Search

Available data on the kinetic processes in H2-O2-O2(a 1Δ g ) mixtures are analyzed theoretically, and the ranges in which the rate constants of these processes can vary are determined. The processes of energy transformation in an O2(a 1Δ g )-H2-H-HO2 system in the approximations of the fast and slow (in comparison with the vibrational relaxation time of the HO2 radical) quenching of the electronically excited state are considered. The experiments on the quenching of singlet delta oxygen (SDO) molecules O2(a 1Δ g ) excited in a microwave discharge at a temperature of 300 K and pressure of 6 Torr in a lean hydrogen-oxygen mixture are simulated (by a lean fuel mixture is meant a mixture in which the ratio of the fuel to the oxidizer mass fraction is less than the stoichiometric ratio, which is 2: 1 for a hydrogen-oxygen mixture). It is shown that, over the experimental observation times, the SDO quenching frequency depends on the concentration of molecular hydrogen, the residual odd oxygen fraction in the gas flow, and the ratio between the rate constants of kinetic processes involving HO2 and HO2* radicals. Simulations of the microwave discharge and the transport of excited oxygen along the drift tube make it possible to determine the residual odd oxygen concentration in the gas flow. Recommendations on the choice of the rate constants for the O2(a 1Δ g ) + HO2)A″, v3″ = 0) ↔ O2 + HO2*(A′, v3′ = 1), HO2*(A′v3′ ≤ 1) + O2(a 1Δ g ) → HO2*(A′,v3′ ≥ 6) + O2, and HO2*(A′,v3′ ≤ 1) + O2(a 1Δ g ) → H + O2 + O2 processes are given. It is shown that, in the case of slow quenching in a H2-O2-O2(a 1Δ g ) mixture at a low temperature, the intensity of hydrogen oxidation is enhanced due to the reaction + HO2*(A′,v3′ ≤ 1) + O2(1Δ) → H + O2 + O2.

Influence of electron excited singlet delta oxygen (SDO) molecules produced in direct current (DC) glow discharged plasma on the induction length decrease in the H2-O2 mixture has been studied via ...

This work is devoted to the study of the possibility of obtaining the highest O2(a 1 � g) yield in ED SOG at the high absolute O2(a 1 � g) concentration needed for developing a powerful oxygen–iodine laser pumped by electric discharge. A singlet oxygen was produced in a transversal rf discharge in the pressure range 10–30 Torr of pure oxygen in the small-diameter (7 mm) quartz tube with HgO coating of the inner walls for removing atomic oxygen to eliminate fast O2(a 1 � g) quenching. It is shown that pd scaling (p—pressure, d—tube diameter) of the rf discharge actually allows an increase of the absolute O2(a 1 � g) density. The increase in the rf frequency from 13.56 to 81 MHz results in the essential increase of the O2(a 1 � g) yield (beyond 15% at such a high oxygen pressure as 15 Torr), but the subsequent transfer to the higher rf frequency of 160 MHz only slightly influences the maximally obtained O2(a 1 � g) yield. The effect of the NO admixture on the O2(a 1 � g) production has been also studied. The rate constant of O2(a 1 � g) quenching by NO k NO = (8.5 ± 1.5) × 10 −17 cm 3 s −1 was directly measured. The NO admixture (up to 20%) resulted in the noticeable increase in the O2(a 1 � g) yield mainly at low energy inputs. But this gain in the O2(a 1 � g) concentration drops with increasing energy input. Nevertheless it is shown that by combining the O2 + NO mixture with the HgO coating of the discharge tube walls one can provide the O2(a 1 � g) yield on the level of ∼21% at 10 Torr, ∼17% at 20 Torr and ∼13% at 30 Torr of O2 with the efficiency of ∼4–6%. The analysis of the NO admixture influence on the discharge structure and O2(a 1 � g) production has been carried out by using the 2D model. It was found that at the low energy input the NO admixture acts as an easily ionized species that enlarges the region occupied by plasma. Thus, in the O2 + NO discharge the normal current density is lower than in the pure oxygen discharge. As a result a higher energetic efficiency of O2(a 1 � g) production is also observed in the case of the O2 + NO mixture and the low energy input. In order to provide the optimal conditions for O2(a 1 � g) production (with regard to the yield and efficiency) in the continuous wave transversal VHF discharge at such high oxygen pressures as of 10–30 Torr it is necessary to find out the range of energy inputs where the VHF discharge operates in the regime of normal current density on the boundary with the abnormal regime and to remove atomic oxygen produced in the discharge by some volume or surface processes.

