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It is demonstrated experimentally and confirmed theoretically that highly defective boron nitride showed outstanding performance for oxidative dehydrogenation of ethylbenzene. The catalyst is derived from carbon-doped hexagonal boron nitride nanosheets synthesized via a two-step reaction when participating the oxidative dehydrogenation reaction. The first step yields a polymeric precursor with the atomic positions of B, C, N relatively constrained, which is conducive for the formation of carbon atomic clusters uniformly dispersed throughout the BN framework. During the oxidative dehydrogenation of ethylbenzene to styrene, the nanoscale carbon clusters are removed and highly defective boron nitride (D-BN) is obtained, exposing boron-rich zigzag edges of BN that act as the catalytic sites. The catalytic performance of D-BN is therefore remarkably better than un-doped h-BN. Our results indicate that dispersed C-doping in h-BN is highly effective in terms of defect formation and resultant enhanced activity in oxidative dehydrogenation reactions.

The microstructure and tensile properties of thermo-mechanically processed ferritic steels alloyed with Mo, Cr, V and Nb were investigated using scanning transmission electron microscopy, atom probe tomography and uniaxial tensile loading. The microstructures consisted of predominantly polygonal ferrite (~4 ± 3 µm average grain size) and a high number density of nano-sized, disc-shaped interphase precipitates (~2-4 nm diameter and 1 ± 0.4 nm thick). Interphase fiber carbides were also present in V, Cr and Nb -alloyed steel. Cluster formation was observed both between the interphase precipitates in rows and in ferrite matrix between the rows. The individual contributions to yield strength arising from different operating strengthening mechanisms were estimated. For the first time, the operation of coherency and modulus strengthening mechanisms for nano-sized interphase precipitates in this class of steels was considered. The major contributions were due to grain boundary strengthening and nano-sized precipitation, in the order of ~280 MPa and ~395 MPa, respectively. Significant cluster strengthening (~150-170 MPa) was also evident.

Electron diffraction coupled with aberration-corrected (AC) scanning transmission electron microscopy (STEM) is used to image, identify and confirm the structure producing double diffracted spots seen in electron diffraction patterns in twinned high-carbon steels. The experimental and simulated data show that regions comprising: (i) overlaps between a twin and the matrix or, (ii) overlapping twins, create projected structures that are similar to the ω phase observed in other metastable bcc systems. Thus, AC STEM is proficient in the definitive identification of twins in bcc high carbon steels or nanoscale phases in metastable bcc systems.

Nanoscale interphase precipitation in microalloyed ferritic steels provides a remarkable (200–400 MPa) strengthening increment, however its origin is unclear. Scanning transmission electron microscopy revealed step formation at the matrix/precipitate interface after both macroscopic uniaxial tension and nanopillar compression testing. Supported by Density Functional Theory modelling, dislocation shearing of nano-sized ( slip–system in the VC nanoparticles.

In this study, hexagonal boron nitride nanosheets (h-BNNS) have been grown on polycrystalline silver substrates via chemical vapor deposition (CVD) using ammonia borane as a precursor. The h-BNNS are of few-atomic-layer thickness and form continuous coverage over the whole Ag substrate. The atomically thin coating poses negligible interference to the reflectivity in the UV–visible range. The nanosheet coating also proves very effective in protecting Ag foil chemically. In contrast to bare Ag foil, the coated foil displayed only minor decolorization under high concentration of H2S. The study indicates that h-BNNS can be a promising protective coating for Ag based items such as jewelry or mirrors used in astronomical telescopes.

Transition metals with desirable valence states have been proposed as efficient non-noble-metal electrocatalytic systems for selective water splitting. In this work, two-dimensional (2D) nitrogen-doped leaf-like carbon matrix arrays functionalized with multi-valence-state transition metal (cobalt) hybrids were successfully prepared by in situ calcination of the corresponding bimetallic leaf-like zeolitic imidazolate framework (ZIF-L) in an inert atmosphere. The 2D morphology of the matrix along with the particle size and surface valence state of the anchored particles has been successfully controlled via precisely adjusting the Co2+/(Zn2+ + Co2+) ratio in the bimetallic ZIF-L precursor. Electrochemical measurements show that the kinetics of and stability towards the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are highly dependent on the particle size as well as the valence states. It was found that the particles with sizes less than 60 nm exhibit mixed Co0/Co2+ valence states, and therefore demonstrate bi-functional electrocatalytic performance. The theoretical simulations revealed that the bi-functional electrocatalytic activity should be attributed to the synergetic effect of mixed Co0/Co2+ and electronic coupling in the hybrids, which are of benefit to the catalytic kinetics and dynamics. High HER and OER activities of the hybrids have been verified, in which overpotentials of 171 and 280 mV to deliver a current density of 10 mA cm−2 for the HER and OER, respectively, were achieved. The obtained correlation between non-noble-metal-based carbon composites and HER/OER activities may be exploited as a rational guideline in the design and engineering of electrocatalysts.

