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Electron energy-loss spectroscopy (EELS) is used to investigate the association of hydrogen with helium bubbles in zirconium. Conventional EELS data yield a signal at 13.5 eV (similar to the hydrogen K-edge, 13 eV), which is spatially distributed around the peripheries of bubbles and may correlate with the concentration of hydrogen/deuterium in the material. Ultra-high energy resolution EELS yields a signal at 148.6 meV (comparable to a range of ZrH bonds, 130–156 meV) from a region containing bubbles and no visible hydrides. These signals are interpreted in the context of either bubble surface chemisorption or bubble stress field trapping mechanisms.

A Ge-SiGe multiple quantum well structure created by low energy plasma enhanced chemical vapour deposition, with nominal well thickness of 5.4 nm separated by 3.6 nm SiGe spacers, is analysed quantitatively using scanning transmission electron microscopy. Both high angle annular dark field imaging and electron energy loss spectroscopy show that the interfaces are not completely sharp, suggesting that there is some intermixing of Si and Ge at each interface. Two methods are compared for the quantification of the spectroscopy datasets: a self-consistent approach that calculates binary substitutional trends without requiring experimental or computational k-factors from elsewhere and a standards-based cross sectional calculation. Whilst the cross section approach is shown to be ultimately more reliable, the self-consistent approach provides surprisingly good results. It is found that the Ge quantum wells are actually about 95% Ge and that the spacers, whilst apparently peaking at about 35% Si, contain significant interdiffused Ge at each side. This result is shown to be not just an artefact of electron beam spreading in the sample, but mostly arising from a real chemical interdiffusion resulting from the growth. Similar results are found by use of X-ray diffraction from a similar area of the sample. Putting the results together suggests a real interdiffusion with a standard deviation of about 0.87 nm, or put another way—a true width defined from 10%–90% of the compositional gradient of about 2.9 nm. This suggests an intrinsic limit on how sharp such interfaces can be grown by this method and, whilst 95% Ge quantum wells (QWs) still behave well enough to have good properties, any attempt to grow thinner QWs would require modifications to the growth procedure to reduce this interdiffusion, in order to maintain a composition of ≥95% Ge.

Electron tomography (ET) is an increasingly important technique for the study of the three-dimensional morphologies of nanostructures. ET involves the acquisition of a set of two-dimensional projection images, followed by the reconstruction into a volumetric image by solving an inverse problem. However, due to limitations in the acquisition process, this inverse problem is ill-posed (i.e., a unique solution may not exist). Furthermore, reconstruction usually suffers from missing wedge artifacts (e.g., star, fan, blurring, and elongation artifacts). Recently, compressed sensing (CS) has been applied to ET and showed promising results for reducing missing wedge artifacts. This uses image sparsity as a priori knowledge to improve the accuracy of reconstruction, and can require fewer projections than other reconstruction techniques. The performance of CS relies heavily on the degree of sparsity in the selected transform domain and this depends essentially on the choice of sparsifying transform. We propose a new image reconstruction algorithm for ET that learns the sparsifying transform adaptively using a dictionary-based approach. We demonstrate quantitatively using simulations from complex phantoms that this new approach reconstructs the morphology with higher fidelity than either analytically based CS reconstruction algorithms or traditional weighted back projection from the same dataset. SCANNING 38:251-276, 2016. © 2015 Wiley Periodicals, Inc.

The nakhlite meteorites are clinopyroxenites that are derived from a ~1300 million year old sill or lava flow on Mars. Most members of the group contain veins of iddingsite whose main component is a fine-grained and hydrous Fe- and Mg-rich silicate. Siderite is present in the majority of veins, where it straddles or cross-cuts the Fe-Mg silicate. This carbonate also contains patches of ferric (oxy)hydroxide. Despite 40 years of investigation, the mineralogy and origins of the Fe-Mg silicate is poorly understood, as is the paragenesis of the iddingsite veins. Nanometer-scale analysis of Fe-Mg silicate in the Nakhla meteorite by electron and X-ray imaging and spectroscopy reveals that its principal constituents are nanoparticles of opal-A. This hydrous and amorphous phase precipitated from acidic solutions that had become supersaturated with respect to silica by dissolution of olivine. Each opal-A nanoparticle is enclosed within a ferrihydrite shell that formed by oxidation of iron that had also been liberated from the olivine. Siderite crystallized subsequently and from solutions that were alkaline and reducing, and replaced both the nanoparticles and olivine. The fluids that formed both the opal-A/ferrihydrite and the siderite were sourced from one or more reservoirs in contact with the Martian atmosphere. The last event recorded by the veins was alteration of the carbonate to a ferric (oxy)hydroxide that probably took place on Mars, although a terrestrial origin remains possible. These results support findings from orbiter- and rover-based spectroscopy that opaline silica was a common product of aqueous alteration of the Martian crust.

