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Steels with sub-micrometre grain sizes usually possess high toughness and strength, which makes them promising for lightweighting technologies and energy-saving strategies. So far, the industrial fabrication of ultrafine-grained (UFG) alloys, which generally relies on the manipulation of diffusional phase transformation, has been limited to steels with austenite-to-ferrite transformation1–3. Moreover, the limited work hardening and uniform elongation of these UFG steels1,4,5 hinder their widespread application. Here we report the facile mass production of UFG structures in a typical Fe–22Mn–0.6C twinning-induced plasticity steel by minor Cu alloying and manipulation of the recrystallization process through the intragranular nanoprecipitation (within 30 seconds) of a coherent disordered Cu-rich phase. The rapid and copious nanoprecipitation not only prevents the growth of the freshly recrystallized sub-micrometre grains but also enhances the thermal stability of the obtained UFG structure through the Zener pinning mechanism6. Moreover, owing to their full coherency and disordered nature, the precipitates exhibit weak interactions with dislocations under loading. This approach enables the preparation of a fully recrystallized UFG structure with a grain size of 800 ± 400 nanometres without the introduction of detrimental lattice defects such as brittle particles and segregated boundaries. Compared with the steel to which no Cu was added, the yield strength of the UFG structure was doubled to around 710 megapascals, with a uniform ductility of 45 per cent and a tensile strength of around 2,000 megapascals. This grain-refinement concept should be extendable to other alloy systems, and the manufacturing processes can be readily applied to existing industrial production lines. Bulk ultrafine-grained steel is prepared by an approach that involves the rapid production of coherent, disordered nanoprecipitates, which restrict grain growth but do not interfere with twinning or dislocation motion, resulting in high strength and ductility.

Nanostructured all-inorganic metal halide perovskites have attracted considerable attention due to their outstanding photonic and optoelectronic properties. Particularly, they can exhibit room-temperature exciton-polaritons (EPs) capable of confining electromagnetic fields down to the subwavelength scale, enabling efficient light harvesting and guiding. However, a real-space nanoimaging study of the EPs in perovskite crystals is still absent. Additionally, few studies focused on the ambient-pressure and reliable fabrication of large-area CsPbBr3 microsheets. Here, CsPbBr3 orthorhombic microsheet single crystals were successfully synthesized under ambient pressure. Their EPs were examined using a real-space nanoimaging technique, which reveal EP waveguide modes spanning the visible to near-infrared spectral region. The EPs exhibit a sufficient long propagation length of over 16 μm and a very low propagation loss of less than 0.072 dB·μm-1. These results demonstrate the potential applications of CsPbBr3 microsheets as subwavelength waveguides in integrated optics.

Thermal annealing of Ti contacts is commonly implemented in the fabrication of MoS2 devices; however, its effects on interface chemistry have not been previously reported in the literature. In this...

Transition metal dichalcogenides have attracted attention as potential building blocks for various electronic applications due to their atomically thin nature and polymorphism. Here, we report an electric-field-induced structural transition from a 2H semiconducting to a distorted transient structure (2Hd) and orthorhombic Td conducting phase in vertical 2H-MoTe2- and Mo1−xWxTe2-based resistive random access memory (RRAM) devices. RRAM programming voltages are tunable by the transition metal dichalcogenide thickness and show a distinctive trend of requiring lower electric fields for Mo1−xWxTe2 alloys versus MoTe2 compounds. Devices showed reproducible resistive switching within 10 ns between a high resistive state and a low resistive state. Moreover, using an Al2O3/MoTe2 stack, On/off current ratios of 106 with programming currents lower than 1 μA were achieved in a selectorless RRAM architecture. The sum of these findings demonstrates that controlled electrical state switching in two-dimensional materials is achievable and highlights the potential of transition metal dichalcogenides for memory applications. A vertical electric field is shown to induce reversible transitions between a semiconducting 2H phase, a distorted transient structure and a conducting Td phase in MoTe2 and Mo1–xWxTe2 multilayers, and used to realize vertical resistive random access memories.

Highly active and durable electrocatalysts are vital for commercialization of direct methanol fuel cells. In this work, a three-dimensional nanocomposite consisting of platinum nanoparticles, W18O49 nanocables, and reduced graphene oxide composite (Pt/W18O49 NCs–rGO) has been prepared as an electrocatalyst for methanol oxidation reaction (MOR). The catalyst is prepared through a two-step method. The W18O49 nanocables and the reduced graphene oxide composite are prepared by a solvothermal process. Then, Pt nanoparticles are loaded on the W18O49 nanocables and the reduced graphene oxide composite by a hydrogen reduction at ambient condition. The obtained catalyst has a special three-dimensional architecture consisting of two-dimensional nanosheets, assembled one-dimensional nanocables, and the loaded nanoparticles on their surface. The Pt/W18O49 NCs–rGO catalyst shows 1.56 time mass activities than the Pt/C, with the current density of the forward anodic peak reaching 1624 mA/mgPt at 0.854 V versus reversible hydrogen electrode potential in 0.1 M HClO4 and 0.5 M CH3OH mixed electrolyte. It also shows a strong antipoisoning property toward CO. For the durability testing, the current density of Pt/W18O49 NCs–rGO shows a 37% decay, whereas the current of Pt/C catalyst shows a 41% degradation from 600 to 3600 s at 0.7 V. The high activity toward MOR, good antipoisoning for intermediate products, and excellent stability are ascribed to strong metal–support interaction effects between the Pt nanoparticles and the W18O49 NCs.

