Synthesis evaluation of nitrogen atom encapsulated fullerenes by optical emission spectra in nitrogen plasmas

The nitrogen atom encapsulated fullerene (N@C₆₀) with relatively high yield has been synthesized by a plasma irradiation method. We have examined the relationship between optical emission spectra of a radio frequency (RF) discharge nitrogen plasma and the synthesis yield of N@C₆₀. As a consequence, the increasing amount of nitrogen molecule ions (N₂⁺) impinging on the sublimated fullerenes are found to enhance the synthesis of N@C₆₀. Furthermore, it is clarified that there is an optimum condition of the nitrogen plasma for the high-yield synthesis of N@C₆₀, which is generated under lower gas pressure and is irradiated to the larger amount of fullerenes.     

Optical properties of carbon-containing titanium oxide nanocomposites obtained by the pulsed plasma chemical method

This paper presents the results of an experimental investigation on the optical properties of the TiO₂ and Ti_xC_yO_z nanopowders, produced by the pulsed plasma chemical method. Pulsed plasma chemical synthesis is realized on the laboratory stand, including a plasma chemical reactor (6 l) and TEA-500 electron accelerator. The parameters of the electron beam are as follows: 400–450 keV electron energy, 60 ns half-amplitude pulse duration, up to 200 J pulse energy, and 5 cm beam diameter. In TiO₂ sample, obtained using the pulsed plasma chemical method, the particles can be divided into two groups: 100–500 nm large spherical particles and tiny complex particles (sized less than 100 nm). For TixCyOz sample, the morphology of the particles is mainly presented with irregular fragment shape. The average size of the particles is ranged from 200 to 300 nm. The band gap for all synthesized samples is within 2.94–3.35 eV.     

Synthesis of nitrogen-rich carbon nitride thin films via magnetic field-assisted inductively coupled plasma sputtering

Carbon nitride (CN_x) thin films were synthesized by magnetic field-assisted inductively coupled plasma (ICP) sputtering. The electron density, electron temperature and optical emission intensity of the plasma state were significantly changed by varying the external magnetic field applied. The CN_x thin film with the highest nitrogen content (N/C=1.16) was obtained when the electron density was at its highest and the electron temperature at its lowest. Additionally, the optical emission from atomic nitrogen was the strongest under the same condition.     

Growth and microstructures of carbon nanotube films prepared by microwave plasma enhanced chemical vapor deposition process

Well-aligned carbon nanotubes (CNTs) were grown on iron coated silicon substrates by microwave plasma enhanced chemical vapor deposition. Effect of plasma composition on the growth and microstructures of CNTs were investigated by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and optical emission spectroscopy. Morphology and microstructure of nanotubes were found to be strongly dependent on the plasma composition. Aligned bamboo-shaped nanotubes consisting of regular cone shaped compartments were observed for C₂H₂/NH₃/N₂ and C₂H₂/NH₃/H₂ gas mixtures. Randomly oriented or no nanotubes growth were observed in C₂H₂/H₂ and C₂H₂/N₂ gas mixtures respectively. CNTs grown in nitrogen rich plasma had more frequent short compartments while compartment length increased with decreasing nitrogen concentration in the plasma. Raman spectroscopy of CNTs samples revealed that CNTs prepared in nitrogen rich plasma had higher degree of disorder than those in low nitrogen or nitrogen free plasma. In-situ optical emission spectroscopy investigations showed that CN and H radicals play very important role in both the growth and microstructure of CNTs. Microstructure of CNTs has been correlated as a function of CN radical concentration in the plasma. It is suggested that presence of nitrogen in the plasma enhances the bulk diffusion of carbon through the iron catalyst particles which causes compartment formation. Based on our experimental observations, growth model of nanotubes under different plasma composition has been suggested using base growth mechanism.     

Accurate measurement and evaluation of the nitrogen depth profile in plasma nitrided iron

Nitrogen depth profile of plasma nitrided pure iron was measured and evaluated by accurate experimental techniques. Plasma nitriding cycles were carried out on high purity iron substrate in an atmosphere of 75% H₂-25% N₂. Nitrogen concentration depth profiles in the compound layer and the diffusion zone were characterized by glow discharge optical emission spectroscopy (GDOES) and secondary ion mass spectroscopy (SIMS), respectively. Nitrogen diffusion depths were measured accurately by optical and scanning electron microscopy as well as SIMS technique at different nitriding times. Experimental results indicated good agreement between SIMS data and microscopic evaluations for various nitriding cycles. The results of SIMS showed the nitrogen diffusion depth of about 2000 μm in the diffusion zone for 10 h plasma nitriding at 550 °C. Such high depth had not been detected in previous investigations in which the conventional methods such as EDS, GDS, XPS, EPMA or ion probe techniques were used.     

