For efficient charge separation and charge transport in optoelectronic materials, small internal reorganization energies are desired. While many p-type organic semiconductors have been reported with low internal reorganization energies, few n-type materials with low reorganization energy are known. Metal phthalocyanines have long received extensive research attention in the field of organic device electronics due to their highly tunable electronic properties through modification of the molecular periphery. In this study, density functional theory (DFT) calculations are performed on a series of zinc-phthalocyanines (ZnPc) with various degrees of peripheral per-fluoroalkyl (-C3F7) modification. Introduction of the highly electron withdrawing groups on the periphery leads to a lowering in the energy of the molecular frontier orbitals as well as an increase in the electron affinity. Additionally, all molecules studies are found to be most stable in their anionic form, demonstrating their potential as n-type materials. However, the calculated internal reorganization energy slightly increases as a function of peripheral modification. By varying the degree of modification we develop a strategy for obtaining an optimal balance between low reorganization energy and high electron affinity for the development of novel n-type optoelectronic materials.

In spite of the phenomenal efficiency progression of the organometal halide perovskite-based solar cells (PSCs) over the past few years, detailed understanding of the working mechanisms and effective measures to overcome the main weaknesses such as the long-term instability are of central importance. This paper provides a brief review of our most recent research on high-performance PSCs including the diethanolamine-modification of NiO surface, the mixed solvent engineering and the mesoporous TiO2 nanobowl (NB) array assisted light harvesting.

In this paper, we report on a multifunctional battery assembly, which possesses a balanced combination of energy storage capability and resistance to electrical failure under mechanical impact loading. The Granular Battery Assembly (GBA) presented here exhibits a mechanical response that emerges from features of granular and cellular media. We demonstrate that for the specific GBA embodiment considered in the present study, the electrical reliability following a mechanical loading event is substantively increased compared to that of plain battery cells. The increased reliability is due to the sacrificial material elements interspersed between the battery units, attributing energy absorption and local stress limiting.

In spite of its frustrated lattice, the multiferroic Lu0.5Sc0.5FeO3 exhibits two consecutive magnetic transitions at TN1 ≈ 175 K and TN2 ≈ 70 K determined from neutron diffraction. In the ordered state, magnetic fluctuations are present, most likely arising from the in-plane frustrated interaction of the Fe hexagonal lattice. Furthermore, a crossover of the magnetic intensity is observed from elastic to inelastic upon warming, indicating that magnetic fluctuations persist well above TN1, a common feature in hexagonal multiferroics.

In this study, three hydrophobic polymers are investigated as potential adhesives for a shape memory polymer nerve cuff. At room temperature, the adhesive candidate exhibited a maximum lap shear stress of 1.7251 MPa, compared to 0.87641 MPa and 2.1815 MPa for two commercially available biocompatible adhesives.

Two dimensional (2D) nanomaterials such as graphene and transition-metal dichalcogenides (TMDCs) have attracted tremendous attention over recent years due to their unique properties and potential for numerous applications. Given the wide range of compositions of 2D-layered materials that have emerged in recent years, it is not surprising that they offer a rich spectrum of properties, ranging from metallic, insulating, superconducting to semiconducting. Here we report on the solution-based production of 2D layered material flakes, in particular graphene and MoS2 where the materials are chemically exfoliated in organic solvents which can then be ink jet printed using a commercially available material printer, for printed electronics applications.

Carbon nanomaterials are viewed as promising building blocks of future nanotechnology because of their superior electrical, thermal, and mechanical properties. Carbon nanomaterials can be synthesized by a variety of methods, in which flames offer a potential route in large quantities at a significantly lower cost. Our group has worked on growth of carbon nanomaterials involving carbon nanotubes (CNTs), carbon nanofibers (CNFs) and graphenes in flames for more than 15 years, and almost 100 journal papers have been published. In this paper, we review the advances in synthesis of carbon nanomaterials from flames in detail together with discussion on the major challenges and opportunities for practical applications.

We discuss the self-folding of patterned metallic sheets using both differential stress and surface forces. The advantageous characteristics of the technique include, (a) The creation of 3D patterned corrugated metamaterials with pattern resolution limited only by that of planar lithography. Since planar lithography is highly versatile, a variety of patterns with different sizes and shapes can be formed. (b) The hands-free and wire-free self-folding of these materials use two orthogonal forces derived from the release of residual stress and the minimization of surface tension. Hence, this process is highly parallel and scalable allowing such materials to be mass produced. (c) Finally, the edges of the materials self-align and seal due to capillary forces of the liquid hinges—this self-sealing enhances overall rigidity and strength of the materials.

