Additional Gas Flow Research Articles

Investigation of a PVT SiC-Growth Set-up Modified by an Additional Gas Flow

Investigation of a PVT SiC-Growth Set-up Modified by an Additional Gas Flow

Human Inspiratory Muscle Fatigue during Strenuous Resistive Loads under Normoxic and Hypoxic Conditions

A study involving nine healthy males was conducted to determine the developmental rate of inspiratory muscle fatigue during resistive loads under normoxic and hypoxic conditions. The subjects aged 19 to 38 years performed a bicycle exercise test of increasing power during an exhaustive inspiratory–expiratory resistive load of 40 cm water column/l s–1 inhaling air or oxygen. The volumetric and temporal respiratory parameters, the partial CO2 pressure in the alveolar gas, the total force of inspiratory muscle contractions, the electrical activity of parasternal muscles (EMG), and the initial inspiratory activity were recorded. The degree of inspiratory muscle fatigue was assessed by the “tension–time” index Pm /Pm maxTI /TT as well as by the ratio of the mean amplitudes of the EMG-signal spectrum in the high-frequency (H) range to the mean spectrum amplitudes in the low-frequency (L) range (H/L). It was established that human working capacity during increasing muscular loads against the background of highly resistive breathing was not a function of the oxygen content in the inhalation mixtures within 21 to 100%; i.e., the maximal power of the work done did not significantly differ. It was shown that pulmonary ventilation, the force generated by inspiratory muscles, the breathing effort values, the initial inspiratory activity value, and the “tension–time” index increased in parallel with the intensity of the exercise when both air and oxygen were inhaled. The Pm /Pm maxTI /TT values in the last minutes of the muscular load significantly exceeded the fatigue zone range, attaining 0.25 to 0.45 in different subjects. By the moment of refusal to continue the work, the H/L ratio had decreased by an average of 36% when air and oxygen were inhaled. The limitation of the physical working capacity of a healthy individual during an exhaustive resistive load is considered to be linked to inspiratory muscle fatigue developing at an equal rate under both normoxic and hyperoxic conditions. An impairment of the arterial blood supply to inspiratory muscles due to occlusion of the intramuscular vessels during intense muscular contractions and a considerable shortening of the time of the relaxation of the respiratory muscles in the expiratory phase is supposed to occur in forced respiration with an additional gas flow obstruction. The fact of the alternation of the electrical activity between the parasternal and other inspiratory muscles within individual inspiratory phases combined with resistive and physical loads is established, which may serve as one of the signs of inspiratory muscle fatigue.

Plasma etch processing of advanced ferroelectric devices

Ferroelectric structures are being used in SRAM devices and are migrating to DRAM devices. A DRAM cell size can be dramatically reduced by employing ferroelectric structures in place of the current silicon oxide capacitor structures. A 5μ2 DRAM cell capacitor can be reduced in size by a factor of 20 using a ferroelectric structure. The current technology used to etch ferroelectric device layers has at least two major shortcomings. The first etch issue is the sloped profiles (i.e. 40°) which are a result of the high ion energies used to etch the relatively non volatile materials (Platinum and PZT). The second etch issue is severe sidewall redeposition when vertical profiles are obtained by using ion mills etc. The etch products that are redeposited on the sidewalls become very difficult or impossible to remove in a manufacturing environment. Profiles of > 75° without heavy redeposition will be required in order for 0.5μ DRAMs to be produced using ferroelectric technology. A series of designed experiments were developed to understand the dependent variables impact on reducing residues and increasing the etched feature's profile angle. Response surfaces were developed for resist selectivity, profile angle, and etch rate versus changes in KHz power, cathode temperature, reactant gas flow and additive gas flow in an HRe − (High Density Reflected Electron) etch system. The process results (optical emission and SEM analysis) were statistically evaluated and process trends developed. The resulting response surface graphs combined with SEM micrographs demonstrate trends in profile control and etch rate. The process trends are reviewed which result in > 75° residue-free etching of ferroelectric devices.

