Plasma Power Density Research Articles

The Plasma Compression Fusion Device—Enabling Nuclear Fusion Ignition

The plasma compression fusion device (PCFD) generates the energy gain by plasma compression-induced nuclear fusion. This concept has the capability of maximizing the product of plasma pressure and energy confinement time to maximize the energy gain, and thus give rise to fusion ignition conditions. The preferred embodiment of this original concept uses a hollow cross-duct configuration of circular cross section in which the concentrated magnetic energy flux from two pairs of opposing curved-headed counter-spinning conical structures (possibly made from an alloy of tungsten with high capacitance) whose outer surfaces are electrically charged compresses a gaseous mixture of fusion fuel into a plasma, heated to extreme temperatures and pressures. The generated high-intensity electromagnetic (EM) radiation heats the plasma and the produced magnetic fields confine it in between the counter-spinning conical structures, named the dynamic fusors (four of them-smoothly curved apex sections opposing each other in pairs). The dynamic fusors can be assemblies of electrified grids and toroidal magnetic coils, arranged within a conical structure whose outer surface is electrically charged. The cross-duct inner surface surrounding the plasma core region is also electrically charged and vibrated in an accelerated mode to minimize the flux of plasma particles (including neutrals) from impacting the PCFD surfaces and initiating a plasma quench. The fusion fuel (preferably deuterium gas) is introduced into the plasma core through the counterspinning conical structures, namely, injected through orifices in the dynamic fusor heads. There is envisioned another even more compact version of this concept, which uses accelerated vibration in a linear-duct configuration (using two counterspinning dynamic fusors only) and would best be suited for fusion power generation on aircraft, or main battle tanks. The concept uses controlled motion of electrically charged matter through accelerated vibration and/or accelerated spin subjected to smooth, yet rapid acceleration transients, to generate extremely high-energy/high-intensity EM radiation (fields of high-energy photons) which not only confines the plasma but also greatly compresses itso as to produce a high power density plasma burn, leading to ignition. The PCFD concept can produce power in the gigawatt to terawatt range (and higher) with input power in the kilowatt to megawatt range and can possibly lead to ignition (selfsustained) plasma burn. Several important practical engineering and operational issues with operating a device such as the PCFD are discussed.

Development of silicon nanowires with optimized characteristics and fabrication of radial junction solar cells with < 100 nm amorphous silicon absorber layer

We report the growth and characterization of Silicon nanowires (SiNWs) via the VLS mechanism with two different tin (Sn) catalyst thicknesses of 2 and 4 nm at 400 and 500 °C by PECVD. The effect of catalyst thickness, plasma power density and growth temperature on the morphology of nanowires is investigated. The structural morphology of the grown NWs is analyzed using FESEM and HRTEM. It has been inferred the density, diameter and length of NWs can be effectively controlled by PECVD process parameters. HRTEM analysis demonstrates a highly crystalline silicon core with (111) plane as preferred orientation. Grazing incidence X-ray diffraction spectra of the samples prepared at two different temperatures confirmed the (111), (220) and (311) plane orientation of the grown NWs. Raman spectra of the SiNWs grown on glass substrate shown broadened spectrum centering at 508 cm-1 confirming the crystalline nature of NWs core surrounded with dense layer of a-Si. Optimized parameters are used to fabricate radial junction solar cells and the effect of catalyst thickness on the performance is explored. Short circuit current density of 13.53 mA/cm2 and open circuit voltage of 0.82 V for 0.25 cm2 solar cell having power conversion efficiency of 6.66% is obtained.

Depth-profiling XPS analysis of He-plasma treated amorphous InGaZnO thin films for use in top-gate coplanar thin-film transistors

A low-resistance amorphous InGaZnO (a-InGaZnO) film obtained with helium (He) plasma treatment is commonly used as the source/drain regions of top-gate planar thin-film transistors. Here we discuss some experimental results for the low-resistance a-InGaZnO films, focusing on depth profiling analysis of X-ray photoelectron spectroscopy signals. We show that the effect of He plasma treatment, which is generation of considerable oxygen vacancies, extends for the entire thickness (over 70 nm) of a-InGaZnO film. We also show that a significantly In-rich layer may be formed beneath the a-InGaZnO surface, depending on the He plasma power density.

