Study of microimpurities and charge states in homogeneous hydrocarbon films (Redeposited from a T-10 tokamak deuterium plasma discharge) using XRF analysis, IR spectroscopy, EPR, and I-V characteristics

Microimpurities and charge states of homogeneous deuterated hydrocarbon films redeposited from a T-10 tokamak deuterium plasma discharge are studied spectroscopically using x-ray fluorescence (XRF) analysis, electron paramagnetic resonance (EPR), infrared (IR) spectroscopy; current-voltage (I-V) charachteristics are also measured. Twelve microimpurities (mainly, those of transition metals Fe, Mo, Cr, Ni, Ti, etc., with relative concentrations of 50–7000 ppm) have been discovered. The resulting broad EPR (9.9 GHz, 6000 G) line with g-factors of g = 2.053–2.093 and g = 4.3 assigned to paramagnetic impurities confirms their presence. The presence of different charge states on two sides of the film (one facing the plasma and another facing the vacuum-chamber wall) and the difference in the IR spectra of these states are established. This can be explained by the process of film formation under the influence of the tokamak plasma.     

Oriented growth of CoPt nanoparticles by pulsed laser deposition

The magnetic nanoparticles of Fe/FeCo/FePt, in the past, in a PLD system were grown by us using argon ambient gas pressure of about 0.1–75.0 mbar, as the ambient gas pressure can be used to tune the energy of the incident plasma plume species, the expansion volume, the growth duration, etc. which can control the particle size. In present paper, we report the direct synthesis of small-sized nanoparticles even when no ambient gas was used, with the experiments being done in higher vacuum of about 10^?5 mbar in PLD chamber. The deposition rate under vacuum condition is significantly higher than the deposition rate at high ambient pressure. The study of inplane and outplane magnetic properties, along with XRD results, confirmed that the as-deposited CoPt nanoparticles thin film has oriented growth. The as-deposited CoPt nanoparticles are in magnetically soft fcc phase and a post deposition annealing at 600°C resulted in phase transition to magnetically hard fct phase.     

Investigation of the electronic properties of Au nanoclusters in SiO<Subscript>2</Subscript> by combined scanning tunneling/atomic force microscopy

The tunneling of electrons through Au nanoc lusters formed by pulsed laser deposition in a SiO₂ thin film on a Si substrate has been investigated by combined scanning/atomic force microscopy (STM/AFM). Conducting Pt-coated Si cantilevers were used. The feedback was maintained via the AFM channel, and the current-voltage (I-V) characteristics of the tunnel contact between the AFM probe and the n ⁺-Si substrate through a =4-nm-thick SiO₂ film with Au nanoclusters =2 nm in diameter were measured simultaneously. The current image of the structure contained areas of increased current (tunnel-current channels) 2–15 nm in size, related to tunneling of electrons through Au nanoclusters in SiO₂. The I-V characteristics recorded in the tunnel-current channels exhibit specific features related to the Coulomb blockade of electron tunneling through Au nanoclusters.     

外磁场对直流等离子体炬放电特性的影响

介绍了新研制的磁约束直流等离子矩设备,计算了螺旋管线圈的磁场分布,通过实验研究了磁场变化对等离子体矩放电特性和伏安特性的影响。     

Magnetron sputtering of YBaCuO target: Effects of discharge voltage and deposition rate variation

The time variations of the discharge voltage and YBaCuO film deposition rate in an on-axis magnetron sputterer are studied. In the case of an YBaCuO ceramic target, the discharge voltage and the rate of superconducting phase deposition decrease with time, exponentially approaching a quasi-steady regime. At a pressure of 100 Pa, a decrease in the magnetic field induction near the target from 1200 to 600 G leads to a rise in the discharge voltage by 25–30% and increases the deposition rate more than twofold. The deposited films offer high electrophysical parameters, as demonstrated with a high-frequency circuit: the intrinsic Q factor of the circuit at 64.5 MHz is found to be 2.7 × 10⁵.     

On stabilization of multipoint negative corona by using ballast resistances

The I-V characteristics of a negative corona discharge initiated by a multipoint cathode in an argon flow are experimentally studied. It is found that adjustable ballast resistances connected to the corona points provide stable operation and uniform filling of the discharge gap by the plasma.     

