Atomic Kinetics Research Articles

Cu–Au nanoparticles produced by the aggregation of gas‐phase metal atoms for CO oxidation

AbstractAlloy nanoparticles (nanoalloys) are widely applied in heterogeneous catalysts, advanced electrodes, biomaterials, and other areas. The properties of nanoalloys can be tuned to a significant extent by their structures and compositions, which are governed by the employed synthetic procedure. Often such synthesis occurs in non‐equilibrium conditions and yields nanoalloys with structures and properties that are different from those obtained in thermodynamic equilibrium. In this work, we characterize how the non‐equilibrium conditions during the synthesis of Cu–Au alloys via physical vapor deposition (PVD) affect their morphology, composition, electronic structure, and reactivity in CO oxidation. We used molecular dynamics to simulate the PVD synthesis of Cu–Au nanoalloys through the non‐isothermal aggregation of Cu and Au atoms at a 3:1 ratio in the Ar atmosphere to obtain realistic structures of Cu–Au nanoparticles. Due to the different aggregation kinetics of Au and Cu atoms, the average Au concentration in the obtained Cu–Au particles varied between 14% and 50% depending on the nanoparticle size and the aggregation time. Density functional simulations revealed that the reactivity of the obtained Cu–Au clusters toward CO and oxygen as well as Brønsted–Evans–Polanyi relations for CO oxidation significantly depend on whether the clusters had fcc, icosahedral, or amorphous structures and do not strongly correlate with the d‐band centers of the adsorption sites. Our study highlights the importance of the non‐equilibrium character of nanoalloy structure and composition for their electronic structure and catalytic properties. The performed analysis of the reactivity of Cu–Au clusters with realistic structures in CO oxidation will help the optimization of Cu–Au catalysts for this societally important reaction.

High-Resolution Electron Tomography of Ultrathin Boerdijk-Coxeter-Bernal Nanowire Enabled by Superthin Metal Surface Coating.

The rapid advancement of transmission electron microscopy has resulted in revolutions in a variety of fields, including physics, chemistry, and materials science. With single-atom resolution, 3D information of each atom in nanoparticles is revealed, while 4D electron tomography is shown to capture the atomic structural kinetics in metal nanoparticles after phase transformation. Quantitative measurements of physical and chemical properties such as chemical coordination, defects, dislocation, and local strain have been made. However, due to the incompatibility of high dose rate with other ultrathin morphologies, such as nanowires, atomic electron tomography has been primarily limited to quasi-spherical nanoparticles. Herein, the 3D atomic structure of a complex core-shell nanowire composed of an ultrathin Boerdijk-Coxeter-Bernal (BCB) core nanowire and a noble metal thin layer shell deposited on the BCB nanowire surface is discovered. Furthermore, it is demonstrated that a new superthin noble metal layer deposition on an ultrathin BCB nanowire could mitigate electron beam damage using an in situ transmission electron microscope and atomic resolution electron tomography. The colloidal coating method developed for electron tomography can be broadly applied to protect the ultrathin nanomaterials from electron beam damage, benefiting both the advanced material characterizations and enabling fundamental in situ mechanistic studies.

How transient effects can change the inferred plasma temperatures when using K-shell sulfur line ratios in a time dependent iron sulfide plasma

This paper describes how the steady state atomic kinetics approximation can underestimate the electron temperature determined from K-shell lines in ps-time-scale transient plasmas. In particular, we model the temperature determination of solid FeS targets used in opacity experiments at the Orion laser facility from the ratio of sulfur He-α to Ly-α lines. Such experiments use short-pulse lasers to heat a thin microdot of FeS buried in a plastic target to temperatures of more than 1 keV and densities of approximately 1–2 g/cm3. Using atomic kinetics calculations based on a temperature history from a radiation hydrodynamic simulation of the target evolution, the peak temperature inferred from the sulfur line ratios is 1.29 keV at 3.1 ps as compared with the input peak temperature of 1.41 keV at 2.0 ps. There is a time lag of 1.2 ps at the peak, and an overall 0.5 ps time lag in the temporal history of the temperature as the plasma cools over the next 10 ps.

OH Radical and Chlorine Atom Kinetics of Substituted Aromatic Compounds: 4-chlorobenzotrifluoride (p-ClC6H4CF3).