A dielectric bulk glass-ceramic of the La 2 O 3 –TiO 2 –SiO 2 –B 2 O 3 system is developed which is able to fulfill the requirements for dielectric loading-based mobile communication technologies. It is shown that the given dielectric requirements can be fulfilled by glass-ceramic materials without being dependent on ceramic processing techniques. The material exhibited permittivity values of 20 ɛ r Qf τ f τ f material with a Qf value of 9500 GHz and ɛ r = 21.4 could be achieved at a ceramming temperature T cer = 870 °C. The material is aimed to provide an alternative to existing, commercially used sintered ceramic materials. Further focus is laid on the investigation of the dominant dielectric loss mechanisms in the GHz frequency range and how they are correlated with the microstructure.

Electric-field (E-field) control of magnetism enabled by multiferroic materials has the potential to revolutionize the landscape of present memory devices plagued with high energy dissipation. To date, this E-field controlled multiferroic scheme has only been demonstrated at room temperature using BiFeO3 films grown on DyScO3, a unique and expensive substrate, which gives rise to a particular ferroelectric domain pattern in BiFeO3. Here, we demonstrate reversible electric-field-induced switching of the magnetic state of the Co layer in Co/BiFeO3 (BFO) (001) thin film heterostructures fabricated on (001) SrTiO3 (STO) substrates. The angular dependence of the coercivity and the remanent magnetization of the Co layer indicates that its easy axis reversibly switches back and forth 45° between the (100) and the (110) crystallographic directions of STO as a result of alternating application of positive and negative voltage pulses between the patterned top Co electrode layer and the (001) SrRuO3 (SRO) layer on which the ferroelectric BFO is epitaxially grown. The coercivity (HC) of the Co layer exhibits a hysteretic behavior between two states as a function of voltage. A mechanism based on the intrinsic magnetoelectric coupling in multiferroic BFO involving projection of antiferromagnetic G-type domains is used to explain the observation. We have also measured the exact canting angle of the G-type domain in strained BFO films for the first time using neutron diffraction. These results suggest a pathway to integrating BFO-based devices on Si wafers for implementing low power consumption and nonvolatile magnetoelectronic devices.

Demonstration of metamaterials with ultrahigh thermal resistance by phonon-level engineering of heterogeneous 2D monolayers., Heterogeneous integration of nanomaterials has enabled advanced electronics and photonics applications. However, similar progress has been challenging for thermal applications, in part due to shorter wavelengths of heat carriers (phonons) compared to electrons and photons. Here, we demonstrate unusually high thermal isolation across ultrathin heterostructures, achieved by layering atomically thin two-dimensional (2D) materials. We realize artificial stacks of monolayer graphene, MoS2, and WSe2 with thermal resistance greater than 100 times thicker SiO2 and effective thermal conductivity lower than air at room temperature. Using Raman thermometry, we simultaneously identify the thermal resistance between any 2D monolayers in the stack. Ultrahigh thermal isolation is achieved through the mismatch in mass density and phonon density of states between the 2D layers. These thermal metamaterials are an example in the emerging field of phononics and could find applications where ultrathin thermal insulation is desired, in thermal energy harvesting, or for routing heat in ultracompact geometries.

Precise control of electronic and/or ionic conductivity in electroceramics is crucial to achieve the desired functional properties as well as to improve manufacturing practices. We recently reported the conventional piezoelectric material Na1/2Bi1/2TiO3 (NBT) can be tuned into a novel oxide-ion conductor with an oxide-ion transport number (tion) > 0.9 by creating bismuth and oxygen vacancies. A small Bi-excess in the nominal starting composition (Na0.50Bi0.50+xTiO3+3x/2, x = 0.01) or Nb-donor doping (Na0.50Bi0.50Ti1−yNbyO3+y/2, 0.005 ≤ y ≤ 0.030) can reduce significantly the electrical conductivity to create dielectric behaviour by filling oxygen vacancies and suppressing oxide ion conduction (tion ≤ 0.10). Here we show a further increase in the starting Bi-excess content (0.02 ≤ x ≤ 0.10) reintroduces significant levels of oxide-ion conductivity and increases tion ∼ 0.4–0.6 to create mixed ionic/electronic behaviour. The switch from insulating to mixed conducting behaviour for x > 0.01 is linked to the presence of Bi-rich secondary phases and we discuss possible explanations for this effect. Mixed conducting behaviour with tion ∼ 0.5–0.6 can also be achieved with lower levels of Nb-doping (y ∼ 0.003) due to incomplete filling of oxygen vacancies without the presence of secondary phases. NBT can now be compositionally tailored to exhibit three types of electrical behaviour; Type I (oxide-ion conductor); Type II (mixed ionic-electronic conductor); Type III (insulator) and these results reveal an approach to fine-tune tion in NBT from near unity to zero. In addition to developing new oxide-ion and now mixed ionic/electronic NBT-based conductors, this flexibility in control of oxygen vacancies allows fine-tuning of both the dielectric/piezoelectric properties and design manufacturing practices for NBT-based multilayer piezoelectric devices.

