Over the past decades, integrated photonics has revolutionized the way we generate and manipulate light, employing micro- and nanoscale structures to shrink full optical systems into chips smaller than a fingernail. By leveraging the infrastructure of semiconductor foundries and fabrication processes, the development and deployment of integrated photonic technologies has been greatly accelerated. The main focus has been in applications for infrared light, such as optical interconnects and communication. Nevertheless, photonic integrated circuits (PICs) have quickly found applications in many other fields, including sensing, ranging, imaging, quantum technologies, biomedicine, spectroscopy, microwave generation, astrophysics, and displays. However, many of these technologies require light at visible wavelengths, where PIC technology is still in its infancy. Visible-light photonics presents several additional and stricter challenges when compared the infrared portion of the spectrum. First, laser sources are not as developed or available. Second, the sensitivity of devices to fabrication variations and the coupling losses are intensified. Third, the range of transparent materials available for waveguiding is more limited, and their technology is not as mature. Lastly, techniques that work well in the infrared spectrum are not as effective in the visible range due to the remarkably different material properties in this spectral window.In this thesis, we explore integrated photonics in the visible spectrum and focus on solving two of its main challenges: the lack of high-performance laser sources, and the high losses of PICs. We develop a low loss, high-confinement silicon nitride (SiN) platform and use it to demonstrate high-performance visible-light lasers from near-ultraviolet (near-UV) to near-infrared (near-IR), to probe the limits of absorption and scattering across the visible spectrum, and to generate multi-octave frequency combs with simultaneous infrared and visible light of all colors of the rainbow. Since our SiN platform is compatible with current photonic foundries, our work lays the foundation for fully-integrated, dense and scalable visible-light PIC systems that combine high-performance lasers and ultra-low loss devices. We envision such chip-scale platform to not only transform existing technologies, but to also enable a whole new generation of applications that have so far been impossible, causing tremendous impact in science, medicine and industry.

Small scale renewable energy harvesting is an attractive solution to the growing need for power in remote technological applications. For this purpose, localized thermal gradients on-chip—created via radiative cooling—could be exploited to produce microscale renewable heat engines running on environmental heat. This could allow self-powering in small scale portable applications, thus reducing the need for non-renewable sources of electricity and hazardous batteries. In this work, we demonstrate the creation of a local thermal gradient on-chip by radiative cooling of a 90 nm thick freestanding silicon nitride nanomechanical resonator integrated on a silicon substrate at ambient temperature. The reduction in temperature of the thin film is inferred by tracking its mechanical resonance frequency, under high vacuum, using an optical fiber interferometer. Experiments were conducted on 15 different days during fall and summer months, resulting in successful radiative cooling in each case. Maximum temperature drops of 9.3 K and 7.1 K are demonstrated during the day and night, respectively, in close correspondence with our heat transfer model. Future improvements to the experimental setup could enhance the temperature reduction to 48 K for the same membrane, while emissivity engineering potentially yields a maximum theoretical cooling of 67 K with an ideal emitter. This thesis first elaborates a literature review on the field of radiative cooling, along with a theoretical review of relevant thermal radiation concepts. Then, a heat transfer model of the radiative cooling experiment is detailed, followed by the experimental method, apparatus, and procedures. Finally, the experimental and theoretical results are presented, along with future work and concluding remarks.

No description available.

Reaction sintered silicon nitride (RSSN) was studied as a substitute coating material on the carbon-carbon material (RCC) presently used as a heat shield on the space shuttle, and on advanced carbon-carbon (ACC), a later development. On RCC, RSSN showed potential in a 538°C (1000°F) screening test in which silicon carbide coated material exhibits its highest oxidation rate; RSSN afforded less protection to ACC because of a larger thermal expansion mismatch. Organosilicon densification and metallic silicon sealing methods were studied as means of further increasing the oxidation resistance of the coating, and some improvement was noted when these methods were employed. / Master of Science

