High Ionization Levels Research Articles

Sensitivity Analysis of Ionization in Two-Temperature Models of Hypersonic Air Flows

Plasma generation in hypersonic flows is analyzed using a two-temperature model of nonequilibrium air. The uncertainties in electron number density predictions are assessed for flow scenarios that correspond to both strongly shocked and strongly expanded flows, and the dependencies of the calculated uncertainties on individual input parameters are quantified. Ionization levels behind 5 and 7 km/s normal shocks are found to be most sensitive to the associative ionization reactions producing O2+ and NO+ in the region of peak electron number density, with nitric oxide kinetics dominating the uncertainty downstream. The higher levels of ionization behind a 9 km/s shock are found to strongly depend on the electron impact ionization of atomic nitrogen as well as the charge exchange between N2+ and N. Recombining flow scenarios depend on many of the same processes that influence the shocked flows, with the notable addition of the reassociation reaction O++N2↔NO++N, which is responsible for large uncertainties in electron number density in net recombining flows. The results provide valuable insight into the typical magnitude of uncertainty associated with plasma formation predictions in hypersonic flows and identify the parameters that should be targeted in efforts to reduce those uncertainties.

Design and Study of a Large-Scale Microwave Plasma Torch with Four Ports

The microwave plasma torch (MPT) has gained popularity in industrial applications due to its high energy density, ionization levels, and high temperature. However, the non-uniform and unstable plasma generated by microwave plasma sources has limited the production of large-scale MPTs. This paper proposes a novel MPT device utilizing a four-port microwave source (2.45 GHz, 4 kW) to address these issues. The improved plasma uniformity and stability are achieved through the new structure, and the microwave efficiency is enhanced by introducing the focusing dielectric in the coupled cavity. Using a 3D electromagnetic field model, microwave plasma model and fluid model, the paper optimizes the geometry and inlet mode of the MPT device. Experimental results show that the novel MPT device can generate a plasma torch with a maximum height of 545 mm, a working range of 10–95 L/min, and a microwave efficiency up to 86%. The proposed device not only competently meets industrial requirements, but also provides design ideas and methods for future MPT devices.

Effect of electron number densities on the radio signal propagation in an inductively coupled plasma facility

Spacecraft entering a planetary atmosphere are surrounded by a plasma layer containing high levels of ionization, due to the extreme temperatures in the shock layer. The high electron number densities cause attenuation of the electromagnetic waves emitted by the on-board antennas, leading to communication blackout for several minutes. This work presents experimental measurements of signal propagation through an ionized plasma flow. The measurements are conducted at the VKI plasma wind tunnel (Plasmatron) using conical horn antennas transmitting in the Ka-band, between 33 and 40 GHz. Testing conditions at 15, 50 and 100 mbar, and powers between 100 and 600 kW cover a broad range of the testing envelope of the Plasmatron as well as a broad range of atmospheric entry conditions. The transmitting antenna is characterized at the UPC anechoic chamber, obtaining the radiation patterns, beamwidth, and gain at the boresight direction; and an optical ray tracing technique is used to describe the electromagnetic waves propagation in the plasma flowfield inside of the Plasmatron chamber. The signal propagation measurements show clear attenuation when the signal is propagating through the plasma, varying between 2 and 15 dB depending on the testing conditions. This attenuation increases with electron number densities, which are driven by the Plasmatron power and pressure settings. Preliminary evidence of Faraday rotation effects caused by the plasma is also observed.

Modelling of Nonthermal Dielectric Barrier Discharge Plasma at Atmospheric Pressure and Role of Produced Reactive Species in Surface Polymer Microbial Purification

A nonthermal atmospheric plasma reactor was used to sterilize polymer surfaces and satisfy safety constraints in a biological medium. A 1D fluid model was developed using COMSOL Multiphysics software® 5.4 with a helium-oxygen mixture at low temperature for the decontamination of bacteria on polymer surfaces. An analysis of the evolution of the homogeneous dielectric barrier discharge (DBD) was carried out through studying the dynamic behavior of the discharge parameters including the discharge current, the consumed power, the gas gap voltage, and transport charges. In addition, the electrical characteristics of a homogeneous DBD under different operating conditions were studied. The results shown that increasing voltage or frequency caused higher ionization levels and maximum increase of metastable species' density and expanded the sterilization area. On the other hand, it was possible to operate plasma discharges at a low voltage and a high density of plasma using higher values of the secondary emission coefficient or permittivity of the dielectric barrier materials. When the discharge gas pressure increased, the current discharges declined, which indicated a lower sterilization efficiency under high pressure. A short gap width and the admixture of oxygen were needed for sufficient bio-decontamination. Plasma-based pollutant degradation devices could therefore benefit from these results.

