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The transmission of a lymphomagenic agent(s) from the bone marrow of irradiated mice to thymic target cells has been demonstrated by: (a) the induction of T cell lymphomas in nonirradiated thymic grafts implanted in irradiated, Thy-l-congenic mice, (b) the induction of T cell lymphomas of host origin in mice infused with bone marrow from irradiated, Thy-l-congenic donors. The latter procedure also yields an appreciable number of pre-B cell lymphomas of uncertain origin. The results confirm Kaplan's theory that radiation induces thymic lymphomas in mice by an indirect mechanism. However, the previously described radiation leukemia virus is clearly not involved in the majority of transferred lymphomas. We propose that the mediating agent in radiation lymphomagenesis is a novel, transmissible agent induced in the bone marrow, but exerting its transforming activity on cells in the thymus. The nature and mode of action of the agent are under investigation.

The mechanisms of volume regulation by cardiac cells in response to hyposmotic conditions was investigated. The study protocol involved optical, biochemical and nuclear magnetic resonance studies of regulatory volume decrease (RVD) by chick heart cells exposed to hyposmotic solution. The results showed that RVD following exposure to hyposmotic solution was due to a substantial loss of the ions Na+ and K+ and the amino acids taurine, glutamate, glycine and aspartate. RVD was also accompanied by production of glutamate and aspartate. The RVD-associated release and production of amino acids could have significant metabolic effects for cardiac muscle cells.

A hybrid global-analytical model of an atmospheric pressure radio-frequency driven capacitive discharge is applied to determine the plasma conditions for TiO2 film deposition. The feed gas is mainly argon with a small fraction of O2 and a smaller fraction of TiCl4. Variations of the discharge parameters and species densities with O2 concentration, discharge power, and flow rate are determined. A simplified chemistry model is developed and compared with the simulation results, showing good agreement. For a base case with Ar/O2/TiCl4 flow rates of 203/30/0.17 sccm, the results indicate that a minimum O2 fraction of 7.3×10-4 is required for pure (un-chlorinated) TiO2 film deposition that the active precursor species is TiO2Cl3, with subsequent abstraction of Cl atoms by dissociative electron attachment and that the deposition rates are around 1 nm/s. [ABSTRACT FROM AUTHOR]

Particle transport in a uniformly magnetized electronegative plasma is studied in two-dimensional (2D) geometry with insulating (dielectric) boundaries. A 2D particle-in-cell (PIC) code is employed, with the results compared to analytic one-dimensional models that approximate the end losses as volume losses. A modified oxygen reaction set is used to scale to the low densities used in PIC codes and also to approximately model other gases. The principal study is the limiting of the transverse electron flow due to strong electron magnetization. The plasma in the PIC calculation is maintained by axial currents that vary across the transverse dimension. For a cosine current profile nearly uniform electron temperature is obtained, which at the B-fields studied (600-1200 G) give a small but significant fraction (0.25 or less) of electron to negative ion transverse loss. For a more transverse-confined current, and approximating the higher mass and attachment reaction rate of iodine, the fraction of electron to negative ion transverse loss can be made very small. The models which have been constructed reasonably approximate the PIC results and indicate that the cross-field transport is nearly classical. [ABSTRACT FROM AUTHOR]

Expanding electronegative (EN) plasmas have been previously observed, experimentally, to generate wave activity. Using a particle-in-cell (PIC) code we have investigated these waves in expanding EN plasmas containing a double layer (DL) between an upstream source region and an expanded downstream region. Oxygen reaction rates were used but modified to correspond more closely to experimental conditions. Under a subset of pressures, for which a DL existed, waves were observed traveling upstream in the expanded region, and growing in amplitude in the direction of travel. Both slow and fast waves were observed. The fast wave existed only over part of the slow wave pressure range. The PIC results were compared to both fluid and kinetic theory, both of which assumed axial uniformity. The results of a somewhat simplified fluid theory, ignoring fast wave coupling and collisions with the background gas, gave a remarkable result: if the theory predicted a slow wave instability for any axial parameters in the downstream region, the instability was observed in the simulation. Conversely, if no instability was predicted at any axial position, no instability was observed. More accurate kinetic calculations, including electron and ion Landau damping, and also collisional damping against the background gas, gave wavelengths and growth rates that were consistent with the PIC simulations, and with the fluid results. The kinetic theory also indicated that the fast waves were always stable but became weakly damped for conditions of unstable slow waves. We postulate that nonlinear and nonuniformity effects excite the fast waves. [ABSTRACT FROM AUTHOR]

We have observed relaxation oscillations in an argon capacitive discharge connected to a peripheral grounded chamber through a slot with dielectric spacers. The oscillations, observed from time-varying optical emission of the main discharge chamber, show, for example, a high frequency (∼40 kHz) relaxation oscillation at 100 mTorr, with absorbed power near that for peripheral breakdown, and a low frequency (∼3 Hz) oscillation, at higher absorbed power. The high frequency oscillation is found to ignite a plasma in the slot, but usually not in the periphery. We interpret the high frequency oscillations using an electromagnetic model of the slot impedance, coupled to a circuit analysis of the system including the matching network. The model results are in general agreement with the experimental observations and indicate a variety of behaviors dependent on the matching conditions. [ABSTRACT FROM AUTHOR]