We report multi-level MoTe 2 based resistive random-access memory (RRAM) devices with switching speeds of less than 5 ns due to an electric-field induced 2H to 2H d phase transition. Different from conventional RRAM devices based on ionic migration, the MoTe 2 -based RRAMs offer intrinsically better reliability and control. In comparison to phase change memory (PCM)-based devices that operate based on a change between an amorphous and a crystalline structure, our MoTe 2 -based RRAM devices allow faster switching due to a transition between two crystalline states. Moreover, utilization of atomically thin 2D materials allows for aggressive scaling and high-performance flexible electronics applications. Multi-level stable states and synaptic devices were realized in this work, and operation of the devices in their low-resistive, high-resistive and intrinsic states was quantitatively described by a novel model.

Domain wall movement at and near engineered 10°, 15°, and 24° tilt and 10° and 30° twist grain boundaries was measured by band excitation piezoresponse force microscopy for Pb(Zr,Ti)O3 films with Zr/Ti ratio of 45/55 and 52/48. A minimum in nonlinear response was observed at the grain boundary for the highest angle twist and tilt grain boundaries, while a maximum in nonlinear response was observed at the 10° tilt grain boundaries. The observed nonlinear response was correlated with the domain configurations imaged in cross section by transmission electron microscopy.

Recently, there has been considerable interest in the perovskite phase Na0.5Bi0.5TiO3 (NBT) as a promising lead-free piezoelectric material. Here we report low levels of Na nonstoichiometry (±2 atom % on the A-site) in the nominal starting composition of NBT ceramics can lead to dramatic changes in the magnitude of the bulk (grain) conductivity (σb) and the conduction mechanism(s). Nominal starting compositions with Na excess exhibit high levels of oxide-ion conduction with σb ∼ 2.2 mS cm–1 at 600 °C and an activation energy (Ea) < 1 eV whereas those with Na deficiency are dielectrics based on intrinsic electronic conduction across the band gap with σb ∼ 1.6 μS cm–1 at 600 °C and Ea ∼ 1.7 eV. Drying of reagents, especially Na2CO3, changes the starting stoichiometry slightly due to a small amount of adsorbed moisture in the raw materials but influences significantly the electrical properties. This demonstrates the bulk electrical properties of NBT to be highly sensitive to low levels of A-site nonstoichiom...

Based on careful design of composition, a two-glassy-phase Cu47.2Zr46.5Al5.5Nb0.8 bulk metallic glass with a large plasticity (∼16%) was successfully prepared. Energy-dispersive spectroscopy and electron energy loss spectroscopy confirm that the bright matrix phase is rich in Zr/Nb while the dark particle phase is rich in Cu/Al. Theoretical calculations suggest that a small difference in shear modulus between phases may be necessary before pronounced plastic deformation can occur.

Magnesium oxide (MgO) has been of interest for several decades as a promising tunable broadband laser due to its vacancy defects (color centers). In this work we introduced color centers into MgO nanocube by electron irradiation in a transmission electron microscope (TEM). Square nano-holes were formed from the electron-exit face using 100 and 300 keV electrons, and a broad O-vacancy (color-center) absorption peak around 4.1–6.6 eV was observed by valence-electron energy-loss spectroscopy (VEELS). We investigated the mechanism of MgO damage by high-energy electron beams. The hole formation is believed to involve a mixed removal of diatomic MgO molecules as well as Mg and O species in stoichiometric proportion. Observations using high-resolution transmission electron microscopy (HRTEM) and VEELS suggest that bulk O-vacancies are generated near the electron-exit face, due to the forward momentum transferred from fast-electron collisions and the Coulomb attraction of negative O-ions by the positively charged MgO surface.

Oxide ion conductors find important technical applications in electrochemical devices such as solid-oxide fuel cells (SOFCs), oxygen separation membranes and sensors1, 2, 3, 4, 5, 6, 7, 8, 9. Na0.5Bi0.5TiO3 (NBT) is a well-known lead-free piezoelectric material; however, it is often reported to possess high leakage conductivity that is problematic for its piezo- and ferroelectric applications10, 11, 12, 13, 14, 15. Here we report this high leakage to be oxide ion conduction due to Bi-deficiency and oxygen vacancies induced during materials processing. Mg-doping on the Ti-site increases the ionic conductivity to ~0.01 S cm−1 at 600 °C, improves the electrolyte stability in reducing atmospheres and lowers the sintering temperature. This study not only demonstrates how to adjust the nominal NBT composition for dielectric-based applications, but also, more importantly, gives NBT-based materials an unexpected role as a completely new family of oxide ion conductors with potential applications in intermediate-temperature SOFCs and opens up a new direction to design oxide ion conductors in perovskite oxides.

Epitaxial tetragonal 425 and 611 nm thick Pb(Zr0.45Ti0.55)O3 (PZT) films are deposited by pulsed laser deposition on SrRuO3-coated (100) SrTiO3 24° tilt angle bicrystal substrates to create a single PZT grain boundary with a well-defined orientation. On either side of the bicrystal boundary, the films show square hysteresis loops and have dielectric permittivities of 456 and 576, with loss tangents of 0.010 and 0.015, respectively. Using piezoresponse force microscopy (PFM), a decrease in the nonlinear piezoelectric response is observed in the vicinity (720–820 nm) of the grain boundary. This region represents the width over which the extrinsic contributions to the piezoelectric response (e.g., those associated with the domain density/configuration and/or the domain wall mobility) are influenced by the presence of the grain boundary. Transmission electron microscope (TEM) images collected near and far from the grain boundary indicate a strong preference for (101)/(01) type domain walls at the grain boundary, whereas (011)/(01) and (101)/(01) are observed away from this region. It is proposed that the elastic strain field at the grain boundary interacts with the ferro-electric/elastic domain structure, stabilizing (101)/(01) rather than (011)/(01) type domain walls, which inhibits domain wall motion under applied field and decreases non-linearity.

