As device geometry shrinks to 0.35 μm and below, the parasitic capacitance between closely spaced metal lines becomes important in terms of resistance‐capacitance time delay in device switching. In this study, we investigated the use of fluorine doped plasma enhanced chemical vapor deposition grown silicon oxide thin film as a low dielectric constant intermetal dielectric material. We evaluated C2F6 and an organometallic liquid source triethoxyfluorosilane as the F dopant. It was found that the dielectric constant generally decreased as the F concentration increased. However, we also found that above a certain F concentration, the F‐doped oxide film would become unstable and absorb moisture from the ambient. At similar F concentrations, the films deposited with the liquid source are always more stable than those deposited with C2F6 . This, in addition to the different stress vs. low frequency radio frequency power behavior between the two types of film, suggests that the already present Si‒F bond in the liquid precursor results in a denser and more stable film compared to the C2F6 doped film where interstitial F may be present.

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This study presents benchmark comparisons between continuum and kinetic simulations of argon microplasmas operating in the direct current and microwave regimes. Kinetic simulations using the particle-in-cell with Monte Carlo collisions (PIC-MCC) method and continuum simulations using the full-momentum equation for both ions and electrons are performed at various operating conditions in order to study the influence of product of pressure and gap size, pd (for a given gap size), influence of gap size (for a given value of pd) and operating frequency. It is shown that using the electron energy distribution function (EEDF) predicted by zero-dimensional Boltzmann solvers (such as BOLSIG+) in continuum simulations of direct current microplasmas leads to a significant under-prediction of plasma number densities with continuum simulations based on the Maxwellian EEDF performing better particularly for higher values of pd. The discrepancy between kinetic and continuum simulations is attributed to the presence of hot electrons created as a result of secondary emission and subsequent acceleration in the sheath. On the other hand, simulations performed for argon microwave microplasmas operating at 0.5 GHz, 0.8 GHz, 2 GHz and 4 GHz demonstrated that continuum simulations performed using the rate constants from BOLSIG+ showed excellent agreement with kinetic simulations for the plasma density profiles in spite of over-predicting the voltage/power required to achieve a given plasma density.

We investigated the use of seaweed-derived agar-based composite films as sound absorbers. Nonporous and porous films of varying concentrations of agar (1% to 5% w/v) and their composite films with glycerol (5% w/w) as the plasticizer and nanocrystalline cellulose (2% to 10% w/w) as the reinforcement material were fabricated. Porous films, of about 80% porosity, were obtained by a freeze-drying technique and nonporous films by drying in a hot air oven. Scanning electron microscopy study showed that porous films had interconnected walls with a pore size of 10 μm. Measured acoustic absorption coefficients using the twomicrophone transfer function method revealed that the porous films were effective in sound absorption. The films of 5% w/v agar concentration had the highest sound absorption. The addition of glycerol enhanced sound absorption, due to the damping nature induced by it, whereas the addition of nanocrystalline cellulose to the glycerol-added films did not alter its acoustic properties.

The flow past a circular cylinder looses stability at Re ∼ 47, via the primary wake (PW) mode. Linear stability analysis of the steady base flow, in two dimensions, is conducted using a stabilized finite element formulation. A new mode, referred to as the secondary wake (SW) mode, is discovered which is found to be unstable for Re ≥ 110.8. The relative roles of the PW and SW mode in the development of Karman vortex shedding are also investigated.

SUMMARYA stabilized finite element method, to carry out the linear stability analysis of a two‐dimensional base flow to three‐dimensional perturbations that are periodic along span, is presented. The resulting equations for the time evolution of the disturbance requires a solution to the generalized eigenvalue problem. The analysis is global in nature and is also applicable to non‐parallel flows. Equal‐order‐interpolation functions for velocity and pressure are utilized. Stabilization terms are added to the Galerkin formulation to admit the use of equal‐order‐interpolation functions and to eliminate node‐to‐node oscillations that might arise in advection‐dominated flows. The proposed formulation is tested on two flow problems. First, the mode transitions in the circular Couette flow are investigated. Two scenarios are considered. In the first one, the outer cylinder is at rest, while the inner one spins. Two linearly unstable modes are identified. The primary mode is real and represents the axisymmetric Taylor vortices. The second mode is complex and consists of spiral vortices. For the counter‐rotating cylinders, the primary transition is via the appearance of spiral vortices. Excellent agreement with results from earlier studies is observed. The formulation is also utilized to investigate the parallel and oblique modes of vortex shedding past a cylinder for the Re = 100 flow. It is found that the flow is associated with a large number of unstable oblique shedding modes. The parallel mode of vortex shedding is a special case of this family of modes and is associated with the largest growth rate. Copyright © 2014 John Wiley & Sons, Ltd.

The computational techniques commonly used for low‐temperature plasma simulations are compared in the context of modeling microplasmas driven by cathodes with high secondary electron emission coefficient. Simulations of 100 µm argon microplasmas operating at pressures of 100 Torr and secondary electron emission coefficient of 0.1 are performed using particle‐in‐cell with Monte Carlo collisions (PIC‐MCC), and fluid model using the full‐momentum equations for both electrons and ions. Results obtained for plasma density, potential, electric field, and electron temperature using continuum simulations are compared with the PIC‐MCC simulations as benchmark. The comparison demonstrates significant discrepancies and a need to calibrate continuum simulation parameters based on kinetic simulations.

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