Effect of Low Temperature RF Plasma Treatment on Electrical Properties of Junctionless InGaAs MOSFETs

In this paper, we study the effect of low-temperature RF plasma treatment in forming gas (10%H2+90%N2) on the electrical characteristics of junctionless MOSFETs with n-In0.53Ga0.47As channel and an Al2O3 gate dielectric. The impact of plasma power density on the device parameters is investigated. It is found that RF plasma annealing with a low power density (0.5 W/cm2) at 150°C for 10 min provides substantial improvement of source/drain contacts resistance and the carrier mobility resulting in a considerable increase of the on-state current and transconductance. It also improves the subthreshold slope and reduces the fixed positive charge in Al2O3 under the gate, shifting the threshold voltage toward positive values. It is demonstrated that non-thermal factors play a principle role in modification of electrical properties of the JL MOSFETs under RF plasma treatment. Such treatment may be an efficient tool for the improvement of the performance of the advanced MOSFETs with III-V channel materials.

Surface Structure Transformation in Double Forged Tungsten upon Single and Sequenced Irradiation Using Different Types of Radiation Facilities

Structural changes in the surface layer of target samples made of double forged tungsten were investigated after successive pulsed plasma irradiation thereof using different irradiation facilities such as plasma focus (PF), plasma gun (PG), and plasma accelerator (PA). The irradiation modes simulated hard conditions occurring under the action of thermonuclear plasma on the material in modern tokamaks in such extreme situations as plasma disruption, vertical displacement, and edge localized mode effects (ELMs). Hydrogen and deuterium were used as working gases. Double forged tungsten (DFW) samples were irradiated using PF facilities (PF-6 and PF-1000U) with a subsequent irradiation using PG or PA, as well as another sequence consisting in the initial irradiation using PA and a subsequent irradiation using PF-6 at the final stage. The DFW samples in the experiments were positioned normal to the incident energy flux. The following irradiation modes were used. The PF-1000U facility provides a power density of the deuterium plasma flux onto the target surface qpl = 109–1010 W/cm2, pulse duration τpl = 50–100 ns, power density of the of fast ion beam (with energy Ei > 100 keV) qfi = 1011–1012 W/cm2, pulse duration τfi = 10–50 ns. The PF-6 facility provides qpl = 109–1010 W/cm2, τpl = 50 ns, qfi = 1010–1011 W/cm2, τfi = 10–50 ns. The PG facility provides energy density Q = 0.8 MJ/m2, density of hydrogen plasma q ≈ 5 × 106 W/cm2, pulse duration τ = 15 μs. The PA facility provides Q = 0.75 MJ/m2, power density of deuterium plasma q = 3.6 × 105 W/cm2, τ = 0.25 ms. General features and peculiarities inherent in tungsten damage and changes in the structural state thereof under the action of energy flows in the hard mode of preliminary irradiation in PF facilities with subsequent radiation exposure in softer modes implemented in PG and PA facilities are considered. It is shown that, in the irradiation modes under investigation, the character of material degradation depends not only on the magnitude and duration of the single energy pulses generated by a testing facility but also on the number of energy pulses. The depth of the apparent damaged layer, wherein the crippling of the material occurs, is about 200 μm in almost all the studied irradiation modes, the damage being of thermal and shock-wave nature.

Power density measurements to optimize AC plasma jet operation in blood coagulation.

In this paper, the plasma power density and corresponding plasma dose of a low-cost air non-thermal plasma jet (ANPJ) device are estimated at different axial distances from the nozzle. This estimation is achieved by measuring the voltage and current at the substrate using diagnostic techniques that can be easily made in laboratory; thin wire and dielectric probe, respectively. This device uses a compressed air as input gas instead of the relatively-expensive, large-sized and heavy weighed tanks of Ar or He gases. The calculated plasma dose is found to be very low and allows the presented device to be used in biomedical applications (especially blood coagulation). While plasma active species and charged-particles are found to be the most effective on blood coagulation formation, both air flow and UV, individually, do not have any effect. Moreover, optimal conditions for accelerating blood coagulation are studied. Results showed that, the power density at the substrate is shown to be decreased with increasing the distance from the nozzle. In addition, both distances from nozzle and air flow rate play an important role in accelerating blood coagulation process. Finally, this device is efficient, small-sized, safe enough, of low cost and, hence, has its chances to be wide spread as a first aid and in ambulance.

