Nanofabrication and Characterization of Nanoelectronic Biosensors Based on Emerging Layered Semiconductors.

Many important biomedical and clinical applications, such as early-stage cancer diagnosis, autoimmune disease treatment, and real-time monitoring of patients’ immune status, demand new integrated multiplexing nanoelectronic/microfluidic biosensors. These biosensors are anticipated to enable fast (minute-scale) quantification of illness-related biomarkers, unprecedented detection sensitivity, fM-level limit-of-detection (LOD), and point-of-care capability. However, these new highly desirable biosensing capabilities have not been realized yet. Atomically layered transition metal dichalcogenides (TMDCs) have gained a lot of attention because of their excellent electronic and structural properties. Especially, semiconducting TMDCs can serve as an essential complement to zero-band-gap graphene and enable novel semiconductor-related applications, such as thin-film transistors, phototransistors, and various types of sensors. More importantly, such TMDCs hold significant potential to be exploited for making new electronic biosensors and realize the highly desirable biosensing capabilities mentioned above. The research presented in this thesis sought to advance the scientific and technical knowledge for fabricating and operating new TMDC-based electronic/microfluidic-integrated biosensors and realizing rapid fM-level quantification of biomarkers. The first part (i.e., the second chapter) is mainly focused on developing a top-down nanofabrication approach for producing orderly arranged, pristine few-layer MoS2 flakes, which holds significant potential to be developed into a upscalable nanomanufacturing technology. The second part (i.e., the third-to-fifth chapters) presents a systematic study on the biosensing characteristics of the TMDC-based transistor sensors fabricated using our nanoprinting techniques. First, multiple sets of MoS2-based transistor biosensors were fabricated using our plasma-assisted nanoprinting method. Second, we studied the underlying device physics governing the response characteristics of TDMC transistor biosensors. Third, we further studied a cycle-wise method for operating MoS2/WSe2-based transistor biosensors to enable rapid, low-noise, highly specific biomolecule quantification at femtomolar levels. The presented research has leveraged the superior electronic properties of emerging layered semiconductors for biosensing applications and advances label-free biosensing techniques toward realizing fast real-time immunoassay for low-abundance biomolecule detection. Moreover, the nanofabrication approaches developed in this research can be generally utilized for making other nanoelectronic devices based on emerging 2D layered materials, and the obtained device physics knowledge is anticipated to greatly leverage the excellent electronic and structural properties of TMDCs for other relevant sensing applications.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135796/1/aquantum_1.pd

Magnetic relaxation phenomena and cluster glass properties of La{0.7-x}Y{x}Ca{0.3}MnO{3} manganites

The dynamic magnetic properties of the distorted perovskite system La{0.7-x}Y{x}Ca{0.3}MnO{3} (0 <= x <= 0.15) have been investigated by ac-susceptibility and dc magnetization measurements, with emphasis on relaxation and aging studies. They evidence for x >= 0.10 the appearance of a metallic cluster glass phase, that develops just below the ferromagnetic transition temperature. The clusters grow with decreasing temperature down to a temperature T(f0) at which they freeze due to severe intercluster frustration. The formation of these clusters is explained by the presence of yttrium induced local structural distortions that create localized spin disorder in a magnetic lattice where double-exchange ferromagnetism is dominant.Comment: Accepted for publication in Phys. Rev.

