The most severe problem for the vacuum arc deposition (VAD) technique is the formation of micron-size particles on the films. These particles degrade the films' properties. The present work studied the generation mechanisms and characteristics of the droplets that are produced in the carbon films deposited by vacuum arc technique. To achieve a better control of the generation mechanism of these droplets, the effect of the arc current, arc duration time, cathode spot temperature and distance between cathode and substrate on the size and population of the micro-droplets are studied. / The micro-droplets are in the range of 0.3 $ mu$m to 2 $ mu$m in diameter, and have a graphite structure. The most probable origin for these particles are the cathode. The size and population of these particles are directly proportional to the cathode spot temperature (i.e., to the arc current and/or arc duration time), and inversely proportional to the distance between the cathode and the substrate. The droplet production is mainly due to the heating effect.

The self preserving free jet in streaming flow has been investigated by studying the equations of mean motion for two-dimensional turbulent flow. It is found that at high Reynolds nurnber the jet may be self preserving if the free stream velocity varies as the downstream co-ordinate to a power which in turn depends on the non-dimensional velocity of the jet. The growth of the jet is then linear. The effect of an upstream boundary-Iayer on the outside of the slot is also considered. This analysis is then applied to the outer part of a wall jet in a similar pressure gradient. The effect of the inner boundary layer on the outer part of the flow is considered and formulae for the growth of the inner boundary-Iayer and the variation of skin friction are given. Also a form for the non-dimensional mean velocity profile including the inner boundary-layer is suggested. The predictions of the theory are found to be in substantial agreement with measurements of the mean velocity, the static pressure and the skin friction in wall jets with an equilibrium pressure gradient. Experimental measurements have also been made for wall jets in streaming flow with zero pressure gradient and wall jets in still air. The results of these experiments compare weIl with those of previous investigators . The law-of-wall and the velocity defect law for wall jets are investigated and the former is found to be limited in application. A simple power law appears to be useful for representing the whole boundary-layer velocity profile and forms the basis for the analysis of the inner boundary-layer .

In this work, the dependence of the vacuum arc spot velocity on physical and electrical properties of different graphite cathode materials is investigated in the presence of a variable magnetic field. A pulsed arc system is used to perform preliminary experiments on the arc mobility for the different types of graphite for the selection of proper material morphology and the design of a continuous vacuum arc system. The characteristics of arc mobility, erosion rate, and carbon ion flux emitted from the continuous carbon source are then evaluated in view of particle-free diamond-like protective coatings. Results show that the arc spot velocity on graphite cathodes is larger on cathodes having larger grain size, lower electrical resistivity and higher apparent density. The spot velocity is also lower for cathodes having larger pore sizes and total porosity. The arc spot velocity is also found to be increased by increasing the magnetic field intensity over the surface of any graphite type. Reduced residence time of the spot on a given site of the cathode resulting from arc velocity increase should lead to a reduction in the heat load input in the cathode spot. This correlates with results on the number of emitted particles, the film thickness and roughness, and the erosion rate that are found to decrease, while the ion flux emission is increased. Diamond-like carbon (DLC) films free of particles are produced in a continuous arc ion plating (AIP) system. The ion energy in the continuous AIP system is found to vary with the graphite surface properties and the intensity of a plasma confining magnetic field in front of the cathode. The ion energies measured vary between 39.8 eV to 62.6 eV.

We develop a coarse grained methodology to study solvent mediated interactions between two or more hydrophobic spheres. The free energy of a configuration of two hydrophobic hard spheres is calculated as a function of their separation to understand the thermodynamic force between them mediated by water. The range of the hydrophobic interaction is found to be of the order of the equilibrium correlation length of water; beyond this range the hydrophobicity induced force is negligible. We also examine the free energy landscape corresponding to the two interacting hydrophobic spheres, and find a new intermediate state between the two states of separate and non-interacting spheres and a weakly bound cluster. The nature of this intermediate state changes depending on the size of the spherical particles, and even disappears beyond a minimum critical radius. Our results are relevant to the understanding of hydrophobic mediated interactions in coarse grained models of protein folding and protein protein interactions which, to date, have only accounted for hydrophobicity in an empirical way.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-11, Section: B, page: 7403. Adviser: William RC Phillips. Includes bibliographical references (leaves 62-64) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--Lehigh University, 2007. / Adviser: Yong W. Kim.