3D CFD modeling of flowing-gas Rb DPALs: effects of buffer gas composition and of ionization of high lying Rb states

A comprehensive three-dimensional computational fluid dynamics (3D CFD) modeling of flowing-gas Rb diode pumped alkali laser (DPAL) is carried out. The cases of H e / C H 4 and pure He buffer gases are investigated, and the output power and optical efficiency are calculated for various pump powers, mole fractions of methane, buffer gas pressures, and flow velocities. The model considers the processes of excitation of high levels of Rb, ionization, ion-electron recombination, and heating of electrons, which affect the diffusion coefficient of Rb ions. Two types of Rb DPAL were studied: a low-power laboratory-scale device with pump power of several tens of watts and a high-power multi-kilowatt laser. Efficient operation of the Rb laser using pure He as buffer gas can be achieved only in a large-scale laser with a pump beam cross-sectional area of several c m 2 . The calculated results for such a device were compared with those reported by Gavrielides et al. [J. Opt. Soc. Am. B 35, 2202 (2018)JOBPDE0740-322410.1364/JOSAB.35.002202], where a simplified three-level model based on the one-dimensional gas dynamics approach was applied.

Investigation of the Physical Processes Involved in GNSS Amplitude Scintillations at High Latitude: A Case Study

The storm onset on 7 September 2017, triggered several variations in the ionospheric electron density, causing severe phase fluctuations at polar latitudes in both hemispheres. In addition, although quite rare at high latitudes, clear amplitude scintillations were recorded by two Global Navigation Satellite System receivers during the main phase of the storm. This work attempted to investigate the physical mechanisms triggering the observed amplitude scintillations, with the aim of identifying the conditions favoring such events. We investigated the ionospheric background and other conditions that prevailed when the irregularities formed and moved, following a multi-observations approach. Specifically, we combined information from scintillation parameters and recorded by multi-constellation (GPS, GLONASS and Galileo) receivers located at Concordia station (75.10°S, 123.35°E) and SANAE IV base (71.67°S, 2.84°W), with measurements acquired by the Special Sensor Ultraviolet Spectrographic Imager on board the Defense Meteorological Satellite Program satellites, the Super Dual Auroral Radar Network, the Swarm constellation and ground-based magnetometers. Besides confirming the high degree of complexity of the ionospheric dynamics, our multi-instrument observation identified the physical conditions that likely favor the occurrence of amplitude scintillations at high latitudes. Results suggest that the necessary conditions for the observation of this type of scintillation in high-latitude regions are high levels of ionization and a strong variability of plasma dynamics. Both of these conditions are typically featured during high solar activity.

A broad absorption line outflow associated with the broad emission line region in the quasar SDSS J075133.35+134548.3

We report on the discovery of unusual broad absorption lines (BALs) in the bright quasar SDSS J075133.35+134548.3 at z ∼ 1, using archival and newly obtained optical and NIR spectroscopic data. The BALs are detected reliably in He i* λ3889, He i* λ10830 and tentatively in Al iii, Mg ii. These BALs show complex velocity structures consisting of two major components: a high-velocity component (HV), with a blueshifted velocity range of Δv HV ∼ −9300 − −3500 km s−1, which can be reliably detected in He i* λ10830, and tentatively in Al iii and Mg ii, whereas it is undetectable in He i* λ3889 and a low-velocity component (LV), with Δ v LV ∼ −3500 − −1800 km s−1, is only detected in He i* and He i* λ10830. With the BALs from different ions, the HV outflowing gas can be constrained to have a density of n H ∼1010.3–1011.4 cm−3, a column density of N H ∼ 1021 cm−2 and an ionization parameter of U ∼10−1.83–10−1.72; inferring a distance of R HV∼0.5 pc from the central continuum source with a monochromatic luminosity λ Lλ (5100) = 7.0×1045 erg s−1 at 5100 Å. This distance is remarkably similar to that of the normal broad line region (BLR) estimated from reverberation experiments, suggesting association of the BLR and the HV BAL outflowing gas. Interestingly, a blueshifted component is also detected in Al iii and Mg ii broad emission lines (BELs), and the Al iii/Mg ii of such a BEL component can be reproduced by the physical parameters inferred from the HV BAL gas. The LV BAL gas likely has a larger column density, a higher ionization level and hence a smaller distance than the HV BAL gas. Further spectroscopy with a high S/N ratio and broader wavelength coverage is needed to confirm this to shed new light on the possible connection between BALs and BELs.