Effect of Cold Atmospheric Pressure Plasma on Maize Seeds: Enhancement of Seedlings Growth and Surface Microorganisms Inactivation

Cold atmospheric pressure ambient air plasma generated by Diffuse Coplanar Surface Barrier Discharge (DCSBD) was investigated for inhibition of native microbiota and potentially dangerous pathogens (Aspergillus flavus, Alternaria alternata and Fusarium culmorum) on the maize surface. Moreover, the improvement of germination and growth parameters of maize seeds was evaluated. Maize (Zea mays L.; cv. Ronaldinio), one of the most important cultivated crops worldwide, was selected as the research material. Electrical measurements confirmed the high volume power density (80 W cm−3) of DCSBD plasma. Non-equilibrium plasma state evaluated using optical emission spectroscopy showed values of vibrational and rotational temperature (2700 ± 300) K and (370 ± 75) K, respectively. Changes on the plasma treated seeds surface were studied by water contact angle measurement, scanning electron microscope analysis and Fourier transform infrared spectroscopy. A complete devitalisation of native microbiota on the surface of seeds was observed after a short treatment time of 60 s (bacteria) and 180 s (filamentous fungi). The plasma treatment efficiency of artificially contaminated maize seeds was estimated as a reduction of 3.79 log (CFU/g) in F. culmorum after a 60-s plasma treatment, 4.21 log (CFU/g) in A. flavus and 3.22 log (CFU/g) in A. alternata after a 300-s plasma treatment. Moreover, the obtained results show an increase in wettability, resulting in a better water uptake and in an enhancement of growth parameters. The investigated DCSBD plasma source provides significant technical advantages and application potential for seed surface finishing without the use of hazardous chemicals.

Study the effect of plasma power density and gold catalyst thickness on Silicon Nanowires growth by Plasma Enhanced Chemical Vapour Deposition

Gold (Au) metal catalysed tapered Silicon Nanowires (SiNWs) of diameter 50–150 nm at the base and length of 0.8–2.5 µm are synthesised by VLS mechanism using Silane (SiH4) as a precursor gas in Plasma Enhanced Chemical Vapour Deposition (PECVD) reactor at a substrate temperature of 650 °C. In this work, the effect of plasma power on the growth morphology of SiNWs is studied with two different thicknesses of Au catalyst layer. The catalyst layers are deposited using thermal evaporation system. Field Emission Scanning Electron Microscopy (FESEM) images confirm the growth of randomly oriented tapered nanowires. From the FESEM studies, it is clear that the density and the length of SiNWs increases with the increase of plasma power. High-resolution Transmission Electron Microscopy (HRTEM) demonstrated that the SiNWs are highly crystalline with (1 1 1) and (2 2 0) plane orientation. Raman spectra of SiNWs have been analysed and the first order optical phonons for SiNWs is observed at 519 cm−1 with 1 nm and 514.82 cm−1 with 2 nm Au catalyst.

Use of a solid carbon precursor for DC plasma nitrocarburizing of AISI 4140 steel

A new surface treatment concept of solid carbon source plasma nitrocarburizing (SCS-PNC) was proposed. Carbon fiber carbon composite (CFC) was used as a solid carbon precursor for conventional DC plasma nitriding process in a nitrogen-hydrogen plasma. The effect of plasma power on the phase composition of the compound layer on AISI 4140 steel was investigated. The results of the SCS-PNC process were compared to conventional DC plasma nitriding (PN) and plasma nitrocarburizing (PNC) using methane as carbon-bearing gas. The SCS-PNC process provides increasing carbon concentration within the compound layer with increasing plasma power density. In the compound layer a constant carbon content of 1.5 wt.-% C was obtained for high plasma power densities and the ε-carbonitride Fe2-3(C,N)x formation was significantly promoted reducing the porous seam zone. Moreover, precipitation of unwanted cementite Fe3C in the compound layer was effectively suppressed for SCS-PNC compared to treatment by PNC with methane addition.

