Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 181-198). / Chalcogenide glasses (ChGs) are amorphous compounds containing the chalcogen elements (S, Se, Te) and exhibit wide infrared transparency windows. They are easy to synthesize in bulk and thin film forms and their compositional flexibility allows tuning of optical properties such as refractive index making them ideal for infrared photonics. We have studied the material attenuation in ChGs that arises due to the presence of impurities in the raw materials and established UV photolithography-based process flows that enable fabrication of chalcogenide glass waveguides and microresonators for near- and mid-IR wavelength ranges. Waveguides and optical resonators are key microphotonic elements for many on-chip applications such as telecommunications and chemical sensing. In this thesis, we show that scattering losses dominate in our ChG microphotonic devices while material attenuation from impurities is low. We demonstrate resonators coated with nanoporous polymers to improve their selectivity against target analytes for sensing applications. We exploit the photosensitivity of As2S3 glass to build silicon-based tunable photonic devices that offer post-fabrication tuning to optimize performance. Resonators also serve as a test platform for studying the effects of radiation on silicon and chalcogenide materials systems. Further, we propose new mid-IR microphotonic device designs using ChG materials and the challenges associated with measuring mid-IR devices along with solutions to address them. We employ input-to-output offsets, standard tapered waveguides, and a fiber collimator to improve mid-IR measurements and demonstrate transparent ChG waveguides with losses as low as 2.5 dB/cm. Finally, we propose a novel design that integrates PbTe detectors with ChG waveguides for on-chip mid-IR detection. Our simulations show that the use of a low-index spacer layer leads to a well-distributed field along the width of the detector due to a reduction in the effective index of the structure. We develop a fabrication process for waveguide-integrated detector designs and fabricate prototype structures that exhibit attenuation at telecom and mid-IR wavelengths. Such an integrated sensor design will enable the creation and deployment of low-cost remote sensor arrays with small footprints, and ultimately lead to "lab-on-a-chip" structures. / by Vivek Singh. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1993. / Includes bibliographical references (leaves 186-196). / by Syun-Ming Jang. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004. / Includes bibliographical references (leaf 41). / In a world where the miniaturization and the portability of electronic devices is king, batteries play an ever-increasingly important role. They are vital components in many consumer electronics such as cell phones and PDAs, in medical devices, and in novel applications, such as unmanned vehicles and hybrids. As the power demands of these devices increases, battery performance must improve accordingly. This thesis is an introductory investigation into the electrochemical properties of a promising new battery cathode material: lithium vanadium phosphate (Li3V2(PO4)3) (LVP). Studies of other members of the phospho-olivine family, which LVP is a part of, indicate that the olivines have high lithium diffusivity but low electronic conductivity. LVP is part of the phosphor- olivine family, which traditionally has been shown to have high lithium diffusivity but low electronic conductivity. LVP was synthesized via a solid-state reaction and cast into composite cathodes. (90/5/5 ratio of LVP, Super P Carbon, and PVDF.) These composite cathodes were used in lithium anode, LiPF6 liquid electrolyte, Swage-type cells that were galvanostatically cycled from 3.OV to 4.2V and from 3.4V to 4.8V at C/20 rates. Electrochemical impedance spectroscopy was carried out on an LVP / liquid electrolyte / LVP cells from 0.01Hz to 1MHz. Finally, temperature conductivity measurements were taken from a die-pressed LVP bar. The results of the experimentation indicate that LVP has much promise as a new battery cathode material, but there are still a number of concerns to address. / (cont.) LVP has a higher operating voltage (4.78V) than the current Li-ion battery standard (3.6V), but there are issues with becoming amorphous, cycleability, and active material accessibility. From the EIS data, passivating films on the surface of the LVP cathode do not seem to be a factor in limiting performance. The conductivity data gives a higher than expected conductivity (4.62* 10-4 S/cm). / by Chwan Hai H. Hsiung. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Block coopolymers(BCP) have become of interest in the pursuit novel methods of nanolithography. Their ability to self-assembly into periodic geometries with nanoscale feature sizes makes them attractive as etching masks and templating materials for microelectronics and nanodevices. BCP provide a scalable and low-cost method that is compatible with existing semiconductor fabrication technologies. Though various studies have looked at several combinations of block copolymers we focus on the use of solvent annealing as a method to tune the morphology of PS-b-PFS and PS-b- PFS-b-PS block copolymers. These polymers have shown promise as precursors to a variety of materials and in particular this combination of block copolymers is attractive because we have at our dispossible etching methods with a high selectivity between these two polymers. / by Juanml Carlos Ybarra. / S.B.