Preparation of carbonitride films in the active and afterglow phases of a glow discharge

The formation of carbonitride (C _x N _y ) films in the active and afterglow phases of a glow discharge in CH₄-N₂ mixtures (as well in these mixtures diluted with argon and helium) was studied experimentally. The dependences of the film growth rate on the discharge current and gas pressure are obtained. The composition (the N/C ratio) and IR absorption spectra of the films are determined. Measurements of the absorption spectra made it possible to identify bonds between C and N atoms. A novel method of carbonitride film deposition in the “double afterglow” mode was proposed. The use of this method appreciably increases the film deposition rate. Possible mechanisms of the formation and destruction of carbonitride films in the active and afterglow phases of the discharge are discussed.     

Polycrystal diamond growth in a microwave plasma torch

Diamond films of different structures were deposited on quartz, WC-Co, and molybdenum substrates in a microwave plasma torch discharge in an argon-hydrogen-methane gas mixture in a sealed chamber at pressures close to atmospheric by using the chemical vapor deposition technique. Images of diamond polycrystal films and separate crystals, as well as results of Raman spectroscopy, are presented. The spectra of optical plasma radiation recorded during film deposition demonstrate the presence of intense H_α hydrogen and C₂ radical bands known as Swan bands.     

Hydrocarbon plasma chemistry in a continuous microwave discharge

A study is made of the relation between the kinetic processes involving carbon-containing species and the intensity ratios of different emission lines in synthesizing diamond films in a microwave discharge plasma. The intensity ratios of the emission lines are measured as functions of the pressure, composition, and flow rate of the gas mixture. The kinetic processes involving carbon-containing components are simulated under conditions close to the experimental ones. It is shown that the intensity ratios of different pairs of lines can be used to control diamond film deposition.     

Studies of pulsed and continuous microwave discharges used to deposit diamond films

Results are presented from optical measurements of the atomic hydrogen density and the gas temperature in a reactor for depositing diamond films from the plasmas of pulsed and continuous microwave discharges at a fixed mean microwave power. The results obtained make it possible to explain the fact that the growth rate of diamond films in the plasma of a pulsed microwave discharge is larger than that in a continuous microwave discharge.     

Simulation and optical spectroscopy of a DC discharge in a CH<Subscript>4</Subscript>/H<Subscript>2</Subscript>/N<Subscript>2</Subscript> mixture during deposition of nanostructured carbon films

Two-dimensional numerical simulations of a dc discharge in a CH₄/H₂/N₂ mixture in the regime of deposition of nanostructured carbon films are carried out with account of the cathode electron beam effects. The distributions of the gas temperature and species number densities are calculated, and the main plasmachemical kinetic processes governing the distribution of methyl radicals above the substrate are analyzed. It is shown that the number density of methyl radicals above the substrate is several orders of magnitude higher than the number densities of other hydrocarbon radicals, which indicates that the former play a dominant role in the growth of nanostructured carbon films. The model is verified by comparing the measured optical emission profiles of the H(n ≡ 3), C ₂ ^* , CH*, and CN* species and the calculated number densities of excited species, as well as the measured and calculated values of the discharge voltage and heat fluxes onto the electrodes and reactor walls. The key role of ion–electron recombination and dissociative excitation of H₂, C₂H₂, CH₄, and HCN molecules in the generation of emitting species (first of all, in the cold regions adjacent to the electrodes) is revealed.     