Effect of the substrate temperature and deposition rate on the initial growth of thin lithium niobate-tantalate films deposited from a thermal plasma

Thin lithium niobate-tantalate (LiNb_0.5Ta_0.5O₃) films are studied at the initial stage of deposition from a thermal plasma. The effect of two deposition parameters (the substrate temperature and the deposition rate) on the film morphology, the film crystallinity, and the density of nuclei growing on a (0001) sapphire substrate are investigated. It is shown that the crystalline structure and roughness of a film are determined, for the most part, in the initial growth stage and therefore depend directly on both parameters. At the optimum temperatures and growth rates for obtaining good characteristics of (0006) texture, crystallinity, and surface roughness of the films, the film nuclei on the substrate have a high density and good epitaxial orientation to it. If the growth conditions are not optimum, the islands are either amorphous or have a low density on the substrate surface. The nucleation activation energy is observed to decrease as the deposition rate increases, which supports the assumption that the species that are active in film deposition are “hot” clusters forming in an oxygen-argon plasma in the immediate vicinity of the substrate.     

磁场-微波等离子体与大面积金刚石薄膜

在磁场辅助下电子回旋共振(ECR)效应在大的空间范围形成高密度的等离子体,为大面积金刚石薄膜的淀积提供有利条件,以CH₄-H₂为原料气体,在Si基片上,在比其他制备方法更低的压强(3Torr附近)下已制备出直径约为5cm的金刚石薄膜,从空间等离子体范围来看且有可能达更大的面积,在分析等离子体发射光谱的基础上,对0.5到50Torr压强的金刚石气相生长条件作了讨论。 关键词：     

氢化硅薄膜光吸收近似特性研究

利用等离子体化学气相沉积系统在直流电压源和射频源的双重激励下,以康宁7059玻璃为衬底制备了氢化硅薄膜．过测定氢化硅薄膜Raman光谱,对薄膜微结构进行了表征;建立氢化硅薄膜的光吸收模型,计算出薄膜的光吸收系数和光学带隙,和实验结果基本一致,说明该模型符合实验结果;并利用该模型计算的光吸收系数和光学带隙,结合AMPS软件对设计的太阳电池结构进行了模拟,给出的I-V特性曲线变化趋势与实验结果基本符合,同时对实验结果与模拟结果存在差异的原因进行了分析,并给出合理解释． 关键词： 氢化硅薄膜 光吸收系数 光吸收模型     

Magnetic relaxation in superconductors with varying creep behavior

The relaxation of an electromagnetic field inside low-and high-temperature superconductors in the case when the magnetic flux occupies the cross section incompletely is studied theoretically in the self-similar approximation. On the macroscopic level, creep is described by phenomenological equations for exponential and power I-V characteristics. A relation between the nonlinearity of the I-V curves and the magnetic relaxation process is found. The range of low electric fields is shown to be of considerable importance for the relaxation in high-temperature superconductors. In this range, the equations for exponential and power I-V curves may differ substantially from those at high fields. Complete analytical solutions are contrasted with a numerical solution to the problem.     

Thin film properties by facing targets sputtering system

In this study, film thickness distribution and c-axis crystalline orientation of deposited thin films were studied after preparing Co–Cr thin films, a promising ultra-high density perpendicular magnetic recording media, with a facing targets sputtering (FTS) apparatus. Electrical discharge characteristics needed for the optimum operation of sputter device was also studied in order to prepare thin films of superior c-axis crystalline orientation with FTS method (apparatus) in which thin film of fine quality can be formed because temperature increase of substrate due to the bombardment of high-energy particles can be restrained.As a result of the study, it is confirmed that the FTS method can give stable working under broad magnetic field and range of gas pressure and stable electrical discharge under low Ar gas pressure. Film thickness of prepared thin film shows fairy regular distribution and could obtain good thin films whose dispersion angle of c-axis crystalline orientation is about 3.5°.     

