Arc Plasma Gun Research Articles

Detached Plasma Studies in GOL-NB with Extra Gas Injection

The magnetic system of an open trap usually includes expansion sections located between highfield magnetic mirrors and end surfaces that receive plasma. In the GOL-NB device, an arc plasma gun is located in one of the expanders, which creates a low-temperature starting plasma in the confinement area. The parameters of the surface plasma sheath affect the electrical connection of the confinement area with the walls and, thereby, affect the contribution of the line-tying effect to the plasma stability and the longitudinal energy losses from the trap. The experiments with additional hydrogen injection into the plasma gun were carried out at GOL-NB. We observed a radiating plasma formation detached from the surface, which visually corresponds to that in radiating divertors in tokamaks. In both standard and detached modes, decaying plasma existed near the receiving electrodes during the entire observation time after the discharge current was terminated. In the central trap of GOL-NB, some structures in the Fourier spectrogram of magnetic fluctuations manifest earlier in the detachment mode than in the standard mode and have lower frequencies. We associate these structures with the onset of interchange-like modes due to the loss of plasma stabilization by the line-tying to the conducting ends. The observed plasma response to the additional gas supply confirmed our understanding of the line-tying effect as the main factor stabilizing the plasma core in the initial phase of density accumulation in the central trap.

The Effect of Plasma Spray Parameters on the Quality of Al-Ni Coatings

The plasma spray method is widely utilized for enhancing wear, surface fatigue, and corrosion properties through coating. The mechanical and surface characteristics of the resulting coating are contingent upon various spraying parameters, including arc current, working current, spraying distance, and plasma gun traversing speed. This study investigates the impact of these manufacturing parameters on the porosity, hardness, and bond strength of a coating produced from an Al-Ni alloy applied to a Q235 steel substrate. An extensive experimental program was conducted to analyze the influence of these parameters on the coating properties. Consequently, a preferred combination of parameters, identified through a comprehensive evaluation method, yielded greater performance benefits compared to the orthogonal experimental groups.

Comparison of chemical composition and wear of iron and nickel aluminide coatings applied by plasma spraying

Given such properties as wear resistance, corrosion resistance, heat resistance, contact and cyclic strength, iron and nickel aluminides can be used as coatings in friction pairs for various purposes. The object of research is the process of obtaining plasma-sprayed coatings from powders based on iron and nickel aluminides. The task of research is the determination and comparison of the structure, chemical composition, and wear resistance of coatings from powders of iron aluminide and nickel aluminide, obtained by the method of atmospheric plasma spraying. To reduce the oxidation of powders during spraying, the conditions for generating a laminar plasma jet were created. Such conditions were provided by the specially developed structure of the electric arc plasma gun and the operating parameters of coating spraying. As a result of the correct choice of spraying modes, completely melted splats were formed during the collision of powder particles with the surface. The resulting coatings had a layered microstructure with microcracks and peeling. The porosity and characteristics of the delamination of the coatings depend on both the modes and the spraying technology. Tribological tests of the coatings were carried out under conditions of dry metal-on-metal sliding friction in a pair with high-speed steel. It is shown that the wear of nickel aluminide coatings under these conditions is 2–2.5 times lower than that of iron aluminide coatings. The coefficient of friction of iron aluminide coatings is slightly lower than that of nickel aluminide coatings. The wear of samples made of 30CrMnSi steel is 3–4 times higher than samples with coatings. The difference in the wear of the coatings is explained by the more intense oxidation of iron aluminide in the friction process. Conclusions were drawn regarding the possibility of using the investigated coatings in various friction pairs of structural elements, in particular in the automotive industry

Influence of different pretreatments on the adhesion of nanodiamond composite films on Ti substrates via coaxial arc plasma deposition

In this study, we report on the novel growth of nanodiamond composite (NDC) films on titanium (Ti) substrates using the coaxial arc plasma deposition (CAPD) at room temperature, which offers several advantages over conventional growth techniques. CAPD employs a unique coaxial arc plasma gun structure that provides a supersaturated condition of highly energetic carbon ions (C+) for ultrafast quenching on the substrate, promoting the growth of nanodiamond grains. This allows for NDC films’ growth on diverse substrates without the need for initial seeding or substrate heating. However, the growth of NDC films on Ti substrates at room temperature is challenging due to the native oxide layer (TiO2). Here, we grew NDC films on Ti substrates using three different pretreatments: (i) hydrofluoric acid (HF) etching, (ii) insertion of a titanium carbide (TiC) intermediate layer, and (iii) in situ Ar+ plasma etching. The morphology and structure of the grown NDC films were examined by 3D laser, high-resolution scanning electron microscopies (HR-SEM), Raman, and x-ray photoelectron (XPS) spectroscopies. Our results demonstrate that in situ Ar+ plasma etching is the most effective pretreatment method for completely removing the native TiO2 layer compared to the other two ex situ pretreatments, in which re-oxidation is more likely to occur after these pretreatments. Furthermore, NDC films grown using the hybrid Ar+ ion etching gun (IG) and CAPD exhibit the highest sp 3 content (63%) and adhesion strength (16 N).

