Ajm Buuron

Fast deposition of amorphous carbon films by an expanding cascaded arc plasma jet

Using an expanding cascaded arc plasma jet, amorphous hydrogenated and fluorohydrogenated carbon films were deposited on silicon, glass, and steel substrates at high rates of tens of nanometers per second and on large areas of up to 100 cm2. The present work was aimed at depositing amorphous carbon films suited for optical and protective applications. Films deposited with the common argon/methane or argon/acetylene mixture tend to delaminate from the substrate when the film is thicker than about 1 μm. For this reason, also trials using other compounds like C7H8 (toluene), CF4, and H2, and mixtures of these, were carried out. Using toluene, several‐μm‐thick films with good adhesion to the substrate were deposited. With spectroscopic ellipsometry and infrared absorption spectroscopy optical parameters were obtained. Appropriate numerical models were developed for analyzing the data, taking into account interference fringes in the spectra due to multiple reflections in the thin film. The hydrogen and oxygen ...

Carbon deposition using an expanding cascaded arc d.c. plasma

Abstract In this work a strongly flowing cascaded arc burning on an argon-hydrogen mixture is used to dissociate and ionize hydrocarbons which are injected inside a nozzle which is mounted in the anode of the arc. The thermal plasma ( T ≈ 10 000 K , p ≈ 0.5 bar ) will then expand supersonically into a vessel where the pressure can be varied between 0.1 mbar and 100 mbar. In the expansion the cracked hydrocarbons are transported towards a substrate opposing the arc where carbon films can grow. The large number of more or less independent operational variables make it possible to grow any kind of carbon film from graphite to diamond to polymers and amorphous hydrogenated carbon (a-C:H). For the amorphous films growth rates up to 200 nm s -1 on an area of 100 cm 2 were achieved, while for polycrystalline diamond films the rate was 25 μm h -1 , on areas of about 3 cm 2 . Graphite has been grown on top of graphite and steel samples at rates up to 3 mm h -1 . The morphology and film parameters of the grown films were investigated with ellipsometry (a-C:H, refractive index etc.), Raman spectroscopy (diamond, graphite, crystallinity and bond structure), electron microscopy (morphology).

Spectroscopic measurement of atomic hydrogen level populations and hydrogen dissociation degree in expanding cascaded arc plasmas

Optical absorption spectroscopy has been applied to measure the absolute population densities of the first excited levels of atomic hydrogen H*(n=2) and argon Ar*(4s) in an expanding cascaded arc plasma in hydrogen‐argon mixture. It is demonstrated that the method allows us to determine both H*(n=2) and Ar*(4s) absolute density radial profiles for H2 admixtures in Ar ranging from 0.7% to 10% with good accuracy. The measured H*(n=2) densities are in the 1014–1016 m−3 range, and Ar*(4s) densities are in the range of 1015–1018 m−3. It has been shown, that the density of hydrogen excited atoms H*(n=2) serves as an indicator of the presence of argon ions and hydrogen molecules in the expanding plasma. A kinetic model is used to understand evolution of H*(n=2) density in the expansion, and to estimate the total atomic hydrogen population density and hydrogen dissociation degree in sub‐ and supersonic regions of the plasma.

Plasma deposited carbon films as a possible means for divertor repair

Abstract Fast deposition of graphitic carbon layers by an expanding cascaded arc plasma was studied as a means for in situ repair of graphite erosion damage in the next step fusion reactor NET/ITER. Amorphous graphite was produced at rates of hundreds of nanometers per second on several square centimeters with an argon-hydrocarbon plasma. Crystalline graphite was produced at rates of 10–50 nm s −1 on several square centimeters by means of an argon-hydrogen-hydrocarbon plasma. Relations between the deposition parameters, morphology (from scanning electron microscopy) and Raman spectra were determined. Using laser thermal shock testing, the erosion resistances of the best crystalline coatings were determined at about 2 MJ m −2 (in a 10 ms pulse).

