Enhancement of thermoelectric properties at room temperature has been recently demonstrated by spark plasma sintered PbTe nanocubes as compared to other PbTe nanostructures as well as Bulk material. The Seebeck coefficient has been reported to be 400 µV/K which is much higher than the bulk. Moreover, a moderate electrical conductivity ∼ 8000 S/m at room temperature results in considerable higher value of power factor S2σ ∼ 1.28 x 10-3 Wm-1K-2. The enhanced thermoelectric properties have been conjectured to be present due to energy filtering effects at numerous interfaces introduced by nanostructuring. We study how the interfacial scattering affects the power factor by performing theoretical modelling based on Boltzmann Transport Equation (BTE). We also investigate in detail, the role of various electronic parameters such as size, shape, mobility and effective mass etc., on interfacial scattering to optimize its effect on power factor.

We recently developed a vacuum assisted micelle confinement synthesis for spherical microparticles of CL-20 with outstanding monodispersity. These microparticles are promising energetic material for explosive devices with enhanced and predictable performances. In this work, to facilitate further development and application of this synthesis, the particle growth process was monitored by in-situ dynamic light scattering measurements. The result was interpreted by a finite element model to obtain critical parameters. These parameters were then used to predict the behavior and product quality of batch synthesis under various operation conditions.

For the past 30 years, the development of durable materials for radionuclide immobilization has been driven by efforts to dispose of wastes generated by the nuclear fuel cycle [National Research Council, ‘Waste Forms Technology and Performance: Final Report’, the National Academies Press, Washington D.C., 2011]. Many materials have been developed, but there still exist large gaps in the knowledge of fundamental modes of waste form degradation in repository environments. An important aspect of waste form science is the behavior of the materials under intense irradiation from decaying actinides and fission products. This irradiation induces a wide range of defects and disorder, the details of which depend on the specific waste form material. At the present time, it is not fully explained how radiation effects will influence the performance of nuclear waste forms and their long-term retention of fission products and actinides under operational conditions. The complex defect behavior and radiation damage must be understood over a range of length scales, from the initial atomic-scale defect structure to the long-range observable material modification. This is particularly challenging and requires advanced characterization techniques. This contribution describes how pair distribution function (PDF) analysis obtained from neutron total scattering experiments can be applied in the research field of waste form science to uniquely characterize radiation effects in a wide range of materials, including crystalline complex oxides and waste glasses. Neutron scattering strength does not have an explicit Z-dependence; this allows access to many low-Z elements, such as oxygen, that cannot be accurately studied with X-rays. In many cases, this can permit a detailed analysis of both cation (often high-Z) and anion (often low-Z) defect behavior. In contrast to traditional crystallography, which relies on long-range order, PDF analysis probes the local defect structure, including changes in site occupation, coordination, and bond distance. This is particularly important when characterizing aperiodic waste glasses with no long-range order at all. In contrast to X-ray characterization which requires very little sample mass (∼0.1 mg), neutron characterization (even at state-of-the-art spallation facilities) requires relatively large sample mass (∼50 - 100 mg). Obtaining this quantity is challenging for studies of irradiated materials, but by tailoring our experimental approach to use high-energy ions (GeV) with very high penetration depth, we are able to produce the required mass.

The mechanism of electrical noise in transition metal dichalcogenides (TMDCs) has mostly been attributed to charge carrier fluctuations between the oxide traps and the conducting channel, in accordance with the McWhorter model. However, the original McWhorter model was formulated for diffusive transport with conducting carriers having extended electronic wave functions. Our work serves to generalize the McWhorter mechanism to include strongly localized systems such as the TMDC family and provides an explanation for the unusual exponential behavior of noise magnitude with temperature.

The gas field ion source (GFIS) is able to generate tightly focused ion beams, which can be used to image or modify a specimen. Among the beam species, helium offers extremely high resolution, however, low sputter yield and sub-surface bubble formation are limiting factors in some applications. Therefore, heavier ions such as neon or nitrogen are used as well. In addition to being a suitable choice for lithographic mask editing, secondary electron (SE) generation by nitrogen beams has been recently shown to be affected by certain types of samples, providing additional contrast compared to helium ions. Here, we report our progress on the study of SE imaging differences between the nitrogen ion microscopy (N2IM) and helium ion microscopy (HIM). SE images of two nano-patterned samples comprising insulator, metal and carbon regions have been imaged by nitrogen and helium ions in two fundamentally different GFIS microscopes. The results corroborate previous reports of significant contrast differences in certain samples caused by the different ion species.