A Multi-Class Multi-Movement Vehicle Counting Framework for Traffic Analysis in Complex Areas Using CCTV Systems

Traffic analysis using computer vision techniques is attracting more attention for the development of intelligent transportation systems. Consequently, counting traffic volume based on the CCTV system is one of the main applications. However, this issue is still a challenging task, especially in the case of complex areas that involve many vehicle movements. This study performs an investigation of how to improve video-based vehicle counting for traffic analysis. Specifically, we propose a comprehensive framework with multiple classes and movements for vehicle counting. In particular, we first adopt state-of-the-art deep learning methods for vehicle detection and tracking. Then, an appropriate trajectory approach for monitoring the movements of vehicles using distinguished regions tracking is presented in order to improve the performance of the counting. Regarding the experiment, we collect and pre-process the CCTV data at a complex intersection to evaluate our proposed framework. In particular, the implementation indicates the promising results of our proposed method, which achieve accuracy around 80% to 98% for different movements for a very complex scenario with only a single view of the camera

Dynamic Spatial Transformer WaveNet Network for Traffic Forecasting

Traffic forecasting has emerged as an important task for developing intelligent transportation systems. Recent works focus on representing traffic as graph operation and using graph neural networks for spatial–temporal prediction. Most of the approaches assume a predefined graph structure based on node distances. However, spatial dependencies change over time in many scenarios of traffic flow. In this regard, this study takes an investigation capturing the spatial and temporal dependencies with no prior knowledge structure of traffic road networks. Specifically, we propose a multi-step prediction model named Dynamic Spatial Transformer WaveNet Network (DSTWN) to capture the dynamic conditions and directions of traffic flow in which a temporal convolution layer is adopted for the long time sequence and a spatial transformer layer is proposed to capture the dynamic spatial dependencies. Furthermore, we introduce a new traffic dataset, which is collected from the vehicle detection system in an urban area (UVDS). In particular, compared with existing benchmark traffic data, UVDS contains more complicated spatial information, which is similar to many real-world scenarios of traffic flow. Experiments on both benchmark traffic datasets indicate the promising results of DSTWN compared with state-of-the-art models in this research field

Diacetylene phospholipid-mediated synthesis of germania nanotubules and nanoparticles

