Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1999. / Includes bibliographical references (p. 145-152). / by Steve M. Ting. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004. / Includes bibliographical references (p. 195-204). / Molecular organic semiconductors have recently been applied widely as active layers in electronic and optoelectronic devices such as organic field-effect transistors and light-emitting devices. The use of organic active layers derives both from materials considerations and from processing advantages. The goal is to enable novel applications and structures that are difficult to produce with conventional materials (e.g., large-area, flexible, or transparent devices). Because charge transport efficiency increases with improved molecular ordering, the formation of large-area single crystals of these materials is essential for achieving integrated active organic structures. This thesis presents (1) an investigation of substrate surface modification as a means of inducing order within polycrystalline organic thin films, and (2) a new method for oriented, in-plane growth of millimeter-scale single crystal needles of molecular organic semiconductors. Two types of modified surfaces are investigated: (a) self-assembled nanofilms (SANFs), and (b) submicron periodic surface-relief structures. Polycrystalline thin films of pentacene and tetracene are vacuum sublimed onto pre-modified substrates. This work initially evaluates the influence of organosilane SANFs on morphology and field-effect transistor performance. It then attempts to use lithographically-defined surface relief to orient pentacene and tetracene grains via graphoepitaxy during thin film deposition. The periodic surface relief selects several preferred grain orientations, but uniaxial in-plane orientation is prevented by insufficient interfacial tension anisotropy. / (cont.) As a second approach to achieving large-area single crystals, solvent-vapor annealing is introduced. Permeation of solvent vapor into an amorphous organic film facilitates dewetting, aggregation, and crystallization via plasticization and interfacial tension effects. When applied to thin films of tris(8-hydroxyquinoline) aluminum (Alq3) on patterned substrates, solvent-vapor annealing yields oriented, millimeter-scale single crystal needles. The use of an appropriate SANF aids the dewetting and aggregation processes. Moreover, periodic surface relief produces anisotropic mass transport of solvated Alq3 via capillary flow, yielding orientation of the crystal needles in a specified in-plane direction. The crystal formation mechanism is expected to be generally applicable to a broad range of soluble organic materials, enabling their use in integrated active structures. / by Debra Jane Lightly Mascaro. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1995. / Includes bibliographical references. / by Augustine Che-Tsung Fou. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013. / Cataloged from PDF version of thesis. "June 2013." / Includes bibliographical references (p. 44-46). / This thesis seeks to correlate hysteretic power loss of tertiary ferrite nanoparticles in alternating magnetic fields to trends predicted by physical models. By employing integration of hysteresis loops simulated from physical models for single-domain ferromagnets, we have identified ferrite materials optimal for remote heating. Several organometallic thermal decomposition methods were adapted to synthesize nanoparticles with anisotropy energies varying over 3 orders of magnitude and transferred into water using a high-temperature ligand exchange protocol. Furthermore, we compare nanoparticles of the same composition and size produced via different synthesis conditions and highlight differences in their materials properties. These analyses identify the synthesis conditions that yield nanoparticles with optimized magnetic properties and with some of the highest power dissipation (specific loss power) found in literature for tertiary ferrite materials. / by Ritchie Chen. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1985. / Includes bibliographical references. / by Leonard E. Dolhert. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1999. / Vita. / Includes bibliographical references (p. 195-200). / by Kin Ha. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005. / Includes bibliographical references. / Initiated chemical vapor deposition (iCVD) was explored as a novel method for synthesis of functional polyacrylic thin films. The process introduces a peroxide initiator, which can be decomposed at low temperatures (<200⁰C) and initialize addition reaction of monomer species. The use of low temperatures limits the decomposition chemistry to the bond scission of initiator, while retaining functional groups of monomers, which has been confirmed in the infrared spectroscopy, nuclear magnetic resonance, and x-ray photoelectron spectroscopy of iCVD poly(glycidyl methacrylate) (PGMA) thin films. Studies of PGMA iCVD deposition kinetics and molecular weights indicate a free radical polymerization mechanism and provide guide for vapor-phase synthesis of other vinyl monomers. The retained epoxy groups can crosslink under e-beam irradiation, resulting in e-beam patterning of iCVD PGMA thin films with 80 nm negative-tone features achieved. iCVD copolymerization was also investigated to further tune film composition and properties. A surface propagation mechanism was proposed based on the study of the monomer reactivity ratios and the copolymer molecular weights during iCVD copolymerization. / (cont.) The synthesized acrylic copolymers have been investigated in applications as positive-tone e- beam resists, CO₂-developable resists, and low surface energy coatings with improved mechanical properties. The process of iCVD polymerization is extendable to vapor-phase polymerization of other vinyl monomers and creates new opportunities for the application of functional polymer thin films. / by Yu Mao. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2002. / Includes bibliographical references. / The layer-by-layer process, whereby aqueous solutions of oppositely charged polymers are alternately and repeatedly deposited onto a substrate, has emerged in recent years as a promising approach for creating thin films with nanoscale control of structure, composition, and surface properties. Applications ranging from surface modification to optical and electronic devices have arisen from the versatility of this nanocomposite fabrication technique. The additional ability to assemble into films a wide variety of biological entities, such as enzymes and DNA, has expanded the use of polyelectrolyte multilayers for biosensor and other biomaterials applications. This thesis further explores the rationale of using multilayers as biomaterials, with particularly emphasis on the importance of the underlying molecular architecture. Many of the results presented here concern films assembled from weak polyions, i.e., ones with pH-dependent charge densities, including poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH). Using weak polyions enables the creation of thin films with chemical and structural properties controlled with nanoscale precision by simply adjusting the pH of the polymer solutions. Under certain assembly conditions, initially nonporous PAA/PAH films become nano- and/or microporous through a simple pH-induced phase separation in acidic water (pH [approx.] 2.4), even with an exposure time of just a few seconds. By adjusting several processing parameters (e.g., the time, temperature, ionic strength, and a secondary rinse with neutral water), it is possible to generate either interconnected or discrete porous morphologies. / (cont.) The interaction of a highly adhesive mammalian NR6WT fibroblast cell line with various PAA/PAH films and other multilayer systems of differing compositions, structures, and charge densities has also been explored. This thesis demonstrates that by manipulating the multilayer pH assembly conditions, which in turn dictates the molecular architecture of the thin films, one may powerfully direct a single multilayer combination to be either cell adhesive or cell resistant. Highly ionically stitched multilayers attract cells, whereas weakly ionically crosslinked multilayers, which swell substantially in physiological conditions and thereby present richly hydrated surfaces, resist cell attachment. This unprecedented ability to fine-tune a multilayer to be either cell adhesive or bioinert, along with the unique feature of controllable porosity, allows polyelectrolyte multilayers to be envisioned for membranes, controlled release, and biocompatible implant coating applications. / by Jonas Daniel Mendelsohn. / Ph.D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005. / Includes bibliographical references (leaves 47-49). / A search of published research on sensing mechanisms of carbon nanotubes was performed to identify applications in which carbon nanotubes might improve on current sensor technologies, in either offering improved performance, reduced cost of manufacture, or both. Using this overview of carbon nanotube-based sensors, specific sensor technologies that could benefit from the use of newly developed techniques for producing aligned and ordered bundles of carbon nanotubes were selected. Reports of chemical/gas, biological, optical, mechanical, and a few other sensor applications of carbon nanotubes are reviewed. Only a few of these applications might benefit from aligned and ordered bundles of carbon nanotubes. Of these potential applications, only applications in semiconducting gas sensors, DNA sensors, and infrared sensors appear to have clearly defined market niches and are sufficiently technologically mature to allow a detailed assessment of commercial potential. It is argued that DNA and infrared sensors have good commercial potential with a medium amount of risks, while gas sensors have a smaller potential. Finally, DNA sensors are believed to derive the most value from aligned and ordered bundles of carbon nanotubes. / by Scott I. Rushfeldt. / M.Eng.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 113-117). / Infrared spectrum, especially mid-infrared range (2.512tm) covers the absorption peaks of many important chemicals including carbon monoxide, methane and water vapor. By analyzing the absorption spectrum of achemical, one can measure the concentration of the chemicals as well as distinguish the chemical species. The purpose of this work is to build a Si CMOS compatible integrated mid-infrared (MIR) platform for sensing. In this work, we evaluated the three major components (materials and devices) comprising an integrated mid-infrared (MIR) sensing platform: the light source, the waveguide sensor and the detector. To build an integrated MIR light source, we evaluated three approaches. 1) Germanium light source, which is the representative of the CMOS compatible semiconductor light source. By applying tensile strain as well as increasing doping and injection level, Ge is tuned to pseudo-direct or direct bandgap structure and the emission wavelength extends to MIR range. 2) Er-doped GaLaS (GLS) platform which is the representative of the rare earth doped material system. A new laser structure is designed for this system with a threshold power of 7.6 ptW and a slope efficiency of 10.26%. 3) Frequency comb generation which is a new area using nonlinearity to generate new frequencies. Thick Si3N4 material for comb structures are designed, fabricated and tested. In the waveguide sensor section, a waveguide structure based on chalcogenide glass (ChG) is built and tested. The sensing limit for methane reaches 2.5 vol. %. Besides, a ChG based small-footprint plasmonic optical switch is designed to work as an optical router for integrated spectrometer applications with a small (167 nm long) footprint. In the last part, a MIR PbTe based integrated detector has been successfully demonstrated for the first time. A further improvement in the material property and device structure yields a responsivity is about 1.4 A/W in the MIR regime. / by Zhaohong Han. / Ph. D.