Nanostructuring magnetic thin films using interference lithography

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2000.Includes bibliographical references.Proliferation of data caused by rapid increases in computer power and the rise of the internet have caused an acute need for advanced data storage technology. Patterned magnetic media and magneto-resistive random-access memory (MRAM) can potentially fulfill this need. The technique of interference lithography is examined in the context of patterning ~100 nm size features. An interferometer is designed and built which will allow exposure of gratings and grids with a minimum spatial period of ~ 170 nm. Etching methods, especially ion-beam etching, or ion milling, is investigated as the optimal choice for patterning sub-100 nm features in thin magnetic films and multi-layer thin film stacks. The advantages and disadvantages of a variety of resist stacks and etch masks are presented. An optimal process for linewidth control and preservation of magnetic properties is found to include a thin phase-shifting resist stack and a tungsten hardmask.by Michael E. Walsh.S.M

A theoretical study of the sea breeze

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Meteorology, February 1974."December, 1973." Vita.Includes bibliographical references (leaves 125-128).The linearized Boussinesq equations with rotation, viscosity, conduction, and a mean stratification are used to model the sea breeze in two dimensions. the motion is forced by a prescribed surface temperature function. The linear model produces a sea breeze with realistic velocities and spatial dimensions. Hydrostatic solutions are found to differ very little from the nonhydrostatic solutions. The phase of the solution depends on the Coriolis parameter f; the only distinguishable feature of the solution at the inertial latitude is a slight amplitude maximum far from the coastline. Both the phase and the amplitude depend on the stability parameter N². An inversion, simulated by a discontinuity in N², reduces the intensity of the circulation. The land-sea temperature difference required by the model to create a net onshore flow in opposition to a basic current agrees well with the empirical criterion defined by Lyons (1972). The computed vertical heat fluxes, when summed along the coastlines of the principal land masses, indicate that the sea breeze effect can account for several per cent of the globally averaged vertical flux of sensible heat at a height of several hundred meters. The nonlinear advection process is studied with a finite difference model based on a series of overlapping grids. The principal effect of the nonlinear terms is a landward advection of the sea breeze circulation.by John E. Walsh.Ph.D

On the design of lithographic interferometers and their application

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Page 300 blank.Includes bibliographical references.Interference lithography is presented as an ideal technique for fabricating large-area periodic structures with sub-100nm dimensions. A variety of interferometer designs are discussed and implemented, each of which emphasizes a different attribute. Curvature of the substrate during exposures in a Mach-Zender interferometer is demonstrated as a method for reducing periodicity variations in the printed pattern down to the level of picometers. A robust Lloyd's-mirror interferometer is developed as a simple and flexible lithography system capable of sub-100nm features. Prospects and designs for the use of grating interferometers for the fabrication of structures with 50nm spatial-periodicity are discussed. A novel, integrated, thin-film interferometer exploiting solid immersion is introduced for the fabrication of features below the diffraction-limit. Using 193nm illumination, 45nm dense features are demonstrated. Aspects of sub-wavelength diffraction and thin-film resonance are discussed in relation to the fabrication of structures with sub-50nm periodicity. A selection of applications are discussed which take advantage of the unique capabilities of interference lithography, including patterned magnetic media, DFB lasers and the templated self-assembly of nano-particles. A novel technique for ion-beam etching, applicable to any material system, is shown to improve the patterning of nanoscale magnetic elements.by Michael E. Walsh.Ph.D

A study of helps given to beginning teachers compared with the helps beginning teachers want

Thesis (Ed.M.)--Boston Universit

Acoustic Characteristics of Lekking Male Greater Prairie-Chicken (\u3ci\u3eTympanuchus cupido pinnatus\u3c/i\u3e) Vocalizations (Supplement)

Boom Cackle Whine Whoo

Kaneohe Bay Sewage Diversion Experiment: Perspectives on Ecosystem Responses to Nutritional Perturbation

