Highlights of 2016

Improved red emission in polyvinylpyrrolidone (PVP)-coated hollow LaF₃:Eu³⁺ nanoparticles by introducing Li⁺ ions was found for the first time via a one-step template-free hydrothermal method. The hollow formation can be attributed to self-recrystallization and a local Ostwald ripening thermodynamic process. Pores were clearly seen and widely distributed in all LaF₃ nanoparticles. The introduction of Li⁺ ions did not introduce new crystalline phases and resulted in little change in size and morphology of the LaF₃ nanoparticles. The main diffraction peaks were found to shift slightly with the Li⁺ doping concentrations, which indicates that Li⁺ changes the crystal field environment of Eu³⁺. The excitation and red emission intensity both doubled when codoped with 7 mol% Li⁺ ions. The widely distributed pores and improved luminescence properties of our nanoparticles facilitated the construction of new nanocomposites for novel biological applications.

In this work, europium and dysprosium doped strontium aluminate (SrAl₂O₄:Eu²⁺,Dy³⁺) nanophosphor is synthesized and its novel application for the detection of latent fingerprints on various contact surfaces is reported. The SrAl₂O₄:Eu²⁺,Dy³⁺ is synthesized using a combustion method and shows long-lasting afterglow luminescence. The powder particles are characterized using field emission scanning electron microscopy (FE-SEM), SEM–energy dispersive x-ray analysis, x-ray diffraction and photoluminescence spectrophotometry. The FE-SEM image analysis reveals that the nanoparticles are mostly 8–15 nm in size with an irregular spherical shape. This nano-structured powder was applied to fresh and aged fingerprints deposited on porous, semi-porous and non-porous contact surfaces, such as ordinary colored paper, glossy paper, glass, aluminum foil, a yellow foil chocolate wrapper, a soft drink can, a PET bottle, a compact disc and a computer mouse. The results are reproducible and show great sensitivity and high contrast in the developed fingermark regions on these surfaces. These nanophosphor particles also show a strong and long-lasting afterglow property, making them a suitable candidate for use as a fingerprint developing agent on luminescent and highly patterned surfaces. These kinds of powders have shown that they can remove the interference from background luminescence, which is not possible using ordinary luminescent fingerprinting powders.

High entropy alloys (HEAs), as a new kind of alloys with equi- or near equi-atomic alloy compositions, have recently received increased interest, but their mechanical properties at micro- and nanoscales are less studied, which could hinder their structural/functional applications in the small scales. In this work, the mechanical responses of single crystalline FCC-structured CoCrCuFeNi HEA micro- and nano-pillars were systematically investigated by an in situ SEM nanoindenter. The yield strengths of the HEA micro-/nano-pillars under uniaxial compression appear to be size-dependent (with the m value of ∼0.46 in the Hall-Petch law relationship), but less sensitive when compared to typical metal/alloy micro- and nano-structures (e.g. with the m values of 0.6–0.9 for FCC metals). We also observed and analyzed the slip systems of the plastically deformed micro-/nano-pillars, and discussed their deformation mechanisms together with the Young's modulus by multiple loading/unloading compressions experiments. Our results could provide useful insights in the design and application of HEA for functional micro- and nano-devices.

We report analysis of electrospun polymer nanofibers fabricated from blends of semicrystalline polyamide-6 (PA-6) and fully amorphous polyamide-6 (PA-6I) in the narrow diameter range of 200–250 nm. The combined differential scanning calorimetry and wide angle x-ray scattering results show the presence of α- and γ-phase crystals in PA-6 nanofibers. Simultaneous small- and wide-angle x-ray scattering investigations confirmed the existence of small elongated domains which were formed during the electrospinning process due to stretching of polymer chains. The Debye–Bueche analysis determined a cross-sectional width of elongated domains in the range of 10.8–16 Å. Additionally, analysis by Ruland's method revealed a decrease in the length of elongated domains with increasing crystalline phase content in the blends. Evaluation of Herman's orientation function suggested that the domains possessed higher molecular anisotropy along the c-axis in PA-6I compared to PA-6 nanofibers. These investigations and the suggested role of the amorphous phase in molecular stretching of polymer chains in electrospun nanofibers, may have broad implications for the size-dependent mechanical properties.

