Hydrogen atom density in a solar plasma reactor

A density of neutral hydrogen atoms was systematically measured in the MESOX solar plasma reactor at different MW powers and flow rates. The H-atom density was measured by a gold fibre optics catalytic probe. The H-atom density was in general increasing with increasing MW power. At a pressure of 40 Pa and a power of 500 W it was about 3.5 × 10²¹ m⁻³ and at a power of 1000 W it was about 4.1 × 10²¹ m⁻³. A degree of dissociation of hydrogen molecules was between 3% and 20% depending on pressure and power. A maximum degree of dissociation was obtained at a pressure of 40 Pa and 1000 W, while the lowest one at 130 Pa and 500 W.     

Applicability of self-consistent global model for characterization of inductively coupled Cl2 plasma

Investigations of the influence of gas pressure and input power on the Cl₂ plasma parameters in the inductively coupled plasma system were carried out. The investigations combined plasma diagnostics by Langmuir probe with plasma modeling represented by the self-consistent global model with Maxwellian approximation for the electron energy distribution function. From the experiments, it was found that the increase of gas pressure in the range of 0.27-3.33 Pa for 400-700 W of input power results in a decrease in both electron temperature (3.3-2.0 eV) and density (6.5×10¹⁶−3.0×10¹⁶ m⁻³ for 400 W and 1.2×10¹⁷-6.7×10¹⁶ m⁻³ for 700 W). For the given range of experimental conditions, the model showed an outstanding agreement with the experiments and provided the data on kinetics of plasma active species, their densities and fluxes.     

Influence of effective pumping speed on oxygen atom density in a plasma post-glow reactor

The density of neutral oxygen atoms in a post-glow reactor was measured with a fibre-optics catalytic probe. The source of O atoms was a microwave discharge generated in Ar-O₂ gas with different flow rates up to 3000 sccm/min. The O density was measured at different power of the microwave generator between 40 and 160 W and different effective pumping speed between 7 and 28 m³/h. It was found to depend on the ratio between O₂ and Ar flow rates. At a constant O₂ flow of 200 sccm/min there was a broad maximum of O density between the Ar flow of 200 and 1000 sccm/min, independent of the effective pumping speed. At a constant O₂ and Ar flow rates of 200 and 1000 sccm/min, respectively, the O density was found to increase both with increasing power and increasing effective pumping speed. The results were explained with collision phenomena in ionized gases and heterogeneous recombination of O atoms on surfaces.     

O density measurements in the pulsed-DC reactive magnetron sputtering of titanium

Using eclipse laser photo-detachment in conjunction with Langmuir probing, the density of O⁻ ions in a reactive pulsed magnetron (100 kHz, 55% duty) plasma has been determined at different times during the pulse period at a set of positions along the centre line axis of the discharge. The magnetron was operated at a fixed average power of 400 W with an oxygen partial pressure of 10% of the total pressure 1.33 Pa. The results show the plasma is weakly electro-negative, with a negative ion-to-electron density ratio α up to a maximum of 0.63.During the plasma on-phase (at all chosen measurement positions) the O⁻ density was found to reach a maximum directly after initiation of the voltage pulse decreasing weakly during the rest of the on-phase. On the transition from on-to-off phases of the pulse the negative ion density was found to fall (by 60% both close and far from the target but only 10% near the discharge centre), with the O⁻ density remaining almost constant during the rest of the afterglow.The spatial structure of the O⁻ density reveals a distinct peak 75 mm from the target close to but not at the position of the null in the magnetic field, falling by a factor of eight for increasing distances up to 30 mm both towards and away from the target. The highest O⁻ density recorded at this position was 1 × 10¹⁶ m⁻³, at a time of 2.12 μs into the pulse. From a comparison between on- and off-phase densities and using an intuitive model of the plasma, the results indicate that most negative ions are created in the bulk plasma. The density of target-borne O⁻ ions is estimated to be about 1 × 10¹⁵ m⁻³ varying little with position, possibly forming a beam-like structure.     

