Mechanical and electrical characterization of CVD-grown graphene transferred on chalcogenide Ge 2 Sb 2 Te 5 layers

G. D'Arrigo, M. Christian, V. Morandi, G. Favaro, C. Bongiorno, A.M. Mio, M. Russo, A. Sitta, M. Calabretta, A. Sciuto, E. Piccinini, L. D'Urso (+1 others)
2018 Carbon  
Traumatic and pathological conditions leading to the disruption of tissue integrity require clinical intervention through either an implantology or a regenerative medicine approach. The integration of medical devices within the surrounding tissues as well as tissue regeneration by tissue engineering constructs depend on the ability of the implanted biomaterials to control the activity of cells. In any natural tissue, this activity is influenced by extracellular matrix (ECM) macromolecules like
more » ... roteins and polysaccharides that present in a spatially-ordered manner specific bioligands to the cell receptors. This nanometric control determines the ability of the cell to migrate, proliferate and ultimately regenerate the tissue. Hence, the design and development of novel biomaterials able to resemble the physicochemical and biological properties of the ECM macromolecules have been widely advocated for the surface functionalisation of both medical implants and tissue engineering products. The lecture will present a novel class of synthetic hyperbranched macromolecules and their grafting to conventional biomaterials to provide implants and 3D scaffolds with new biological properties. Examples of these synthetic macromolecules and their applications in a range of clinical applications will be illustrated and critically discussed in the light of the elicited in vitro and in vivo biological responses as well as in the light of their industrial sustainability. After a brief introduction on renewable energy sources and the opportunity of printed organic photovoltaics I will turn to the emergent hybrid perovskites field. Perovskites have the potential to overcome the performance limits of current technologies and achieving low cost and high integrability. Hybrid halide perovskite, e.g. CH3NH3PbX3 [X = Cl, Br, or I], are usually deposited as polycrystalline thin-films with variable mesoscale morphology depending on the growth conditions. I will demonstrate that the electronhole interaction is sensitive to the microstructure of the material. By controlling the material processing during fabrication both free carrier and Wannier excitonic regimes are accessible, with strong implications for applications in optoelectronic. The simple solution processability at room temperature exposes lead halide perovskite semiconductors to a non-negligible level of unintentional structural and chemical defects. I will report on the use of excitation correlation photoluminescence (ECPL) spectroscopy to investigate the recombination dynamics of the photo-generated carriers in lead bromide perovskites. This experiments allows to identify the energetics of the defects. In fact, in the case of polycrystalline films, depending on the synthetic route, we demonstrate the presence of both deep and shallow carrier traps. The shallow defects, which are situated at about 20meV below the conduction band, dope the semiconductor leading to a substantial enhancement of the photoluminescence quantum yield in spite of carrier trapping. At excitation densities relevant for lasing we observe breakdown of the rate-equation model indicating a build-up of a highly correlated regime of the photo-carrier population that suppresses the non-radiative Auger recombination. Wide band gap semiconductors for power electronics and sensor applications Energy storage and water splitting Smart surfaces and functionalization 13 Dec -PM2 Materials and processes for environmental protection and sustainability Nanobiocomposites for in-vitro diagnostics and targeted drug Wide band gap semiconductors for power electronics and sensor applications Growth and synthesis of 2D materials Smart surfaces and functionalization 14 Dec -AM Photovoltaics Nanobiocomposites for in-vitro diagnostics and targeted drug Wide band gap semiconductors for power electronics and sensor applications Growth and synthesis of 2D materials Smart surfaces and functionalization 14Dec -PM1 Photovoltaics Nanobiocomposites for in-vitro diagnostics and targeted drug Electronic/optical/magnetic/quantum properties of 2D materials Materials under extreme conditions and ultra-fast transitions Printed electronics 15 Dec -AM Magnetic materials for medicine Biological applications of 2D materials Electronic/optical/magnetic/quantum properties of 2D materials 3D printing materials in biomedical research Organic electronics 15 Dec -PM1 Photovoltaics Chemistry and functionalization of 2D materials Magnetism and spintronics Materials under extreme conditions and ultra-fast transitions Organic electronics 15 Dec -PM2 Photovoltaics Chemistry and functionalization of 2D materials Magnetism and spintronics Materials under extreme conditions and ultra-fast transitions Thermoelectrics Dec -AM Microcapsules are small particles which contain an active agent or core material surrounded by a coating or shell. The encapsulation of materials for protection and phase separation has evolved into a major interdisciplinary research focus. 