Growth of single-phase c-axis aligned La1.2Ca1.8Mn2O7 films on SrTiO3 (001)

We report the growth of single phase, c-axis aligned thin films of La_1.2Ca_1.8Mn₂O₇ on SrTiO₃ (001) substrates using a controlled pulsed laser deposition method. In this method, constraint of epitaxy is utilized to stabilize the Ruddlesdon-Popper (RP) phase of La_1.2Ca_1.8Mn₂O₇. Oxygen ambient pressure and the rate of deposition play a very important role in influencing the epitaxial growth as well as maintaining phase purity of the material. The oxygen pressure inside the deposition chamber was very precisely controlled and varied during the layer-by-layer growth of the film. Films, prepared by our method, show excellent electrical and magnetic characteristics with a sharp metal-insulator transition at T_M-I=90 K, closely followed by a magnetic transition at T_C=91 K.     

Spectroscopic study of a brush cathode plasma in a magnetic field

The brush cathode helium discharge in the magnetic field has been operated stably at discharge currents larger than those without magnetic field. The diameter of the plasma column has been determined by the configuration of the magnetic field. The measurements of the spectral intensities of the recombination continuum followed by the 2³S-n³P series reveals that the electron density is 1·8 × 10¹³ cm^-3 and the electron temperature is 0·17 eV at a discharge current of 500 mA and a pressure of 0·9 torr for a magnetic flux density of 1·3 kG. The principal quantum number for line merging is 20.     

The effect of oxygen rf discharge on pulsed laser deposition of oxide films

In this work final results on TiO₂ film deposition by Plasma Assisted Pulsed Laser Deposition (PAPLD) with an rf biased substrate are presented. In previous work it has been shown that PAPLD is an improvement over conventional PLD for the elimination of particulates in high refractive index thin film deposition. This paper will give a comparison between conventional PLD and PAPLD on the stoichiometry, morphology, and optical properties of deposited TiO₂ films. It will be demonstrated that oxygen rf discharge during the PLD process makes incorporation of oxygen into the depositing films extremely effective. This effect of the rf discharge allows operation of the PLD process at a lower oxygen background pressure while enhancing the deposition rate. Also, the production of a good quality TiO₂ film by PAPLD using a pure metal titanium target will be shown. PACS 79.20.Ds; 52.80.Pi     

Effect of E × B electron drift and plasma discharge in dc magnetron sputtering plasma

Study of electron drift velocity caused by Etimes B motion is done with the help of a Mach probe in a dc cylindrical magnetron sputtering system at different plasma discharge parameters like discharge voltage, gas pressure and applied magnetic field strength. The interplay of the electron drift with the different discharge parameters has been investigated. Strong radial variation of the electron drift velocity is observed and is found to be maximum near the cathode and it decreases slowly with the increase of radial distance from the cathode. The sheath electric field, E measured experimentally from potential profile curve using an emissive probe is contributed to the observed radial variation of the electron drift velocity. The measured values of the drift velocities are also compared with the values from the conventional theory using the experimental values of electric and magnetic fields. This study of the drift velocity variation is helpful in providing a useful insight for determining the discharge conditions and parameters for sputter deposition of thin film.     

Spectroscopic study of an atmospheric pressure plasma generated for the deposition of titanium dioxide thin films

TiO₂ thin films are applied in various domains, e.g. air or water purification, self-cleaning surfaces etc. The deposition of titanium dioxide at industrial scale remains challenging. Atmospheric pressure plasma chemical vapor deposition methods are currently developed to provide an easy and viable method for deposition at industrial scale. Even though those methods lead to promising applicative coatings their formation mechanisms remain poorly investigated. In order to investigate the effect of the plasma parameters, i.e. plasma power and introduction of oxygen, on the plasma chemistry, optical emission spectroscopy (OES) is employed to monitor the various species present in the discharge. X-ray Photoelectron Spectroscopy (XPS) analyses of the deposited thin films are carried out and show that by either decreasing the plasma power or introducing oxygen the carbon impurities in the layer can be reduced. By comparing OES and XPS data, the ratio of carbon containing species (CH and C₂) to oxygen, i.e. I_CH/I_O or I_C2/I_O, in the discharge is shown to be related to the carbon/oxygen composition ratio in the layer.     