Self-consistent global model for inductively coupled Cl2 plasma: Comparison with experimental data and application for the etch process analysis

The investigations of the influence of gas pressure and input power on the Cl₂ plasma parameters in the inductively coupled plasma system were carried out. The investigations combined plasma diagnostics by Langmuir probe and plasma modeling using the self-consistent global model with Maxwellian approximation for electron energy distribution function. From the experiments, it was found that an increase of gas pressure in the range of 0.27-3.33 Pa at 400-700 W input power results in decreasing both electron temperature (3.3-2.0 eV) and density (6.6 × 10¹⁰ − 3.0 × 10¹⁰ cm^− 3 for 400 W and 1.2 × 10¹¹ − 6.4 × 10¹⁰ cm^− 3 for 700 W). The model showed an outstanding agreement with the experiments and provided the data on densities and fluxes of active species. These data combined with the model of etch kinetics demonstrated the possibility of different etch rate behaviors depending on the input process parameters as well as on the properties of the etched surface.     

A new asymmetric supercapacitor based on λ-MnO2 and activated carbon electrodes

Lithium-ion intercalated compound λ-MnO₂ was used as positive electrode in asymmetric supercapacitor with activated carbon used as negative electrode in 1 mol L^− 1 Li₂SO₄ aqueous electrolyte solution. Phase composition, morphology and particle sizes of λ-MnO₂ were studied by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrochemical capacitive performance of the asymmetric supercapacitor was tested by cyclic voltammetry and galvanostatic charge-discharge tests. The results show that the asymmetric supercapacitor has electrochemical capacitance performance within wide potential range of 0-2.2 V. The specific capacitance is 53 F g^− 1 at a constant current density of 10 mA cm^− 2. The energy density is 36 W h kg^− 1 with a power density of 314 W kg^− 1. It is obvious that λ-MnO₂ is a potential electrode material for asymmetric supercapacitor.     

Improved thermoelectric properties by adding Al for Zn in (ZnO)mIn2O3

The grain size and density of the sintered (Zn_1 − xAl_xO)_mIn₂O₃ bodies decreased with the small Al₂O₃ content (≤ 0.012), and then increased gradually by further increasing the Al₂O₃ content. The addition of Al for Zn in the (ZnO)_mIn₂O₃ led to an increase in both the electrical conductivity and the absolute value of the Seebeck coefficient. This indicates that the power factor was significantly enhanced by adding Al for Zn. The thermoelectric power factor was maximized to 1.67 × 10^− 3 W m^− 1 K^− 2 at 1073 K for the (Zn_0.992Al_0.008O)_mIn₂O₃ sample.     

Effect of rf power on the growth of silicon nanowires by hot-wire assisted plasma enhanced chemical vapor deposition (HW-PECVD) technique

Silicon nanowires (SiNWs) were synthesized by simultaneous evaporation of Au and Si deposition using H₂ diluted SiH₄. The deposition techniques combined hot-wire (HW) and plasma enhanced chemical vapor deposition (PECVD). Au wires were placed on the filament and heated simultaneously with the activation of the rf plasma for the dissociation of SiH₄ and H₂ gases. Five set of samples were deposited on ITO-coated glass substrate at different rf power varied from 20 to 100 W in an interval of 20 W, keeping other deposition parameters constant. High yield of SiNWs with diameter ranging from 60 to 400 nm and length about 10 μm were grown at rf power of 80 W (power density ~ 1018 mW cm⁻²). Rf power of 100 W (power density ~ 1273 mW cm⁻²) suppressed the growth of these SiNWs. The growth mechanisms of SiNWs are tentatively proposed. The nanocrystalline structure of SiNWs is confirmed by Raman spectra and HRTEM measurement.     