The Nb-Ru system is of interest because the ∼NbRu phase has potential for high temperature shape memory alloys. Previous workers have identified the phase transformation variously as involving twinning, of cubic-to-tetragonal and tetragonal–to-orthorhombic (or monoclinic) transformations. As well as the terminal (Nb) and (Ru) solid solutions, two intermetallic phases have been identified: ∼NbRu and ∼NbRu3 / ∼Nb3Ru5 / ∼NbRu2, but the boundaries between the different phases are still not fully established. This investigation looked at six as-cast alloys of different compositions across the Nb-Ru system, which were made from 99.95 % purity Nb and Ru. The samples were made by arc-melting under an argon atmosphere, using titanium as an oxygen-getter. These samples were sectioned and prepared metallographically for optical microscopy, SEM and XRD analyses, the latter using an X’pert database. The phases found were (Nb), (Ru), ∼NbRu and “∼NbRu3”, as expected. Although the samples were mainly homogeneous, there was porosity in the (Ru) phase between the “∼NbRu3” dendrites in the Nb28.5:Ru71.5 at.% sample. The Nb14.2:Ru85.8 at.% sample was mainly single-phase (Ru).

The chemical decoration of biosilica shells (frustules) from microalgae with several classes of organic molecules is a convenient, scalable biotechnological route to silica nanostructures with applications ranging from photonics to biomedicine. Here we report for the first time the in vivo staining of Thalassiosira weissflogii diatoms with a two photon red emitting triphenylamine-based fluorescent dye bearing a triethoxysilyl functional group (tPhA-Silane). In vivo staining of the cells has been investigated with confocal microscopy and hybrid silica structures comprising the dye embedded into the biosilica have been isolated by proper protocols able to remove the organic protoplasm.

Full thickness rotator cuff tears (RCT) and the associated muscle degeneration that results due to this injury presents a significant clinical burden. The prevention or recovery from this degeneration requires the synchronized behavior of many cells that participate in regeneration. Strategies that tune the inflammatory cascade that is initiated after injury serves as a powerful way to influence tissue repair. Here, we use the local, sustained delivery of the immunomodulatory small molecule FTY720 to examine whether the recruitment of pro-regenerative myeloid cells affects the healing outcome. We find that PLGA microparticles have an atrophic effect on the muscle that is ameliorated with the release of FTY720. However, the inability of FTY720 delivery to induce pro-regenerative monocyte and macrophage recruitment and our findings demonstrating enrichment of CD4+ T cells suggest that effects of this small molecule are context dependent and that the underlying mechanisms behind this RCT associated muscle degeneration require further studies.

The transconductance degradation caused by the non-linear resistance of access regions in III-nitride high electron-mobility transistors (HEMTs) is mainly responsible for limiting the RF linearity of the transistor. In this paper, we use Landauer’s transmission theory to develop an analytic electrothermal current-voltage (I-V) model of access regions in III-nitride HEMTs. With only 12 parameters, most of which have a physical origin and can be obtained through experimental calibration, the model is able to correctly predict the I-V behavior in access regions from the drift-diffusive to the quasi-ballistic transport regimes. Model accuracy is demonstrated by comparing the results against experimental and numerical hydrodynamic simulations of ungated transmission line structures with length scales ranging from few 10’s of nanometers to 10’s of micrometers.

We live at present with a largely linear materials economy. Our use of natural resources is characterized by the sequence “take – make – use – dispose” as materials progress from mine, through product, to landfill. Increasing population, rising affluence and the limited capacity for the planet to provide resources and absorb waste argue for a transition towards a more circular way of using materials (F. Blomsma, and G. Brennan, J. Industrial Ecology 21, 603 (2017); W. McDonough and M. Braungart, Cradle to cradle, remaking the way we make things, (North Point Press, New York, 2002)).

When products come to the end of their lives the materials they contain are still there. Repair, reuse and recycling (the three “Rs”) can return these to active use creating a technological cycle that, in some ways, parallels the carbon, nitrogen cycle and hydrological cycles of the biosphere. Repair, reuse and recycling are not new ideas; they have been used for centuries to recirculate materials and, in less-developed economies, they still are. But in developed nations they dwindled as the cost of materials fell and that of labor rose over time, making all three Rs less attractive. This and the complexity of current products has led to loss reparability and, therefore, reuse. So, what is novel about the contemporary idea of a circular materials economy? Haven’t we been there before?

Over the last decade, the idea of deploying rather than consuming materials, has gained economic as well as environmental appeal. Governments now sign up to programs to foster circular economic ideas and mechanisms begin to appear to advance them. Here we examine the background, the successes and the challenges of implementing a circular materials economy and the degree to which it can deliver the ultimate goal – that of reducing the drain on non-renewable natural resources to as close to zero as possible.