Controlling the characteristics of a repetitive volume discharge in CFC-12 and its mixtures with argon

The parameters of a repetitive volume discharge in CF₂Cl₂ (CFC-12) and its mixtures with argon at pressures of P(CF₂Cl₂)≤0.4 kPa and P(Ar)≤1.2 kPa are studied. The discharge was ignited in an electrode system consisting of a spherical anode and a plane cathode by applying a dc voltage U_ch≤1 kV to the anode. The electrical and optical characteristics of a volume discharge (such as the current-voltage characteristics; the plasma emission spectra; and the waveforms of the discharge voltage, the discharge current, and the total intensity of plasma emission) are investigated. It is found that, by shunting the discharge gap with a pulsed capacitor with a capacitance of C₀≤3.5 nF, it is possible to control the amplitude and duration of the discharge current pulses, as well as the characteristics of the pulsed plasma emission. The increase in the capacitance C₀ from 20 to 3500 pF leads to a significant increase in the amplitude and duration of the discharge current pulses, whereas the pulse repetition rate decreases from 70 to 3 kHz. The glow discharge exists in the form of a domain with a height of up to 3 cm and diameter of 0.5–3.0 cm. The results obtained can be used to design an untriggered repetitive germicidal lamp emitting in the Cl₂(257/200 nm) and ArCl (175 nm) molecular bands and to develop plasmachemical methods for depositing amorphous fluorocarbon and chlorocarbon films.     

Effect of the dc field on the near-surface plasma of a highly nonuniform microwave discharge

The effect of the dc electric field on the near-surface plasma of an electrode microwave discharge at pressures of 1?C5 Torr was studied by the emission spectroscopy method. It is shown that the dc field weakly affects the vibrational distribution of nitrogen molecules in the C₃??_u state, but changes the structure of the near-surface plasma (shifting the intensity maxima of the emission bands) and the strength of the microwave field near the electrode surface. It is also found that the ratio between the intensities of bands of different sequences of the second positive system of nitrogen radiated from the same state depends on the position along the discharge axis.     

Optimization of Electrodeposited p‐Doped Sb2Te3 Thermoelectric Films by Millisecond Potentiostatic Pulses

A systematic optimization of p‐type Sb₂Te₃ thermoelectric films made by potentiostatic electrodeposition on Au and stainless steel substrates is presented. The influence of the preparative parameters of deposition voltage, concentration, and the deposition method are investigated in a nitric acid solution. As a postdeposition step, the influence of annealing the films is investigated. The use of a potential‐controlled millisecond‐pulsed deposition method could improve both the morphology and the composition of the films. The samples are characterized in terms of composition, crystallinity, Seebeck coefficient, and electrical resistivity. Pulsed‐deposited films exhibit Seebeck coefficients of up to 160 μV K^?1 and an electrical conductivity of 280 S cm^?1 at room temperature, resulting in power factors of about 700 μW m^?1 K^?2. After annealing, power factors of maximum 852 μW m^?1 K^?2 are achieved. Although the annealing of DC‐deposited films significantly increased the power factor, they do not reach the values of the pulsed‐deposited films in the preannealing state. Structural analysis is performed with X‐ray diffraction and shows the crystalline structure of Sb₂Te₃ films. The performance is tuned by annealing of deposited films up to 300 °C under He atmosphere while performing in‐situ X‐ray diffraction and resistivity measurements. The chemical analysis of the films is performed by inductively coupled plasma optical emission spectroscopy (ICP‐OES) as well as scanning electron microscope energy dispersive X‐ray analysis (SEM‐EDX).     

Microwave cellular discharge in fine powder mixtures

The excitation of microwave discharges in fine semiconductor powders and powder mixtures of metals and dielectrics is studied. The plasma is produced due to local sparks generated in microsecond microwave pulses. The time delay in the onset of a discharge amounts to several milliseconds for intensities on the order of 10 kW/cm². As the discharge develops, both microwave absorption and the discharge glow intensity increase. Intense nonuniform heating of the powder is observed.     