Synthesis of novel core@shell of MgAl layered double hydroxide @ porous magnetic shell (MgAl-LDH@PMN) as carrier for ciprofloxacin drug

MgAl-layered double hydroxide (MgAl-LDH) derived from a metal-organic framework (MOF), was synthesized by hydrothermal method. A biocompatible MgAl-LDH core-porous magnetic nanoparticles (PMN) shell (MgAl-LDH@PMN) was synthesized using solvothermal method and modified with amino groups as a potential pH-controlled drug delivery carrier. MgAl-LDH with a sheet-like morphology was coated with porous Fe3O4 or porous magnetite via the functionalization of (3-aminopropyl) triethoxysilane using a post-synthesis route (MgAl-LDH@PMN-NH2). The core@shell was characterized using a range of techniques such as x-ray diffraction patterns (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic light scattering (DLS) and transmission electron microscopy (TEM). The MgAl-LDH@PMN-NH2 core@shell indicated a spherical morphology and good porosity. Ciprofloxacin (CIPRO) drug was incorporated in the pore channels and surface of the MgAl-LDH@PMN-NH2 and the drug release properties were examined at pH 4.0 and 7.4. The TG results demonstrated that drug loading contents on the modified carrier was 40%. The delayed release property exhibited by MgAl-LDH@PMN-NH2 was attributed to the strong interactions of the drug molecules with the surface amino-functionality and the charged LDH surface. The characterization and drug release was also investigated for the un-modified carrier (MgAl-LDH@PMN) with drug loading 15% under identical conditions. The porosity and functionalization of the PMN shell and the surface charge density of the layered structure of MgAl-LDH are the major reasons for the controlled release of the CIPRO drug. Moreover, the favorable delay in drug release from both core@shells at pH 4 was attributed to the high level of ionization and dissolution. Biocompatibility was evaluated by examination of the cell line MCF-7 response to the un-modified and modified carriers.

Lyman continuum escape fraction and mean free path of hydrogen ionizing photons for brightz∼ 4 QSOs from SDSS DR14

Context.One of the main challenges in observational cosmology is related to the redshift evolution of the average hydrogen (HI) ionization in the Universe, as evidenced by the changing in ionization level of the intergalactic medium (IGM) through cosmic time. Starting from the first cosmic reionization, the rapid evolution of the IGM physical properties in particular poses severe constraints for the identification of the sources responsible for maintaining its high level of ionization up to lower redshifts.Aims.In order to probe the ionization level of the IGM and the ionization capabilities of bright quasi-stellar objects (QSOs) atz = 4, we selected a sample of 2508 QSOs drawn from the Sloan Digital Sky Survey (SDSS, DR14) in the redshift interval 3.6 ≤ z ≤ 4.6 and absolute magnitude range −29.0 ≲ M1450 ≲ −26.0. Particularly, we focus on the estimate of the escape fraction of HI-ionizing photons and their mean free path (MFP), which are fundamental for characterizing the surrounding IGM.Methods.Starting from UV/optical rest-frame spectra of the whole QSO sample from the SDSS survey, we estimated the escape fraction and free path individually for each of the QSOs. We calculated the Lyman continuum (LyC) escape fraction as the flux ratio blueward (∼900 Å rest frame) and redward (∼930 Å rest frame) of the Lyman limit. We then obtained the probability distribution function (PDF) of the individual free paths of the QSOs in the sample and studied its evolution in luminosity and redshift, comparing our results with those in literature.Results.We find a lower limit to the mean LyC escape fraction of 0.49, in agreement with the values obtained for both brighter and fainter sources at the same redshift. We show that the free paths of ionizing photons are characterized by a skewed distribution function that peaks at low values, with an average of ∼49 − 59 proper Mpc atz ∼ 4, after possible associated absorbers (AAs) were excluded. This value is higher than the one obtained at the same redshift by many authors in the literature using different techniques. Moreover, the PDF of free path gives information that is complementary to the MFP derived through the stacking technique. Finally, we also find that the redshift evolution of this parameter might be milder than previously thought.Conclusions.Our new determination of the MFP atz ∼ 4 implies that previous estimates of the HI photoionization rate ΓHIavailable in the literature should be corrected by a factor of 1.2−1.7. These results have important implications when they are extrapolated at the epoch of reionization.