Nanostructured ternary composite of polyaniline (PANI), Co₃O₄ nanoparticles, and Chitosan (CS) has been prepared by an in situ chemical oxidation method, and the nanocomposites (CPAESCO) were used as supercapacitor electrodes. The Co₃O₄ nanoparticles are uniformly coated with CS and PANI layers in it. Different techniques (Fourier transform infrared spectrophotometry, x-ray diffraction, thermal gravimetric analysis, UV−visible spectroscopy, scanning electron microscopy, transmission electron microscopy and electro chemical analysis-cyclic voltammetry, galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy) were used to analyse the optical, structural, thermal, chemical and supercapacitive aspects of the nanocomposites. Core/double shell ternary composite electrode exhibits significantly increased specific capacitance than PANI/Co₃O₄ or PANI/CS binary composites in supercapacitors. The ternary nanocomposite with 40% nanoparticle exhibits a highest specific capacitance reaching 687 F g⁻¹, Energy density of (95.42 Wh kg⁻¹ at 1 A g⁻¹) and power density of (1549 W kg⁻¹ at 3 A g⁻¹) and outstanding cycling performance, with, 91% capacitance retained over 5000 cycles. It is found that this unique bio compatible nano composite with synergy is a new multifunctional material which will be useful in the design of supercapacitor electrodes and other energy conversion devices too.

Green laser irradiation successfully activated self-healing processes in epoxy-acid networks modified with low amounts of gold nanoparticles (NPs). A bio-based polymer matrix, obtained by crosslinking epoxidized soybean oil (ESO) with an aqueous citric acid (CA) solution, was self-healed through molecular rearrangements produced by transesterification reactions of β-hydroxyester groups generated in the polymerization reaction. The temperature increase required for the triggering of these thermally activated reactions was attained by green light irradiation of the damaged area. Compression force needed to assure a good contact between crack faces was achieved by volume dilatation generated by the same temperature rise. Gold NPs dispersed in the polymer efficiently generated heat in the presence of electromagnetic radiation under plasmon resonance, acting as nanometric heating sources and allowing remote activation of the self-healing in the crosslinked polymer.

In this work, an alternative technique to the traditional micromechanical exfoliation of two-dimensional materials is proposed, consisting of isolated flakes of graphite and molybdenum disulphide onto polymeric surfaces films. The set made up of polymer and flakes is fabricated by using a hot-press machine called polymeric stamp. The polymeric stamp was used to allocate flakes and also to allow the exfoliation process to take place just in one face of isolated flake. Optical microscopy, Raman spectroscopy and photoluminescence spectroscopy results showed that multilayers, bilayers and single layers of graphene and MoS₂ were obtained by using a polymeric stamp as tool for micromechanical exfoliation. These crystals were more easily found because the exfoliation process concentrates them in well-defined locations. The results prove the effectiveness of the method by embedding two-dimensional materials into polymers to fabricate fewer layers crystals in a fast, economic and clean way.