Heterostructures, which can possess advantages of materials with different properties, have attracted enormous attention in various research fields including solar cells, photocatalysts, and optical electronic devices. In this work, a 2D/3D atomic epitaxial heterostructure with ultrathin BiOCl nanosheets and YF3:Yb, Tm octahedral crystals was fabricated via the halogen atom exchange method in the solution phase. The epitaxial heterointerface can facilitate energy transfer between BiOCl and YF3:Yb, Tm and suppress the energy quenching induced by grain boundaries. By carrying out single-particle confocal characterization, the energy upconverted by YF3:Yb, Tm is quantitatively confirmed to be transferred to ultrathin BiOCl nanosheets. As a result, YF3:Yb, Tm@BiOCl displays outstanding NIR-driven water splitting and waste-water cleaning properties. This study paves the way to fabricate 2D/3D epitaxial heterostructures, which helps to broaden the application of typical 2D materials.

In-situ electron backscattering diffraction was used to track microstructure and texture development in polycrystalline copper during uniaxial tension. Characteristic of face-centred-cubic materials, copper develops a double fibre texture comprising a relatively strong " open=" 111 fibre and a weak " open=" 100 fibre parallel to the tensile axis. The observation of small stacking faults via transmission electron microscopy indicates that partial slip contributes to strain accommodation during uniaxial tension. The visco-plastic self-consistent model was applied to simulate the macroscopic stress-strain curve and crystallographic texture development by considering the effects of the grain-matrix interaction mode, latent hardening, perfect and partial slip. The simulations demonstrate that an intermediate grain-matrix interaction scheme coupled with weak latent hardening, dominant perfect slip and limited partial slip returns the best agreement between the experimental and simulated textures.

For the first time, deformation twinning and martensitic transformation were observed in retained austenite in a low-alloyed transformation-induced plasticity steel using nanoindentation in conjunction with electron backscattering diffraction and transmission electron microscopy. Dislocation glide, martensite formation and deformation twinning were correlated to pop-ins and deviation from linearity in the load-displacement curve. Deformation twinning was found to enhance the stability of retained austenite. This observation furthers our understanding of RA stability during straining of low-alloyed multiphase TRIP steel.

Dynamic and metadynamic recrystallisation behaviour of Ni-30Fe-Nb-C model alloys during plane strain compression was investigated by optical and electron microscopy. The dynamically recrystallised grains were primarily located at the pre-existing grain boundaries with few additional new recrystallised grains in the prior grain interior. A limited nucleation of recrystallised grains at >400 nm size NbC particles was also evident. On the other hand, smaller semi-coherent particles (~10–150 nm) severely inhibit the dislocations rearrangement and subgrain boundary mobility, thus leading to sluggish or even suppressed dynamic and metadynamic recrystallisation. These smaller NbC particles maintained cube-on-cube orientation relationship with austenite matrix ( 001 ) NbC || ( 001 ) γ , [ 001 ] NbC || [ 001 ] γ . The shape of the NbC particles changes from nearly ellipsoidal to octahedral followed by hexagonal and tetra-kai-decahedral by truncation of { 111 } facets by { 001 } ones.

For the first time, a combination of scanning transmission electron microscopy and electron back-scattering diffraction is used to elucidate the early stages of particle stimulated recrystallisation at Nb carbides in Ni-30wt.%Fe alloy subjected to high temperature plane strain compression. While particles with sizes even below 1 μm were found to induce dynamic or metadynamic recrystallisation, only a small fraction of coarse particles served as nucleation sites.

In twinning induced plasticity (TWIP) steel, the question of what leads to the onset of twinning in grains whose 〈100〉 orientations are near parallel to the tensile axis at high tensile strains has not been resolved. Using aberration corrected scanning transmission microscopy we present first-hand evidence that extrinsic stacking faults serve as nuclei for twins in 〈100〉 grains and also contribute to twin growth in a low carbon TWIP steel uniaxially tensile loaded up to its ultimate tensile strength of ~ 1080 MPa; which corresponds to a tensile true strain of 48%. The results corroborate and validate our previous Schmid factor–based predictions on the feasibility of twinning nucleation via extrinsic stacking faults in 〈100〉 grains at high tensile strains.

