Inert Gas Pressure Research Articles

Pulsed laser deposition of metals in low pressure inert gas

The influence of an ambient Ar gas on the pulsed laser deposition (PLD) of metallic systems (Ag, Fe, Fe/Ag) is examined. Time-of-flight (TOF) measurements and measurements of the deposition rate are presented showing a reduction of particle energy with increasing Ar pressure and a reduction of resputtering and interface mixing. The determined Ar pressure for significant changes of the effective sputter yield is about 0.04 mbar. The experimental results are explained by scattering of a dense cloud of ablated material in a diluted gas.

Isokinetic relationships for nucleophilic substitution at the saturated carbon atom. Reactions with anions in the gas phase and various solvents

Isokinetic relationship (IKR) with the parameters Tiso = 6103 K and logkiso = 10.402 is applicable to the rate constants for 165 reactions of nucleophilic substitution at the saturated carbon atom involving anionic nucleophiles in proton-donor and polar aprotic solvents and their mixtures. For analogous reactions in the gas phase proceeding via a specific mechanism, IKR is obtained with the parameters Tiso = 1505 K and logkiso = 9.972, which is applicable to the reactions occurring under various pressures of an inert gas.

Size Measurement and Classification of Ultrafine Refractory Metal Particles Produced by Laser Irradiation.

Refractory metal ultrafine particles were synthesized by the irradiation of two synchronized-pulse Nd: YAG lasers on a refractory metal substrate in a low pressure inert gas atmosphere. A size distribution of the refractory metal ultrafine particles was measured by a low pressure differential mobility analyzer (LP-DMA) developed by ourselves for each pressure condition. The experimental results showed the peak of the size distribution was shifted from the several nm to the tens of nm level with increasing the pressure. The ultrafine particles of a 10 nm-size (σg=1.12) were precisely classified by the LP-DMA. We could control the shape of the particles from agglomeration condition to spherical one by using an electric furnace. In conclusion, the size classification of narrow distribution and the shape of the generated ultrafine particles could be well controlled.

High Etch Rate Gallium Nitride Processing Using an Inductively Coupled Plasma Source

The ongoing development of III-nitride laser diode and light emitting diode fabrication has been made possible by dry etching techniques. Conventional wet etching of these materials has proved difficult and while Reactive Ion Etch (RIE) plasma systems can be used as an alternative, the Inductively Coupled Plasma (ICP) offers an enhanced dry etch route. In this paper, high etch rate (>1.25 μm/min) gallium nitride (GaN) processing is reported using the Surface Technology Systems (STS) ICP system. This is the fastest etch rate published for an ICP system. The etched material exhibits smooth anisotropic profiles and is free from residues. The effect of plasma parameters such as power, pressure and flow of reactive and inert process gases are presented. The use of both chlorine (Cl2) and boron trichloride (BCl3) as reactive etch gases is also studied.

Synthesis and TEM study of nanoparticles and nanocrystalline thin films of silver by high pressure sputtering

High pressure magnetron sputtering is a very promising technique for the controlled synthesis of nanocrystalline thin films as well as nanoparticles of various systems. Here we discuss the conditions necessary for the synthesis of nanocrystalline silver both in the thin film and powder forms. The formation of the nanophase material occurs in a relatively high pressure of inert gas and at low substrate temperatures (77–300 K). The mean crystallographic domain size of the nanocrystalline silver thus synthesized was found to lie in the 3–60 nm range. The growth pattern and morphology of the sputter-deposited nano-grains were studied in detail using transmission electron microscopy and atomic force microscopy.

Agflotherm® Process for Efficient Simultaneous Upgrading of Low Rank Coals and Heavy Oils at Atmospheric Pressure in Inert Gas

Work initiated in 1980 at the University of Alberta and the Alberta Research Council led to the development of the Agflotherm® process for low rank coals (LRC) beneficiation. This process can be considered as low-severity co-processing; upgrading two low grade fossil fuels, namely low rank coals and heavy oils, in a single process. The Agflotherm® process consists of two operations: preparation of coal/oil aggregates followed by their thermal treatment. The main products of this process are: •low moisture and ash solid fuel with properties similar to that of high quality thermal coals, and •an asphaltene-free value-added distillable oil characterized by reduced viscosity and heteroatom content. Numerous coal-oil combinations have been tested using the Agflotherm® process. In virtually every case, significant upgrading of low rank coals and heavy oils was achieved. This paper summarizes the result of developmental work carried out over a period of 10 years and financially supported by different government agencies and private industry.

