Cluster model of aluminum dense vapor plasma

The chemical model of aluminum vapor plasma, that take into account the formation of neutral and charged clusters, is suggested. Caloric and thermal equations of state and composition of plasma were received using the available information about properties of metal clusters. It is shown, that aluminum vapors are clusterized with decrease of temperature and with increase of density. Pressure dependence on internal energy is calculated and comparison with experimental data is made. The important role of aluminum clusters, especially in an initial phase of the metals vapor heating, is demonstrated. It is shown, that the region of plasma clusterization in gaseous phase agree with known literature data for binodal of vapor-liquid transition from gaseous region. Suggested cluster model may be used to forecast the location of metal vapors binodal. The conductivity of aluminum vapor plasma was calculated. The satisfactory agreement with available experimental data is received.     

Dust particles in collisionless plasma sheath with arbitrary electron energy distribution function

Dust particles often appear in industrial plasmas as undesirable product of the plasma-wall interactions. Large particles of several micrometers in diameter are concentrated in a thin layer (the sheath) above the lower electrode of the rf driven parallel plate device, where the electric force is strong enough to compensate particle’s gravity. Experimental and theoretical uncertainties are significantly increased in the plasma sheath. Common models of dust charging in the plasma sheath suppose the Maxwellian electron energy distribution function (EEDF) in conjunction with a flux of cold ions satisfying classical Bohm criterion at the sheath edge. In this paper we generalize this model to arbitrary EEDF with adapted Bohm criterion. We limit our considerations to collisionless or slightly collisional plasma, where the EEDF inside the sheath is expressed through the EEDF in the plasma bulk. Derived theoretical formulas are incorporated into numerical model, describing collisionless radio frequency (rf) plasma sheath together with the electrical charge, various kinds of forces, balancing radius and oscillation frequency of particles.     

Potential formation in a bounded two-electron temperature plasma system with floating collector that emits electrons

Formation of the plasma potential in a plasma that contains energetic electrons and is bounded by a floating collector that emits electrons is studied theoretically. The problem is treated by a static. kinetic plasma-sheath model of Schwager and Birdsall [Phys. Fluids B2 (1990) 1057], which we have extended in order to include additional energetic electron population. The distribution of these electrons is assumed to be a high-temperature Maxwellian. They are called hot electrons. In the paper we study effects of the density and temperature of the hot electrons on the formation of the plasma potential. The model shows that for certain densities and temperatures of the hot electron population plasmas with two different plasma potentials can coexist in the system. These two plasmas are separated spatially by a double layer. For the case when there is no emission of electrons from the collector, results of the model are compared with computer simulation and very good agreement between the model and the simulation is found. The simulation also confirms existence of two plasmas with two different potentials separated by a double layer.     

Octupole inhomogeneity tensor of ion microfield in Debye plasma at ionized emitter

The first constrained moments of the microfield octupole inhomogeneity tensor at ionized emitter have been calculated for the first time. Calculations were performed for three-component Debye plasmas using cluster expansion method in Baranger-Mozer scheme.     

Composition and thermodynamic functions of non-ideal plasma

A general method is proposed for the computation of the composition and thermodynamic properties of a non-ideal fluid system in thermodynamic equilibrium. The method is based on minimizing the system’s Gibbs energy to compute at constant pressure or Helmholtz energy to compute at constant volume, using successive approximations. The computation algorithm is implemented into the computer program in the C++ language. The method described has been used to compute the composition and thermodynamic properties of a system made up of products of SF₆ dissociation and ionization.     

Dye-sensitized solar cells based on TiO2 nanotube/porous layer mixed morphology

Titania porous layer has been fabricated on titania nanotubes for dye sensitized solar cells and the photovoltaic performance of solar cells with mixed morphology has been investigated. The porous layer results in a similar improvement in the short circuit current density to conventional TiCl₄ treatment, although the mechanisms responsible for the observed increase in the efficiency are different. This enables further improvements of the photovoltaic performance by combining the TiCl₄ treatment and porous layer deposition, so that the efficiency in the case of ∼5 μm long tubes increases on average from ∼1.6 to ∼2.2%.     