Recent simulation and experimental work on polymer nanocomposites composed of polymer grafted particles and free matrix polymers, where the graft and matrix homopolymers are chemically dissimilar and exhibit lower critical solution temperature behavior with temperature, has shown that wetting to dewetting is a gradual and distinct transition from the sharp particle dispersion–aggregation transition. In this study, using coarse-grained molecular simulations, we demonstrate that the extent of wetting of the grafted polymer layer and the particle dispersion–aggregation transition are tuned using the composition of graft and matrix polymers. Specifically, we study composites where the graft and matrix chains are random copolymers composed of attractive and athermal monomers. We maintain a dense grafting density on the spherical particles of diameter five times the monomer diameter and study matrix lengths five times that of the graft chain length or equal graft and matrix chain lengths. We vary the fraction of attractive monomers in the graft $({f}_{{\rm{G}}})$ and matrix $({f}_{{\rm{M}}})$ chains, graft–matrix chain composition ratio $({f}_{{\rm{G}}}/{f}_{{\rm{M}}}),$ and the graft–matrix interaction strength, as characterized by the Flory–Huggins interaction parameter between graft and matrix attractive monomers: ${\chi }_{{\rm{GM}}}.$ When ${\chi }_{{\rm{GM}}}$ is negative, decreasing ${f}_{{\rm{G}}}$ and/or ${f}_{{\rm{M}}}$ decreases the extent of grafted layer wetting by matrix chains because the enthalpic driving force for wetting is reduced. As the ${\chi }_{{\rm{GM}}}$ increases and becomes positive, the extent of wetting decreases gradually till it reaches the wetting of analogous athermal composites. That value of ${\chi }_{{\rm{GM}}}$ where the extent of wetting is the same as that of an analogous athermal polymer nanocomposite marks the onset of dispersion–aggregation transition. For symmetric graft and matrix chain compositions $({f}_{{\rm{G}}}={f}_{{\rm{M}}})$, the magnitude of ${f}_{{\rm{G}}}$ and ${f}_{{\rm{M}}}$ tunes the overall extent of wetting of the grafted particles in the dispersed state but not the dispersion–aggregation transition. Varying the asymmetry of the graft and matrix chain composition (i.e. f_G/f_M) tunes both the extent of wetting of the grafted layer and the dispersion–aggregation transition.

The plant root extract mediated green synthesis method produces monodispersed spherical shape silver nanoparticles (AgNPs) with a size range of 15–30 nm as analyzed by atomic force and transmission electron microscopy. The material showed potent antibacterial and antifungal properties. Synthesized AgNPs display a characteristic surface plasmon resonance peak at 420 nm in UV–Vis spectroscopy. X-ray diffractometer analysis revealed the crystalline and face-centered cubic geometry of in situ prepared AgNPs. Agar well diffusion and a colony forming unit assay demonstrated the potent biocidal activity of AgNPs against Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Klebsiella pneumoniae, Pseudomonas diminuta and Mycobacterium smegmatis. Intriguingly, the phytosynthesized AgNPs exhibited activity against pathogenic fungi, namely Trichophyton rubrum, Aspergillus versicolor and Candida albicans. Scanning electron microscopy observations indicated morphological changes in the bacterial cells incubated with silver nanoparticles. The genomic DNA isolated from the bacteria was incubated with an increasing concentration of AgNPs and the replication fidelity of 16S rDNA was observed by performing 18 and 35 cycles PCR. The replication efficiency of small (600 bp) and large (1500 bp) DNA fragments in the presence of AgNPs were compromised in a dose-dependent manner. The results suggest that the Thalictrum foliolosum root extract mediated synthesis of AgNPs could be used as a promising antimicrobial agent against clinical pathogens.

Chronic dopamine (DA) monitoring is a critical enabling technology to identify the neural basis of human behavior. Carbon fiber microelectrodes (CFM), the current gold standard electrode for in vivo fast scan cyclic voltammetry (FSCV), rapidly loses sensitivity due to surface fouling during chronic neural testing. Periodic voltage excursions at elevated anodic potentials regenerate fouled CFM surfaces but they also chemically degrade the CFM surfaces. Here, we compare the dimensional stability of 150 μm boron-doped ultrananocrystalline diamond (BDUNCD) microelectrodes in 1X PBS during 'electrochemical cleaning' with a similar-sized CFM. Scanning electron microscopy and Raman spectroscopy confirm the exceptional dimensional stability of BDUNCD after 40 h of FSCV cycling (∼8 million cycles). The fitting of electrochemical impedance spectroscopy data to an appropriate circuit model shows a 2x increase in charge transfer resistance and an additional RC element, which suggests oxidation of BDUNCD electrode surface. This could have likely increased the DA oxidation potential by ∼34% to +308 mV. A 2x increase in BDUNCD grain capacitance and a negligible change in grain boundary impedance suggests regeneration of grains and the exposure of new grain boundaries, respectively. Overall, DA voltammogram signals were reduced by only ∼20%. In contrast, the CFM is completely etched with a ∼90% reduction in the DA signal using the same cleaning conditions. Thus, BDUNCD provides a robust electrode surface that is amenable to repeated and aggressive cleaning which could be used for chronic DA sensing.

