Effect of diluent gas on silicon film deposition from a free jet of monosilane-diluent mixture activated by electron-beam plasma

Thin silicon films were synthesized by the gas-jet electron beam plasma chemical vapor deposition method from monosilane-argon, monosilane-argon-helium, and monosilane-argon-hydrogen mixtures. Addition of argon to the argon-silane mixture increased the deposition rate of silicon films, whereas addition of helium and hydrogen to the same mixture decreased the growth rate. It is shown that the process of silicon film deposition by this method from argon-monosilane mixture is primarily governed by fast secondary electrons, and argon dilution of mixture leads to increasing concentration of fast secondary electrons and increasing deposition rate of silicon films. Dilution of the initial mixture with helium or hydrogen causes a decrease in the deposition rate either due to gas-dynamic behavior of the supersonic jet of the mixture of light and heavy gases, or due to the etching effect of metastable helium atoms or hydrogen atoms on the surface of the growing silicon film.     

H2 vibrational CARS thermometry

TheQ-branch spectra of molecular hydrogen have been used to determine rotational temperatures bycoherentanti-StokesRamanscattering (CARS). A supersonic jet expansion through a constant flow nozzle of adjustable temperature served as hydrogen source in the temperature range 300 to 2500 K. The analysis of the high-temperature data reveals details of the internal energy transfer in jet expansion.     

Ignition of hexane-air mixtures by highly under-expanded hot jets

We report an experimental study of ignition of flammable mixtures by highly unexpanded, supersonic hot jets. The high-pressure, hot-gas reservoir supplying the jet is created by impacting a projectile on a plunger to rapidly compress and ignite a rich n-hexane/air mixture, resulting in a peak reservoir pressure of more than 20 MPa. A locking mechanism was used to prevent the plunger from rebounding and the jet was created by rupturing a diaphragm covering a nozzle with an exit diameter between 0.25 and 1 mm. The jet development and ignition processes in the main chamber filled with hexane-air mixture were visualized using high-speed schlieren and OH* chemiluminescence imaging. The ignition threshold was determined as a function of composition in the jet and main chamber, the nozzle diameter, and the initial pressure in the main chamber. Unlike the case of subsonic jets in which ignition occurs at the shear layer near the nozzle exit, ignition of combustion in the main chamber was found to take place downstream of the Mach disk terminating the supersonic expansion and within the turbulent mixing region created by the startup of the supersonic jet. The results are interpreted using a constant-pressure, well-stirred reactor model simulating the mixing between the hot jet and cold ambient gas. The critical conditions for ignition are determined by the competition between energy release due to chemical reactions initiated by the hot jet gas and cooling due to mixing with the cold chamber atmosphere. The critical value (maximum for which ignition occurs) of the mixing rate was computed using a detailed chemical reaction model and found to be a useful qualitative guide to our observations.     

Condensation in pulsed free jets of silane-argon mixture: Time characteristics of the pulses

Condensation of a 5% SiH₄ + 95% Ar mixture in pulsed supersonic jets was studied. The sequence of process steps was determined from time characteristics of the jet that were recorded by pulse molecular-beam mass spectrometry. It is shown that pulsed jet condensation of the silane-argon mixture causes selective heating of the components, the heating process being dependent on the density of the mixture in the settling chamber of a nozzle.     

Visualisation des ondes de choc dans un ejecteur supersonique

Shock waves generated in a supersonic ejector are visualized by light scattering by use of a laser beam directed into a region where jet expansion gives rise to a high density of tiny droplets.     

Rayleigh Scattering Experiment for the Measurement of Hydrogen Cluster Size

The hydrogen clusters are produced at liquid nitrogen temperature in a supersonic adiabatic expansion of moderate backing pressure gases into vacuum through a Laval nozzle and their averaged size are measured by Rayleigh scattering. The average cluster size N^-c is about 250 hydrogen atoms at a backing pressure 1.0 MPa in these measurements.     

On the light amplification in the reactions of atoms with condensing gases

Results of the experimental investigations of the reactions of oxygen or hydrogen atoms with gaseous NO, which is rapidly cooling in the supersonic jet, are discussed. It is shown that the intense chemiluminescence arises in the reaction of atoms with cluster droplets (NO)_n. The possibility is shown of light amplification in photorecombination reactions of atoms with condensing gases. Such heterophase reactions have a variety of advantages in laser applications compared with reactions in the homogeneous gaseous phase.     