Thesis (Ph.D.)--Lehigh University, 2009. / Adviser: Arnold Kritz.

Many technological and biomedical applications ranging from water filtration and oil extraction to arteriosclerosis and vein thrombosis rely upon the transport of solids in liquids. Particulate matter suspended in liquid flowing through channels that are often microscopic or millimeters in size which leads to clogging. This dissertation examines the clogging behavior of microscopic channels by microscopic particles suspended in liquid. We physically model clogging in microchannels by flowing microparticles through microfluidic channels. Unlike previous studies, we choose non-uniform microchannels; specifically, we study clogging in microchannels whose width narrows over the length of the channel. Converging channels are inspired by the pore size variations in real porous media like membrane filters and sandstone. Initially we study the clogging behavior of microparticles in arrays of parallel microchannels as we vary the microchannel entrance (mouth) width and microchannel length. We measure the time until each channel clogs and we calculate the number of particles that pass prior to clogging. Contrary to expectation, we show that the number of particles passing through a pore increases exponentially with increasing mouth width but decreases linearly as the channel length increases. Changing the dimensions of the channels changes the particulate suspension’s flow rate which in turn changes the shear stresses that particles experience near the channel wall. When particles experience higher near-wall shear stress, the particles are less likely to adhere to channel walls and engender clogging. We confirm the effect of flow rate on channel clogging by demonstrating that the number of particles needed to clog a tapered channel increases as the pressure applied to the particulate suspension increases. The connection between flow rate and clogging highlights the interplay between hydrodynamic forces and intermolecular forces that govern particle attachment and ultimately clogging. We further explore this relationship by modulating the interaction between the particle and channel wall in a single tapered channel. While observing single channels clogging, we also resolve individual particles gradually building up on channel walls and forming clogs. Interestingly, particles also cluster on upstream channel walls only to later detach and clog at the downstream constriction. At low pressures, the channel clogs when particles accumulate individually near the constriction. At high pressures, the channel clogs when particle clusters detach from channel walls upstream and flow into the constriction. Finally, we compare the clogging behavior of particles with long, electrosteric stabilizing molecules on the surface to the clogging behavior of particles with shorter electrostatic stabilizing molecules on the surface. We also compare the clogging behavior of both particle types in the presence of varying concentrations of a monovalent salt. We show that clogging is mitigated when Debye length is comparable to the length of the stabilizing molecule on the particle’s surface. / Engineering and Applied Sciences - Applied Physics

No description available.

Measurements of reflectivity and Hall effect have been made on polycrystalline n-type samples of GaAs and alloys of the systems GaAs xSb1-x and Ga1-xAlxAs to find values of electron effective mass at the bottom of the conduction band m*00/m . The experimental data were obtained with a Baird monochromator which was modified to give double beam operation and extended wavelength range up to 30 mum, so that measurements of the free carrier reflectivity could be made on samples with low carrier concentration. The reflection coefficient R and hence the index of refraction eta were obtained from the experimental measurements. The variation of eta2 was plotted as a function of the square of the wavelength. For each sample, the graphical result (eta 2 vs lambda2) was found to be a straight line and it was extrapolated to zero wavelength to obtain the optical dielectric constant epsilon infinity. The slope of the line also was determined and used to obtain the value of effective mass at the bottom of the conduction band. For the systems GaAsxSb1-x the alloy compositions were determined by the X-ray powder photograph method. For the two alloy systems GaAsxSb1-x and Ga 1-xAlxAs, optical dielectric constant and effective mass values were measured from infrared reflectivity for the first time. The values of the effective masses were determined by the simultaneous solution of the integrals giving the statistical carrier concentration and the slope of the free carrier reflectivity under the condition of the general degeneracy, the lattice contribution to the slope being taken into account. Theoretical values of the effective masses in the (000) conduction band as a function of alloy composition were calculated for the alloy system GaAs xSb1-x using the disorder equation (73W) and Kane equation (57K) for the effective masses. The experimental results were found to be in better agreement with the disorder equation of the effective mass than with the Kane equation. Finally, to complete the outline of the project, it should be mentioned that the values of optical Fermi energy, dielectric constant, optical relaxation time, optical mobility and optical conductivity were calculated for 12 samples of the alloys GaAsxSb1-x and Ga1-xAl xAs.