1,575 research outputs found

    Functionalization of two-dimensional tungsten diselenide and MXene for tunable optical property

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    Since the discover of graphene in 2004, two-dimensional (2D) materials have gained tremendous attention because of their distinctive properties relative to their bulk form. Particularly, transition metal dichalcogenides (TMDs) and 2D transition metal carbides and nitrides (MXenes) have shown promising applications in flexible electrical and optoelectronic devices. Due to the atomically thin nature, the electronic band structures of these materials are very sensitive to the small changes in the lattice and the surface functionalization, offering a dimension to tune the properties of the materials. In this thesis, approaches to functionalize monolayer WSe2 and MXene were explored. The as-grown chemical vapor deposition (CVD) monolayer WSe2 flakes were treated by plasma assisted doping method. Specifically, Methane plasma was used as carbon dopant source to introduce p-type lattice doping into monolayer WSe2. In addition, chemical reactions between perfluorophenylazides (PFPA) organic molecules and WSe2 flakes were conducted where the PFPA molecules may covalently bonded to the WSe2 surface. Similarly, the PFPA functionalization was applied to MXene, an emerging 2D material with high conductivity. Shifts and intensity change were observed in Raman spectra after the functionalization, indicating structural and electric structure changes might be introduced. Further characterizations of the structures and electric properties will be taken in the near future

    A bioinspired optoelectronically engineered artificial neurorobotics device with sensorimotor functionalities

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    Development of the next generation of bio- and nano-electronics is inseparably connected to the innovative concept of emulation and reproduction of biological sensorimotor systems and artificial neurobotics. Here, we report for the first time principally new artificial bioinspired optoelectronic sensorimotor system for the controlable immitation of opto-genetically engineered neurons in the biological motor system. The device is based on inorganic optical synapse (In-doped TiO2 nanofilm) assembled into a liquid metal (galinstan) actuator. The optoelectronic synapse generates polarised excitatory and inhibitory postsynaptic potentials to trigger the liquid metal droplet to vibrate and then mimic the expansion and contraction of biological fibre muscle. The low-energy consumption and precise modulation of electrical and mechanical outputs are the distinguished characteristics of fabricated sensorimotor system. This work is the underlying significant step towards the development of next generation of low-energy the internet of things for bioinspired neurorobotic and bioelectronic system

    Optoelectronics and Bio Devices on Paper Powered by Solar Cells

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    The employment of printing techniques as cost-effective methods to fabricate low cost, flexible, disposable and sustainable solar cells is intimately dependent on the substrate properties and the adequate electronic devices to be powered by them. Among such devices, there is currently a growing interest in the development of user-oriented and multipurpose systems for intelligent packaging or on-site medical diagnostics, which would greatly benefit from printable solar cells as their energy source for autonomous operation

    Few-molecule reservoir computing experimentally demonstrated with surface enhanced Raman scattering and ion-gating stimulation

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    Reservoir computing (RC) is a promising solution for achieving low power consumption neuromorphic computing, although the large volume of the physical reservoirs reported to date has been a serious drawback in their practical application. Here, we report the development of a few-molecule RC that employs the molecular vibration dynamics in the para-mercaptobenzoic acid (pMBA) detected by surface enhanced Raman scattering (SERS) with tungsten oxide nanorod/silver nanoparticles (WOx@Ag-NPs). The Raman signals of the pMBA molecules, adsorbed at the SERS active site of WOx@Ag-NPs, were reversibly perturbated by the application of voltage-induced local pH changes in the vicinity of the molecules, and then used to perform RC of pattern recognition and prediction tasks. In spite of the small number of molecules employed, our system achieved good performance, including 95.1% to 97.7% accuracy in various nonlinear waveform transformations and 94.3% accuracy in solving a second-order nonlinear dynamic equation task. Our work provides a new concept of molecular computing with practical computation capabilities.Comment: 22 pages, 4 figure

    Electrical Transport and Photoconduction of Ambipolar Tungsten Diselenide and n-type Indium Selenide

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    In today\u27s silicon age in which we live, field-effect transistors (FET) are the workhorse of virtually all modern-day electronic gadgets. Although silicon currently dominates most of these electronics, layered 2D transition metal dichalcogenides (TMDCs) have great potential in low power optoelectronic applications due to their indirect-to-direct band gap transition from bulk to few-layer and high on/off switching ratios. TMDC WSe2 is studied here, mechanically exfoliated from CVT-grown bulk WSe2 crystals, to create a few-layered ambipolar FET, which transitions from dominant p-type behavior to n-type behavior dominating as temperature decreases. A high electron mobility μ\u3e150 cm2V-1s-1 was found in the low temperature region near 50 K. Temperature-dependent photoconduction measurements were also taken, revealing that both the application of negative gate bias and decreasing the temperature resulted in an increase of the responsivity of the WSe2 sample. Besides TMDCs, Group III-VI van der Waals structures also show promising anisotropic optical, electronic, and mechanical properties. In particular, mechanically exfoliated few-layered InSe is studied here for its indirect band gap of 1.4 eV, which should offer a broad spectral response. It was found that the steady state photoconduction slightly decreased with the application of positive gate bias, likely due to the desorption of adsorbates on the surface of the sample. A room temperature responsivity near 5 AW-1 and external quantum efficiency of 207% was found for the InSe FET. Both TMDC’s and group III-VI chalcogenides continue to be studied for their remarkably diverse properties that depend on their thickness and composition for their applications as transistors, sensors, and composite materials in photovoltaics and optoelectronics

