Gas-jet Method Research Articles

An experimental platform for investigation of the Zeeman effect in strong magnetic fields.

An experimental platform is developed for the investigation of the Zeeman effect in strong magnetic fields. Mega-Gauss magnetic fields are generated by a 1 MA Zebra pulsed power machine using metal rod loads. A gas jet or CH oil on the load is the source of hydrogen. Excited hydrogen atoms are backlit by black body radiation from the rod load. Hydrogen absorption spectra are recorded with a grating spectrometer and intensified gated CCD camera. The experimental platform enables the observation of the quadratic Zeeman effect in hydrogen gas jets using the spectral shift of the central line in the Zeeman triplet. Other gases can be studied using the gas jet method.

Газоструйный MPCVD синтез алмазных покрытий на подложках из различного материала

The results of an experimental study of the possibility of applying diamond coatings to substrates made of various materials by a new gas-jet method with microwave activation of precursor gases are presented. The developed experimental setup for applying diamond coatings is described. Diamond coatings are deposited on substrates of molybdenum, silicon with an oxide film or silicon carbide on the surface, tungsten carbide, titanium nitride, fused quartz, and on a diamond crystal. Under conditions of high temperatures and high heat fluxes to the substrate, it was possible to ensure its integrity due to the use of a specially developed substrate holder design. The resulting samples of diamond coatings were studied by scanning electron microscopy (SEM) and Raman spectroscopy (RS) and are currently being tested under the conditions required for various applications.

The Use of a Supersonic Jet of Gas Activated in a Microwave Discharge in Diamond Deposition

The gas-jet method of the deposition of diamond-like structures using super-high-frequency (SHF) discharge for activating gases is considered. Direct statistical simulation is applied to analyze the gasdynamic processes occurring in the conditions of the gas-jet deposition of diamond structures. An activated gas flow in a nozzle is investigated and a considerable influence of the processes in the compressed layer formed near the substrate on the rate of synthesis of diamond structures is established. The regimes of flow of mixture components activated in the discharge chamber toward the substrate are determined and a considerable deceleration of heavy components in the compressed layer is found to exist. It is shown that with increase in the pressure in the deposition chamber from 10 to 80 Torr the crystal growth rate increases fourfold at the expense of an increase in the specific flux of the activated components toward the substrate.

Structure of a diamond deposited from microwave plasma by a new gas-jet method

Diamond coatings on a molybdenum substrate were obtained by gas-phase deposition from a high-speed jet of activated gases. In the most common case, diamond film is formed as a result of the appearance of discrete nuclei on the substrate, their growing and competing. We observed the formation of coatings consisting of separate isometric aggregates with different types of packaging (111) or (100) plates depending on the process parameters (gas flow, the H2/CH4 ratio, the substrate temperature). The study of coating morphology using optical and electron scanning microscopy suggests that the particles were in the gas phase for a long time and increased to the size of tens of microns, and then deposited on the substrate. This process can be explained by the charged state of the particles, according to the charged cluster model of Hwang (1996). The study of the structure and phase composition by XRD and Raman spectroscopy revealed amorphous carbon, disordered and crystalline graphite, molybdenum carbide with the dominant contribution of diamond). The broadband luminescence of the coating under UV excitation is related to amorphous carbon, whereas 532 nm excitation causes the glow of vacancy centers such as (NV−) and (SiV−).

Deposition of Amorphous and Microcrystalline Films of Silicon by the Gas-Jet Plasma-Chemical Method

Uniform thin films of amorphous and microcrystalline silicon are obtained within the forevacuum range of pressures by the gas-jet plasma-chemical method with the activation of gas by an electron beam. The effect of the flow rate of the carrier gas argon, the concentration of monosilane, the pressure in the reaction chamber, material of the substrate, and value of the current of the activating electron beam on the rate of deposition, photosensitivity, and crystallinity of the layers of silicon is investigated. For the amorphous silicon films, deposition rates of >1 nm/s are achieved, and for layers with a crystallinity exceeding 60%, the rate of deposition exceeded 0.6 nm/s. It is found that the substrate material does not have an effect on the structure of the deposited layers of silicon and the rate of their deposition.

