New optoelectronic devices using GaAs-GaAlAs epitaxy

Three subjects related to epitaxial GaAs-GaAlAs optoelectronic devices are discussed in this thesis. They are:

1. Embedded Epitaxy

This is a technique of selective multilayer growth of GaAs- Ga_1-xAl_xAs single crystal structures through stripe openings in masking layers on GaAs substrates. This technique results in prismatic layers of GaAs and Ga_1-xAl_xAs "embedded" in each other and leads to controllable uniform structures terminated by crystal faces. The dependence of the growth habit on the orientation of the stripe openings has been studied. Room temperature embedded double heterostructure lasers have been fabricated using this technique. Threshold current densities as low as 1.5 KA/cm² have been achieved.

2. Barrier Controlled PNPN Laser Diode

It is found that the I-V characteristics of a PNPN device can be controlled by using potential barriers in the base regions. Based on this principle, GaAs-GaAlAs heterostructure PNPN laser diodes have been fabricated. GaAlAs potential barriers in the bases control not only the electrical but also the optical properties of the device. PNPN lasers with low threshold currents and high breakover voltage have been achieved. Numerical calculations of this barrier controlled structure are presented in the ranges where the total current is below the holding point and near the lasing threshold.

3. Injection Lasers on Semi-Insulating Substrates

GaAs-GaAlAs heterostructure lasers fabricated on semi-insulating substrates have been studied. Two different laser structures achieved are: (1) Crowding effect lasers, (2) Lateral injection lasers. Experimental results and the working principles underlying the operation of these lasers are presented. The gain induced guiding mechanism is used to explain the lasers' far field radiation patterns. It is found that Zn diffusion in Ga_1-xAl_xAs depends on the Al content x, and that GaAs can be used as the diffusion mask for Zn diffusion in Ga_1-xAl_xAs. Lasers having very low threshold currents and operating in a stable single mode have been achieved. Because these lasers are fabricated on semi-insulating substrates, it is possible to integrate them with other electronic devices on the same substrate. An integrated device, which consists of a crowding effect laser and a Gunn oscillator on a common semi-insulating GaAs substrate, has been achieved.

Polilaktida oinarri duten inplante polimeriko biodegradagarrien diseinu, fabrikazio eta propietateak

[EU]3D inprimaketa gaur egun, biomedikuntzaren garapenerako aukera ezberdinak ematen dituen teknologia iraultzaile gisa aurkezten da; bai medikuntza arloan formazio eta ikerkuntzarako erreminta gisa, baita dispositibo berrien diseinu eta fabrikaziorako. Bere abantailarik aipagarriena prototipaketa azkarra da. Gainera, teknologia honek barne egitura eta forma ezberdineko objektuak fabrikatzea ahalbidetzen du koste lehiakor batean. Lan honen helburua 3D inprimagailuen bidezko prototipoen fabrikazioan zentratzen da, horretarako lehengai bezala polimero biodegradagarri eta biobateragarria erabiliz. Horrez gain, metodo tradizionalarekin konparatuz teknologia honek izan ditzakeen abantailak ere aztertu nahi dira, ez bakarrik alde ekonomikoari edo denborari begira, baita fabrikatutako objektuen propietateei begira ere. Dena dela, horrekin hasi aurretik ezaugarritze fisiko eta termikoa burutu beharko zaie lehengaiei, 3D inprimagailuaren parametroen aukeraketa egokia egiteko eta parametro horien eta amaierako produktuaren kalitate, egitura eta propietateen artean erlazio egokia ezartzeko. Lan hau aurrera eramateko poli(L-laktida)-rekin (PLLA) egingo da lan, bai ehun ingeniaritzan baita hezurren apurketen finkapenerako dispositiboetan oso erabilia izan den polimeroa.

Acceleration Sensing, Feedback Cooling, and Nonlinear Dynamics with Nanoscale Cavity-Optomechanical Devices

Light has long been used for the precise measurement of moving bodies, but the burgeoning field of optomechanics is concerned with the interaction of light and matter in a regime where the typically weak radiation pressure force of light is able to push back on the moving object. This field began with the realization in the late 1960's that the momentum imparted by a recoiling photon on a mirror would place fundamental limits on the smallest measurable displacement of that mirror. This coupling between the frequency of light and the motion of a mechanical object does much more than simply add noise, however. It has been used to cool objects to their quantum ground state, demonstrate electromagnetically-induced-transparency, and modify the damping and spring constant of the resonator. Amazingly, these radiation pressure effects have now been demonstrated in systems ranging 18 orders of magnitude in mass (kg to fg).