Plasmonic slow light waveguide and cavity

In this work, we present a detailed analysis of optical properties of metal–insulator and metal–insulator–metal (MIM) structure-based surface-plasmon waveguides and cavities. It is shown from the dispersion relation, the field distribution, the quality factor Q, and the transmission spectrum that the MIM structure can be designed as a high-Q cavity, supporting slow light with tolerable pulse distortion and lower propagation loss in the axial direction.     

High repetition rate femtosecond laser nano-machining of thin films

Thin film laser micromachining has been utilized for repairing semiconductor masks, creating solar cells and fabricating MEMS devices. A unique high repetition rate femtosecond fiber laser system capable of variable repetition rates from 200 KHz to 25 MHz along with helium gas assist was used to study the effect of pulse repetition rate and pulse energy on femtosecond laser machining of gold-coated silicon wafer. It was seen that high repetition rates lead to smaller craters with uniform line width. Craters created at 13 MHz pulse repetition rate with 2.042 J/cm² beam energy fluence measured 110 nm in width and had a heat affected zone of 0.79 μm. It was found that pulse repetition rate only played a significant role in the size of the heat affected zone in the lower pulse energy ranges. In the future, a 1 W laser system will be acquired to find the optimal repetition rate that would create the minimal feature size with the least heat affected zone. Using this kind of setup along with techniques such as radial polarization and a different gas assist may enable us to create sub 100 nm feature size with good quality.     

High-sensitivity bunch charge monitor

The conceptual design for a high-sensitivity bunch charge monitor is presented. The device operates with short, spaced bunches. For optimal performance, the bunch duration should be less than 10 ns and bunch spacing should be more than 100 ns. Sensitivity of the monitor is close to 10 V per nanocoulomb. The equivalent scheme and the output signal shape are also presented. Such a monitor seems to be promising for the bunch charge measurements of beams like those in TESLA or ILC projects. The text was submitted by the authors in English.     

Computational study of plasma-solid interaction in argon plasma with inclusion of magnetic field

In the presented contribution two groups of techniques of computational physics were used for the study of sheath structure in the DC glow discharge in argon plasma – the fluid modelling describing macroscopic plasma phenomena and the particle modelling providing more detailed insight into the plasma processes. A comparison of different computational methods is given with attention to the efficiency of computer codes in two dimensions. Another point of interest is the inclusion of external magnetic field into the models and its effect on the sheath structure.     

Hybrid computer simulations: electrical charging of dust particles in low-temperature plasma

This paper is focused on the study of the electrical charging process of micron-sized particles immersed into low-temperature argon plasma by the methods of computer modelling. The hybrid computer simulations are performed for a set of particles with the radius up to in order to determine the dependence of the electric charge on the surface of the particulate on its radius. This dependence seems to be linear. The distribution of the electric potential in the vicinity of the particulate is obtained from the fluid model. Afterwards, the non self-consistent particle simulation is performed in order to determine both the reaction rates and the electric charge on the surface of the particulate. The most important collision processes of charged particles in plasma and the appropriate dependence of the collision cross-section on the particle energy are considered (elastic scattering of electrons on neutrals, excitation of neutrals into all important energetic states, ionisation of Argon atoms by fast electrons, elastic scattering of positively charged ions etc.). The presented algorithm provides an effective way, how the key quantity in dusty plasma physics – electric charge on the surface of the particulate – can be determined.     

Optical absorption in early stage low temperature laser produced plasma

We describe a new technique to measure the UV/visible absorption spectrum of the ablated material during the laser pulse. The technique utilizes the continuum emission from one laser produced plasma as a light source to measure the absorption properties of a second laser produced plasma which is formed on a semi-transparent target with an array of 40 μm holes. A 6 ns, 1064 nm laser was used to ablate a Ag target and the plasma absorption was measured in the range 450–625 nm for a laser fluence of 1 J cm⁻². The total absorption cross-section is (0.5–1.5)×10⁻¹⁷ cm² in the range 450–540 nm. By comparing the measured absorption with a calculation using the plasma spectroscopy code FLYCHK it can be concluded that, in the wavelength region examined here, the absorption is mainly due to bound-bound transitions.     