Scattering contrast measurements were performed on thin films of amorphous carbon and polycrystalline Au, as well as single-crystal MgO nanocubes. Based on the exponential absorption law, mass-thickness can be obtained within 10% accuracy by measuring the incident and transmitted intensities in the same image. For mass-thickness measurement of a thin amorphous specimen, a small collection semiangle improves the measurement sensitivity, whereas for the measurement of polycrystalline or single-crystal specimens, a large collection semiangle should be used to reduce diffraction-contrast effects. EELS thickness measurements on MgO nanocubes suggest that the Kramers–Kronig sum-rule method (with correction for plural and surface scattering) gives 10% accuracy at medium collection semiangles but overestimates the thickness at small collection semiangles, due to underestimation of the surface-mode scattering. The log-ratio method, with a formula for inelastic mean free path proposed by Malis et al. (1988), provides 10% accuracy at small collection semiangle, while that proposed by Iakoubovskii et al. (2008a) is preferable for medium and large collection semiangles. As a result of this work, we provide recommendations of preferred methods and conditions for local-thickness measurement in the TEM., Applications of EELS in Materials and Physics Research, 20–24 September 2011, Brazil

The microstructural properties of melt-spun ribbon of the ferromagnetic shape-memory Heusler alloy Ni2FeGa have been investigated by transmission electron microscopy. Two kinds of micromodulated structures, Fe-rich and Ga-rich, have been established. The Fe-rich micromodulated structure is formed by Fe atoms partially replacing Ga atoms on {3 5 0} planes in the L2(1) structure. The Ga-rich micromodulated structure concerns Ga atoms partially replacing Fe atoms on {3 + n, 5 + n, 0}(n >= 0) planes. The Fe-rich and Ga-rich micromodulated structures originate from spinodal decomposition of the Fe and Ga compositions, which is closely related to the difference of atomic sizes of Ni, Fe and Ga. Crown Copyright (C) 2010 Published by Elsevier Ltd. on behalf of Acta Materialia Inc. All rights reserved.

Microstructure and mechanical property of CO2 laser beam welded IN 718 superalloy were studied by electron microscopy and hardness testing. The use of a welding filler wire produced a sound fusion zone with no cracking but grain boundary microfissuring occurred in the heat affected zone (HAZ) and was observed to be significantly influenced by pre-weld heat treatment and laser welding speed. Crack-free weld was produced by a pre-weld heat treatment that minimised non-equilibirum grain boundary boron segregation and inhibited grain growth. While post-weld heat treatment (PWHT) reduced the difference between the hardness values of the base alloy, HAZ and the fusion zone, it resulted in increased HAZ cracking, which was likely aided by pre-existing cracks. The PWHT cracking was, however, avoided by subjecting pre-weld material to the heat treatment condition that produces crack-free weld during welding process.

Among all-solid-state batteries, rechargeable Al-ion batteries have attracted most attention because they involve three-electron-redox reactions with high theoretic specific capacity. However, the solid Al-ion conductor electrolytes are less studied. Here, the microscopic path of Al3+-ion conduction of NASICON-type (Al0.2Zr0.8)20/19Nb(PO4)3 oxide is identified by temperature-dependent neutron powder diffraction and aberration-corrected scanning transmission electron microscopy experiments. (Al0.2Zr0.8)20/19Nb(PO4)3 shows a rhombohedral structure consisting of a framework of (Zr,Nb)O6 octahedra sharing corners with (PO4) tetrahedra; the Al occupy trigonal antiprisms exhibiting extremely large displacement factors. This suggests a strong displacement of Al ions along the c axis of the unit cell as they diffuse across the structure by a vacancy mechanism. Negative thermal expansion behavior is also identified along a and b axes, due to folding of the framework as temperature increases.

In pursuit of superconductivity in p-type silicon (Si), we are using a single atomic layer of aluminum (Al) sandwiched between a Si substrate and a thin Si epi-layer. The delta layer was fabricated starting from an ultra high vacuum (UHV) flash anneal of Si(100) surface, followed by physical vapor deposition of Al monolayer. To activate the Al dopants, the sample was then annealed in-situ at 550 °C for 1 min. The Si capping layer was electron-beam evaporated in-situ at room temperature, followed by an ex-situ anneal at 550 °C for 10 min to recrystallize the Si capping layer. Low temperature magnetotransport measurements yield a maximum hole mobility of 20 cm2/V/s at a carrier density 1.39 × 1014 holes/cm2, which corresponds to ≈ (0.93 ± 0.1) holes per dopant atom. No superconductivity was observed in these devices even at T < 300 mK. Atom probe tomography and energy-dispersive X-ray spectroscopy analyses suggest that the Al dopants become distributed over ≈ (17 to 25) nm thickness. Redistribution of Al dopants reduces Al atomic concentration in Si matrix below the critical density to observe superconductivity.

An analytical transmission electron microscopy study was performed on the nature of nanosize secondary phase precipitates that form in standard heat-treated commercial nickel base superalloy IN 738. In addition to M5B3 borides and M23C6 carbides, the precipitates were found to also consist of particles of M2B-type boride phase, which is previously unreported in the alloy and rarely reported in nickel base superalloys. The M2B borides exhibited a dual crystallographic structure: body centered tetragonal and face centered orthorhombic. Analyses of electron diffraction patterns and high-resolution transmission electron microscopy images indicated that both crystal structures can co-exist in a single M2B particle as an intergrowth with the formation of planar defects. Crystallographic relationship between microconstituent phases in the heat-treated alloy were elucidated and the influence of the borides on resistance to grain boundary liquation cracking during high-temperature material processing, such as lase...

