Integrating Metal-Oxide-Decorated CNT Networks with a CMOS Readout in a Gas Sensor

We have implemented a tin-oxide-decorated carbon nanotube (CNT) network gas sensor system on a single die. We have also demonstrated the deposition of metallic tin on the CNT network, its subsequent oxidation in air, and the improvement of the lifetime of the sensors. The fabricated array of CNT sensors contains 128 sensor cells for added redundancy and increased accuracy. The read-out integrated circuit (ROIC) was combined with coarse and fine time-to-digital converters to extend its resolution in a power-efficient way. The ROIC is fabricated using a 0.35 μm CMOS process, and the whole sensor system consumes 30 mA at 5 V. The sensor system was successfully tested in the detection of ammonia gas at elevated temperatures

Optics of atomically thin films and van der Waals heterostructures made from two-dimensional semiconductors

This thesis discusses optical investigations of two-dimensional metal-chalcogenide semiconductor materials and their heterostructures. Topics include a study of continuous wave (cw) and time-resolved photoluminescence (PL) of GaTe and GaSe thin films. Based on experimental evidence, we propose a model explaining the strong PL intensity decrease for thin films as a result of non-radiative carrier escape via surface states. We investigate the stability of thin films of InSe and GaSe using a combination of PL and Raman spectroscopies. By comparing signal intensities in films exposed to ambient conditions for up to 100 hours, we find notable degradation in GaSe and high stability of InSe. We continue our study with the investigation of optical properties of light emitting diodes (LED) made of van der Waals (vdW) heterostructures comprising graphene as transparent contacts, hexagonal boron nitride as tunnel barriers and transition metal dichalcogenides (TMDC), MoS2 and WS2, as the semiconductor active regions. Single and multiple 'quantum well' structures were fabricated with an aim to enhance the external quantum efficiency (EQE) under electrical injection. We also present PL characterisation of LEDs based on vdW heterostructures comprising WSe2 and MoSe2 as active layers. Temperature dependent experiments show unusual enhancement of the EQE with temperature in WSe2 in contrast to MoSe2, where both electroluminescence and PL are reduced with temperature. A theoretical approach to explain this behaviour is proposed, which is based on the strong spin-orbit interaction present in both materials

Spatial Dependence of Photocurrent & Photogeneration Mechanisms in Graphene Field Effect Transistors

Graphene is a fascinating 2D material, known for its unique charge transport and optical properties due to its low dimensionality and unique band structure. Although photocurrents in graphene have been heavily studied, there is little consensus on the photogeneration mechanisms contributing to photocurrents in applied graphene devices. There are two primary contributors to photocurrent that we investigate herein: the photovoltaic effect and the photothermoelectric effect. For short-circuit measurement configurations, the photobolometric effect is negligible due to requiring a non-zero bias voltage. Understanding the role each mechanism plays can aid in the design and operation of graphene-based photodetectors. If the mechanisms’ contributions are tunable, we can design a photodetector such that the most photoresponsive mechanism dominates, resulting in greater photosensitivity. We report simultaneous photocurrent and micro-Raman measurements in mono- and bi-layer graphene rectangular transistors of at least 2 μm width and 4 μm length, on Si substrate with 300 nm SiO2 layer at room temperature and ambient pressure in source-drain configuration, seeking to disambiguate the contribution between photovoltaic and photothermoelectric effects from spatial and power dependencies. Devices presented demonstrated photoresponsivities of up to (229.4±2.5) μA W−1 for bilayer and (159±2) μA W−1 for monolayer when comparable in size and shape. To ensure consistent and comparable results throughout our experiments, we measure Raman spectra during the photoresponse measurements, as well as gate sweeps before each set of measurements. We found that in order to yield reproducible results without a vacuum, we must employ a laser-annealing technique to reduce the influence of surface moisture. Adsorbed water molecules dope the graphene with holes, affecting transport, but through laser annealing we can ensure that the sample is in the same initial state before each experiment. We measured the photocurrents while observing their dependence on laser spot position on the sample and on laser power intensity. The photocurrent exponents extracted ranged from 0.6 to 1.1, indicating that likely both photovoltaic and photothermoelectric effects contribute to the total photocurrent in varying amounts, with photovoltaic being the dominant effect close to the contacts, likely due to limitations of the electron mean free path of around 7-200 nm and laser spot FWHM between 0.3 μm and 0.4 μm. We also noted that some sample properties evolved over the course of hours or days, suggesting perhaps a shift in charge density during the course of longer experiments experiment