In this work we will focus on three diverse experiments in three different optomechanical devices which span the fields of inertial sensors, closed-loop feedback, and nonlinear dynamics. The mechanical elements presented cover 6 orders of magnitude in mass (ng to fg), but they all employ nano-scale photonic crystals to trap light and resonantly enhance the light-matter interaction. In the first experiment we take advantage of the sub-femtometer displacement resolution of our photonic crystals to demonstrate a sensitive chip-scale optical accelerometer with a kHz-frequency mechanical resonator. This sensor has a noise density of approximately 10 micro-g/rt-Hz over a useable bandwidth of approximately 20 kHz and we demonstrate at least 50 dB of linear dynamic sensor range. We also discuss methods to further improve performance of this device by a factor of 10.

In the second experiment, we used a closed-loop measurement and feedback system to damp and cool a room-temperature MHz-frequency mechanical oscillator from a phonon occupation of 6.5 million down to just 66. At the time of the experiment, this represented a world-record result for the laser cooling of a macroscopic mechanical element without the aid of cryogenic pre-cooling. Furthermore, this closed-loop damping yields a high-resolution force sensor with a practical bandwidth of 200 kHZ and the method has applications to other optomechanical sensors.

The final experiment contains results from a GHz-frequency mechanical resonator in a regime where the nonlinearity of the radiation-pressure interaction dominates the system dynamics. In this device we show self-oscillations of the mechanical element that are driven by multi-photon-phonon scattering. Control of the system allows us to initialize the mechanical oscillator into a stable high-amplitude attractor which would otherwise be inaccessible. To provide context, we begin this work by first presenting an intuitive overview of optomechanical systems and then providing an extended discussion of the principles underlying the design and fabrication of our optomechanical devices.

Do encontro ao sentido: o cuidado aos sujeitos adoecidos de câncer

Esta pesquisa objetivou compreender como se dão as práticas de cuidado dirigidas ao sujeito adoecido de câncer no cotidiano dos serviços de saúde. Para tanto, partimos do entendimento que o processo de adoecer traz repercussões nos modos de andar a vida dos sujeitos, especialmente no que diz respeito ao câncer, patologia que traz consigo metáforas ligadas à morte, sofrimento e dor. Ao dar início à busca pelos serviços de saúde, os sujeitos se deparam com uma série de entraves que podem não proporcionar alívio, não suprindo as necessidades que essa nova condição impõe. Encontramos, em muitos momentos, práticas que negam o caráter subjetivo da experiência da doença, não valorizando a narrativa dos sujeitos. Como trajetória metodológica, escolhemos desenvolver um estudo de natureza qualitativa, utilizando como instrumento privilegiado a entrevista semi aberta. Iniciamos as entrevistas com a consigna: conte como se deu o tratamento de sua doença desde a descoberta até o momento em que se encontra. Os dados coletados a partir do encontro com os sujeitos adoecidos foram complementados por informações contidas nos prontuários médicos, bem como por observações obtidas no momento da interação. O local de realização da pesquisa foi um hospital estadual de grande porte localizado na cidade de Fortaleza, estado do Ceará. As entrevistas foram realizadas no serviço de oncologia clínica do referido hospital. Ao todo foram entrevistados doze sujeitos que estavam em tratamento ambulatorial no serviço. Dos doze sujeitos, cinco eram mulheres e sete eram homens. As idades variaram de 29 a 65 anos. A análise dos dados se deu após imersão no material empírico, posteriormente materializado nas transcrições das entrevistas. Procuramos deixar que os sentidos aflorassem, confrontando com o material que já tínhamos disponível, surgindo daí as categorias empíricas. Dividimos as categorias em duas dimensões, a do sujeito e a da rede de serviços de saúde. Ao final da análise, constatamos alguns pontos que consideramos importantes no sentido de se tornarem dispositivos de mudança. Foi possível confirmar que os sujeitos sabem de si, e realizam um processo de construção do sentido sobre sua doença e das práticas terapêuticas. A doença produz mudanças no sujeito, e os força a ressignificarem sua rotina e hábitos de vida. Foi possível observar que o encontro com os serviços de saúde tem se dado de forma truncada. A luta pelo direito a saúde é árdua: pela demora na confirmação do diagnóstico, pela demora em conseguir marcar exames e receber seus resultados, pela falta de especialistas que saibam o que estão fazendo. Os sujeitos têm descoberto a doença quando esta se encontra avançada. A importância do diálogo, da escuta, da percepção do que o outro necessita é importante, por isso, valorizar os relatos dos sujeitos adoecidos de câncer se faz urgente.