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1999. / Includes bibliographical references (leaves 194-196). / A Gel Plating Process for selective gold metallization was developed in this thesis. The Gel Plating Process selectively plates metal on catalytic features without exposing sensitive area, of the substrate surface to a corrosive plating bath. This process utilizes an electroless plating bath and polymeric thickening agent to formulate a gel. The gel is selectively printed onto the areas of the substrate that require plating. Plating occurs autocatalytically at an elevated temperature by the simultaneous anodic oxidation of the reducing agent and catalytic reduction of the metal complex onto the catalytic features under the gel print. The substrate is cleaned, leaving a selectively metallized substrate surface. Aluminum nitride (AIN) is a potential packaging material for high power electronic applications; however, it is severely corroded in the alkaline gold electroless plating solutions often used to selectively plate packaging substrates with electrically isolated lines. An ammonium ion selective electrode was used to study the in situ corrosion of AlN as a function of pH. It was shown that the aluminum trihydroxide corrosion product created on the surface of AlN during exposure to aqueous solutions acts as a barrier layer that decreases the corrosion of AlN in the pH range where this aluminum trihydroxide product is insoluble. An aluminum oxynitride layer of 200 angstroms was found to act as an insoluble barrier layer to corrosion of AIN at a pH of 9.5. A plating gel was formulated for use in the Gel Plating Process by adding a polymeric thickening agent to an electroless gold plating bath chemistry. The plating chemistry incorporated sodium gold thiosulfate as the gold complex and sodium ascorbate as the reducing agent . The gold concentration in the plating gel was increased to 40 g/L gold from the 4 g/L gold found in typical commercial electroless plating baths. This resulted in a high ion concentration plating solution that was thickened with a hydroxyethyl celJulose (HEC) thickening agent. A stabilizer, 2-mercaptobenzimidazole, was found to increase the room temperature and plating temperature stability of the plating gel. Addition of excess sodium ascorbate caused a significant improvement in plate color. Addition of a surfactant to the plating gel formulation enhanced the printability of the plating gel and reduced extraneous plating of gold onto the noncatalytic areas of the substrate. The rest viscosity of the plating gel was found to be 70,000 cP at 25 °C and 38,000 cP at 60 °C, the highest plating temperature used. The plating mechanism of the Gel Plating Process was found to be reaction rate controlled at short times and diffusion controlled at longer times. A reaction rate model and a diffusion model with a heterogeneous reaction were fit to plating rate data at 50 °C and 60 °C. The reaction rate model was used to determine the rate constant, k, for the cathodic reaction at the plating surf ace at short times. A diffusion model with a heterogeneous chemical reaction was used to identify the diffusion coefficient, D, of the gold complex in the plating gel at long times. At 60 °C, it was found that k = 1.5 x 10-6 emfs and D = 4 x 10·7 cm2/s. At 50 °C, it was found that k = 3 x 10·6 emfs and D = 2 x 10·7 cm2/s. The thickening agent was found to decrease both the reaction rate constant for the cathodic reaction at the plating surface and the diffusivity of the gold complex. The gold plate thickness and microstructure was found to be influenced by the gold complex and reducing agent chemistry, the stabilizer concentration, and thickening agent additions. Plating through a gel resulted in a fine grained microstructure. Plating through a solution resulted in a large grained microstructure.- SEM cross sections indicated that a dense gold plate resulted from gel plating. The gold film obtained by the Gel Plating Process is free of trapped organics. / by Lynne Miriam Svedberg. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2002. / Includes bibliographical references (p. 194-206). / Motivated by the challenges in understanding important features of protein adsorption, the interactions between (-helical peptides and a carefully selected set of model surfaces were studied. The peptide sequences contained three blocks of two to five residues each, with the side chains of the N-terminal and C-terminal blocks having negative and positive charges, respectively, and the central block having uncharged side chains. The conformation of a variety of such peptides was studied in solution by circular dichroism (CD) and H nuclear magnetic resonance (NMR) spectroscopy, in order to characterize the degree of xc-helicity in solution, as a function of temperature, pH, and chemical denaturant (urea) concentration. Intramolecular electrostatic interactions arising from the charged side chains, together with the central block of gc-helix-forming alanine residues, were found to stabilize oc-helicity. These interactions were balanced by the natural tendency toward disordered structures, which resulted in fractional oc-helicities between 25% and 50% when in solution. Adsorption isotherms for the peptide Ac-DDDDAAYAARRRR-Am on amorphous colloidal silica nanoparticles were studied in detail. A greater amount of peptide was adsorbed at basic pH than at neutral pH. The was fit with Langmuir and Frumkin isotherms, and the free energy, enthalpy, and entropy of adsorption were calculated. The enthalpy of adsorption at pH 9 (-17 kJ mol'1) was consistent with calculations of the electrostatic interaction between the screened silica surface charge and the dipolar charge distribution on the peptide arising from the charged side chains. / The entropy of adsorption at pH 9 (15 J mol'l K-) arose in part from conformational changes which were observed in the CD and NMR spectra of adsorbed molecules. Solution 1H NMR spectra of peptide adsorbed to colloidal silica resolved resonances from aspartate and alanine, but not from arginine; this was shown to arise from selective immobilization of positively-charged arginine side chains due to electrostatic interactions with the negatively-charged silica, which resulted in a specific orientation of the peptide on the surface. Conformationally-sensitive resonances from aspartate and alanine residues displayed peak shifts characteristic of reduced ac-helicity. The CD spectra of adsorbed peptides also indicated a decrease in oc-helicity. Taken together, these measurements supported the view that loss