Thermal plasma synthesized nano-powders of (LaCe)B6 starting from oxide-based precursors and its field electron emission performance

High temperature synthesis process of microcrystalline and nanocrystalline (LaCe)B₆ using Self-propagating High temperature Synthesis (SHS) and arc plasma gas phase condensation methods, respectively have been investigated. These methods are rapid and economically viable processes used for the synthesis of technologically important refractory hexaborides. Microcrystalline powders of (LaCe)B₆ were synthesized using the SHS process, starting from oxide precursors of lanthanum, cerium, and boron. The powders obtained using SHS process were used as a precursor to getting nanocrystalline (LaCe)B₆ using the thermal plasma route. The thermal plasma synthesis was carried out using nitrogen and argon plasmas, respectively. In-situ plasma diagnostics were used to identify evaporated species and determine plasma temperature during the formation of nanocrystalline (LaCe)B₆ using optical emission spectroscopy. Further, an effect of plasma input parameters on the structural and optical properties of as synthesized nanocrystalline (LaCe)₆ were investigated using XRD analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. A thorough investigation of morphological and structural properties of synthesized nanocrystalline (LaCe)₆ was carried out using transmission electron microscopy. Finally, field effect electron emission properties of the microcrystalline and nanocrystalline product were investigated and current density, turn on field, stability of emission performance were determined.     

Optical electron-beam diagnostics of free supersonic jet of nitrogen activated by electron-beam-generated plasma

Electron-beam-induced optical emission spectroscopy has been used for the first time to measure the rotational temperature and number density of gas in a free supersonic neutral nitrogen jet and in that activated by electron-beam plasma. The electron-beam plasma was generated by a low-energy electron beam at a distance of 10 mm downstream from the edge of a conical supersonic nozzle. For diagnostics of the activated jet, the spectrum of intrinsic optical emission of plasma was subtracted from the spectrum of emission induced by the probing electron beam in the activated jet. It was established that the rotational temperature in the activated jet is increased as compared to that in the neutral jet, while the density at the jet axis is decreased. The electron-beam activation of nitrogen in the jet leads to a 35% increase in the rotational temperature.     

Features of the spectra of optical emission from high-frequency discharge plasma during bismuth ferrite sputtering

he spectra of optical emission from plasma of the RF discharge in oxygen during the sputtering of bismuth ferrite (BiFeO₃) and iron-containing alloy targets have been studied. Two anomalously intense lines of emission from iron atoms at 613.6 and 306.7 nm have been observed during the sputtering of bismuth ferrite, which are much less pronounced in the case of metal targets. The lines of emission from bismuth atoms are completely absent. A mechanism responsible for excitation of the anomalous emission lines during the sputtering of BiFeO₃ is proposed.

     

Nano-crystalline CVD diamond films deposited on cemented carbide using high current extended DC arc plasma process

Nano-crystalline diamond (NCD) films have been grown on cemented carbide substrates by high current extended DC arc plasma process using Ar/H₂/CH₄ gas mixture at low gas pressure. The plain view and cross section of films are characterized with scanning electron microscopy. A uniform and smooth surface morphology of NCD thin films is observed. Raman spectroscopy has been used to investigate purity of the NCD films. Experimental results on the synthesis and characterization of the NCD films on cemented carbide substrates are discussed in this article.     

Plasma oxidation of electron beam evaporated cadmium thin films

Thin films of pure cadmium have been deposited using electron beam evaporation technique. Effect of radio frequency (RF) plasma oxidation on structural, optical and electrical properties of cadmium thin films has been investigated. It was found that the RF plasma treatment affects on the physical properties of the oxidized cadmium films. Transmittance values of 87% in the visible region and 90% in the near infrared region have been obtained for cadmium oxide (CdO) film oxidized at a plasma-processing power of 600 W. The optical energy gap, E_g, was found to increase as the RF plasma-processing power increases. The resistivity values of 3 × 10^− 3 and 5 × 10^− 3 (Ω cm) have been obtained for CdO films oxidized at RF plasma-processing powers of 550 and 600 W respectively.     