Thick carbon deposition by cascaded arcs

An expanding cascaded arc plasma is used for the deposition of different types of carbon layers at high growth rates. Single diamond crystals of 60 {mu}m and 25 {mu}m-thick continuous films are deposited within 1 h on areas of {approximately}3 cm{sup 2}. In recent experiments, pyrolytic graphite films have been deposited. Films up to 200 {mu}m thick have been produced within 20 min on an area of {approximately} 12 cm{sup 2}. The film type and growth rate depend on the choice of the optimum reactor parameter settings. To maximize the growth rate and crystallinity of the film, the reactor settings are varied. High growth rates (maximum of 762 nm/s) have been obtained at high temperatures (600 to 1000{degrees}C). Several diagnostic techniques are used to analyze the film. The purity of the films has been confirmed by Auger electron spectroscopy.

Absolute density of the argon first excited states in plasmas used for carbon deposition as determined by absorption spectroscopy

Abstract In order to study the possible excitation transfer from argon metastables to the admixed species in an expanding cascaded arc plasma the densities of the Ar(3 p 5 4 s ) states in a deposition plasma were studied with absorption spectroscopy. For a purely argon plasma the Ar(3 p 5 4 s ) density lies in the range 10 16 –10 18 m −3 at a chamber pressure of 40 Pa. The effect on the densities of the addition of moderate amounts of methane and oxygen is small. The addition of hydrogen to the argon plasma leads to a rapid disappearance of the argon 4 s states. Possible explanations are a lowering of the argon ion density by dissociative recombination and the direct excitation energy transfer with the H ∗ ( n = 2, 3) levels.

A new absorption spectroscopy setup for the sensitive monitoring of atomic and molecular densities

This paper deals with the specifications and the possibilities of a novel highly sensitive optical absorption spectroscopy method. It consists of a cascaded arc as an extremely bright broadband light source with a high resolution spectrometer as a detector. Its interest for a continuous quantitative monitoring of the densities of waste atoms and molecules in the atmosphere is investigated. To this end, theoretical considerations are given with respect to the detection limits and the resolution necessary for selective spectrochemical analysis. In the first measurements with the setup, on a laboratory argon‐hydrogen plasma, the versatility and sensitivity of the technique for measuring low species densities is demonstrated. Densities of the sublevels of the argon first excited state, the four Ar(3p54s) metastable and resonant substates, were measured simultaneously in one measuring sequence. The data were analyzed using an efficient line of sight integration technique. The densities of these substates are o...

Atomic hydrogen and argon ground state density determination in a recombining plasma using visible light absorption spectroscopy

The atomic radical density in the first excited state, obtained by the technique of optical absorption spectroscopy, and a simple kinetic model are used to determine the radical ground state density in a recombining expanding plasma. The kinetic model used does not require knowledge of the shape of the electron energy distribution function. The information on electron density and electron temperature has been derived from the Thomson-Rayleigh scattering diagnostic. The method is demonstrated for the determination of the absolute ground state densities of atomic hydrogen H(n=1) and argon Ar(3p6) in a freely expanding plasma jet.

Optical Diagnostics for High Electron Density Plasmas

Nowadays high electron density plasmas are, beside their fundamental interest, widely used for many applications, e.g., light sources and plasma processing. The well known examples of high electron density plasmas can be found among the class of thermal plasmas as, e.g., the Inductively Coupled Plasma (ICP) and the Wall Stabilized Cascaded Arc (WSCA). Usually the pressure of the plasma is high, i.e., sub atmospheric to atmospheric. Other examples are the plasmas generated in tokamaks for fusion purposes and the recently exploited plasmas for etching and deposition devices such as the Electron Cyclotron Resonance plasmas. For the plasmas mentioned, the electron density is typical in the range of 1018 to 1023 m−3, and the electron velocity distribution is close to a Maxwellian velocity distribution.

Fast deposition of a-C:H and a-Si:H using an expanding thermal plasma beam

Summary form only given. A fast deposition method, utilizing a thermal plasma which expands into a vacuum vessel, has been used to deposit amorphous hydrogenated silicon and carbon layers (a-Si:H and a-C:H, respectively). The deposited layers are produced by admixing silane and methane (or acetylene) to the argon carrier plasma. In contrast to the conventional plasma enhanced chemical vapour deposition where the deposition is diffusion limited, in this deposition device the deposition mechanism is flow determined. As a result, the deposition rates are large, typically 100 nm/s for a-C:H and 10 nm/s for a-Si:H. The a-Si:H layers are deposited on crystaline silicon and Corning glass substrates, and the a-C:H layers are deposited on either steel, zinc or silicon substrates.