Characterisation and Functionalisation of Ultrabithorax Materials for Biosensing

Ultrabithorax (Ubx) is a Hox transcription factor, which self-assembles into protein films and fibres at the air-water interface. Ubx materials are bio- and cyto-compatible, and can be functionalised with DNA, proteins, and growth factors to benefit from functions such as supporting cell proliferation. This thesis investigated the optical, electrical, and mechanical properties of Ubx fusion fibres in conditions relevant to applications in biosensing and tissue engineering. The steady-state and time-resolved spectra of the fibres were measured using an ultrafast laser source. The dityrosine emission peak red-shifted by 50nm in fibres compared to Ubx fusion solutions, and resonance energy transfer between dityrosine and enhanced green fluorescent protein (EGFP) was observed in the EGFP-Ubxprotein fusion. The electrical properties of Ubx fusion fibres were tested, and anincrease in their electrical conductivity by 3 orders of magnitude was measuredwith rising relative humidity. Tensile tests of Ubx fusion fibres revealed that thefibres were less extensible but stronger after prolonged storage and rehydration,which could influence the design of Ubx materials for tissue engineering. Significant binding of DNA aptamers to Ubx in solution and in fibres was observed. A fluorescence-based method to assess binding eciency of bacteria and the SARSCoV-2 spike RBD protein was developed. Some indication of increased specific pathogen binding was observed using long oligonucleotide sequences bound to Ubx fusion fibres, and improvements to this system were suggested. Alginate and collagen are biomaterials widely used in tissue engineering. Preliminary experiments were conducted that showed the feasibility of production of composite materials made of Ubx and alginate or collagen, which could be applied to createfunctional tissue scaffolds. Ubx-based platforms and composite materials couldbenefit from the intrinsic properties of Ubx, and Ubx functionalisation with proteins,growth factors and DNA aptamers for applications in biosensing and tissueengineering