Microstructural study of laser-beam-welded IN 738 superalloy was carefully performed to better understand the causes of heat-affected zone (HAZ) cracking and to determine an improved approach of alleviating the weldability problem. The HAZ cracks in the alloy were intergranular liquation cracks that resulted from the liquation reaction of both secondary solidification products (MC carbides and γ-γ′ eutectic) and solid-state reaction products (γ′ particles) present in the preweld material. In contrast to the expectation based on Chadwick’s equation, a reduction of grain boundary liquid film thickness did not produce a decrease in HAZ cracking owing to increased base alloy hardness that accompanied a preweld heat treatment designed to reduce the intergranular liquation. Moreover, a major factor limiting the effectiveness of an existing preweld heat treatment with low base alloy hardness in reducing HAZ cracking was found to be the formation of intergranular M5B3 boride particles during the heat treatment. These borides can widen the HAZ brittle temperature range (BTR) during weld cooling and increase the propensity for cracking. Based on the results, a new preweld heat treatment that induces a moderate hardness and precludes grain boundary boride formation was found and was shown to produce a significant reduction in HAZ cracking in the welded alloy compared to the most effective pre-existing preweld heat treatment.

Analytical transmission electron microscopy study of intergranular regions in directionally solidified (DS) RENE 80 superalloy was performed. In addition to the generally reported M3B2-type boride particles that form in the alloy during ingot solidification, considerable presence of a different type of boride particles, M5B3, which has not been generally reported in the alloy, was observed. Extensive formation of these particles along the grain boundaries in the DS alloy is pertinent to high-temperature performance of the material.

Rene 80 is a precipitation hardened nickel-based superalloy, which is widely used to manufacture components of gas turbine engines for aerospace and power generation applications. It is designed to withstand service temperatures of up to 980 C [1] and possesses remarkable hot corrosion resistance, long-term microstructural stability, and hightemperature strength produced primarily by precipitation hardening by ordered intermetallic Ni3(Al,Ti) c0 precipitates. Directional solidification (DS) processing of the alloy results in further improvement of its elevated temperature properties and permits the use of a higher service temperature, which improves the thermal efficiency of gas turbines [2–5]. It has been reported that in DS Rene 80, the tensile strength is increased by about 10–15% and the creep rupture life is extended by 2–4 times relative to conventionally cast material [5]. Boron is an essential minor elemental addition to these heat resistant materials primarily to improve their creep rupture properties [3, 4]. Nevertheless, it has been recognized that the mode in which boron exists on grain boundary regions, either in austenitic solid solution form or selectively partitioned into second phase particles, can significantly influence the creep properties of superalloys [6, 7]. Experimental study is crucial in establishing the presence and nature of intergranular borides in multi-component superalloys due to the influence of interfacial elemental segregation that is not generally considered during thermodynamic equilibrium calculations of theoretical models [8]. The objective of this investigation was to perform transmission electron microscopy (TEM) study of heat-treated DS Rene 80 superalloy to understand the nature of boron rich second phase particles present along its grain boundary regions. The composition of the DS Rene 80 material used in this study was (wt%) 0.2C, 14.1Cr, 9.52Co, 4.0W, 3.98Mo, 0.02Nb, 0.18Fe, 2.9Al, 4.98Ti, 0.028Zr, 0.013B balance nickel. The alloy was subjected to standard solution heat treatment for 2 h at 1200 C and was subsequently aged at 1025 C for 16 h. Thin foils from the aged material for TEM study were prepared by mechanical polishing and dimpling to a thickness of less than 10 lm followed by ion milling in a Gatan precision ion polishing system (PIPS). TEM microchemical and crystal-structure analyses were performed in a field emission gun JEOL 2100F scanning transmission electron microscope equipped with Oxford energy dispersive spectrometer (EDS), Gatan imaging filter (GIF) system, and electron energy-loss spectrometer (EELS). High-resolution TEM micrographs were filtered using an inverse fourier fast transform (FFT) program in Gatan Digital Micrography software. A TEM boron post-edge electron energy loss image of the heat-treated alloy consisting of c0 precipitates and particles of a different phase along the grain boundary and inside the grain identified with arrows is shown in Fig. 1a. Microchemical analysis by X-ray energy dispersive spectroscopy indicated that the particles are rich in Cr, Mo, W, and B (Fig. 1b), and have much different composition from the adjoining regions (Fig. 1c). The presence of boron in the particles was further confirmed by EELS analysis (Fig. 1d) and EELS-based energy filtered transmission electron microscopy (EFTEM) elemental mapping (Fig. 1e). TEM Electron diffraction pattern (EDP) analysis was performed by systematic titling of particle of this phase along certain crystallographic directions to determine its crystal structure. Figure 2a is a [001] zone-axis EDP showing a fourfold symmetry of the phase. Figure 2b and c were obtained by H. R. Zhang O. A. Ojo (&) Department of Mechanical and Manufacturing Engineering, University of Manitoba, Winnipeg, MB, Canada R3T 5V6 e-mail: ojo@cc.umanitoba.ca

Grain boundary microconstituents in aged nickel-based superalloys were studied by transmission electron microscopy techniques. A nanosized M 5 B 3 boride phase, possibly formed by intergranular solute desegregation-induced precipitation, was positively identified. The presence of these intergranular nanoborides provides reasonable clarification of a previously reported reduction of grain boundary liquation temperature during the weld heat affected zone thermal cycle.