of o-helicity of adsorbed molecules propagates from the arginine terminus, which is directly adjacent to the surface, into the alanine and arginine segments, which extend into solution. Because conformational changes have important implications for the functionality of adsorbed molecules, the extent of c-helicity loss was measured quantitatively as a function of temperature and pH for the peptide Ac-DDDDAAAARRRRR-Am. At neutral pH, the c-helicity of adsorbed peptides decreased with increasing temperature, much like the behavior observed for peptides in solution. In contrast, at basic pH, the ca-helicity of adsorbed peptides increased with increasing temperature. These results were interpreted using a statistical model based on modifications to existing theories of the helix-coil transition to include residue-specific electrostatic interactions between the surface and charged peptide side chains. / by Michael J. Read. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1989. / Includes bibliographical references (leaves 138-143). / by Michael Maloney. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1984. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / by Han-ill Yoo. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Charge-containing polymers are used in a wide variety of commercial products including fuel cell membranes, heat sealing packages, and golf ball covers. Traditionally made as random copolymers of charged and uncharged monomers, morphological understanding and control is limited due to the lack of long range order and small length scale of the structural inhomogeneities. Moreover, the charge functionality is typically introduced in a permanent way that is not modifiable after synthesis, locking in a chemistry and structure that may not be optimal for the ultimate application. This thesis develops and studies the morphologies of a model block copolymer which is controllably charged in a novel way: by protonating a weak base. This polymer is composed of one hydrophilic but uncharged block, poly(oligoethylene glycol methyl ether methacrylate) (POEGMA), and one weak polyelectrolyte, poly(2-vinylpyridine) (P2VP) which can be controllably charged by varying the amount of acid to which it is exposed. This thesis presents the synthesis and morphological characterization of this polymer using scanning probe microscopy and small angle X-ray scattering. First, the ability of P2VP protonation to change the morphology of the diblock is demonstrated; while miscible in the absence of charge, the diblock undergoes a disorder to order transition upon protonation by a variety of acids. Thin films with varying levels of polyelectrolyte protonation are created and the efficacy of several polar aqueous and organic annealing solvents are presented. The introduction of acid in either the vapor or liquid phase is also shown to induce microphase separation. This is followed by a thorough treatment of the bulk morphologies of POEGMA-P2VP as a function of acid content, temperature, and minority block volume fraction. For all diblocks, protonation is found to increase the segregation strength between the two blocks and disorder to order transitions are observed with increasing protonation and temperature. Polymers with minority block volume fractions closest to 0.5 are the most immiscible, while those richer in majority block require more acid and higher temperatures to demix. Finally, the effect of acid type is investigated in detail by the comparison of two monoprotic with one diprotic acid. The diprotic acid is found to be more efficient at inducing microphase separation than either monoprotic acid for two diblocks of differing composition. / by Charlotte Roberta Stewart-Sloan. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / Includes bibliographical references. / Thin film rings can be an alternative geometry of magnetic memory cells, in which data bits are stored by the chirality of the flux-closed or 'vortex' state of the ring. The absence of the stray field in the vortex state is advantageous of high density data storage. Elliptical rings with 3 / 2 pm major / minor diameter and widths of 300 nm above were fabricated from multi-layer thin film structures such as the ferromagnetic-antiferromagnetic exchange bias bilayer or giant magnetoresistance (GMR) spin valve structure, and their magnetic and magnetoelectric properties were investigated. Exchange-biased elliptical rings show an interplay between shape anisotropy and exchange anisotropy. When both the exchange bias and applied field are oriented along the major axis, an elliptical ring shows a shifted hysteresis loop and strong in-plane anisotropy. The switching behavior and vortex state stability of the rings are strongly dependent on the pinning direction and applied field direction relative to the major axis of the ellipse. It has proven difficult to control the vortex chirality in a simple manner. A model is described that predicts the vortex chirality of an elliptical magnetic ring as a function of the direction of the applied field and of the exchange bias, based on the change in the energy of the system as the domain walls move. Experimental measurements of the chirality in Co and Co / IrMn magnetic rings with a 3.2 pm major axis are in excellent agreement with the model. / (cont.) The vortex circulation direction can therefore be tailored with an appropriate combination of the applied field direction and exchange bias direction with respect to the major axis. NiFe / Cu / Co / IrMn spin valve elliptical rings with 3.2 / 1.9 pm major / minor diameter and the width of 340 - 370 nm were fabricated and the magnetoresistance (MR) of the rings were measured with applying an in-plane field. Spin valve rings show asymmetric MR curves with three different MR states. Minor loop MR measurements, which give rise to switching of only the free layer of the spin valve ring, demonstrate that an individual control of the vortex chirality in each ferromagnetic layer is possible in a ring-shaped multilayered structure, such as a spin valve ring. / by Wonjoon Jung. / Ph.D.