Layered materials, such as the transition metal dichalcogenide molybdenum disulfide (MoS₂), are promising materials for ion storage in electrodes of rechargeable batteries. To extend the application range of these materials to ions beyond lithium-ions, we used van der Waals corrected density functional theory simulations to study the intercalation and diffusion of lithium (Li), sodium (Na), and magnesium (Mg) in the 2H structure of MoS₂ as a function of interlayer spacing. All three species exhibit an optimal intercalation energy, which is reached at about 11% expansion for Li and Mg, and 23% expansion for Na. Similarly, the slow diffusion kinetics of large Na and divalent Mg-ions can be improved by layer expansion. When the interlayer spacing is increased by about 35% from its equilibrium value, the diffusion of Na and Mg-ions becomes more facile than the diffusion of small, monovalent Li-ions, with diffusion barriers similar to those of Li in graphene. Our results indicate that interlayer expansion is a promising technique to improve intercalation kinetics and thermodynamics for large and/or multivalent ions in MoS₂, which can be a major limitation to battery performance. The rationalization of our results in terms of bonding geometries forms the basis of a battery electrode design framework with applications for a wide range of layered materials.

Development of chemoresistive ammonia sensor that does not suffer with humidity interference is highly desirable for practical environmental monitoring systems. We report enhanced ammonia sensing using chemically reduced graphene oxide (RGO) and rose bengal (RB) nanocomposite fabricated in a very simple and cost effective manner. The RGO–RB nanocomposites were synthesized using three different concentrations (2 mg mL⁻¹, 5 mg mL⁻¹ and 10 mg mL⁻¹) of RB keeping the RGO concentration same. Ammonia and humidity sensing of these three different composites were explored. Interestingly, it was observed that with increasing concentration of RB, the sensitivity of the sensor towards ammonia was increased but the sensitivity towards humidity was decreased. The response of the nanocomposites varied from ∼9–45% against 400−2800 ppm of ammonia whereas intrinsic RGO showed a response of merely 17% against 2800 ppm of ammonia. On the other hand the response of the nanocomposite based sensor was reduced from 18% to 7% against 100% relative humidity. Also, the sensor was found to be selective towards ammonia when tested against other toxic volatile organic compounds. The limit of detection of the RGO–RB based sensor was calculated to be as low as 0.9 ppm. Field emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy and UV–vis spectroscopy were carried out for the detailed structural characterizations of the sensing layer. These results are believed to be very useful for the cost effective fabrication of graphene based ammonia sensors which have reduced effects of humidity.

Cerium-doped silica glass has been prepared for ionizing radiation dosimetry applications, using the sol–gel route and densification under different atmospheres. In comparison with the glass densified under air atmosphere, the one obtained after sintering the xerogel under helium gas presents improved optical properties, with an enhancement of the photoluminescence quantum yield up to 33%, which is attributed to a higher Ce³⁺ ions concentration. Such a glassy rod has been jacketed in a quartz tube and then drawn at high temperature to a cane, which has been used as active material in a fibered remote x-ray radiation dosimeter. The sample exhibited a reversible linear radioluminescence intensity response versus the dose rate up to 30 Gy s⁻¹. These results confirm the potentialities of this material for in vivo or high rate dose remote dosimetry measurements.