Large-area single-crystalline vanadium dioxide nanoflakes were first fabricated via a thermal reduction method in a tube furnace. The sample was characterized by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The results show that VO2 nanoflakes are single-crystalline with a monoclinic structure. The VO2 nanoflakes have a width of 200–300 nm, a thickness of 50–100 nm, and a length up to 1–2 μm. It is found that single-crystalline VO2 nanoflakes show a novel and complicated 5–7-step Li-storage behavior for an insertion amount of 2.

Researchers have demonstrated that BiFeO3 exhibits ferroelectric hysteresis but none have shown a strong ferromagnetic response in either bulk or thin film without significant structural or compositional modification. When remanent magnetisations are observed in BiFeO3 based thin films, iron oxide second phases are often detected. Using aberration-corrected scanning transmission electron microscopy, atomic resolution electron energy loss spectrum-mapping and quantitative energy dispersive X-ray spectroscopy analysis, we reveal the existence of a new Fe2O3-rich perovskite nanophase, with an approximate formula (Fe0.6Bi0.25Nd0.15)3+ Fe3+O3, formed within epitaxial Ti and Nd doped BiFeO3 perovskite films grown by pulsed laser deposition. The incorporation of Nd and Bi ions on the A-site and coherent growth with the matrix stabilise the Fe2O3-rich perovskite phase and preliminary density functional theory calculations suggest that it should have a ferrimagnetic response. Perovskite-structured Fe2O3 has been reported previously but never conclusively proven when fabricated at high-pressure high-temperature. This work suggests the incorporation of large A-site species may help stabilise perovskite-structured Fe2O3. This finding is therefore significant not only to the thin film but also to the high-pressure community.

The interaction of grain boundaries with ferroelectric domain walls strongly influences the extrinsic contribution to piezoelectric activity in Pb(Zr,Ti)O3 (PZT), ubiquitous in modern transducers and actuators. However, the fundamental understanding of these phenomena has been limited by complex mechanisms originating from the interplay of atomic-level domain wall pinning, collective domain wall dynamics, and emergent mesoscopic behavior. This contribution utilizes engineered grain boundaries created by depositing epitaxial PZT films with various Zr:Ti ratio onto 24o SrTiO3 tilt bicrystals. The nonlinear piezoelectric response and surface domain structure across the boundary are investigated using piezoresponse force microscopy whilst cross section domain structure is studied using transmission electron microscopy. The grain boundary reduces domain wall motion over a width of 800±70 nm for PZT 45:55 and 450±30 nm for PZT 52:48. Phase field modeling provides an understanding of the elastic and electric fields associated with the grain boundary and local domain configurations. In conclusion, this study demonstrates that complex mesoscopic behaviors can be explored to complement atomic-level pictures of the material system.

Nearly monodisperse flowerlike CeO2 microspheres were synthesized via a simultaneous polymerization-precipitate reaction, metamorphic reconstruction, and mineralization under hydrothermal condition as well as subsequent calcination. The obtained CeO2 microsphere consists of 20-30 nm thick nanosheets as petals. It has an open three-dimensional (3D) porous and hollow structure and possesses high surface area, large pore volume, and marked hydrothermal stability. It can be doped easily after synthesis, and the initial 3D texture is maintained. The controlling factors and a possible formation mechanism are discussed in detail. This novel material can be used as a support for catalysts with various purposes. With CuO loaded on flowerlike CeO2, the catalytic activities and hydrothermal stability of Cu/CeO2 for ethanol stream reforming were examined. At 300 degrees C, the H2 selectivity reached a maximum value of 74.9 mol %, while CO was not detected within the precision of the gas chromatogram. It produced a hydrogen-rich gas mixture in the wide temperature range (300-500 degrees C) and showed excellent hydrothermal stability at high temperature (550 degrees C), which is a good choice for ethanol processors for hydrogen fuel cell applications.

In this paper, hollow and porous Cu2O nanoparticles were prepared by adjusting the cationic surfactant cetyltrimethylammonium (CTAB) concentration in the solution-phase reaction. Structural investigations reveal that Cu2O nanoparticles can be either well-defined hollow nanoboxes or porous nanocubes depending on the synthesis conditions. The transmission electron microscopy (TEM) observations demonstrated that the nanoparticles in general are composed of small grains coherently growing along certain preferred orientations.

Uniform-sized gold nanoparticles were synthesized by a facile method, which is comprised of three steps: the first step to prepare Au colloid in aqueous, the second to transfer the particles into organic solvent and the third to reflux organic solution. The 2D/3D superlattices of as-prepared gold nanoparticles were fabricated by evaporating solvent from colloid solution at optimal concentration.

Pvramid-like Fe3O4 nanostructures (see Figure) are formed over large areas on alpha-Fe2O3(0001) substrates using a plasma-sputtering technique. No catalysts or templates are used in the reaction process. This nanostructure resembles Egyptian pyramids, possessing many layers and standing perpendicular to the substrate surface. These structures may have potential applications in constructing nanoscale magnetic and high-density storage devices.