Consequently, the self-folding of patterned and sealed “egg-crate” shaped metamaterials was realized. Patterns were incorporated in the form of “smart” patches on the walls of the egg-crates which can be selectively functionalized with biomolecules. Apart from the intellectual appeal of these hands-free, self-sealing materials, we envision applicability of these egg-crate like microstructures in lab-on-a-chip assays as functionalized microwells and as light weight mechanical metamaterials.

In disposing of high-level radioactive waste, the drop in pH in the repository as the iron overpack corrodes must be considered. Plutonium migration behavior may be affected by the pH of pore water in compacted bentonite barriers in high-level waste repositories. To examine the effect of pH on migration behavior, H-bentonite was prepared by treating Japanese Na-bentonite, Kunipia-F, with hydrochloric acid. Diffusion experiments were performed with mixtures of Na- and H-bentonites. The pH value in the pore water of the water-saturated bentonite mixtures decreased from 8 to 3 as the mixing ratio of H-bentonite increased. Diffusion experiments were carried out by using 238Pu then apparent diffusion coefficients were determined from the plutonium distribution in the specimens. The apparent diffusion coefficients were on the order of 10-13 to 10-12 m2/s at pH values lower than 4, whereas they were less than 10-14 m2/s at pH values higher than 6.5. These results indicate that plutonium diffused faster as Pu3+ or PuO22+ due to disproportionation at lower pH while plutonium could be retarded as Pu(OH)40 by sorption on bentonite at higher pH.

Textiles, in combination with advances in materials and design, offer exciting new possibilities for human and environmental interaction, including biometric and touch-based sensing. Previous fabric-based or flexible touch sensors have generally required a large number of sensing electrodes positioned in a dense XY grid configuration and a multitude of wires. This paper investigates the design and manufacturing of a planar (two-dimensional, XY location) touch fabric sensor with only two electrodes (wires) to sense both planar touch and pressure, making it ideal for applications with limited space/complexity for wiring. The proposed knitted structure incorporates a supplementary method of sensing to detect human touch on the fabric surface, which offers advantages over previous methods of touch localization through an efficient use of wire connections and sensing materials. This structure is easily manufactured as a single component utilizing flatbed knitting techniques and electrically conductive yarns. The design requires no embedded electronics or solid components in the fabric, which allows the sensor to be flexible and resilient. This paper discusses the design, fabrication, sensing methods, and applications of the fabric sensor in robotics and human-machine interaction, smart garments, and wearables, as well as the highly transdisciplinary approach pursued in developing medical textiles and flexible embedded sensors.

In this paper a photodetector working as an active optical filter device is used to detect modulated visible optical signals for applications based on Visible Light Communication (VLC). The proposed application demonstrates the viability of indoor positioning using VLC technology established by the modulation of indoor ultra-bright RGB white LEDs. The signals of the internal red and blue chips of the white LEDs were modulated at specific frequencies and the generated photocurrent was measured by a pin-pin photodetector based on a-SiC:H/a-Si:H. This device operates as a visible optical filter with controlled wavelength sensitivity through the use of adequate optical biasing light. Thus it is able to detect different wavelengths which allow the detection of the individual components of the tri-chromatic white LED. This possibility is the basis for the indoor location algorithm. We demonstrate the possibility of decoding four transmission optical channels supplied by two different wavelengths of white LEDs modulated under different bit sequences. The identification of the signals received by the photodetector allows the location identification of the photodetector position and supplies indoor navigation.

In this work, we present an approach towards achieving a detailed knowledge on the effects of irradiation in iron-based superconductors with high-energy heavy ions. Ba1−xKxFe2As2 single crystals (x = 0.42) were irradiated with 250 MeV Au-ions. The crystals were shaped to be thin plates with thickness lower than the ion implantation depth and bases perpendicular to the c-axis. By means of the quantitative magneto-optical imaging technique we attained the local current density in pristine and irradiated sample regions without any model assumption. After irradiation a strong critical current density (Jc) enhancement was measured, overcoming a factor 3 at T = 4 K with an irradiation fluence φ = 9.7 × 109 cm-2. Moreover, correlating point by point Jc and induction magnetic field maps, a contribution of the Au-ion induced defects to the anisotropic out of plane pinning (i.e. pinning in the direction parallel to the ion path) turned up. This contribution shows a maximum at applied fields quite lower than the nominal dose equivalent field. Furthermore, the temperature dependence of the penetration depth was evaluated before and after high-fluence irradiations by investigating the high-frequency behavior of these crystals using a microwave coplanar resonator technique. Fitting the experimental curves with a power law, we found a decrease of the power exponent, more pronounced at the higher fluences, that can supports the s± wave model.