The etching characteristics of Al2O3 thin films in an inductively coupled plasma

In this study, the etching characteristics of ALD deposited Al₂O₃ thin film in a BCl₃/N₂ plasma were investigated. The experiments were performed by comparing the etch rates and the selectivity of Al₂O₃ over SiO₂ as functions of the input plasma parameters, such as the gas mixing ratio, the DC-bias voltage, the RF power, and the process pressure. The maximum etch rate was obtained at 155.8 nm/min under a 15 mTorr process pressure, 700 W of RF power, and a BCl₃ (6 sccm)/N₂ (14 sccm) plasma. The highest etch selectivity was 1.9. We used X-ray photoelectron spectroscopy (XPS) to investigate the chemical reactions on the etched surface. Auger electron spectroscopy (AES) was used for the elemental analysis of the etched surfaces.     

Rapid synthesis of nano-magnetite by thermal plasma route and its magnetic properties

Thermal plasma method has been used to process mild steel scrap for nanopowder synthesis by changing the operating current. The phase analysis of the product nanopowders was studied by X-ray diffraction and the chemical composition was studied by energy dispersive spectroscopy. The morphology, particle size and particle size distribution of the samples were investigated by field emission scanning electron microscope. In addition to the above, the magnetic properties of the samples were investigated by superconducting quantum interface device magnetometer and high temperature vibrating sample magnetometer (HTVSM). From this study, the results indicate that the processed nanopowders were magnetite and exhibit spherical morphology. The magnetic properties, such as, saturation magnetization (M_S), coercivity (H_C), and Curie temperature (T_c) were estimated. The M–H loops exhibited soft magnetism and samples corresponding to 60 and 70A showed the highest M_S and H_C, respectively. The Curie temperature was determined for the sample corresponding to 60A using HTVSM as 852 and 840?K from the heating and cooling curves, respectively. The outcome of the results suggests that thermal plasma is a contaminant-free process and is suitable for processing metal scrap.     

The optical characteristics of plasma formed by laser erosion of CdGa2Se4 and CdGa2S4 crystals

The optical emission from fragments formed during a laser-induced erosion of the surface of CdGa₂Se(S)₄ single crystals was studied. The laser plasmas were generated by pulsed radiation of a Nd laser with a beam power density of (1–2)×10⁹ W/cm². The laser plasma exists in the form of a nucleus with a diameter of 2–3 mm, while no plasma torch is formed in the space above the target surface. In the 200–600 nm spectral range, the main emission lines observed in the spectrum of the plasma obtained from a laser-eroded CdGa₂Se₄ crystal corresponded to transitions from the lowest atomic energy levels of Ga(I), as well as to the intense transitions between the electron states of Se(II) and Se(III). The emission spectra of the plasma from a laser-eroded CdGa₂S₄ crystal surface exhibited a single intense line at 532.1 nm showing evidence of a prevailing contribution of the S(II) (4s–4p) transitions. The optical data agree with the results of the mass spectrometric analysis of the laser plasma generated from cadmium thiogallate crystals. The emission characteristics are of interest from the standpoint of the plasma diagnostics and optimization of the technology of laser sputter deposition of thin films with complicated compositions.     

Spatial distributions of the intensity of optical emission lines studied during bismuth ferrite film deposition in high-frequency discharge plasma

We have studied spatial distributions of the intensity of optical emission lines in plasma of the RF discharge in oxygen during the deposition of bismuth ferrite (BiFeO₃) films. The intensities of characteristic emission lines in the visible, near-UV and near-IR spectral ranges have been measured as functions of the distance from the probed plasma layer to the target. The intensity profiles of the emission lines of oxygen ions, oxygen atoms, and iron atoms exhibit different behavior. Differences in the spatial distributions of intensity have been also observed for the two characteristic emission lines (at 613.7 and 688.6 nm) of iron.     

PECVD沉积和原位退火时间对h-BN薄膜组成及光学带隙的影响

采用射频等离子增强化学气相沉积设备, 以高纯N₂和B₂H₆为气源, 制备了系列h-BN薄膜, 得到适合生长h-BN薄膜的最佳工艺条件。在此条件下, 研究了不同沉积时间和退火时间对薄膜组成和光学带隙的影响。采用傅立叶变换红外光谱仪、紫外可见光分光光度计和场发射扫描电子显微镜对样品进行了表征。实验结果表明: 在衬底温度、射频功率和气源流量比率一定的条件下, 沉积时间对h-BN薄膜成膜质量和光学带隙都有较大影响, 且光学带隙与膜厚呈指数关系变化。700℃原位退火不同时间对h-BN薄膜的结晶质量有所影响, 而物相和光学带隙基本没有改变。     

Spectra and kinetics of emission from the products of explosive decomposition of silver azide

The spectrum and kinetics of optical emission from the products of explosive decomposition of silver azide (AgN₃) initiated by a pulsed electron beam (0.5 MeV, 1 kA/cm², 20 ns) have been experimentally studied. The stage of preexplosion luminescence is followed by the formation of a continuous emission spectrum due to a dense plasma of decomposition products. This spectrum exhibits variations within a time interval of 0.6–0.9 μs, which can be related to the self-heating of plasma from 3000 to 3600 K as a result of the exothermal reaction 2N₃ → 3N₂.     