Broadcast-oriented wireless network-on-chip : fundamentals and feasibility

Premi extraordinari doctorat UPC curs 2015-2016, àmbit Enginyeria de les TICRecent years have seen the emergence and ubiquitous adoption of Chip Multiprocessors (CMPs), which rely on the coordinated operation of multiple execution units or cores. Successive CMP generations integrate a larger number of cores seeking higher performance with a reasonable cost envelope. For this trend to continue, however, important scalability issues need to be solved at different levels of design. Scaling the interconnect fabric is a grand challenge by itself, as new Network-on-Chip (NoC) proposals need to overcome the performance hurdles found when dealing with the increasingly variable and heterogeneous communication demands of manycore processors. Fast and flexible NoC solutions are needed to prevent communication become a performance bottleneck, situation that would severely limit the design space at the architectural level and eventually lead to the use of software frameworks that are slow, inefficient, or less programmable. The emergence of novel interconnect technologies has opened the door to a plethora of new NoCs promising greater scalability and architectural flexibility. In particular, wireless on-chip communication has garnered considerable attention due to its inherent broadcast capabilities, low latency, and system-level simplicity. Most of the resulting Wireless Network-on-Chip (WNoC) proposals have set the focus on leveraging the latency advantage of this paradigm by creating multiple wireless channels to interconnect far-apart cores. This strategy is effective as the complement of wired NoCs at moderate scales, but is likely to be overshadowed at larger scales by technologies such as nanophotonics unless bandwidth is unrealistically improved. This dissertation presents the concept of Broadcast-Oriented Wireless Network-on-Chip (BoWNoC), a new approach that attempts to foster the inherent simplicity, flexibility, and broadcast capabilities of the wireless technology by integrating one on-chip antenna and transceiver per processor core. This paradigm is part of a broader hybrid vision where the BoWNoC serves latency-critical and broadcast traffic, tightly coupled to a wired plane oriented to large flows of data. By virtue of its scalable broadcast support, BoWNoC may become the key enabler of a wealth of unconventional hardware architectures and algorithmic approaches, eventually leading to a significant improvement of the performance, energy efficiency, scalability and programmability of manycore chips. The present work aims not only to lay the fundamentals of the BoWNoC paradigm, but also to demonstrate its viability from the electronic implementation, network design, and multiprocessor architecture perspectives. An exploration at the physical level of design validates the feasibility of the approach at millimeter-wave bands in the short term, and then suggests the use of graphene-based antennas in the terahertz band in the long term. At the link level, this thesis provides an insightful context analysis that is used, afterwards, to drive the design of a lightweight protocol that reliably serves broadcast traffic with substantial latency improvements over state-of-the-art NoCs. At the network level, our hybrid vision is evaluated putting emphasis on the flexibility provided at the network interface level, showing outstanding speedups for a wide set of traffic patterns. At the architecture level, the potential impact of the BoWNoC paradigm on the design of manycore chips is not only qualitatively discussed in general, but also quantitatively assessed in a particular architecture for fast synchronization. Results demonstrate that the impact of BoWNoC can go beyond simply improving the network performance, thereby representing a possible game changer in the manycore era.Avenços en el disseny de multiprocessadors han portat a una àmplia adopció dels Chip Multiprocessors (CMPs), que basen el seu potencial en la operació coordinada de múltiples nuclis de procés. Generacions successives han anat integrant més nuclis en la recerca d'alt rendiment amb un cost raonable. Per a que aquesta tendència continuï, però, cal resoldre importants problemes d'escalabilitat a diferents capes de disseny. Escalar la xarxa d'interconnexió és un gran repte en ell mateix, ja que les noves propostes de Networks-on-Chip (NoC) han de servir un tràfic eminentment variable i heterogeni dels processadors amb molts nuclis. Són necessàries solucions ràpides i flexibles per evitar que les comunicacions dins del xip es converteixin en el pròxim coll d'ampolla de rendiment, situació que limitaria en gran mesura l'espai de disseny a nivell d'arquitectura i portaria a l'ús d'arquitectures i models de programació lents, ineficients o poc programables. L'aparició de noves tecnologies d'interconnexió ha possibilitat la creació de NoCs més flexibles i escalables. En particular, la comunicació intra-xip sense fils ha despertat un interès considerable en virtut de les seva baixa latència, simplicitat, i bon rendiment amb tràfic broadcast. La majoria de les Wireless NoC (WNoC) proposades fins ara s'han centrat en aprofitar l'avantatge en termes de latència d'aquest nou paradigma creant múltiples canals sense fils per interconnectar nuclis allunyats entre sí. Aquesta estratègia és efectiva per complementar a NoCs clàssiques en escales mitjanes, però és probable que altres tecnologies com la nanofotònica puguin jugar millor aquest paper a escales més grans. Aquesta tesi presenta el concepte de Broadcast-Oriented WNoC (BoWNoC), un nou enfoc que intenta rendibilitzar al màxim la inherent simplicitat, flexibilitat, i capacitats broadcast de la tecnologia sense fils integrant una antena i transmissor/receptor per cada nucli del processador. Aquest paradigma forma part d'una visió més àmplia on un BoWNoC serviria tràfic broadcast i urgent, mentre que una xarxa convencional serviria fluxos de dades més pesats. En virtut de la escalabilitat i del seu suport broadcast, BoWNoC podria convertir-se en un element clau en una gran varietat d'arquitectures i algoritmes poc convencionals que milloressin considerablement el rendiment, l'eficiència, l'escalabilitat i la programabilitat de processadors amb molts nuclis. El present treball té com a objectius no només estudiar els aspectes fonamentals del paradigma BoWNoC, sinó també demostrar la seva viabilitat des dels punts de vista de la implementació, i del disseny de xarxa i arquitectura. Una exploració a la capa física valida la viabilitat de l'enfoc usant tecnologies longituds d'ona milimètriques en un futur proper, i suggereix l'ús d'antenes de grafè a la banda dels terahertz ja a més llarg termini. A capa d'enllaç, la tesi aporta una anàlisi del context de l'aplicació que és, més tard, utilitzada per al disseny d'un protocol d'accés al medi que permet servir tràfic broadcast a baixa latència i de forma fiable. A capa de xarxa, la nostra visió híbrida és avaluada posant èmfasi en la flexibilitat que aporta el fet de prendre les decisions a nivell de la interfície de xarxa, mostrant grans millores de rendiment per una àmplia selecció de patrons de tràfic. A nivell d'arquitectura, l'impacte que el concepte de BoWNoC pot tenir sobre el disseny de processadors amb molts nuclis no només és debatut de forma qualitativa i genèrica, sinó també avaluat quantitativament per una arquitectura concreta enfocada a la sincronització. Els resultats demostren que l'impacte de BoWNoC pot anar més enllà d'una millora en termes de rendiment de xarxa; representant, possiblement, un canvi radical a l'era dels molts nuclisAward-winningPostprint (published version