Pure phase CeO2 nanorods (about 40?50?nm in diameter and 0.3?2??m in length) were synthesized through a solvothermal synthesis method. The addition of ethylenediamine is critical to obtain CeO2 nanorods. Other experimental conditions, such as the solvent composition, surfactant and the cerium source precursor were of importance in the final product morphology. The reaction temperature and reaction time also had significant influence on the yield of CeO2 nanorods. A possible formation mechanism of CeO2 nanorods was discussed mainly based on the dependences of controlling parameters on the final morphologies. In addition, the optical properties of CeO2 nanorods were investigated. The UV?visible adsorption spectrum and photoluminescence spectrum of the CeO2 nanorods showed unusual red-shift and enhanced light emission, respectively.

Carbon nanotube (CNT) bundles are synthesized on rough polycrystalline ceramic wafers by pyrolyzing ferrocene/melamine mixtures through a three-step process in a single stage furnace in an Ar atmosphere. The CNTs are multi-walled and have outer diameters from 10 to 90 nm and lengths from 20 to 100 microns. These CNTs display a bamboo-like structure with open graphite layers and defects at the outer surfaces. Field electron emission (FEE) measurements show that the turn-on electrical field is 2.9 V/μm and the field enhancement factor is 2700.

Without catalyst and at a low temperature (550 °C), well-aligned ZnO nanorods and nanowires were prepared on porous silicon substrates using a simple method. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results confirm that both the nanorods and the nanowires are perfect single crystals with the wurtzite structure. The diameters range from 40 to 100 nm. The growth directions are along the [0 0 0 1] axis. Photoluminescence (PL) spectra show that the UV emission shifts slightly to low frequency and the intensity of green emission decreases with the improvement of ZnO crystallization.

The microstructures of a single-crystal nickel-base superalloy were observed by transmission electron microscopy (TEM) before and after thermo-mechanical fatigue. Both dislocation configurations and γ′ precipitate morphologies under in-phase (IP) testing were found to be clearly different from those under out-of-phase (OP) testing. Under IP testing, dense hexagonal dislocation networks were found on the horizontal interfaces, and irregular dislocation networks on the vertical interfaces. With decreasing mechanical strain amplitude, rafting of γ′ precipitates was more pronounced. Under OP testing, no dislocation networks were found on the γ/γ′ interfaces; also, γ′ precipitates were sheared by superlattice stacking faults, and were not clearly rafted. The characteristic dislocation networks and partials of the stacking fault are analysed and the rafting mechanism of the γ′ precipitates is discussed.

We report on the controlled growth of novel self-assembled nanostructures (nanoaeroplanes, nanocombs, and tetrapod-like networks of zinc oxide) by a simple thermal evaporation technique in a single-stage furnace. Scanning electron microscopy and transmission electron microscopy are used to investigate their morphologies and structures. Shapes are regular and unit sizes vary from 80 nm to 5 µm. The relationship between the preparation conditions and the nanomorphologies in the experiments is helpful for controlling the physical properties of the nanosystems and, hence, is described in some detail. A possible growth mechanism is discussed.

WO3� x nanorods were grown on the tips of electrochemical etched W filaments by in-situ heating under different growth conditions. This kind of nanorods has the average diameter of 20 nm and the length of 1–2 lm. Transmission-electron microscopy investigations indicate that the sub-stoichiometric WO3 nanorods, prepared at about 830 C under the atmosphere of H2 and Ar mixture, could grow along the either h 00 1i or h 11 0i direction with evident stacking faults and textural structure. Nanorods prepared without H2 atmosphere are found to be respectively W18O49 grown at around 900 C and WO2:9 grown at 800 C. 2004 Elsevier B.V. All rights reserved.

Hollow polyhedra and cubes of nanostructured Cu(2)O particles have been synthesized by reduction of CuSO(4) with ascorbate acid in the solution phase. The nanostructures were obtained when the cetyltrimethylammonium (CTAB) concentration ranged from 0 to 0.03 M in the presence of NaOH. Structural characterizations, by means of x-ray photoelectron spectroscopy (XPS) for measuring Cu valence states and by electron microscopy for microstructure and chemical analyses, suggest that most Cu(2)O nanoparticles are covered with a thin CuO shell arising possibly from reaction of the adsorbed oxygen on the Cu(2)O particle surface. The blue shift is observed as microstructures of Cu(2)O nanoparticles changed from cubic to hollow in ultraviolet and visible (UV-visible) absorption spectra. Both the Cu(2)O hollow and cubic nanostructures show certain quantum-confined effects. A cationic CTAB template mechanism is proposed to interpret the formation of the Cu(2)O nanoparticles.

Transmission electron microscopy study of brazed joint microstructure in a Ni3Al-based intermetallic alloy IC 6 was performed. A continuously distributed microconstituents consisting of γ solid-solution, M 3B2-type and M23B6-type borides, which were likely formed by eutectic-type reaction(s) from residual liquated insert during cooling from brazing temperature, were observed along the joint centreline. Consideration of possible incipient melting due to eutectic-type transformation reaction of these phases is pertinent to development of post braze heat treatment for modifying the brazement microstructure. © 2010 Springer Science+Business Media, LLC.