The mechanisms for the OH radical and Cl atom gas-phase reaction kinetics of substituted aromatic compounds remain a topic of atmospheric and combustion chemistry research. 4-Chlorobenzotrifluoride (p-chlorobenzotrifluoride, p-ClC6H4CF3, PCBTF) is a commonly used substituted aromatic volatile organic compound (VOC) in solvent-based coatings. As such, PCBTF is classified as a volatile chemical product (VCP) whose release into the atmosphere potentially impacts air quality. In this study, rate coefficients, k1, for the OH + PCBTF reaction were measured over the temperature ranges 275-340 and 385-940 K using low-pressure discharge flow-tube reactors coupled with a mass spectrometer detector in the ICARE/CNRS (Orléans, France) laboratory. k1(298-353 K) was also measured using a relative rate method in the thermally regulated atmospheric simulation chamber (THALAMOS; Douai, France). k1(T) displayed a non-Arrhenius temperature dependence with a negative temperature dependence between 275 and 385 K given by k1(275-385 K) = (1.50 ± 0.15) × 10-14 exp((705 ± 30)/T) cm3 molecule-1 s-1, where k1(298 K) = (1.63 ± 0.03) × 10-13 cm3 molecule-1 s-1 and a positive temperature dependence at elevated temperatures given by k1(470-950 K) = (5.42 ± 0.40) × 10-12 exp(-(2507 ± 45) /T) cm3 molecule-1 s-1. The present k1(298 K) results are in reasonable agreement with two previous 296 K (760 Torr, syn. air) relative rate measurements. The rate coefficient for the Cl-atom + PCBTF reaction, k2, was also measured in THALAMOS using a relative rate technique that yielded k2(298 K) = (7.8 ± 2) × 10-16 cm3 molecule-1 s-1. As part of this work, the UV and infrared absorption spectra of PCBTF were measured (NOAA; Boulder, CO, USA). On the basis of the UV absorption spectrum, the atmospheric instantaneous UV photolysis lifetime of PCBTF (ground level, midlatitude, Summer) was estimated to be 3-4 days, assuming a unit photolysis quantum yield. The non-Arrhenius behavior of the OH + PCBTF reaction over the temperature range 275 to 950 K is interpreted using a mechanism for the formation of an OH-PCBTF adduct and its thermochemical stability. The results from this study are included in a discussion of the OH radical and Cl atom kinetics of halogen substituted aromatic compounds for which only limited temperature-dependent kinetic data are available.

New insights in GeTe growth mechanisms

The compound GeTe, despite its simple stoichiometry, is rather unconventional and has been investigated both from a fundamental and technological perspective: it is of high interest for several technologies such as data-storage (phase change memories) and thermoelectricity. The understanding of GeTe growth is thus a key issue for technological applications and fundamental understanding. In this work, GeTe crystallization kinetics is compared to Ge/Te reactive diffusion kinetics using in situ X-ray diffraction measurements, as well as in situ transmission electron microscopy. GeTe crystallization from an amorphous solid solution exhibiting the stoichiometry of the compound GeTe is found to occur at the same temperature as for the reactive diffusion of an amorphous Ge layer on top of a polycrystalline Te layer. Furthermore, GeTe growth is of tridimensional type in the two cases, and can be modeled by the Johnson-Mehl-Avrami-Kolmogorov model. Using this model, the activation energies of nucleation and growth were determined for both crystallization and reactive diffusion. The results suggest that GeTe exhibits nucleation/reaction kinetics unusually low compared to atomic transport kinetics, contrasting with other germanides.

Using tabulated NLTE data for Hohlraum simulations

Non-local thermodyamic equilibrium (NLTE) atomic kinetics is necessary in inertial confinement fusion Hohlraum simulations for adequately modeling high-Z walls and dopants but is computationally very expensive. We present here an approach for tabulating NLTE material data in an economical manner. Material properties for an arbitrary radiation field are provided through tabulated data for a limited set of radiation fields plus derivatives with respect to components of those radiation fields. We have implemented this method in a radiation-hydrodynamics code and compare Hohlraum simulations done with inline NLTE calculations with those done with tables constructed from the same atomic data. The results demonstrate that NLTE tables can replace inline calculations in Hohlraum simulations without a significant loss of accuracy.