Gas Jet Deposition of Diamond onto a Steel Surface Covered by a Tungsten Carbide or Molybdenum Layer

Results of studying the growth of diamond structures on steel specimens with the use of intermediate layers of molybdenum or tungsten carbide cemented by cobalt are reported. The interlayers are deposited by means of detonation spraying. Subsequent deposition of diamond films onto the clad steel specimens is formed by the gas jet method and a special thermocatalytic reactor with extended activating surfaces. The nucleation process on the interlayer surfaces is intensified by preliminary seeding of the specimens in a colloid solution containing nanodiamonds. Information about the phase and structural composition of the resultant specimens and about the film surface morphology is obtained by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction analysis. The tribology of the specimens is studied with the use of hardness nansensors and by the Rockwell hardness indentation method.

The Gas-Jet Method of Deposition of Nanostructured Silver Films

The synthesis of thin silver films by the gas-jet deposition method is experimentally and theoretically studied. When the metal is deposited onto silicon substrates from a supersonic jet of silver vapor with a helium carrier gas, nanostructured films with a 3−30 nm size of nanostructures are obtained for a 1230−1380 K range of jet source temperatures. The data on Ag–He gas-jet dynamics when it is expanded into vacuum (velocity, temperature, concentration, flux of particles onto a substrate) depending on parameters at the source (vapor temperature, flow rate of a carrier gas) are obtained by the method of direct simulation Monte Carlo. The range of optimal helium flow rates, when the efficiency of a gas-jet source is maximal, is determined. It is established that the presence of a background gas in a deposition chamber at pressure higher than 1 Pa decreases the flow of particles onto a substrate, and a simple way of its evaluation is proposed. Conditions for formation of silver clusters in the jet are determined by using the simulation. It is shown that for experimental deposition regimes there are no clusters in the jet, and the observed silver nanostructures are formed on the substrate surface.

Deposition of Silicon Films Doped with Boron and Phosphorus by the Gas-Jet Plasma-Chemical Method

Doped silicon films are fabricated using diborane and phosphine as doping gases by gas-jet plasma-chemical deposition with the application of an electron beam. The influence of the dopant-gas concentration, the addition of a fluorine-containing gas, and the background pressure on the conductivity and crystalline structure of silicon layers is investigated. Boron-doped amorphous films (a-Si:H) with a conductivity up to 5.2 × 10–3 (Ω cm)–1 are fabricated; when doping with phosphorus, microcrystalline silicon films (mc-Si:H) with a crystallinity up to 70% and conductivity at a level of 1 (Ω cm)–1 are fabricated.

Влияние науглероживания вольфрама на активацию газа при синтезе алмазных структур

In order to develop a gas-jet method of diamond structures deposition, the flow of hydrogen and methane mixture through heated tungsten coaxial cylindrical channels with a built-in tungsten spiral is studied. The main attention is paid to the study of the carburization of tungsten surfaces during gas-jet deposition and the effect of carburization on the deposition rate and the morphology of the deposited coatings. A series of experiments to study the carburization of tungsten surfaces under different conditions for feeding a mixture of hydrogen and methane is performed. The flow parameters are investigated by the direct simulation Monte Carlo method. The possible ways of delivering methane and its fragments onto the surface of the spiral are determined.

Superheavy element chemistry at GARIS

A gas-jet transport system has been installed to the RIKEN GAs-filled Recoil Ion Separator, GARIS to start up SuperHeavy Element (SHE) chemistry. This system is a promising approach for exploring new frontiers in SHE chemistry: background radioactivities from unwanted by-products are suppressed, a high gas-jet transport yield is achieved, and new chemical reactions can be investigated. Useful radioisotopes of 261 Rfa ,b , 262 Db, and 265 Sga ,b for chemical studies were produced in the reactions of 248 Cm(18 O,5n )261 Rfa ,b , 248 Cm(19 F,5n )262 Db, and 248 Cm(22 Ne,5n )265 Sga ,b , respectively. They were successfully extracted to a chemistry laboratory by the gas-jet method. Production and decay properties of 261 Rfa ,b , 262 Db, and 265 Sga ,b were investigated in detail with the rotating wheel apparatus for α- and spontaneous fission spectrometry. Present status and perspectives of the SHE chemistry at GARIS are also briefly presented.