Plasma Processes in Activated Thin Film Deposition

This paper deals with plasma aspects in physical and chemical vapour deposition processes. A systematic representation of deposition methods is given and possibilities of plasma diagnostic are summerized. Characteristic parameters of electron kinetics (mean free paths, collision frequencies, energy distribution functions) and rate equations for calculation of particle densities are discussed for a plasma in plasma activated physical vapour deposition device. Theoretical results are compared with measurements (T_e, N_e, E_z) in the plasma of a TiN_x-deposition device with hollow cathode arc evaporator. Mechanism of plasma polymerisation is discussed. Results of experimental investigations of the plasma in an Ar-hexamethyldisiloxane D.C. low pressure glow discharge are presented and compared with results of modelling of this plasma taking into account direct-, stepwise- and Penning-ionization. The necessivity of knowledge of reactive cross sections for understanding of plasma assisted thin film formation processes is accentuated.     

Characteristics of nitrogen-incorporated silicon oxycarbide films and plasmas for plasma enhanced chemical vapor deposition with TMOS/N2/NH3

Plasma enhanced chemical vapor deposition of nitrogen-incorporated silicon oxycarbide thin films obtained from the gas mixture of TMOS (tetramethoxysilane), N₂, and NH₃ is studied. The effects of the TMOS to N₂ pressure ratio on the properties of the film and the plasma are investigated. The deposited films are analyzed by in situ ellipsometry, ex situ Fourier transform infrared spectroscopy (FTIR), and by X-ray photoelectron spectroscopy (XPS). The plasma is characterized by using optical emission spectroscopy (OES). The mass spectra of the constituents in the plasma are obtained by quadrupole mass spectroscopy. The correlation between the film properties and the plasma characteristics is explained wherever possible. As the partial pressure of N₂ is decreased, the refractive index begins to decrease, reaches a minimum, and then saturates. The FTIR absorption bands are observed from about 850 to 1000 cm⁻¹ and from 1000 to 1250 cm⁻¹, and can be attributed to the formation of a nitrogen-incorporated silicon oxycarbide thin film. The variation of the refractive index is discussed in relationship with the deposition rate, the OES spectra, the mass spectra of the plasma, the film composition obtained by XPS, and FTIR spectra.     

Characteristics of a cylindrical magnetron and reactive sputtering of binary compound films

The characteristics of a cylindrical magnetron, such as the dependences of the discharge voltage, chamber pressure, and plasma radiation intensity on the reactive gas flow rate and discharge current, are studied. In this magnetron, titanium nitride (TiN) and titanium dioxide (TiO₂) films are obtained by reactive magnetron sputtering. The transmission and reflection spectra of the films in the visual range are taken. From the transmission data for the TiO₂ films, their refractive index and absorption factor in the wavelength range 350–800 nm, as well as the porosity, are found by the Valeev method. The variation of the fundamental absorption edge with film thickness is determined with the Urbach formula.     

Effect of oxygen pressure on microstructure and magnetic properties of strontium hexaferrite (SrFe12O19) film prepared by pulsed laser deposition

The effects of oxygen pressure during deposition on microstructure and magnetic properties of strontium hexaferrite (SrFe₁₂O₁₉) films grown on Si (100) substrate with Pt (111) underlayer by pulsed laser deposition have been investigated. X-ray diffraction pattern confirms that the films have c-axis perpendicular orientation. The c-axis dispersion (Δθ₅₀) increases and c-axis lattice parameter decreases with increasing oxygen pressure. The films have hexagonal shape grains with diameter of 150-250 nm as determined by atomic force microscopy. The coercivities in perpendicular direction are higher than those in in-plane direction, which shows the films have perpendicular magnetic anisotropy. The saturation magnetization and anisotropy field for the film deposited in oxygen pressure of 0.13 mbar are comparable to those of the bulk strontium hexaferrite. Higher oxygen pressure leads to the films having higher coercivity and squareness. The coercivity in perpendicular and in-plane directions of the film deposited in oxygen pressure of 0.13 mbar are 2520 Oe and 870 Oe, respectively.