Relaxation oscillations in charged particle densities are seen in low-pressure inductive discharges, if attaching gases such as SF[SUB6] and Ar/SF[SUB6] mixtures are used, such that the plasma contains negative ions. These oscillations occur in the neighborhood of the transition between lower power capacitive operation and higher power inductive operation. An instability, which occurs around this transition, can be described by a global model, that consists of time-dependent equations for the electrons, ions, and electron temperature. The model qualitatively agrees with experimental observations, but leaves significant quantitative differences to be explained. To understand the reasons for the model's inability to make quantitative predictions, the local conditions for instability are determined for a model somewhat simplified from the one that approximates the experiment, but retains most of the important physics. The simplified model allows explicit determination for the local transition to instability and identifies two parameters that govern the transition. The local criteria are related to the global criterion that all fixed points are unstable. The importance for the instability of the physical parameters of the ion wall loss and of the ratio of capacitive to inductive power transfer has led to a reexamination of the size of these factors, and gives better quantitative agreement of the model to experiments. [ABSTRACT FROM AUTHOR]

We have observed instabilities in low-pressure planar inductive discharges in CF[sub 4] gas, in many ways similar to those seen in other attaching gases. The plasma emitted light exhibits oscillations, with the intensity modulated from 15% to 100%. The instability regions were investigated as a function of pressure, CF[sub 4] flow rate and radio-frequency power. Two matching configurations were used. When the terminus of the planar spiral antenna was directly connected to ground, we observed low-frequency oscillations between 0.5 Hz and 15 Hz. When a 400 pF capacitance was added between the terminus and ground (i.e., the capacitive coupling was reduced), the oscillation frequencies ranged from 100 Hz to 1.5 kHz. Oscillations in the concentrations of unsaturated radicals (CF and CF[sub 2]) were measured during the instability, using time-resolved laser induced fluorescence. The radical dynamics were significant at frequencies of about 1 kHz. Mechanisms are proposed for these variations, including gas temperature changes and chemical reactions. A global model originally developed for SF[sub 6] chemistry was adapted to this system. The appropriate rate coefficients for CF[sub 4] were incorporated and an expression for the positive ion flux in the low electronegativity case was developed. Gas heating effects were also included. [ABSTRACT FROM AUTHOR]

We report on the effect of Ar addition to an O[sub 2] plasma on photoresist etching in an inductively coupled, traveling wave driven, large area plasma source (LAPS). We also develop a simplified spatially varying O[sub 2]/Ar mixture discharge model corresponding to the LAPS in a two-dimensional geometry in order to account for the effect of Ar addition. A photoresist etch kinetics model and spatially varying O[sub 2]/Ar mixture discharge model are used to explain the experimental data. We find that the addition of 50% Ar increases the plasma density and etch rate approximately by a factor of 2. From the simulation we find that argon metastables (Ar*) play an important role in the mixture plasma. The simulation predicts an enhancement in O-atom density due to Ar addition, even in the presence of dilution of the feed gas. The experimental data and predicted etch rates from the simulation are generally in good agreement, indicating that the increase in the etch rate with Ar addition is due to both the increase in the plasma density and the enhancement in O-atom density attributable to the dissociation of O[sub 2] by Ar*. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on the effect of ion energy on photoresist etching in an inductively coupled large area plasma source driven by a 13.56 MHz traveling wave with oxygen gas. To control the ion energy at the substrate surface, the electrode on which the substrate is placed is independently driven by a capacitively coupled 1 MHz power source. The etch rate increases with increasing ion energy for gas pressure ranging from 1 to 100 mTorr. Ion-induced desorption rate constants (etch yields) are shown to be proportional to the square root of the ion energy. An increase in the ion energy leads to etch-uniformity improvement over the processing area of 40 cmx50 cm, particularly at a low gas pressure of 5 mTorr. A modified photoresist etch kinetics model combined with a spatially-varying oxygen discharge model is used to explain these experimental results. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on experimental and modeling results for photoresist etching with oxygen gas in an inductively coupled large area plasma source (LAPS). The source is driven by a 13.56 MHz traveling wave launched along a serpentine antenna embedded in the plasma and has a processing area as large as 40 cmx50 cm. We describe a new series-parallel antenna coil configuration, and we present experimental observations for oxygen plasma density profiles, photoresist etch rates, and etch profiles. We introduce a simplified spatially varying oxygen discharge model corresponding to a two-dimensional LAPS geometry in order to account for the generation and loss of both etchant atoms (O atoms) and bombarding ions. The model and experimental results on plasma density are compared. A simplified photoresist etch kinetics model combined with the spatially varying oxygen discharge model is then described. The ion flux and O-atom density predicted by the model are compared with the etch rate data. In order to gain insight into the underlying physical mechanism, we also compare the data with the scaling behavior of the etch rates predicted by a volume-averaged (global) oxygen discharge model. The models and experimental results are generally in good agreement. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]