286 research outputs found
Velocity saturation in few-layer MoS2 transistor
No full texthttp://www.gianlucafiori.org/articles/fiori_MoS2.pd
An Optimal Subgradient Algorithm with Subspace Search for Costly Convex Optimization Problems
No full textThis paper presents an acceleration of the optimal subgradient algorithm OSGA (Neumaier in Math Program 158(1–2):1–21, 2016) for solving structured convex optimization problems, where the objective function involves costly affine and cheap nonlinear terms. We combine OSGA with a multidimensional subspace search technique, which leads to a low-dimensional auxiliary problem that can be solved efficiently. Numerical results concerning some applications are reported. A software package implementing the new method is available.© The Author(s) 201
Piezoresistive 2D MoS2 : pressure sensor simulation and fabrication
No full textLAUREA MAGISTRALEIl mondo dei materiali due dimensionali (2D) è unico per quanto riguarda le straordinarie proprietà elettriche, ottiche e meccaniche. Questi materiali sono caratterizzati da un legame atomico planare molto più forte rispetto a quello fuori dal piano e possono essere ottenuti rompendo il legame van der Waals in un solido. Recentemente metodi di deposizione, come deposizione chimica o fisica da vapore (CVD o PVD), sono stati sviluppati per una crescita del materiale su un'area più estesa. Negli ultimi decenni, questa classe di materiali ha ricevuto un'enorme attenzione per molteplici applicazioni, dall'elettronica moderna o in altri campi tecnici. I dicalcogenuri dei metalli di transizione (TMDs) stanno ricevendo grande interesse, e in particolare il solfuro di molibdeno (MoS2) è ampiamente studiato per le sue varie funzionalità e la sua compatibilità in un ampio raggio di applicazioni nell'elettronica, nell'optoelettronica e nei sistemi nanoelettromeccanici (NEMS). Il presente lavoro è focalizzato sullo studio delle proprietà elettriche del MoS2 cresciuto secondo la tecnica dell'epitassia in fase vapore metallo-organica (MOVPE) e la sua applicazione nel campo dei sensori NEMS. Dopo una caratterizzazione elettrica delle proprietà fondamentali, viene analizzato l'effetto piezoelettrico del MoS2. Questo fenomeno viene quantificato attraverso estensimetri a cui viene applicato un carico esterno attraverso il quale è possibile estrarre il gauge factor (GF). Quest'ultimo risulta essere compreso tra -50 e -100, che corrisponde ad un buon intervallo di valori se comparato ai materiali tradizionalmente utilizzati nella tecnologia del silicio. Sfruttando questo effetto, nel presente lavoro, viene mostrata la possibilità di utilizzare il MoS2 come materiale detettore in sensori di pressione NEMS basati su una membrana piezoresistiva. Questi sensori vengono dapprima simulati tramite il software COMSOL Multiphysics e successivamente fabbricati. C'è ancora un margine di miglioramento nella fabbricazione del sensore, ma il MoS2 presenta un grosso potenziale nella miniaturizzazione dei sensori e per lo sviluppo e creazione in altre applicazioni nel campo dei NEMS.Two dimensional (2D) inorganic materials are unique in their remarkable electrical, optical, chemical, and mechanical proprieties. Their in-plane atomic bonding is much stronger than that along the out-of-plane direction. These materials can be derived from layered van der Waals solids, but recently there are technologies to grow them with large areas. In the last decade, this class of material received a lot of attention for many kinds of applications in modern electronic and other technical fields. Especially, the interest in 2D layered transition metal dichalcogenides (TMDs) is increasing and, particularly, 2D molybdenum disulfide (MoS2) is being heavily studied due to its novel functionalities and its suitability for a wide range of application in electronic, in optoelectronic, and nanoelectromechanical systems (NEMS). The present work focuses on the investigation of the electrical proprieties of Metalorganic Vapor-Phase Epitaxy (MOVPE) MoS2 and its application in NEMS sensors. After an electrical characterization, the piezoresistive effect of the material is investigated. This phenomenon is quantified through strain sensor devices and the gauge factor can be extracted. The latter is between -50 and -100, which is an interesting range of values when compared to what observed in materials from traditional silicon technology. Taking advantage of this effect, piezoresistive NEMS pressure sensors are simulated through COMSOL Multiphysics and manufactured using MoS2 membrane. There is still a margin of improvement for the device fabrication, but MoS2 shows a great potential for future miniaturization of sensors and the development in other NEMS applications
Weltliche Freuden im Bannkreis der letzten Vier Dinge. Renward Cysats Tragicocomedi Convivii Process (1593)
No full textWorldly pleasures under the spell of the last four things. Renward Cysat’s tragicomedy “Convivii Process”(1593).