    2D semiconductor nanomaterials and heterostructures : controlled synthesis and functional applications

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    Two-dimensional (2D) semiconductors beyond graphene represent the thinnest stable known nanomaterials. Rapid growth of their family and applications during the last decade of the twenty-first century have brought unprecedented opportunities to the advanced nano- and opto-electronic technologies. In this article, we review the latest progress in findings on the developed 2D nanomaterials. Advanced synthesis techniques of these 2D nanomaterials and heterostructures were summarized and their novel applications were discussed. The fabrication techniques include the state-of-the-art developments of the vapor-phase-based deposition methods and novel van der Waals (vdW) exfoliation approaches for fabrication both amorphous and crystalline 2D nanomaterials with a particular focus on the chemical vapor deposition (CVD), atomic layer deposition (ALD) of 2D semiconductors and their heterostructures as well as on vdW exfoliation of 2D surface oxide films of liquid metals

    Transparent and Conductive Carbon Nanotube Multilayer Thin Films Suitable as an Indium Tin Oxide Replacement

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    Transparent electrodes made from metal oxides suffer from poor flexibility and durability. Highly transparent and electrically conductive thin films based on carbon nanotubes (CNTs) were assembled as a potential indium tin oxide (ITO) replacement using layer-by-layer (LbL) assembly. The ultimate objective of this dissertation work is to produce CNT-based assemblies with sheet resistance below 100 Omega/sq and visible light transmission greater than 85 percent. The alternate deposition of positively charged poly(diallyldimethylammonium chloride) [PDDA] and CNTs stabilized with negatively charged deoxycholate (DOC) exhibit linear film growth and thin film properties can be precisely tuned. Ellipsometry, quartz crystal microbalance, and UV-vis were used to measure the growth of these films as a function of PDDA-CNT bilayers deposited, while TEM, SEM, and AFM were used to visualize the nanostructure of these films. Following a literature review describing potential ITO substitutes and LbL technology, the influence of CNT type on optoelectronic performance of LbL assemblies is described. Three different types of nanotubes were investigated: (1) multiwalled carbon nanotubes (MWNTs), (2) few-walled carbon nanotubes (FWNT), and (3) purified single-walled carbon nanotubes (SWNTs). SWNTs produced the most transparent (>85 percent visible light transmittance) and electrically conductive (148 S/cm, 1.62 kOmega/sq) 20-bilayer films with a 41.6 nm thickness, while MWNT-based films are much thicker and more opaque. A 20-bilayer PDDA/(MWNT DOC) film is approximately 103 nm thick, with a conductivity of 36 S/cm and a transmittance of 30 percent. In an effort to improve both transparency and electrical conductivity, heat and acid treatments were studied. Heating films to 300 degree C reduced sheet resistance to 701 Omega/sq (618 S/cm conductivity, 38.4 nm thickness), with no change in transparency, owing to the removal of insulating component in the film. Despite improving conductivity, heating is not compatible with most plastic substrates, so acid doping was investigated as an alternate means to enhance properties. Exposing SWNT-based assemblies to HNO3 vapor reduced sheet resistance of a 10 BL film to 227 Omega/sq. Replacing SWNTs with double walled carbon nanotubes (DWNTs) provided further reduction in sheet resistance due to the greater metallic of DWNT. A 5 BL DWNT film exhibited the lowest 104 Omega/sq sheet resistance (4200 S/cm conductivity, 22.9 nm thickness) with 84 percent transmittance after nitric acid treatment. DWNT-based assemblies maintained their low sheet resistance after repeated bending and also showed electrochemical stability relative to ITO. This work demonstrates the excellent optoelectronic performance, mechanical flexibility, and electrochemical stability of CNT-based assemblies, which are potentially useful as flexible transparent electrodes for a variety of flexible electronics

