Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005. / Includes bibliographical references (leaf 36). / An analysis was carried out on the process of Supramolecular Nano-Stamping (SuNS) in order to determine whether or not the science involved has market potential in the DNA microarray industry. This industry is rapidly expanding and succeeding in such an atmosphere would generate a large amount of revenue. Supramolecular Nano-Stamping provides a way to reproduce DNA microarrays at a significantly lower cost than current competitors who manufacture chips of a similar quality. The results indicate that Supramolecular Nano-Stamping has the potential to succeed in the DNA microarray industry. There are many factors which must first be examined before these conclusions can be reached, including analysis of current and potential competition, as well as the growth and development of the DNA microarray industry as a whole. This is done through a detailed intellectual property search and formation of a cost model and eventual business strategy. / by Christina Maria DePalma. / M.Eng.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996. / In title on t.p., "[mu]" is the lower-case Greek letter. / Includes bibliographical references (leaves 175-183). / by Ann Marie Jansen. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1999. / Includes bibliographical references (leaves 46-48). / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014. / Cataloged from PDF version of thesis. In title on title page, [d̳e̳l̳t̳a̳] appears as lower case Greek letter. / Includes bibliographical references (pages [95]-[100]). / While the properties of functional oxide thin films often depend strongly on oxygen nonstoichiometry (6), there have been few means available for its measurement and control in a reliable and in-situ fashion. In this work, we investigate means for extracting the oxygen nonstoichiometry of dense oxide thin films as a function of temperature and oxygen partial pressure from an analysis of the chemical capacitance (Cchem) obtained by impedance spectroscopy, and the use of electrical bias as a means of systematically controlling the non-stoichiometry. We selected the PrxCeIx02-6 (PCO) solid solution system as a model system given its mixed ionicelectronic conductivity, well described defect equilibria and transport properties, and stability over with limits of temperature and oxygen partial pressure. PrCel-02-6 (PCO) thin films with x=0.01, 0.10 and 0.20 were prepared as thin film cathodes by pulsed laser deposition onto single crystalline YO. 16Zro.84 01.9 2 electrolyte substrates. The cathode reactions were examined as a function of electrode geometry, temperature, oxygen partial pressure by means of electrochemical impedance spectroscopy (EIS). A DC bias range of JE = - 100 mV to 100 mV was used to polarize the PCO films and examine the impact on area specific resistance (ASR) and film non-stoichiometry. The PCO cathodes exhibited typical mixed ionic electronic behavior including large chemical capacitance and electrode performance, as reflected in the magnitude of the ASR, found to be limited by surface oxygen exchange kinetics. With the aid of a defect equilibrium model, expressions relating chemical capacitance directly to non-stoichiometry, without need for fitting parameters, were derived. By examining the dependence of non-stoichiometry on temperature and PO2, the thermodynamic constants defining defect generation were extracted. While general agreement of these constants with bulk values derived by thermogravimetric analysis was found, confirming the suitability of using Cciie,n to measure oxygen non-stoichiometry of thin oxide films, the films were found to reduce somewhat more readily than bulk PCO. Potential sources of error observed in earlier Cchem studies on perovskite structured oxide films are also discussed. When a DC bias was applied, the non-stoichiometry of the PCO films calculated from the measured Cien, agreed well with predicted values assuming that the effective change in oxygen activity, P 0 2, eective corresponded to the value expected based on the applied Nernst potential. These results confirm the suitability of using bias across an electrochemical cell to conveniently and precisely control 6 of oxide thin films in an in-situ fashion. Of further interest was the ability to readily reach oxygen activities equivalent to PO2s as high as 280 atm. Calculated values for the surface exchange coefficient, k, were found to be comparable in magnitude to those exhibited by other popular mixed ionic electronic conductors, therefore confirming the suitability of PCO as a model mixed conducting cathode material. Interestingly, the magnitude of k was found to be largely dependent on the non-stoichiometry in the PCO films, rather than the oxygen activity in the gas phase, at all temperatures studied. This indicates the important role that defects (electronic defect and oxygen vacancy) play in the cathode reaction. / by Di Chen. / Ph. D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2001. / Includes bibliographical references (p. 206-215). / Selective epitaxial growth (SEG) of SiGe on patterned SiO2/Si substrates by ultra-high vacuum chemical vapor deposition (UHVCVD) shows promise for the fabrication of novel SiGe microelectronic structures. This work explores selective growth conditions in the SiH2Cl2/SiH4/GeH4/H2 system between 650-850⁰C, without the addition of C12 or HC1, on substrates patterned by both conventional and interferometric lithography. We have achieved several important milestones for the fabrication of vertical MOSFETs by selective growth in 100 nm SiO2 features patterned by interferometric lithography. We have observed excellent selectivity to SiO2 masks with SiH2C12 at 750⁰C, perfect epitaxial Si filling of SiO2 features, the facet morphology during growth, and the effects of n-type doping on selective growth. We have also fabricated extremely sharp p-n diode doping profiles. With the above accomplishments we have demonstrated the feasibility of vertical MOSFET fabrication through selective epitaxial growth. To realize the advantages of advanced MOSFET designs on silicon-on-insulator (SOI) substrates, we have developed a facet-free raised source/drain process