During the past two decades, the scallop (Argopecten Purpuratus) culture developed in the Peruvian coastal bays. The trophic availability linked to the upwelling system supports the production scallop. However, the Peruvian coasts are also known to have a high environmental variability especially in oceanic domain. Although scallop farms are vulnerable to production hazards (mortality, low growth), environmental variability in coastal bays of Peru and its effects on growth, reproduction and survival of this socially sensitive resource have been poorly studied. Paracas Bay in Pisco Peru is a traditional farming area where scallop highs and lows in productivity related to environmental conditions were recorded throughout its history. In order increase our knowledge on this issue, this study arises from three approaches : (1) observation in situ, (2) experimental physiology and (3) modelling of the energy budget of A. Purpuratus. An environmental monitoring conducted in the Paracas Bay shows that the oceanographic variability can be important, especially during the summer. Temperature variations of 8°C and oxic conditions ranging from supersaturation to anoxia (absence of oxygen) in the course of a day were observed. The high frequency monitoring has revealed a chronic, severe and prolonged hypoxic condition in Paracas Bay. Scallops grown on the bottom, where exposure to hypoxia was important (47% of the observed time) showed lower growth and reproductions conditions. However, during the summer, prolonged and severe hypoxic events affected both deep culture – scallops grown in suspension and on bottom- causing weight somatic tissue losses and cessation of reproduction. During the laboratory experiments, scallops showed significant ability to regulate their oxygen uptake face to decreased oxygen saturation up to 24%. Surprisingly, we found that this species is able to maintain filtration, although diminished, even at low oxygen saturations (5%). Based on the physiological responses of the Peruvian scallops face to hypoxia and the energy performance aerobic end anaerobic metabolism ; it is hypothesized that there exist a restriction in the energy flow available for metabolism at oxygen saturations below the regulation capacity of the organism. Model simulations including this energy restriction (on assimilation and reserves mobilization fluxes) against hypoxia can reproduce successfully field observations of Paracas Bay : greater exposure to hypoxia results in a reduced growth and reproductive conditions. Although the scallop has physiological adaptations/metabolism to deal with limited oxygen conditions, growth and reproduction can be compromised, affecting culture productivity of this species (according to the frequency, duration and intensity hypoxia). The results of observations, experiments and simulations obtained during this study provide useful information to better manage of Peruvian scallop cultures (ex. Load capacity estimates in the bays, evaluations of adequate areas/depths for culture, etc.).Au cours de ces deux dernières décennies, la culture du pétoncle (Argopecten purpuratus) s’est développée dans les baies côtières péruviennes. La disponibilité trophique liée au système d’upwelling est favorable à la production du pétoncle. Cependant, les côtes péruviennes sont également connues pour présenter une forte variabilité environnementale surtout en domaine océanique. Bien que les élevages du pétoncle soient vulnérables aux aléas de production (mortalité, croissance faible), la variabilité environnementale dans les baies côtières du Pérou et ses effets sur la croissance, la reproduction et survie de cette ressource socialement sensible ont été peu étudiées. La baie de Paracas au Pisco-Pérou est une zone traditionnelle de culture du pétoncle où des hauts et des bas productifs liés aux conditions environnementales ont été enregistrés au long de son histoire. Dans le but d’approfondir nos connaissances sur cette problématique, cette étude se pose sous trois approches : (1) l’observation in situ, (2) l’expérimentation en physiologie et (3) la modélisation du bilan énergétique de A. Purpuratus. Un suivi environnemental mené dans la baie de Paracas montre que la variabilité océanographique peut être importante, en particulier pendant l’été. Des variations de température de 8°C et des conditions oxiques allant de la sursaturation à l’anoxie (absence d’oxygène) dans le cours d’une journée ont été observées. L’enregistrement haute fréquence a permis de révéler une exposition chronique, sévère et prolongée de la baie de Paracas aux conditions hypoxiques. Les pétoncles cultivés sur le fond, où l’exposition à l’hypoxie était importante (47% du temps observé) ont montré une croissance et les conditions de reproduction plus faibles. Cependant, au cours de l’été, les événements hypoxiques prolongés et sévères ont touché les deux profondeurs de culture- les pétoncles cultivés en suspension comme sur le fond-, causant des pertes de poids de tissu somatique ainsi que l’arrêt de la reproduction. Durant les expériences en laboratoire, les pétoncles ont montré une importante capacité à réguler leur respiration face à la diminution de la saturation en oxygène jusqu’à 24%. De manière surprenante, nous avons trouvé que cette espèce est capable de maintenir une filtration, quoique diminuée, même à des saturations en oxygène basses (5%). Sur la base des réponses physiologiques du pétoncle face à l’hypoxie et le rendement énergétique moindre du métabolisme anaérobie par rapport au métabolisme aérobie, nous faisons l’hypothèse d’une diminution de l’ensemble du métabolisme à des saturations en oxygène en dessous de la capacité de régulation de l’espèce. Des simulations d’un modèle incluant cette restriction énergétique (sur les flux d’assimilation et de mobilisation de la réserve) en conditions d’hypoxie parviennent à reproduire avec succès les observations de terrain effectuées dans la baie de Paracas : une plus grande exposition à l’hypoxie a pour conséquence une croissance réduite et un arrêt de la reproduction. Alors que le pétoncle possède des adaptations physiologique /métaboliques pour faire face à des conditions limitantes en oxygène, la croissance et la reproduction peuvent être compromises, affectant ainsi la productivité des cultures de cette espèce (cela en fonction de la fréquence, durée et intensité de l’hypoxie). Les résultats des observations, des expériences et des simulations réalisées lors de cette étude fournissent des informations utiles pour mieux gérer la culture de pétoncle péruvien. Sur la base de ces travaux, des estimations de capacité de charge des baies, et des évaluations de zones et profondeurs favorables pour la culture de ces pétoncles pourront être réalisées

MoS₂ Transistors Fabricated <i>via</i> Plasma-Assisted Nanoprinting of Few-Layer MoS₂ Flakes into Large-Area Arrays