Broadcast-oriented wireless network-on-chip : fundamentals and feasibility

Premi extraordinari doctorat UPC curs 2015-2016, àmbit Enginyeria de les TICRecent years have seen the emergence and ubiquitous adoption of Chip Multiprocessors (CMPs), which rely on the coordinated operation of multiple execution units or cores. Successive CMP generations integrate a larger number of cores seeking higher performance with a reasonable cost envelope. For this trend to continue, however, important scalability issues need to be solved at different levels of design. Scaling the interconnect fabric is a grand challenge by itself, as new Network-on-Chip (NoC) proposals need to overcome the performance hurdles found when dealing with the increasingly variable and heterogeneous communication demands of manycore processors. Fast and flexible NoC solutions are needed to prevent communication become a performance bottleneck, situation that would severely limit the design space at the architectural level and eventually lead to the use of software frameworks that are slow, inefficient, or less programmable. The emergence of novel interconnect technologies has opened the door to a plethora of new NoCs promising greater scalability and architectural flexibility. In particular, wireless on-chip communication has garnered considerable attention due to its inherent broadcast capabilities, low latency, and system-level simplicity. Most of the resulting Wireless Network-on-Chip (WNoC) proposals have set the focus on leveraging the latency advantage of this paradigm by creating multiple wireless channels to interconnect far-apart cores. This strategy is effective as the complement of wired NoCs at moderate scales, but is likely to be overshadowed at larger scales by technologies such as nanophotonics unless bandwidth is unrealistically improved. This dissertation presents the concept of Broadcast-Oriented Wireless Network-on-Chip (BoWNoC), a new approach that attempts to foster the inherent simplicity, flexibility, and broadcast capabilities of the wireless technology by integrating one on-chip antenna and transceiver per processor core. This paradigm is part of a broader hybrid vision where the BoWNoC serves latency-critical and broadcast traffic, tightly coupled to a wired plane oriented to large flows of data. By virtue of its scalable broadcast support, BoWNoC may become the key enabler of a wealth of unconventional hardware architectures and algorithmic approaches, eventually leading to a significant improvement of the performance, energy efficiency, scalability and programmability of manycore chips. The present work aims not only to lay the fundamentals of the BoWNoC paradigm, but also to demonstrate its viability from the electronic implementation, network design, and multiprocessor architecture perspectives. An exploration at the physical level of design validates the feasibility of the approach at millimeter-wave bands in the short term, and then suggests the use of graphene-based antennas in the terahertz band in the long term. At the link level, this thesis provides an insightful context analysis that is used, afterwards, to drive the design of a lightweight protocol that reliably serves broadcast traffic with substantial latency improvements over state-of-the-art NoCs. At the network level, our hybrid vision is evaluated putting emphasis on the flexibility provided at the network interface level, showing outstanding speedups for a wide set of traffic patterns. At the architecture level, the potential impact of the BoWNoC paradigm on the design of manycore chips is not only qualitatively discussed in general, but also quantitatively assessed in a particular architecture for fast synchronization. Results demonstrate that the impact of BoWNoC can go beyond simply improving the network performance, thereby representing a possible