Enhancing the efficiency of upconversion nanoparticles (UCNPs) and therefore their brightness is the critical goal for this emerging material to meet growing demands in many potential applications including sensing, imaging, solar energy conversion and photonics. The distribution of the photon sensitizer and activator ions that form a network of energy transfer systems within each single UCNP is vital for understanding and optimizing their optical properties. Here we employ synchrotron-based X-ray Photoelectron Spectroscopy (XPS) to characterize the depth distribution of Yb3+ sensitizer ions in host NaYF4 nanoparticles and systematically correlate the structure with the optical properties for a range of UCNPs with different sizes and doping concentrations. We find a radial gradient distribution of Yb3+ from the core to the surface of the NaYF4 nanoparticles, regardless of their size or the sensitizer's concentration. Energy dispersive X-ray Spectroscopy (EDX) was also used to further confirm the distribution of the sensitizer ions in the host matrix. These results have profound implications for the upconversion optical property variations.

EBSD in combination with aberration-corrected STEM is used to study the interfacial layer forming at Ni electrode - PbTe thermoelectric material interfaces. Contrary to previous studies, both orthorhombic and monoclinic phases are identified within the interfacial layer. EBSD and STEM data at interphase boundaries demonstrate an approximately smooth transition from orthorhombic to monoclinic phase with almost no crystal defects due to the small differences in lattice parameters and the prevalence of one of two previously unknown orientation relationships between the phases. Moreover, the presence of special boundaries resulting in orientation domains within both phases throughout the interfacial nickel telluride layer needs to be considered when fabricating future thermoelectric devices. Keywords: NiTe, Electron back-scattering diffraction (EBSD), Orientation relationships, High angle annular darkfield, Scanning transmission microscopy (HAADF-STEM)

Spin-wave excitations in α-Fe

The effect of strain during uniaxial compression on mechanical behavior of Ti–10V–2Fe–3Al alloy produced by blended elemental powder metallurgy and containing a metastable β matrix with ~0.1 fraction of α phase was investigated. A detailed scanning transmission electron microscopy study revealed the initiation of slip and deformation-induced α′′ martensite and ωD formation at the beginning of plastic deformation in the stress plateau region of stress-strain curve. {332} twinning occurred at a later stage. Deformation-induced ωD formed in the β matrix and within {332} twins, but was consumed by other deformation products at strains exceeding 0.2. Formation of {112} twins within {332} twins and along their interfaces with the matrix was uncovered. The rate of development of deformation products among the β phase grains was non-uniform with many being fully transformed to α′′ martensite by 0.4 strain, whereas others experienced deformation conditions related to stress plateau region (

The evolution of microstructure and micro-texture during discontinuous dynamic recrystallisation of an austenitic Ni-30Fe-Nb-C model alloy subjected to interrupted plane strain compression at strains (e) of 0.23, 0.35, 0.68, 0.85 and 1.2 was investigated using electron backscattering diffraction and transmission electron microscopy. Throughout the strain range, the majority of dynamic recrystallisation events comprised nucleation in necklace-like arrangements located at and along grain boundaries via bulging. At e ≥ 0.68, discrete nucleation events were also observed within grain interiors. Grain growth during dynamic recrystallisation is characteristic of strain induced boundary migration. The initial texture comprised Cube-RD ({013}〈100〉), Cube-ND ({001}〈310〉) and Cube ({001}〈100〉) orientations. Up to e ≤ 0.35, the unrecrystallised grain fractions comprised the Brass ({110}〈112〉) or Copper ({112}〈111〉) orientations and an intensity spread near Rotated Goss ({011}〈011〉). Between 0.68 ≤ e ≤ 1.2, the texture of the unrecrystallised grain fractions was similar to that of the recrystallised grains throughout the strain range; both of which are dominated by the Cube orientation. The dominance of the Cube orientation in the secondary deformed and recrystallised grains can be ascribed to its low stored energy and orientation stability.