Direct association equilibrium in the Fourier-transform ion cyclotron resonance ion trap: the hydration equilibrium of protonated 18-crown-6

Direct associative equilibrium provides probably the best way to measure the thermochemical properties of ion–neutral complexes. This approach has been widely used in high pressure mass spectrometry (HPMS). We describe the establishment and observation of equilibrium at low pressure in the Fourier-transform ion cyclotron resonance (FT-ICR) spectrometer, using the hydration reaction of protonated 18-crown-6 as a test case. The measured enthalpy and entropy of monohydration are in agreement with the prior HPMS results, with the advantage that the present measurements were possible in a temperature range nearly 100°C lower. The low pressure regime of the FT-ICR technique makes accessible complexes bound by 10–15 kcal higher than for a corresponding HPMS experiment. Modeling of the equilibrium experiment was carried out using the Standard Hydrocarbon estimates of association kinetics. The strongly coupled domains of pressure, binding energy, temperature, and molecular size were mapped out for which it should be possible to establish and observe equilibrium under FT-ICR conditions. The particular difficulties raised by small molecule size and high binding energy were noted, and the possibility was noted that use of a high pressure of inert bath gas could alleviate these problems by accelerating the attainment of equilibrium.

Mechanics of a Particle in a Riemannian Manifold

This work experimentally demonstrates the supercontinuum (SC) generation in a three-hole arsenic free Ge20Sb15Se65 chalcogenide suspended-core fiber. Mechanical drilling was used to prepare the chalcogenide glass preform, which was drawn into suspended-core fibers. The zero-dispersion wavelength of the fiber is moved toward the shorter wavelength of about 3.2 μm through changing the fiber core diameter by controlling the pressure of inert gas during fiber drawing. When a 15 cm-long fiber with a core diameter of 6 μm is pumped using 150 fs pulses at 3.3 μm, SC spanning from ∼3 μm to ∼8 μm was generated.

Optical properties of transparent nanocrystalline Cu 2O thin films synthesized by high pressure gas sputtering

We report the controlled synthesis of nanocrystalline thin films of Cu 2O as well as metallic Cu on glass substrates at room temperature by the versatile high pressure magnetron sputtering technique. Deposition of nanophase materials takes place in a relatively high pressure of inert gas (2–600 mTorr) at 300 K. The average primary grain size of the materials thus synthesized was found to lie in the 4–14 nm range and could be controlled by proper choice of process parameters (nature and the pressure of the sputtering gas, applied power, substrate temperature, and system geometry). In general, nanocrystalline thin films were formed at 300K, while loosely aggregated nanoparticles deposited at 77K. We define the conditions under which it is possible to deposit optically transparent, nanocrystalline thin films of semiconducting, single phase Cu 2O on glass or quartz.

Multilayer structures deposited by laser ablation

TiN/Si structures were deposited on Si wafers by pulsed laser deposition technique. The highly conductive TiN films were grown on heated (100) Si substrates by laser ablation of a high purity Ti target in nitrogen reactive atmosphere. Subsequently, the Si layer was deposited by laser ablation of a Si target in vacuum (down to 10 −6 mbar) or in low pressure inert gas. The nitrogen gas pressure and the substrate temperature were found to strongly influence the TiN film structure and orientation. The degree of crystallinity of the Si layer grown on the TiN film was found to depend on Si/TiN collector temperature. Values below 550°C (the threshold of TiN oxidation activation) were used in the experiments. Techniques as X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), High Resolution Transmission Electron Microscopy (HRTEM), Scanning Force Microscopy (SFM) have been used to characterize the deposited structures. The TiN/Si structure rectifying properties were tested. The obtained Si/TiN/Si structure could be suitable for the building of Permeable Base Transistor (PBT, vertical MESFET) devices.

Effect of carbonization pressure on carbon yield in a unit volume

Abstract The present paper reports the effect of the carbonization pressure on the densification behavior of various pitch-based C/C composites in correlation with the densification behavior of pitch alone. The carbon yield in a unit volume is proposed to evaluate the densification behavior of pitch instead of the normal carbon yield, which has been used in the carbon industry. Under 100 MPa of inert gas pressure, the carbon yield in a unit volume was useful to predict densification behavior. On the other hand, under 1 MPa, the carbon yield in a unit volume was not close to the actual experimental results. Second phases affected the densification behavior of pitch under 1 MPa of carbonization pressure.