To be or not to be: the case of the hot WHIM absorption in the blazar PKS 2155–304 sight line

The cosmological missing baryons at z < 1 most likely hide in the hot (T ≳ 105.5 K) phase of the warm hot intergalactic medium (WHIM). While the hot WHIM is hard to detect due to its high ionisation level, the warm (T ≲ 105.5 K) phase of the WHIM has been very robustly detected in the far-ultraviolet (FUV) band. We adopted the assumption that the hot and warm WHIM phases are co-located and therefore used the FUV-detected warm WHIM as a tracer for the cosmologically interesting hot WHIM. We performed an X-ray follow-up in the sight line of the blazar PKS 2155–304 at the redshifts where previous FUV measurements of O VI, Si IV, and broad Lyman-alpha (BLA) absorption have indicated the existence of the warm WHIM. We looked for the O VII Heα and O VIII Lyα absorption lines, the most likely hot WHIM tracers. Despite the very large exposure time (≈1 Ms), the Reflection Grating Spectrometer unit 1 (RGS1) on-board XMM-Newton data yielded no significant detection which corresponds to upper limits of log N(O VII(cm−2)) ≤ 14.5−15.2 and log N(O VIII(cm−2)) ≤ 14.5−15.2. An analysis of the data obtained with the combination of the Low Energy Transmission Grating (LETG) and the High Resolution Camera (HRC) on-board Chandra yielded consistent results. However, the data obtained with the LETG, combined with the Advanced CCD Imaging Spectrometer (ACIS) lead to the detection of an feature resembling an absorption line at λ ≈ 20 Å at simple one-parameter confidence level of 3.7σ, consistent with several earlier LETG/ACIS reports. Given the high statistical quality of the RGS1 data, the possibility of RGS1 accidentally missing the true line at λ ∼ 20 Å is very low: 0.006%. Neglecting this, the LETG/ACIS detection can be interpreted as Lyα transition of O VIII at one of the redshifts (z ≈ 0.054) of FUV-detected warm WHIM. Given the very convincing X-ray spectral evidence for and against the existence of the λ ∼ 20 Å feature, we cannot conclude whether or not it is a true astrophysical absorption line. Considering cosmological simulations, the probability of the LETG/ACIS λ ∼ 20 Å feature being due to the astrophysical O VIII absorber co-located with the FUV-detected O VI absorber is at the very low level of ≲0.1%. We cannot completely rule out the very unlikely possibility that the LETG/ACIS 20 Å feature is due to a transient event located close to the blazar.

Al2O3 thin films deposition by reactive evaporation of Al in anodic arc with high levels of metal ionization

The results of studying the parameters of the plasma generated in an arc with a self-heating hollow cathode and a vaporizable anode placed in a magnetic field of two oppositely connected solenoids are presented. Compression of the discharge column in an inhomogeneous magnetic field provides an increase in power density on the surface of the crucible anode to ~1 kW/cm2 and an increase in the degree of ionization of the metal vapor to 50–80%. Using the method of reactive evaporation of aluminum in the Ar/О2 gas mixture we obtained Al2O3 coatings at the rate of 4–8 μm/h under an ion current density of 6–11 mA/cm2, a bias voltage of 50–200 V, and a temperature of 620 °С. It is shown that, with an increase in the ion current density and ion energy, the fraction of the α-phase in the Al2O3 coating increases to 100%. The single-phase α-Al2O3 coatings are characterized by the predominant orientation of crystallites (300).