The structural properties of Ni(2)FeGa Heusler alloy synthesized by melt-spinning technique have been systematically studied by means of in situ heating and cooling transmission electron microscopy. It was found that the Ni(2)FeGa alloy was annealed into a well-defined L2(1) structure at around 980 K, and complex microstructural domains appeared along with lowering temperature. At room temperature (293 K), a rich variety of micromodulated domains were observed. The domain structures were aligned along the or directions resulting to complex tweed structures. Below martensitic transformation (MT) temperature (M(s),similar to 142 K), the cubic parent phase transformed into unmodulated martensitic variants and modulated martensitic variants. The variants were alternated along the direction with various arrangements and steplike incommensurate boundaries. The modulated martensitic variants were composed of lamellar structures that have predominately a 5M modulation structure along the directions. The electron energy-loss spectroscopy analysis of the low-loss region and the electron energy-loss near-edge fine structure revealed a visible change of the electronic structure along with MT, which can be well interpreted by means of intra-atomic or intraband charge redistribution due to spd orbital hybridization among the Ni-Fe-Ga atoms.

Electron energy-loss spectroscopy (EELS) is routinely used to estimate local specimen thickness in a TEM. The relative specimen thickness is conveniently estimated from the low-loss spectrum using log-ratio method with a formula t/λ = ln(Iₜ /I₀). Here λ is an inelastic mean free path (IMFP) for the material in question, I₀ is the area under zero-loss peak (ZLP) and Iₜ the total area under the whole spectrum. An absolute thickness t measurement requires knowledge of the IMFP, which depends on the specimen material, electron energy and collection semiangle. The most commonly used IMFP formula, incorporated into Gatan Digital Micrograph software, was developed by Malis et al. and exhibits a smooth dependence on atomic number Z., Proceedings of Microscopy & Microanalysis 2011, August 7-11, 2011, Nashville, Tennessee

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Guided propagation of neutrons in thin films was directly observed in a ${\mathrm{TiO}}_{2}$/Ti/Si waveguide by exciting one of its discrete guided modes from an external neutron beam. The condition found experimentally for exciting this particular mode agrees well with theory. The measured intensity of the guided neutrons was also in good agreement with a calculation based on a previous coupling theory.

Mn-doped 3C-SiC nanoparticles have been fabricated by a sol-gel and carbothermal reduction method. The average particle size of the nanoparticles is about 126 nm. Raman scattering studies indicate that the transverse optical and the longitudinal optical modes shift to low wave number and the full widths at half-maximum of Raman peaks increase after Mn was doped. Extended x-ray absorption fine structure reveals that the doped-Mn atoms substitute for the C sites in the 3C-SiC lattice. Magnetic measurement results show that the room temperature intrinsic ferromagnetism (FM) order is established. The origin of the FM has been discussed in detail.

A seed-mediated method was employed here for CTAB-assisted gold nanoparticle growth. 3–4 nm silver aqueous colloid was stabilized by sodium citrate and used as seed solution to initial gold particle growth. The concentration of seed solution was calculated based on its relationship with silver atom concentration and seed particle statistical mean volume. It was found that there is a maximum seed concentration of 8.57 × 10 −12 M( ∼25 μ l0 .343 × 10 −8 M seed solution added) in 10 ml 2.5 × 10 −4 M HAuCl4 growth solution for growth of rodlike particles. Below this seed amount, the aspect ratio of nanorods could be controlled by varying the silver seed amount, i.e. nanorods with aspect ratio ∼18.9 were obtained when the seed concentration in the growth solution was 0.343 × 10 −12 M by adding 1 μ l0 .343 × 10 −8 M silver seed solution and nanorods with aspect ratio ∼9.69 were obtained when the seed concentration in the growth solution was 1.715 × 10 −12 M by adding 5 μ l0 .343 × 10 −8 M silver seed solution. As the seed concentration in the growth solution was more than 8.58 × 10 −12 M( 25μ l0 .343 × 10 −8 M silver seed solution was added), there were no rodlike particles formed but spherical ones instead. These spheres were further studied by TEM and found to all be hollow structures. It was suggested that there were probably two different nucleation processes for growth of nanorods and spheres. For hollow spheres, the reaction between Ag seeds and Au ions formed hollow structures based on the Ag particle template effect. Then further growth of Au on these hollow structures produced hollow gold nanospheres. For nanorods, due to the very low concentration of silver seed (molar ratio of Ag seed: Au = 3.426 × 10 −8 ), the growth process here probably was started by silver-induced Au nucleation, in which reduction of gold ions by silver resulted in small gold clusters. These gold clusters further grew up into nanoparticles and nanorods in the presence of CTAB. S Supplementary data are available from stacks.iop.org/Nano/18/115608

Visible and infrared photoluminescence was observed from AlN:Er films grown by reactive radio-frequency magnetron sputtering under different powers. X-ray diffraction indicates that the films have a c-axis oriented hexagonal wurtzite structure with an average crystallite size of about 59-83 nm and a strain of about (1.12-1.69) x 10(-3). Green emissions (similar to 540 and 558 nm) from the AlN: Er films are due to the intra-4f(n) transition of Er3+ from H-2(11/2) and S-4(3/2) to I-4(15/2), and infrared (similar to 1535 nm) emissions correspond to I-4(13/2) to I-4(15/2) transitions. Increasing the sputtering power results in larger grain size, lower strain, and enhancement of the luminescence intensity. (c) 2006 American Institute of Physics.

Strong photoluminescence (PL) is observed in nanostructured crystalline tungsten oxide thin films that are prepared by thermal evaporation. Two kinds of films are investigated—one made of nanoparticles and another of nanowires. At room temperature, strong PL emissions at ultraviolet-visible and blue regions are found in both of the films. Compared with the complete absence of emission of bulk phase tungsten oxide powder under the same excitation conditions, our results clearly demonstrate the quantum-confinement-effect-induced photoluminescence in nanostructured tungsten oxides.