utilizing moderate n-type doping of Si selective growth and <110>-oriented vertical SiO2 sidewalls. However, to improve SiO2 spacer dimension fidelity and eliminate Si substrate overetching, a novel SiO2/Si3N4 spacer process was developed. The keys to the SiO2/Si3N4 spacer process are removal of the Si3N4 layer prior to growth and increased Si ELO growth by moderate in situ n-type doping. This process has wide ranging application to both SOI and bulk Si technologies for fabrication of low-resistance contacts in advanced devices. / (cont.) By a combination of interferometric lithography Si/SiO2 substrate patterning and Ge selective epitaxial growth, we have demonstrated threading dislocation blocking at the oxide sidewall which shows promise for dislocation filtering and the fabrication of low defect density Ge on Si for III-V device integration. Defects at the Ge film surface only arise at the merging of epitaxial lateral overgrowth (ELO) fronts from neighboring holes. These results confirm that epitaxial necking can be used to reduce threading dislocation density in any lattice-mismatched systems where dislocations are not parallel to growth directions. Investigation of Ge selective growth in micron-sized SiO2 features by plan-view TEM shows that substrate patterning on the order of microns is insufficient to filter dislocations in a large mismatch system ([epsilon] > 2%). Ge p-i-n photodetectors were selectively grown in micron-sized SiO2/Si features to correlate materials properties with electrical characteristics. For chemical protection and compatibility with Si microelectronics, Ge photodetector regions were capped with a thin n+ Si layer. Photodetectors fabricated on unpatterned substrates demonstrated leakage currents comparable to published results on Ge on Si photodetectors while leakage currents were noticeably degraded in devices grown on patterned substrates. / by Thomas Andrew Langdo. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1988. / Vita. / Includes bibliographical references. / by Gregory N. Haidemenopoulos. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005. / Includes bibliographical references (p. 47-52). / Atomic force microscopy (AFM) has been a powerful instrument that provides nanoscale imaging of surface features, mainly of rigid metal or ceramic surfaces that can be insulators as well as conductors. Since it has been demonstrated that AFM could be used in aqueous environment such as in water or various buffers from which physiological condition can be maintained, the scope of the application of this imaging technique has been expanded to soft biological materials. In addition, the main usage of AFM has been to image the material and provide the shape of surface, which has also been diversified to molecular-recognition imaging - functional force imaging through force spectroscopy and modification of AFM cantilevers. By immobilizing of certain molecules at the end of AFM cantilever, specific molecules or functionalities can be detected by the combination of intrinsic feature of AFM and chemical modification technique of AFM cantilever. The surface molecule that is complementary to the molecule at the end of AFM probe can be investigated via specificity of molecule-molecule interaction. / (cont.) Thus, this AFM cantilever chemistry, or chemical functionalization of AFM cantilever for the purpose of chemomechanical surface characterization, can be considered as an infinite source of applications important to understanding biological materials and material interactions. This thesis is mainly focused on three parts: (1) AFM cantilever chemistry that introduces specific protocols in details such as adsorption method, gold chemistry, and silicon nitride cantilever modification; (2) validation of cantilever chemistry such as X-ray photoelectron spectroscopy (XPS), AFM blocking experiment, and fluorescence microscopy, through which various AFM cantilever chemistry is verified; and (3) application of cantilever chemistry, especially toward the potential of force spectroscopy and the imaging of biological material surfaces. / by Sunyoung Lee. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references (p. 187-208). / Interfaces are defects present in all materials. Interface transitions are characterized by abrupt changes in interface structure, chemistry and/or morphology under suitable conditions. They exist in many material systems and often produce profound changes in material properties. Several interface transitions in crystalline and soft materials that have not been previously well understood were studied in this thesis. In the first part of this thesis, a diffuse-interface thermodynamic framework was developed for grain boundary structural and chemical transitions. A graphical construction method was developed to predict conditions for grain boundary transitions. A grain boundary premelting transition is predicted for systems of fixed stoichiometry. When extended to binary systems, the diffuse-interface model predicts the existence of a coupled grain boundary premelting/prewetting transition, which produces cooperative grain boundary disordering and segregation at sub-eutectic and sub-solidus temperatures. The analysis rationalizes the thermodynamic origin of intergranular glassy films (IGFs) widely observed in multi-component ceramics and alloys, for which thermodynamic stability has not been well explained in previous research. Predictions on the conditions for IGF's formation are consistent with experiments. As part of this work, a prototype of "grain boundary complexion diagrams" was constructed which delineates the stability domains of different grain boundary "complexions" on bulk phase diagrams. Morphological transitions of interfaces in soft materials such as surfactant self-assembled structures were investigated in the second part of this thesis. A phase-field model was developed for simulating morphological evolution of surfactant aggregates in solutions. / (cont.) The model captures both the self-assembling behavior of surfactants and the effect of interface-curvature elastic-energy on the morphologies of self-assembled structures. Simulations of single surfactant micelle growth in dilute solutions reveal several previously unknown morphological