Experimental study of H<sub>2</sub>SO<sub>4</sub> aerosol nucleation at high ionization levels

Abstract. One hundred and ten direct measurements of aerosol nucleation rate at high ionization levels were performed in an 8 m3 reaction chamber. Neutral and ion-induced particle formation from sulfuric acid (H2SO4) was studied as a function of ionization and H2SO4 concentration. Other species that could have participated in the nucleation, such as NH3 or organic compounds, were not measured but assumed constant, and the concentration was estimated based on the parameterization by Gordon et al. (2017). Our parameter space is thus [H2SO4] =4×106-3×107 cm−3, [NH3+ org] = 2.2 ppb, T=295 K, RH = 38 %, and ion concentrations of 1700–19 000 cm−3. The ion concentrations, which correspond to levels caused by a nearby supernova, were achieved with gamma ray sources. Nucleation rates were directly measured with a particle size magnifier (PSM Airmodus A10) at a size close to critical cluster size (mobility diameter of ∼ 1.4 nm) and formation rates at a mobility diameter of ∼ 4 nm were measured with a CPC (TSI model 3775). The measurements show that nucleation increases by around an order of magnitude when the ionization increases from background to supernova levels under fixed gas conditions. The results expand the parameterization presented in Dunne et al. (2016) and Gordon et al. (2017) (for [NH3+org] = 2.2 ppb and T=295 K) to lower sulfuric acid concentrations and higher ion concentrations. The results make it possible to expand the parameterization presented in Dunne et al. (2016) and Gordon et al. (2017) to higher ionization levels.

Measurement of the charging state of 4–70 nm aerosols

The charging state of aerosols in an 8m3 reaction chamber was measured using an electrostatic classifier with a condensation particle counter at different levels of ionization in the chamber. By replacing the Kr-85 neutralizer in the classifier with a radioactively neutral dummy we were able to measure only the aerosols that were charged inside our reaction chamber. These measurements were then compared with measurements using the neutralizer to get the charging state of the aerosols, which refers to the charged fraction of the aerosols compared to an equilibrium charge distribution. Charging states were measured for both positively and negatively charged aerosols while the ionization in the chamber was varied using external gamma sources. We find that the negatively charged aerosols were overcharged (relative to the equilibrium) by up to about a factor of 10 below 10nm and at 16±2% from 10 to 70nm. At higher levels of radiation on the chamber the smaller aerosols were less overcharged while the large aerosols were more overcharged (23±2%). For the positively charged aerosols only the smallest aerosols were overcharged while those over 10nm were undercharged (relative to the equilibrium) by 21±3%. Increasing the radiation on the chamber increased the undercharge above 10nm to 25±2% while the overcharge below 10nm disappeared. The split between positive and negative charges above 10nm can be explained by differences in mobility of small negative and positive ions. The overcharge below 10nm can be explained by ions participating in the formation of aerosols of both signs, while the reduction in this overcharge at higher levels of ionization may be explained by faster recombination.

Study of spatial distributions of highly ionized nonequilibrium helium plasma at atmospheric pressures

Experimental study of helium plasma in the state of quasistationary heating under atmospheric pressure was made. The plasma state is shown to fail to be described by Saha- Boltzmann approximation at high ionization levels αi = 0.5-0.9, temperatures 2.5-4.0 eV and electron concentrations about 1017 cm-3. The deviation from the equilibrium state of the plasma is caused by lack of spatial uniformity due to charged particles loss by ambipolar diffusion. In order to thoroughly study the temporal changes of plasma radiation characteristics, spectroscopic analysis was carried out with DFS-452 spectrometer and high-speed CMOS camera Andor iStar attached to its output. The system yields the spatial resolution of 30-50 μm and temporal resolution of 5-50 μs. Electron concentration ne was measured from the half-width of the local Hei spectrum line contours having dominant quadruple Stark effect with well-known constants. In order to determine the temperature of heavy particles, Doppler component of HeI line triplet at 1083 nm was studied. The temporal evolution of the following important characteristics has been determined for helium plasma during pulsed heating: current power, intensities of a number of HeI and HeII spectral lines, electron temperatures and concentrations.