DNA-Mediated Charge Transport Devices for Protein Detection

Detection of biologically relevant targets, including small molecules, proteins, DNA, and RNA, is vital for fundamental research as well as clinical diagnostics. Sensors with biological elements provide a natural foundation for such devices because of the inherent recognition capabilities of biomolecules. Electrochemical DNA platforms are simple, sensitive, and do not require complex target labeling or expensive instrumentation. Sensitivity and specificity are added to DNA electrochemical platforms when the physical properties of DNA are harnessed. The inherent structure of DNA, with its stacked core of aromatic bases, enables DNA to act as a wire via DNA-mediated charge transport (DNA CT). DNA CT is not only robust over long molecular distances of at least 34 nm, but is also especially sensitive to anything that perturbs proper base stacking, including DNA mismatches, lesions, or DNA-binding proteins that distort the π-stack. Electrochemical sensors based on DNA CT have previously been used for single-nucleotide polymorphism detection, hybridization assays, and DNA-binding protein detection. Here, improvements to (i) the structure of DNA monolayers and (ii) the signal amplification with DNA CT platforms for improved sensitivity and detection are described.

First, improvements to the control over DNA monolayer formation are reported through the incorporation of copper-free click chemistry into DNA monolayer assembly. As opposed to conventional film formation involving the self-assembly of thiolated DNA, copper-free click chemistry enables DNA to be tethered to a pre-formed mixed alkylthiol monolayer. The total amount of DNA in the final film is directly related to the amount of azide in the underlying alkylthiol monolayer. DNA monolayers formed with this technique are significantly more homogeneous and lower density, with a larger amount of individual helices exposed to the analyte solution. With these improved monolayers, significantly more sensitive detection of the transcription factor TATA binding protein (TBP) is achieved.

Using low-density DNA monolayers, two-electrode DNA arrays were designed and fabricated to enable the placement of multiple DNA sequences onto a single underlying electrode. To pattern DNA onto the primary electrode surface of these arrays, a copper precatalyst for click chemistry was electrochemically activated at the secondary electrode. The location of the secondary electrode relative to the primary electrode enabled the patterning of up to four sequences of DNA onto a single electrode surface. As opposed to conventional electrochemical readout from the primary, DNA-modified electrode, a secondary microelectrode, coupled with electrocatalytic signal amplification, enables more sensitive detection with spatial resolution on the DNA array electrode surface. Using this two-electrode platform, arrays have been formed that facilitate differentiation between well-matched and mismatched sequences, detection of transcription factors, and sequence-selective DNA hybridization, all with the incorporation of internal controls.

For effective clinical detection, the two working electrode platform was multiplexed to contain two complementary arrays, each with fifteen electrodes. This platform, coupled with low density DNA monolayers and electrocatalysis with readout from a secondary electrode, enabled even more sensitive detection from especially small volumes (4 μL per well). This multiplexed platform has enabled the simultaneous detection of two transcription factors, TBP and CopG, with surface dissociation constants comparable to their solution dissociation constants.

With the sensitivity and selectivity obtained from the multiplexed, two working electrode array, an electrochemical signal-on assay for activity of the human methyltransferase DNMT1 was incorporated. DNMT1 is the most abundant human methyltransferase, and its aberrant methylation has been linked to the development of cancer. However, current methods to monitor methyltransferase activity are either ineffective with crude samples or are impractical to develop for clinical applications due to a reliance on radioactivity. Electrochemical detection of methyltransferase activity, in contrast, circumvents these issues. The signal-on detection assay translates methylation events into electrochemical signals via a methylation-specific restriction enzyme. Using the two working electrode platform combined with this assay, DNMT1 activity from tumor and healthy adjacent tissue lysate were evaluated. Our electrochemical measurements revealed significant differences in methyltransferase activity between tumor tissue and healthy adjacent tissue.

