VictorJuiz/thesis huggingface dataset:
Germanium as an optical emitter for monolithic integration on silicon [electronic resource]

A silicon (Si) compatible laser for applications in telecommunication and optical interconnect systems has been an interesting topic for several years now, but has yet to be practically demonstrated. The main problem is finding an appropriate lasing material at 1550 nm which can be monolithically integrated on silicon with conventional CMOS processes. Germanium (Ge) is compatible with Si and has a direct band gap of 0.8 eV, corresponding to the required optical communication wavelength of 1550 nm. The small difference of 0.134 eV between the direct and indirect band gaps of Ge suggests the possibility of a radiative direct band gap transition. Strategies to improve the luminescence properties of germanium have included large tensile strain, tin alloying, and electron band filling. In this talk, we focus on the last approach since the emission wavelength from such a method stays near the desired 1550 nm. We first show how Ge direct band emission can be improved by using electron band filling of the conduction band. To achieve high electron band filling, an in-situ doping technique was applied during the growth of epitaxial Ge on Si. A strong enhancement from direct band photoluminescence (PL) was observed from highly-doped (1E19 cm^-3) n-type epi-Ge, demonstrating that electron band filling improves the direct band emission strength. We then successfully demonstrate room temperature direct band electroluminescence (EL) from Ge n+/p light emitting diodes (LED) on a Si substrate, which is a key step towards a CMOS-compatible laser. The contribution of electron band filling and the temperature dependence to the device efficiency will also be discussed. Additionally, we fabricate and optically characterize epitaxial Ge microdisks on Si. These microdisk resonators are successfully coupled to fiber tapers and display clear whispering gallery modes (WGM) in transmission as well as photoluminescence. Finally, we combined the LED structure and the microdisk cavity to demonstrate an electrically-pumped Ge resonator diode. Both our optical and electrical resonators are currently limited by the Ge doping concentration, which prevents sufficient electron band filling to allow material gain or lasing. Possible solutions to this problem will also be discussed.

Keywords: Materials Science and Engineering
Advisor: Brongersma Mark L. primary advisor. Thesis advisor
Nishi Yoshio
Vuckovic Jelena advisor. Thesis advisor
Ge/SiGe quantum well waveguide modulator for optical interconnect systems [electronic resource]

Thanks to the development of silicon VLSI technology over the past several decades, we can now integrate far more transistors onto a single chip than ever before. However, this also imposes more stringent requirements, in terms of bandwidth, density, and power consumption, on the interconnect systems that link transistors. The interconnect system is currently one of the major hurdles for the further advancement of the electronic technology. Optical interconnect is considered a promising solution to overcome the interconnect bottleneck. The quantum-confined Stark effect in Ge/SiGe quantum well system paves the way to realize efficient optical modulation on Si in a fully CMOS compatible fashion. In this dissertation, we investigate the integration of Ge/SiGe quantum well waveguide modulators with silicon-on-insulator waveguides. For the first time, we demonstrate the selective epitaxial growth of Ge/SiGe quantum well structures on patterned Si substrates. The selective epitaxy exhibits perfect selectivity and minimal pattern sensitivity. Compared to their counterparts made using bulk epitaxy, the p-i-n diodes from selective epitaxy demonstrate very low reverse leakage current and high reverse breakdown voltage. Strong quantum-confined Stark effect (QCSE) is, for the first time, demonstrated in this material system in the telecommunication C-band at room temperature. A 3 dB optical modulation bandwidth of 2.8 THz is measured, covering more than half of the C-band. We propose, analyze, and experimentally demonstrate a novel approach to realize butt coupling between a SOI waveguide and a selectively grown Ge/SiGe quantum well waveguide modulator using a thin dielectric spacer. Through numerical simulation, we show that the insertion loss penalty for a thin 20 nm thick spacer can be as low as 0.13 dB. Such a quantum well waveguide modulator with a footprint of 8 [Mu]m2 has also been fabricated, demonstrating 3.2 dB modulation contrast with merely 1V swing at a speed of 16 Gpbs.

Keywords: Electrical Engineering
Advisor: Harris J. S. (James Stewart)
Miller D. A. B. primary advisor. Thesis advisor
Saraswat Krishna advisor. Thesis advisor
Giant magnetoresistive nanosensors for ultrasensitive in vitro diagnostics and biomolecular kinetics [electronic resource]