Kaneohe Bay, Hawaii, received increasing amounts of sewage from the 1950s through 1977. Most sewage was diverted from the bay in 1977 and early 1978. This investigation, begun in January 1976 and continued through August 1979, described the bay over that period, with particular reference to the responses of the ecosystem to sewage diversion. The sewage was a nutritional subsidy. All of the inorganic nitrogen and most of the inorganic phosphorus introduced into the ecosystem were taken up biologically before being advected from the bay. The major uptake was by phytoplankton, and the internal water-column cycle between dissolved nutrients, phytoplankton, zooplankton, microheterotrophs, and detritus supported a rate of productivity far exceeding the rate of nutrient loading. These water-column particles were partly washed out of the ecosystem and partly sedimented and became available to the benthos. The primary benthic response to nutrient loading was a large buildup of detritivorous heterotrophic biomass. Cycling of nutrients among heterotrophs, autotrophs, detritus, and inorganic nutrients was important. With sewage diversion, the biomass of both plankton and benthos decreased rapidly. Benthic biological composition has not yet returned to presewage conditions, partly because some key organisms are long-lived and partly because the bay substratum has been perturbed by both the sewage and other human influences

Scalable Focused Ion Beam Creation of Nearly Lifetime-Limited Single Quantum Emitters in Diamond Nanostructures

The controlled creation of defect center---nanocavity systems is one of the outstanding challenges for efficiently interfacing spin quantum memories with photons for photon-based entanglement operations in a quantum network. Here, we demonstrate direct, maskless creation of atom-like single silicon-vacancy (SiV) centers in diamond nanostructures via focused ion beam implantation with $\sim 32$ nm lateral precision and $< 50$ nm positioning accuracy relative to a nanocavity. Moreover, we determine the Si+ ion to SiV center conversion yield to $\sim 2.5\%$ and observe a 10-fold conversion yield increase by additional electron irradiation. We extract inhomogeneously broadened ensemble emission linewidths of $\sim 51$ GHz, and close to lifetime-limited single-emitter transition linewidths down to $126 \pm13$ MHz corresponding to $\sim 1.4$-times the natural linewidth. This demonstration of deterministic creation of optically coherent solid-state single quantum systems is an important step towards development of scalable quantum optical devices

Multipolar endocardial mapping of the right atrium during cardiac catheterization: description of a new technique

AbstractObjectives. Using a new mapping system that allows the simultaneous acquisition of date from 25 right atrial bipolar electrodes during cardiac catheterization, we mapped normal sinus rhythm and atrial reentrant tachycardia in 24 sheep (20 to 49 kg) and 7 pigs (25 to 35 kg).Background. Rapid, high resolution mapping during cardiac catheterization may shorten ablation procedures and permit ablation of otherwise refractory arrhythmias.Methods. A flexible, elliptic, basket-shaped recording catheter has five spokes, each with 10 electrodes arranged as 5 bipolar pairs. Catheter shape, electrode spacing and introduction technique were modified in response to the results of experiments in the first 23 animals. In the most recent eight animals, retraction of a string attached to the distal tip distended the basket, providing safe tissue contact. Filtered (30 to 250 Hz) bipolar recordings from all 25 electrode pairs, as well as a surface electrocardiogram, were recorded and digitized at 1,000 Hz using custom software. An activation map was digitally constructed and superimposed on anteroposterior and lateral fluoroscopic catheter images. Bipolar recordings were made in normal sinus rhythm (31 animals), with adequate signals recorded from >95% of electrode pairs. Rapid burst pacing and intentional right atrial air embolus (30 to 50 ml) induced sustained atrial reentrant tachycardia in five animais, which was also adequately recorded.Results. Catheter positioning and complete atrial mapping required <10 min after venous access in the most recent eight experiments. The catheter was left in position for up to 4 h. Postmortem evaluation revealed minor superficial abrasion of the venae cavae or right atrial endocardium in six animals and moderate abrasion in two. No other damage was observed.Conclusions. This new system may ultimately assist in mapping simple or complex atrial arrhythmias during cardiac eatheterization

A decision support system for sustainable agriculture and food loss reduction under uncertain agricultural policy frameworks

The EU Green Deal requires the reduction in pesticides and fertilisers in food crop production, whilst the sustainable development goals require reductions in food loss and food waste. In a complex and interacting system like the food system, these goals are difficult to coordinate. Here, we show an approach using Bayesian network modelling for decision support. Bayesian networks are important tools for modelling complex systems which may develop emergent behaviour and for providing quantitative comparisons for different candidate policies, approaches or interventions under the Integrating Decision Support System paradigm. Using lettuce as an exemplar crop, we demonstrate that expected food loss changes under different agricultural input reduction and integrated pest management combinations can be quantified to aid decision making for growers