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.

Evaluation and Bias Correction of the Secondary Inorganic Aerosol Modeling over North China Plain in Autumn and Winter

Secondary inorganic aerosol (SIA) is the key driving factor of fine-particle explosive growth (FPEG) events, which are frequently observed in North China Plain. However, the SIA simulations remain highly uncertain over East Asia. To further investigate this issue, SIA modeling over North China Plain with the 15 km resolution Nested Air Quality Prediction Model System (NAQPMS) was performed from October 2017 to March 2018. Surface observations of SIA at 28 sites were obtained to evaluate the model, which confirmed the biases in the SIA modeling. To identify the source of these biases and reduce them, uncertainty analysis was performed by evaluating the heterogeneous chemical reactions in the model and conducting sensitivity tests on the different reactions. The results suggest that the omission of the SO2 heterogeneous chemical reaction involving anthropogenic aerosols in the model is probably the key reason for the systematic underestimation of sulfate during the winter season. The uptake coefficient of the “renoxification” reaction is a key source of uncertainty in nitrate simulations, and it is likely to be overestimated by the NAQPMS. Consideration of the SO2 heterogeneous reaction involving anthropogenic aerosols and optimization of the uptake coefficient of the “renoxification” reaction in the model suitably reproduced the temporal and spatial variations in sulfate, nitrate and ammonium over North China Plain. The biases in the simulations of sulfate, nitrate, ammonium, and particulate matter smaller than 2.5 μm (PM2.5) were reduced by 84.2%, 54.8%, 81.8%, and 80.9%, respectively. The results of this study provide a reference for the reduction in the model bias of SIA and PM2.5 and improvement of the simulation of heterogeneous chemical processes.

Chemical deposition and mechanical application of semiconductors thin films

Features and main technological methods of forming thin layers of semiconductor materials by methods of chemical deposition and mechanical application are analyzed. The disadvantages of thermal sputtering and cathodic sputtering of thin films in vacuum for multicomponent semiconductor compounds are indicated. Features of chemical deposition of semiconductor films from the gas (steam) phase are presented. Such deposition involves the transfer of source material from the evaporator zone with higher temperature in the form of volatile compounds to the colder surface of the substrate, where the film growth occurs as a result of reaction of transported compounds or their decomposition. It is shown that the growth of the film during chemical vapor deposition is a process of layer-by-layer condensation of atoms or molecules, with the advantageous difference that during chemical deposition the latter are formed as a result of a heterogeneous chemical reaction when there is no need for average free path length of the gas molecules to be larger than the size of the deposition chamber, i.e. no need for critical degree of vacuum. Chemical deposition of thin films from solution is characterized as a process of precipitation of solute which occurs due to the fact that the ionic product exceeds the product of solubility, i.e. it is greater than the constant value characteristic of a saturated solution in the equilibrium state. We emphasize, that chemical deposition from an water solution allows to obtain homogeneous in thickness and structure fine-grained non-textured mechanically stable polycrystalline films with good adhesion to substrates and the required set of properties. The method of pulverization with subsequent pyrolysis is described. This is deposition from intracomplex organometallic compounds, which is based on thermally stimulated reactions between clusters of atoms, chemically active substances of liquid or vapor phase. The method of electrolytic deposition on electrically conductive substrates is characterized. The method is using appropriate salt solutions by co-deposition of individual components, or by deposition on the cathode of one of the components with its subsequent interaction with others present in the solution. We also describe the method of obtaining epitaxial thin films of semiconductor deposition materials. We note that the analyzed methods or their modifications are necessary tool today to create thin-film semiconductor structures with predetermined properties. In the same time, in each particular case the features of each method of obtaining thin semiconductor films should be comprehensively evaluated and, depending on the chemical composition, structure, topology and complex of expected properties, the most effective method should be applied.

The Topology Within Recirculating Flow in the Atomic Layer Deposition Thin Film Process

Nanotechnology fabrication has become a popular field in the development of advanced and cutting-edge technologies. Deposition processes are industrialized to achieve nano-thin films with absolute control over the film thickness, conformal and uniform film growth over complex structures, and minimal to no defects or pinholes. Atomic layer deposition (ALD) has revealed itself as a possible candidate to achieve these requirements. However, the in-depth understanding of the physical and chemical formation of the thin film is still unfamiliar to reactor designers, engineers and scientists. For the purposes of this study, the interest involves the mechanistic factors of geometry influences, fluid flow, and mass transportation on the heterogeneous chemical reaction process. Through an industrial ALD process recipe, the transitional and recirculation phenomena observed in the Atomic Layer Deposition (ALD) thin film process are seen to exert a significant influence on the effective formation and growth of the thin film on the substrate. Topological fluid dynamics are used to analyze the two-dimensional numerical simulations of the backward-facing step (BFS) phenomena and the recirculation flow patterns typically found within a horizontal ALD reactor. Focus is placed on investigating the saddle points in the resulting vortex shedding, eddy distortion and recirculation due to the BFS phenomena. The topological analysis is conducted for symmetrical step heights of 7.5mm and 10 mm respectively. Findings revealed close similarities to experimental studies.