game changer in the manycore era.Avenços en el disseny de multiprocessadors han portat a una àmplia adopció dels Chip Multiprocessors (CMPs), que basen el seu potencial en la operació coordinada de múltiples nuclis de procés. Generacions successives han anat integrant més nuclis en la recerca d'alt rendiment amb un cost raonable. Per a que aquesta tendència continuï, però, cal resoldre importants problemes d'escalabilitat a diferents capes de disseny. Escalar la xarxa d'interconnexió és un gran repte en ell mateix, ja que les noves propostes de Networks-on-Chip (NoC) han de servir un tràfic eminentment variable i heterogeni dels processadors amb molts nuclis. Són necessàries solucions ràpides i flexibles per evitar que les comunicacions dins del xip es converteixin en el pròxim coll d'ampolla de rendiment, situació que limitaria en gran mesura l'espai de disseny a nivell d'arquitectura i portaria a l'ús d'arquitectures i models de programació lents, ineficients o poc programables. L'aparició de noves tecnologies d'interconnexió ha possibilitat la creació de NoCs més flexibles i escalables. En particular, la comunicació intra-xip sense fils ha despertat un interès considerable en virtut de les seva baixa latència, simplicitat, i bon rendiment amb tràfic broadcast. La majoria de les Wireless NoC (WNoC) proposades fins ara s'han centrat en aprofitar l'avantatge en termes de latència d'aquest nou paradigma creant múltiples canals sense fils per interconnectar nuclis allunyats entre sí. Aquesta estratègia és efectiva per complementar a NoCs clàssiques en escales mitjanes, però és probable que altres tecnologies com la nanofotònica puguin jugar millor aquest paper a escales més grans. Aquesta tesi presenta el concepte de Broadcast-Oriented WNoC (BoWNoC), un nou enfoc que intenta rendibilitzar al màxim la inherent simplicitat, flexibilitat, i capacitats broadcast de la tecnologia sense fils integrant una antena i transmissor/receptor per cada nucli del processador. Aquest paradigma forma part d'una visió més àmplia on un BoWNoC serviria tràfic broadcast i urgent, mentre que una xarxa convencional serviria fluxos de dades més pesats. En virtut de la escalabilitat i del seu suport broadcast, BoWNoC podria convertir-se en un element clau en una gran varietat d'arquitectures i algoritmes poc convencionals que milloressin considerablement el rendiment, l'eficiència, l'escalabilitat i la programabilitat de processadors amb molts nuclis. El present treball té com a objectius no només estudiar els aspectes fonamentals del paradigma BoWNoC, sinó també demostrar la seva viabilitat des dels punts de vista de la implementació, i del disseny de xarxa i arquitectura. Una exploració a la capa física valida la viabilitat de l'enfoc usant tecnologies longituds d'ona milimètriques en un futur proper, i suggereix l'ús d'antenes de grafè a la banda dels terahertz ja a més llarg termini. A capa d'enllaç, la tesi aporta una anàlisi del context de l'aplicació que és, més tard, utilitzada per al disseny d'un protocol d'accés al medi que permet servir tràfic broadcast a baixa latència i de forma fiable. A capa de xarxa, la nostra visió híbrida és avaluada posant èmfasi en la flexibilitat que aporta el fet de prendre les decisions a nivell de la interfície de xarxa, mostrant grans millores de rendiment per una àmplia selecció de patrons de tràfic. A nivell d'arquitectura, l'impacte que el concepte de BoWNoC pot tenir sobre el disseny de processadors amb molts nuclis no només és debatut de forma qualitativa i genèrica, sinó també avaluat quantitativament per una arquitectura concreta enfocada a la sincronització. Els resultats demostren que l'impacte de BoWNoC pot anar més enllà d'una millora en termes de rendiment de xarxa; representant, possiblement, un canvi radical a l'era dels molts nuclisAward-winningPostprint (published version