The study aims to develop a novel composite, with a combined contribution of reduced graphene oxide, poly(dimethyl-siloxane), and sodium bentonite (organoclay), for flame protection. Thermogravimetric analysis revealed an outstanding thermal stability of the composite as compared to its constituents. The superior composite is demonstrated to efficiently protect a polymer layer that burns instantly upon exposure to flame. The char residue of the composite indicated the formation of a spherical structure that acted as barrier layer to the underlying material to avoid any structural damage caused due to the exposure of the flame.

We study the dynamic nuclear polarization of nitrogen-vacancy (NV) centers in diamond through optical pumping. The polarization is enhanced due to the hyperfine interaction of nuclear spins as applied magnetic fields vary. This is a result of the averaging of excited states due to fast-phonon transitions in the excited states. The effect of dephasing, in the presence of a vibronic band, is shown to have little effect during the dynamic polarization.

Compared with the normal relation between temperature (T) and elastic modulus (E) in most materials, martensitic transformation (MT) and magnetic transition could result in the softening of elastic modulus (dE/dT > 0) within a narrow range of T (<100 °C). It becomes possible in MnFeCu alloys to tune this range and broaden it to about 200 °C through combining MT and paramagnetic-antiferromagnetic (P-A) transition. The alloying elements and their contents play a key role in making MT separate from P-A transition, in which first-order MT made a greater contribution to this maximum value than second-order P-A transition. The intrinsic mechanism is that MT can continue causing the modulus to soften even after the P-A transition ends. This wide range keeps stable under different cooling/heating rates. An expression for dE/dT is deduced based on the proposed free energy model and the corresponding theoretical curve (dE/dT-T) gives a reasonable explanation on the experimental results in MnFeCu alloys. A modulus–temperature–composition phase diagram is obtained to describe such critical behaviors and it is found that there exists a specific triangle zone in which dE/dT > 0. The present results may enrich approaches to designing new functional materials, e.g. the elastic and Elinvar alloys.

Recently, membrane-type acoustic metamaterials have been found useful in eliminating low-frequency sound/noise. Those materials exhibit unusual vibroacosutic behavior and have a negative value in mass density. In this study, we present a new design of acoustic metamaterials that can effectively broaden sound attenuation zone and achieve acoustic negativity in mass density/bulk modulus. The proposed structure is comprised of two membranes and two ring masses which are attached on membrane surfaces, respectively. Both dipolar and monopolar resonance exist in the proposed coupled system, which makes acoustic negativity possible. By altering mass magnitude and membrane tension the transmission loss peak frequency can be easily tuned. With two membranes having two rings of different magnitudes, the attenuation bandwidth can be effectively broadened.

Herein, we report one step facile chemical vapor deposition method for synthesis of single-layer MoSe₂ nanosheets with average lateral dimension ∼60 μm on 300 nm SiO₂/Si and n-type silicon substrates and field emission investigation of MoSe₂/Si at the base pressure of ∼1 × 10⁻⁸ mbar. The morphological and structural analyses of the as-deposited single-layer MoSe₂ nanosheets were carried out using an optical microscopy, Raman spectroscopy and atomic force microscopy. Furthermore, the values of turn-on and threshold fields required to extract an emission current densities of 1 and 10 μA cm⁻², are found to be ∼1.9 and ∼2.3 V μm⁻¹, respectively. Interestingly, the MoSe₂ nanosheet emitter delivers maximum field emission current density of ∼1.5 mA cm⁻² at a relatively lower applied electric field of ∼3.9 V μm⁻¹. The long term operational current stability recorded at the preset values of 35 μA over 3 hr duration and is found to be very good. The observed results demonstrates that the layered MoSe₂ nanosheet based field emitter can open up many opportunities for their potential application as an electron source in flat panel display, transmission electron microscope, and x-ray generation. Thus, the facile one step synthesis approach and robust nature of single-layer MoSe₂ nanosheets emitter can provide prospects for the future development of practical electron sources.