Diethyl ether oxidation: Revisiting the kinetics of the intramolecular hydrogen abstraction reactions of its primary and secondary peroxy radicals

Diethyl ether is an attractive alternative to diesel fuel for its high autoignition propensity, high energy density, and potential to reduce pollutant emissions. Low-temperature oxidation kinetics play an important role governing fuel autoignition in engines. Peroxy radical intramolecular hydrogen atom abstraction reactions are key isomerization steps in the chain branching reaction sequence at low temperatures. In this study, the kinetics of intramolecular hydrogen atom abstraction reactions of the primary and secondary peroxy radicals were revisited using the multistructural torsional variational transition state theory with small curvature tunneling corrections. High-pressure limit rate constants within a broad temperature range were obtained, which differ from those previously reported for the investigated reactive systems due to the differences in the estimated barrier heights, the role played by multistructural torsional anharmonicity, and the effects of tunneling. We also observed that some higher energy conformers of the saddle point species, some of which with diastereomers, play a surprisingly large role. Similarly, tunneling is pronounced at low temperature combustion conditions, claiming for robust methods to estimate this effect. Different kinetic models for diethyl ether were used to test our calculated rate constants and NASA polynomials for both diethyl ether peroxy radicals, and the results showed an overall slightly better performance in the prediction of ignition delay times at high pressures.

Pressure broadening of 772.376 and 772.421 nm argon lines and kinetics of argon metastable atoms

Tunable diode laser absorption spectroscopy is used for recording the spectrally mixed profiles of argon 772.376 nm (2p7–1s5) and 772.421 nm (2p2–1s3) lines at different argon background pressures between 0.3 and 1 atmosphere. The absorbing atoms in the Ar*(1s5) and Ar*(1s3) metastable states are produced in a plane-to-plane dielectric barrier glow discharge operating at 20 kHz. The pressure broadening coefficient w and wavelength shift, s of the lines, deduced from the analysis of their variation versus pressure of recorded profiles, are w1=28.3 ± 2.0 pm (14.2 ± 1.0 GHz) and s1=11.5 ± 0.8 pm (-5.8 ± 0.4 GHz) for 772.376 nm line and w2=36.3 ± 0.5 pm (18.2 ± 0.3 GHz) and s2=12.8 ± 0.7 pm (-6.4 ± 0.4 GHz) for 772.4207 nm line, at 1 bar and 300 K. The progressive enhancement with argon pressure of the peak densities ratio [Ar*(1s3)]/[Ar*(1s5)], reaching 0.3 at 1 bar, reveals the importance of Ar-induced collisions for the population transfer from resonant 1s2 to the metasTable 1s3 state. Also, the time variation of Ar*(1 s) densities indicates the presence of a weak excitation channel outside the discharge current pulse initiated by the breakdown. This channel results from the heating of electrons by the electric field seen by the gas in the DBD gap.

Multiscale modeling of ultrafast melting phenomena

Ultraviolet Nanosecond Laser Annealing (LA) is a powerful tool for both fundamental investigations of ultrafast, nonequilibrium phase-change phenomena and technological applications (e.g., the processing of 3D sequentially integrated nano-electronic devices) where strongly confined heating and melting is desirable. Optimizing the LA process along with the experimental design is challenging, especially when involving complex 3D-nanostructured systems with various shapes and phases. To this purpose, it is essential to model critical nanoscale physical LA-induced phenomena, such as shape changes or formation and evolution of point and extended defects. To date, LA simulators are based on continuum models, which cannot fully capture the microscopic kinetics of a solid–liquid interface. In this work a fully atomistic LA simulation methodology is presented, based on the parallel coupling of a continuum, finite elements, μm-scale electromagnetic-thermal solver with a super-lattice Kinetic Monte Carlo atomistic model for melting. Benchmarks against phase-field models and experimental data validate the approach. LA of a Si(001) surface is studied varying laser fluence and pulse shape, assuming both homogeneous and inhomogeneous nucleation, revealing how liquid Si nuclei generate, deform and coalesce during irradiation. The proposed methodology is applicable to any system where the atom kinetics is determined by a strongly space- and time-dependent field, such as temperature or strain.