Physical limitations in ferromagnetic inductively coupled plasma sources

The ferromagnetic inductively coupled plasma (FICP) source, which is a version of the common inductively coupled plasma sources, has a number of well known advantages such as high efficiency, high level of ionization, low minimal gas pressure, very low required driver frequency, and even a possibility to be driven by single current pulses. We present an experimental study of such a FICP source which showed that above a certain value of the driving pulsed power the properties of this device changed rather drastically. Namely, the plasma became non-stationary and non-uniform contrary to the stationary and uniform plasmas typical for this kind of plasma sources. In this case, the plasma appeared as a narrow dense spike which was short compared to the driving pulse. The local plasma density could exceed the neutral atoms density by a few orders of magnitude. When that happened, the afterglow plasma decay time after the end of the pulse was long compared to an ordinary case with no plasma spike. Experiments were performed with various gases and in a wide range of pressures which enabled us to understand the physical mechanism and derive the parameters responsible for such plasma behavior. A qualitative model of this phenomenon is discussed.

A VLT VIMOS IFU study of the ionisation nebula surrounding the supersoft X-ray source CAL 83

CAL83 is a prototype of the class of Super Soft X-ray Sources (SXS). It is a binary consisting of a low mass secondary that is transferring mass onto a white dwarf primary and is the only known SXS surrounded by an ionisation nebula, made up of the interstellar medium (ISM) ionised by the source itself. With the VIMOS IFU we obtained spectra over a 25\times25" field of view, encompassing one quarter of the nebula. Emission line maps - H I, He II, [O III], [N II], and [S II] - are produced in order to study the morphology of the ionised gas. We include CAL83 on diagrams of various diagnostic ion ratios to compare it to other X-ray ionised sources. Finally we computed some simple models of the ionised gas around CAL83 and compare the predicted to the observed spectra. CAL83 appears to have a fairly standard ionisation nebula as far as the morphology goes: the edges where H is recombining are strong in the low stage ionisation lines and the central, clumpy regions are stronger in the higher stage ionisation lines. But the He II emission is unusual in being confined to one side of CAL83 rather than being homogeneously distributed as with the other ions. We model the CAL83 nebula with cloudy using model parameters for SXSs found in the literature. The He II emission does not fit in with model predictions; in fact none of the models is able to fit the observed spectrum very well. The spectral line images of the region surrounding CAL83 are revealing and instructive. However, more modelling of the spectrum of the ionised gas is necessary, and especially for the high-ionisation level emission from CAL83. In particular, we wish to know if the He II emission and the other nebular lines are powered by the same ionising source.

Interaction of nanosecond laser pulse with tetramethyl silane (Si(CH3)4) clusters: Generation of multiply charged silicon and carbon ions

Present work reports significantly high levels of ionization, eventually leading to Coulomb explosion of Tetramethyl silane (TMS) clusters, on interaction with laser pulses of intensity ∼109 W/cm2. Tetramethyl silane clusters, prepared by supersonic expansion were photoionized at 266, 355 or 532 nm and the resultant ions were detected using time-of-flight mass spectrometer. It is observed that wavelength of irradiation and the size of the cluster are crucial parameters which drastically affect the nature of charge species generated upon photoionization of cluster. The results show that clusters absorb significantly higher energy from the laser field at longer wavelengths (532 nm) and generate multiply charged silicon and carbon ions which have large kinetic energies. Further, laser-cluster interaction at different wavelengths has been quantified and charge densities at 266, 355 and 532 nm are found to be 4x 1010, 5x 1010 and 5x 1011 charges/cm3 respectively. These unusual results have been rationalized based on dominance of secondary ionization processes at 532 nm ultimately leading to Coulomb explosion of clusters. In another set of experiments, multiply charged ions of Ar (up to +5 state) and Kr (up to +6 state) were observed when TMS doped inert gas clusters were photoionized at 532 and 355 nm. The extent of energy absorption at these two wavelengths is clearly manifested from the charge state of the atomic ions generated upon Coulomb disintegration of the doped cluster. These experiments thus demonstrate a novel method for generation of multiply charged atomic ions of inert gases at laser intensity of ∼ 109 W/cm2. The average size of the cluster exhibiting Coulomb explosion phenomena under giga watt intensity conditions has been estimated to be ∼ 6 nm. Experimental results obtained in the present work agree qualitatively with the model proposed earlier [D. Niu, H. Li, F. Liang, L. Wen, X. Luo, B. Wang, and H. Qu, J. Chem. Phys. 122, 151103(2005)] and point towards interaction of quasi-free electrons, generated during primary multiphoton ionization step, with a given wavelength in the presence of Coulombic field.