Characterization of carburized layer on low-alloy steel fabricated by hydrogen-free carburizing process using carbon ions

Hydrogen-free carburized layer was fabricated by irradiating the carbon ions onto a heated low-alloy steel JIS SCM420 substrate using a coaxial arc plasma gun and controlling the diffusion of carbon atoms. The maximum hardness of carburized layer was 733 HV, and the hardness decreased reflecting the carbon concentration distribution in the depth direction of the substrate. The carburized layer was formed to depth of 200 μm. A martensitic structure was observed in the cross-sectional structure observation. Surface elemental analysis by SEM-EDS did not show segregation of chromium or oxygen to grain boundaries. Hydrogen concentration analysis by thermal desorption spectroscopy revealed that the concentration of diffusible hydrogen, which contributes to hydrogen embrittlement, was 0.0064 wt. ppm. Susceptibility to hydrogen embrittlement test was conducted using the three-point bending slow strain rate tensile test. The hydrogen-free carburized layer exhibited about 2.7 times the strength and about 2.3 times the elongation to the hydrogen charged layer after hydrogen-free carburizing. These results led us to conclude that the hydrogen-free carburizing method is notably effective in preventing hydrogen embrittlement.

Corrosion‐Resistive and Low Specific Contact Resistance Ohmic Contacts to Semiconducting Diamonds Using Nanocarbon Electrodes

The realization of diamond‐based advanced devices is interrelated with the fabrication of practical ohmic contacts. Contrary to boron‐doped, the phosphorus‐doped diamonds with interface carbide forming Ti‐based conventional ohmic contacts find their limitation in device fabrication due to the high contact resistance. Herein, nanocarbon ohmic contacts are deposited by a coaxial arc plasma gun on semiconducting diamonds, and their composite structure which facilitates exceptional contact properties is explored. A comparative electrical characterization between nanocarbon ohmic contacts and conventional Ti‐based contacts is performed on a heavily phosphorus‐doped diamond, and they exhibited one‐order declination in specific contact resistance. In addition to the low contact resistance, an ideal ohmic electrode is preferable to have good mechanical adhesion and corrosion resistance for device applications. The contact behavior of n‐type diamond/nanocarbon against an extremely corrosive environment realized by boiling H2SO4 + HNO3 solution is analyzed. The nanocarbon ohmic contacts exhibit excellent corrosion resistance and mechanical adhesion over conventional Ti‐based contacts. A similar trend is also observed for nanocarbon contacts on boron‐doped diamonds. The modest effect on the transfer length of the nanocarbon contacts with respect to acid treatment sessions indicates a tightly bonded diamond/nanocarbon interface and actively suggests their application in highly‐corrosive and harsh environments.

Formation of Starting Plasma Flow in an Open Trap Using Arc Plasma Gun

Formation of Starting Plasma Flow in an Open Trap Using Arc Plasma Gun

Comparison of CO2 Reduction Performance with NH3 and H2O between Cu/TiO2 and Pd/TiO2.

The aim of this study is to clarify the effect of doped metal type on CO2 reduction characteristics of TiO2 with NH3 and H2O. Cu and Pd have been selected as dopants for TiO2. In addition, the impact of molar ratio of CO2 to reductants NH3 and H2O has been investigated. A TiO2 photocatalyst was prepared by a sol-gel and dip-coating process, and then doped with Cu or Pd fine particles by using the pulse arc plasma gun method. The prepared Cu/TiO2 film and Pd/TiO2 film were characterized by SEM, EPMA, TEM, STEM, EDX, EDS and EELS. This study also has investigated the performance of CO2 reduction under the illumination condition of Xe lamp with or without ultraviolet (UV) light. As a result, it is revealed that the CO2 reduction performance with Cu/TiO2 under the illumination condition of Xe lamp with UV light is the highest when the molar ratio of CO2/NH3/H2O = 1:1:1 while that without UV light is the highest when the molar ratio of CO2/NH3/H2O = 1:0.5:0.5. It is revealed that the CO2 reduction performance of Pd/TiO2 is the highest for the molar ratio of CO2/NH3/H2O = 1:1:1 no matter the used Xe lamp was with or without UV light. The molar quantity of CO per unit weight of photocatalyst for Cu/TiO2 produced under the illumination condition of Xe lamp with UV light was 10.2 μmol/g, while that for Pd/TiO2 was 5.5 μmol/g. Meanwhile, the molar quantity of CO per unit weight of photocatalyst for Cu/TiO2 produced under the illumination condition of Xe lamp without UV light was 2.5 μmol/g, while that for Pd/TiO2 was 3.5 μmol/g. This study has concluded that Cu/TiO2 is superior to Pd/TiO2 from the viewpoint of the molar quantity of CO per unit weight of photocatalyst as well as the quantum efficiency.