On the competiting role of mean-field and residual interactions in flow observables

Theoretical analyses of heavy-ion reactions are performed in the framework of the semi-classical Landau-Vlasov approach. The incident energies are investigated in the range from intermediate to low energy regimes, where transverse collective motion has been experimentally evidenced. The influence of the equation of state (E.O.S.) parameters on various collective observables is studied in relation with the action of the residual interactions. From the sensitivity to both aspects, and taking into account the experimental biases limitations, our investigation indicates that E.O.S. signatures should be more expected at energies below 100 MeV per nucleon.     

On the chaining dynamics of inclusions in SmC* free standing films

A simplified model of an inclusion represented by (+1)-wedge disclination and an accompanying hyperbolic defect ((−1)-wedge disclination) in smectic C* free standing films is used to describe the early stage of the ordering process of inclusions into chains. The elastic interaction between inclusions and their associated hyperbolic defects is used to discuss the dynamics observed experimentally during the inclusion chaining when inclusions are at distances much larger than their radii. This work was also supported by Grant No. 202/02/0840 of the Grant Agency of the Czech Republic and by the research project AV0Z1-010-914.     

Propagation of terawatt laser pulses in the air

One of the problems when increasing the intensity of a femtosecond laser pulse is the propagation of the beam. As the intensity increases nonlinear effects begin to play a significant role. When arriving to the terawatt domain, nonlinear effects and filamentation give rise to a new phenomenology in the propagation. The aim of this paper is to analyze new possibilities to control the beam shape to Taylor the interaction of the beam with the target at large distances.     

Nuclear moments and the change in the mean square charge radius of neutron deficient thallium isotopes

The hyperfine structure, isotope and isomeric shifts in the atomic transition 6p ² P _3/2–7s ² S _1/2, =535 nm have been measured for theI=7 andI=2 states of^{190, 192, 194, 196}Tl; theI=1/2 andI=9/2 states of¹⁹¹Tl and the I=7 isomer of¹⁸⁸Tl. The thallium isotopes were prepared as fast atomic beams at the GSI on-line mass separator following fusion reactions and — in some cases — subsequent-decay. The nuclear dipole moments, electric quadrupole moments and the change in the nuclear mean square charge radius are evaluated. Theuu-isotopes show an isomeric shift which changes sign between¹⁹²Tl and¹⁹⁴Tl.Dedicated to P. Armbruster on the occasion of his 60th birthday     

Strong-coupling theory of mobility collapse in GaN layers

Within the framework of strong-coupling theory we study the effect of highly negatively charged threading dislocations on the electron mobility collapse in n-GaN layers. An analytical expression is derived showing the way in which the electrically active dislocations establish the critical carrier concentration at which the collapse occurs. Results are presented suggesting that the experimental collapse data can be utilized for determining the characteristic magnitude of the statistical filling factor of dislocation related traps in the GaN bandgap.     

SBN thin films growth by RF plasma beam assisted pulsed laser deposition

SBN thin films were grown on MgO and Silicon substrates by PLD and RF-PLD (radiofrequency assisted PLD) starting from single crystal Sr_0.6Ba_0.4Nb₂O₆ and ceramic Sr_0.5Ba_0.5Nb₂O₆ stoichiometric targets. Morphological and structural analyses were performed on the SBN layers by AFM and XRD and optical properties were measured by spectroellipsometry. The films composition was determined by Rutherford Backscattering Spectrometry. The best set of experimental conditions for obtaining crystalline, c-axis preferential texture and with dominant 31° in-plane orientation relative to the MgO (100) axis is identified.     

The formation of relativistic electromagnetic solitons in plasma Bragg gratings induced by two counter-propagating laser pulses

The generation of relativistic electromagnetic solitons in plasma with spatiotemporal density modulation is investigated. When two counter-propagating laser pulses overlap in underdense plasma, the interaction between the pulses and plasma modulates the electron and ion densities resulting in localized, stable, long-living relativistic electromagnetic solitons. They are caused by the Stimulated Raman Scattering instability. The dependence of the formation of relativistic electromagnetic solitons on the ion motion, plasma parameters, and laser parameters is studied by particle-in-cell simulations as well.