Electrochemical vapor deposition of a graded titanium oxide-yttria stabilized zirconia layer

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996.by Andrew Gouldstone.B.S

Micromechanics of deformation and stress evolution in thin films and patterned lines on substrates

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2001.Includes bibliographical references (p. 123-129).In this thesis, we investigated the mechanical behavior of small volume structures, with specific application to thin metal films and patterned metal lines on substrates. The first part of this investigation dealt with the elastoplastic behavior of interconnect lines during thermal cycling. A robust computational method was developed to predict volume-averaged stresses in unpassivated and passivated lines in response to changes in temperature, as a function of line geometry, material properties and thermal history. The computational model also facilitated the extraction of substrate curvature. In addition, a simple analytical method was developed to allow extraction of volume-averaged stresses in unpassivated lines upon yielding due to thermal stresses, via experimental curvature methods. The second part of the investigation involved the systematic nanoindentation of a wide range of FCC single crystals and polycrystals, in bulk and thin film form. For shallow (</= 100 nm) depths, the experimentally obtained P-h curves displayed elastic loading portions alternated with inelastic displacement bursts, for all specimens. The bursts were attributed to dislocation nucleation and motion within the crystal, which occurred when stresses underneath the indenter tip approached the critical shear strength of the material. Theories of dislocation activity were confirmed with planar TEM photos of nanoindented Cu films. In order to examine the atomistics of such phenomena, an experimental 2-D atomic simulation was developed, via an extension of the classical soap bubble raft, to simulate elastic contact and defect nucleation at low loads. Dislocation nucleation inside crystals of low defect density, ostensibly requiring stresses on the order of the theoretical shear strength, was found to occur under blunt indenters, providing a mechanistic justification for bursts observed during nanoindentation experiments. Finally, the experimental nanoindentation results for thin films were analyzed in the context of elastoplastic indentation, incorporating elastic loading and inelastic bursts. Stiffnesses thus obtained were found to increase as film thickness decreased, displaying a similar trend to literature thin film strength values obtained via substrate curvature methods.by Andrew Gouldstone.Ph.D

Instrumented Indentation of Lung Reveals Significant Short Term Alteration in Mechanical Behavior with 100% Oxygen

In critical care, trauma, or other situations involving reduced lung function, oxygen is given to avoid hypoxia. It is known that under certain conditions and long time (several hours) exposure, oxygen is toxic to the lungs, the possible mechanisms being direct cellular damage or surfactant dysfunction. Our key objective was to investigate possible changes in lung function when exposed to 100% oxygen in the short term (several tidal volumes). We performed mechanical tests on lobar surfaces of excised mammalian lungs inflated with air or 100% oxygen, examining (i) stiffness, (ii) non-linear mechanical response and (iii) induced alveolar deformation. Our results showed that within five tidal volumes of breathing 100% oxygen, lung mechanics are significantly altered. In addition, after five tidal volumes of laboratory air, lung mechanical behavior begins to return to pre-oxygen levels, indicating some reversibility. These significant and short-term mechanical effects of oxygen could be linked to oxygen toxicity

Feasibility study of silica bead thermoluminescence detectors (TLDs) in an external radiotherapy dosimetry audit programme

Purpose: Investigating the feasibility of using low-cost commercially available silica beads as novel thermo-luminescence dosimeters (TLD) for postal dosimetry audit. Methods: A mail-based dosimetry audit was designed to assess the positional and dosimetric accuracy of SABR-lung treatment delivery using alanine and EBT3-film, placed in a CIRS-anthropomorphic thorax phantom. In conjunction, the silica beads were dosimetrically characterised as TLDs and cross-calibrated against the alanine. A CT-scan of the phantom with pre-delineated volumes was sent to 20 RT centres and used to create a SABR plan using local current protocols and techniques. The silica beads were held in an insert, designed to match that of the alanine holder and ionisation chamber to give the same measurement length. The doses determined by the silica beads were compared to those measured by alanine, the local ionisation chamber, film and the TPS calculation. Results: The mean percentage difference between the doses measured by the silica beads and the calculated doses by the TPS was found to be 0.7% and differed by 0.6%, 0.7%, and 1.3% from the alanine, film and local ionisation chamber measurements respectively. Conclusions: Results obtained with the silica beads agree well with those obtained from conventional detectors including alanine, film and ionisation chambers. This together with the waterproof and inert characteristics and minimal dose fading associated with silica bead TLDs confirm their potential as a postal dosimetry audit tool in both water and plastic phantoms which could withstand challenges of temperature and humidity variation, as well as postal service delays