Renward Cysat’s tragicomedy “mirror of abundance and abuse in favour of the belly and worldly pleasures” (“Convivii Process”), an adaptation of the French allegory La Condamnation de Banquet, was staged in Lucerne during carnival in 1593. The nucleus of the plot of both plays is simple: excessive eating and drinking brings about visitations of the personified diseases and death. The plays end with a trial and condemnation of gluttony. The French author considers revelry merely as a health issue whereas Cysat, town clerk of the municipality and director of the prestigious wine market plays, interprets the vice of Gula and affiliated misbehavior in a much wider context. In addition to the threat of physical health he points out the social aspects of vicious habits, such as poverty, neglect and moral decay, and depicts the dreadful consequences for the afterlife. Purposeful introducing religious knowledge Cysat transforms the carnival play into a medium of propaganda for the catholic reform and the spiritual guidance provided by the Jesuits
Flexible complementary metal oxide semiconductor logic circuits based on 2D transition metal dichalcogenides
No full textTwo-dimensional materials have emerged as promising candidates for a wide range of potential future applications in electronics owing to their exceptional electrical, optical, and mechanical properties. Besides graphene, many other 2D materials are being investigated, such as hexagonal boron nitride (h-BN) and transition metal dichalcogenides (TMDCs). They are crystalline materials consisting of a single or a few layers of atoms with strong in-plane atomic bonding and weaker bonding along the out-of-plane direction. In particular, TMDCs have attracted attention for thin-film transistor (TFT) technology. TMDCs like molybdenum disulfide (MoS₂) and tungsten diselenide (WSe₂) exhibit unique electronic properties, including a bandgap, a crucial requirement for TFT operation. Furthermore, their atomic-scale thickness enables flexibility, making them ideal for flexible electronics. Research into TMDC-based TFTs aims to optimize their electrical properties, enhance device stability, and develop scalable manufacturing processes, opening up the possibility for the next generation of lightweight and flexible electronics. TMDCs offer a pathway to high-performance TFTs, with potential applications like flexible displays, sensors, and wearable devices. In this PhD thesis, the potential of TMDC transistors for CMOS applications in flexible electronics is explored. Specifically, MoS₂ and WSe₂ were utilized as n- and p-type channels for metal-oxide-field-effect transistors (MOSFETs), respectively. Achieving proper CMOS operation necessitates stable operation of both n- and p-type FETs. An innovative scalable encapsulation method for MoS₂-FETs, utilizing h-BN monolayers as barrier layers between each Al₂O₃ and MoS₂ interface, was investigated. This heterostructure demonstrated a reduction in n-doping induced by Al₂O₃ encapsulation, along with decreased hysteresis for ultra-slow sweeping times, attributed to an improved dielectric interface. Several contact metals were tested to optimize p-type conduction in WSe₂-FETs, with palladium top contacts emerging as superior, showcasing better FET performance (higher mobility and currents levels). After the fabrication of TFT on a flexible foil, the flexibility of these devices was evaluated under various levels of strain, enduring up to 3000 bending cycles without significant degradation. Once n- and p-type transistors were obtained, they were externally connected to realize CMOS inverters, fundamental building blocks for both digital and analogue electronics. These inverters exhibited excellent performance, demonstrating ideal switching behaviour with high gain (up to 100), high noise margin (0.87 VDD), and low average static power consumption (40 pW). These results surpass previous TMDC-based flexible inverters. A scalable process for integrating two different 2D materials on the same foil was then also developed and used for realizing more complex circuits. Inverters, ring oscillators, transmission gates, and multiplexers (2:1 MUX and 4:1 MUX) were successfully demonstrated on both rigid and flexible substrates, showing no major differences in functionality for both substrates. The remarkable performance achieved by these circuits marks a significant advancement in highlighting the potential of TMDCs as promising candidates for flexible electronic circuits
Graphene based electronic and optoelectronic sensors, stability, reliability and wafer scale integration
No full textGraphene, the two dimensional crystal of carbon, provides outstanding electronic, optical and mechanical properties for a wide range of applications for future electronics and opto-electronics. It presents ultimately high carrier mobility due to the zero band gap nature between the conduction and valance bands. This semi-metallic material has been widely studied in the past decade after its first experimental discovery in 2004. Due to the high carrier mobility, graphene has been demonstrated as an ideal material for Hall sensors and radio frequency electronics. Additionally, surface enhancement of graphene via functional materials has been demonstrated as an efficient method for achieving various sensory devices such as colloidal quantum dot (CQD) enhanced graphene based photo-detectors. Graphene based sensors with such methods outperforming the conventionally used semiconductors by means of