Investigation of an electrode-driven hydrogen plasma method for in situ cleaning of tin-based contamination

To prolong the service life of optics,the feasibility of in situ cleaning of the multilayer mirror(MLM)of tin and its oxidized contamination was investigated using hydrogen plasma at different power levels.Granular tin-based contamination consisting of micro-and macroparticles was deposited on silicon via physical vapor deposition(PVD).The electrodedriven hydrogen plasma at different power levels was systematically diagnosed using a Langmuir probe and a retarding field ion energy analyzer(RFEA).Moreover,the magnitude of the self-biasing voltage was measured at different power levels,and the peak ion energy was corrected for the difference between the RFEA measurements and the self-biasing voltage(E_(RFEA)-eV_(self)).XPS analysis of O 1s and Sn 3d peaks demonstrated the chemical reduction process after 1 W cleaning.Analysis of surface and cross-section morphology revealed that holes emerged on the upper part of the macroparticles while its bottom remained smooth.Hills and folds appeared on the upper part of the microparticles,confirming the top-down cleaning mode with hydrogen plasma.This study provides an in situ electrode-driven hydrogen plasma etching process for tin-based contamination and will provide meaningful guidance for understanding the chemical mechanism of reduction and etching.

THE IMPROVEMENT OF ELECTRON FIELD EMISSION FROM AMORPHOUS CARBON FILMS DUE TO HYDROGEN PLASMA CHEMICAL ANNEALING EFFECT

Hydrogenated amorphous carbon films were fabricated by using layer-by-layer deposition method and hydrogen dilution method in a small d.c.-assisted plasma enhanced chemical vapor deposition system. It was found that the hydrogen plasma treatment could change the sp2/sp3 ratio to some extent by chemical etching. The improvements of field emission characteristics were observed compared with that from conventionally deposited a-C films, which can be attributed to the large field enhancement effect due to the inhomogeneous distribution of nanometer scale sp2 clusters and the reduction of the surface emission barrier due to the hydrogen termination.

Current–voltage characteristics of hydrogen DC plasma torches with different sizes in an external axial magnetic field

Current-voltage （l-V） characteristics of hydrogen DC plasma torches with different sizes in an external axial magnetic field under atmospheric pressure are reported. Three anodes with different diameters are adopted in a 50-kW torch： 25 mm, 30 mm, and 35 nun, respectively. Two different diameters of anodes, that is, 100 mm and 130 mm, are adopted in a 1-MW plasma torch. The arc voltage shows a negative trend with the increase of arc current under the operating regimes. On the contrary, arc voltage shows a positive trend as the flow rate of carder gas increases, and a similar trend is found with increasing the external magnetic flux density. A similarity formula is constructed to correlate the experimental data of the torches mentioned above. Linear fitting shows that the Pearson correlation coefficient is 0.9958.

Diagnosis of Hydrogen Plasma in a Miniature Penning Ion Source by Double Probes

Parameters of hydrogen plasma in a miniature Penning discharge ion source, including the electron temperature and the electron density, were measured by using double probes. The results indicate that the electron density increases and the electron temperature decreases with the increase in gas pressure and the discharge current. The electron temperature is about 5 - 9 eV and the electron density is 6.0× 10^13 ～ 1.2 × 10^14 m^-3 while the discharge current is in a range of 50 - 120 μA.

Hematite reduction by hydrogen plasma:Where are we now?

Currently,iron is extracted from ores such as hematite by carbothermic reduction.The extraction process includes several unit steps/processes that require large-scale equipment and significant financial investments.Additionally,the extraction process produces a substantial amount of harmful carbon dioxide(CO_(2)).Alternative to carbothermic reduction is the reduction by hydrogen plasma(HP).HP is mainly composed of exciting species that facilitate hematite reduction by providing thermodynamic and kinetic advantages,even at low temperatures.In addition to these advantages,hematite reduction by HP produces water,which is environmentally beneficial.This report reviews the theory and practice of hematite reduction by HP.Also,the present state of the art in solid-state and liquid-state hematite reduction by HP has been examined.The in-flight hematite reduction by HP has been identified as a potentially promising alternative to carbothermic reduction.However,the in-flight reduction is still plagued with problems such as excessively high temperatures in thermal HP and considerable vacuum costs in non-thermal HP.These problems can be overcome by using non-thermal atmospheric HP that deviates significantly from local thermodynamic equilibrium.