Improvement of plasma spraying efficiency and coating quality

A commercial torch has been modified to introduce an additional anti-vortex and shroud gas flow to counter the detrimental effects brought about by the vortex plasma gas flow which is used to stabilize the cathode arc attachment and to increase the anode life. Deposition efficiency and coating quality are used as criteria to judge the modified versus the nonmodified torch. High-speed videography and computerized image analysis systems are used to determine the particle trajectories, velocities, and the plasma jet geometry. The results show that the additional anti-vortex and shroud gas flow to the torch can keep the particles closer to the torch axis and reduce the amount of entrainment of cold air into the plasma jet. The consequence is that deposition efficiency and coating quality are substantially improved.

Gas chromatographic determination of organometallic compounds with atomic emission detection

We describe the effect of a modified gas chromatography-atomic emission detection (GC-AED) instrumental setup on the analysis of organometallic compounds. It is shown that the installment of an additional makeup gas flow positively effects the performance of the Hewlett Packard (HP) atomic emission detector. In addition, a partially sealed transfer line capillary end providing a narrowed central flow substantially improved the sensitivity. Lower detectable levels were achieved for several of the investigated elements. The parameters makeup gas flow, additional makeup gas flow, and transfer line outlet diameter were optimized and their effects on the peak shapes and detectable levels were evaluated. GC-AED analysis was performed for the first time for the speciation of volatile metal-containing compounds present in diesel particulate matter. Compounds containing iron, chromium, and manganese were successfully detected. © 1996 John Wiley & Sons, Inc.

Oblique angle sputtering procedure for the deposition of biaxially aligned layers on polycrystalline metallic substrates

A considerable disadvantage of IBAD is the need for a separate ion source, which is expensive and problematic. Instead, here two variants of a new sputtering procedure to deposit biaxially aligned layers without a separate ion-beam gun are presented. The substrate is sputter deposited under the above angle of 55°. In any sputter process one can observe a flux of high energy particles impinge on the substrate, in addition to the low energy deposit. Thus the necessary bombardment is supplied without extra energy. The very critical ratio of particle bombardment energy and flux vs. deposition rate can be adjusted in two different ways. The first method uses an additional grounded ring-electrode between cathode and substrate, which divides the process chamber in two regions. The region between cathode and ring-electrode generates the plasma and produces sputtered particles with a cathode-bias-dependent kinetic energy. An additional plane electrode behind the substrate extracts Ar ions from the plasma and accelerates them onto the substrate. Thus the deposition rate is a function of the r.f. power at the cathode and the particle bombardment flux and energy can be controlled by the potential of the plane substrate electrode. The second method uses an extreme off-axis configuration to prevent energetic bombardment of the substrate. An additional gas flow transports the material from the cathode to the substrate in a thermalized state. The deposition rate can be controlled easily by the gas flow and the r.f. power at the cathode. A second plasma between a ring-anode and a ring-cathode near the substrate causes bombardment of the substrate with Ar ions. The bombardment depends only on the parameters of the second plasma and can be adjusted independently of the deposition rate.

Heterogeneous hydride generation in a packed membrane cell

Volatilization of arsenic, selenium and antimony for sample introduction in atomic absorption spectrometry has been performed by pumping an acidic sample through an anion exchanger in the tetrahydroborate (III) form packed as a bed in the liquid channel of a gas-liquid separation membrane cell. The hydrides generated in the heterogeneous reaction between bound tetrahydroborate (III) ions and the analytes are rapidly transferred with the aid of the concomitantly generated hydrogen gas through the gas-permeable membrane into the gas phase and swept to the spectrometer by an additional hydrogen gas flow. This instant transfer of the hydrides to the gas phase kinetically discriminates the reaction of the hydride with metal borides and metal colloids, whose formation by reaction with tetra-hydroborate (III) is slower than the hydride reaction. The susceptibility to interference by transition metal ions is thus markedly reduced, as compared with both batch hydride generation methods and a previously presented heterogeneous reaction scheme. The detection limits for arsenic, selenium, and antimony were 1.2, 3.7, and 10 μg/l, respectively. The calibration graphs were linear from the detection limit up to 125 μg/l for arsenic, 150 μg/l for selenium, and 250 μg/l for antimony. The relative standard deviations at concentration levels of 10 and 100 μg/l were 1.8 and 0.7% for arsenic and 2.3 and 1.2% for selenium. Corresponding figures for 50 and 100 μg/l antimony were 2.5 and 1.6%.