sensitivity and operation speed have been demonstrated. However, power requirements to operate these sensors together with the long term stability and the wafer scale integration to the conventional fabrication line have not been addressed adequately. In this presented work, graphene based electronic and optoelectronic devices such as Hall sensors and metal-insulator-graphene diode based photo-detectors with scalable fabrication approach are demonstrated along with the extensive stability and wafer scale fabrication analysis. Presented graphene based Hall sensors on flexible substrate are not only outperforming the existing state-of-the-art conventional semiconductor based Hall sensors, but also highly competitive with all other existing high performance graphene based technologies manufactured with non-scalable approach. In addition, CQD enhanced graphene based photo-detectors with a novel device structure, working in the visible and near infrared wavelengths, are demonstrated. The demonstrated photo-detectors show orders of magnitude lower power consumption than other demonstrated graphene based technologies and yet outperforming the conventional semiconductor based photo-detectors. Furthermore, a comprehensive analysis of the status for the wafer scale integration and stability of the graphene based devices are provided. These results indicate the potential of graphene for low cost and high performance sensory applications and pinpoint the arguments to be addressed to bring highly reliable and advantageous graphene based devices into the semiconductor market
Alcohol-Supported Cu-Mediated 18F-Fluorination of Iodonium Salts under “Minimalist” Conditions
No full textIn the era of personalized precision medicine, positron emission tomography (PET) and related hybrid methods like PET/CT and PET/MRI gain recognition as indispensable tools of clinical diagnostics. A broader implementation of these imaging modalities in clinical routine is closely dependent on the increased availability of established and emerging PET-tracers, which in turn could be accessible by the development of simple, reliable, and efficient radiolabeling procedures. A further requirement is a cGMP production of imaging probes in automated synthesis modules. Herein, a novel protocol for the efficient preparation of 18F-labeled aromatics via Cu-mediated radiofluorination of (aryl)(mesityl)iodonium salts without the need of evaporation steps is described. Labeled aromatics were prepared in high radiochemical yields simply by heating of iodonium [18F]fluorides with the Cu-mediator in methanolic DMF. The iodonium [18F]fluorides were prepared by direct elution of 18F− from an anion exchange resin with solutions of the corresponding precursors in MeOH/DMF. The practicality of the novel method was confirmed by the racemization-free production of radiolabeled fluorophenylalanines, including hitherto unknown 3-[18F]FPhe, in 22–69% isolated radiochemical yields as well as its direct implementation into a remote-controlled synthesis unit
Graphene-based integrated photonics for next-generation datacom and telecom
No full textGraphene is an ideal material for optoelectronic applications. The photonic properties of graphene reveal several advantages and complementarities compared with Si photonics. For example, graphene exhibits electro-absorption modulation, electro-refraction modulation with an electro-optical index change exceeding 10−3, switchable optical add-drop multiplexing based on electro-absorption switch-off and thermoelectric-based ultrafast optical detection that may generate a voltage without a trans-impedance amplifier. In this Review, we present our vision for graphene-based integrated photonics. We review state-of-the-art graphene-based transceivers and compare these devices with existing technologies. Strategies for improving power consumption, manufacturability and wafer-scale integration are addressed. Also, we outline a roadmap of the technological requirements for the demands of the datacom and telecom markets and show that graphene-based integrated photonics could enable ultra-high spatial density, low power consumption for board connectivity and connectivity between data centres, access networks, metropolitan, core, regional and long-haul optical communications
Graphene with Ni-Grid as Semitransparent Electrode for Bulk Heterojunction Solar Cells (BHJ-SCs)
No full textIn this work, we present the fabrication and characterization of bulk-heterojunction solar cells on monolayer graphene (MLG) with nickel-grids (Ni-grid) as semitransparent conductive electrode. The electrodes showed a maximum transmittance of 90% (calculated in 300–800 nm range) and a sheet resistance down to 35 Ω/□. On these new anodes, we fabricated TCO free BHJ-SCs using PTB7 blended with PC70BM fullerene derivative as active layer. The best device exhibited a power conversion efficiency (PCE) of 4.2% in direct configuration and 3.6% in inverted configuration. The reference solar cell, realized on the ITO glass substrate, achieved a PCE of 6.1% and 6.7% in direct and inverted configuration respectively; for comparison we also tested OSCs only with simple Ni-grid as semitransparent and conductive electrode, obtaining a low PCE of 0.7%. The proposed approach to realize graphene-based electrodes could be a possible route to reduce the overall impact of the sheet resistance of this type of electrodes allowing their use in several optoelectronic devices
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