The effects of a static magnetic field on the microwave absorption of hydrogen plasma in carbon nanotubes: a numerical study

We theoretically investigate the microwave absorption properties of hydrogen plasma in iron-catalyzed high- pressure disproportionation-grown carbon nanotubes under an external static magnetic field in the frequency range 0.3 GHz to 30 GHz, using the Maxwell equations in conjunction with a general expression for the effective complex permittivity of magnetized plasma known as the Appleton Hartree formula. The effects of the external static magnetic field intensity and the incident microwave propagation direction on the microwave absorption of hydrogen plasma in CNTs are studied in detail. The numerical results indicate that the microwave absorption properties of hydrogen plasma in iron-catalyzed high-pressure disproportionation-grown carbon nanotubes can be obviously improved when the exter- nal static magnetic field is applied to the material. It is found that the specified frequency microwave can be strongly absorbed by the hydrogen plasma in iron-catalyzed high-pressure disproportionation-grown carbon nanotubes over a wide range of incidence angles by adjusting the external magnetic field intensity and the parameters of the hydrogen plasma.

Selective Heating of Transition Metal Usings Hydrogen Plasma and Its Application to Formation of Nickel Silicide Electrodes for Silicon Ultralarge-Scale Integration Devices

We developed an apparatus for producing high-density hydrogen plasma. The atomic hydrogen density was 3.1 × 1021 m?3 at a pressure of 30 Pa, a microwave power of 1000 W, and a hydrogen gas flow rate of 10 sccm. We confirmed that the temperatures of transition-metal films increased to above 800。C within 5 s when they were exposed to hydrogen plasma formed using the apparatus. We applied this phenomenon to the selective heat treatment of nickel films deposited on silicon wafers and formed nickel silicide electrodes. We found that this heat phenomenon automatically stopped after the nickel slicidation reaction finished. To utilize this method, we can perform the nickel silicidation process without heating the other areas such as channel regions and improve the reliability of silicon ultralarge-scale integration devices.

Hydrogen cold plasma for synthesizing Pd/C catalysts: the effect of support-metal ion interaction

It has been found that cold plasma is a facile and environmentally benign method for synthesizing supported metal catalysts, and great efforts have been devoted to enlarging its applications. However, little work has been done to disclose the influence mechanism, which is significant for controllable synthesis. In this work, hydrogen cold plasma was adopted to synthesize a palladium catalyst supported on activated carbon （Pd/C-P） using HzPdC14 as a Pd precursor followed by calcination in hydrogen gas to remove the chlorine ions. The Pd/C-P catalyst was found to be made of larger Pd nanoparticles showing a decreased migration to the support outer surface than that prepared by the conventional thermal hydrogen reduction method （Pd/C-C）. Meanwhile, the pore diameter of the activated carbon support is small （,-~4 nm）. Therefore, Pd/C-P exhibits lower CO oxidation activity than Pd/C-C. It was proposed that the strong interaction between the activated carbon and PdC142-, and the enhanced metal-support interaction caused by hydrogen cold plasma reduction made it difficult for Pd nanoparticles to migrate to the support outer surface. The larger-sized Pd nanoparticles for Pd/C-P may be due to the Coulomb interaction resulting in the disturbance of the metal-support interaction. This work has important guiding significance for the controllable synthesis of supported metal catalysts by hydrogen cold plasma.

Nano-composite Particles Synthesized by a Hydrogen Arc Plasma

Nano-composite particles can be synthesized by a hydrogen arc plasma method, which possesses the advantages of high productivity, controllable size distribution and low electric energy consumption comparing with conventional gas condensation method. With this method, not only the nanoparticles of metals and alloys, but also the nano-composite particles with shell structure can be synthesized. The microstructures, compositions and the formation mechanism of the nano composite particles were studied

The mechanism of hydrogen plasma passivation for poly-crystalline silicon thin film

The mechanism of hydrogen plasma passivation for poly-crystalline silicon （poly-Si） thin films is investigated by optical emission spectroscopy （OES） combined with Hall mobility, Raman spectra, absorption coefficient spectra, and so on. It is found that different kinds of hydrogen plasma radicals are responsible for passivating different defects in polySi. The Ha with lower energy is mainly responsible for passivating the solid phase crystallization （SPC） poly-Si whose crystallization precursor is deposited by plasma-enhanced chemical vapor deposition （PECVD）. The H＊ with higher energy may passivate the defects related to teh Ni impurity around the grain boundaries more effectively. In addition, Hβ and H7 with the highest energy are required to passivate intra-grain defects in the poly-Si crystallized by SPC but whose precursor is deposited bv low pressure chemical vapor deposition（LPCVD）

Erosion research of CX-2002U carbon composites under low-temperature high-flux hydrogen plasma