The prospective utilization of nanoscale superconductors as micro/nanocoils or circuits with superior current density and no electrical resistance loss in next-generation electronics or electromagnetic equipment represents a fascinating opportunity for new microsystem technologies. Here, a family of superconducting liquid metals (Ga–In–Sn alloys) and their nanodroplets toward printable and stretchable superconducting micro/nanoelectronics is developed. By tuning the composition of liquid metals the highest superconducting critical temperature (Tc) in this family can be modulated and achieved as high as 6.6 K. The liquid metal nanodroplets retain their bulk superconducting properties and can be easily dispersed in different solvents as inks. The printable and stretchable superconducting micro/nano coils, circuits and electrodes have been fabricated by inkjet printer or laser etching by using superconducting nanodroplets inks. This novel superconducting system greatly promotes the commercial utilization of superconductors into advanced flexible micro/nanoelectronic devices and offers a new platform for developing more application with superconductors.

This is the first transmission Kikuchi diffraction (TKD) study to report the indexing of nano-sized cementite as distinct structures and its orientation relationship with the body-centered cubic matrix in a quenched and tempered steel. Crystallographic analysis via TKD and selected area diffraction returned the well-known Bagaryatskii and Isaichev orientation relationships. However, the indexing of nano-sized cementite via TKD was sensitive to the thickness of the electron transparent region such that TEM remains the most precise method to characterise such precipitates.

A metastable β Ti–10V–3Fe–3Al–0.27O (wt.%) alloy was subjected to thermo-mechanical processing to induce α and ω phase formation, so that the alloy can exhibit the features responsible for both transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) behaviour during deformation. The alloy thereafter was deformed at different strain rates (10−3, 10−1, 101, 102 s−1) at ambient temperature. At slow strain rate (≤10−3 s−1), in addition to slip the alloy displayed a dominant deformation mechanism with α′′ martensite formation, where mechanical {332}〈113〉β twinning and deformation-induced ω phase were also activated. At an intermediate strain rate, 10−1 s−1, there was a competition between stress-induced phase transformations and stress-induced twinning deformation mechanisms. With increasing strain rate to 101 s−1 or higher; it was found that the dominant deformation mode was twinning. These results have been correlated with the β phase stability of the samples.

The quality of hexagonal boron nitride nanosheets (h-BNNS) is often associated with the most visible aspects such as lateral size and thickness. Less obvious factors such as sheet stacking order could also have a dramatic impact on the properties of BNNS and therefore its applications. The stacking order can be affected by contamination, cracks, and growth temperatures. In view of the significance of chemical-vapour-decomposition (CVD) assisted growth of BNNS, this paper reports on strategies to grow carbon- and crack-free BNNS by CVD and describes the stacking order of the resultant BNNS. Pretreatment of the most commonly used precursor, ammonia borane, is necessary to remove carbon contamination caused by residual hydrocarbons. Flattening the Cu and W substrates prior to growth and slow cooling around the Cu melting point effectively facilitate the uniform growth of h-BNNS, as a result of a minimal temperature gradient across the Cu substrate. Confining the growth inside alumina boats effectively minimizes etching of the nanosheet by silica nanoparticles originating from the commonly used quartz reactor tube. h-BNNS grown on solid Cu surfaces using this method adopt AB, ABA, AC', and AC'B stacking orders, which are known to have higher energies than the most stable AA' configuration. These findings identify a pathway for the fabrication of high-quality h-BNNS via CVD and should spur studies on stacking order-dependent properties of h-BNNS.

Few-layered porous boron nitride nanosheets (BNNS) have been prepared using a dynamic magnesium diboride (MgB2) template and ammonium chloride (NH4Cl) etchant. Magnesium-based intermediates serve as layer separators in the synthesis and prevent extensive aggregation, resulting in few-layered BNNS. The resultant BNNS are hierarchically porous and show good CO2/N2 adsorption selectivity.

While silicon nanocrystals (ncSi) embedded in silicon dioxide thin films have been intensively studied in physics, the potential of batch synthesis of silicon nanocrystals from the solid-state disproportionation of SiO powder has not drawn much attention in chemistry. Herein we describe some remarkable effects observed in the diffraction, microscopy and spectroscopy of SiO powder upon thermal processing in the temperature range 850-1100 °C. Quantum confinement effects and structural changes of the material related to the size of the silicon nanocrystals nucleated and grown in this way were established by Photoluminescence (PL), Raman, FTIR and UV-Visible spectroscopy, PXRD and STEM, pinpointing that the most significant disproportionation transformations happened in the temperature range between 900 and 950 °C. With this know-how a high yield synthesis was developed that produced polydispersions of decyl-capped, hexane-soluble silicon nanocrystals predominantly with near infrared (NIR) PL. Using size-selective precipitation, these polydispersions were separated into monodisperse fractions, which allowed their PL absolute quantum yield (AQY) to be studied as a function of silicon nanocrystal size. This investigation yielded volcano-shaped plots for the AQY confirming the most efficient PL wavelength for ncSi to be located at around 820-830 nm, which corresponded to a size of 3.5-4.0 nm. This work provides opportunities for applications of size-selected near infrared emitting silicon nanocrystals in biomedical imaging and photothermal therapy.