Magnesium hydroxide nanoplates ca. 50 nm in thickness can be prepared over minute timescales via hydrothermal synthesis in a multimode cavity (MMC) microwave reactor. This approach allows ca. 1 g of single-phase Mg(OH)2 to be synthesised in less than 3 minutes without the requirement of surfactants or non-aqueous solvents. The hydroxide nanomaterial dehydrates at temperatures >200 K below that of the equivalent bulk material and can be utilised as a precursor for the pseudomorphic synthesis of nanoplates of MgO as investigated by TG-DTA-MS, PXD and SEM measurements. Equally, the pseudomorphic synthesis can be performed by irradiating the Mg(OH)2 nanomaterial with microwaves for 6 minutes to produce single-phase MgO.

A detailed characterization of nanostructured thin zirconium oxide films formed during aqueous corrosion of a nuclear-grade zirconium alloy (Zircaloy-4) has been carried out by means of two novel, ultra-high-spatial-resolution grain mapping techniques, namely automated crystal orientation mapping in the transmission electron microscope (TEM) and transmission electron backscatter diffraction (t-EBSD). While the former provided excellent spatial resolution with the ability to identify tetragonal ZrO2 grains as small as ∼5 nm, the superior angular resolution and unambiguous indexing with t-EBSD enabled verification of the TEM observations. Both techniques revealed that in a stress-free condition (TEM foil prepared by focused ion beam milling), the oxide consists mainly of well-oriented columnar monoclinic grains with a high fraction of transformation twin boundaries, which indicates that the transformation from tetragonal to monoclinic ZrO2 is a continuous process, and that a significant fraction of the columnar grains transformed from stress-stabilized tetragonal grains with (0 0 1) planes parallel to the metal-oxide interface. The TEM analysis also revealed a small fraction of size-stabilized, equiaxed tetragonal grains throughout the oxide. Those grains were found to show significant misalignment from the expected (0 0 1) growth direction, which explains the limited growth of those grains. The observations are discussed in the context of providing new insights into corrosion mechanisms of zirconium alloys, which is of particular importance for improving service life of fuel assemblies used in water-cooled reactors. © 2014 Acta Materialia Inc. Published by Elsevier Ltd.

Scanning transmission electron microscopy (STEM) data with atomic resolution can contain a large amount of information about the structure of a crystalline material. Often, this information is hard to extract, due to the large number of atomic columns and large differences in intensity from sublattices consisting of different elements. In this work, we present a free and open source software tool for analysing both the position and shapes of atomic columns in STEM-images, using 2-D elliptical Gaussian distributions. The software is tested on variants of the perovskite oxide structure. By first fitting the most intense atomic columns and then subtracting them, information on all the projected sublattices can be obtained. From this, we can extract changes in the lattice parameters and shape of A-cation columns from annular dark field images of perovskite oxide heterostructures. Using annular bright field images, shifts in oxygen column positions are also quantified in the same heterostructure. The precision of determining the position of atomic columns is compared between STEM data acquired using standard acquisition, and STEM-images obtained as an image stack averaged after using non-rigid registration. © The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Atomic resolution scanning transmission electron microscopy (STEM) data contain a large amount of information about the structure of a crystalline material. Often, this information is hard to extract, due to the large number of atomic columns and large differences in intensity from sublattices consisting of different elements. Atomap is a semi-automatic, free and open source software tool for analysing both the position and shapes of atomic columns in STEM-images, using 2-D elliptical Gaussian distributions. In this work, the Atomap software is used on variants of the perovskite oxide structure, obtaining quantitative information from projected sublattices. Changes in the lattice parameters and shape of Acation columns from annular dark field images of perovskite oxide heterostructures are obtained. Furthermore, we demonstrate the functionality of Atomap by quantifying deviation from centrosymmerty of light atomic oxygen columns. © Microscopy Society of America 2017. This is the authors’ submitted manuscript to the article.

