Controlling the Functional Properties of Oligothiophene Crystalline Nano/Microfibers via Tailoring of the Self‐Assembling Molecular Precursors

Oligothiophenes are π‐conjugated semiconducting and fluorescent molecules whose self‐assembly properties are widely investigated for application in organic electronics, optoelectronics, biophotonics, and sensing. Here an approach to the preparation of crystalline oligothiophene nano/microfibers is reported based on the use of a “sulfur overrich” quaterthiophene building block, ? T4S4 ? , containing in its covalent network all the information needed to promote the directional, π–π stacking‐driven, self‐assembly of Y‐T4S4‐Y oligomers into fibers with hierarchical supramolecular arrangement from nano‐ to microscale. It is shown that when Y varies from unsubstituted thiophene to thiophene substituted with electron‐withdrawing groups, a wide redistribution of the molecular electronic charge takes place without substantially affecting the aggregation modalities of the oligomer. In this way, a structurally comparable series of fibers is obtained having progressively varying optical properties, redox potentials, photoconductivity, and type of prevailing charge carriers (from p‐ to n‐type). With the aid of density functional theory (DFT) calculations, combined with powder X‐ray diffraction data, a model accounting for the growth of the fibers from molecular to nano‐ and microscale is proposed.     

Dynamic Photoswitching of Electron Energy Levels at Hybrid ZnO/Organic Photochromic Molecule Junctions

The functionality of interfaces in hybrid inorganic/organic (opto)electronic devices is determined by the alignment of the respective frontier energy levels at both sides of the heterojunctions. Controlling the interface electronic landscape is a key element for achieving favourable level alignment for energy and charge transfer processes. Here, it is shown that the electronic properties of polar ZnO surfaces can be reversibly modified using organic photochromic switches. By employing a range of surface characterization techniques combined with density functional theory calculations, it is demonstrated that self‐assembled monolayers (SAMs) of photochromic phosphonic acid diarylethenes (PA‐DAEs) can be employed to reversibly change the electronic properties of polar ZnO/SAM structures by light stimuli. The highest occupied molecular orbital level of PA‐DAE is raised by 0.7 eV and the lowest unoccupied one lowered by 0.9 eV, respectively, upon illumination by ultraviolet light and the levels shift back to their original position upon illumination by green light. The results thus provide a pathway to tailor hybrid interface electronic properties in a dynamic manner upon simple light illumination, which can be exploited to reversibly tune the electrical properties of photoswitchable (opto)electronic devices.     

Liquid Phase Exfoliated Indium Selenide Based Highly Sensitive Photodetectors

Layered semiconductors of the IIIA–VIA group have attracted considerable attention in (opto)electronic applications thanks to their atomically thin structures and their thickness‐dependent optical and electronic properties, which promise ultrafast response and high sensitivity. In particular, 2D indium selenide (InSe) has emerged as a promising candidate for the realization of thin‐film field effect transistors and phototransistors due to its high intrinsic mobility (>10² cm² V^?1 s^?1) and the direct optical transitions in an energy range suitable for visible and near‐infrared light detection. A key requirement for the exploitation of large‐scale (opto)electronic applications relies on the development of low‐cost and industrially relevant 2D material production processes, such as liquid phase exfoliation, combined with the availability of high‐throughput device fabrication methods. Here, a β polymorph of indium selenide (β‐InSe) is exfoliated in isopropanol and spray‐coated InSe‐based photodetectors are demonstrated, exhibiting high responsivity to visible light (maximum value of 274 A W^?1 under blue excitation 455 nm) and fast response time (15 ms). The devices show a gate‐dependent conduction with an n‐channel transistor behavior. Overall, this study establishes that liquid phase exfoliated β‐InSe is a valid candidate for printed high‐performance photodetectors, which is critical for the development of industrial‐scale 2D material‐based optoelectronic devices.     

Dielectric behavior of some polar high polymers at ultra-high frequencies (microwaves)