Nanotechnology has the unique capability of manipulating and sensing matter at the molecular scale with unprecedented speed, sensitivity, and throughput. The medical application of nanotechnology, nanomedicine, has leveraged nanoscience tools for the advancement of medical diagnostics, therapy, and basic science research. In this work, arrays of magnetically responsive nanosensors, originally developed for use as read heads in computer hard disk drives, have been utilized to achieve in-depth proteomic studies for the advancement of medical diagnostics and therapy. In particular, this dissertation will focus on the following four topics of applying magnetic nanotechnology to science and medicine. First, the application of magnetic nanosensor arrays to early cancer diagnostics and monitoring response to chemotherapy. The utility of magnetic nanosensors as a molecular diagnostics tool capable of profiling a patient's disease state and leveraging a patient's unique molecular signature will be demonstrated. Second, this report will discuss a novel mathematical model expressly developed to describe the kinetic interactions of magnetically labeled biomolecules binding to capture agents immobilized on a surface. Third, a novel autoassembly immunoassay capable of screening for antibody cross-reactivity in a high-density, high-fidelity, and rapid manner will be described. Finally, this report will address the utility of the autoassembly immunoassay in conjunction with a miniaturized magnetic nanosensor platform for point-of-care diagnostics in a cost-effective and easy-to-use (e.g. wash-free) process that can make a significant contribution to global health.

Keywords: Bioengineering.
Advisor: Wang Shan primary advisor. Thesis advisor
Liao Joseph advisor. Thesis advisor
Yock Paul G. advisor. Thesis advisor
Glucocorticoids increase CNS inflammation, worsening acute neurological injury [electronic resource]

Glucocorticoids (GCs) are stress hormones that are well-known for their potent and pleiotropic anti-inflammatory effects. In the injured CNS, their anti-inflammatory properties could be particularly beneficial due to the often detrimental effects of excessive inflammation in the brain. In more recent years, however, it has become clear that GCs do not always decrease inflammation and can even augment aspects of the immune response. The research presented in this doctoral dissertation describes the impact of this increased inflammatory response in the CNS using animal models of excitotoxicity and hypoxia/ischemia. Specifically, both exogenous GC treatments and the endogenously released GCs post-injury were found to increase immune cell activation (both in phenotype and in p65 nuclear translocation) in both rat and mouse models of excitotoxic hippocampal neuron death and in a mouse MCAO stroke model. These increased inflammatory responses are likely to be mediated by an unexpected GC-suppression of several anti-inflammatory cytokines including CX3CL1 and CD22 and failure of GCs to activate some of their normal anti-inflammatory targets like IkBa, IL-1ra, and MKP-1. Furthermore, these GC-augmented inflammatory responses are necessary for GCs to make more neurons die from either of these injuries. Taken together, this work demonstrates that cellular inflammation is not kept in check by GCs in the forebrain; instead, GCs worsen hippocampal and cortical neuron death, at least in part, by increasing the neurotoxicity of CNS inflammation.

Keywords: Biology.
Advisor: Sapolsky Robert M. primary advisor. Thesis advisor
Barres Ben
Dhabhar Firdaus (Firdaus S.) advisor. Thesis advisor
Wyss-Coray Anton advisor. Thesis advisor
GMR spin-valve biochips and interface electronics for ultrasensitive in-vitro diagnostics [electronic resource]

Nanotechnology has had a transformative effect on medical diagnostics due to the influx of new sensing modalities and transducers. Magnetic nanotechnologies, in particular, have shown significant potential in several areas of nanomedicine such as imaging, therapeutics, and early disease detection. Giant magnetoresistive spin-valve (GMR SV) sensors, commonly used in hard disk drives, coupled with magnetic nanotags have shown great promise as biosensors. In this work, we present several custom designed circuit interface and readout systems tailored to specific application spaces and their unique needs. Taken together, we have demonstrated that innovative electronic circuits play an indispensable role in unlocking the tremendous potential of nanosensors in the biomedical arena. The first system was designed for ultrasensitive early cancer diagnostics and built using off-the-shelf components for an 8x8 array of GMR SV sensors. At the core of this design, we demonstrate a new circuit architecture based on a transimpedance amplifier (TIA) with a carrier suppression technique to reduce the dynamic range requirement and a multiplexing scheme to reduce the readout time. This system is capable of real-time, multiplex detection with a detection limit of 5 femtomolar (fM) and over 6 orders of linear dynamic range. The second system is a miniaturized, portable platform called the nanoLAB. Although there is a growing need for point-of-care (POC) testing for global health, the current options are bulky, slow, expensive, and often not sensitive. The nanoLAB addresses these needs and pushes the state of the art with sensitive 8-plex detection using a wash-free assay that can be run by anyone, anywhere. This platform was tested and validated using human immunodeficiency virus (HIV) biomarkers with detection down to 50 fM in as little as 15 minutes. We also show how a GMR SV biosensor can be integrated into a continuous time sigma delta modulator. This proof-of-concept hybrid sigma delta modulator has a peak SNR of 99.3 dB and a dynamic range of over 92 dB in a 1 kHz bandwidth using the sensor as part of the first integrator. The carrier suppression and multiplexing concepts were also incorporated into the hybrid sigma delta modulator. Lastly, we conclude by describing an integrated platform for a large 16x16 array of GMR SV sensors implemented in a 0.18 [mu]m CMOS technology. Arranged like an imager chip, each of the 16 column level readout channels contains an analog front-end and an analog-to-digital converter. Each readout channel occupies less than 0.2 mm^2 of chip area and consumes 3.4 mW of power. This system is designed as a replacement for optical protein microarrays while being fully quantitative and providing real-time readout.