Mid-infrared intersubband absorption from p-Ge quantum wells with Si 0.5 Ge 0.5 barriers grown on a Si substrate is demonstrated from 6 to 9 μm wavelength at room temperature and can be tuned by adjusting the quantum well thickness. Fourier transform infra-red spectroscopy measurements demonstrate clear absorption peaks corresponding to intersubband transitions among confined hole states. The work indicates an approach that will allow quantum well intersubband photodetectors to be realized on Si substrates in the important atmospheric transmission window of 8–13 μm.

Methods are described for measuring accurate absolute experimental inelastic mean free paths and differential cross-sections using DualEELS. The methods remove the effects of surface layers and give the results for the bulk materials. The materials used are VC0.83, TiC0.98, VN0.97 and TiN0.88 but the method should be applicable to a wide range of materials. The data was taken at 200keV using a probe half angle of 29mrad and a collection angle of 36mrad. The background can be subtracted from under the ionisation edges, which can then be separated from each other. This is achieved by scaling Hartree-Slater calculated cross-sections to the edges in the atomic regions well above the threshold. The average scaling factors required are 1.00 for the non-metal K-edges and 1.01 for the metal L-edges (with uncertainties of a few percent). If preliminary measurements of the chromatic effects in the post-specimen lenses are correct, both drop to 0.99. The inelastic mean free path for TiC0.98 was measured as 103.6±0.5nm compared to the prediction of 126.9nm based on the widely used Iakoubovskii parameterisation.

JAM would like to acknowledge the School of Chemistry, University of St Andrews for the allocation of a PhD studentship through the EPSRC doctoral training grant (EP/ K503162/1). The work carried out at the University of St Andrews and Queens University Belfast was carried out as part of an EPSRC-funded collaboration (EP/P02453X/1 and EP/P024637/1). The work carried out at the University of Glasgow was carried out as part of the EPSRC-funded CDT in Photonic Integration and Advanced Data Storage (EP/L015323/1). TTT and PSH thank the Welch Foundation (Grant E-1457) and NSF (DMR-1503573) for support. Since the observation that the properties of ferroic domain walls (DWs) can differ significantly from the bulk materials in which they are formed, it has been realized that domain wall engineering offers exciting new opportunities for nanoelectronics and nanodevice architectures. Here, a novel improper ferroelectric, CsNbW2O9, with the hexagonal tungsten bronze structure, is reported. Powder neutron diffraction and symmetry mode analysis indicate that the improper transition (TC = 1100 K) involves unit cell tripling, reminiscent of the hexagonal rare earth manganites. However, in contrast to the manganites the symmetry breaking in CsNbW2O9 is electronically driven (i.e., purely displacive) via the second-order Jahn-Teller effect in contrast to the geometrically-driven tilt mechanism of the manganites. Nevertheless CsNbW2O9 displays the same kinds of domain microstructure as those found in the manganites, such as the characteristic six-domain "cloverleaf" vertices and DW sections with polar discontinuities. The discovery of a completely new material system, with domain patterns already known to generate interesting functionality in the manganites, is important for the emerging field of DW nanoelectronics. Postprint

Highly reflective dielectric mirror coatings are critical components in a range of precision optics applications including frequency combs, optical atomic clocks, precision interferometry and ring laser gyroscopes. A key limitation to the performance in these applications is thermal noise, arising from the mechanical loss of the coatings. The origins of the mechanical loss from these coatings is not well understood. Recent work suggests that the mechanical loss of amorphous Ta 2 O 5 coatings can drop by as much as 40% when it is doped with TiO 2 . We use a combination of electron diffraction data and atomic modelling using molecular dynamics to probe the atomic structure of these coatings, and examine the correlations between changes in the atomic structure and changes in the mechanical loss of these coatings. Our results show the first correlation between changes in the mechanical loss and experimentally measured changes in the atomic structure resulting from variations in the level of TiO 2 doping in TiO 2 -doped Ta 2 O 5 coatings, in that increased homogeneity at the nearest-neighbour level appears to correlate with reduced mechanical loss. It is demonstrated that subtle but measurable changes in the nearest-neighbour homogeneity in an amorphous material can correlate with significant changes in macroscopic properties.

Graphical abstract, Highlights • Direct nanopatterning of titanium using nanopatterned diamond based stamps. • Quantify nanopillar matrix imprint depth with regards to feature size and density. • An account of a novel method of reducing the imprint load required to emboss titanium. • TEM and EELS analysis following our load reduction treatment. • The first demonstration of nanopatterning curved, bulk titanium., In this work the direct transfer of nanopatterns into titanium is demonstrated. The nanofeatures are imprinted at room temperature using diamond stamps in a single step. We also show that the imprint properties of the titanium surface can be altered by anodisation yielding a significant reduction in the required imprint force for pattern transfer. The anodisation process is also utilised for curved titanium surfaces where a reduced imprint force is preferable to avoid sample deformation and damage. We finally demonstrate that our process can be applied directly to titanium rods.

