray field has an intensity of >5 x 10(18) W/cm(2) and is in the 3 keV range