Circular economy (CE) is closely linked with the ideas of a low-carbon economy, management of supply risks, value generation through the service-based economy and efficient resource management. CE implies a design that focusses on material legacy, creating an economy that retains or regenerates materials over many life cycles, hence not consuming but using materials.

Granta Design has a history of involvement with material circularity, through collaborative develop of tools to aid teaching of engineering and design courses and industrial decision-making. The paper concludes with a brief discussion of these.

Temperature-dependent variations in electric switching and transverse resistance of phase-change [(GeTe)2(Sb2Te3)]n (n=4 and 8) chalcogenide superlattice (CSL) films were studied using conductive scanning probe microscopy (SPM). Three temperature regions with different electric transport properties were recognized in point current-voltage (I-V) spectra and the surface potential maps measured with tantalum and platinum-coated SPM cantilevers. At around 80°C the switching voltage decreased abruptly from ∼2 V to 0.5 V and the thermal coefficient of resistance changes its sign, indicating different carrier transport mechanisms. The observed changes correlated with decrease in the surface potential by ∼150 meV from 25 to 150°C. The results were ascribed to an opening of the CSL electronic band gap near the Fermi energy caused by thermal stress, which led to the transition from a Dirac-like semimetal to a narrow-gap semiconductor.

Fast imaging in Atomic Force Microscopy enhances the capability of studying phase transitions and surface properties of materials at variable temperatures. This is demonstrated by measurements of several polymers [poly(diethylsiloxane), low-density polyethylene and ethylene-octene copolymer] and bitumen at low (down to -20°C) and high (up to +150°C) temperatures. Monitoring of structural transitions was performed at small and large (up to 40 μm) areas with 1-5°C/min cooling/heating rates. Novel data about dynamics and structural transitions of mesomorphic transitions and crystallization were obtained.

In an effort to utilize their unique photoactive properties, porphyrin monomers were assembled into tetragonal microparticles by a surfactant-assisted neutralization method through the cooperative interactions between the porphyrin building blocks including π-π stacking, J-aggregation and metal-ligand coordination. Electron microscopy characterization in combination with x-ray diffraction confirmed the three-dimensional ordered tetragonal microstructures with stable crystalline frameworks and well defined external surface morphology. Optical absorption and fluorescence spectroscopy revealed enhanced absorbance properties as compared with the raw porphyrin material, favourable for chromophore excitation and energy transport. With active and responsive optical properties, these new porphyrin microparticles look to serve as promising components for a wide range of applications including sensing, diagnostics, solar cells, and optoelectronic devices.

All-inkjet-printed organic thin-film transistors take advantage of low-cost fabrication and high compatibility to large-area manufacturing, making them potential candidates for flexible, wearable electronics. However, in real-world applications, device instability is an obstacle, and thus, understanding the factors that cause instability becomes compelling. In this work, all-inkjet-printed low-voltage organic thin-film transistors were fabricated and their stability was investigated. The devices demonstrate low operating voltage (<3 V), small subthreshold slope (128 mV/decade), good mobility (0.1 cm2 V−1 s−1), close-to-zero threshold voltage (−0.16 V), and high on/off ratio (>105). Several aspects of stability were investigated, including mechanical bending, shelf life, and bias stress. Based on these tests, we find that water molecule polarization in dielectrics is the main factor causing instability. Our study suggests use of a printable water-resistant dielectric for stability enhancement for the future development of all-inkjet-printed organic thin-film transistors.

In this research we can demonstrate, that fission technetium-99 can be successfully immobilized as tetravalent cation in solid state refractory oxides such as pyrochlores and perovskites. Pyrochlores show excellent performance in ASTM C1220-10 type corrosion testing and have the ability to structurally bond Tc-99 and therefore avoid the formation of highly-mobile, pertechnetate species under conditions of a generic repository. We have fabricated lanthanide technetium oxides using either dry-chemical ceramic processing, or wet-chemical coprecipitation methods. Tc pyrochlores have shown better Tc retention and corrosion resistance compared with Tc-containing LAWE4-type borosilicate glass, combined with 50-times higher waste loading. However, mechanical properties (fracture toughness, compressive strength) of the pyrochlores are lacking and the microstructure shows high open porosity of about 50 %. To improve these properties we tested a variety of measures such as hot-pressing or the combination of hot pressing and high-temperature synthesis, but the improvement was minor and Tc and the surrogate Ru were partly reduced. The presence of metallic inclusions has strong impact on Tc retention and release rates increased more than tenfold. We have further developed a wet-chemical coprecipitation synthesis route followed by calcination and a 4-days high-temperature sintering cycle for the model composition Sm2(Ru0.5Ti0.5)2O7 where titanium oxide was added as sintering agent. The ceramic surrogate waste forms showed improved theoretical densities of about 73 % combined with sufficient mechanical strength, while maintaining ruthenium in the tetravalent state.