There is significant interest to develop cheap CMOS compatible sensors that operate in the mid-infrared (MIR). To meet these requirements, Ge-on-Si is proving to be an exciting platform. There is the potential to realize waveguide integrated quantum well infrared photodetectors (QWIPs) based on Ge quantum wells (QWs). Intersubband absorption from p-Ge QWs has been demonstrated in the important atmospheric transmission window of 8-13 μm. An alternative strategy for sensing in the MIR is demonstrated through highly n-type doped Ge plasmonic antennas. These antennas demonstrate vibrational sensing of polydimethylsiloxane (PDMS) spin coated layers at 12.5 μm wavelength. These demonstrate enhanced sensing capabilities due to the localized hot spots of the antenna resonant modes.

Ge on Si micro-disk, ring and racetrack cavities are fabricated and strained using silicon nitride stressor layers. Photoluminescence measurements demonstrate emission at wavelengths ≥ 2.3 μm, and the highest strained samples demonstrate in-plane, tensile strains of > 2%, as measured by Raman spectroscopy. Strain analysis of the micro-disk structures demonstrate that shear strains are present in circular cavities, which can detrimentally effect the carrier concentration for direct band transitions. The advantages and disadvantages of each type of proposed cavity structure are discussed.

Mid-infrared intersubband absorption from p-Ge quantum wells with Sio.sGeo.s barriers grown on a Si substrate is demonstrated from 6 to 9 μm wavelength at room temperature and can be tuned by adjusting the quantum well thickness.

The discovery of unusual nanorod precipitates in bismuth ferrite doped with Nd and Ti is reported. The atomic structure and chemistry of the nanorods are determined using a combination of high angle annular dark field imaging, electron energy loss spectroscopy, and density functional calculations. It is found that the structure of the BiFeO3 matrix is strongly modified adjacent to the precipitates; the readiness of BiFeO3 to adopt different structural allotropes in turn explains why such a large axial ratio, uncommon in precipitates, is stabilized. In addition, a correlation is found between the alignment of the rods and the orientation of ferroelastic domains in the matrix, which is consistent with the system's attempt to minimize its internal strain. Density functional calculations indicate a finite density of electronic states at the Fermi energy within the rods, suggesting enhanced electrical conductivity along the rod axes, and motivating future investigations of nanorod functionalities.

Lanthanum doping of zirconium rich lead zirconate titanate gives rise to incommensurate, long-period antiferroelectric structures. The structure of two stacking sequences in this incommensurate phase is determined using quantitative analysis of high-resolution scanning transmission electron microscopy images, with the lead atom positions located with an exceptional precision of about 6 pm. This allows the estimation of local polarisation variations across the stacking units, and the polarisation varies in an approximately sinusoidal fashion along the stacking direction. The measured peak Pb atom displacements of about 28 pm and peak polarisation values of about 60 mu C cm-2 match extremely well to reported values for the commensurate antiferroelectric PbZrO3 phase.

Parallel stacking faults on (010) planes are frequently observed in hot-pressed Y2Si2O7. A combination of conventional dark-field imaging and high-resolution transmission electron microscopy was used to investigate the structure of these faults and it was found that they consist of the repeat of one layer of the two layer γ-Y2Si2O7 structure with an associated in-plane rigid body displacement. The resulting structure was confirmed by image simulation of high-resolution images from two perpendicular projections. A model for the formation of the stacking faults is proposed as a consequence of a transformation from β-Y2Si2O7 to γ-Y2Si2O7 in the hot pressing.

