High-temperature Hydrogen Plasma Research Articles

Preparation of diamond on GaN using microwave plasma chemical vapor deposition with double-substrate structure

Combining diamond with GaN can significantly improve the heat dissipation performance of GaN-based devices. However, how to avoid the destructive damage to the GaN epi-layer caused by high-temperature hydrogen plasma during the diamond growth is still a problem. This study employed a Si transition layer and double-substrate structure microwave plasma chemical vapor deposition (MPCVD) to prepare diamond film on GaN epi-layer. The effects of double-substrate structure on the diamond growth were studied. The microwave plasma parameters of both single-substrate structure and double-substrate structure MPCVD diagnosed by emission spectra were comparatively investigated. It has been found that the microwave plasma energy of double-substrate structure MPCVD is relatively more concentrated and has higher radicals activity, which is beneficial to the diamond growth. The impacts of the Si transition layer on the diamond growth were also investigated. It demonstrates that the Si transition layer can effectively protect the GaN epi-layer from being etched by hydrogen plasma and improve the diamond growth. The relationship between the thickness of the Si transition layer and the diamond growth and the relationship between diamond film thickness and adhesion has been studied in detail.

Hydrogen transport in a niobium-foil assembly under the action of high-temperature hydrogen plasma on a plasma focus setup

The process of hydrogen transport under the action of hydrogen-plasma pulses in the Plasma Focus (PF-4) setup in an assembly of niobium foils with thicknesses of 110 μm each is studied. It is established that the implanted hydrogen is transported to large depths in the Nb foils under the action of the hydrogen plasma. These depths considerably exceed the paths of hydrogen ions from the plasma as the maximum ion velocities are on the order of 108 cm/s. The highest concentration of hydrogen (up to 60 at %) is reached on the surface of the third Nb foil of the assembly. The discovered phenomenon can be explained by the action of shock waves of arising stresses upon the transport and redistribution of hydrogen to considerable depths.

Abnormally deep penetration of hydrogen into niobium under the influence of the pulse high-temperature plasma

The process of storing and redistributing hydrogen atoms under the action of pulse high-temperature hydrogen plasma obtained on the PF-4 plasma focus (PF) plant in an assembly of three high-purity niobium foils is studied by the elastic recoil detection (ERD) method. It is determined that, as the number of hydrogen plasma pulses increases, the implanted hydrogen atoms are redistributed at larger depths in an assembly of niobium foils which significantly exceed the projected range of hydrogen ions (when their maximal velocity reaches ∼108 cm/s). A maximum hydrogen concentration of up to 60 at % is reached in the nearest (to PF-4) surface of the third Nb foil under the action of 20 hydrogen plasma pulses. The observed phenomenon can be attributed to the ejections of implanted hydrogen atoms under the action of high-power shock waves created in niobium foils by the pulse hydrogen plasma and/or by the accelerating diffusion of hydrogen atoms under the action of compression-straining waves at the front of the shock wave with redistributions of hydrogen atoms at larger depths. Similar behavior is found in assemblies of two or three and more nickel, vanadium, niobium, and tantalum foils of different thicknesses, including foil assemblies made of heterogeneous materials, which were also studied.

Anomalously deep penetration of hydrogen and deuterium in assemblies from Nb foils and deuterated polyethylene (CD2) n under the pulse high temperature hydrogen plasma

Studies of the storage and redistribution of hydrogen atoms under pulse high temperature hydrogen plasma that was obtained using a PF-4 Plasma Focus facility in a multilayered structure (sandwich) which consists of two high-purity niobium foils and a deuterium polyethylene film pressed between them have been carried out using the method for elastic recoil detection (ERD). It was established that, with an increase in pulses of the PF-4 facility, the redistribution of implanted hydrogen atoms for large depths occurs in the two Nb foils and deuterated polyethylene. The depths substantially exceed the projective range of paths of hydrogen ions (at their maximum velocity of ∼108 cm/s). A maximum hydrogen concentration of 45 at % is reached in the nearest surface of the second Nb foil to the PF-4 at 20 pulses of hydrogen plasma. An X-ray diffraction analysis showed the presence of a niobium hydride phase in both Nb foils. The redistribution of deuterium atoms from the bound state of deuterated polyethylene into the near-surface layer and the bulk material of the second Nb foil was detected as well. This phenomenon can be attributed to the transfer of implanted hydrogen atoms through the foil assembly and the transfer of deuterium from deuterated polyethylene into the near-surface layer of the second foil under the effect of powerful shock waves that are created by pulse hydrogen plasma and by acceleration in the diffusion of hydrogen and deuterium in the strain field induced by the shock wave.

Improvement of Electron Field Emission in Patterned Carbon Nanotubes by High Temperature Hydrogen Plasma Treatment

In this paper, we report a significant improvement of electron field emission property in patterned carbon nanotubes films by using a high temperature (650 °C) hydrogen plasma treatment. This treatment was found to greatly increase the emission current, emission uniformity and stability. The mechanism study showed that these enhanced properties are attributed to the lowering of the potential barrier and the creation of geometrical features through the removal of amorphous carbon, catalyst particles and the saturation of dangling bonds after such a hydrogen plasma treatment.

Improvement of Electron Field Emission in Patterned Carbon Nanotubes by High Temperature Hydrogen Plasma Treatment

Improvement of Electron Field Emission in Patterned Carbon Nanotubes by High Temperature Hydrogen Plasma Treatment

On the electrical conductivity of semiclassical two-component plasmas

Starting from a memory-function formalism coupled with the Green– Kubo formula and an approximate expression for the generalized Coulomb logarithm, the electric conductivity of a dense high-temperature hydrogen plasma is studied. A pseudopotential model, taking account of short-range quantum effects and long-range screening-field effects, is employed to include quantum mechanical and polarization effects. An analytical formula for the Coulomb logarithm is proposed when the thermal de Broglie wavelengths are rather smaller than the Debye radius. A minimum in the curve of electrical conductivity is found and some physical evidence for its appearance is produced.

