VictorJuiz/thesis huggingface dataset:
Scaled planar floating-gate NAND flash memory technology [electronic resource] : challenges and novel solutions
Keywords: Electrical Engineering

NAND flash memories are ubiquitous in their use as portable storage media in cellphones, cameras, music players, and other portable electronic devices. The NAND flash memory device, consisting of a floating-gate transistor cell, is the most aggressively scaled electronic device, as evidenced by ever-increasing memory capacities. In this work, we will examine possible problems arising from continued scaling of these structures, and discuss novel solutions to overcome them. Firstly, we investigate scaling of the conventional poly-silicon floating-gate, aimed at reducing cell-to-cell interference. We experimentally delineate a new reliability concern for the first time, with programming current through ultra-thin poly-silicon floating-gates becoming increasingly ballistic. We also experimentally demonstrate doping-related issues in the poly-silicon floating-gate. We then apply a novel metal-based floating-gate cell for the first time, designed to overcome the problems discussed above. We explore factors that influence the choice of metal, and demonstrate excellent functionality in ultra-thin metal floating-gate cells scaled down to 3 nm TiN floating-gate thickness, thus greatly reducing cell-to-cell interference. Finally, in order to facilitate continued scaling of the control dielectric, we explore replacement of the conventional silicon oxide-nitride dielectric with high-k dielectric materials. We integrate poly-silicon and metal floating-gate cells with Al2O3 high-k control dielectric. Further, we establish that a deeper work-function control gate is helpful in reducing gate-injection. Combining ultra-thin metal floating-gate, high-k control dielectric and deep work-function control gate, we enable the planar floating-gate cell as a scalable candidate.
The search for dark matter [electronic resource] : from colliders to direct detection experiments
Keywords: Physics

This thesis is devoted to searches for dark matter at colliders and direct detection experiments. The first half of the work focuses on the Tevatron and LHC. Jets and missing energy searches at these colliders are sensitive to a broad class of models and dark matter candidates. I show that current jets plus missing energy analyses can miss signals for new physics, and suggest an alternative model-independent search strategy that broadens the reach of these experiments I also discuss searches for Higgs bosons that decay to light pseudoscalars. Information about the Higgs sector obtained through such searches may hint at the nature of the dark matter. The second half of the thesis turns to direct detection experiments, with a focus on inelastic dark matter. I discuss the prospects for discovering inelastic dark matter at upcoming experiments, and present two models with inelastically scattering dark matter. One of these models posits composite dark matter and has unique phenomenology that can be studied with directional detection experiments.
Self extension into robots [electronic resource] : an examination of variables that promote overlap in the concepts of self and robot
Keywords: Communication

Current research on the psychological aspects of human-robot interaction tends to focus on social encounters between humans and autonomous robots. However, many robots today are controlled by human operators. Numerous features of robot teleoperation are predictors of self extension, whereby an object comes to represent and maintain the self. Understanding the causes of self extension into robots is increasingly important, as some tasks benefit from minimizing self extension, and others from maximizing self extension. This dissertation presents an evaluation of five variables predicated to affect self extension. Study 1 examined the effects of robot form and operator robot-building experience on self extension in a 2 (robot form: humanoid vs. car) x 2 (assembler: self vs. other) between-participants experiment design (N = 56). Significant main effects demonstrated that anthropomorphic form inhibits self extension, while functional form promotes self extension and elicits positive evaluations of robot personality. Results also revealed that an operator's experience interacting with a robot before controlling it can affect self extension, as participants who operated a robot they assembled demonstrated greater self extension and more positive affect than participants who operated an identical but different robot than the one they assembled. Study 2 examined the effects of robot autonomy, mediation, and artificiality on self extension in a 2(autonomy: autonomous v. teleoperated) x 2(mediation: direct view v. mediated view) x 2(artificiality: artificial v. actual) between-participants design (N=96). Results indicated that autonomy and actuality promote self extension and positive evaluations of robots. Mediation had little direct effect on participants, suggesting that artificiality has a more powerful impact on attitudes and self extension. A number of significant interactions are presented, and theoretical and design implications are discussed.
The self-protective function of the model minority myth for white Americans [electronic resource]
Keywords: Business.