Cubic boron phosphide, BP, is notorious for its difficult synthesis, thus preventing it from being a widely used material in spite of having numerous favorable technological properties. In the current work, three different methods of synthesis are developed and compared: from the high temperature reaction of elements, Sn flux assisted synthesis, and a solid state metathesis reaction. Structural and optical properties of the products synthesized from the three methods were thoroughly characterized. Solid state metathesis is shown to be the cleanest and most efficient method in terms of reaction temperature and time. Synthesis by Sn flux resulted in a novel Sn-doped BP compound. Undoped BP samples exhibit an optical bandgap of ∼2.2 eV while Sn-doped BP exhibits a significantly smaller bandgap of 1.74 eV. All synthesized samples show high stability in concentrated hydrochloric acid, saturated sodium hydroxide solutions, and fresh aqua regia.

The interaction between phosphorene and SiO₂, Al₂O₃, and h-BN surfaces has been analyzed by first-principles calculations. Our work demonstrates that phosphorene forms strong bonds with O-terminated SiO₂ (0001) and Al- and O-terminated Al₂O₃ (0001) surfaces, and the structure of phosphorene changes drastically. We find that phosphorene adsorbs on the h-BN surface through van der Waals interactions. The 2D planar structure of h-BN is free of dangling bonds, which provides an ideal substrate for phosphorene to sit on. The bandgap of the phosphorene/h-BN system monotonically decreases with increasing vertical electric fields. A semiconductor-to-metal transition occurs at about 6 V nm⁻¹. The calculations suggest that phosphorene/h-BN heterostructures could provide a viable route to phosphorene-based electronic devices.

Size-controllable monodisperse CdSe nanocrystals with different organic capping were prepared based on the hot-injection method. The effective separation of nucleation and growth was achieved by rapidly mixing two highly reactive precursors. As a contrast, we prepared CdSe/CdS nanocrystals (NCs) successfully based on the selective ion layer adsorption and reaction (SILAR) technique. This inorganic capping obtained higher photoluminescence quantum yield (PLQY) of 59.3% compared with organic capping of 40.8%. Furthermore, the CdSe-epoxy resin (EP) composites were prepared by adopting a flexible ex situ method, and showed excellent stability in the ambient environment for one year. So the composites with both high PLQY of nanocrystals and excellent stability are very promising to device application.

The measurements on magnetization (M), resistivity (ρ) and specific heat (C) were carried out for the ferromagnetic CeTi${}_{1-x}$ Ni_xGe₃ (0.0 $\leqslant$ x $\leqslant$ 0.45) system. It was found that the Curie temperature, T_C, decreases with increasing Ni content, x, and reaches zero kelvin near a critical content x_cr = 0.44. A new phase diagram is constructed based on these measurements. The non-Fermi liquid (nFL) behavior in ρ(T), and $\mathrm{log}$(T₀/T) relationship in C/T in the samples near x_cr, demonstrate that strong spin fluctuation emerges in these samples, indicating that they are near a quantum critical point (QCP). Our results indicate that CeTi${}_{1-x}$ Ni_xGe₃ may provide another platform to study exotic quantum phenomena near ferromagnetic QCP.

In the present contribution, perovskite absorbers have been combined with few layer thick MoS₂ semiconductor to put together a solar cell allowing broad spectrum harvesting of solar radiations. Such modification allows to achieve solar light harvesting at the band edges, addressing a drawback of CH₃NH₃PbI₃ absorbers. We recorded an improved efficiency from 3.7% to 4.3% on the back of this methodology. We have also worked out a novel methodology to synthesize TiO₂/MoS₂ nanocomposite by in situ dispersion of liquid exfoliated MoS₂ sheets in the sol gel reaction.