Development of MoS2–CNT Composite Thin Film from Layered MoS2 for Lithium Batteries

Layered MoS₂ prepared by liquid‐phase exfoliation has been blended with single‐walled carbon nanotubes (SWNTs) to form novel composite thin films for lithium battery applications. The films were formed by vacuum filtration of blended dispersions onto nitrocellulose membranes. The resulting composite films were transferred onto Cu foil electrodes via a facile filtration/wet transfer technique from nitrocellulose membranes. The morphology of the film was characterised by field emission scanning electron microscopy, which suggests that the MoS₂‐SWNT composite film shows good adherence to the Cu foil substrate. The MoS₂‐SWNT composite thin films show strong electrochemical performance at different charge‐discharge rates. The capacity of a MoS₂‐SWNT composite film with thickness of 1 μm is approximately 992 mAh g^?1 after 100 cycles. The morphology study showed that the MoS₂‐SWNT thin film retains structural integrity after 100 cycles, while the MoS₂ thin film without SWNTs displays significant cracking. In addition, the novel composite thin film preparation and transfer protocols developed in this study could be extended to the preparation of various layered‐material‐based composite films, with the potential for new device designs for energy applications.     

Determination of the electron density and electric field in the plasma of a low-pressure microwave electrode discharge in hydrogen from the measured spectral line intensities

The parameters of the plasma of a microwave electrode discharge in hydrogen at pressures of 1–8 torr and incident powers of 20–80 W are measured by the so-called “relative intensity” method. The method allows one to determine the electron density and electric field in plasma by measuring the relative intensities of the H_α, H_β, and 763.5-nm Ar line emission and calculating the electron-impact rate constants from the homogeneous Boltzmann equation. The measurements show that there are regions in the discharge where the electron density is higher (a bright electrode sheath) and lower (a spherical region) than the critical density for the frequency 2.45 GHz (n_cr～7×10¹⁰ cm^?3). Inside the spherical region, the electric field varies slightly over the radius and the electron density increases as the discharge boundary is approached. The observed discharge structure can be attributed to the presence of a self-sustained discharge zone (electrode sheath); a non-self-sustained discharge zone (spherical region); and a decaying plasma region, which is separated from the active discharge zone by an electric double layer.     

Diagnostics of a nonequilibrium nitrogen plasma from the emission spectra of the second positive system of N2

A method is proposed for determining the electron density N _e and the electric field E in the non-equilibrium nitrogen plasma of a low-pressure discharge from the spectra of the second positive system of N₂. The method is based on measuring the specific energy deposition in the plasma and the distribution of nitrogen molecules over the vibrational levels of the C ³Π _u state, as well as on modeling this distribution for a given energy deposition. The fitting parameters of the model are the values of N _e and E. A kinetic model of the processes governing the steady-state density of the C ³Π _u nitrogen molecules is developed. The testing of this method showed it to be quite reliable. The method is of particular interest for diagnosing electrodeless discharges and provides detailed information on the processes occurring in the discharge plasma. Preliminary data are obtained on the plasma parameters in a cavity microwave discharge and an electrode microwave discharge. In particular, it is found that the electric field in an electrode microwave discharge in nitrogen is lower than that in a hydrogen discharge. This effect is shown to be produced by stepwise and associative processes with the participation of excited particles in nitrogen.     

Electrode microwave discharge in nitrogen: Structure and gas temperature

Electrode microwave discharges in nitrogen at pressures of 1–16 Torr and input microwave powers of 30–180 W have been studied by space-resolved emission spectroscopy. It is shown that the discharge is highly nonuniform. The relative intensities of the first and second positive nitrogen bands, as well as of the first negative band of nitrogen ions, are found to vary significantly throughout a discharge because, in different discharge regions, emitting particles are excited by different mechanisms. The gas temperature was determined by the method of the unresolved rotational structure of different sequences of the emission spectra of the second positive system of nitrogen.     

Application of microwave discharge for the synthesis of TiB2 and BN nano- and microcrystals in a mixture of Ti-B powders in a nitrogen atmosphere

Synthesis of titanium diboride and boron nitride nano- and microcrystals by means of a pulsed microwave discharge in a mixture of Ti-B powders in a nitrogen atmosphere is considered. For this purpose, a new type of reactor with a free surface of the powder mixture was used. The reactor design permits free expansion of the reaction products into the reactor volume and their deposition on the reactor walls. Conditions for the synthesis of TiB₂ and BN compounds were studied as functions of the energy input in the discharge, the powder component ratio, the rate of the nitrogen flow through the reactor, and the structure and phase composition of the compounds deposited on the reactor walls. The synthesis of boron nitride and titanium diboride in crystal structures is proven. An important role in the process of synthesis is played by the heating of the mixture due to the titanium diboride synthesis reaction, its behavior in the bulk of the reactor, and the titanium concentration in the powder mixture. It is also found that, as the number of discharges in the bulk of the reactor increases, a dust cloud forms. The luminescence of this cloud indicates that the initiated discharge proceeds not only on the powder surface and in the powder bulk, but also in the reactor volume.     