I investigated the hypothesis that endorsing the model minority stereotype—the belief that Asian Americans are intelligent, hard-working, and successful--increases Whites Americans' self-esteem. I argue that this occurs because Whites' self-esteem is threatened by the possibility that they do not deserve their position in society. The model minority stereotype provides evidence for Whites that minority groups can succeeded based on merit, bolstering the belief that society is fair and Whites deserve what they have. In four studies, I demonstrate the link between the model minority stereotype and self-esteem as well as for the idea that the model minority stereotype impacts self-esteem because of Whites' concerns over system legitimacy.
Semiconductor crystal islands for three-dimensional integration [electronic resource]
Keywords: Electrical Engineering

The critical operation needed to achieve 3-dimensional integrated circuits (3DICs) is obtaining single-crystal, device-quality semiconductor material on upper circuit layers without damaging circuits below (400°C temperature limit). Simulation shows that microsecond pulse 532 nm Nd:YAG laser can melt and crystallize amorphous Si or Ge layers without excessively heating the circuit layers underneath. However, experimental results of unseeded (graphoepitaxy) and seeded (RMG) crystallization of Si and Ge indicate that much longer pulse lengths are required for high-quality single-crystal formation, rendering the approach not 3DIC compatible. A more straightforward approach is to directly attach high-quality crystal islands for upper-layer device fabrication. A variety of viable low-temperature ([less than or equal to]400°C) bonding methods have been investigated: fusion bonding (SiO2-SiO2, Si-SiO2, Ge-SiO2), thermo-compressive bonding (Cu-Cu, Ti-Ti), as well as Al-Ge eutectic bonding. The unique advantages of AlGe technique for 3DICs are reported for the first time. They include superior bond strength, low void density, non-stringent roughness requirement, use of thin films and CMOS friendly materials. Finally, we present a completed 3DIC compatible process of obtaining single crystal Si or Ge islands for upper layer device fabrication via SmartCut® and CMP finish.
Semi-supervised learning on graphs [electronic resource] : a statistical approach
Keywords: Statistics

Data on graphs are growing tremendously in size and prevalence these days; consider the World Wide Web graph or the Facebook social network. In semi-supervised learning on graphs, features observed at one node are used to estimate missing values at other nodes. Many prediction methods have been proposed in the machine learning community over the past few years. In this thesis we show that several such proposals are equivalent to kriging predictors based on a fixed covariance matrix driven by the link structure of the graph. We then propose a data-driven estimator of the correlation structure that exploits patterns among the observed response values. We also show how we can scale some of the algorithms to large graphs. Finally, we investigate the fundamental smoothness assumption underlying many prediction methods by exploring some normality properties arising from empirical data analysis.
Sequential methods for rare event simulation [electronic resource] : theory and applications
Keywords: Statistics

We consider rare events modeled as a Markov Chain hitting a certain rare set. A sequential importance sampling with resampling (SISR) method is introduced to provide a versatile approach for computing such probabilities of rare events. The method uses resampling to track the zero-variance importance measure associated with the event of interest. A general methodology for choosing the importance measure and resampling scheme to come up with an efficient estimator of the probability of occurrence of the rare event is developed and the distinction between light-tailed and heavy-tailed problems is highlighted. Applications include classic tail probabilities for sums of independent light-tailed or heavy-tailed random variables. Markovian extensions and simultaneous simulation are also given. The heuristics and the methodology can also be applied to more complex Monte Carlo problems that arise in recent works on the dynamic portfolio credit risk model.
Sex-specific structure and function of the olfactory system in Drosophila melanogaster [electronic resource]
Keywords: Neurosciences.

For my graduate work, I have chosen to investigate sex-specific patterning and function of the olfactory system in the fruit fly, Drosophila melanogaster, by addressing three questions: 1) What is the developmental genetic regulation of the sexual dimorphism in numbers of olfactory sensilla? 2) Do olfactory receptor neurons (ORNs) expressing Or47b (Or47b-ORNs) stimulate courtship in males and females? 3) Which genes are regulated by male-specific fruitless isoforms (FRUM) in olfactory and other peripheral sensory neurons? In Drosophila, terminal sexual differentiation is orchestrated by the activity of the transcription factors fruitless (fru) and doublesex (dsx). I have shown that the action of dsx alone is necessary and sufficient to specify sex-appropriate numbers of olfactory sensilla (the peripheral sensory unit). The dsx locus encodes sex-specific isoforms that differentially organize the developing antenna to specify sex-appropriate numbers of different types of olfactory sensilla. The female-specific DSX isoform promotes female-appropriate numbers of basiconic sensilla and depresses the number of trichoid sensilla on the antenna. Male-specific DSX promotes male-appropriate numbers of trichoid sensilla but appears to have little effect on determining numbers of basiconic sensilla. Inferred from the expression pattern of dsx, the DSX proteins do not show significant overlap with olfactory sensilla precursors. These data and other lines of evidence suggest that it is likely that dsx controls numbers of olfactory sensilla cell non-autonomously. One subtype of sexually dimorphic trichoid sensilla is innervated by ORNs that express the receptor Or47b and respond to a pheromone produced by males and females. I asked whether these ORNs promote male courtship and female receptivity. I have shown that Or47b-ORNs may promote courtship in males, but they appear to play no detectable role in stimulating female receptivity. Finally, in an effort to elucidate how sexual dimorphism is built into the developing olfactory system, I have collaborated with David Mellert (a former graduate student) to identify genes that are regulated by male-specific fru isoforms in peripheral sensory neurons of the olfactory and gustatory systems, as well as in mechanosensory neurons of the genitalia. We used laser capture microdissection to collect fru-expressing neurons in the antennae, prothoracic forelegs, and genitalia from fru+ and fru-null males. By comparing the whole-genome expression profiles of these samples, we were able to identify candidate targets of FRUM regulation in these tissues. For the antenna, this yielded a promising list of ~100 candidates that are in the process of being validated. Moreover, we found essentially no overlap in the candidate lists for different tissues, suggesting that FRUM regulates different genes in different tissues.
Shear adhesion, friction, and wear of multi-point micro- and nano-scale contacts [electronic resource]
Keywords: Mechanical Engineering