The Impact of Amount of Cu on CO2 Reduction Performance of Cu/TiO2 with NH3 and H2O

This study has investigated the impact of molar ratio of CO2 to reductants NH3 and H2O as well as that of Cu loading on CO2 reduction characteristics over Cu/TiO2. No study to optimize the reductants’ combination and Cu loading weight in order to enhance CO2 reduction performance of TiO2 has been investigated yet. This study prepared Cu/TiO2 film by loading Cu particles during the pulse arc plasma gun process after coating TiO2 film by the sol-gel and dip-coating process. As to loading weight of Cu, it was regulated by change in the pulse number. This study characterized the prepared Cu/TiO2 film by SEM and EPMA. Additionally, the performance of CO2 reduction has been investigated under the illumination condition of Xe lamp with or without ultraviolet (UV) light. It is revealed that the molar ratio of CO2/NH3/H2O is optimized according to the pulse number. Since the amount of H+ which is the same as that of electron is needed to produce CO decided following the theoretical CO2 reduction reacting with H2O or NH3, larger H+ is needed with the increase in the pulse number. It is revealed that Cu of 4.57 wt% for the pulse number of 200 is the optimum condition, whereas the molar quantity of CO per unit weight of Cu/TiO2 with and without UV light illumination is 34.1 mol/g and 12.0 mol/g, respectively.

FT-IR for Carbon Nanostructure on Ag Surfaces Formed by Arc Plasma Gun

FT-IR for Carbon Nanostructure on Ag Surfaces Formed by Arc Plasma Gun

Temperature-Dependent Impedance Spectra of Nitrogen-Doped Ultrananocrystalline Diamond Films Grown on Si Substrates

Nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous-carbon (UNCD/a-C:H) composite films, grown on Si substrates by the coaxial arc plasma gun, were investigated using temperature-dependent impedance spectroscopy. The measurements were carried out in frequency and temperature ranges of 100 Hz–2 MHz and 300–400 K, respectively. Structurally, the nitrogen incorporation into the deposited films as well as sp2/sp3 ratio was studied by X-ray photoemission spectroscopy (XPS), measured with synchrotron radiation. The results of temperature-dependent electrical conductance characterization of the examined films revealed that the heterogeneous structure possesses a low-frequency conduction mechanism with an activation energy of 46 meV. This possibly originated from charge carriers hopping in the deposited composite. Furthermore, the results manifested a relaxation process, with an activation energy of 41 meV, originated from space charges in grain boundaries of the films. Cole-Cole plots of measured and fitted impedance spectra exhibited equivalent resistance due to grain boundaries that are much smaller than that related to UNCD grains. This is owing to the nitrogen incorporated in the composite film inside the grain boundaries instead of the grains. This increases the concentration of charge carriers within the grain boundaries and therefore enhances their conductivity. Moreover, the deduced capacitance corresponding to grain boundaries was larger than that originated from the UNCD grains. This is due to the difference between the grain-size and grain-boundary width of the UNCD/a-C:H composite.

Substrate for Surface-Enhanced Raman Spectroscopy Formed by Gold Nanoparticles Buried in Poly(methyl methacrylate).

In this work, we present some properties and use of a nanocomposite formed by gold nanoparticles (NPs) into poly(methyl methacrylate) (PMMA) and its application as substrates for surface-enhanced Raman spectroscopy (SERS). The nanocomposite was formed using low-energy (49 eV) ion implantation of gold in PMMA using a cathodic arc plasma gun. The gold NPs are formed spontaneously from the implanted ions and they remain isolated from each other by the polymer medium surrounding them, ensuring a spacing between the NPs of less than 10 nm (hot spot places). The NPs form below the surface, protected from the environment, guaranteeing the stability of the composite layer. Moreover, here, we present an interesting approach to concentrate analyte molecules closer to the metal surface using the swelling effect in PMMA. Using absorption of the analyte, the molecules stay in the gaps between NPs, which is a good solution for one of the biggest challenges in SERS, that is, to guide molecules to the hot spot places.