Improvements in the angular current density of inductively coupled plasma ion source for focused heavy ion beams

A compact inductively coupled plasma ion source (ICPIS) is developed for producing high current micron size beams for high speed micromachining applications. Angular current density (J_Ω) of the beam extracted from ICPIS is measured and found to be three orders higher than that of the conventional liquid metal ion sources. An improvement in J_Ω by >30% is achieved through the increase of RF power density in the plasma by reducing the plasma volume instead of operating ion source at high RF power. Studies on J_Ω show that heavier ions have maximum J_Ω at lower power and vice versa for the lighter ions. Ion beams of Neon, Argon, Krypton and Xenon extracted at 5 kV, have J_Ω of 57, 51, 37 and 30 mA/Sr respectively at RF power in the range of 75 W–200 W. Measurements on proton beam which is very important for imaging applications show J_Ω of 45 mA/Sr at 200 W.     

Laser induced plasma in the formation of surface-microstructured silicon

The plasma induced by femtosecond laser pulses irradiated on silicon surface has been investigated by optical emission spectroscopy. The plasma emission spectra show strong dependence on the structuring ambient gas species and pressure. Among the four ambient gases (SF₆, N₂, air and vacuum), the plasma obtained in sulfur hexafluoride (SF₆) shows the strongest signals. The emission intensities increase initially with the gas pressure, and achieve strongest at the pressure of about 70 kPa, then decrease as the pressure further increases. The stronger plasma emission signals indicate stronger reactions, resulting in sharper sample morphology, which provides an insight into the reaction process.     

Chemical-reaction dependence of plasma parameter in reactive silane plasma

Electron temperature in a silane glow-discharge plasma, being an important plasma parameter for determining photo-induced instability in the resulting hydrogenated amorphous silicon (a-Si:H), has been studied under various film-preparation conditions. We have used an optical-emission-intensity ratio of Si^* to SiH^* (I_si*/I_siH^*) which corresponds to the high-energy-tail slope of the electron-energy-distribution function in the plasma as a measure of electron temperature in a reactive silane glow-discharge plasma. We have found quite differently from the conventional non-reactive glow-discharge plasma such as hydrogen plasma that the electron temperature in the silane plasma is strongly modified by the substrate temperature (gas temperature) especially under high silane-gas partial-pressure condition. This anomalous behavior of the electron temperature in the silane plasma has been explained by means of gas-phase-polymerization reaction and electron-attachment process to the polymers in the plasma. The electron temperature has been remarkably reduced when a hydrogen-dilution method and a cathode-heating method are used which are considered to control polymer-formation reactions in the silane plasma together with utilization of conventional electron-temperature-controlling methods such as a very high plasma-excitation frequency and an application of magnetic field for electron-confinement. As a consequence of the reduction of electron temperature in the silane plasma, highly stabilized a-Si:H has been successfully obtained even under high growth rate conditions of 1.5 nm s^-1.     

Low-temperature nitriding of titanium in low-energy electron beam excited plasma

The effect of an electron beam and the related plasma on the structure, phase state, and microhardness of the surface of titanium has been studied in a broad range of beam currents (0.1–2.5 A), electron energies (0.1–1 keV), and gas pressures (0.01–1 Pa). This range was ensured by the grid stabilization of emissive properties of the plasma electron source, which formed a wide (∼40 cm²) electron beam in a space charge layer between the beam-excited plasma and the grid bounding the plasma cathode. The sample temperature (350–900°C) was determined by the electron beam parameters. The plasma density was additionally controlled by changing the gas (N₂ or Ar-N₂ mixture) pressure. It is established that, during the low-temperature nitriding process in low-energy electron beam plasma, the ion sputtering significantly affects the microhardness of a processed surface and the rate of growth of the hardened layer thickness. The possibility of nitriding at a low (−50 V) or floating potential of the sample eliminates the development of a surface relief and allows the process to be carried out in deep and narrow slits.