The breast cancer susceptibility protein, BRCA1, is a tumor suppressor that helps maintain genomic integrity. Changes in BRCA1 that effect DNA repair processes can fuel cancer induction. The Kelly lab, at the Virginia Tech Carilion Research Institute, has recently developed a new methodology that employs silicon nitride (SiN) microchips to isolate BRCA1 assemblies from the nuclear material of breast cancer cells. These microchips are coated with adaptor proteins that include antibodies against target proteins of interest. The adaptor proteins are added in sequential steps to the coated microchips, followed by an aliquot of sample containing the protein of interest, such as BRCA1. The Kelly lab, partnered with Protochips Inc., developed these devices as a robust, tunable platform to monitor molecular processes, and refer to them as 'Cryo-SiN' in cryo-Electron Microscopy (EM) imaging. We are currently using Cryo-SiN to recruit BRCA1 protein assemblies to the microchip surface under mild conditions, while simultaneously preparing them for cryogenic preservation and EM imaging. This strategy presents a viable alternative to antibody affinity columns that require stringent elution steps to obtain protein complexes from the column. Another advantage of the microchip strategy is that it requires only a 30-minute nuclear extraction, a 60-minute enrichment procedure, and a 5-minute microchip capture step--a total of 95 minutes from initially lysing the cells to plunge-freezing the EM specimens. Therefore, these novel approaches represent a major departure from classical separation procedures that often require days to complete, during which time active protein assemblies can readily dissociate or become inactive. Overall, our use of BRCA1-specific microchips may reveal changes in the BRCA1 architecture during various stages of cancer progression--a major gap in knowledge that persists in cancer research. / M. S.

An environmentally friendly, and contamination free process for etching and cleaning semiconductors is critical to future of the IC industry. Under the right conditions, water has the ability to meet these requirements. Water becomes more reactive as a function of temperature in part because the number of hydronium and hydroxyl ions increase. As water approaches its boiling point, the concentration of these species increases over seven times their concentrations at room temperature. At 150 °C, when the liquid state is maintained, these concentrations increase 15 times over room temperature. Due to its enhanced reactivity, high temperature water (HTW) has been studied as an etch and clean of thermally grown SiO2, Si3N4, and low-k films. High temperature deuterium oxide (HT-D2O) behaves similarly to HTW; however, it dissociates an order of magnitude less than HTW resulting in an equivalent reduction in reactive species. This allowed for the effects of reactive specie concentration on etch rate to be studied, providing valuable insight into how HTW compares to other high temperature wet etching processes such as hot phosphoric acid (HPA). Characterization was conducted using Fourier transform infrared spectroscopy (FTIR) to determine chemical changes due to etching, spectroscopic ellipsometry to determine film thickness, profilometry to measure thickness change across the samples, scanning electron microscopy (SEM), contact angle to measure changes in wetting behavior, and UV-Vis spectroscopy to measure dissolved silica in post etch water. HTW has demonstrated the ability to effective etch both SiO2 and Si3N4, HT-D2O also showed similar etch rates of Si3N4 indicating that a threshold reactive specie concentration is needed to maximize etch rate at a given temperature and additional reactive species do not further increase the etch rate. Because HTW has no hazardous byproducts, high temperature water could become a more environmentally friendly etchant of SiO2 and Si3N4 thin films.

Ternary indium aluminum nitride (InXAl1-XN) semiconductor is an attractive material with a wide-range bandgap energy varied from ultraviolet (Eg(AlN): 6.2 eV) to near infrared (Eg(InN): 0.7 eV). With tuning composition, it can be widely used to many optoelectronic device applications. In this thesis, I have studied InXAl1-XN film deposited on Si (111) substrate using natural and isotopically enriched nitrogen as reactive gas by reactive magnetron sputter epitaxy (MSE). Four series of experiments were performed, which are I. InAlN presputtering, II. InAlN sputter deposition, III. InAlN direct deposition, and IV. InAlN direct deposition using isotopically enriched nitrogen. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The θ-2θ XRD scan confirms that the designed composition x = 0.17 of InXAl1-XN film was obtained. TEM images shows that an amorphous interlayer with a thickness ranging from 1.2 nm to 1.5 nm was formed between Si substrate and InXAl1-XN film. However, high-resolution TEM shows that the interlayer actually contains partial crystalline structures. EDX line profile indicates that the chemical composition of the amorphous interlayer is silicon nitride (SiNX). By comparing d-spacing measurement of partial crystalline structures with EDX line profile, it reveals that partial SiNX crystal is formed in the interlayer. Nonetheless, the samples (IAD01, IAD02, IAD03, IAD04), grown without presputtering procedure, contain both crystalline SiNX and InXAl1-XN embedded in the amorphous interlayer. It means that SiNX and InXAl1-XN film can be directly grown on the substrate in the beginning of deposition. Moreover, the samples (IAD01, IAD03), quenched directly after deposition, have less crystalline structures in the interlayer then the samples (IAD02, IAD04), maintained at 800℃ for 20 min.