Beam-plasma interaction in a hybrid plasma waveguide in the pulsed mode of microwave generation

Results are presented from experimental studies of the energy spectra of an electron beam in a model beam-plasma oscillator based on a hybrid plasma waveguide in the pulsed mode of microwave generation with a pulse duration of 1 µs or shorter. The beam energy spent on sustaining the beam-plasma discharge in a slow-wave structure is measured. A correlation between the type of excited waves and the generation of a group of accelerated beam electrons with energies exceeding the injection energy is revealed. It is shown that the pulsed mode of microwave generation is related to the time variations in the plasma density profile in the waveguide and the trapping of beam electrons by the excited microwave field.     

Polarized photoacoustic, absorption and fluorescence spectra of chloroplasts and thylakoids oriented in polyvinyl alcohol films

The polarized photoacoustic, absorption and fluorescence spectra of chloroplasts and thylakoids in unstretched and stretched polyvinyl alcohol films were measured. The intensity ratios of fluorescence bands at 674 nm, 700 nm, 730 nm and 750 nm, and the polarized fluorescence excitation spectra are strongly dependent on light polarization and film stretching. In stretched films, thylakoids exhibit predominantly 674 nm emission. The ratio of photoacoustic signal to absorption is different for light polarized parallel and perpendicular to film stretching. This difference is large in the region of chlorophyll a and carotenoids absorption in which the fluorescence excitation spectra are also strongly dependent on light polarization and film stretching. The observed spectral changes are explained by reorientation of pigment molecules influencing the yield of excitation transfer between different pigments.     

Characteristics of the Electrode Plasma of an Electrode Microwave Discharge in Hydrogen

The electrode region of an electrode microwave discharge in hydrogen at pressures of 0.5–4 torr and absorbed powers of up to 12 W is studied using emission spectroscopy and actinometry. It is shown that the gas temperature is at most 700 K and the degree of dissociation does not exceed several percent. Direct electron impact is shown to be the main factor governing all the processes in the electrode region of the discharge, including the excitation of the recorded emission. In particular, the Balmer-series H_α line emission is related to the dissociative electron-impact excitation of hydrogen molecules in the ground state.     

Molecular dynamics simulation of the Al2O3 film structure during atomic layer deposition

Based on an understanding of atomic layer deposition (ALD) from prior experimental and computational results, all-atom molecular dynamics (MD) simulations are used to model the Al₂O₃ film structure and composition during ALD processing. By separating the large time-scale surface reactions from the small time-scale structural relaxation, we have focused on the growth dynamics of amorphous Al₂O₃ films at the atomic scale. The simulations are able to reproduce some important properties and growth mechanisms of Al₂O₃ ALD films, and hence provide a bridge between atomic-level information and experimental measurements. Information about the evolution of the microscopic structures of the Al₂O₃ films is generated, and the influence of operation parameters on the Al₂O₃ ALD process. The simulations predict a strong influence of the initial surface composition and process temperature on the surface roughness, growth rate and growth mode of the deposited films.     

Study of the hard component of pulsed X-ray emission of micropinch discharge plasma

A set of spectrometers that allow simultaneous measurements of the spectra of pulsed X-ray and electron emission from a micropinch discharge in a wide energy range (1.5?C500 keV) is described. The experimental results of the study of electron and X-ray spectra of micropinch discharge plasma are discussed. The mechanism for the formation of hard X-rays is caused by acceleration processes in micropinch discharge plasma.