The development of oxygen reduction reaction (ORR) electrocatalysts based on earth-abundant nonprecious materials is critically important for sustainable large-scale applications of fuel cells and metal-air batteries. Herein, a hetero-single-atom (h-SA) ORR electrocatalyst is presented, which has atomically dispersed Fe and Ni coanchored to a microsized nitrogen-doped graphitic carbon support with unique trimodal-porous structure configured by highly ordered macropores interconnected through mesopores. Extended X-ray absorption fine structure spectra confirm that Fe- and Ni-SAs are affixed to the carbon support via FeN4 and NiN4 coordination bonds. The resultant Fe/Ni h-SA electrocatalyst exhibits an outstanding ORR activity, outperforming SA electrocatalysts with only Fe- or Ni-SAs, and the benchmark Pt/C. The obtained experimental results indicate that the achieved outstanding ORR performance results from the synergetic enhancement induced by the coexisting FeN4 and NiN4 sites, and the superior mass-transfer capability promoted by the trimodal-porous-structured carbon support.

A metastable-β titanium alloy, Ti-10V-3Fe-3Al (wt. %), was subjected to thermo-mechanical processing including the compression test at 725 °C, which is below the β transus temperature (780 °C), and at strain rate of 10−3 s−1. The presence of phases was determined using transmission electron microscopy and X-ray diffraction. Although the dynamic recovery took place together with slip, both deformation-induced α” martensite and ω were detected as other operating mechanisms for the first time in metastable-β titanium alloy deformed in α + β region. The volume fraction of stress-induced α” was higher than that of the same alloy deformed at room temperature due to a higher strain applied. Stress-induced twinning was not operational, which could be related to the priority of slip mechanism at high temperature resulted from thermally-assisted nucleation and lateral migration of kink-pairs.

A metastable β-Ti alloy, Ti–10V–3Fe–3Al (wt.%), was subjected to thermos-mechanical processing including the compression test at 725°C, which is below the β transus temperature (780°C), and at strain rate of 10-3s-1. The presence of phases was determined using transmission electron microscopy and X-ray diffraction. Although the dynamic recovery took place together with slip, both deformation-induced α˝ martensite and ω were detected as other operating mechanisms for the first time in metastable-β Ti alloys deformed in α+β region. The volume fraction of stress-induced α˝ was higher than that of the same alloy deformed at room temperature due to higher strain applied. Stress-induced twinning was not operational, which could be related to the priority of slip mechanism at high temperature resulted from thermally-assisted nucleation and lateral migration of kink-pairs.

We report on partitioning of alloying elements during the formation of fine intragranular α plates in a Ti-55521 alloy after thermo-mechanical processing (TMP) and isothermal ageing at 923 K. The microstructures were characterised using atom probe tomography and high-resolution transmission electron microscopy. The partitioning of Mo, V and Al are strongly affected by their diffusivities and their mutual interaction. This leads to a deviation of the measured contents of alloying elements in the two phases from the predicted equilibrium values. The alloying elements at the broad faces and tips of α plates were found to exhibit different pile-up and segregation behaviours, which is thought to affect the lengthening and thickening kinetics of the α plates. As a result, the aspect ratio of α plates decreased rapidly with increasing ageing time. This study suggests that careful selection of alloying elements could be an effective way in controlling the growth anisotropy of α plates and thus α + β microstructures in near-β Ti alloys.

Necessity-oriented materials design has become a priority for every nation conscious of the well-being of the environment. A suitable environmentally friendly microwave-hydrothermal reaction was used to synthesize BaZrO3. A study of the properties of pure Si doped, and Bi–Si co-doped BaZrO3 semiconductors is presented. Crystalline structure, morphology and optical properties were dependent on the concentration of bismuth. Well faceted and spherical particles with increasing sizes from 90 up to 500 nm were obtained as the bismuth concentration increased. The highly crystalline compounds produced, maintain the BaZrO3 cubic perovskite phase even at bismuth–silicon concentrations as high as 50 and 1.5 mol%, respectively. The optical absorption edge shifts into the visible-light region and the band gap narrows as the bismuth concentration increases. Suitable compounds were obtained at reaction times of 1 and 4 h at 170 °C in water–ethanol solvent for non-doped BaZrO3 and doped BaZrO3, respectively. Since similar properties of other semiconductor materials have practical application as visible light-active photocatalysts, we propose the potential use of nanocomposite BaZrO3 as a green photocatalyst. The effects of bismuth–silicon inclusions on the properties of BaZrO3 and its relation with photocatalytic properties are exposed. HREM, HAADF and dopant distributions inside the perovskite structure are presented.