Flatten the Li‐ion Activation in Perfectly Lattice‐Matched MXene and 1T‐MoS2 Heterostructures via Chemical Functionalization

AbstractThe complexity of the ionic and electronic dynamics in MXene based hybrids, which are normally involved for device integration, triggers both challenges and opportunities for its application. Herein, as a prototype of metallic hybrids of MXene, heterostructures consisting of Ti3C2T2 (T = None, O and F atoms) and metallic MoS2 (1T phase) are investigated for lithium‐ion battery (LIB) applications. It is found that different surface atomic groups in MXene significantly alter the affinity, redox reaction and kinetics of Li atoms in the interface of the Ti3C2T2 and 1T‐MoS2. Through examining the three possible pathways of Li by first‐principles calculations and ab‐initio molecular dynamics, the diffusion curve becomes significantly flattened from the naked to O‐ and F‐terminated Ti3C2 MXene with activation barriers reducing dramatically from 0.80 to 0.22 and 0.29 eV, respectively, and accordingly promoted diffusion coefficients. The functionalization with O or F eliminates the steric hindrance of Li intercalation by breaking the strong interaction between two layers and provides additional adsorption sites for Li diffusion in the meantime. The work suggests that surface functional groups play a significant role in Ti3C2T2/1T‐MoS2 modification and similar strategy via chemical modification of metallic hybrids provides hints for designing high performance anode material for LIBs.

Itô – Stratonovich dilemma in the problem of laser cooling of atoms: limits of applicability of the semiclassical approximation

We report a comparative analysis of the limits of laser cooling of atoms in light fields both on the basis of a numerical solution of the quantum kinetic equation for the atomic density matrix, which makes it possible to accurately take into account quantum recoil effects during the interaction of atoms with field photons, and within the framework of the semiclassical approach using various forms of the Fokker – Plank equation. The analysis allows one to outline the limits of applicability of the semiclassical approach, as well as to choose an unambiguous form for introducing the diffusion contribution to the Fokker – Planck equation in the semiclassical description of atomic kinetics.

Effects of single-photon double photoionization and direct double Auger decay on K-shell ionization kinetics of Ar atoms interacting with XFEL pulses

In studies investigating the interaction of matter with ultraintense, ultrashort x-ray free electron laser (XFEL) pulses, the evolution kinetics are generally described by directly solving a time-dependent rate equation that considers single-photon and single-electron processes. In the present study, we show the effects of single-photon double photoionization and direct double Auger decay in the K-shell ionization kinetics of XFELs interaction with argon atoms. Because a huge number of coupled transition channels are present in the K-shell ionization, we develop a Monte Carlo method to simulate the complex ionization kinetic processes and give the level population evolution of ions and charge state distribution (CSD). The K-shell-dominated ionization dynamics of Ar irradiated by XFEL pulses with photon energies of 5000, 5500 and 6500 eV are investigated and compared with available experimental observations of the CSD. The results show that the population fractions of Ar5+, Ar6+ and Ar9+ are increased by 78%, 152% and 144%, respectively, by these higher-order processes at a photon energy of 5000 eV. Including the direct double-electron processes, the predicted CSDs are in better agreement with the experiments carried out at the photon energies of 5000, 5500 and 6500 eV. It is expected that the developed theoretical formalism can be used to more accurately calibrate the beam profile and intensity of XFELs.

Exploring extreme magnetization phenomena in directly driven imploding cylindrical targets

This paper uses extended-magnetohydrodynamics (MHD) simulations to explore an extreme magnetized plasma regime realizable by cylindrical implosions on the OMEGA laser facility. This regime is characterized by highly compressed magnetic fields (greater than 10 kT across the fuel), which contain a significant proportion of the implosion energy and induce large electrical currents in the plasma. Parameters governing the different magnetization processes such as Ohmic dissipation and suppression of instabilities by magnetic tension are presented, allowing for optimization of experiments to study specific phenomena. For instance, a dopant added to the target gas-fill can enhance magnetic flux compression while enabling spectroscopic diagnosis of the imploding core. In particular, the use of Ar K-shell spectroscopy is investigated by performing detailed non-LTE atomic kinetics and radiative transfer calculations on the MHD data. Direct measurement of the core electron density and temperature would be possible, allowing for both the impact of magnetization on the final temperature and thermal pressure to be obtained. By assuming the magnetic field is frozen into the plasma motion, which is shown to be a good approximation for highly magnetized implosions, spectroscopic diagnosis could be used to estimate which magnetization processes are ruling the implosion dynamics; for example, a relation is given for inferring whether thermally driven or current-driven transport is dominating.

Observation of ionization trends in a laboratory photoionized plasma experiment at Z.