The effect of substrate holder size on the electric field and discharge plasma on diamond-film formation at high deposition rates during MPCVD

The effect of the substrate holder feature dimensions on plasma density (ne), power density (Qmw) and gas temperature (T) of a discharge marginal plasma (a plasma caused by marginal discharge) and homogeneous plasma were investigated for the microwave plasma chemical vapor deposition process. Our simulations show that decreasing the dimensions of the substrate holder in a radical direction and increasing its dimension in the direction of the axis helps to produce marginally inhomogeneous plasma. When the marginal discharge appears, the maximum plasma density and power density appear at the edge of the substrate. The gas temperature increases until a marginally inhomogeneous plasma develops. The marginally inhomogeneous plasma can be avoided using a movable substrate holder that can tune the plasma density, power density and gas temperature. It can also ensure that the power density and electron density are as high as possible with uniform distribution of plasma. Moreover, both inhomogeneous and homogeneous diamond films were prepared using a new substrate holder with a diameter of 30 mm. The observation of inhomogeneous diamond films indicates that the marginal discharge can limit the deposition rate in the central part of the diamond film. The successfully produced homogeneous diamond films show that by using a substrate holder it is possible to deposit diamond film at 7.2 μm h–1 at 2.5 kW microwave power.

Fast low-temperature plasma reduction of monolayer graphene oxide at atmospheric pressure

We report on an ultrafast plasma-based graphene oxide reduction method superior to conventional vacuum thermal annealing and/or chemical reduction. The method is based on the effect of non-equilibrium atmospheric-pressure plasma generated by the diffuse coplanar surface barrier discharge in proximity of the graphene oxide layer. As the reduction time is in the order of seconds, the presented method is applicable to the large-scale production of reduced graphene oxide layers. The short reduction times are achieved by the high-volume power density of plasma, which is of the order of 100 W cm−3. Monolayers of graphene oxide on silicon substrate were prepared by a modified Langmuir–Schaefer method and the efficient and rapid reduction by methane and/or hydrogen plasma was demonstrated. The best results were obtained for the graphene oxide reduction in hydrogen plasma, as verified by x-ray photoelectron spectroscopy and Raman spectroscopy.

Development of Al2O3 electrospun fibers prepared by conventional sintering method or plasma assisted surface calcination

In this paper, the electrospinning method was used for preparation of α-Al2O3 microfibers from PAN/Al(NO3)3 precursor solution. The precursor fibers were thermally treated by conventional method in furnace or low-temperature plasma induced surface sintering method in ambient air. The four different temperatures of PAN/Al(NO3)3 precursors were chosen for formation of α-Al2O3 phase by conventional sintering way according to the transition features observed in the TG/DSC analysis. In comparison, the low-temperature plasma treatment at atmospheric pressure was used as an alternative sintering method at the exposure times of 5, 10 and 30min. FTIR analysis was used for evaluation of residual polymer after plasma induced calcination and for studying the mechanism of polymer degradation. The polycrystalline alumina fibers arranged with the nanoparticles was created continuously throughout the whole volume of the sample. On the other side the low temperature approach, high density of reactive species and high power density of plasma generated at atmospheric pressure by used plasma source allowed rapid removal of polymer in preference from the surface of fibers leading to the formation of composite ceramic/polymer fibers. This plasma induced sintering of PAN/Al(NO3)3 can have obvious importance in industrial applications where the ceramic character of surface with higher toughness of the fibers are required.

Modeling plasma-assisted growth of graphene-carbon nanotube hybrid

A theoretical model describing the growth of graphene-CNT hybrid in a plasma medium is presented. Using the model, the growth of carbon nanotube (CNT) on a catalyst particle and thereafter the growth of the graphene on the CNT is studied under the purview of plasma sheath and number density kinetics of different plasma species. It is found that the plasma parameter such as ion density; gas ratios and process parameter such as source power affect the CNT and graphene dimensions. The variation in growth rates of graphene and CNT under different plasma power, gas ratios, and ion densities is analyzed. Based on the results obtained, it can be concluded that higher hydrocarbon ion densities and gas ratios of hydrocarbon to hydrogen favor the growth of taller CNTs and graphene, respectively. In addition, the CNT tip radius reduces with hydrogen ion density and higher plasma power favors graphene with lesser thickness. The present study can help in better understanding of the graphene-CNT hybrid growth in a plasma medium.