    Thin film MoS2 nanocrystal based ultraviolet photodetector

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    Cataloged from PDF version of article.We report on the development of UV range photodetector based on molybdenum disulfide nanocrystals (MoS2-NCs). The inorganic MoS2-NCs are produced by pulsed laser ablation technique in deionized water and the colloidal MoS2-NCs are characterized by transmission electron microscopy, Raman spectroscopy, X-ray diffraction and UV/VIS absorption measurements. The photoresponse studies indicate that the fabricated MoS2-NCs photodetector (MoS2-NCs PD) operates well within 300-400 nm UV range, with diminishing response at visible wavelengths, due to the MoS2-NCs absorption characteristics. The structural and the optical properties of laser generated MoS2-NCs suggest promising applications in the field of photonics and optoelectronics. (C) 2012 Optical Society of Americ

    Electrolyte-Gated Tungsten Oxide Transistors: Fabrication, Working Mechanism, Device Performance

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    Le transistor est l'un des composants clés des ordinateurs, des téléphones cellulaires intelligents, des moniteurs et d'autres produits électroniques qui ont affecté le progrès technologique et scientifique de notre société. Ces dernières années, l'attention a été consacrée à l'étude des transistors utilisant la commutation électrolytique, au lieu de diélectriques solides conventionnels. Bien que l'utilisation d'électrolytes dans l'électronique ne soit pas un nouveau concept, la commutation électrolytique est importante pour le développement de l’électronique flexible et biocompatible. Les transistors à commutation électrolytique ont, en effet, attiré l'attention en raison de leur faible tension d'alimentation (< 2 V) ainsi que de la possibilité d'obtenir une densité de charge aussi élevée que 1014-1015 cm-2 en raison de la capacité élevée de l’interface électrolyte/canal du transistor (1-10 μF·cm-2). Mis à part leur intérêt technologique intrinsèque, les transistors à commutation électrolytique constituent aussi une plateforme expérimentale pour étudier des aspects fondamentaux. Ils sont en effet utilisés pour étudier le transport combiné électronique et ionique, le transport de charge à haute densité de charge et le contrôle électrique des transitions de phase. Différents électrolytes ont été utilisés comme grille électrolytique, tels que des solutions aqueuses d'électrolyte, des polyélectrolytes, des polymères électrolytiques et des liquides ioniques. Parmi ceux-ci, les liquides ioniques se distinguent par leurs propriétés physico-chimiques uniques. En effet, les liquides ioniques peuvent être conçus pour posséder des caractéristiques de volatilité limitée, bonne conductivité ionique, faible viscosité, stabilité thermique élevée et large fenêtre de stabilité électrochimique (jusqu'à environ 5 V), en sélectionnant la structure appropriée pour le cation et l'anion. Les oxydes métalliques sont de candidats prometteurs en tant que matériaux de canal pour les transistors à grille électrolytique. Les semi-conducteurs à base d'oxydes de métaux ont été intensément étudiés au cours des dernières décennies pour les transistors, en particulier pour des applications de type affichage, en raison de leur mobilité de charge élevée, de leur transparence optique, de leur stabilité chimique, facilité de mise en forme et faible coût. Dans cette thèse, nous nous concentrons sur l'oxyde de tungstène qui peut être synthétisé par de simples méthodes en solution, est sensible à la lumière visible et présente de transitions intéressantes isolant-métal (métallisation).----------Abstract Transistors are one of the key components in computers, smart cell phones, monitors and other electronics products, which have affected the technological and scientific progress of our society. In recent years, attention has been dedicated to the study of electrolyte-gated transistors, which utilize electrolytes as the gating layer instead of conventional solid dielectric. Although the use of electrolytes in electronics is not a new concept, new printable, fast-response electrolytes are expanding the potential applications of electrolyte-gated transistors in flexible, rollable and biocompatible electronics. Electrolyte-gated transistors are indeed attracting attention because of their low driving voltages (< 2 V) as well as the possibility of achieving charge carrier density as high as ca. 1014 −1015 cm−2, owing to the high capacitance of the electrolyte/transistor channel interface (ca. 1−10 μF·cm−2). The intrinsic technological interest of electrolyte-gated transistors is paralleled by their relevance as experimental platforms to study fundamental aspects of electrochemistry, solid state physics and electronic engineering. Particular attention is devoted to combined electronic and ionic transport, charge carrier transport at high charge density and electrical control of phase transitions. Different electrolytes have been used as gating media in electrolyte-gated transistors, such as aqueous electrolyte solutions, polyelectrolytes, electrolyte polymers and ionic liquids. Among these, ionic liquids stand out due to their unique physicochemical properties. Indeed, ionic liquids can be designed to exhibit limited volatility, good ionic conductivity, low viscosity, high thermal stability, and a wide electrochemical stability window (up to ca. 5 V) by appropriate choice of structure for the cation and anion. Promising channel material candidates for electrolyte-gated transistors are metal oxides. Metal oxide semiconductors have been intensively investigated over the past decades for transistors, particularly in display applications due to their high charge carrier mobility, high optical transparency, chemical stability, low temperature processability and low cost. In this thesis, we focus on tungsten oxide that features solution processability, insulator-to-metal transition and visible light sensitivity
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