Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006. / Includes bibliographical references (p. 164-171). / The dramatic advances in Si/SiO2-based microelectronic processing witnessed over the past several decades can largely be attributed to relatively material-independent device scaling. However, with physical and economic limitations to the continued scaling of such devices appearing on the horizon, it is likely that near-term advances will come from the integration of novel and previously underrepresented materials. One of the most promising ways to enhance performance comes from the integration of judiciously chosen lattice-mismatched materials with Si. However, the integration of such structures typically poses significant technical challenges. The work contained in this thesis seeks to address several of these important issues, primarily through the use of relaxed, graded SiGe buffers on Si (i.e. Vx[Si1-xGex]/Si). Several new phenomena in relaxed graded SiGe buffers are developed in this thesis. A rise in threading dislocation density was observed in high-Ge content relaxed graded SiGe layers grown at relatively high temperatures, which was attributed to dislocation nucleation. This observation is contrary to conventional graded buffer theory in which high growth temperatures are expected to result in reduced threading dislocation densities (TDDs). / (cont.) Additionally, a coupling effect between the effective strain and the growth rate was observed, as evidenced by increased TDD values at reduced growth rates. This observation is attributed to reduced growth rates allowing more time for the surface to evolve (i.e. roughen) during growth, thereby trapping mobile dislocations and necessitating the nucleation of additional dislocations to continue relaxing the structure. Also detailed in this thesis is the creation of two novel CMOS-compatible platforms for high-power applications: strained-silicon on silicon (SSOS) and strained-silicon on silicon-germanium on silicon (SGOS). SSOS substrate has an epitaxially-defined, tensilely strained silicon (-Si) layer directly on bulk silicon wafer without an intermediate SiGe or oxide layer. SSOS is a homochemical heterojunction, i.e. a heterojunction defined by strain state only and not by an accompanying compositional change, and therefore in principle SSOS may ease metal-oxide-semiconductor (MOS) -Si fabrication as SiGe is absent from the structure. SGOS has an epitaxially-defined SiGe layer between the strained silicon channel and the Si substrate, which is likely necessary to prevent excessive off-state leakage in MOS devices due to overlap of the source-drain contacts and the interfacial misfit array. / (cont.) The thesis concludes with a study of utilizing buried -Si layers for improving the fabrication of SSOI substrate via the hydrogen induced layer exfoliation process. Previous work involving tensile -Si.4Geo.6 layers in relaxed Ge/Vx[SiixGex/Si demonstrated that significant hydrogen gettering via the formation of strain-relieving platelets occurred within the tensile -Sio.4Ge.6 layers, leading to an overall increase in layer transfer efficiency for GOI substrate fabrication. Buried tensile -Si layers in relaxed SilGex for SSOI fabrication, however, demonstrate markedly different hydrogen gettering behavior that is dependent on a combination of both the degree of tensile strain as well the amount of damage present in the adjacent Si.xGex alloy. It was determined that a tensile strain level of approximately 1.6% in Si (corresponding to a Sio.6Ge.4-based donor structure) was needed to create sufficient engineered damage to overcome the implantation damage in the adjacent Sio.6Ge.4 layers and result in enhanced layer exfoliation. Lastly, an advanced Sio.6Geo.4-based structure which incorporated -Si layers as transfer, hydrogen gettering, and etchstop layers was demonstrated. Such a structure may prove useful for the reuse of significant portions of the original SSOI donor structure, thereby potentially speeding commercial adoption of the SSOI platform. / by David Michael Isaacson. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references. / The optical logic unit cell is the photonic analog to transistor-transistor logic in electronic devices. Active devices such as InP-based semiconductor optical amplifiers (SOA) emitting at 1550 nm are vertically integrated with passive waveguides using the asymmetric twin waveguide technique and the SOAs are placed in a Mach-Zehnder interferometer (MZI) configuration. By sending in high-intensity pulses, the gain characteristics, phase-shifting, and refractive indices of the SOA can be altered, creating constructive or deconstructive interference at the MZI output. Boolean logic and wavelength conversion can be achieved using this technique, building blocks for optical switching and signal regeneration. The fabrication