Distribution of tellurium in melt-grown ZnSe(Te) crystals

The properties of semiconductor scintillation crystals are largely determined by the presence and distribution of the activator dopant. Influence of growth technological parameters (overheating Δ T, inert gas pressure P, crystallization rate V k) upon distribution of tellurium dopant was studied for ZnSe(Te) crystals grown by Bridgman technique in compression furnaces. Values of the “apparent” distribution coefficient of tellurium ( k Te) over crystal length were shown to be dependent on Δ T and the related value of charge carry-over (Δ m/ m 0). It was established that at Δ m/ m 0=12%, K Te=1; at Δ m/ m 0<12%, K Te<1; at Δ m/ m 0>12%, K>1. This relationship is explained by assuming a competition between two processes affecting the distribution coefficient of tellurium: movement to the tail part in accordance with the phase diagram of the ZnSe–ZnTe pseudobinary system and thermal desorption of ZnTe due to its high volatility. Conditions required for preparation of ZnSe(Te) crystals of highly uniform composition are determined.

Predictions for Upscaling Sonoluminescence

stable single-bubble sonoluminescence (SBSL) has been explored so far. We predict that decreasing the acoustic driving frequency f upscales SBSL. More specifically, at f ­= 5 kHz we expect more than 100 times as many photons per flash as at f ­ 20 kHz and a flash width of about 1000 ps. The application of lower frequencies has to be assisted by reducing the partial inert gas pressure of the dissolved gas (e.g., stronger degassing) to maintain diffusive stability of the bubbles.

Inert Gas Pressure Effects on Phase Stability of Oxides.

Phase stability of Y-Ba-Cu-O superconducting phases was evaluated as a function of temperature, oxygen partial pressure and total gas pressure by the hot isostatic pressing method using argon and oxygen mixtures as a surrounding atmosphere. The phase transformation temperature from Y2Ba4Cu7Oy to YBa2Cu4O8 increased with increasing the total gas pressure, even if the oxygen partial pressure was kept constant. It indicates that the equilibrium partial pressure of a gas involving the chemical reaction changes if a solid-gas reaction is progressed under high total gas pressure. Dependence of chemical potential of the reactant gas on the inert gas pressure was thermodynamically discussed on the basis of Lewis-Randall's empirical scaling law and Ishizaki's approximation. These two approximations resembled each other at pressures less than the usual HIPing pressure.

Analysis of the dynamic characteristics of gas flow inside a laser cut kerf under high cut-assist gas pressure

The behaviour of the cut-assist gas jet inside a simulating laser cut kerf for a supersonic and a conical nozzle tip were studied by a shadowgraphic technique under conditions of inlet stagnation pressure from 3 to 7 bar. The effects of the stand-off distance, kerf width, material thickness and the inlet stagnation pressure upon the dynamic characteristics and momentum thrust of the gas flow inside the cut kerf were investigated. It was found that under a gas pressure of 7 bar, the gas jet from a conical nozzle tip expands radially and the jet momentum deteriorates rapidly inside the kerf. The behaviour of the jet is strongly influenced by the stand-off distance and thickness of the workpiece. On the other hand, the gas jet from a supersonic nozzle inside the cut kerf has tidy boundary and uniform distribution of pressure and thrust. The sensitivity to the stand-off distance and the workpiece thickness of the supersonic nozzle are much less as compared with the conical nozzle. With the supersonic nozzle, a dross free clean cut on 5 mm stainless steel can be achieved at an inert cut-assist gas pressure as low as 5 bar instead of the normal operating range of 10 bar or above for the conical nozzle.

Application of the gas phase condensation to the preparation of nanoparticles

The evaporation of materials in ultra-high vacuum leads to the growth of thin films on appropriated substrates. In the presence of an inert gas (pressure above 10 −1 Torr), the evaporated materials lose kinetic energy by collisions with the inert gas molecules in the gas phase and condense in the form of nanometric size crystallites that can be collected on the substrate as an ultrafine powder. In the present communication, we discuss how thin film deposition methods can be modified to collect ultrafine powders instead of continuous films. We describe, with some examples, the use of the gas phase condensation in the preparation of two different types of materials as nanometric powders. On one hand, CdS nanoparticles have been obtained in the form of homogeneous spheres with a mean particle size of 16 nm in diameter. This material, with applications in catalysis and optical devices, has been characterised by UV– VIS Absorption Spectroscopy, Transmission Electron Microscopy and X-ray Diffraction. On the other hand, magnetic nanoparticles of Co have also been prepared as nanostructured materials with an average particle size of 10 nm. Transmission Electron Microscopy, X-Ray Photoelectron Spectroscopy and X-ray Diffraction have been used to characterise this sample. The formation of an interesting material, consisting of Co cores covered by an oxide passivation layer, has been demonstrated.