We review the discovery of a new phase BN (named Q-BN) which has been created by nanosecond laser melting in the super undercooled state and quenching rapidly with rates exceeding several billion degrees per second. This phase, sequel to our earlier discovery of Q-Carbon, has amorphous structure from which phase-pure c-BN is formed in the form of nanodots, microcrystals, nanoneedles, and microneedles. Large-area single c-BN are formed by providing a template for epitaxial growth during quenching of super undercooled liquid BN. Since there is a rapid crystal growth from liquid, both n- and p-type dopants can be incorporated into electrically active substitutional sites with concentrations exceeding solubility limits through the phenomenon of solute trapping. We have grown diamond on c-BN by pulsed laser deposition of carbon at 500°C without the presence of hydrogen, and created c-BN and diamond epitaxial composites. We discuss the mechanism of epitaxial c-BN and diamond growth on lattice matching c-BN template under pulsed laser evaporation of amorphous carbon. This discovery on direct conversion of h-BN into phase-pure c-BN at ambient temperatures and pressures in air, represents a seminal contribution to the field of boron nitride, which is quite complementary to our discovery of graphite to diamond conversion. We have bypassed thermodynamics with the help of kinetics and time control. This research represents a major breakthrough for c-BN and diamond based high-power electronic and photonic devices, and host of other applications related to high-speed machining, deep-sea drilling, field-emission displays and biomedical applications.

Soft transient electronics of polymeric substrates and silver-ink electronics are studied for correlated mechanical-electrical properties. Experimental and predictive finite element analysis are used to understand, explain and predict delamination, cracking, buckling, and failure of printed conductive components of such systems. An active transient polymer system consisting of poly(vinyl alcohol) and sodium bicarbonate is introduced that results in byproducts (alkaline and bubbles) when undergoing transiency. These byproducts are facilitated to control and expedite transiency of the electronic components based on redispersion of metallic nano/micro materials. Complete mechanical and electrical characterization of such systems is reported.

The Shuttleworth effect ensures that at an interface, where one of the phases is an elastic solid, surface stress is not equal to the surface energy. In this paper, we provide a free energy based approach to quantify the impact of the Shuttleworth effect in the adhesion of a rigid, spherical particle on an elastic solid. Our paper has four key findings. Firstly, we demonstrate that the difference in the elastic-solid-particle surface stress and surface energies is linearly proportional to the adhesion energy. Secondly, we establish that the surface stresses being larger than the surface energies provide the sufficient condition for an energetically favorable adhesion. Thirdly, we show that for a given adhesion energy and solid-vapor surface energy increase in particle-vapor surface energy makes the adhesion, in presence of the Shuttleworth effect, more favorable. Finally, and most importantly, we identify the necessary parameter space corresponding to which the Shuttleworth effect may or may not enhance the adhesion as compared to the case that does not account for the Shuttleworth effect. We anticipate that our findings will significantly impact our understanding of a plethora of problems involving adhesion and indentation on soft surfaces, such as nanoparticle adhesion on cells, nanoindentation based characterization of soft solids, applications of adhesion-based soft lithography techniques, etc.

Thermal emission impacts a wide variety of applications, including thermophotovoltaics, photovoltaics, photon-enhanced thermionic emission, selective solar absorption, incandescent lighting, and spectroscopy. Ordinary structures generally emit a broad range of wavelengths, angles, and polarizations. However, highly selective thermal emission has potential to greatly improve performance in many of these applications. While prior work has explored a wide range of structures to provide some degree of control of one or more of these attributes, there is an ongoing challenge in combining readily-fabricated, simple structures made of appropriate (e.g., heat-resistant) materials with the desired functionality. Here, we will focus on using metasurfaces in conjunction with refractory materials as a platform for achieving selective control of emission. These structures are built from sub-wavelength elements that support localization of surface plasmon polaritons or electromagnetic resonant modes with appropriate attributes. Modeling is performed using rigorous coupled wave analysis (RCWA), plus Kirchhoff’s law of thermal radiation, which is further validated using finite-difference time domain (FDTD) simulations and coupled-mode analysis. Such structures can be considered arbitrarily directional sources that can be carefully patterned in lateral directions to yield a thermal lens with a designed focal length and/or concentration ratio; the benefit of this approach is that it can enhance the view factor between thermal emitters and receivers, without restricting the area ratio or separation distance. This design and modeling platform is then applied to exclude thermal radiation over a certain range of angles. In this work, we study the effect of controlling the angular width and direction on the view factor, and we explore angular dependence of these angular selective structures.