The dielectric behavior of different polar high polymers at ultra-high frequencies has been investigated by means of a dielectrometer, suitably modified to permit measurements at different temperatures. Experimental measurements were made at about 9 × 10⁹ cps over the temperature range of ?150 to 200°C. for polyoxymethylene, polythiomethylene, poly(3,3′-chloromethyl)oxetane (Penton), polycarbonate of 4,4′-dioxydiphenyl-2,2′-propane (Makrolon), poly(vinyl alcohol), poly(vinyl acetate), poly(vinyl chloride), vinyl chloride–vinyl acetate copolymer, and two ABS plastics, type B (blend) and type G (graft). On comparing the dielectric behavior of the examined materials at ultra-high frequencies with the corresponding ones determined at low or at radiofrequencies, it is observed that, in the microwave region, all relaxation peaks, either connected with cooperative motions in main chain (primary processes) or with local motions in the backbone or in side chains (secondary processes), usually observed at lower frequencies, tend to disappear; the corresponding relaxation effects, however, manifest themselves through a progressive increase of losses with increasing temperature, which is particularly marked above the glass transition temperature T_g. The latter transition, in spite of the very high frequency, is easily distinguished, in most cases, by the sudden change of slope in the tan δ versus temperature curve which accompanies its onset. This is explained on the basis of the very wide distribution times of molecular relaxation processes in polymers and the increase in strength of the secondary relaxation effects, which is verified at T_g, as a consequence of the increased kinetic energy of macromolecules and of the larger free volume for orientation of side chains. Each case is discussed separately and the experimental results interpreted on the basis of the molecular structure and chain mobility of the examined polymers.     

Development and characterization of a microthermoelectric generator with plated copper/constantan thermocouples

This work reports the development and the characterization of a microthermoelectric generator (μTEG) based on planar technology using electrochemically deposited constantan and copper thermocouples on a micro machined silicon substrate with a SiO₂/Si₃N₄/SiO₂ thermally insulating membrane to create a thermal gradient. The μTEG has been designed and optimized by finite element simulation in order to exploit the different thermal conductivity of silicon and membrane in order to obtain the maximum temperature difference on the planar surface between the hot and cold junctions of the thermocouples. The temperature difference was dependent on the nitrogen (N₂) flow velocity applied to the upper part of the device. The fabricated thermoelectric generator presented maximum output voltage and power of 118 mV/cm² and of 1.1 μW/cm², respectively, for a device with 180 thermocouples, 3 kΩ of internal resistance, and under a N₂ flow velocity of 6 m/s. The maximum efficiency (performance) was 2 × 10^?3 μW/cm² K².     

Reactive blending of commercial PET and PC with freshly added catalysts

Reactive blending of commercial poly(ethylene terephthalate) (PET) and bisphenol A polycarbonate (PC), with catalysts added in the form of powder dispersed on the polymers just before melt mixing, was performed in a Brabender Plasticord 2000 apparatus at 275°C. Catalytic activity of the catalysts freshly added to polymers was found to be much higher as compared with that of the residues of the same type of catalysts remaining in PET after its synthesis. Furthermore, the catalytic activity appeared to be strongly dependent on the structure of the ligand that influences the catalyst solubility in the polymer melt. N.m.r. spectroscopy, selective degradation of PC fragments, solubility tests in methylene chloride and d.s.c. measurements made it possible to range the catalysts studied according to their catalytic activity.     

Fundamental Solutions in the Theory of Thermoelasticity for Solids with Double Porosity

In this article, the linear theory of thermoelasticity for solids with double porosity is considered. The fundamental solutions for the systems of steady vibrations (including quasi-static case) and equilibrium equations are constructed by means of elementary functions; the basic properties of such solutions are also established.     

Titania solar cells: new photovoltaic technology

Titania solar cells are a new type of photovoltaic device invented by Professor Michael Grätzel at Ecole Polytechnique Federale de Lausanne (Switzerland). Titania solar cells convert sunlight directly into electricity through a process similar to photosynthesis. It has performance advantages over other solar cells, which include the ability to perform well in low light and shade, and to perform consistently well over a wide range of temperatures. Titania solar cells can be fabricated to be either transparent or opaque in appearance. The simple materials, construction technique and processing equipment make Titania modules attractive for affordable power generation. Applications of such a module include many consumer and professional products, including vertically mounted solar tiles used as integrated building materials and, in future, used as power generating windows.     

On the Heat-Flux Dependent Thermoelasticity for Micropolar Porous Media

In the present paper, in the context of the linear theory of heat-flux dependent thermoelasticity for micropolar porous media, we derive a uniqueness theorem with no positive definiteness assumption on the elastic constitutive coefficients. Moreover, we prove, under non homogeneous initial conditions, a reciprocal relation and a variational principle. These generalize previous results about inhomogeneous and anisotropic micropolar thermoelastic materials.     

ARTE: An Application-specific Run-Time managEment framework for multi-cores based on queuing models

This paper presents an Application-specific Run-Time managEment (ARTE) framework to tackle the problem of managing computational resources in an application specific multi-core system. The ARTE framework run-time goal is to minimize applications’ response times while meeting the applications’ computational demands and fitting within the available power budget.