The net erosion yield of CX-2002U carbon fiber composites under high-flux low-temperature hydrogen plasma is investigated using a linear plasma device.It is found that the net erosion yield decreases rapidly first,and then tends to saturate with the increase of hydrogen–plasma flux.When the temperature of the sample eroded by hydrogen plasma is above 300°C,the hybridization of electrons outside the carbon atom would change.Then the carbon atoms combine with hydrogen atoms to form massive spherical nanoparticles of hydrocarbon compounds and deposit on the surface at the flux condition of 1.77×10^(22) m^(−2)·s^(−1).Under the irradiation of hydrogen plasma loaded with negative bias,the surface morphology of the matrix carbon is changed dramatically.Moreover,the energy dependence of mass loss does not increase in proportion to the increase of hydrogen–plasma energy,but reaches a peak around 20 V negative bias voltage.Based on the analysis of different samples,it can be concluded that the enhancement of energy could make a contribution to chemical erosion and enlarge the size of pores existing on the surface.

Effect of hydrogen plasma implantation on the micro-structure and magnetic properties of hcp-Co_(80)^(57)Fe_(4)Ir_(16)thin films

We present detailed investigations of structural and static/dynamic magnetic properties of hydrogenated hcp-Co_(80)^(57)Fe_(4)Ir_(16) soft magnetic thin films.Two different kinds of defects,i.e.,destructive and non-destructive,were demonstrated by controlling the negative bias voltage of the hydrogenation process.Our results show that the structure and magnetic properties of our sample can be tuned by the density of the induced defects.These results provide better understanding of the hydrogenation effect and thus can be used in the future for materials processing to meet the requirements of different devices.

Electrical and optical properties of hydrogen plasma treatedβ-Ga_(2)O_(3) thin films

The behavior of H inβ-Ga_(2)O_(3) is of substantial interest because it is a common residual impurity that is present inβ-Ga_(2)O_(3),regardless of the synthesis methods.Herein,we report the influences of H-plasma exposure on the electric and optical properties of the heteroepitaxialβ-Ga_(2)O_(3) thin films grown on sapphire substrates by chemical vapor deposition.The results in-dicate that the H incorporation leads to a significantly increased electrical conductivity,a greatly reduced defect-related photolu-minescence emission,and a slightly enhanced transmittance,while it has little effect on the crystalline quality of theβ-Ga_(2)O_(3) films.The significant changes in the electrical and optical properties ofβ-Ga_(2)O_(3) may originate from the formation of shallow donor states and the passivation of the defects by the incorporated H.Temperature dependent electrical properties of the H-in-corporatedβ-Ga_(2)O_(3) films are also investigated,and the dominant scattering mechanisms at various temperatures are dis-cussed.

Behavior of an indigenously fabricated transferred arc plasma furnace for smelting studies

The utilization of industrial solid waste for metal recovery requires high-temperature tools due to the presence of silica and alumina, which is reducible at high temperature. In a plasma arc furnace, transferred arc plasma furnace（TAP） can meet all requirements, but the disadvantage of this technology is the high cost. For performing experiments in the laboratory, the TAP was fabricated indigenously in a laboratory based on the different inputs provided in the literature for the furnace design and fabrication. The observed parameters such as arc length, energy consumption, graphite electrode consumption, noise level as well as lining erosion were characterized for this fabricated furnace. The nitrogen plasma increased by around 200 K（200 ℃） melt temperature and noise levels decreased by ~10 d B compared to a normal arc.Hydrogen plasma offered 100 K（100 ℃） higher melt temperature with ~5 d B higher sound level than nitrogen plasma. Nitrogen plasma arc melting showed lower electrode and energy consumption than normal arc melting, whereas hydrogen plasma showed lower energy consumption and higher electrode consumption in comparison to nitrogen plasma. The higher plasma arc temperature resulted in a shorter meltdown time than normal arc with smoother arcing. Hydrogen plasma permitted more heats, reduced meltdown time, and lower energy consumption, but with increased graphite consumption and crucible wear. The present study showed that the fabricated arc plasma is better than the normal arc furnace with respect to temperature generation, energy consumption, and environmental friendliness. Therefore, it could be used effectively for smelting-reduction studies.

Understanding hydrogen plasma processes based on the diagnostic results of 2.45 GHz ECRIS at Peking University

Optical emission spectroscopy（OES）, as a simple in situ method without disturbing the plasma, has been performed for the plasma diagnosis of a 2.45 GHz permanent magnet electron cyclotron resonance（PMECR） ion source at Peking University（PKU）. A spectrum measurement platform has been set up with the quartz-chamber electron cyclotron resonance（ECR） ion source [Patent Number： ZL 201110026605.4] and experiments were carried out recently. The electron temperature and electron density inside the ECR plasma chamber have been measured with the method of line intensity ratio of noble gas. Hydrogen plasma processes inside the discharge chamber are discussed based on the diagnostic results. What is more, the superiority of the method of line intensity ratio of noble gas is indicated with a comparison to line intensity ratio of hydrogen. Details will be presented in this paper.