Radio frequency sputter deposition of high-quality conductive and transparent ZnO:Al films on polymer substrates for thin film solar cells applications

Thick aluminum-doped zinc oxide films were deposited at substrate temperatures from 100 °C to room temperature on polyethylene terephthalate by radio frequency magnetron sputtering, varying the deposition parameters such as radio frequency power and working pressure.Structural, optical and electrical properties were analyzed using an x-ray diffractometer, a spectrophotometer and a four-point probe, respectively. Films were polycrystalline showing a strong preferred c-axis orientation (002). The best optical and electrical results were achieved using a substrate temperature of 100 °C. Furthermore, high transmittances close to 80% in the visible wavelength range were obtained for those films deposited at the lowest Argon pressure used of 0.2 Pa. In addition, resistivities as low as 1.1 × 10^− 3 Ω cm were reached deposited at a RF power of 75 W. Finally, a comparison of the properties of the films deposited on polymer and glass substrates was performed, obtaining values of the figure of merit for the films on polymer comparable to those obtained on glass substrates, 17,700 Ω^− 1 cm^− 1 vs 14,900 Ω^− 1 cm^− 1, respectively.     

Behaviour of neutral hydrogen atom density in the presence of a sample holder in a plasma reactor

The behaviour of density of neutral hydrogen atoms in the presence of a sample holder in a MESOX reactor was studied. The MESOX reactor is used for studying interaction of hydrogen atoms with solid state surfaces at extreme conditions. Concentrated solar radiation with power of approximately 6 kW is collimated to a spot with the surface in the order of magnitude 1 cm² thus allowing for independent sample heating above 2000 K. Hydrogen plasma is generated in a MW (microwave) discharge. The H-atom density is measured with a FOCP (Fibre Optics Catalytic Probe). The H-atom density in the empty reactor depends slightly on the pressure and MW power and is about 5 × 10²¹ m⁻³ at a power of 1000 W. The sample holder made from quartz glass was mounted in the centre of the reactor and the H-atom density was measured versus time. The H-atom density in the loaded reactor was decreasing continuously. After a time period in the order of 2 min, the H-atom density was reduced by approximately a factor of 3 in regards to the original value. The results were explained by taking into account a temperature dependence of the recombination coefficient for heterogeneous recombination of H atoms on the quartz surface.     

Controlled density of vertically aligned carbon nanotubes in a triode plasma chemical vapor deposition system

We report on the growth mechanism and density control of vertically aligned carbon nanotubes using a triode plasma enhanced chemical vapor deposition system. The deposition reactor was designed in order to allow the intermediate mesh electrode to be biased independently from the ground and power electrodes. The CNTs grown with a mesh bias of + 300 V show a density of ∼ 1.5 μm^− 2 and a height of ∼ 5 μm. However, CNTs do not grow when the mesh electrode is biased to − 300 V. The growth of CNTs can be controlled by the mesh electrode bias which in turn controls the plasma density and ion flux on the sample.     

XPS study of oxygen plasma activated PET

A study on oxygen plasma functionalization of polyethyleneterephthalate (PET) is presented. Samples were exposed to a weakly ionized, highly dissociated RF oxygen plasma with an electron temperature of 5 eV, a density of positive ions of 8×10¹⁵ m⁻³ and a density of neutral oxygen atoms of 4×10²¹ m⁻³. The oxygen pressure was 75 Pa and the discharge power was 200 W. The wettability of plasma-modified samples was determined by measuring the contact angle of a water drop, while the appearance of the functional groups on the sample surface was determined by using a high-resolution X-ray photoelectron spectrometer (XPS). Already in the order of seconds of the plasma treatment the samples were covered by the surface functional groups. These results were explained by the high flux of oxygen atoms onto the sample surface. The stability of functional groups on the plasma-modified PET surface stored in a dry plastic box was monitored by using XPS as a function of the ageing time. After 1 day of ageing, the concentration of newly formed functional groups decreased by about 15%.     