of these devices is complex and the fabrication of two generations of devices is described in this thesis, including optimization of the mask design, photolithography, etching, and backside processing techniques. Testing and characterization of the active and passive components is also reported, confirming gain and emission at 1550 nm for the SOAs, as well as verifying evanescent coupling between the active and passive waveguides. In addition to the vertical integration of photonic waveguides, Esaki tunnel junctions are investigated for vertical electronic integration. Quantum dot formation and growth via molecular beam epitaxy is investigated for emission at the technologically important wavelength of 1310 nm. The effect of indium incorporation on tunnel junctions is investigated. The tunnel junctions are used to epitaxially link multiple quantum dot active regions in series and lasers are designed, fabricated, and tested. / by Ryan Daniel Williams. / Ph.D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1988. / Includes bibliographical references. / by Robert I. Park. / B.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996. / Includes bibliographical references (leaves 59-61). / by Lynn Louise Chalfoun. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references. / The development of nanoscale polymeric materials for mechanical applications necessitates advances in small-volume experimental techniques and analyses that reflect the viscoelastoplastic behavior of such materials. In this thesis, the time-dependence and response of homogeneous engineering polymers under confined contact loading are characterized as a function of polymer physical and structural properties. The validity of the time-independent metric indentation hardness Hi is evaluated through the combination of nanoindentation and atomic force microscopy imaging. In addition, the classic, time-dependent metric creep compliance J(t) is used to establish the experimental conditions necessary for linear elastic behavior for a set of thermoplastic and thermoset materials. For large indentations (hmax > 1 um), properties are tacitly assumed to reflect the properties of bulk polymer; however, this assumption does not hold within 100 nm of a free surface or interface of amorphous polymers such as polystyrene and polycarbonate. The contact deformation mechanism near an amorphous polymer surface is found to scale with the surface area of contact, suggesting the dynamic formation of a structural interphase region. Chemical probe functionalization experiments are developed to explore the effects of probe surface charge on the probe-polymer interface and contribute to the understanding of the interphase that dominates nanocomposite material response. A technique to rapidly screen mechanical response of combinatorial polymer libraries is presented, to establish structure-property-processing relationships of such chemomechanically defined interfaces before nanoscale deformation mechanisms in confined polymers are fully understood. / (cont.) Finally, material design for elastic, viscoelastic, and viscoelastoplastic mechanical properties is discussed in terms of polymer physical length and time scales. / by Catherine Anne Tweedie. / Ph.D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references (leaf 54). / Twenty - first opportunities for Gigascale Integration will be governed in part by a hierarchy of physical limits on interconnect. Microprocessor performance is now limited by the poor delay and bandwidth performance of the on - chip global wiring layer. This thesis is envisioned as a critical showstopper of electronic industry in the near future. The physical reason behind the interconnect bottleneck is the resistive nature of metals. The introduction of copper in place of aluminum has temporarily improved the interconnect performance, but a more disruptive solution will be required in order to keep the current pace of progress, optical interconnect is an intriguing alternative to metallic wires. Many - core microprocessors will push performance per chip from the 10 gigaflop to the 10 teraflop range in the coming decade. Pin limitations, the energy cost of electrical signaling, and the non - scalability of chip - length global wires are significant bandwidth impediments. Silicon nanophotonic based many core architecture are introduced in order to meet the bandwidth requirements at acceptable power levels. / by Zhoujia Xu. / M.Eng.