14- by 22-Foot Subsonic Tunnel Laser Velocimeter Upgrade

A long-focal length laser velocimeter constructed in the early 1980's was upgraded using current technology to improve usability, reliability and future serviceability. The original, free-space optics were replaced with a state-of-the-art fiber-optic subsystem which allowed most of the optics, including the laser, to be remote from the harsh tunnel environment. General purpose high-speed digitizers were incorporated in a standard modular data acquisition system, along with custom signal processing software executed on a desktop computer, served as the replacement for the signal processors. The resulting system increased optical sensitivity with real-time signal/data processing that produced measurement precisions exceeding those of the original system. Monte Carlo simulations, along with laboratory and wind tunnel investigations were used to determine system characteristics and measurement precision

Single-molecule fluorescence spectroscopy

Single-molecule fluorescence spectroscopy is a powerful tool for the study of physical and biological processes through the use of fluorescent probes. By combining the femtoliter-sized observation volume of a confocal microscope with low concentrations of analytes, single fluorescent molecules can be observed as they freely diffuse in solution. From the many parameters of the fluorescence signal, a wealth of information is obtained about the structure, dynamics and interactions of the studied system. The objective of this thesis was the development, implementation and application of quantitative single-molecule fluorescence methods. To this end, a software framework for the analysis of solution-based single-molecule measurements of Förster resonance energy transfer (FRET) has been developed as part of the PAM software package. In addition, the new method of three-color photon distribution analysis (3C-PDA) is introduced in this thesis, enabling a quantitative analysis of single-molecule three-color FRET experiments. The developed analysis framework has been applied to elucidate coordinated conformational changes in the Hsp70 chaperone protein BiP, to study the conformational dynamics of a small fragment of the cellulosome, to investigate energy transfer pathways in complex artificial dye arrangements and to quantify the nanosecond dynamics of an intrinsically disordered peptide. For several studies, molecular dynamics (MD) simulations have also been used to support and cross-validate the experimental results. Here, the focus is to provide a comprehensive overview of the used methodologies, their theoretical background and their application to the various experimental systems

Single-molecule fluorescence spectroscopy

Single-molecule fluorescence spectroscopy is a powerful tool for the study of physical and biological processes through the use of fluorescent probes. By combining the femtoliter-sized observation volume of a confocal microscope with low concentrations of analytes, single fluorescent molecules can be observed as they freely diffuse in solution. From the many parameters of the fluorescence signal, a wealth of information is obtained about the structure, dynamics and interactions of the studied system. The objective of this thesis was the development, implementation and application of quantitative single-molecule fluorescence methods. To this end, a software framework for the analysis of solution-based single-molecule measurements of Förster resonance energy transfer (FRET) has been developed as part of the PAM software package. In addition, the new method of three-color photon distribution analysis (3C-PDA) is introduced in this thesis, enabling a quantitative analysis of single-molecule three-color FRET experiments. The developed analysis framework has been applied to elucidate coordinated conformational changes in the Hsp70 chaperone protein BiP, to study the conformational dynamics of a small fragment of the cellulosome, to investigate energy transfer pathways in complex artificial dye arrangements and to quantify the nanosecond dynamics of an intrinsically disordered peptide. For several studies, molecular dynamics (MD) simulations have also been used to support and cross-validate the experimental results. Here, the focus is to provide a comprehensive overview of the used methodologies, their theoretical background and their application to the various experimental systems