Synthesis of morphology-controlled carbon hollow particles by carbonization of resorcinol–formaldehyde precursor microspheres and applications in lithium-ion batteries

The morphology-controlled carbon hollow particles, derived from resorcinol–formaldehyde (RF) particles, were prepared by using an (oil phase) O/(water phase) W/(oil phase) O inverse-emulsion system which was formed by adding RF precursor (water phase) to n-hexane (oil phase) with Span-80 as surfactant and the following carbonization. This simple method led to the formation of various morphologies of RF carbon precursor particles such as hollow spheres, bowl-like hollow structures, microcapsules, or solid microspheres by adjusting the pH values of the RF precursor. The synthesized carbon particles exhibited porous characters with the surface area of 659 m² g⁻¹ and the total pore volume of 0.44 cm³ g⁻¹. Additionally, the electrochemical behavior of the typical RF carbon particles in lithium-ion batteries revealed that the RF carbon microcapsules displayed a high initial discharge capacity of 1059 mAh g⁻¹ and stabilized at about 330 mAh g⁻¹, indicating its excellent power property and cycle durability.     

Effect of process parameters on the growth and properties of impurity-doped zinc oxide transparent conducting thin films by RF magnetron sputtering

Zinc oxide transparent conducting thin films co-doped with aluminum and ruthenium were grown on polyethylene terephthalate substrates at room temperature using RF magnetron sputtering. The crystal growth and physical properties of the films were investigated with respect to the variation of discharge power density from 1.5 to 6.1 W/cm² and sputtering pressure from 0.13 to 2.0 Pa. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) showed that the films grown with 3.6 W/cm² power density and sputtering pressure of 0.4 Pa had the best crystallinity and larger pyramid-like grains. The optimized electrical resistivity had a lowest measured value of about 9 × 10⁻⁴ Ω cm. The low carrier mobilities of the films (3-8.9 cm² V⁻¹ s⁻¹) have been discussed in terms of what is believed to be the dominant effect of ionized impurity scattering, but in addition chemisorption of oxygen on the film surface and effect of grain boundaries are also thought to be significant. The transmittances of the films in the visible range are greater than 80%, while the optical band gaps are in the order of 3.337-3.382 eV.     

Study on Raman line at 1080.2 cm in ZnO thin films prepared under high RF power

ZnO thin films were prepared on glass or on homo-buffer/glass by a RF magnetron sputtering method at RF power of 100-550 W. The structural and Raman characteristics of the films were analyzed by X-ray diffraction and Raman scattering. There appeared a sharp peak of 1080.2 cm⁻¹ near the A₁(2LO) mode (1156 cm⁻¹) of ZnO in the Raman spectra when the RF power was higher than 300 W. In this case, the (100) peak of ZnO film appeared obviously. It was speculated that the Raman mode at 1080.2 cm⁻¹ was induced by the ordered distribution of Zn_i defects in ZnO lattice.     

Preparation and characterization of nanostructured NiO/MnO2 composite electrode for electrochemical supercapacitors

Nanostructured nickel-manganese oxides composite was prepared by the sol-gel and the chemistry deposition combination new route. The surface morphology and structure of the composite were characterized by scanning electron microscope and X-ray diffraction. The as-synthesized NiO/MnO₂ samples exhibit higher surface area of 130-190 m² g⁻¹. Cyclic voltammetry and galvanostatic charge/discharge measurements were applied to investigate the electrochemical performance of the composite electrodes with different ratios of NiO/MnO₂. When the mass ratio of MnO₂ and NiO in composite material is 80:20, the specific capacitance value of NiO/MnO₂ calculated from the cyclic voltammetry curves is 453 F g⁻¹, for pure NiO and MnO₂ are 209, 330 F g⁻¹ in 6 mol L⁻¹ KOH electrolyte and at scan rate of 10 mV s⁻¹, respectively. The specific capacitance of NiO/MnO₂ electrode is much larger than that of each pristine component. Moreover, the composite electrodes showed high power density and stable electrochemical properties.     