A 2D self-consistent simulation of an rf discharge in a gas flow in pure oxygen over a wide range of discharge parameters was carried out. The simulation was made at the experimental conditions of Part I of this paper for the discharge tube with an HgO coating where the most effective production of O2(a?1?g) was experimentally observed. The simulation goal is to study the features of transversal rf discharge self-organization at different rf frequencies, 13.56 and 81?MHz, to reveal the most optimal conditions for both the O2(a?1?g) yield and its energy efficiency. It was shown that the energy part absorbed by electrons increases with the frequency. The spatial discharge structure was studied at both frequencies. It was revealed that at the higher rf of 81?MHz the discharge operates in a mode of the normal current density even at high input powers. The kinetic processes which determined both O2(a?1?g) loss and production at experimental conditions were studied and discussed. The increase in rf frequency from 13.56 to 81?MHz reveals an increase in the SO yield and efficiency. It also connects with the decreasing of input energy losses in the sheaths.

The scaling on pressure for a discharge singlet oxygen generator based on the rf discharge excitation of O2 flow is studied in the context of the problem of oxygen?iodine laser pumping. With this aim, the evolution of O2(a?1??g) and molecules as well as O(3P) atoms in 13.56 and 81?MHz discharges at pressures up to 15?Torr has been investigated in detail. It is shown that fast quenching of O2(a1?g) by atomic oxygen with increasing pressure and energy input causes rapid saturation of the O2(a1?g) density in the discharge and limits the O2(a?1??g) yield on a rather low level of a few per cent. Covering of the discharge tube walls with mercury oxide for fast catalytic removal of oxygen atoms allows us to greatly increase the O2(a?1??g) yield as well as to avoid fast quenching of O2(a?1??g) in the early afterglow. It enables us to succeed in obtaining the rather high O2(a?1??g) yields at such high pressure as 10?15?Torr. So the singlet oxygen yield is ~10?12% at ~10?Torr. The transition to the higher frequency of 81?MHz even increases greatly the O2(a?1??g) yield up to ~16%.

Single (SF) and dual frequency capacitively coupled plasma (DF CCP) in (0–50%) H2/Ar mixtures was studied numerically with 1D hybrid (Particle-in-cell with Monte Carlo Collision + fluid) model. In SF (81 MHz) discharge the effect of hydrogen dilution is studied for the fixed discharge input power. Mechanisms of the plasma density decrease and variation of ions composition with H2 percentage are discussed. The effect of low-frequency voltage on plasma density, ions composition, ions fluxes, and ions energy was studied in DF CCP (1.76–81 MHz) discharge in 5% H2/Ar gas mixture at low (20 mTorr) and high (100 mTorr) pressures.

Spectra in the vacuum-ultra violet range (VUV, 30 nm–200 nm) as well as in the ultra-violet(UV) and visible ranges (UV+vis, 200 nm–800 nm) were measured from Ar/CF3I and Ar/CF4 discharges. The discharges were generated in an industrial 300 mm capacitively coupled plasma source with 27 MHz radio-frequency power. It was seen that the measured spectra were strongly modified. This is mainly due to absorption, especially by CF3I, and Ar self-trapping along the line of sight, towards the detector and in the plasma itself. The estimated unabsorbed VUV spectra were revealed from the spectra of mixtures with low fluorocarbon gas content by means of normalization with unabsorbed I* emission, at 206 nm, and CF band (1B1(0,v',0)A1(0,,0)) emission between 230 nm and 430 nm. Absolute fluences of UV CF emission were derived using hybrid 1-dimensional (1D) particle-in-cell (PIC) Monte-Carlo (MC) model calculations. Absolute calibration of the VUV emission was performed using these calculated values from the model, which has never been done previously for real etch conditions in an industrial chamber. It was seen that the argon resonant lines play a significant role in the VUV spectra. These lines are dominant in the case of etching recipes close to the standard ones. The restored unabsorbed spectra confirm that replacement of conventional CF4 etchant gas with CF3I in low-k etching recipes leads to an increase in the overall VUV emission intensity. However, emission from Ar exhibited the most intense peaks. Damage to low-k SiCOH glasses by the estimated VUV was calculated for blanket samples with pristine k-value of 2.2. The calculations were then compared with Fourier transform infrared (FTIR) data for samples exposed to the similar experimental conditions in the same reactor. It was shown that Ar emission plays the most significant role in VUV-induced damage.