静态真空对超声喷流气体团簇制备的实验研究

研究了靶室静态真空对超声喷流气体团簇产生和制备的影响.通过瑞利散射方法测量了不同静态真空度下超声喷流氩团簇的尺度和密度参数,发现在喷嘴出口附近团簇尺度和密度受静态真空度的影响较小;在距离喷嘴较远处,氩气团簇存在同氢气团簇类似的自限制效应,验证了自限制效应在团簇制备、输运过程中的重要作用.该结果对于建造基于激光聚变原理的桌面中子源具有较大的参考意义,可据此简化真空装置以降低运行和维护成本.     

二元混合超声气流的剖面和质量分布

用气相电子衍射法和质谱相联合,分析了二元混合超声气流的剖面和质量分布情况。证明质谱利于确定气流剖面和气流中粒子的质量分布,而电子衍射则可以给出气流剖面和气流中生成了何种固相的信息。     

Micronozzle Chocking under Diffusion Combustion of Hydrogen

The results of experimental investigations of the micronozzle-chocking phenomenon under diffusion combustion of a hydrogen microjet at a high outflow velocity in the case of ignition of hydrogen near the nozzle cut are presented. It is found that the cause of micronozzle chocking is the heating of the nozzle walls from the flame-neck region retained up to transonic velocities and preventing nozzle cooling and the passage of the hydrogen jet to the supersonic-flow velocity. It is shown that hydrogen ignition far from the nozzle cut with a developed hydrogen supersonic flow into the flooded space leads to the disappearance of the flameneck region, flame detachment from the nozzle cut, and, correspondingly, termination of the nozzle heating and the possibility of the microjet coming out at the supersonic-flow velocity for the hydrogen jet. It is established that the flame-neck region is a stabilizing factor for the subsonic combustion of a hydrogen microjet up to transonic velocities. In the second case, the presence of supersonic cells stabilizes the supersonic diffusion combustion of the hydrogen microjet.     

Diamond deposition with plasma jet at reduced pressure

Carburizing and diamond deposition experiments were done on titanium, niobium, and molybdenum substrates with argon-methane-hydrogen gas mixture plasma jets at a pressure of 200 torr for various hydrogen concentrations. Diamond deposition was obtained at a volume of 7% hydrogen added to the plasma jet. The deposits were markedly different on the different metal substrates. Diamond deposits with habit planes were clearly observed on niobium and molybdenum, while the deposit on titanium consisted of ball-like particles. The emission spectra from the plasma jet were the same, for all the substrates, proving that the difference in the diamond deposit depends on the substrate characteristics. CH, C₂, hydrogen, and carbon atoms were identified in the plasma jet. The difference in the deposits is attributed to the reactivity of carbon species in the plasma with the metal surface as well as to the solubility of hydrogen in metals     

进口条件对超燃冲压发动机氢气燃烧流场特性的影响分析

对不同进口条件下的超燃冲压发动机燃烧室内氢气喷流超声速燃烧流动特性进行了数值模拟与分析.宽范围超燃冲压发动机是吸气式高超声速飞行器推进系统设计中的热点问题之一,受实验设备硬件条件及实验技术限制,数值模拟技术仍然是超燃冲压发动机燃烧室内燃气燃烧特性及流场特性的主要研究手段.采用基于混合网格技术的多组元N-S方程有限体积方法求解器,在不同进口Mach数及压强条件下,对带楔板/凹腔结构的燃烧室模型氢气喷流燃烧流场进行了数值模拟,对比分析了氢气喷流穿透深度、喷口前后回流区结构、掺混效率及燃烧效率等流场结构与典型流场参数的变化特性及影响规律.研究成果可为宽范围超燃冲压发动机喷流燃烧流动特性分析提供参考.      

GAS DYNAMIC PROBLEMS CAUSED BY THE GENERATION OF THE RADICALS IN A SUPERSONIC JET

A simplified one-dimensional model was proposed to treat the gas dynamic problems in a supersonic jet, which was used to produce radicals cooled by supersonic expansion, Based on this model, the gas dynamic equations can be integrated directly to obtain the evolution or the translational temperature and the rotational temperature of free radicals as well as the molecule density. The results show that the heating position where the radicals are generated and the initial rotational temperature of radicals have little effect on the rotational temperature at the down stream detection point, if the heating position is close to the nozzle orifice.     

A gasdynamic jet carrying excited metal atoms as a spectral light source and a chemical reactor

A gasdynamic jet is described, which carries excited metal atoms in subsonic or supersonic flow. The excitation is performed by a hot hollow cathode discharge. The jet expands parallel into an atmosphere of a few mbar. Its use will be in atomic and molecular spectroscopy, in chemistry and spectroscopy of free radicals, and in electronic-transition chemical laser design.     