transitions, including a disk-to-cylinder micellar shape transition and a tip-splitting instability of cylindrical micelles. It is proposed that the observed morphological instabilities provide kinetic pathways to the formation of branch points between individual cylindrical micelles, whose presence has significant effects on the rheological properties of solutions. Surface wetting transitions often display simultaneous changes in interface structure and morphology. Despite the extremely broad technical applications of the Si/SiO2 structure The equilibrium wetting properties of silicon oxide on silicon are poorly understood, This is partly due to the extremely low equilibrium oxygen activity for SiO2/Si coexistence (e.g. 10-37 torr at 700°C), which cannot be reached by current ultra-high vacuum techniques. In the third part of this thesis, a solid-state buffer method was developed to access oxygen partial pressures near the Si/SiO2 equilibrium with systematic control. It was discovered from experiments that silicon oxide does not perfectly wet Si(001) surfaces near the equilibrium oxygen activity, with the wetting morphology being oxide islands coexisting with a thin oxide layer of ~0.4nm on top of Si. / by Ming Tang. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009. / 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 (p. 155-167). / Electronic structure calculations are becoming more widely applied to complex and realistic materials systems and devices, reaching well into the domain of nanotechnology, with applications that include metal-molecule junctions, carbon-nanotube field effect transistors, and nanostructured metals or semiconductors. For such complex systems, characterizing the properties of the elementary building blocks becomes of fundamental importance. In this thesis we employ first-principles calculations based on density-functional theory (DFT) to investigate fundamental properties of molecular-scale devices. We focus initially on the constituent components of these devices (polymers, metal surfaces, carbon nanotubes), following with studies of entire device geometries (nanotube/metal interfaces). We first study a proposed molecular actuating system in which the interaction between oligothiophenes is the driving force behind an electromechanical response. The oligothiophenes are attracted to each other through p-stacking interactions driven by redox reactions. We show that counterions strengthen this interaction further through enhanced screening of the electrostatic repulsion. Many molecular scale devices require contact with a metallic conductor, we also study the fundamental properties of metal surfaces in the slab-supercell approximation; in particular layer relaxation, surface energy, work function, and the effect that slab thickness has on these properties. The surfaces of interest are the low index, (111), (100), and (110) surfaces of Al, Au, Pd, and Pt and the close packed (0001) surface of Ti. / (cont.) We show that these properties are well converged for slabs that have between 5 and 10 layers, depending on the property considered and the surface orientation. We then focus on understanding and characterizing devices. Since it is widely proposed that carbon nanotubes (CNTs) could replace Si in future transistor devices, we examine the work function of single-wall CNTs and the effects that covalent functionalization could have in engineering performance. Electrostatic dipoles form due to the charge asymmetries in the functionalized CNT unit cell, and the use of periodic boundary conditions affects our calculations. We correct for these spurious dipole-dipole interactions with a real-space potential derived directly from the solution to Poisson's equation in real-space with open boundary conditions. We find that the functionalizations can be clearly labeled as electropositive and electronegative, and that they decrease or increase the work function of the CNT accordingly. Finally, we join metal surfaces and CNTs to study Schottky barrier heights (SBHs) that form at the interface. We take Al(111) and Pd(111) as examples of low- and high-work function metal surfaces and contact them with the semiconducting (8,0) CNT. We find that in all cases a surface dipole forms that shifts the band structure of the CNT locally. In these systems, we investigate the effects of surface roughness and functionalization on SBHs, and find that controlling the electrostatics at the interface (with functionalization, adsorbates, and device geometry) can lead to further engineering of the SBHs. / by Nicholas E. Singh-Miller. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2000. / Includes bibliographical references (p. 48). / In order to lower fuel consumption and reduce emissions, aluminum is being considered as an alternative to steel in large scale production of autobodies. This study evaluates the prospects of aluminum sheets as a cost efficient alternative to steel in autobodies with the unibody design. The study focuses on the processing technologies and alloy selection for aluminum automotive sheets and looks at the impact of these on the total part forming cost of the unibody. Technical cost modeling was used to analyze the costs of traditional direct chill casting and subsequent rolling of aluminum alloy sheet and compared the technology to the alternative continuous casting fabrication method. A change to continuous casting displayed large potential cost savings and was believed to be crucial in order for aluminum to be competitive with steel. A large cost penalty is associated with the alloying and heat treatment of 6xxx series sheet for outer body panels as opposed to 5xxx series sheet for interior panels. Changes in production method for 6xxx series sheet or a replacement by 5xxx series sheet will have large impact on the cost of the autobody. The volatility in the price of aluminum ingot has a critical influence on the price of sheet. Changes in the price level have been shown to be equally critical for the final sheet cost as substantial technical improvements. Recent developments of high strength steel have shown promise for substantial weight reduction in steel automobiles and make the challenge even greater for aluminum as its possible successor. / by Harald Hoegh. / S.B.