Carbon nanotubes (CNTs) possess superior mechanical, physical and chemical properties that make them ideal candidates for making sensors. However, challenges restricting their widespread applications in sensors still exist. To make the CNTs-based sensors own higher performance, nature has offered us with scientific and technological clues from the formation of biological composites using common organic components via naturally mild approaches. This paper reviews the recent progress on the bio-inspired synthesis of the CNTs-based sensors and their unique structures and novel properties.

Three MFCs with different catalyst incorporated on carbon felt cathode, viz. nickel phthalocyanine-MnOx (NiPc-MnOx) composite (MFC-1), platinum (MFC-2), control MFC with bare carbon felt (MFC-3) were used for treating distillery wastewater. The linear sweep voltammetry studies revealed that a maximum current density of 3.7 Am-2 was achieved for NiPc-MnOx/C catalysed cathode, which is 13-folds higher than that for control cathode (0.27 Am-2). Consequently, MFC-1 demonstrated a power density of 48.8 mWm-2, which was around 3.3-folds higher than the control MFC (14.9 mWm-2) owing to the improved oxidation reduction kinetics in case of NiPc-MnOx/C catalysed cathode. Coulombic efficiency (CE) was enhanced by a margin of about 11 % for MFC-1 (24.8 %) in comparison to MFC-3 (13.4 %). MFC-2 having platinum cathode catalyst exhibited a power density of 61.3 mWm-2, which was slightly higher than that achieved by MFC-2. However, NiPc-MnOx was prepared at 3-fold less cost as compared to platinum. Hence, NiPc-MnOx/C can be used as an alternative to platinum as cathode catalyst in MFC treating distillery wastewater.

Bismuth triiodide (BiI3) is a potential candidate for application in solar cell due to its good optoelectronic properties and because it is free of toxic elements. It can be used as the absorber material in solar cells or converted into the perovskite-like material MA3Bi2I9, suitable also for photovoltaic applications. Bismuth triiodide has been prepared by physical vapour transport (PVT) and by solution process through spin coating. In this work we present optical and structural/topological properties of BiI3 deposited by thermal evaporation under high vacuum. The films are slightly tensile, polycrystalline, homogenously distributed and with good adherence on several substrates, with an indirect bandgap of 1.81 eV, index of refraction of 3.3 (630 nm), photoluminescence centered at 1.74 eV and a Raman peak at 118cm-1 associated with the Ag mode.

PNIPAM hydrogels are widely studied materials which swell in a great extent in water and water like solvents (e.g. alcohols). The hydrophilic nature of PNIPAM networks is very attractive however it is an important disadvantage at the moment of encapsulating hydrophobic drugs, which minimize their use in other fields. In this work we studied the swelling in different solvent mixtures with water and also in pure nonaqueous solvents, some of them immiscible with water. Accordingly, PNIPAM gels swell strongly in highly polar solvents (e.g. chloroform) but it does not swell in slightly polar solvents (e.g. toluene). The main interaction between the solvent and the polymer chain seems to involve the hydrogen bonding with the amide group, according to the calculated Hansen parameters (δh). It is possible to swell the gel in binary or ternary mixtures containing toluene. In that way, non-polar substances can be loaded inside the gel to change its properties. As a proof of concept, polyaniline (PANI) solubilized in chloroform using camphorsulfonate as solubilizing counterion. The obtained nanocomposites become sensitive to pH changing color and conductivity when exposed to basic or acidic aqueous solutions.

In this contribution we report on the synthesis of n-type Bismuth vanadate (BiVO4) nanorods prepared via the use of aqueous extracts of Callistemon viminalis. X-ray diffraction analysis confirmed the formation of highly crystalline monoclinic BiVO4 nanorods post annealing of the Bismuth vanadate precursor powder at 500 °C. Scanning Electron Microscopy and High Resolution Transmission Electron Microscopy showed that BiVO4 nanorods have a high aspect ratio. Using UV-Vis absorption measurements the optical band gap of the nanorods is estimated to be 2.4 eV which makes the bio-synthesized BiVO4 powder a good candidate for sunlight driven photocatalysis.