Method of power density determination in microwave discharge, sustained in hydrogen–methane gas mixture

We present the results of studying a continuous microwave discharge maintained at a frequency of 2.45GHz in a CVD reactor based on a cylindrical resonator excited at the TM013 mode. The discharge was ignited in hydrogen and a gaseous mixture of hydrogen and methane and was studied by the method of optical emission spectroscopy. Density of atomic hydrogen and gas temperature were measured, as well as the spatial distribution of both optical emission intensity of the plasma and intensity of the Hα line of atomic hydrogen. The main parameters of the discharge were calculated numerically using the two-dimensional self-consistent model of the discharge. Basing on the obtained results, we proposed a method for high-precision experimental determination of the plasma volume and calculation of the specific energy contribution to the plasma, i.e., microwave power density in plasma (MWPD), with minimal errors. According to the calculations, in the experiment performed, the microwave power density in the plasma varied from 50 to 550W/cm3 as the gas pressure increased from 80 to 350Torr. The method allows one to perform unified MWPD calculations in different CVD reactors and to compare diamond film deposition regimes.

Amorphous/microcrystalline transition of thick silicon film deposited by PECVD

Thick silicon films were deposited by plasma-enhanced chemical vapor deposition at different plasma power densities. Annealing treatment was performed on these deposited films. As-deposited and annealed films were characterized by X-ray diffraction, Raman scattering spectroscopy and reflectance spectroscopy. Before annealing, only the film deposited at the plasma power density of 500 mW/cm2 exhibits a diffraction peak corresponding to the (111) plane orientation. Raman spectrum of this film confirms the presence of crystalline phase. After annealing, a transition from amorphous phase to crystalline one occurs for all samples. This transition is accompanied by an increase of the crystalline fraction volume deduced from Raman spectra analysis and by a reduction of optical gap energy.

Development of a plate-to-plate MPCVD reactor configuration for diamond synthesis

The design and performance of a microwave plasma chemical vapor deposition (MPCVD) reactor based on compressed microwave waveguides and plate-to-plate substrate holders are described. This reactor can be operated at pressures from 10 to 40kPa with microwave power of 0.4–1.2kW, and a high plasma power density up to 500W/cm3 can be obtained. The single-crystal diamond (lower substrate holder) and polycrystalline diamond (upper substrate holder) have been grown by the plate-to-plate MPCVD reactor using high pressure CH4-H2 mixture gases. Experimental results show that high quality single-crystal diamond and polycrystalline diamond were simultaneously synthesized at a growth rate of 25μm/h and 12μm/h, respectively. The results indicate that our MPCVD reactor is unique for the synthesis of diamond with high efficiency.

Liquid‐Assisted Plasma‐Enhanced Chemical Vapor Deposition of Catechol and Quinone‐Functionalized Coatings: Insights into the Surface Chemistry and Morphology

Liquid‐assisted plasma‐enhanced chemical vapor deposition (LA‐PECVD) provides a convenient approach toward the preparation of functional surfaces. In this work, the LA‐PECVD approach is reported for the high deposition rate of tuneable catechol and quinone‐functionalized coatings from plasma polymerization of vinyltrimethoxysilane (VTMOS) and dopamine acrylamide (DOA). Most particularly, the influence of the liquid precursor delivery rate and of the plasma power density on the chemistry and morphology of the formed layers are investigated. Precursor delivery rate and plasma power conditions are found, through mass measurement, XPS, FTIR, and Raman spectroscopy, to enable the high deposition rate of cross‐linked coatings. Interestingly, the integration and conservation of the catechol functional group from the DOA monomer are highlighted through the reduction of a silver nitrate solution and silver nanoparticles formation observation via SEM/EDX. Due to the presence of oxidant species and to the bombardment of the layer with highly energetic species, quinone groups formation is likely to occur during the plasma treatment and is then highlighted via ToF‐SIMS analyses of a surface successfully derivatized with a β‐lactamase. The conservation of both functional groups on the surface makes this type of layer promising for numerous applications. Quinone groups provide a real platform for the immobilization of biomolecules with various properties, e.g., antibiotics degradation, antibacterial, while the catechol groups are interesting for trapping radicals or metal ions for water treatment applications.