Adomain computation of radiative-convective bi-directional stretching flow of a magnetic non-Newtonian fluid in porous media with homogeneous–heterogeneous reactions

In the present communication, the laminar, incompressible, hydromagnetic flow of an electrically conducting non-Newtonian (Sisko) fluid over a bi-directional stretching sheet in a porous medium is studied theoretically. Thermal radiation flux, homogeneous–heterogeneous chemical reactions and convective wall heating are included in the model. The resultant nonlinear ordinary differential equations with transformed boundary conditions via similarity transformation are then solved with the semi-analytical Adomain Decomposition Method (ADM). Validation with earlier studies is included for the nonradiative case. Extensive visualization of velocity, temperature and species concentration distributions for various emerging parameters is included. Increasing the magnetic field and inverse permeability parameter is observed to decelerate both the primary and secondary velocity magnitudes whereas they increase temperatures in the regime. Increasing sheet stretching ratio weakly accelerates the primary flow throughout the boundary layer whereas it more dramatically accelerates the secondary flow near sheet surface. Temperature is consistently reduced with increasing stretching sheet ratio whereas it is strongly enhanced with greater radiative parameter. With greater Sisko non-Newtonian power-law index the primary velocity and temperature are decreased whereas the secondary velocity is increased. Increasing both homogenous and heterogeneous chemical reaction parameters is found to weakly and more strongly, respectively, deplete concentration magnitudes whereas greater Schmidt number enhances them.

Homogeneous–heterogeneous reaction mechanism on MHD carbon nanotube flow over a stretching cylinder with prescribed heat flux using differential transform method

Hydromagnetic nanofluid flow through an incompressible stretching cylinder accompanying with homogeneous–heterogeneous chemical reaction has been executed in current literature. SWCNTs (single-walled carbon nanotubes) and MWCNTs (multiwalled carbon nanotubes) as nanoparticles in appearance of prescribed heat flux are accounted here. Leading equations of the assumed model have been normalized through similarity practice and succeeding equations resolved numerically by spending RK-4 shooting practice and analytically by engaging differential transform method. The impulse of promising flow constraints on the flow characteristic is finalized precisely through graphs and charts. We perceived that velocity outlines and temperature transmission are advanced in MWCNT than SWCNT in every case.

Buoyancy effects on nanoliquids film flow through a porous medium with gyrotactic microorganisms and cubic autocatalysis chemical reaction

This article is based on the mathematical model constructed to analyze the simultaneous flow and heat transfer of two nanoliquids (Casson and Williamson) in the presence of gyrotactic microorganisms and cubic autocatalysis chemical reaction through a porous medium under the potentiality of buoyancy forces. Heterogeneous reaction existing on the surface is described by isothermal cubic autocatalytic chemical reaction, whereas homogeneous reaction is taking place at far field described by first-order kinetics. Similarity transformations are used to get the different order differential equations from the governing equations which are solved via an efficient technique namely homotopy analysis method. The effects of all the non-dimensional parameters on velocity, temperature, concentration, and density of motile microorganisms are shown through graphs and elucidated. Velocity increases with the Weissenberg parameter and decreases with the Casson nanofluid parameter in the presence of magnetic field and porous medium. Temperature decreases with the high values of slip condition. The dual behavior of concentration profile for the strength of homogeneous reaction parameter is observed. Flow of microorganisms decreases based on the parameters of porous medium, magnetic field, and heterogeneous chemical reaction. There exists an excellent agreement between the present and published work.

Entropy generation in radiative flow of Ree-Eyring fluid due to due rotating disks

Purpose This paper aims to address the flow features of Ree–Eyring fluid between two rotating disks subject to the magnetic field. Heat transfer features are discussed through viscous dissipation and nonlinear thermal radiation. Impact of thermophoresis and Brownian movement are elaborated. Physical characteristics of entropy generation optimization in nanofluid with homogeneous and heterogeneous chemical reaction are discussed. Design/methodology/approach The nonlinear system leads to ordinary one through the implementation of adequate transformation and then tackled analytically for a convergent series solution by homotopy analysis method. Findings The prime objective of the present research has been given to investigate entropy generation in Ree–Eyring fluid flow between two rotating disks subjected to the magnetic field. Vital features, namely, Brownian motion and thermophoresis have been addressed. Total entropy rate is computed using the second law of thermodynamics. Originality/value No such work yet exists in the literature.

Computational Study of Chemical Reactions During Heat and Mass Transfer in in Magnetized Partially Ionized Nano-Liquid

Homogeneous and heterogeneous chemical reactions in partially ionized magneto-nano-liquid are investigated theoretically using finite element method (FEM). The effects of ions and electrons collisions on the transport of heat and mass are analyzed for both the cases of heterogeneous and homogeneous chemical reactions. The simultaneous effects of dispersion of nanosized particles in partially ionized nano-liquid in the presence of magnetic field are also investigated. Through numerical experiments, it is noted that the temperature of partially ionized nano-liquid increases when electrons collision rate and ion collisions are increased. The transport rate of reacting species decreases when heterogeneous and homogeneous chemical reactions strengths are increased. It is also observed that the effect of electron collisions on the flow in y-direction is the same to that of ion collisions on the flow in y-direction. Homogeneous and heterogeneous chemical reactions have similar effects on concentration of chemically reacting species in qualitative sense. However, in quantitative sense, homogeneous chemical reaction has more significant effect on the concentration reacting species as compared to heterogeneous chemical reaction.