The phase transformations and compositional changes occurring during thermo-mechanical processing and subsequent high temperature ageing of Ti–5Al–5Mo–5V–2Cr–1Fe (wt.%) were investigated using scanning transmission electron microscopy (STEM) and atom probe tomography (APT). High resolution STEM revealed nano-sized α (

A metastable β-Ti alloy, Ti–10V–3Fe–3Al (wt.%), was subjected to thermomechanical processing (TMP), where the temperature of isothermal holding in the α + β phase field was varied in order to change the volume fraction of the α phase and, correspondingly, the β phase stability. Following TMP, compression tests were performed at room temperature to evaluate the deformation mode. Microstructural features induced by compression were identified using transmission electron microscopy. It was found that {3 3 2}〈1 1 3〉β deformation twinning along with stress-induced products (α″ martensite and ω lamellae) and slip were operational in the least stable β. The co-existence of {3 3 2}〈1 1 3〉β and {1 1 2}〈1 1 1〉β twinning was found at intermediate β stability along with other deformation products. With further increasing of β phase stability, no {3 3 2}〈1 1 3〉β twinning was detected whereas other deformation modes remained unchanged. In stable β phase, dislocation glide was the only deformation mode to be found. It was revealed that triggering stress required inducing the deformation products increases with the β phase stability. Based on the findings, a modification of the lower portion of the Bo ‾ – Md ‾ phase stability diagram is proposed.

The key to produce inorganic heterogeneous nanostructures, and to integrate multiple functionalities, is to enhance or at least retain the functionalities of different components of materials. However, this ideal scenario is often deteriorated at the interface of the heterogeneous nanostructures due to lattice mismatches, resulting in downgraded performance in most hybrid nanomaterials. Here, we report that there is a narrow window in controlling temperature in a Lewis acid–base reaction process to facilitate epitaxial alignment during the synthesis of hybrid nanomaterials. We demonstrate a perfectly fused NaYF4:Yb,Tm@ZnO heterogeneous nanostructure, in which the semiconductor ZnO shell can be epitaxially grown onto lanthanide-doped upconversion nanoparticles. By achieving a matched crystal lattice, the interface defects and crystalline grain boundaries are minimized to enable more efficient energy transfer from the upconversion nanoparticles to the semiconductor, resulting in both enhanced upconversion luminescence intensity and superior photoelectrochemical properties. This strategy provides an outstanding approach to endow lanthanide-doped upconversion nanoparticles with versatile properties.

In this chapter, recent advances in scanning/transmission electron microscopic techniques and their applications to nanomaterials are highlighted. Aberration corrected electron microscopy is now routinely employed to study carbon nanomaterials, nanoparticles, 2D materials, alloys and heterostructures, etc. However, there have been several significant achievements in employing this technique towards the study of the various nanostructures. Aberration corrected TEM/STEM imaging tends to be very successful in identifying new nanoalloys, enables understanding of the growth mechanisms as well as the behaviour of supported atoms/clusters towards catalytic reactions, etc. HAADF-STEM imaging in combination with spectroscopy is an essential tool for the characterization of new 2D materials, such as borophenes and phosphorenes. At the same time, it provides insights into the structure of hetero-interfaces as well as enables identifying defects and new phases associated with these materials. It is now possible to go down in accelerating voltages upto 15 kV in both TEM/STEM modes and image specimens with minimal damage. It is foreseen, that these new developments in advanced electron microscopic techniques will provide significant possibilities for unravelling new phenomena, as well as explore novel properties of nanomaterials enabling new applications.