Adhesion, friction, and wear are the principal failure mechanisms that have limited the use of contacting and sliding surfaces in commercial MEMS applications. As the size of mechanical structures reaches the micro- and nano-scales, surface forces such as van der Waals, capillary, and electrostatic forces dominate the interactions between contacting surfaces. At these scales, the magnitude of the friction force is very sensitive to the complicated interaction between the surface properties, material properties, contact conditions, and environmental conditions. This work investigates the role of the contact conditions on the friction forces and wear rate of a MEMS probe array of small-scale tips in contact with a flat sliding surface. The friction measurement experiment involves a laterally unconstrained slider that sits on top of a MEMS probe array. As the array is laterally actuated, solely friction forces at the tips govern the motion of the slider. MEMS probe arrays enable precise control over the shape and the total number of contact points between the two surfaces. The results show that the friction forces are very sensitive to small changes in the contact or environment conditions. But for a given, well-controlled set of conditions, the friction forces scale linearly with the normal force. However, the friction coefficient is strongly dependent on the total number of contact points and the local conditions around those contact points. Factors such as humidity or adsorbed water on the surfaces further increase the linear relationship between the friction forces and the number of contacts. In addition, the wear rate of the tips is linearly related to the normal force acting at each tip. Factors such as the presence of water on the surface and a stiff vertical contact also lead to high wear rates. This work concludes with a set of recommendations to minimize the detrimental effects of friction and wear at the micro- and nano-scales.
Shocks to the system [electronic resource] : the politics of decision making in San Francisco public schools
Keywords: Education.

I trace the history of two education policies in San Francisco that flared into public controversy during the onset of a major crisis. The first controversy, which transpired in the wake of the 1906 Earthquake, involved the San Francisco Board of Education's attempt to segregate Japanese students. The second was the drive for school construction during the Great Depression. School officials and other political actors resiliently pursued their agendas even when faced with the turmoil caused by the crises. Politics did not subside; in fact, politics gave meaning to chaos. Two generalizations help to explain this finding. First, political actors searched for opportunities in crisis. When crises radically altered the physical and material infrastructure of the school department, people seized whatever resources they could to achieve their goals. Second, crises forced political actors to adjust their rhetoric by adapting their language to fit the circumstances. Prior to the earthquake and depression, political actors attempted to sway the public in their favor by defining the core values involved in segregation and school construction. The crises generated a new set of values. Political actors adjusted their rhetoric by integrating new values into the old political discourse.
Sieves and lenses [electronic resource] : essays on the role of categories in social valuation
Keywords: Sociology.

Systems of classification are pervasive and consequential in economic life, as they are in the social world more generally. Membership in socially defined categories, such as industries or genres, constitutes a core part of an organization's identity, and, as such, profoundly impacts how the organization, its products and actions are evaluated. This dissertation includes three essays that analyze the ways in which similar actions in market settings are interpreted and assessed quite differently depending on the categorical identity of the performer. The first essay introduces the idea that categories of organizations (e.g., industries) differ in status and that status differences at the category level influence the social standing of individual members of the category. The second essay tests and finds support for the idea that category status impacts the way in which an organization's actions are perceived and evaluated. In particular, I find that earnings restatements from members of high-status categories are viewed less negatively than those from lower-status categories. Finally, the third essay, co-authored with Ming Leung, provides evidence of an audience-driven penalty for multiple-category membership in markets.
Silicon based photonic crystal light sources [electronic resource]
Keywords: Electrical Engineering