Characteristics of the effect of swirling gas jet assisted laser percussion drilling based on machine vision

In this paper, a machine vision-based system is used for in-situ monitoring and characterization of the effect of swirling gas jet assisted laser percussion drilling. Feasibility of laser percussion drilling on highly reflective materials, i.e., Al5052 with the implementation of assisting swirling gas jet, was explored. The influence of the gas jet type on the mechanism of material removal and resulting spatter is reported. The authors conclude that the swirling gas jet method greatly reduces spatter formation around the hole exit during the laser-drilling process. Consequently, in order to understand and monitor the gas jet effects in laser drilling, real-time in situ metrology is employed to observe the details. Compared with the results obtained when using a straight gas jet, laser drilling with a swirling gas jet reduces the drilled hole debris by 0.69 and increases the drilled hole efficiency by a factor of up to 1.5. Experimental results show that both the drilling depth and machining quality can be greatly and simultaneously improved. Effects of the swirling flow on the drilling efficiency and spatter thickness of the holes are investigated.

Continuous-wave laser drilling assisted by intermittent gas jets

We describe a study of the laser drilling of stainless steel (SUS304) using a fiber laser with a wavelength of 1090 nm, assisted by intermittent gas jets. By comparing with the results obtained with the conventional continuous gas jets used in assisted laser drilling, we demonstrate that the use of the intermittent gas jets can effectively increase the material removal rate and reduce the consumption of assist gas. The intermittent gas jets can be modulated according to the frequency to effectively reduce the overcooling effect of the assist gas. Experimental results show that both the drilling depth and machining quality can be greatly and simultaneously improved. Two types of intermittent gas jets, namely, straight and swirling jets, are considered, and the effects of the intermittent frequencies and gas pressures on the laser drilling are investigated and discussed. We conclude that the intermittent gas jet method greatly reduces heat loss and slag formation around the hole exit in the laser drilling process. Compared with the results obtained when using a continuous straight gas jet, laser drilling with a 20-Hz intermittent straight gas jet reduces the drilled hole entrance diameter and increases the drilled hole depth by a factor of up to 1.7. The intermittent gas jet method can reduce the quantity of assist gas being used, and therefore the cost, especially when expensive gases such as helium and argon are being used.

Production of 88Nb and 170Ta for chemical studies of element 105, Db, using the GARIS gas-jet system

A technology to utilize radioisotopes of Nb and Ta was developed for chemical studies of element 105, Db, by coupling a gas-jet transport system to the RIKEN gas-filled recoil ion separator (GARIS). 88Nb and 170Ta were generated via the natGe(19F, xn)88Nb and natGd(19F, xn)170Ta reactions, respectively. They were separated by GARIS and extracted by the gas-jet method to a chemistry laboratory under the almost same experimental conditions for 262Db produced in the 248Cm(19F, 5n)262Db reaction. Yields of 88Nb and 170Ta at the chemistry laboratory were optimized by changing the setting parameters of the GARIS gas-jet system, such as magnetic field of GARIS, energy degrader and shutter for recoil ions, and volume of the recoil transfer chamber.

Effects of Polymer Viscosity and Nanofillers on Morphology of Nanofibers Obtained by a Gas Jet Method

Abstract This research evaluates the effects of molecular weight, polymer solution concentration, and carbon nanotube concentration on diameter distribution of polymer nanofibers produced with gas jet fiber (GJF) method. In GJF method, the shear and extensional forces of high-velocity gas jets are used to spin fibers from polymer solutions. The correlation between polymer molecular weight and fiber diameter distribution is studied along with the effect of multi-walled carbon nanotubes (MWCNT) on fiber diameter distribution. The paper also assesses how carbon nanotubes distribute in bi-component polymer nanofibers. It is found that polymer chain entanglement is a key determinant of fiber diameter. MWCNTs do not show preference for distribution in polyvinylidene pyrrole (PVP) and polyvinylacetate (PVAc) and instead appear on the surfaces of the fibers. A negative value of spreading coefficient supports this observation.

Experiment on Intermittent Gas Jet Assisted Modulated Fiber Laser Drilling

In this paper, intermittent gas jet assisted laser drilling on stainless steel (SUS304) with a fiber laser of wavelength 1090 nm is studied. Compared with the conventionally used continuous gas jets in assisting laser drilling, the intermittent gas jet assisting can effectively increase the material removal rate. The intermittent gas jet can be modulated with the frequency to effectively reduce the over-cooling effect by the assist gas. Experimental result shows that the drilling depth and machining time can be improved. The effects of the intermittent gas jet pressures and the synchronicity of gas and laser pulses on the laser drilling are investigated and discussed. It is observed that the intermittent gas jet method obviously reduces heat loss and increases the machining efficiency during the laser drilling. Compared with result of using the continuous gas jet, laser drilling with the intermittent gas jet at 40 Hz increases the drilling depth with an improvement of 10%. It is worth noting that the intermittent gas jet method can also reduce the quantity and cost of gas while the gases such as helium and argon gases are applied.

