Direct Current Discharge Plasma Research Articles

Crystalline diamond/graphite nanoflake hybrid films

Freestanding crystalline diamond/graphite nanoflake hybrid films have been deposited in H 2/CH 4 gas mixtures using a high pressure (1.3 × 10 4 Pa) direct current plasma discharge. Sacrificial layers of close-packed silica microspheres were used as a matrix to produce dual gas chemistries on the plasma-facing and reverse sides of the microspheres. A continuous polycrystalline diamond film was formed on the front surface whilst graphite was deposited in the form of nanoflakes as a thinner hemispherical layer on the reverse side of the silica spheres respectively. Chemical etching of the silica matrix yielded crystalline diamond/well-aligned graphite nanoflakes hybrid films.

Liquid-crystal phase transition by electron shower in a direct current complex plasma

The Coulomb crystal of strongly coupled fine particles is formed by electron shower in a direct current discharge plasma, where the electron shower is injected from an auxiliary plasma which is situated below a main plasma. In case of electron shower injection, the phase transition of dust particles is controlled under the constant argon pressure. The characteristic properties of electron shower injection are discussed theoretically by using a simple collisional sheath model. The calculation analysis clearly shows that electron injection causes the change in charges on fine particles, resulting in a liquid-solid phase transition as in the experiment.

Generation of two-dimensional dust vortex flows in a direct current discharge plasma

The two-dimensional dust vortex flows are observed in a direct current discharge plasma near the edge of a metal plate which is situated in the dust-particle levitation region. Applying negative dc potential to the metal plate, dust particles are strongly accelerated toward the metal plate edge, and two symmetric dust vortex flows are generated on both sides of the metal plate. Numerical calculation including the effect of the ion drag force well demonstrates the dust vortex formation as in the experiment. A mechanism of the dust vortex generation could be explained by effect of an asymmetry of ion drag force near the metal plate.

Direct Current Discharge Plasma Chemical Vapor Deposition of Nanocrystalline Graphite Films on Carbon Fibers

Nanocrystalline graphite films were synthesized on carbon fibers by the direct current discharge plasma chemical vapor deposition method. The morphology and microstructure of the obtained products were characterized by scanning electron microscopy, Raman spectroscopy, and transmission and high-resolution transmission electron microscopy. The results showed that the size and thickness of graphite nanosheets were about 0.3−2 μm and 5−20 nm, respectively, and the purity and graphitization degree of the films can be improved by increasing the deposition time of graphite nanosheets. The down-shift of the G peak in Raman spectra can be attributed to the temperature differences of samples heating by laser radiation. In comparison with the products grown on silicon substrate under similar experimental parameters, carbon fiber substrate is more favorable for the deposition of graphite structure.

Evaluation of the Distribution Depth of Charge Injected by Direct-Current Discharge Plasma into Thin Polyimide and Poly(ethylene terephthalate) Films

The dynamic capacitor method was proposed for determining the distribution depth of negative charge induced in the surface layers of thin polymer films under exposure to a dc discharge as a result of trapping plasma-injected electrons, and equations for calculation were obtained. Charge distribution in thin poly(pyromellitimide) and poly(ethylene terephthalate) films with different thickness (1–6 μm) was experimentally studied, and the negative charge due to the injection of electrons from plasma was found penetrate to a depth greater than 0.5 μm.

Kinetic Simulation of an Ion Acoustic Wave with Charge Exchange Process in Direct Current Discharge Plasma

A charge exchange model is set and its simulation results are compared to those of previous friction model in the lower current branch of a discharge plasma. A remarkable delocalization of a high f...

Plasma environment during hot cathode direct current discharge plasma chemical vapor deposition of diamond films

The plasma characteristics have been investigated in situ by using optical emission spectroscopy (OES) and the Langmuir probe during hot cathode direct current discharge plasma chemical vapor deposition of diamond films. The changes of atomic H and CH radical in the ground state have been calculated quantitatively according to the results of OES and the Langmuir probe measurement as discharge current density varied. It is shown that atomic H and CH radicals both in the ground state and in the excited state increase with the enhancement of the discharge current density in the plasma. The electron density and CH emission intensity increase linearly with the enhancement of discharge current densities. The generation of different carbon-containing radicals is related to the elevation of electron temperature. Combining the growth process of diamond films and the diagnostic results, it is shown that atomic H in the excited state may improve the diamond growth efficiently, and the increase of electron temperature and density plays an important role in the increase of the deposition rate of diamond films.

Early formation of thick diamond films on Si substrates

The early formation of the thick diamond films has been investigated to obtain a better understanding of the characteristic of diamond nucleation. At the early stage in hot cathode direct current discharge plasma chemical vapor deposition of diamond films, well-distributed black spots of 0.3 mm in diameter are found on the Si substrates, the spacing of two adjacent spots is about 1 mm. For the X-ray photoelectron spectroscopy experiment of the Si surface with spots, SiC is detected in the spot regions. The SEM analysis indicates that the nuclei and growth of diamond particles may preferentially occur on the spot regions. The result implies that the existing of these spots is beneficial to enhance the adhesion between diamond films and Si substrates.

Diagnostics of plasma emission spectra during electron assisted chemical vapor deposition of diamond films

Diamond films were deposited by hot cathode direct current discharge plasma chemical vapor deposition from a CH4–H2 gas mixture. Optical emission spectroscopy was employed to investigate in situ the plasma emission characterization during diamond synthesis. The dependence of plasma emission spectra on the input CH4/H2 ratio and the substrate temperature was investigated. A significant variation in the emission intensity of the CH radical was measured with a change in the CH4 concentration. C2 was detected only at high CH4 concentration. In addition, the relative emission intensity of the C2 species was sensitive to a high substrate temperature. The correlation between the spectra of some species and the quality of diamond films was studied. These results suggest that CH and CH+ are all important precursor species in the diamond deposition reaction, while C2 is associated with the presence of a nondiamond phase in the films.

A direct current plasma discharge cleaning method to eliminate background signals in secondary ion mass spectrometry

A simple technique has been developed to reduce background signals due to contaminants in a time-of-flight secondary ion mass spectrometer. This technique uses an argon dc plasma discharge and allows for rapid (10–15 min), routine cleaning of the interior instrument surfaces and vacuum chamber walls.

Mechanism of the direct current plasma discharge decomposition of disilane

Etude par spectrometrie de masse en presence ou non de NO. Les produits observes sont H 2 , SiH 4 , Si 3 H 8 , Si 4 H 10 et un film de Si hydrogene amorphe. L'introduction de NO dans la decharge reduit les rendements