Enhancing the efficiency of upconversion nanoparticles (UCNPs) and therefore their brightness is the critical goal for this emerging material to meet growing demands in many potential applications including sensing, imaging, solar energy conversion and photonics. The distribution of the photon sensitizer and activator ions that form a network of energy transfer systems within each single UCNP is vital for understanding and optimizing their optical properties. Here we employ synchrotron-based X-ray Photoelectron Spectroscopy (XPS) to characterize the depth distribution of Yb

Self-supported electrocatalysts being generated and employed directly as electrodes for energy conversion has been intensively pursued in the fields of materials chemistry and energy. Herein, we report a synthetic strategy to prepare freestanding hierarchically structured, nitrogen-doped nanoporous graphitic carbon membranes functionalized with Janus-type Co/CoP nanocrystals (termed as HNDCM-Co/CoP), which were successfully applied as a highly efficient, binder-free electrode in the hydrogen evolution reaction (HER). Benefited from multiple structural merits, such as a high degree of graphitization, three-dimensionally interconnected micro/meso/macropores, uniform nitrogen doping, well-dispersed Co/CoP nanocrystals, as well as the confinement effect of the thin carbon layer on the nanocrystals, HNDCM-Co/CoP exhibited superior electrocatalytic activity and long-term operation stability for HER under both acidic and alkaline conditions. As a proof-of-concept of practical usage, a 5.6 cm × 4 cm × 60 μm macroscopic piece of HNDCM-Co/CoP was prepared in our laboratory. Driven by a solar cell, electroreduction of water in alkaline conditions (pH 14) was performed, and H

A detailed investigation examines how the size of allylbenzene-capped silicon nanocrystals (ncSi:AB) affects their chemical reactivity with gaseous O2, H2O, and O2/H2O as probed by in situ luminescence spectroscopy. Specifically, changes in the photoluminescence (PL) of size-separated ncSi:AB are monitored through alterations of their PL absolute quantum yield (AQY) as well as the wavelength and intensity of their PL spectra over time. These experiments, conducted under both continuous and intermittent illumination, help elucidate the roles of O2, H2O, and mixtures of O2/H2O, with respect to oxidation of ncSi:AB as a function of their size, providing vital information for any perceived application in advanced materials and biomedical devices.

MoS2 has been the focus of extensive research due to its potential applications. More recently, the mechanical properties of MoS2 layers have raised interest due to applications in flexible electronics. In this article, we show in situ transmission electron microcsopy (TEM) observation of the mechanical response of a few layers of MoS2 to an external load. We used a scanning tunneling microscope (STM) tip mounted on a TEM stage to induce deformation on nanosheets of MoS2 containing few layers. The results confirm the outstanding mechanical properties on the MoS2. The layers can be bent close to 180°. However, when the tip is retrieved the initial structure is recovered. Evidence indicates that there is a significant bond reconstruction during the bending with an outstanding capability to recover the initial bond structure. The results show that flexibility of three layers of MoS2 remains the same as a single layer while increasing the bending modulus by 3 orders of magnitude. Our findings are consistent w...

The size-dependence of the absolute luminescence quantum yield of size-separated silicon nanocrystals reveals a "volcano" behavior, which switches on around 5 nm, peaks at near 3.7-3.9 nm, and decreases thereafter. These three regions respectively define: i) the transition from bulk to strongly quantum confined emissive silicon, ii) increasing confinement enhancing radiative recombination, and iii) increasing contributions favoring non-radiative recombination.

Here we describe for the first time the synthesis of colloidally stable, brightly luminescent perfluorodecyl-capped silicon nanocrystals and compare the properties of solutions and films made from them with those of their perhydrodecyl-capped relatives. The perfluorodecyl capping group compared to the perhydrodecyl capping group yields superior hydrophobicity and much greater resistance to air oxidation, the enhanced electron-withdrawing character induces blue shifts in the wavelength of photoluminescence, and the lower-frequency carbon-fluorine stretching modes disfavor non-radiative relaxation pathways and boost the absolute photoluminescence quantum yield. Together these attributes bode well for advanced materials and biomedical applications founded upon perfluorodecyl-protected silicon nanocrystals.

As the cylindrical sp(2)-bonded carbon allotrope, carbon nanotubes (CNTs) have been widely used to reinforce bulk materials such as polymers, ceramics, and metals. However, both the concept demonstration and the fundamental understanding on how 1D CNTs reinforce atomically thin 2D layered materials, such as graphene, are still absent. Here, we demonstrate the successful synthesis of CNT-toughened graphene by simply annealing functionalized CNTs on Cu foils without needing to introduce extraneous carbon sources. The CNTs act as reinforcing bar (rebar), toughening the graphene through both π-π stacking domains and covalent bonding where the CNTs partially unzip and form a seamless 2D conjoined hybrid as revealed by aberration-corrected scanning transmission electron microscopy analysis. This is termed rebar graphene. Rebar graphene can be free-standing on water and transferred onto target substrates without needing a polymer-coating due to the rebar effects of the CNTs. The utility of rebar graphene sheets as flexible all-carbon transparent electrodes is demonstrated. The in-plane marriage of 1D nanotubes and 2D layered materials might herald an electrical and mechanical union that extends beyond carbon chemistry.