A mechanochemical activation route has been applied in order to obtain the n = 1–4 and ∞ members of the Sr 2 [Sr n − 1 Ti n O 3 n + 1 ] Ruddlesden–Popper series from different ( n + 1)SrO:nTiO 2 mixtures. The mechanosynthesis of SrTiO 3 and Sr 2 TiO 4 was observed during the milling process from the initial stoichiometric mixture, but in the cases of the n = 2–4 members, a subsequent thermal treatment was needed. The synthesis protocol of Sr 3 Ti 2 O 7 has been greatly improved and this compound can be isolated as a single, crystalline phase after annealing at 800 °C. In the case of Sr 4 Ti 3 O 10 and Sr 5 Ti 4 O 13 , the formation temperature was also decreased, but members with n = 3 and 4 could not be isolated. Detailed investigations using electron microscopy methods (TEM, HREM and SAED) were carried out in the samples corresponding to n = 2–4. Although a single ordered Sr 3 Ti 2 O 7 structure is dominant in the sample corresponding to n = 2, a few intergrowths of other Ruddlesden–Popper phases were observed. In the cases of n = 3 and 4, the intergrowths of Ruddlesden–Popper phases are more frequent than in the n = 2 composition and are randomly distributed in the sample. The more frequent occurrence of such stacking faults, with increasing n value, leads to a somewhat disordered layer stacking sequence.

Hot-pressed yttrium disilicate ceramics have been characterized using analytical transmission electron microscopy (TEM). The microstructure consists of large grains of the γ phase of stoichiometric γ-Y2Si2O7 containing rounded glassy Y-doped SiO2 inclusions; excess glassy SiO2-rich material is also found at the grain boundaries. Two main reasons are found for the inhomogeneity: a slight SiO2 excess is inferred from the composition measurements, and the LiF flux used in hot pressing would also promote glass formation. Improved high-temperature mechanical properties would only be possible if residual glass formation was minimized, strategies for doing so are discussed, and the importance of analytical TEM for studying such submicron scale inhomogeneity is underlined.

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.

Ultramicroscopy 154, 57-63 (2015). doi:10.1016/j.ultramic.2015.03.016, Published by Elsevier Science, Amsterdam

The atomic structure and chemistry of thin films of Bi(Fe,Mn)O-3 (BFMO) films with a target composition of Bi2FeMnO6 on SrTiO3 are studied using scanning transmission electron microscopy imaging and electron energy loss spectroscopy. It is shown that Mn4+-rich antiphase boundaries are locally nucleated right at the film substrate and then form stepped structures that are approximately pyramidal in three dimensions. These have the effect of confining the material below the pyramids in a highly strained state with an out-of-plane lattice parameter close to 4.1 angstrom. Outside the area enclosed by the antiphase boundaries, the out-of-plane lattice parameter is much closer to bulk values for BFMO. This suggests that to improve the crystallographic perfection of the films whilst retaining the strain state through as much of the film as possible, ways need to be found to prevent nucleation of the antiphase boundaries. Since the antiphase boundaries seem to form from the interaction of Mn with the Ti in the substrate, one route to perform this would be to grow a thin buffer layer of pure BiFeO3 on the SrTiO3 substrate to minimise any Mn-Ti interactions.

The filoviruses Ebolavirus (EBOV) and Marburgvirus cause fatal hemorrhagic fevers in humans and other mammals, known as Ebola virus disease (EVD), with mortality rates approaching 90% [1] which makes it listed as world health organization risk group 4 pathogen. Ebola virus caused the 2013–2015 epidemic in West Africa, which has resulted in at least 9,268 confirmed deaths and 23,034 suspected cases as of 18 Feb 2015 [2]. Consequently, considerable effort is focused on developing therapeutics and vaccines to prevent infections.

Materials science and technology : MST 32(3, Special Issue: SI), 242-247 (2015). doi:10.1179/1743284715Y.0000000115, Published by Taylor and Francis, London

We report the synthesis of stearate functionalized nanobubbles of SiO2 with a few aniline\ud molecules inside, represented as C6H5NH2@SiO2@stearate, exhibiting fluorescence with red-shifted\ud emission. Stearic acid functionalization allows the materials to be handled just as free molecules, for dissolution,\ud precipitation, storage etc. The methodology adopted involves adsorption of aniline on the surface of\ud gold nanoparticles with subsequent growth of a silica shell through monolayers, followed by the selective\ud removal of the metal core either using sodium cyanide or by a new reaction involving halocarbons. The\ud material is stable and can be stored for extended periods without loss of fluorescence. Spectroscopic and\ud voltammetric properties of the system were studied in order to understand the interaction of aniline with\ud the shell as well as the monolayer, whilst transmission electron microscopy has been used to study the\ud silica shell.