1 The utility of microcapsules for efficient cargo storage and targeted release is of considerable importance in self-healing materials, nutrient preservation, agricultural applications, fragrance release, and drug delivery. 2 One of the most challenging tasks and the ultimate purposeof developing delivery systems is to modulate the release of encapsulated cargo substances. Strategies such as heat treatment, ionic strength, magnetic fieldsand light-induced morphology change have been used to alter the shell density and integrity, and then to influence capsule permeability. 3 As one of the most interesting parts of stimuli-responsive capsules, photostimuli responsive capsules are capable of affecting their micro-/nano-structures in the form of remote control triggered by external light e.g., sun light, without requirement of direct contact or interactions. Moreover, triggering the release of microcapsules by light has a number of advantages over other external stimuli: (i) photons do not contaminate the reaction systems and they have very low or negligible toxicity in contrast to chemicals; (ii) the excitation wavelength can be controlled through the design of the photo-responsive molecule, (iii) it is easy to control the time and/or local excitation. 4 The development of such highly light sensitive vesicles is of great importance, especially in the fields of surface sciences and environmental applications, where sometimes light would be the only available stimulus to drive the systems. In this presentation, some examples of lightsensitive polymeric microcapsules will be described, that also show how the wavelength of the triggering light can be moved from the UV to the visible region, depending on the desired final application. Control on the movement of fluids and an efficient mixing are basic steps to perform a number of chemical and biological microfluidic processes. The progress in microfluidic technologies has made possible complicated manipulations of solutions at the microscale [1], but many devices rely on external instruments such as microsyringe pumps or power sources. Moreover, liquid flow in microchannels is completely laminar and uniaxial, with a very low Reynolds number regime [2]. To increase fluid mixing, complex three-dimensional networks inducing chaotic advection have to be designed. Alternatively, turbulence in the liquid can be generated by active mixing methods or by adding small quantities of viscoelastic polymers to the working liquid [3]. We have used polyelectrolyte multilayer capsules (PMCs) embodying a catalytic polyoxometalate complex, Ru 4 POM [4] to propel fluids inside microchannels and to create elastic turbulence. These chemical systems are functional actuators, that is, materials systems that respond to reagents/stimuli at the molecular level (input) and produce a mechanical effect (output) at the macroscale level. The overall effect is enhanced and controlled by feeding the polyoxometalate-modified capsules through hydrogen peroxide, H 2 O 2 , thus triggering an on-demand propulsion due to oxygen evolution resulting from H 2 O 2 decomposition [5]. In this frame, the capillary dynamics of the aqueous mixtures with different H 2 O 2 concentrations flowing across microchannels have been analyzed to quantify key dynamic parameters such as speed, pressure, viscosity, as well as, Reynolds and Weissenberg numbers. Increase in fluid speed together with the capsule-induced turbulence effects have been found to be proportional to the H 2 O 2 [6]. The catalytic system has been also studied in hydrodynamic pumping conditions: pressure and volumetric flow rate have been monitored by means of microfluidic sensors. Moreover, the effects of the catalytic reaction on a polydimethylsiloxane (PDMS) membrane bulge have been evaluated and then we have demonstrated the membrane can be used as chemically actuated diaphragm to move fluids within microfludic systems. Finally, a decreasing of mixing time between fluid lamellae has been demonstrated in a serpentine microreactor in presence of such self-propelling systems. Compared to other materials, our chemical system is expected to be more convenient due to (i) a controlled oxygen production in situ, (ii) minimized interference in chemical and biochemical processes, and (iii) fuel-dependent elastic properties of our materials. Shape memory materials (SMM) belong to the class of smart materials. Their main characteristic consists in the ability to recover their original shape after they underwent a deformation, thanks to the application of an external stimulus. This effect is known as shape memory effect (SME). [1] Among SMM, shape memory polymers (SMP) represent an important part of this class of materials. In this study the synthesis of an epoxy liquid crystalline elastomer (LCE) is presented. SME in LCEs is thermally triggered, exploiting the phase transition from anisotropic to isotropic phase. [2, 3] What we have aimed was the realization of lightly cross-linked liquid crystalline elastomer films filled with multi-walled carbon nanotubes (MWCNT), in order to obtain nanocomposites