As differential activity was observed between colorectal tumor tissue and healthy adjacent tissue, ten tumor sets were subsequently analyzed for DNMT1 activity both electrochemically and by tritium incorporation. These results were compared to expression levels of DNMT1, measured by qPCR, and total DNMT1 protein content, measured by Western blot. The only trend detected was that hyperactivity was observed in the tumor samples as compared to the healthy adjacent tissue when measured electrochemically. These advances in DNA CT-based platforms have propelled this class of sensors from the purely academic realm into the realm of clinically relevant detection.

Development of Microfluidic Devices with the Use of Nanotechnology to Aid in the Analysis of Biological Systems Including Membrane Protein Separation, Single Cell Analysis, and Genetic Markers

Computation technology has dramatically changed the world around us; you can hardly find an area where cell phones have not saturated the market, yet there is a significant lack of breakthroughs in the development to integrate the computer with biological environments. This is largely the result of the incompatibility of the materials used in both environments; biological environments and experiments tend to need aqueous environments. To help aid in these development chemists, engineers, physicists and biologists have begun to develop microfluidics to help bridge this divide. Unfortunately, the microfluidic devices required large external support equipment to run the device. This thesis presents a series of several microfluidic methods that can help integrate engineering and biology by exploiting nanotechnology to help push the field of microfluidics back to its intended purpose, small integrated biological and electrical devices. I demonstrate this goal by developing different methods and devices to (1) separate membrane bound proteins with the use of microfluidics, (2) use optical technology to make fiber optic cables into protein sensors, (3) generate new fluidic devices using semiconductor material to manipulate single cells, and (4) develop a new genetic microfluidic based diagnostic assay that works with current PCR methodology to provide faster and cheaper results. All of these methods and systems can be used as components to build a self-contained biomedical device.

Everybody Farts: Celebrating the Body and Refuting Medical Paternalism in Joyce's Ulysses

James Joyce’s Ulysses celebrates all facets of daily life in its refusal to censor raw human emotions and emissions. He adopts a critically medical perspective to portray this honest, unfiltered narrative. In doing so, he reveals the ineffectiveness of the physician-patient relationship due to doctors’ paternalistic attitudes that hinder nonjudgmental, open listening of this unfiltered narrative. His exploration of the doctor’s moral scrutiny, cultural prejudices, and authoritative estrangement from the patient underscore the importance in remembering that physicians and patients alike are ultimately just fellow human beings. Wryly, he drives this point to literal nausea, as his narrative proudly asserts the revulsive details of public health, digestion, and death. In his gritty ruminations on the human body’s material reality, Joyce mocks the physician’s highbrow paternalism by forcing him to identify with the farting, vomiting, decaying bodies around him. In celebrating the uncensored human narrative, Joyce challenges physician and patient alike to openly listen to the stories of others.

HYBRID PHOTOVOLTAIC DEVICES BASED ON ORGANIC SEMICONDUCTING POLYMERS AND INORGANIC NANOSTRUCTURED ELECTRODES

La fotovoltaica orgánica es una tecnología solar emergente que todavía no ha entrado en el mercado. El objetivo de esta tesis ha sido acercar un poco más la industrialización de dicha tecnología mediante el incremento de la eficiencia y la durabilidad de estos dispositivos solares. Para la consecución de dicho objetivo se identificaron las limitaciones existentes y se diseñó una hora de ruta con diversas estrategias para poder superar cada uno de los problemas. Así, mediante un exhaustivo control de la nano morfología del film fotoactivo y la introducción de electrodos nanoestructurados se ha conseguido incrementar la eficiencia. La sustitución de los electrodos estándares por nuevos electrodos basados en óxidos metálicos confiere durabilidad al sistema. Por último, la sustitución del óxido de indio y estaño como electrodo transparente por nanohilos metálicos de plata habilita la posibilidad de fabricar dispositivos solares flexibles de bajo coste.

Charge and spin transport in graphene devices

170 p.