Large-area few-layer-MoS₂ device arrays are desirable for scale-up applications in nanoelectronics. Here we present a novel approach for producing orderly arranged, pristine few-layer MoS₂ flakes, which holds significant potential to be developed into a nanomanufacturing technology that can be scaled up. We pattern bulk MoS₂ stamps using lithographic techniques and subsequently transfer-print prepatterned MoS₂ features onto pristine and plasma-charged SiO₂ substrates. Our work successfully demonstrates the transfer printing of MoS₂ flakes into ordered arrays over cm²-scale areas. Especially, the MoS₂ patterns printed on plasma-charged substrates feature a regular edge profile and a narrow distribution of MoS₂ flake thicknesses (<i>i</i>.<i>e</i>., 3.0 ± 1.9 nm) over cm²-scale areas. Furthermore, we experimentally show that our plasma-assisted printing process can be generally used for producing other emerging atomically layered nanostructures (<i>e</i>.<i>g</i>., graphene nanoribbons). We also demonstrate working n-type transistors made from printed MoS₂ flakes that exhibit excellent properties (<i>e</i>.<i>g</i>., ON/OFF current ratio 10⁵–10⁷, field-effect mobility on SiO₂ gate dielectrics 6 to 44 cm²/(V s)) as well as good uniformity of such transistor parameters over a large area. Finally, with additional plasma treatment processes, we also show the feasibility of creation of p-type transistors as well as pn junctions in MoS₂ flakes. This work lays an important foundation for future scale-up nanoelectronic applications of few-layer-MoS₂ micro- and nanostructures

Enhancement of Photovoltaic Response in Multilayer MoS₂ Induced by Plasma Doping

Layered transition-metal dichalcogenides hold promise for making ultrathin-film photovoltaic devices with a combination of excellent photovoltaic performance, superior flexibility, long lifetime, and low manufacturing cost. Engineering the proper band structures of such layered materials is essential to realize such potential. Here, we present a plasma-assisted doping approach for significantly improving the photovoltaic response in multilayer MoS₂. In this work, we fabricated and characterized photovoltaic devices with a vertically stacked indium tin oxide electrode/multilayer MoS₂/metal electrode structure. Utilizing a plasma-induced p-doping approach, we are able to form p–n junctions in MoS₂ layers that facilitate the collection of photogenerated carriers, enhance the photovoltages, and decrease reverse dark currents. Using plasma-assisted doping processes, we have demonstrated MoS₂-based photovoltaic devices exhibiting very high short-circuit photocurrent density values up to 20.9 mA/cm² and reasonably good power-conversion efficiencies up to 2.8% under AM1.5G illumination, as well as high external quantum efficiencies. We believe that this work provides important scientific insights for leveraging the optoelectronic properties of emerging atomically layered two-dimensional materials for photovoltaic and other optoelectronic applications

Syntheses and solar cell applications of conjugated copolymers containing tetrafluorophenylene units

Novel conjugated copolymers containing tetrafluorophenylene unit have been synthesized and evaluated in bulk heterojunction solar cell. The tetrafluorophenylene unit, as the strong electron deficient moeity, has been applied for the syntheses of donor-acceptor type copolymers with a narrow-band-gap for bulk heterojunction solar cells. DTBT, tetrafluorophenylene and four types of BDT derivatives as the electron rich units were incorporated using Stille polymerization to generate PE-BDTF, PO-BDTF, PE-BDTTF and PO-BDTTF. The introduction of even 1% of tetrafluorophenylene unit substituting DTBT of BDTDTBT type of polymers results in significant decrease of the band gap of the polymers. The device with PO-BDTF: PC71BM (1:1) showed an open-circuit voltage (V-OC) of 0.75 V, a short circuit current (J(SC)) of 11.80 mA/cm(2), and a fill factor (FF) of 0.59, which yields PCE of 5.22%. (C) 2015 Elsevier Ltd. All rights reservedclose