HRTEM‐EELS cross‐sectional structural analyses of glassy carbon substrate irradiated by platinum ions using a coaxial arc plasma gun

A glassy carbon (GC) substrate was irradiated by Pt ions using a coaxial arc plasma gun in vacuum. The structure of the substrate was studied in the atomic scale using high‐resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) with a thin foil specimen prepared by cross‐sectioning using focused ion beam milling. HRTEM combined with the EELS measurements of the cross‐sectioned sample indicated a disordering of the GC substrate surface and the detection of phenol‐type species, carbon atoms in aliphatic chain molecules, and carboxyl groups, which are considered to have been formed by chemical reaction between the carbon atoms of the GC substrate surface and hydrogen or oxygen atoms. Penetrated Pt atoms were observed inside the GC substrate, and the surface position of the GC substrate was located from the depth profiles of the EELS spectra. STEM‐EELS analyses of a pristine GC substrate without Pt ion irradiation were also conducted for reference.

Results of the first plasma campaign in a start configuration of GOL-NB multiple-mirror trap

The first plasma campaign was completed in a start configuration of the GOL-NB multiple-mirror trap. The device included a 4 m long high-field section, two end sections of magnetic flux expanders and a short temporary section for the commissioning of two 25 keV, 0.75 MW neutral beams. Low-temperature start plasma was created using a coaxial arc plasma gun. The main objective of the first experiments is to develop and characterize the low-temperature plasma stream that will be used later for filling the central trap of GOL-NB with the start plasma. The plasma parameters and operation regimes are reported.

HRTEM-EELS cross-sectional characterization of HOPG substrate with platinum nanoparticles deposited using a coaxial arc plasma gun

Platinum nanoparticles were deposited on a highly oriented pyrolytic graphite (HOPG) substrate using a coaxial arc plasma gun. The Pt-deposited HOPG substrate was cross-sectioned to prepare a thin foil specimen using focused ion beam milling, and was analyzed by using high resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, and electron energy loss spectroscopy. The surface of the HOPG substrate was observed to be disordered by the Pt ion irradiation. The surface was located using the depth profiles of π + σ plasmon peaks and the full width at half maximum of π⁎ peaks. The denaturation of the HOPG substrate by the Pt ion irradiation was observed to a depth of approximately 12 nm.

HRTEM and STEM-EELS Characterization of the Graphite Particles Irradiated by Platinum Ions Ejected from a Coaxial Arc Plasma Gun

HRTEM and STEM-EELS Characterization of the Graphite Particles Irradiated by Platinum Ions Ejected from a Coaxial Arc Plasma Gun

Effects of Deposition Temperature on Synthesis of Ultrananocrystalline Diamond/Amorphous Carbon Composite Films on Cemented Carbide Substrate By Coaxial Arc Plasma Deposition

Synthesis of hard carbon coatings on cutting tools is indispensable for machining the nonferrous materials and carbon fiber composites. Diamond, an allotrope of carbon, is classified at the top of carbon coatings for its unique characteristics, it has the highest known hardness and thus provides superior wear resistance. A diamond crystal consists of carbon atoms tetrahedrally bonded with sp3 hybrid bonds. On the basis of its crystal size, polycrystalline diamond is categorized to microcrystalline, nanocrystalline, and ultrananocrystalline diamond. Ultrananocrystalline diamond/amorphous carbon composite (UNCD/a-C) films, wherein a large number of diamond grains with diameters of less than 10 nm are embedded in an amorphous carbon matrix. A high hardness of UNCD/a-C films is attributed to the refinement of grains in nanoscale and its resultant high content of sp3-bonded carbon. To provide highly energetic carbon atoms and thus sp3-rich amorphous carbon films, cathodic arc discharge has ever been employed. In addition to the merits of cathodic arc discharge, coaxial arc plasma deposition technique (CAPD) has the following distinctive feature: a coaxial arc plasma gun is equipped with an anodic cylinder that can bunch ions ejected from a cathodic graphite rod located inside the cylinder. Owing to this structure, a supersaturated condition with highly energetic ions can be realized, which is desired for the growth of UNCD crystallites In this work, the influences of deposition temperature on growth and mechanical properties of the UNCD/a-C films were studied. The films were deposited at different temperatures on cemented carbide (WC-6wt.% Co) plate substrates by using CAPD. The hardness and elastic modulus were investigated by nanoindentation. Structural characterizations of the films have been examined by X-ray diffraction, scanning electron microscopy, hard X-ray photoelectron spectroscopy, and energy-dispersive X-ray. The revealed mechanical and structural properties will be presented.

