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.

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.

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.

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）

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.

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.

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.

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.

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.

Pathways of liquefied petroleum gas pyrolysis in hydrogen plasma:A density functional theory study

A density functional theory （DFT） study has been conducted in this work to investigate the pyrolysis pathways of propane and n-butane, which are the main components of liquefied petroleum gas （LPG）, for better understanding the pyrolysis behavior of LPG in hydrogen thermal plasma. Over 60 possible reactions are considered. The reaction enthalpies and activation energies of these reactions are calculated and analyzed with a Gaussian method of B3LYP and basic set of 6-31G （d,p）. A most possible reaction pathway is brought up. According to this reaction pathway, the main products of LPG pyrolysis are acetylene, ethylene, methane, ethane and extra hydrogen. Acetylene mainly comes from the pyrolysis of propylene and ethylene, and hydrogen abstraction reactions are the main source of extra hydrogen gas. Active H. radicals are found to play a very important role in many reactions, and they can remarkably lower the energies needed for reactions.

Methane Coupling Using Hydrogen Plasma and Pt/γ-Al_2O_3 Catalyst

In this paper, methane coupling at ambient temperature, under atmospheric pressure and in the presence of hydrogen was firstly investigated by using pulse corona plasma and Pt/g-Al2O3 catalyst. Experimental results showed that Pt/g-Al2O3 catalyst has catalytic activity for methane coupling to C2H4. Over sixty percent of outcomes of C2 hydrocarbons were detected to be ethylene.

Direct Preparation of Hydrogen and Carbon Nanotubes by Microwave Plasma Decomposition of Methane over Fe/Si Activated by Biased Hydrogen Plasma

Methane was decomposed to hydrogen and carbon nanotubes (CNTs) by microwave plasma, using Fe/Si catalyst activated by biased (—150 V) hydrogen plasma for various treatment times. Upon exposure to biased hydrogen plasma, the catalyst surface becomes lumpy within 1 min, coheres between 5 and 10 min and forms particles after 20 min. The methane conversion increased up to 93% over the treatment time of 5 min. The hydrogen yield showed as similar tendency as the methane conversion and kept 83% at treatment time of 5 min. The treatment time up to 1 min increased the amount of deposited carbon, and after treatment time of 5 min it dropped;then again after treatment time of 20 min, it increased to reach a maximum value of 22 gc/gcat. Deposited carbon was found to be consisted of carbon nanotubes. It grew vertically on the catalyst surface and reached a maximum length of 30.7 nm after treatment time of 10 min. Multiple types of CNTs were present, and the CNT diameters decreased with increasing plasma treatment time.

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.

Reduced defect density in microcrystalline silicon by hydrogen plasma treatment

The effect of hydrogen plasma treatment （HPT） during the initial stage ofmicrocrystalline silicon （μc- Si） growth on the defect density of μc-Si has been investigated. Lower absorption coefficient in the 0.8-1.0 eV indicated less defect density compared to its counterpart without HPT. The infrared spectroscopy of μc-Si with HPT shows an increase in 2040 cm-1, which reveals more Si-H in the amorphous/crystalline interfaces. We ascribe the decrease of defect density to hydrogen passivation of the dangling bonds. Improved performance of μc-Si solar cell with HPT is due to the reduced defect density.

Evaluation of hydrogen effect on the fatigue crack growth behavior of medium-Mn steels via in-situ hydrogen plasma charging in an environmental scanning electron microscope

Fatigue crack growth(FCG)tests were conducted on a medium-Mn steel annealed at two intercritical annealing temperatures,resulting in different austenite(γ)to fe rrite(α)phase fractions and differentγ(meta-)stabilities.Novel in-situ hydrogen plasma charging was combined with in-situ cyclic loading in an environmental scanning electron microscope(ESEM).The in-situ hydrogen plasma cha rging increased the fatigue crack growth rate(FCGR)by up to two times in comparison with the reference tests in vacuum.Fractographic investigations showed a brittle-like crack growth or boundary cracking manner in the hydrogen environment while a ductile transgranular manner in vacuum.For both materials,the plastic deformation zone showed a reduced size along the hydrogen-influenced fracture path in comparison with that in vacuum.The difference in the hydrogen-assisted FCG of the medium-Mn steel with different microstructures was explained in terms of phase fraction,phase stability,yielding strength and hydrogen distribution.This refined study can help to understand the FCG mechanism without or with hydrogen under in-situ hydrogen charging conditions and can provide some insights from the applications point of view.

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.

Reduction of TiO_2 with hydrogen cold plasma in DC pulsed glow discharge

The reduction of TiO2 to Ti2O3 with hydrogen cold plasma generated by a DC pulsed glow discharge was realized under 2500Pa at 1233K. Only a little of Ti<sup>10 O<sup>19 and Ti9O<sup>17 was detected for using molecular hydrogen. Enhancement effects of hydrogen cold plasma on the reduction were discussed in terms of thermodynamic coupling, kinetics and plasma sheath. The exited hydrogen species are considered more effective reducing agents. It is instructive to reduce refractory oxides with plasma hydrogen at the reduced temperature.

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

Changes of the electron dynamics in hydrogen inductively coupled plasma

Changes of the electron dynamics in hydrogen （H2） radio-frequency （RF） inductively coupled plasmas are investigated using a hairpin probe and an intensified charged coupled device （ICCD）. The electron density, plasma emission intensity, and input current （voltage） are measured during the E to H mode transitions at different pressures. It is found that the electron density, plasma emission intensity, and input current jump up discontinuously, and the input voltage jumps down at the E to H mode transition points. And the threshold power of the E to H mode transition decreases with the increase of the pressure. Moreover, space and phase resolved optical emission spectroscopic measurements reveal that, in the E mode, the RF dynamics is characterized by one dominant excitation per RF cycle, while in the H mode, there are two excitation maxima within one cycle.