<p>Spark Plasma Sintering (SPS) is a promising rapid consolidation technique that allows a better understanding and manipulating of sintering kinetics and therefore makes it possible to obtain Si₃N₄-based ceramics with tailored microstructures, consisting of grains with either equiaxed or elongated morphology.</p><p> The presence of an extra liquid phase is necessary for forming tough interlocking microstructures in Yb/Y-stabilised α-sialon by HP. The liquid is introduced by a new method, namely by increasing the O/N ratio in the general formula RE_xSi_12-(3x+n)Al_3x+nO_nN_16-n while keeping the cation ratios of RE, Si and Al constant. </p><p>Monophasic α-sialon ceramics with tailored microstructures, consisting of either fine equiaxed or elongated grains, have been obtained by using SPS, whether or not such an extra liquid phase is involved. The three processes, namely densification, phase transformation and grain growth, which usually occur simultaneously during conventional HP consolidation of Si₃N₄-based ceramics, have been precisely followed and separately investigated in the SPS process.</p><p>The enhanced densification is attributed to the non-equilibrium nature of the liquid phase formed during heating. The dominating mechanism during densification is the enhanced grain boundary sliding accompanied by diffusion- and/or reaction-controlled processes. The rapid grain growth is ascribed to a <i>dynamic ripening</i> mechanism based on the formation of a liquid phase that is grossly out of equilibrium, which in turn generates an extra chemical driving force for mass transfer. Monophasic α-sialon ceramics with interlocking microstructures exhibit improved damage tolerance. Y/Yb- stabilised monophasic α-sialon ceramics containing approximately 3 vol% liquid with refined interlocking microstructures have excellent thermal-shock resistance, comparable to the best β-sialon ceramics with 20 vol% additional liquid phase prepared by HP. </p><p>The obtained sialon ceramics with fine-grained microstructure show formidably improved <i>superplasticity</i> in the presence of an electric field. The compressive strain rate reaches the order of 10^-2 s^-1 at temperatures above 1500oC, that is, two orders of magnitude higher than that has been realised so far by any other conventional approaches. The high deformation rate recorded in this work opens up possibilities for making ceramic components with complex shapes through super-plastic forming. </p>

Dans le cadre d'exigences environnementales toujours plus strictes, l'allègement des véhicules automobiles, à un coût maitrisé, est aujourd'hui un objectif fondamental des constructeurs. Jusqu'à aujourd'hui, l'effort d'innovation consenti par les sidérurgistes a permis à l'acier de conserver sa position dominante sur les alliages légers. Néanmoins, les performances des nuances actuelles au carbone montrent une évolution asymptotique. La métallurgie des aciers à l'azote constitue d'ores et déjà une solution disruptive qui promet de dépasser largement ces performances. Les alliages Fe-Si-N obtenus par nitruration à 570 °C donnent notamment lieu à des réactions de précipitations inédites. Il a été montré que la phase précipitant au cours de la nitruration est le nitrure stoechiométrique Si3N4. Il se présente sous forme de cuboïdes nanométriques dont la structure est amorphe. L'origine de cette morphologie se trouve dans la minimisation de l'énergie élastique engendrée par la précipitation. Ces précipités entrainent un durcissement considérable de la matrice ferritique et abaisse la densité globale du composite final. Les précipités amorphes sont susceptibles de subir une transition vers le cristal si les alliages nitrurés sont ensuite recuits dans une atmosphère dénitrurante. Les cristallites obtenues se présentent sous forme de prismes hexagonaux et ont une structure appartenant au groupe spatial P62c. La composition Si3N4 reste par contre inchangée. Enfin, il a été démontré que cette transition peut être modélisée à l'aide d'un modèle cinétique de précipitation développé spécifiquement dans ce travail pour prendre en compte les particularités du traitement de nitruration / In the context of ever more stringent environmental regulations, cost-effective weight savings have become a high-priority objective for car makers. Until today, the research effort deployed by steel makers has kept steel in a dominating position on this market against light alloys. However, the performances of current carbon steel grades start to show an asymptotic evolution. Nitrogen steel metallurgy represents a disruptive concept which is bound to outperform by far these current grades. Fe-Si-N alloys obtained through nitriding at 570 °C give rise to unexpected precipitation reactions. It has been shown that the species precipitating during nitriding is the stoichiometric nitride Si3N4. The precipitates display the unusual combination of an amorphous structure with a cuboidal morphology. This morphology can be explained by considering the minimization of the precipitation-induced elastic stress. This precipitation results in substantial hardening of the ferritic matrix and contributes to lowering the density of the final composite. The amorphous precipitates undergo a transition to a crystalline structure when the nitride alloys are subjected to annealing in a denitriding atmosphere. The occurring crystallites precipitate in the form of hexagonal prisms and exhibit a structure belonging to the P62c space group. Their composition however remains Si3N4. Finally, it has been demonstrated that such a transition can be modeled by the means of a kinetic model specifically developed in the present work to account for characteristic aspects of the nitriding treatment