The structural, mechanical, electronic, optical, and dynamical properties of BaLiF₃, BaLiH₃, and SrLiH₃ cubic perovskite materials are theoretically investigated by using first principles calculations. Obtained results are in reasonable agreement with other available theoretical and experimental studies. The considered materials are found to be mechanically stable in the cubic structure. We found that all materials are brittle. The modified Becke–Johnson (mBJ) exchange potential has been used here to obtain an accurate band order. The calculated band-gap energy value of BaLiF₃ (8.26 eV) within the mBJ potential agrees very well with the experimentally reported value of 8.41 eV. In order to have a deeper understanding of the bonding mechanism and the effect of atomic relaxation on the electronic band structure, the total and partial density of states have also been calculated. We have investigated the fundamental optical properties, such as the real ε₁(ω) and imaginary ε₂(ω) parts of the dielectric function, absorption coefficient α(ω), reflectivity R(ω), and refractive index n(ω) in the energy range from 0 to 40 eV within the mBJ potential. The band-gap energy obtained from the absorption spectrum is around 8.76, 3.99, and 3.31 eV for BaLiF₃, BaLiH₃, and SrLiH₃ crystals, respectively. It should be noted that BaLiF₃ could be a strong potential candidate as a laser material for the development of a vacuum-ultraviolet light emitting diode once direct transition is confirmed by experimental studies. Finally, we have calculated the lattice dynamical properties of BaLiF₃, BaLiH₃, SrLiH₃, and SrLiF₃ crystals. The full phonon dispersion curves of these materials are reported for the first time. Our results clearly indicate that the materials are dynamically stable, except for SrLiF₃, in the cubic structure. The obtained zone-center phonon frequencies of BaLiF₃, BaLiH₃, and SrLiH₃ accord very well with previous experimental measurements.

We have developed efficient nanostructures of Cu–Co–Ni alloy with varied stoichiometry as an alternative to the costly Pt-based alloys for hydrogen evolution reaction (HER). These nanoparticles were synthesized using the reverse micellar method. The size of the alloy nanoparticles varied from 40 to 70 nm. An enhanced catalytic activity as evident from high current density was observed for these Cu–Co–Ni (111) alloys which follows the Volmer–Heyrovsky mechanism. They have excellent stability (up to 500 cycles) and significant activity in acid media which might be due to the low hydrogen binding energy.

Nano-twinned structures are mechanically stronger, ductile and stable than its non-twinned form. We have investigated the effect of varying twin spacing and twin boundary width (TBW) on the yield strength of the nano-twinned copper in a probabilistic framework. An efficient surrogate modelling approach based on polynomial chaos expansion has been proposed for the analysis. Effectively utilising 15 sets of expensive molecular dynamics simulations, thousands of outputs have been obtained corresponding to different sets of twin spacing and twin width using virtual experiments based on the surrogates. One of the major outcomes of this work is that there exists an optimal combination of twin boundary spacing and twin width until which the strength can be increased and after that critical point the nanowires weaken. This study also reveals that the yield strength of nano-twinned copper is more sensitive to TBW than twin spacing. Such robust inferences have been possible to be drawn only because of applying the surrogate modelling approach, which makes it feasible to obtain results corresponding to 40 000 combinations of different twin boundary spacing and twin width in a computationally efficient framework.

Monolayer two-dimensional transition metal dichalcogenides (TMDCs) such as MoS₂ with broken inversion symmetry possesses two degenerate yet inequivalent valleys that can be selectively excited by circularly polarized light. This unique property renders interesting valley physics. The ability to manipulate valley degrees of freedom with light or external field makes them attractive for optoelectronic and spintronic applications. There is great demand for large area monolayer (ML) TMDCs for certain measurements and device applications. Recent reports on large area ML TDMCs focus on chemical vapor deposition growth. In this work, we report a facile approach to grow largescale continuous ML MoS₂ nearly free of overgrowth and voids, by sulfurizing evaporated molybdenum trioxide ultrathin films. Photo conductivity scales with device sizes up to 4.5 mm, suggesting excellent film uniformity. The growth mechanism is found to be vaporization, diffusion, sulfurization and lateral growth, all at local micrometer scale. Our approach provides a new pathway for large-area ML TMDC growth and lithography-free device fabrication.