Due to the wide bandgap and other key materials properties of 4H-SiC, SiC MOSFETs offer performance advantages over competing Si-based power devices. For example, SiC can more easily be used to fabricate MOSFETs with very high voltage ratings, and with lower switching losses. Silicon carbide power MOSFET development has progressed rapidly since the market release of Cree’s 1200V 4H-SiC power MOSFET in 2011. This is due to continued advancements in SiC substrate quality, epitaxial growth capabilities, and device processing. For example, high-quality epitaxial growth of thick, low-doped SiC has enabled the fabrication of SiC MOSFETs capable of blocking extremely high voltages (up to 15kV); while dopant control for thin highly-doped epitaxial layers has helped enable low on-resistance 900V SiC MOSFET production. Device design and processing improvements have resulted in lower MOSFET specific on-resistance for each successive device generation. SiC MOSFETs have been shown to have a long device lifetime, based on the results of accelerated lifetime testing, such as high-temperature reverse-bias (HTRB) stress and time-dependent dielectric breakdown (TDDB).

Whispering gallery modes (WGMs) have been widely studied over the past 20 years for various applications, including biological sensing. While the WGM-based sensing approaches reported in the literature have shown tremendous performance down to single molecule detection, at present such sensing technologies are not yet mature and still have significant practical constraints that limit their use in real-world applications. Our work has focused on developing a practical, yet effective, WGM-based sensing platform capable of being used as a dip sensor for in-vivo biosensing by combining WGM fluorescent microresonators with silica Microstructured Optical Fibers (MOFs).

We recently demonstrated that a suspended core MOF with a dye-doped polymer microresonator supporting WGMs positioned onto the tip of the fiber, can be used as a dip sensor. In this architecture the resonator is anchored to one of the MOF air holes, in contact with the fiber core, enabling a significant portion of the evanescent field from the fiber to overlap with the sphere and hence excite the fluorescent WGMs. This architecture allows for remote excitation and collection of the WGMs. The fiber also permits easy manipulation of the microresonator for dip sensing applications, and hence alleviates the need for a complex microfluidic interface. More importantly, it allows for an increase in both the excitation and collection efficiency compared to free space coupling, and also improves the Q factor.

In this paper we present our recent results on microstructured fiber tip WGM-based sensors and show that this sensing platform can be used in clinical diagnostics, for detecting various clinically relevant biomarkers in complex clinical samples.

The emergence of hydrogen and fuel cell technologies in transportation and stationary power sectors offers the world important and potentially transformative environmental and energy security benefits. In recent years, research supported by the U.S. Department of Energy’s (DOE) Fuel Cell Technologies Office has contributed substantially to the development of these technologies. Enhanced performance and reduced cost in automotive fuel cells are important examples of achievement. The research investments are clearly paying off, as commercial fuel-cell electric vehicles (FCEVs) are being rolled out by major car manufacturers today. With increasing market penetration of FCEVs, enabling technologies for the affordable and widespread production, storage and delivery of renewable hydrogen are becoming increasingly important. Long term commercial viability of hydrogen and fuel cells in the commercial marketplace will rely on continued materials research on several important fronts. Examples include the discovery and development of: (1) non-platinum-group-metal catalysts for next-generation fuel cells; (2) durable, high-performance photocatalytic materials systems for direct solar water splitting; (3) advanced materials-based systems for low-pressure, high-volumetric-density hydrogen storage; and (4) low-cost, hydrogen-compatible pipeline materials for hydrogen delivery and distribution. Research innovations in macro-, meso- and nano-scale materials are all needed for pushing forward the state-of-the-art in these areas. New approaches in accelerated materials development facilitated by a national Energy Materials Network of advanced scientific resources in theory, computation and experimentation are being adopted at DOE. Application of these approaches to address the key materials challenges in hydrogen and fuel cell technologies are discussed.

Four decades of advanced research about Non-Conventional Materials and Technologies (NOCMAT) such as bamboo and composites reinforced with natural fibers have shown that it is now possible to produce and use high performance NOCMAT. Bamboo and composites reinforced with vegetable fibers are capable, meeting most engineering demand in terms of strength, stiffness, toughness and energy absorption capability. The greatest challenge of the 21st century is the need for cost-effective, durable and eco-friendly construction materials that will meet the global needs of infrastructure regeneration and rehabilitation which alone can enhance the quality of life for all the people of the world. This paper summarizes some results of judicious combination of different matrix reinforced with vegetable fibers, especially bamboo. These sustainable ecological materials are strong, ductile and capable of absorbing large amounts of energy. They could find extensive applications in the engineering particularly in developing countries. Specifically, the development of durable composites reinforced with vegetable fibers and bamboo poses an important challenge to the science and skills of engineering. This challenge could create the most useful, eco-friendly construction materials backed by an endless supply of renewable natural resources. In addition the paper presents results of some ongoing research concerning bamboo and how vegetable fibers such as hemp plant, before the invention of Nylon was the most used materials in all aspects of human life around the globe and why it was banned.