Topological Design of Strain Sensing Nanocomposites

High-performance piezoresistive nanocomposites have attracted extensive attention because of their significant potential as next-generation sensing devices for a broad range of applications, such as monitoring structural integrity and human performance. While various piezoresistive nanocomposites have been successfully developed using different material compositions and manufacturing techniques, current development procedures typically involve empirical trial and error that can be laborious, inefficient, and, most importantly, unpredictable. Therefore, this paper aims to propose and validate a topological design-based methodology to strategically manipulate the piezoresistive effect of nanocomposites to achieve a wide range of optimized strain sensitivities without changing the material system. In particular, this work designed patterned nanocomposite thin films with stress-concentrating and stress-releasing topologies. The strain sensing properties of the different topology nanocomposites were characterized and compared via electromechanical experiments. Those results were compared to both linear and nonlinear piezoresistive material model numerical simulations. Both the experimental and computational results indicated that the stress-concentrating topologies could enhance strain sensitivity, whereas the stress-releasing topologies could significantly suppress bulk film piezoresistivity.

Ultrathin Films of Pentacene on Ag(111): Charge-Transfer Bonding and Inter-Adsorbate Interactions

Temperature programmed desorption (TPD) was used to examine the surface binding and intermolecular interactions of mono- and multi-layer thin films of the polycyclic aromatic acene, pentacene, deposited on a Ag(111) surface. The TPD spectra of sub-monolayer cov- erages revealed the presence of three distinct phases (denoted as α1, α2, and α3). The α1 phase was attributed to adsorption on step sites, while the α2 and α3 phases were assigned to adsorption on terrace sites under different local molecular densities. A physical model was constructed to describe the desorption kinetics from each of the three monolayer phases, including intermolecular repulsion from interfacial dipoles produced as a result of charge transfer bonding between pentacene and the Ag substrate. Fit analysis of the sub-monolayer spectra revealed desorption energies in the zero-coverage limit of 218±8, 166±8, and 162±9 kJ/mol for the α1, α2, and α3 phases, respectively. The interface dipoles of the α2 and α3 terrace adsorption sites were found to be effectively invariant (within error) and deduced as 18±7 and 23±10 D, respectively. These values suggest a partial charge transfer of 0.6 to 0.7 electrons from each pentacene molecule to the Ag substrate and is equivalent to 0.13 electrons per aromatic ring. The TPD spectra from the multilayer films also exhibited three phases. Leading edge analysis of the lowest temperature multilayer peak yielded a desorption energy of 121±15 kJ/mole, while simulations predicted desorption energies ca. 10-15 kJ/mole higher for the higher temperature phases. The three multilayer phases were assigned, from lowest to highest temperature, as an amorphous bulk film, a thin film, and polycrystalline structures.

Ultrathin Films of Pentacene on Ag(111): Charge-Transfer Bonding and Inter-Adsorbate Interactions

Temperature programmed desorption (TPD) was used to examine the surface binding and intermolecular interactions of mono- and multi-layer thin films of the polycyclic aromatic acene, pentacene, deposited on a Ag(111) surface. The TPD spectra of sub-monolayer cov- erages revealed the presence of three distinct phases (denoted as α1, α2, and α3). The α1 phase was attributed to adsorption on step sites, while the α2 and α3 phases were assigned to adsorption on terrace sites under different local molecular densities. A physical model was constructed to describe the desorption kinetics from each of the three monolayer phases, including intermolecular repulsion from interfacial dipoles produced as a result of charge transfer bonding between pentacene and the Ag substrate. Fit analysis of the sub-monolayer spectra revealed desorption energies in the zero-coverage limit of 218±8, 166±8, and 162±9 kJ/mol for the α1, α2, and α3 phases, respectively. The interface dipoles of the α2 and α3 terrace adsorption sites were found to be effectively invariant (within error) and deduced as 18±7 and 23±10 D, respectively. These values suggest a partial charge transfer of 0.6 to 0.7 electrons from each pentacene molecule to the Ag substrate and is equivalent to 0.13 electrons per aromatic ring. The TPD spectra from the multilayer films also exhibited three phases. Leading edge analysis of the lowest temperature multilayer peak yielded a desorption energy of 121±15 kJ/mole, while simulations predicted desorption energies ca. 10-15 kJ/mole higher for the higher temperature phases. The three multilayer phases were assigned, from lowest to highest temperature, as an amorphous bulk film, a thin film, and polycrystalline structures.