Effects of Quenching Environment on the Structure of Melt- Spun Nd2Fe14B

ABSTRACTMelt-spun Nd2Fe14B (2–14–1) ribbons were produced under active vacuum and different partial pressures of inert gases of Ar and He. Microstructure and thermal analyses were performed to understand the microstructural evolution and glass formability (GF) of the ribbons. He atmosphere enhances the quenchability of the ribbons over Ar and vacuum. Ribbons made under 250 Torr He have more uniform microstructure and smoother surfaces than those under 760 Torr He. The higher quenchability induced by He, which increases the interfacial heat transfer coefficient between the melt and rotating wheel during melt spinning, is due to its higher thermal conductivity compared to Ar. The lower pressure stabilizes the turbulence between the melt-pool and Cu wheel, enhancing the heat transfer resulting in a more uniform quench. As a result, a more uniform ribbon microstructure can be obtained at relatively low wheel speeds.

Microstructural Evolution in Copper Films Undergoing Laser Pulsing at High Pressures

AbstractA novel process of pulse-heating copper films under high pressure has been developed for filling high-aspect-ratio vias and contact holes with copper. A copper film is sputter-deposited on to an oxidised silicon substrate containing an array of via holes with varied aspect ratios. The film, which is thick enough to bridge over the via holes, is then subjected to laser pulse heating under selected pressures of inert gas. Via filling has been achieved, up to an aspect ratio of 6 for 0.35 μm diameter holes. The microstructure of the pulse-heated copper films has been investigated by X-ray diffraction, and by focused ion beam microscopy (FIB) including sectioning. The FIB images of the film over a via pattern show a ‘chequer-board’ pattern of grains corresponding to the square pattern of via holes underneath. This pattern can be explained by transient melting of the film under pulse-heating and subsequent solidification in which each via hole acts as a nucleation site and has a crystal associated with it. Even though the as-deposited films are fine-grained and have (111) texture, the treated films can show (111) or (100) texture, depending on processing conditions. The origins of the final film texture and the possibilities for microstructural control are discussed.

Nuclear spin state relaxation of formaldehyde in mixtures with inert gases

AbstractMeasurements of the rate constant of the ortho‐para conversion of monomeric gaseous formaldehyde H2CO in mixtures with He, Ar, H2, N2, CO, O2, CH3F and SF6 are described. Separation of the nuclear spin isomers of formaldehyde was obtained by selective UV laser photolysis of ortho‐formaldehyde in the natural ortho‐para mixture. Inert gas pressure was varied up to atmospheric pressure, formaldehyde pressure was 2.8 mbar in all experiments. At low pressures a linear increase of the rate constant with the inert gas pressure was found in all gases. With the noble gases, this increase was very small. In mixture with H2, N2, O2 and SF6 the rate constant rises up to a maximum and then shows a steep decrease as a function of the inert gas pressure. With the noble gases, CO and CH3F only the increase of the rate constant with pressure could be measured. The results are compared to the theory of Curl et al. [37]for the pressure dependence of the nuclear spin state relaxation of formaldehyde.

Formation and size control of a Ni cluster by plasma gas condensation

We have constructed a plasma-gas-condensation type cluster deposition apparatus and tried to find the optimum operation conditions for controlling the cluster size. Transmission electron microscope (TEM) observation has been done to evaluate sizes of Ni clusters produced when varying the volume of a cluster growth region, sputtering power, and inert gas pressure. The mean cluster size decreases by decreasing the volume of growth region and the sputtering power. The smallest cluster obtained in this work is about 2.3 nm in diameter. We have considered the following two models for the cluster growth: (1) a cluster–cluster collision growth and (2) an atomic vapor condensation growth. The cluster growth speed estimated from the former is too slow, while that from the latter is reasonable in comparison with the present experiments. When stable embryos are made from atom collisions, they grow up faster and the final cluster sizes estimated from the latter model are consistent with those observed by TEM.