Formation of light-emitting nanostructures in layers of stoichiometric SiO2 irradiated with swift heavy ions

Thermally grown SiO2 layers have been irradiated with 700-MeV Bi ions with doses of (3–10) × 1012 cm−2. It is found that, even after a dose of 3 × 1012 cm−2, a photoluminescence band in the region of 600 nm appears. Its intensity levels off at a dose of ∼5 × 1012 cm−2. The nature of the emission centers is studied by the methods of infrared transmission, Raman scattering, X-ray photoelectron spectroscopy, ellipsometry, and the reaction to passivating low-temperature anneals. It is established that irradiation brings about a decrease in the number of Si-O bonds with a relevant increase in the Si-Si bonds. It is assumed that the photoluminescence is caused by nanostructures containing an excess Si and/or having a deficit of O. The reaction of reduction of SiO2 proceeds in ion tracks due to high levels of ionization and heating within these tracks. The dose dependence is used to estimate the diameter of a track at 8–9 nm.

Nanostructured hard coatings deposited by cathodic arc deposition: From concepts to applications

The vacuum cathodic arc deposition (CAD) process is now widely used on an industrial scale to prepare protective hard coatings on cutting tools, metal molds, etc.… It has been recognized that high ionization levels of cathodic arc discharges and high ion energy can provide advantages such as enhanced adhesion required for mechanical applications involving high loads. CAD allows deposition of a wide range of hard compounds as nitrides or carbonitrides. However, CAD is also often associated macrodroplet generation that degrades the surface roughness of coatings. The recent trend is to develop advanced nanostructured hard coatings in order to enhance properties as hardness, toughness, and oxidation resistance. This paper recalls the basic aspects of both CAD technology and nanostructured thin films synthesis. Deposition and characterization of both nanocomposite and nanolayered hard coatings are described. Mechanical behaviors of nitrides can be significantly enhanced by nanolayering. The first example deals with the development of hard nanolayered nitrides coatings for cutting tools protection. It is clearly shown in this example that TiN/AlTiN coatings perform better than CrN/AlTiN and TiN/CrN for the same periods and the best performance is reached for the thinnest periods. It is also shown, in a second example, how silicon addition in CrN can lead to enhancement of oxidation resistance associated with the nanocomposite structure. Thus, relationships are established between deposition conditions, nanostructure and mechanical behaviors or oxidation resistance of the coatings. This short review recalls that CAD remains a powerful and industrial technology for nanostructured hard coatings deposition.

$\hbox{CrN}_{\rm x}$ Films Prepared by DC Magnetron Sputtering and High-Power Pulsed Magnetron Sputtering: A Comparative Study

CrN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> (0 ≤ x ≤ 0.91) films synthesized using high-power pulsed magnetron sputtering, also known as high-power impulse magnetron sputtering (HiPIMS), have been compared with those made by conventional direct-current (dc) magnetron sputtering (DCMS) operated at the same average power. The HiPIMS deposition rate relative to the DCMS rate was found to decrease linearly with increasing emission strength from the Cr ions relative to Cr neutrals, in agreement with the predictions of the target-pathway model. The low deposition rate in HiPIMS is thus a direct consequence of the high ionization level (~56%) of the target material and effective capturing of Cr ions by the cathode potential. Although the HiPIMS deposition rate did not exceed 40% of the DCMS rate, the drop in the relative deposition rate upon increasing the N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -to-Ar flow ratio, f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N2/Ar</sub> , was found to be similar for both sputtering techniques. Films prepared by HiPIMS contained similar amounts of atomic nitrogen as the dc-sputtered samples grown at the same f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N2/Ar</sub> indicating that the nitride formation at the substrate takes place mostly during the time period of the high-power pulses, and the N2 uptake between the pulses is negligible. The microstructure evolution in the two types of CrN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> films, however, differed clearly from each other. A combination of a high substrate bias and a high flux of doubly charged Cr ions present during the HiPIMS discharge led to a disruption of the grain growth and renucleation, which resulted in column-free films with nanosized grains not observed in the conventional DCMS-based process. The comparison of nanoindentation hardness as a function of f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N2/Ar</sub> revealed superior properties of HiPIMS-sputtered films in the entire range of gas compositions.