Efficient light generation on silicon is desirable for a variety of applications because of its low fabrication cost relative to III/V semiconductors and because it will enable monolithic integration with electronic components on the same Si platform. We studied silicon-rich silicon nitride with emission in the visible and erbium-doped silicon nitride (Er:SiNx) with emission at 1540 nm. Both of these materials are compatible with the mainstream complementary metal-oxide semiconductor (CMOS) processing technology. This thesis discuses our results on using photonic crystal (PC) cavities to enhance luminescence from these materials. Nano-resonators modify the optical density of states (DOS) to enhance the emission in a fundamentally different way than what is accessible through materials engineering. Specifically, photon emission rate can be enhanced at a particular wavelength because the optical DOS is higher at the cavity resonance, which in turn improves efficiency and allows faster modulation rates. We have demonstrated up to 11-fold enhancement at photonic crystal resonance relative to smooth film at 730 nm and over 20-fold enhancement at 1540 nm. Time resolved measurements on erbium-doped sample confirmed significant enhancement of spontaneous emission rate. In addition, we have observed cavity line-width narrowing with increasing pump power in the erbium-doped sample, resulting from decrease in ground-state absorption by erbium ions as more of them are excited. We achieved excitation of up to 31% of Er ions at cryogenic temperature. This is an important step toward realizing a laser or amplifier based on Er:SiNx in the future.
Silicon-based photonic, plasmonic, and optomechanic devices [electronic resource]
Keywords: Electrical Engineering

The integration of optical devices and electronic devices on the same platform is currently a gateway into many research and practical applications. Because silicon and silicon compatible materials have dominated electronic development, optical devices must also conform to the silicon platform. One of the greatest challenges in building such an integrated opto-electronic system is the development of an efficient Si-compatible light emitter. In this thesis, we develop several Si-based nano-photonic devices for the control of light at the nano-scales. However, several Si-compatible materials and light emitters have low index of refraction, and high degrees of confinement using only index contrast and total internal reflection is difficult. We design high quality (Q-) factor photonic crystal nanobeam cavities for a variety of materials with low index, such as silicon dioxide, silicon rich oxide, and silicon nitride, all with high Q sand low mode volumes. We employ these cavity designs to a variety of active materials, including Si-nanocrystal doped silicon oxide, Er-doped amorphous silicon nitride, and InAs quantum quantum dots in GaAs. By placing emitters in these ultrasmall, high-Q cavities, we demonstrate that the cavity enhances emission and absorption processes, such as free carrier absorption, gain, and lasing. We also design plasmonic cavity and grating structures, which have lower Q compared to photonic crystal cavities due to metal ohmic losses, but have low mode volumes that break the diffraction limit. We propose and study a planar distributed Bragg reflector plasmonic cavity analogous to the nanobeam photonic cavity. We also demonstrate the enhancement of emission from silicon nanocrystals coupled to wide area plasmonic grating modes and Er-doped silicon nitride coupled to metal-insulator-metal modes confined between two metal layers. We demonstrate the control of emission wavelength by changing the device dimensions in both cases, and in the case of the Er material, observe an order of magnitude increase in collected emission compared to a sample with only one side contacting the metal. Finally, we demonstrate resonant actuation of a mechanical mode with optical gradient forces in a Si nanobeam cavity. The optical cavity enhances the optomechanical coupling between the optical mode and the mechanical vibration, and enables detectable mechanical motions with small optical powers driving an optical cavity mode.
Single-Molecule AFM Cantilever for THz Force Detection
Keywords: Physics
Atomic Force Microscope (AFM)
Inelastic Tunneling Spectroscopy (IETS)
Thesis

Increasing the resonance frequency of an Atomic Force Microscope (AFM) cantilever is necessary to effectively probe short-range chemical forces. Current AFM cantilevers have frequencies of about 100−200 kHz, limiting the minimum force-gradient that can be measured to the order of 10 pN/nm. This study demonstrates the ability of Inelastic Tunneling Spectroscopy (IETS) to probe THz vibrational modes of a single CO molecule attached to the tip of a low-temperature Scanning Tunneling Microscope (STM). Using molecular manipulation, a CO molecule is transferred to the end of the STM tip and lock-in techniques are used to measure 𝑑2𝐼/𝑑𝑉2 tunneling spectra. Shifts in the frequency of specific vibrational modes of the CO molecule are analyzed as a function of the tip-to-sample distance. This shows that a single molecule can be used as an AFM cantilever for force spectroscopy with the ability to measure small force-gradients to the order of 10−6 pN/nm. IETS with a CO terminated STM tip is also performed over adsorbed CO molecules on a Cu(111) surface revealing a novel vibrational mode due to coupling between the two CO molecules. In future, the small force-gradients detected by STM-IETS can be used to resolve single atoms within a molecule to reveal additional molecular structure.