Organic-based electronic devices are rapidly increasing in popularity, making it essential to understand and characterize the interface between organic materials and metallic electrodes. This work reports on the characterization of the interface between thin films of an emerging organic ferroelectric, vinylidene fluoride (VDF) oligomer, and Co, an important high Curie temperature ferromagnet. Using a wide battery of experimental techniques, it is shown that VDF oligomer thin films as thin as 15 nm can halt, or prevent, Co oxidization in atmospheric conditions, a necessary condition for device applications. Selectivity of magnetic properties, such as remanent magnetization, is enabled by the clarification of the time scale of Co oxidation, a topic on which there are many conflicting reports. Furthermore, this work shows evidence of chemical bonding at the interface between VDF oligomer and Co, a result with important implications for organic spintronic devices. These results establish the suitability of VDF oligomer for organic-based electronic devices.

During flash sintering, ceramic materials can sinter to high density in a matter of seconds while subjected to electric field and elevated temperature. This process, which occurs at lower furnace temperatures and in shorter times than both conventional ceramic sintering and field-assisted methods such as spark plasma sintering, has the potential to radically reduce the power consumption required for the densification of ceramic materials. This paper reviews the experimental work on flash sintering methods carried out to date, and compares the properties of the materials obtained to those produced by conventional sintering. The flash sintering process is described for oxides of zirconium, yttrium, aluminium, tin, zinc, and titanium; silicon and boron carbide, zirconium diboride, materials for solid oxide fuel applications, ferroelectric materials, and composite materials. While experimental observations have been made on a wide range of materials, understanding of the underlying mechanisms responsible for the onset and latter stages of flash sintering is still elusive. Elements of the proposed theories to explain the observed behaviour include extensive Joule heating throughout the material causing thermal runaway, arrested by the current limitation in the power supply, and the formation of defect avalanches which rapidly and dramatically increase the sample conductivity. Undoubtedly, the flash sintering process is affected by the electric field strength, furnace temperature and current density limit, but also by microstructural features such as the presence of second phase particles or dopants and the particle size in the starting material. While further experimental work and modelling is still required to attain a full understanding capable of predicting the success of the flash sintering process in different materials, the technique non-etheless holds great potential for exceptional control of the ceramic sintering process.

Recently, the covalent functionalization of graphene with π-conjugated semiconductors has attracted a tremendous amount of research interest, as this approach offer excellent solutions with which to overcome the inherent drawbacks of graphene. For example, the chemical modification graphene with organic semiconductors can not only tailor the various features of graphene, including its bulk and surface properties, but also impart novel characteristics through closely linked interactions between two distinct constituents. Owing to their unique structure–property relationships and good versatility, hybrid materials composed of graphene and an organic semiconductor have been widely considered as promising candidates for emerging energy-related and optoelectronic applications. In addition, the great potential of this combination has been demonstrated in the form of enhanced performance when utilizing them in suitable devices with the additional advantages of good processability and operational stability. Herein, we summarize the recent progress in the covalent functionalization of graphene with organic π-conjugated materials. In addition, challenges and future perspectives in this emerging field are discussed.

A vital and challenging task for materials researchers is to determine relationships between material characteristics and desired properties. While the measurement and assessment of material properties can be complex, quantitatively characterizing their structure is frequently a more challenging task. This issue is magnified for materials researchers in the areas of nanoscience and nanotechnology, where material structure is further complicated by phenomena such as self-assembly, collective behavior, and measurement uncertainty. Recent progress has been made in this area for both self-assembled and nanostructured surfaces due to increasing accessibility of imaging techniques at the nanoscale. In this context, recent advances in nanomaterial surface structure characterization are reviewed including the development of new theory and image processing methods.