Development of a dedicated ion injector for accelerator-based nanoprobe facilities

The paper discusses possible ways of increasing beam brightness in ion injectors. The argon/helium ion injector comprising a newly designed RF ion source and, a Wien filter has been designed for use in accelerator-based nanoprobe facilities. The phase set degradation due to aberrations in the injector ion-optic system was simulated with allowance for multipole and fringing fields. The RF ion sources with different permanent magnet systems were tested. Experiments were performed with argon and helium. A plasma density of up to 3×10¹¹ cm⁻³ and beam brightness of ∼100 A/(m² rad² eV) were obtained. The ion current density inside an extracting electrode in the source was 10 mA/cm² for an emission hole diameter of 0.6 mm. Measurements of the current value and emittance were performed with ion source testing equipment permitting measurements of the ion beam current, emittance, mass composition, and RF power input into the plasma.     

Power and pressure effects upon magnetron sputtered aluminum doped ZnO films properties

In this work, polycrystalline aluminum doped zinc oxide (ZnO:Al) films with c-axis (002) orientation have been grown on glass and silicon substrates by RF (radio frequency) magnetron sputtering technique, at room temperature. A systematic study of the effect of sputtering deposition parameters (i.e. RF power and argon gas pressure) on the structural, optical and electrical properties of the films was carried out. We observed that, with increasing RF power the growth rate increased, while it decreased with increasing gas pressure. As mentioned above, the films were polycrystalline in nature with a strong preferred (002) orientation. The intrinsic compressive stress was found to decrease with both increasing RF power and gas pressure, and near stress-free film was obtained at 200 W RF power and 2 × 10^− 1 Pa gas pressure. The obtained ZnO:Al films, not only have an average transmittance greater than 90% in the visible region, but also have an optical band gap between 3.33 and 3.47 eV depending on the sputtering parameters. Moreover, a low value of the electrical resistivity (~ 1.25 × 10^− 3 Ω cm) was obtained for the film deposited at 200 W and 2 × 10^− 3 mbar.     

Discharge power dependence of structural and electrical properties of Al-doped ZnO conducting film by magnetron sputtering (for PDP)

In order to investigate the possible application of ZnO films as a transparent conducting oxide (TCO) electrode for AC PDP, ZnO:Al films were prepared by DC magnetron sputtering method. The effects of discharge power and doping concentration on the structural and electrical properties of ZnO films were mainly studied experimentally. Five-inch PDP cells using either a ZnO:Al or indium tin oxide (ITO) electrode were also fabricated separately under the same manufacturing conditions. The luminous properties of both the PDP cells were measured and compared with each other.By doping the ZnO target with 2 wt% of Al₂O₃, the film deposited at a discharge power of 40 W resulted in the minimum resistivity of 8.5 × 10⁻⁴ Ω-cm and a transmittance of 91.7%. However, a high doping concentration of 3 wt% of Al₂O₃ and excessive sputtering power over 40 W may induce high defect density and limit the growth of small grains. Although the luminance and luminous efficiency of the cell using ZnO:Al are lower than those of the cell with the ITO electrode by about 10%, these values are sufficient enough to be considered for the normal operation of AC PDP.     

Ionization vacuum gauge with a carbon nanotube field electron emitter combined with a shield electrode

The applicability of carbon nanotubes to an electron source for a Bayard-Alpert type vacuum gauge has been investigated. Three gauge configurations are designed to optimize the gauge performance. The optimized gauge, in which an additional shield electrode is fixed on a gate electrode, exhibits good measurement of linearity between ion current and system pressure from 10⁻⁷ to 10⁻² Pa. A gauge sensitivity of 0.05 Pa⁻¹ has been achieved under 100 μA emission current for nitrogen, comparable with 0.07 Pa⁻¹ of commercial ionization gauges.