We report experimental and modeling results for the charge state distribution of laboratory photoionized neon plasmas in the first systematic study over nearly an order of magnitude range of ionization parameter ξ∝F/N_{e}. The range of ξ is achieved by flexibility in the experimental platform to adjust either the x-ray drive flux F at the sample or the electron number density N_{e} or both. Experimental measurements of photoionized plasma conditions over such a range of parameters enable a stringent test of atomic kinetics models used within codes that are applied to photoionized plasmas in the laboratory and astrophysics. From experimental transmission data, ion areal densities are extracted by spectroscopic analysis that is independent of atomic kinetics modeling. The measurements reveal the net result of the competition between photon-driven ionization and electron-driven recombination atomic processes as a function of ξ as it affects the charge state distribution. Results from radiation-hydrodynamics modeling calculations with detailed inline atomic kinetics modeling are compared with the experimental results. There is good agreement in the mean charge and overall qualitative similarities in the trends observed with ξ but significant quantitative differences in the fractional populations of individual ions.

Predicting the energetics and kinetics of Cr atoms in Fe-Ni-Cr alloys via physics-based machine learning

The energy and activation barrier distributions of Cr atoms in austenitic alloys are investigated over a multiplicity of modeling samples across a wide range of chemical (e.g. solid solutions vs. segregated states) and microstructural (e.g. bulk vs. grain boundaries) environments. Assisted with a physics-based machine learning algorithm, it is found that the thermodynamic and kinetic behaviors of Cr atoms can be reliably predicted according to the local electronegativity (χ) and free volume of local atomic packing (Vv). The corresponding predictive maps in the χ−Vv parameter space are established, which are in line with existing experiments and validated by a parallel modeling with a different interatomic force field. The implications of the present study regarding its potential to guide the design of austenitic alloys with desired properties are also discussed.

The influence of non-stationarity and interphase curvature on the growth dynamics of spherical crystals in a metastable liquid

This manuscript is concerned with the theory of nucleation and evolution of a polydisperse ensemble of crystals in metastable liquids during the intermediate stage of a phase transformation process. A generalized growth rate of individual crystals is obtained with allowance for the effects of their non-stationary evolution in unsteady temperature (solute concentration) field and the phase transition temperature shift appearing due to the particle curvature (the Gibbs-Thomson effect) and atomic kinetics. A complete system of balance and kinetic equations determining the transient behaviour of the metastability degree and the particle-radius distribution function is analytically solved in a parametric form. The coefficient of mutual Brownian diffusion in the Fokker-Planck equation is considered in a generalized form defined by an Einstein relation. It is shown that the effects under consideration substantially change the desupercooling/desupersaturation dynamics and the transient behaviour of the particle-size distribution function. The asymptotic state of the distribution function (its 'tail'), which determines the relaxation dynamics of the concluding (Ostwald ripening) stage of a phase transformation process, is derived. This article is part of the theme issue 'Transport phenomena in complex systems (part 1)'.

Oxygen atoms and nitrogen molecules as spectroscopic probes for the temperature determination in non-equilibrium cryogenic helium plasma jets

Determination of the gas temperature in the afterglow plasma jet of pre-cooled helium propagating inside a dense helium vapor at 1.4 K is a difficult task. In this work we analyze the possibility of using the emission spectra from oxygen atoms and nitrogen molecules for deducing the local temperature of the gas. Oxygen is always present as a trace impurity (∼1 ppm) in helium gas and strong emission of the atomic 777 nm triplet lines can be a good candidate because the energy gaps of 3.67 cm−1 (T ∼ 5.3 K) and 2.02 cm−1 (T ∼ 2.9 K) between the sub-levels of its upper state O(5P J ), with J = 1, 2 and 3, are comparable to the kinetic energy of atoms in a cryogenic environment. A detailed analysis of the kinetics of atoms in the O(5P J ) state indicates that at temperatures lower than 10 K, the population transfers between sub-levels are not efficient enough for the establishment of a Boltzmann equilibrium within the sublevels before the radiative decay of O(5P J ) atoms. We suggest the presence of small energy barriers in the He-O(5P J ) transient molecule formed during the collision. It was also shown that the temperature of a gas in non-equilibrium cryogenic helium plasmas containing at least 100 ppm of nitrogen can be determined from the rotational spectra of the 2–0 and 3–1 bands of the first positive system and the 8–3 band of the infrared afterglow system of molecular nitrogen. The application of PGOPHER software (1-T method) gives the rotational temperature of N2 molecules averaged over the observation area and is optimal for the gas temperature determination in locally homogeneous plasmas or mapping the temperature in inhomogeneous plasmas with high spatial resolution. A home-made code to simulate rotational spectra with two temperatures (2-T method) allows determination of the temperature span within the observation region of an inhomogeneous plasma.