The salient feature of a supercapacitor is its ability to deliver much higher power density than a battery. A hierarchical design and a cost-effective approach to fabricate high performance supercapacitors using functional carbon nano-particles is reported. A special arc synthesis method is used to produce amorphous/crystalline composite with nitrogen and boron co-doped high charge density carbon nanoparticles. Upon etch removal of the amorphous phase in the composite nanoparticle, a crystalline carbon framework emerges, consisting of a mixture of nano-graphitic sheets mostly in the middle and single nanohorns distributed around the surface of the nanoparticle. These nanoparticles have large internal/external surfaces with subnano channels and sharp nano-tips for high speed charge transport and local charge accumulation. To deliver high power density, the internal resistance of the device is reduced by assembling the nanoparticles via electro-spraying and compacting them into dense films (without any binder) under 700 MPa of pressure before supercapacitor assembly. Taken together, the hierarchical processed supercapacitor has a very high (compared to literature values) power density of nearly 4.5 kW cm−3 and a respectable energy density of 2.45 mWh cm−3. Combining these carbon nanoparticles with large area spraying coating, it can lead to a cost-effective production of high performance supercapacitors.

Three-dimensional self-organized nanoporous thin films integrated into a heterogeneous Fe2O3/Fe3C-graphene structure were fabricated using chemical vapor deposition. Few-layer graphene coated on the nanoporous thin film was used as a conductive passivation layer, and Fe3C was introduced to improve capacity retention and stability of the nanoporous layer. A possible interfacial lithium storage effect was anticipated to provide additional charge storage in the electrode. These nanoporous layers, when used as an anode in lithium-ion batteries, deliver greatly enhanced cyclability and rate capacity compared with pristine Fe2O3: a specific capacity of 356 μAh cm(-2) μm(-1) (3560 mAh cm(-3) or ∼1118 mAh g(-1)) obtained at a discharge current density of 50 μA cm(-2) (∼0.17 C) with 88% retention after 100 cycles and 165 μAh cm(-2) μm(-1) (1650 mAh cm(-3) or ∼518 mAh g(-1)) obtained at a discharge current density of 1000 μA cm(-2) (∼6.6 C) for 1000 cycles were achieved. Meanwhile an energy density of 294 μWh cm(-2) μm(-1) (2.94 Wh cm(-3) or ∼924 Wh kg(-1)) and power density of 584 μW cm(-2) μm(-1) (5.84 W cm(-3) or ∼1834 W kg(-1)) were also obtained, which may make these thin film anodes promising as a power supply for micro- or even nanosized portable electronic devices.

Spin-wave excitations in α-Fe2O3 nanorods were directly detected using time-of-flight inelastic neutron spectroscopy. The dispersive magnon features are compared with those in bulk α-Fe2O3 particles at various temperatures to highlight differences in mode intensity and width. The interchanged spectral intensities in the nanorod are a consequence of a suppressed spin orientation, and this is also evident in the neutron diffraction which demonstates that the weak ferromagnetic phase survives to 1.5 K. Transmission electron microscopy shows that the ellipsoidal particles are single-crystalline with a typical length of 300 ± 100 nm and diameter of 60 ± 10 nm. The main magnon features are similar in bulk and nanoforms and can be explained using a model Hamiltonian based on Samuelson and Shirane's classical theory with exchange constants of J 1 = -1.03 meV, J 2 = -0.28 meV, J 3 = 5.12 meV and J 4 = 4.00 meV. Numerical simulations show that two distinct mechanisms may contribute to the magnon line broadening in the nanorods: a distribution of exchange interactions caused by disorder, and a shortened quasiparticle lifetime caused by the scattering of spin waves at surfaces.

CdSe nanowires (CdSe-NWs) at large scale were obtained through a simple and clean method. The reaction was carried out without complexing agents which often facilitate the preferential nanostructure growth. In this work, CdSe-NWs with lineal and zigzag shape around 40 and 130 nm in diameter with a wurtzite-type structure were synthesized. Quantitative EDX analysis indicated the stoichiometric formation of CdSe, while both HRTEM and HAADF-STEM analysis ruled out the presence of other phases such as CdO or nanotubes formation, respectively. Diameter and length of the nanowires varied with the reaction time and temperature. This synthesis method makes the nanostructures purification process easier and also is non-toxic and its high conversion make it an efficient method for obtaining CdSe-NWs.