Keywords: Electrical Engineering
Advisor: Murmann Boris primary advisor. Thesis advisor
Wang Shan primary advisor. Thesis advisor
Wooley Bruce A.
"Great is the power of steady misrepresentation" : racial inequality and social representations of human evolution [electronic resource]

Lay narratives about human evolution contain references to leaving Africa, describe evolution as linear, and celebrate Western advances as evidence of humanity's superior intellect. Furthermore, popular images of human evolution depict a timeline beginning with a dark, apelike creature on the left and ending with a White male on the right. I argue that these commonplace representations of human evolution contain vestiges of an explicit racial hierarchy from the 19th century and affect people's understanding of racial inequality today. Across three studies, White participants exposed to these representations were more likely to demonstrate indifference to and even justification of racial inequality, both present and historic. In two additional studies I demonstrate that the representation of evolution can negatively affect Black participants in an academic context, by invoking a threat of dehumanization. Although inaccuracies in the representations of human evolution are well documented, such inaccuracies not only pose challenges for the teaching and learning of science, but also for current day race relations.

Keywords: Psychology
Advisor: Eberhardt Jennifer L. (Jennifer Lynn) primary advisor. Thesis advisor
Lowery Brian
Markus Hazel Rose advisor. Thesis advisor
Green technology adoption in response to environmental policies [electronic resource]

New technologies are crucial in dealing with the problem of air and water pollution, which is an increasingly important issue with serious health and environmental consequences. However, adoption of environmentally friendly technologies can be slow if the new technologies are not superior in terms of the firms' private incentives, if firms have long equipment replacement cycles, or if firms do not have sufficient information to evaluate whether or not a switch to a green technology is in their private interests. To evaluate these potential explanations and the policies designed to address them, I use an importance sampling technique with simulated maximum likelihood estimation to estimate two separate dynamic, durable good replacement models with entry and exit for garment cleaning firms in southern California, where alternative cleaning technologies have seen only limited adoption to date. The first model is a single-agent model, whereas the second model allows firms' profits to depend on the states of their competitors. I utilize a unique data set comprised of equipment permitting information, grant recipient lists, and product demonstration attendance lists, and I control for and exploit changing legislation to estimate the effect of fees and incentives on green equipment purchases, as well as the effect of the product demonstrations. The single-agent models are used to perform counterfactual analyses to compare the predicted adoption and entry/exit decisions by firms under different regulatory regimes. While the models are tailored to the garment cleaning industry, it can be adapted to other applications involving the diffusion of technologies in regulated industries.

Advisor: Hartmann Wesley R. (Wesley Robert)
Nair Harikesh S. (Harikesh Sasikumar)
Narayanan Sridhar
Reiss Peter advisor. Thesis advisor
Green technology adoption in response to environmental policies [electronic resource]

New technologies are crucial in dealing with the problem of air and water pollution, which is an increasingly important issue with serious health and environmental consequences. However, adoption of environmentally friendly technologies can be slow if the new technologies are not superior in terms of the firms' private incentives, if firms have long equipment replacement cycles, or if firms do not have sufficient information to evaluate whether or not a switch to a green technology is in their private interests. To evaluate these potential explanations and the policies designed to address them, I use an importance sampling technique with simulated maximum likelihood estimation to estimate two separate dynamic, durable good replacement models with entry and exit for garment cleaning firms in southern California, where alternative cleaning technologies have seen only limited adoption to date. The first model is a single-agent model, whereas the second model allows firms' profits to depend on the states of their competitors. I utilize a unique data set comprised of equipment permitting information, grant recipient lists, and product demonstration attendance lists, and I control for and exploit changing legislation to estimate the effect of fees and incentives on green equipment purchases, as well as the effect of the product demonstrations. The single-agent models are used to perform counterfactual analyses to compare the predicted adoption and entry/exit decisions by firms under different regulatory regimes. While the models are tailored to the garment cleaning industry, it can be adapted to other applications involving the diffusion of technologies in regulated industries.