Defect examination of diamond crystals by surface hydrogen-plasma etching

A method to examine the defects and defect distribution in diamond crystals has been developed. To make the crystal defects visible, a high-temperature hydrogen-plasma etching was employed. By a combination of scanning electron microscopy and atomic force microscopy, the etch pits of the (001) diamond faces parallel to the substrate were observed and analyzed. The defect distribution of chemical-vapor-deposited diamond crystallites corresponds exactly with that observed by transmission electron microscopy, and can be related to the growth mode during film deposition.

Measurements of Cloud Densities Surrounding Impurity Carbon Pellets

Cloud densities surrounding plastic carbon impurity pellets (polystyrene) injected into high-temperature hydrogen plasma are measured from Stark broadening of spectral lines. The line profiles from carbon ions are observed by a 1 m visible spectrometer and multichannel optical system. Electron densities measured from C+ and C+5 ions are 1-1.5×1017 and 4×1014 cm-3, respectively. The results are compared with calculations from an ablation model.

Velocity relaxation of injected H/sup 0/ particles into a high-temperature hydrogen plasma

The velocity relaxation of an H/sup 0/ beam injected into high-temperature plasma is analyzed by deriving a Fokker-Planck-type equation. The diffusion rate in the velocity space of an H/sup 0/ particle is directly proportional to the plasma temperature. Thus the effective energy relaxation of the H/sup 0/ beam in the high-temperature plasma would be expected. It is shown that the Fokker-Planck-type equation satisfies the Boltzmann H theorem in the absence of particle loss. The constant of time decay of the beam density due to ionization with plasma ions, the thermalizing effect, and a method of possible analysis of trapped ions are also discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

New density diagnostic method based on emission line intensity ratio of neutral hydrogen in an ionizing phase plasma

For high temperature hydrogen plasmas in the ionizing phase, the population density of the excited levels has been calculated for a wide range of electron densities and temperatures. In the calculation we employed the most recent and reliable cross-section data for excitation between discrete levels and the ionization cross-section data from these levels. The line intensity ratios calculated under conditions of optical thinness are presented graphically for the Lyman and Balmer series lines. The intensity ratios are found to be rather insensitive to the electron temperature for temperatures higher than 10 eV. These values may be used for determining the electron density in the region of 1017 ⪅ ne ⪅ 1021 m−3, which is relevant to fusion research plasmas. Radiation loss from the plasma and energy loss from the plasma electrons are also presented for a wide range of electron densities and temperatures.

An Improvement of Secondary Emission Detector for Energy Analysis of Charge-Exchange Neutrals Emitted from High-Temperature Plasma

Secondary emission detector (SED) is improved for ion temperature measurement of high-temperature plasma by charge-exchange neutral analysis. This improvement is based on the incident energy (E) dependency of the ratio of secondary electron yield for an incident angle θ to that for normal incidence, defined as k( θ, E). The ratio k( θ, E) is investigated as functions of E and θ for hydrogen atom incidence. To examine and demonstrate the usefulness of the improved SED, both experimental simulation and computer simulation of the charge-exchange neutral analysis with the improved SED are used. In the experimental simulation, facsimile neutrals are produced by neutralization of an ion beam on a solid surface and are analyzed by the improved SED. The result is compared with that obtained by using normal charge-stripping type analyzer. In the computer simulation, a simple model of the charge-exchange neutral emission of high-temperature hydrogen plasma is assumed and the usefulness of the improved SED as a hydrogen plasma diagnostic technique is evaluated under the influences of strong plasma radiation conditions.

Measurement of ultraviolet Argon(II) transition probabilities

The transition probabilities of twelve Ar(II) lines around 300nm have been measured in a stationary arc experiment at 1 atm. The reported data are based on absolute intensities, calibrated by the continuum radiation of a high temperature hydrogen plasma. For two lines the maximum emission coefficient at 26500 K has been used for an immediate determination of the respective A mn -values. These data serve for temperature measurements at lower arc currents, where the other lines are investigated. The results, the uncertainty of which should be below ±15%, agree satisfactorily with coulomb approximation calculations, but show severe discrepancies as compared with more recent NBS tables.

Radiation losses in a dense high-temperature hydrogen plasma containing impurities

The authors calculate the radiation intensity of a hydrogen plasma containing small amounts of impurity in the form of bare nuclei and hydrogen-, helium-, lithium- and beryllium-like ions with a nuclear charge Z in the range 5 ≤ Z ≤ 18. They consider electron concentrations of 1016 ≤ ne ≤ 1020 cm−3 and electron temperatures of 0.05 ⩽ kT/Z2 Ry ⩽ 3 (Ry = 13.6eV), which are typical of the radiating zone of the plasma focus. The results show, among other things, that the radiation from the impurities may substantially limit the life-time of the high-temperature zone in the plasma focus.

The Spectra of Highly Ionized Light Elements in a High Temperature Plasma

By introducing small proportions of appropriate gases into a high-temperature hydrogen plasma produced by the toroidal discharge apparatus SCEPTRE IV, the spectra of highly ionized B, C, N, O, F, and Ne have been obtained and investigated in the wavelength range 200-7000 Å. New as well as previously observed resonance lines of Li I-like ions have been measured. Hydrogen-like transitions of O VI have been observed, the wavelengths of which agree within the experimental errors with the predictions of a polarization formula. According to this formula, the ionization limit of O VI is 1114010 cm-1. New lines of Ne VII, Ne VI, and Ne IV have been measured and new energy levels have been obtained.