Thermal Conductivity of Ultrananocrystalline Diamond/Nonhydrogenated Amorphous Carbon Composite Films Prepared By Coaxial Arc Plasma Deposition

Diamond possesses the highest thermal conductivity (2 × 103 Wm-1K-1) in all bulk materials, owing to low phonon scattering in diamond. Since phonon scattering is drastically enhanced by grain boundaries, the thermal conductivity of polycrystalline diamond films is strongly dependent on the grain size. The thermal conductivity of ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite (UNCD/a-C:H) films comprising a large number of UNCD grains with diameters of less than 10 nm and an a-C:H matrix have been prepared mainly by chemical vapor deposition (CVD). The highest thermal conductivity reported so far is 12 Wm- 1K- 1, which is comparable with that of sp3-rich non-hydrogenated amorphous carbon (a-C). It has been reported for a-C:H and UNCD/a-C:H films that the thermal conductivity is degraded by the incorporation of H atoms in the films. Recently we have realized the formation of UNCD/a-C films comprising UNCD grains and an a-C matrix, by coaxial arc plasma deposition (CAPD). CAPD does not necessarily require a hydrogen atmosphere during the deposition for the formation of diamond grains. So far, the thermal conductivity of hydrogen-free UNCD/a-C films has never been studied because H atoms are unintentionally incorporated into the films from source gases in CVD. In this study, UNCD/a-C films were deposited under a base pressure, and the thermal conductivity of the films were measured for the first time to our knowledge. UNCD/a-C films were deposited on n-Si substrates at base pressures of less than 10-4 Pa and the substrate temperature of 550 °C using coaxial arc plasma gun equipped with a graphite target. Mo films with the thickness of 80 nm were deposited on the UNCD/a-C films by sputtering for the TDTR. The thermal conductivity of the UNCD/a-C films was measured by a time-domain thermoreflactance (TDTR) technique. The thermal conductivity of the UNCD/a-C films was estimated to be 23.7 Wm- 1K- 1 by TDTR. The thermal conductivity is evidently higher than that of UNCD/a-C:H prepared by CVD. Two reasons for it are supposed. One is that an a-C in UNCD/a-C is probably advantageous for thermal conduction as compared with an a-C:H in UNCD/a-C:H, since it has been reported for a-C:H that the thermal conductivity decreases with increasing hydrogen content in a-C:H. The other is that UNCD/a-C does not contain hydrogen atoms that prevent from phonon scattering, whereas the preferential existence of hydrogen atoms at grain boundaries between UNCD grains and those between UNCD grains and an a-C:H matrix enhances phonon scattering for UNCD/a-C:H films prepared by CVD, which results in a decrease in the thermal conductivity. Further details will be presented in the conference.

Iron films deposited on porous alumina substrates

Iron films were deposited on porous alumina substrates using an arc plasma gun. The pore sizes (120 – 250 nm) of the substrates were controlled by changing the temperature during the anodic oxidation of aluminum plates. Iron atoms penetrated into pores with diameters of less than 160 nm, and were stabilized by forming γ-Fe, whereas α-Fe was produced as a flat plane covering the pores. For porous alumina substrates with pore sizes larger than 200 nm, the deposited iron films contained many defects and the resulting α-Fe had smaller hyperfine magnetic fields. In addition, only a very small amount of γ-Fe was obtained. It was demonstrated that the composition and structure of an iron film can be affected by the surface morphology of the porous alumina substrate on which the film is grown.

Possible formation of one-dimensional chains of C20 fullerenes observed by scanning tunneling microscopy

We found one-dimensional chains of carbon particles on Ag(111) and Au(111) surfaces after the deposition of carbon using an arc-plasma gun (APG). The observed periodicity of the chains on Ag(111) was 0.58–0.6 nm. Ex situ Fourier transform infrared (FT-IR) spectroscopy indicated two peaks at 1343 and 1406 cm−1. The simulation of the infrared spectrum for a tetramer of C20 fullerenes showed good agreement with the experimental result. From these findings, we propose the formation of chains of C20 fullerenes as the most probable explanation of the results of both scanning tunneling microscopy (STM) and FT-IR spectroscopy.