Low temperature plasma processing for cell growth inspired carbon thin films fabrication

The recent bio-applications (i.e. bio-sensing, tissue engineering and cell proliferation etc.) are driving the fundamental research in carbon based materials with functional perspectives. High stability in carbon based coatings usually demands the high density deposition. However, the standard techniques, used for the large area and high throughput deposition of crystalline carbon films, often require very high temperature processing (typically >800 °C in inert atmosphere). Here, we present a low temperature (<150 °C) pulsed-DC plasma sputtering process, which enables sufficient ion flux to deposit dense unhydrogenated carbon thin films without any need of substrate-bias or post-deposition thermal treatments. It is found that the control over plasma power density and pulsed frequency governs the density and kinetic energy of carbon ions participating during the film growth. Subsequently, it controls the contents of sp3 and sp2 hybridizations via conversion of sp2 to sp3 hybridization by ion's energy relaxation. The role of plasma parameters on the chemical and surface properties are presented and correlated to the bio-activity. Bioactivity tests, carried out in mouse fibroblast L-929 and Sarcoma osteogenic (Saos-2) bone cell lines, demonstrate promising cell-proliferation in these films.

Microwave Plasma-Activated Chemical Vapor Deposition of Nitrogen-Doped Diamond. I. N2/H2 and NH3/H2 Plasmas.

We report a combined experimental/modeling study of microwave activated dilute N2/H2 and NH3/H2 plasmas as a precursor to diagnosis of the CH4/N2/H2 plasmas used for the chemical vapor deposition (CVD) of N-doped diamond. Absolute column densities of H(n = 2) atoms and NH(X(3)Σ(-), v = 0) radicals have been determined by cavity ring down spectroscopy, as a function of height (z) above a molybdenum substrate and of the plasma process conditions, i.e., total gas pressure p, input power P, and the nitrogen/hydrogen atom ratio in the source gas. Optical emission spectroscopy has been used to investigate variations in the relative number densities of H(n = 3) atoms, NH(A(3)Π) radicals, and N2(C(3)Πu) molecules as functions of the same process conditions. These experimental data are complemented by 2-D (r, z) coupled kinetic and transport modeling for the same process conditions, which consider variations in both the overall chemistry and plasma parameters, including the electron (Te) and gas (T) temperatures, the electron density (ne), and the plasma power density (Q). Comparisons between experiment and theory allow refinement of prior understanding of N/H plasma-chemical reactivity, and its variation with process conditions and with location within the CVD reactor, and serve to highlight the essential role of metastable N2(A(3)Σ(+)u) molecules (formed by electron impact excitation) and their hitherto underappreciated reactivity with H atoms, in converting N2 process gas into reactive NHx (x = 0-3) radical species.

Mechanical strains in pecvd SiNx:H films for nanophotonic application**Project supported by RFBR (Grant No. 14-03-91154 NNSF) and the National Natural Science Foundation of China (Grant No. 61411130212).

Hydrogenated amorphous silicon nitride films (SiNx:H) are deposited at low temperature by high-frequency plasma-enhanced chemical vapor deposition (HF PECVD). The main effort is to investigate the roles of plasma frequency and plasma power density in determining the film properties particularly in stress. Information about chemical bonds in the films is obtained by Fourier transform infrared spectroscopy (FTIR). The stresses in the SiNx:H film are determined from substrate curvature measurements. It is shown that plasma frequency plays an important role in controlling the stresses in SiNx:H films. For silicon nitride layers grown at plasma frequency 40.68 MHz initial tensile stresses are observed to be in a range of 400 MPa–700 MPa. Measurements of the intrinsic stresses of silicon nitride films show that the stress quantity is sufficient for film applications in strained silicon photonics.