at different content of nanofillers (0,75%, 1,50%, 3,00%). In order to obtain a homogeneous incorporation of MWCNT within the polymer matrix, a compatibilization strategy of nanofillers through the grafting of epoxy monomers, on their surface was performed. Thanks to this procedure an enhancement of thermoactuation properties of the nanocomposites with respect to the neat resin was achieved. Moreover, the nanocomposites presented an increase in the sensitivity to the applied thermomechanical stress. These effect of nanotubes on the shape memory features of the prepared systems was related to their microstructure, defined through morphological, thermal and mechanical analysis. Thanks to these properties, LCEs have the potential to be used in different fields, ranging from the biomedical, aerospace to the electronic engineering. In the first part of the talk I will present a new type of light-activated motors with unprecedented efficiency[1] (see movie at https://www.youtube.com/watch?time_continue=4&v=-NX-vNCWWS0). These consist in asymetric microfabricated gears covered by an absobing coating that converts the energy of wide-field illumination into rotational motion. These micromotors are suspended at an air-liquid interface and produce a non-homogenous heating of the fluid that, in turn, causes a surface tensiondriven torque spinning the rotor up to 300 rpm. It is shown that these microdevices have an efficiency orders of magnitude higher than rotors relying on direct optical momentum transfer or on thermophoresis. In the second part of the talk I will show how we #008 -The Diels-Alder reaction applied to polymers from renewable resources: thermal reversibility and recyclability The Diels-Alder (DA) reaction applied to monomers incorporating furan and maleimide moieties is discussed in terms of the synthesis of different macromolecular structures based on renewable resources, including linear, branched and crosslinked architectures of homo-and co-polymers. Emphasis is placed, on the one hand, on the interest associated with this strategy regarding the thermal reversibility of these DA materials, which allows their mendability and recyclability to be readily attained, and, on the other hand, on the specific application of these features to monomers or polymers from renewable resources, such as plant oils, starch, cellulose and natural rubber, quite apart from the ubiquitous presence of the furan heterocycle in all the systems described. #009 -Eco-friendly thermoplastic composite laminates: mechanical properties and morphological issues In the last decades, the increasingly widespread use of plastics with enhanced functional and structural peculiarities for industrial applications and the simultaneous growing awareness of the environmental issues associated with their disposal have driven the interest of both academic and industrial research toward the development of new eco-friendly materials. These latter, best known as biocomposites or green composites, are based on polymer matrices intrinsically biodegradable as poly(lactic acid) resins (PLAs) or from renewable raw materials as polyhydroxy alkanoates (PHAs) or from plastic wastes and natural fibers (e.g. jute, flax, cotton, kenaf, sisal, coconut, bamboo). Poly(lactic acid) resins (PLAs), among biodegradable resins, are widely used because of their good mechanical properties similar to those of polystyrene, its degradability in relatively short period of time in contrast to conventional plastics and high productivity compared with other biodegradable resins. About the recycling of plastic waste streams, taking into account that polyolefins like polyethylene and polypropylene resins, given their outstanding physical, mechanical, thermal and chemical properties, are largely involved in plastic products for packaging and automotive applications, special attention has been paid to the mechanical recycling of these fractions in designing and manufacturing of items for civil and building applications. Finally, regarding the reinforcement, the use of natural fibers, eventually pre-treated to improve the interfacial adhesion with the reference hosting matrix, in place of synthetic ones as glass fibers or carbon fibers, even so far mainly dedicated to the reinforcement of petrochemical based resins, have been reviewed by several authors. Among them, jute has been largely considered due to its low cost, large amount of production and high specific strength. In the frame of the above considerations, activities were focused on the development of various environmentally friendly composite laminates prepared by conventional techniques as the film stacking and compression molding and mainly validated in terms of mechanical performances. Specifically, laminated plates based on PLA and recycled polyolefin wastes reinforced with commercial plain wave fabrics of jute or glass fibers were evaluated under static and dynamic flexural loadings as well as by lowvelocity impact tests. Mechanical results were also interpreted by visual inspections and morphological analysis (scanning electron microscopy) of damaged areas.
doi:10.1016/j.carbon.2018.02.046 fatcat:wiqrs5krczgrrahoa7hl2rgtcm