Study of waveguide and anisotropy effects upon surface acoustic wave velocities in thin films

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998.Includes bibliographical references (leaf 50).Impulsive Stimulated Thermal Scattering (ISTS) is an in-situ non-destructive characterization technique based on laser excitation and detection of surface acoustic waves (SAWs) for mechanical properties of thin metal films in the microelectronic industry. In this work, the effect of elastic anisotropy from silicon wafers on ISTS measurements has been studied. It has been shown that for films of submicron thickness, the anisotropic effects on acoustic velocities are substantial. Moreover, at a particular orientation of propagating SAWs, two surface acoustic modes are observed rather than only one acoustic mode as in an isotropic model. With regard to dispersive behavior, a previously unknown result has been established that the pseudo-surface wave branch of an uncoated substrate is a qd->O limit for the second-order acoustic waveguide mode of a film-substrate system. Theoretical analysis for calculating acoustic modes of a supported film for arbitrary orientation, along with an experimental technique featuring optically heterodyned signal detection, provide an adequate basis for accurate characterization of thickness and elastic properties of thin films on anisotropic substrates. Furthermore, in the preliminary study of the waveguide effect on Damascene Structure, it has been considered that the widths of the bar structures as well as the spaces between the bar structures should be included in the scaling parameters for dispersion curves.by Ariya Akthakul.S.M

An elastic second skin

We report the synthesis and application of an elastic, wearable crosslinked polymer layer (XPL) that mimics the properties of normal, youthful skin. XPL is made of a tunable polysiloxane-based material that can be engineered with specific elasticity, contractility, adhesion, tensile strength and occlusivity. XPL can be topically applied, rapidly curing at the skin interface without the need for heat- or light-mediated activation. In a pilot human study, we examined the performance of a prototype XPL that has a tensile modulus matching normal skin responses at low strain (<40%), and that withstands elongations exceeding 250%, elastically recoiling with minimal strain-energy loss on repeated deformation. The application of XPL to the herniated lower eyelid fat pads of 12 subjects resulted in an average 2-grade decrease in herniation appearance in a 5-point severity scale. The XPL platform may offer advanced solutions to compromised skin barrier function, pharmaceutical delivery and wound dressings

Design of chemistry and morphology of polymer filtration membranes

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2003.Vita.Includes bibliographical references.To improve membrane materials in water filtration, which currently display broad pore size distribution, hydrophobic chemistry, and fouling behavior, a novel design of chemistry and morphology of membranes is employed. First, through fundamental studies of morphological formation both in bulk by lattice-Boltzmann (LB) simulation methods and at the surface by observation of electron micrographs, it is illustrated that phase separation via spinodal decomposition is responsible for pore development. This understanding suggests the possibility to tailor a uniform and interconnected porous membrane by using the spinodal structure. Considering that the control of spinodal porous structure on a nanoscale can be challenging, an alternative approach to achieve a similar interconnected morphology by utilizing the self-assembled structure of a graft copolymer is presented. This graft copolymer permits not only the design of morphology through its architecture, but also the design of chemistrythrough its chemical components. Here, a comb-type structure of a copolymer is applied; this structure contains a hydrophobic poly(vinylidene fluoride) (PVDF) backbone for structural integrity and hydrophilic poly(ethylene oxide) (PEO) side chains for preferential water transport. A membrane with the microphase-separated structure of this copolymer at the surface is then utilized to clean oily water wastes where the membrane rejects more than 99.9% of the oil without fouling. This membrane can also perform molecular sieving, serve as a chromatography instrument, and isolate a product of a designated size distribution on a nanoscale via its tunability of channel sizes, as demonstrated in the uniform size dispersity of gold nanoparticles. Moreover, gold nanoparticles are introduced as a probe to study sieving characteristics of the membrane by tailoring their size and chemistry. The success in regulating transport across the membrane through the self-assembled platform leads to a new family of filtration membranes that could offer much broader applications for nanoscale separation.by Ariya Akthakul.Ph.D