Role of Liquid Jet Stretching and Bending Instability in Nanofiber Formation by Gas Jet Method

In this work, the mechanism of fiber formation from polymer solutions under the action of gas jets in a process named gas jet fibers (GJF) method is studied. The GJF method relies on high velocity gas jet converting polymer solutions streaming from a nozzle into a liquid jet and then into fibers. Polymer nanofibers with diameter as low as 100 nm are continuously produced from polymer solutions. A series of interrelated phenomena including polymer jet initiation and stretching, flapping motion, bending instabilities, and concurrent solvent evaporation were found to influence fiber formation. Specifically, the behavior of the liquid jets, stretching rates, and the onset of the bending instabilities are revealed using high speed video photography. The results indicate that both the initial stretching from flapping and the extension from bending instabilities play important roles in fiber attenuation.

Gas-jet method for deposition of metal nanoparticles into the fluorine-polymer matrix

The work deals with the obtaining by the vacuum gas-jet technique of the metal-polymer composites consisting of silver nanoparticles introduced into a fluorocarbon polymer matrix and the investigation of their optical properties. The dependence of the optical density in the visible range of frequencies on the structure of obtained samples has been investigated. The obtained composites are found to possess the plasmon resonance effect.

Fine mechanisms of the interaction of silver nanoparticles with the cells of Salmonella typhimurium and Staphylococcus aureus

Silver nanoparticles possess antibacterial effect for various bacteria; however mechanisms of the interaction between Ag-NPs and bacterial cells remain unclear. The aim of our study was to obtain direct evidence of Ag-NPs penetration into cells of Gram-negative bacterium S. typhimurium and Gram-positive bacterium S. aureus, and to study cell responses to Ag-NPs. The Ag-NPs (most 8-10 nm) were obtained by gas-jet method. S. typhimurium (7.81 × 10⁷ CFU), or S. aureus (8.96 × 10⁷ CFU) were treated by Ag-NPs (0.05 mg/l of silver) in orbital shaker at 190 rpm, 37 °C. Bacteria were sampled at 0.5, 1, 1.5, 2, 5 and 23 h of the incubation for transmission electron microscopy of ultrathin sections. The Ag-NPs adsorbed on outer membrane of S. typhimurium and cell wall of S. auereus; penetrated and accumulated in cells without aggregation and damaging of neighboring cytoplasm. In cells of S. aureus Ag-NPs bound with DNA fibers. Cell responses to Ag-NPs differed morphologically in S. typhimurium and S. aureus, and mainly were presented by damage of cell structures. The cytoplasm of S. aureus became amorphous, while S. typhimurium showed lumping and lysis of cytoplasm which led to formation of "empty" cells. Other difference was fast change of cell shape in S. typhimurium, and late deformation of S. aureus cells. The obtained results showed how different could be responses induced by the same NPs in relatively simple prokaryotic cells. Evidently, Ag-NPs directly interact with macromolecular structures of living cells and are exert an active influence on their metabolism.

Effect of Gas-Jet Ignition Technique on the Extension of CNG Lean Combustion Limit

Lean combustion of CNG has the advantage of high thermal efficiency and fewer pollutants than other fossil fuels. However, problems such as ignitability, cyclic variation and high THC emission were common at combustion leaner than equivalence ratio φ=0.7. The application of gas-jet ignition method to lean combustion was able to address such problems. This paper introduces the concept of gas-jet ignition method, which ensures ignitability at lean bulk equivalence ratio. Moreover, this method is applied to a real CNG engine. Results of engine performance experiment shows that two-stage injection method combined with gas-jet ignition has successfully widen the operating range of a CNG engine from low to high load at corresponding φ=0.17 to 1.1.

Experience in depositing carbon coatings by the gas-jet method

The gas-jet deposition of carbon and diamond-like films on a substrate with precursor gas activation by a hot wire mesh has been studied experimentally. Several designs of the wire activator for depositing films from a gaseous mixture of CH4, H2, and Ar have been tested. The carbon structure of obtained films was determined by Raman spectroscopy.