Theoretical study of the kinetics of F-atom abstraction reactions from F2, CF2(OF)2, CF3OF and SF5OF by CO

The kinetics of the fluorine atom abstraction reactions RF+CO→R+FCO (with R=F, CF2(OF)O, CF3O, and SF5O) has been theoretically studied using the density functional theory and ab initio composite models. The derived average activation energies for the reactions of CO with F2 and with CF2(OF)2 of 15.4 kcal mol−1, at 290–320 K, and 23.1 kcal mol−1, at 386–420 K, are in good agreement with the experimental ones. For the F-atom abstraction from the CF3OF and SF5OF molecules, values of 22.7 and 22.5 kcal mol−1 were calculated. Over the 290–320 and 386–420 K temperature ranges, preexponential factors of 1.1 × 10−12 and 4.4 × 10−12 cm3 molecule−1 s−1 were respectively determined for the reactions of CO with F2 and CF2(OF)2 which are 60% larger than the experimental. Values of 2.3 × 10−12 and 1.2 × 10−12 cm3 molecule−1 s−1 were obtained for the reactions corresponding to the SF5OF and CF3OF molecules at 353–383 and 383–423 K, respectively. Unexpectedly, the ωB97X-D, M06-2X and BMK functionals lead to energy barriers much higher than those predicted by other quantum-chemical models.

ПАРАМЕТРЫ ГАЗОВОЙ ФАЗЫ И РЕЖИМЫ РЕАКТИВНО-ИОННОГО ТРАВЛЕНИЯ Si И SiO2 В БИНАРНЫХ СМЕСЯХ Ar + CF4/C4F8

The comparative study of plasma electro-physical parameters, steady-state gas phase compositions and reactive-ion etching kinetics for Si and SiO2 in binary CF4 + Ar and C4F8 + Ar gas mixtures were studied under conditions of 13.56 MHz inductive RF discharge. As fixed input parameters, we used the total pressure of feed gas (6 mTorr) as well as power levels supplied by plasma excitation source (700 W) and bias source (200 W). The investigation approach combined plasma diagnostics experiments with double Langmuir probe and 0-dimensional (global) model for the chemistry of neutral species. It was shown that investigated gas mixtures exhibit quite close properties in respect to both ions-related parameters and electron gas while are characterized by sufficient differences in kinetics of atoms and radicals. The features of C4F8 + Ar gas under the given set of processing conditions are the higher density of polymerizing radicals, the lower density of F atoms as well as the weaker sensitivity the last parameter to the change in Ar fraction in a feed gas. Etching experiments indicated that a) an increase in Ar fraction in CF4 + Ar and C4F8 + Ar gas mixtures results in qualitatively different changes in Si and SiO2 etching rates; and b) obtained dependencies of etching rates on Ar fraction in both gas mixtures contradict with the behavior of F atom flux. Obviously, such situation corresponds to the change in reaction probability of F atoms with the treated surface. It was suggested that an increase of Ar fraction in the low-polymerizing CF4 + Ar plasma activates the heterogeneous chemical reaction through the intensification of ion-stimulated desorption of etching products and/or surface amorphization. The similar effect for the high-polymerizing C4F8 + Ar plasma may be related to decreasing fluorocarbon film thickness that provides the better access of F atoms to the etched surface.

Comparative study of Cl2 + O2 and HBr + O2 plasma chemistries in respect to silicon reactive-ion etching process

The comparative study of Cl2 + O2 and HBr + O2 plasma chemistries in respect to Si reactive-ion etching process was carried out. Both plasma diagnostics and modeling tools were applied to compare effects of gas mixing ratios on steady-state plasma parameters and densities of active species as well as to determine key processes in respect to Cl and Br atom kinetics. It was found that a) the variation of Cl2/O2 and HBr/O2 mixing ratios produces opposite changes in both electrons-related and ions-related plasma parameters in corresponding gas systems; b) the stepwise dissociation pathways, such as Cl2 + O/O(1D) → ClO + Cl and HBr + O/O(1D) → OH + Br, have no principal influence on the halogen atom formation rates; and c) the higher formation rate and the lower recombination frequency for Cl atoms always provide the condition [Cl] > [Br]. The data on fluxes of plasma active species provided the analysis of Si etching kinetics in terms of process-condition-dependent reaction probability and etching yield. It was suggested that both parameters are sensitive to O atom flux through the oxidation of reaction products into the lower volatile SiClxOy and SiBrxOy compounds.