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 147-157). / The long-term goal of my Ph.D. study has been controlling the self-assembly of various materials using state-of-the-art nanofabrication techniques. Electron-beam lithography has been used for decades to generate nanoscale patterns, but its throughput is not high enough for fabricating sub-10-nm patterns over a large area. Templated block copolymer(BCP) self assembly is attractive for fabricating few-nanometer-scale structures at high throughput. On an unpattermed substrate, block copolymer self-assembly generates dense arrays of lines or dots without long-range order. Fortunately, physical features defined by electron lithography can guide the self-assembly of block copolymer. In our previous work, the orientation of cylindrical phase block copolymer was controlled simply by changing the distance between physical features, and resulting polymer patterns were analyzed by an image analysis program. Here, we first demonstrated high throughput sub-10-nm feature sizes by applying the same approach to a cylindrical morphology 16kg/mol PS-PDMS block copolymer. The half-pitch of the PDMS cylinders of this block copolymer film is 9 nm, so sub-10-nm structures can be fabricated. We also applied the similar approach to a triblock terpolymer to achieve dot patterns with square symmetry. To achieve a more complex pattern, electron-beam induced cross-linking of a block copolymer and second solvent-annealing process was used. By using this method, a line-dot hybrid pattern was achieved. Despite that the block copolymer self-assembly area had been heavily studied, researchers had yet to ascertain how to design nanostructures to achieve a desired target pattern using block copolymers. To address this problem, we developed a modular method that greatly simplifies the nanostructure design, and using this method, we achieved a circuit-like block-copolymer pattern over a large area. The key innovation is the use of a binary set of tiles that can be used to very simply cover the desired patterning area. Despite the simplicity of the approach, by exploiting neighbor-neighbor interactions of the tiles, a complex final pattern can be formed. The vision is thus one of programmability of patterning by using a simple instruction set. This development will thus be of interest to scientists and engineers across many fields involving self-assembly, including biomolecule, quantum-dot or nanowire positioning; algorithmic self-assembly; and integrated-circuit development. We applied this concept - controlling the assembly of materials using nanostructures - to a different material, protein. Single-molecule protein arrays are useful tools for studying biological phenomena at the single-molecule level, but have been developed only for a few specific proteins using the streptavidin-biotin complex as a linker. By using carefully designed gold nanopatterns and cysteine-gold interaction, we developed a process to make single-molecule protein arrays that can be used for patterning a broad range of proteins. / by Jae-Byum Chang. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994. / Includes bibliographical references (leaves 174-180). / by Ambuj D. Sagar. / Ph.D.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1987. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 78-80. / by Adebisi Oladimeji Oladipupo. / Sc.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, June 2005. / Includes bibliographical references (p. 38-39). / In this thesis, the chemical/mechanical properties and biocompatibility of gelatin were investigated to produce a gelatin scaffold for the release of bone morphogenetic proteins (BMPs) from composite particles. This delivery system, designed to regenerate bone, holds much promise as an alternative to bone grafts. The chemical properties of gelatin were examined through zeta potential measurements, swelling studies, optical microscopy, environmental scanning electron microscopy (ESEM), and collagenase degradation. Compressive tests and mercury porosimetry were performed to study the mechanical and structural properties of the scaffold. The biocompatibility of the scaffold was determined through cell optical imaging and DNA quantification studies. Based on findings of this research, the material choices were made and the synthesis method for the gelatin scaffold was developed. Gelatin A, 300B, derived from bovine collagen, with an isoelectric point of [approx.] 9, was selected. Crosslinking was accomplished by reacting 10 w/v% glutaraldehyde with 10 w/v% gelatin solution. The most effective crosslinking condition was found to be 5 hours at room temperature. Glycine rinses were conducted to cap any non- reacted (toxic) aldehyde groups, and the necessary length of time was found to be at least 48 hours at 37⁰C. Finally, based on pore size distribution and mechanical stability, an optimal lyophilization method was developed with initial freezing at -20⁰C for 1 day, followed by lyophilization of the scaffold for 1-2 days. In terms of mechanical properties of the gelatin and amount of protein delivered, the most effective loading of poly(lactic-co-glycolic acid)/apatite/protein composite particles was found to be 10% of the mass of the gelatin. / by Elizabeth A. Hager. / S.B.