Keywords: Business.
Advisor: Hartmann Wesley R. (Wesley Robert)
Nair Harikesh S. (Harikesh Sasikumar)
Narayanan Sridhar
Reiss Peter C. (Peter Clemens) advisor. Thesis advisor
Health Insurance Pooling Between Thin and Obese in Europe

Numerous studies have found that obese workers are paid lower wages than the nonobese, even when controlling for skill level and productivity. Bhattacharya and Bundorf (2009) find that in the United States, this wage differential is only significant in jobs that provide health insurance to their employees and that this wage differential largely results from the increased cost of insuring obese workers. I examine European data from the Survey on Health Retirement and Aging in Europe (SHARE) to determine whether obese workers are paid lower wages than the non-obese, even where the majority of health insurance is provided by the state. I find that there is no significant wage differential between the obese and non-obese in Europe as a whole and that to the extent that wage differentials exist in individual countries, these are highly correlated with the prevalence of employer-provided health insurance in those countries.

Keywords:  Department of Economics
Stanford Department of Economics
Obesity
Health Insurance
Insurance Pooling
Europe
Survey on Health Retirement and Aging in Europe
Thesis
Advisor: Bhattacharya Jayanta
The heritage of aftermath [electronic resource] : making "heritage at risk" in post-tsunami Banda Aceh

This dissertation examines the construction of cultural heritage in the aftermath of large-scale destruction, in Banda Aceh, Indonesia. It is concerned with the traditions that negotiate this process, focusing on the intersection between existing cultural traditions of Banda Aceh and the vernacularization of a global tradition of preservation, a philosophy and practice that is concerned with interrupting the destruction of material culture. The latter is examined through the construct of 'heritage at risk', a rhetorical device that regulates the deployment of preservation at the global level. However, this is a construct that has little application to the emergence of new heritage places as it is observed in Aceh following the 2004 Indian Ocean tsunami. This demands a re-evaluation of the ways that vulnerability and heritage have been blended and naturalized in discourse and practice. In the context of an Acehnese claim to uniqueness, the successful vernacularization of a preservation practice is evident in the formalization of distinct ways to represent history, identity and a recent assimilation of a 'culture of disaster', into coherent heritage assemblages. However, the heritage construct that is articulated in Aceh does not fit the already established boundaries of 'non-Western' or 'Asian' heritage, instead it creatively weaves elements of Western and Asian established preservation philosophies, to preserve specific cultural values of significance. As such, the heritage of Aceh does not wait to be legitimized by the global heritage discourse or its experts, as it responds to localized structures of legitimacy and democratization. Arguments in this dissertation challenge the persistent absence of culture in cultural heritage preservation methodologies, suggesting ways in which cultural heritage should be constructed and debated as situated knowledge. This dissertation goes beyond a case study of heritage management. It is a critical assessment of the construction of heritage categories outside of a risk-centered framework that necessarily eliminates the ageism that is characteristic of heritage constructs. It is centered instead on the contributions of an ethnographic approach to recognizing locally situated practices of preservation that produce heritage places in the context of post-tsunami Aceh.

Keywords: Anthropology.
Advisor: Meskell Lynn primary advisor. Thesis advisor
Byrne Denis (Denis Richard)
Ebron Paulla A.
Hodder Ian advisor. Thesis advisor
High performance III-V PMOSFET [electronic resource]

As scaling of Silicon CMOS technology is only yielding marginal returns, III-V materials are being actively explored as (a) channel materials for future technology nodes for providing high performance at low operating voltages and (b) as enabling materials for optical interconnects. This research is primarily being driven by high electron mobility and direct bandgap in III-V semiconductors. Three major challenges facing the III-V CMOS community right now are (1) development of a III-V pMOSFET with high hole mobility to compliment the III-V nMOSFET (2) development of a high-k dielectric with low interface state densities, suitable for use as gate dielectric (3) integration of III-V materials on Silicon. In this thesis our contributions in overcoming first two challenges and development of an III-V pMOSFET with InGaSb channel material and Al2O3 dielectric will be described. (1) Firstly, we start with bandstructure calculations and modeling to identify the optimal material, strain configuration and heterostructure design for enhancing hole mobility in III-V channels, which had traditionally lagged in comparison to Silicon. (2) Compressively strained InGaSb quantum-well channels, identified from modeling results have been investigated for obtaining high hole-mobility. Parameters such as strain, valence band offset etc. have been experimentally measured. Transport and bandstructure have been quantified by studying these 2D hole gases under high magnetic field. (3) After establishing the feasibility of these materials for hole-transport, we have worked towards development of a pMOSFET with an Sb-based channel. Al2O3 dielectric with mid-bandgap density of interface states of 3 x 1011/cm2eV on GaSb substrate was developed. Finally, surface/buried channel III-V pMOSFETs with sub-threshold slope of 120mV/decade, ION/IOFF > 1 x 104 and having more than 50/100% mobility gain on germanium over the entire sheet range have been fabricated using a sub 350°C self-aligned process flow.

Keywords: Electrical Engineering
Advisor: Nishi Yoshio
Saraswat Krishna primary advisor. Thesis advisor
Harris J. S. (James Stewart)