Effects of Hydrogen on the Methane Coupling under Non-equilibrium Plasma

In this paper, hydrogen is first utilized in the study on methane coupling under nonequilibrium plasma. Results indicate that the addition of hydrogen is beneficial. to the methane coupling so as to increase the conversion rate of methane and the yield of C2 hydrocarbon with a gradual increase in the addition of hydrogen in a certain range of proportionality. This conclusion explores a new route of hydrogenated methane coupling.

Plasmas Created in the Interaction of Antiprotons with Atomic and Ionized Hydrogen Isotopes. Suggested Fuels for Space Engines

The main objective of the present work is to investigate the properties of plasmas created by injecting a thermalized beam of antiprotons in two types of media. The first is hydrogen, deuterium, or tritium atoms localized in palladium crystals. The second medium is composed of protons, deuterons, or tritons localized in a magnetic cavity. Particularly, it is demonstrated that huge amounts of energy are released in both cases which could be used as fuels for space shuttle engines. A novel mathematical scheme is employed to calculate the energy yields in real space at different incident energies of the antiprotons.

Influence of Atomic Hydrogen on Transparent Conducting Oxide During Hydrogenated Microcrystalline Si Preparation by PECVD

The hydrogen plasma degradation of transparent conduction oxides （TCO） is studied for hydrogenated microcrystalline Si（μc-Si：H）prepared by plasma enhanced chemical vapor deposition （PECVD）. TCO films such as SnO2 and SnO2/ZnO bi-layer films were exposed to atomic H at various substrate temperatures and for various treatment times. A decrease in the transmittance due to reduction by atomic H was scarcely observed for SnO2 / ZnO bi-layer,while a decrease for SnO2 was found to depend strongly on the substrate temperature. The resistivity of SnO2 films decreases significantly when substrate temperature exceeds 150℃in H-plasma. However, H-plasma treatment has little impact on the resistivity of SnO2/ZnO bi-layer film. The reason for the decrease in the transmittance is the appearance of metallic Sn on the surface, and under this condition no μc-Si： H film is deposited. SnO2/ZnO bi-layer is very effective for the suppression of the reduction of TCO during μc-Si：H deposition. The performance of microcrystalline silicon solar cells fabricated on ZnO/SnO2/glass is also investigated.

Synthesis of Co Nanoparticles and Their Catalytic Effect on the Decomposition of Ammonium Perchlorate

The monodispersed Co nanoparticles were successfully prepared by means of hydrogen plasma method in inert atmosphere. The particle size, specific surface area, crystal structure and morphology of the samples were characterized by transmission electron microscopy （TEM）, BET equation, X-ray diffraction （XRD）, and the corresponding selected area electron diffraction （SAED）. The catalytic effect of Co nanoparticles on the decomposition of ammonium perchlorate （AP） was investigated by differential thermal analyzer （DTA）. Compared with the thermal decomposition of pure AP, the addition of Co nanoparticles （2%-10%, by mass） decreases the decomposition temperature of AP by 145.01-155.72℃. Compared with Co3O4 nano-particles and microsized Co particles, the catalytic effect of Co nanoparticles for AP is stronger. Such effect is attributed to the large specific surface area and its interaction of Co with decomposition intermediate gases. The present work provides useful information for the application of Co nanoparficles in the AP-based propellant.

Thick c-BN films deposited by radio frequency magnetron sputtering in argon/nitrogen gas mixture with additional hydrogen gas

The excellent physical and chemical properties of cubic boron nitride(c-BN) film make it a promising candidate for various industry applications. However, the c-BN film thickness restricts its practical applications in many cases. Thus, it is indispensable to develop an economic, simple and environment-friend way to synthesize high-quality thick, stable c-BN films. High-cubic-content BN films are prepared on silicon(100) substrates by radio frequency(RF) magnetron sputtering from an h-BN target at low substrate temperature. Adhesions of the c-BN films are greatly improved by adding hydrogen to the argon/nitrogen gas mixture, allowing the deposition of a film up to 5-μm thick. The compositions and the microstructure morphologies of the c-BN films grown at different substrate temperatures are systematically investigated with respect to the ratio of Hgas content to total working gas. In addition, a primary mechanism for the deposition of thick c-BN film is proposed.