This work is devoted to the experimental and theoretical study of rf frequency influence on the discharge structure and the O 2 (a 1 D g ) yield in a rf discharge in the tubes with HgO coating for removing atomic oxygen to avoid fast O 2 (a 1 D g ) quenching. Two series of experiments were carried in two discharge sets up: 1 - tube of large diameter of 14 mm, electrode length of 30 cm; 2 - tube of small diameter of 7 mm, electrode length of 10 cm. In the first series, the increase of rf frequency from 13.56 MHz to 81 MHz resulted in the singlet oxygen (SO) yield Y >15% at such high oxygen pressure as 10 Torr. 2D self-consistent model was developed to simulate the rf discharges in gas flow in a wide rage of discharge parameters both with and without HgO coating. Results of the simulation agreed very well with the experimental data. It is shown that at the high rf frequency the discharge operates in a mode of the normal current density so that the energy absorbed by electrons from the rf field increases with the frequency. In the second series we scaled up the rf discharge on the pd parameter ( p -pressure, d -tube diameter) to increase the oxygen pressure. The pd discharge scaling at the high rf frequency allowed to reach the O 2 (a 1 D g ) yield Y > 15% at oxygen pressure up to ~17 Torr. The effect of NO admixture on the O 2 (a 1 D g ) production has been studied in series 2 at rf frequency of 160 MHz. NO admixture (5÷20%) results in the noticeable increase in the O 2 (a 1 D g ) yield in comparison with the discharge tube without HgO coating. It is shown that combination of O 2 + NO mixture with HgO coating of the discharge tube walls provides the most optimal O 2 (a 1 D g ) production with the efficiency up to 7-10 % and allows to reach the threshold yield in 15 % at oxygen pressure even above ~20 Torr.

The production and loss kinetics of CF2 and CF radicals in the CF4 glow discharge were studied with using the time— resolved LIF technique. The effective rate constants of the CF4 dissociation into the chanhels with CF2 and CF production were determined in a wide range of reduced electric field: 80-250 Td. It is shown that besides of the CF4 dissociation by direct electron impact there is also another source conditioned by fluorocarbon plasma polymerization processes. The detailed analysis of growth and decay dynamics of radical concentrations at the discharge modulation has allowed us to separate different channels of the radical production and consequently to determine the constants of CF4 dissociation rate by electron impact KCF2 KCF and A comparison of received KCF2 and KCF with calculations made on the base of solving the Boltzman equation by Monte-Carlo technique with using the available data on electron scattering cross-sections on CF4 molecules, has in part allowed us to renormalize the partial dissociation cross-sections near the threshold and to build up the model cross-sections of neutral dissociation of CF4 by electron impact It is shown, that the polymerization processes substantially contribute (particularly at low values of E/N) to production of radicals, as in a plasma volume, and on a surface of the discharge tube. The analysis of the obtained data on characteristic frequencies (times) of these processes has allowed us to study mechanisms of fluorocarbon's polymerization in CF4 plasma in conditions of high relative concentration of fluorine atoms and low ion energy. So it is shown, that with increasing pressure, when the concentration of polymer fragments CxFy in bulk of plasma is comparable with concentration of simple fluorocarbon radicals CFx (x=1-3), the dissociation of these fragments by electronic impact and the reactions of unsaturated fluorocarbon fragments CnF2m+1 as in volume, and on a surface of a fluorocarbon film, covering discharge tube walls become the main production channels of CF2 and CF. Since with lowering pressure a major channel of CF2 and CF destruction is connected with their heterogeneous losses on tube walls, the surface loss probabilities of CF2 and CF radicals in conditions of the fluorinated fluorocarbon film surface are determined. It is shown, that the most probable mechanism of heterogeneous loss of CF2 and CF under these conditions is the surface recombination of chemisorbed fluorine atoms Fch and physadsorbed radicals CFxPh (x=1-2) through the formation of an activated surface complex. The analysis of the experimental data with using this approach has allowed us to estimate the approximate values of activation energies for the formation of the surface complexes Fch. CF2ph and Fh. CFPh - 750 ± 70 K and 1030 ± 100 K respectively.

The effect of low-pressure He plasma on properties of nanoporous organosilicate glasses low-k films with 24% and 33% open porosity is studied. The influence of ions, VUV radiation, and metastable atoms are extracted separately using a special experimental system designed for this purpose. The low-k films treated in He plasma were exposed to O or H atoms in the downstream of high-pressure O2 or H2 rf discharge. The changes in chemical composition and structure occurring in low-k films were measured before and after all treatments. The loss probabilities of oxygen and hydrogen atoms on the low-k film surface were measured for both treated and pristine films. It is shown that the film pretreatment in He plasma leads to the noticeable densification of the top surface layer up to complete sealing all the films studied. The sealing layer prevents O atoms from deep penetration to the film bulk and carbon extraction. The sealing mechanism related to the joint impact of low-energy ions and VUV photons with metasta...