INFLUENCE OF DEFECTS ON MAGNETIC CHARACTERISTICS OF FERRITE-GARNET FILMS

В работе рассмотрено влияние объемных дефектов, связанных с локальным механическим повреждением и термическим лазерным воздействием, на доменную структуру и магнитные характеристики эпитаксиальных висмутсодержащих магнитных пленок феррит-граната (Bi :ФГ). Установлено, что одноосные пленки Bi: ФГ устойчивы к объемным дефектам, размер которых не превышает ширину доменов пленки. Показано, что рассмотренные объемные дефекты пленки оказывают влияние на процесс намагничивания пленки, ход кривых намагничивания, на величину коэрцитивной силы. Воздействие лазерным импульсом с плотностью мощности 800 Дж/см приводит к увеличению коэрцитивной силы локального участка пленки в 4 раза (с 0,33 Э до 1,44 Э) This paper presents a study of the effect of volumetric (bulk) defects associated with the local mechanical damage and thermal laser action on the domain structure and magnetic characteristics of epitaxial bismuth-containing garnet-ferrite (Bi: FG) magnetic films. It was found that uniaxial Bi: FG films are resistant to bulk defects, the size of which does not exceed the width of the film domains. It is shown that the considered bulk film defects affect the process of the film magnetization, the form of the magnetization curves, the magnitude of the coercive force and the ratio of the displacement field to the coercive force. Effect of femtosecond laser pulses exposure with a power density of 800 J/cm on the coercivity of film was found. The 4 - fold increase of the coercive field near a defect is discovered (from 0,33 Oe to 1,44 Oe).

Sequential molecular doping of non-fullerene organic solar cells without hole transport layers

Sequential doping with F6-TCNNQ dopants enables to modify the semi-conductive properties of non-fullerene organic solar cells with negligible damage to bulk film morphology and no need to use conventional hole transporting layers.

Great advance in high Tc for hybrid photoelectric-switch bulk/film coupled with dielectric and blue-white light

The hybrid compound [ASD]2[ZnBr4] demonstrates excellent multi-channel, high Tc of 380 K, super-flexibility and broad-band blue-white light emitting bulk/film.

Slow cooling and highly efficient extraction of hot carriers in colloidal perovskite nanocrystals

Hot-carrier solar cells can overcome the Shockley-Queisser limit by harvesting excess energy from hot carriers. Inorganic semiconductor nanocrystals are considered prime candidates. However, hot-carrier harvesting is compromised by competitive relaxation pathways (for example, intraband Auger process and defects) that overwhelm their phonon bottlenecks. Here we show colloidal halide perovskite nanocrystals transcend these limitations and exhibit around two orders slower hot-carrier cooling times and around four times larger hot-carrier temperatures than their bulk-film counterparts. Under low pump excitation, hot-carrier cooling mediated by a phonon bottleneck is surprisingly slower in smaller nanocrystals (contrasting with conventional nanocrystals). At high pump fluence, Auger heating dominates hot-carrier cooling, which is slower in larger nanocrystals (hitherto unobserved in conventional nanocrystals). Importantly, we demonstrate efficient room temperature hot-electrons extraction (up to ∼83%) by an energy-selective electron acceptor layer within 1 ps from surface-treated perovskite NCs thin films. These insights enable fresh approaches for extremely thin absorber and concentrator-type hot-carrier solar cells.

Experimental characterization of tensile properties of epoxy resin by using micro-fiber specimens

In unidirectional carbon fiber-reinforced plastic laminates, the distance between fibers can varies from submicron to micron length scales. The mechanical properties of the matrix at this length scale are not well understood. In this study, processing methods have been developed to produce high quality epoxy micro-fibers with diameters ranging from 100 to 150 µm that are used for tensile testing. Five types of epoxy resin systems ranging from standard DGEBA to high-crosslink TGDDM and TGMAP epoxy systems have been characterized. Epoxy macroscopic specimens with film thickness of 3300 µm exhibited brittle behavior (1.7 to 4.9% average failure strain) with DGEBA resin having the highest failure strain level. The epoxy micro-fiber specimens exhibited significant ductile behavior (20 to 42% average failure strain) with a distinct yield point being observed in all five resin systems. In addition, the ultimate stress of the highly cross-linked TGDDM epoxy fiber exceeded the bulk film properties by a factor of two and the energy absorption was over 50 times greater on average. The mechanism explaining the dramatic difference in properties is discussed and is based on size effects (the film volume is about 2000 times greater than the fiber volume within the gage sections) and surface defects. Based on the findings presented in this paper, the microscale fiber test specimens are recommended and provide more realistic stress–strain response for describing the role of the matrix in composites at smaller length scales.