Visualization and force measurement of high-temperature,supersonic impulse jet impinging on baffle plate

The flow visualization and force measurement of a supersonic impinging jet on a center-holed vertical baffle plate were investigated. Center-holed baffle plates of 2d to 5d in diameter, with a 1d center hole were tested, where d is the bore of the launch tube. The standoff distance of the baffle plates from the open end of the launch tube were varied to be from 2d to 5d. The supersonic impulse jet, with an incident shock wave of Mach 2.89 was produced by a high-enthalpy blast-wave simulator. The direction-indicating color schlieren method produced a two-dimensional density gradient of the flow field around the baffle plate. In addition, the flow fields were numerically analyzed, using two-dimensional asymmetric Euler equations. The results of the numerically-analyzed and the experimentally-visualized flow field agreed well. The visualized flow field indicates that the baffle plate should be at least 3.5d in diameter to deflect the supersonic impinging jet at an angle greater than a right angle. We have concluded that the representative method of designing muzzle brakes for military purpose accurately predicts the force yielded by the supersonic impinging impulse jet on the vertical baffle plate only when there is a large ratio of the baffle-plate diameter to the bore of the launch tube.     

Generation of intense x-rays during ejection of a fast water jet from a metal channel to atmosphere

The radiation processes associated with a supersonic water jet exhausting from a narrow channel are considered. It has been found for the first time that the output of the channel and the initial portion of the jet are sources of intense X-radiation, generation of which is related to cavitation processes in the water jet bulk and subsequent excitation of shock waves. The frequency of X-radiation depends on the types of atoms on a radiating surface (for a jet, it is water; for a channel, the metal atoms on the surface) and increases with the charge of atoms. The total X-ray activity of an experimental setup in the mode of jet exhaust reaches 0.1 Ci. It is found for the first time that the impact of shock acoustic waves, which are formed in the air as a result of cavitation jets of water, on distant screens leads to the generation of a quasi-coherent directional X-ray emission from the back side of these screens. The spatial parameters of this radiation depend on the shape and cross section of the screen and the spatial characteristics of the shock wave.     

氢气扩散火焰中辐射源项湍流脉动特征的PDF模拟

采用κ-ε湍流模型、标量联合的概率密度函数(PDF)输运方程和层流火焰面模型相结合,模拟氢气自由扩散火焰中辐射源项湍流脉动特征.给出了主燃区内辐射源项湍流脉动的频率图.辐射源项的样本点分布集中,大约95%以上的样本落在其系综的±3倍方差以内,频谱图为单峰.     

Nonclassical rotations of single molecules in small helium and hydrogen clusters: Manifestation of “microscopic superfluidity”

The studies of small helium clusters (up to 100 atoms) and molecular-hydrogen clusters (up to 20 molecules) that are formed in a supersonic gas jet and are coupled by the weak van der Waals interaction with a linear chromophore molecule are reviewed The shift of the frequency of the fundamental vibration of the chromophore, as well as a change in the moment of inertia of a cluster with its growth, has been detected by their rotational and vibrational-rotational spectra. A nonclassical behavior of the moment of inertia manifested in its decrease beginning with a certain number of attached He atoms (H₂ molecules) has been revealed. This behavior indicates that a part of a cluster is decoupled from the rotational motion of a molecule. The key question of these studies is whether such behavior of the moment of inertia is the manifestation of the super-fluidity of helium and hydrogen at microscopic level. The results are compared to the spectroscopy of molecules and hydrogen clusters in liquid-helium nanodroplets.     

Shape and width of IR absorption lines of ammonia expanded in a supersonic jet

Line-width and-shape of absorption lines of the ₂ vibration of ammonia were measured for a series of transitions starting from vibrational groundstate levels with a different rotational energy. An increase in linewidth was found for larger rotational energies of the initial states. This effect has been attributed to the spatial rotational non-equilibrium in the supersonic jet expansion.For expansion of NH₃ seeded in He and Ar a very pronounced dip in the absorption profile has been observed, due to the formation of clusters.     

Magnetic trapping of hydrogen after multistage Zeeman deceleration

We report the first experimental realization of magnetic trapping of a sample of cold radicals following multistage Zeeman deceleration of a pulsed supersonic beam. H atoms seeded in a supersonic expansion of Kr have been decelerated from an initial velocity of 520 m/s to 100 m/s in a 12-stage Zeeman decelerator and loaded into a magnetic quadrupole trap by rapidly switching the fields of the trap solenoids.