Orientador: Leandro Russovski Tessler / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-09-11T21:07:05Z (GMT). No. of bitstreams: 1 BiggemannTejero_DanielCarlos_D.pdf: 10164089 bytes, checksum: 92ca23a6073fc8197bc0a0519b8227b1 (MD5) Previous issue date: 2005 / Resumo: Nesse trabalho apresentamos o estudo da otimização da fotoluminescência (PL) de filmes finos de a-SiNx:H<Nd> preparados pela técnica de RF co- sputtering. A PL foi estudada em função da concentração de nitrogênio e de neodímio. Foi observado que os íons são excitados através da matriz amorfa. O mecanismo de excitação é mais eficiente em amostras com gap óptico E04 aproximadamente igual ao dobro da transição 4 I 9/2 ® 3 F 3/2 , indicando um processo de excitação dos íons dominantemente via recombinações não-radiativas de elétrons da cauda de banda de condução nas dangling bonds. O modelo mais adequado para descrever a excitação dos íons Nd 3+ é o DRAE (Defect Related Auger Excitation), que foi proposto originalmente para o Er 3+ em a-Si:H. Foi feito um estudo da PL com o tratamento térmico das amostras até temperaturas de 700°C. Os resultados de medidas de micro-Raman e HRTEM (High Resolution Transmission Electron Microscopy) mostram que as mudanças na estrutura dos filmes (presença de nano-cristais de Si e/ou Si3 N4 ) aparecem quando a PL não é mais detectável. Isso implica que o tratamento térmico aumenta a PL principalmente deixando o entorno químico dos íons Nd3+ mais favorável para as transições 4f. Em amostras na geometria de guia de onda planar, fizermos medidas de ganho óptico, tempo de vida da PL em função da temperatura e da potência de excitação. Os resultados mostram ganho óptico no material somente a baixas temperaturas e sob excitações acima de 5 kW/cm 2 . A PL em função da intensidade de excitação apresenta mudança de derivada também acima de 5 kW/cm 2 . Esses resultados permitem considerar o material como promissor para aplicações em amplificadores ópticos integrados / Abstract: In this work, we report a study of the photoluminescence (PL) optimization of a-SiNx:H<Nd> thin films prepared by RF co-sputtering. The PL was investigated as a function of nitrogen and neodymium concentrations. We observed that the Nd ions are excited through the amorphous matrix. The excitation mechanism is more efficient in samples where the optical gap E04 is twice the 4 I 9/2 ® 3 F 3/2 transition of Nd ions, showing an excitation process mostly dominated by non-radiative recombinations of electrons from conduction band tails into dangling bonds. The most adequate model to describe the excitation of Nd 3+ ions is the DRAE model (Defect Related Auger Excitation), originally proposed for Er 3+ in a-Si:H. We study the PL of the samples with thermal annealing at temperatures up to 700°C. Micro Raman and HRTEM (High Resolution Transmission Electron Microscopy) measurements show that small structural changes (presence of Si and/or Si3 N4 nano crystals) appear when no more PL is detectable. This implies that the annealing enhances the PL mainly modifying the chemical neighborhood of the Nd3+ ions to be more favorable for the 4f transitions. In samples with planar waveguide geometry, we performed optical gain measurements, PL lifetime as a function of temperature and excitation power. The results showed optical gain only at low temperatures and under excitation intensities higher than 5 kW/cm 2. The behavior of the PL as a function of excitation intensity shows a change in its derivate also at an excitation power higher than 5 kW/cm 2 . These results allow us to consider this material as promising for applications in integrated optical amplifiers / Doutorado / Física da Matéria Condensada / Doutor em Ciências