The paper presents an overview of a number of unusual phase transformations which take place in pearlitic steels in conditions of the severe deformation, i.e. combination of high pressure and strong shear strain. Strain-induced cementite dissolution is a well-documented phenomenon, which occurs during cold plastic deformation of pearlitic steels. Recently new results which can shed additional light on the mechanisms of this process were obtained thanks to 3DAP and HRTEM investigations of pearlitic steel deformed by high pressure torsion (HPT). It was shown that the process of cementite decomposition starts by carbon depletion from the carbides, which indicates that the deviation of cementite’s chemical composition from the stoichiometric is the main reason for thermodynamic destabilisation of cementite during plastic deformation. Important results were obtained regarding the distribution of released carbon atoms in ferrite. It was experimentally confirmed that carbon segregates to the dislocations and grain boundaries of nanocrystalline ferrite. Another unusual phase transformation taking place in nanocrystalline pearlitic steel during room temperature HPT is a stress induced α→γ transformation, which never occurs during conventional deformation of coarse grained iron and carbon steels. It was concluded that this occurred due to a reverse martensitic transformation. The atomistic mechanism and the thermodynamics of the transformation, as well as issues related to the stability of the reverted austenite will be discussed.

High-resolution transmission electron microscopy and three-dimensional atom probe observations show clearly that a reverse transformation of body-centred cubic ferrite to face-centred cubic austenite occurs during severe plastic deformation of a pearlitic steel resulting in a nanocrystalline structure, something that never occurs in conventional deformation of coarse-grained iron and steels. The driving force and the mechanisms of this reverse transformation are discussed. It is shown that nanostructure and shear stresses are essential for this process, and the results confirm molecular dynamics predictions of such transformations in nanocrystalline iron.

Transmission electron microscopy has been used to investigate the junction between two lamellar bands in a tetragonal lead zirconate titanate (PZT) ceramic. It is found that significant bending occurs in the area due to the matching of different domains on planes. Analysis of CBED patterns shows that the orientation relationships between the long boundaries between lamellae is much as expected and allows quantification of local c/a ratios. The short boundaries at the band junction, however, are highly stressed and deviate significantly from ideal misorientation values. This reveals that the areas between the 4- domain junctions in the band junction are highly stressed with peak stresses in the GPa range, which are highly likely to function as the source of microcracks under the additional strains found in device application.

Electron diffraction and high-resolution transmission electron microscopy show the presence of austenite in a heavily-deformed, initially pearlitic steel. This austenite must have formed as a result of the deformation, and it is shown that it could only originate from a reverse martensitic transformation from ferrite to austenite, stimulated by the high shear strains in the deformation. This reverse transformation could play the role of an additional and novel deformation mechanism in nanocrystalline steels.

Recent studies of nanocrystalline materials have often found that the deformation mechanisms are radically different to those in coarse-grained materials, resulting in quite different mechanical properties for such materials. The use of pearlitic steels for the study of the deformation mechanisms in bcc materials with ultrafine grain sizes is quite convenient, because it is relatively straightforward to obtain a homogenous nanocrystalline structure with a mean grain size as small as 10 nm using various modes of severe plastic deformation (SPD). In this paper we show that highpressure torsion of an initially pearlitic steel results in a nanostructured steel in which austenite has been formed at or close to room temperature. The orientation relationship between neighboring ferrite and austenite grains is the well-known Kurdjumov-Sachs orientation relationship, i.e. the same observed in temperature-induced martensitic transformation of iron and steels. It is shown that this must have resulted from a reverse martensitic transformation promoted by the high shear strains experienced by the material during severe plastic deformation of the nanocrystalline structure. This transformation represents an alternative deformation mechanism that can be activated when conventional deformation mechanisms such as slip of lattice dislocations become exhausted.

The microstructure evolution in PtMn-based bottom spin-filter spin valves was investigated to clarify the alteration of the sensor performance caused by different annealing treatments during manufacturing. Neither unidirectional field annealing (UDA) nor stress annealing (SA) for 38 h, which simulates the final quality test of the finished read-write head, have any significant influence on the texture of the sensor stack. UDA causes the appearance of domain boundaries in the PtMn layer as a consequence of the fcc–fct transformation together with some disturbance in the functional layers of the sensor, neither of which affect the giant magneto-resistive performance. The SA treatment causes an inter-diffusion in the NiFeCr/NiFe seed layers, some grain growth in PtMn, more serious disturbance of the functional layers, and complete amorphization of the Ta cap layer. In comparison to other studies of spin valves, the intermixing of seed layers in the present study does not appear to influence the PtMn/CoFe interface. The alteration of the sensor performance seems to be mainly caused by the inter-diffusion of the functional layers.

Carbon onions have been known since Iijima first observed them in 1980 [1]. In 1992 Ugarte et al. made carbon onions by irradiating carbon soot by an intense electron beam in a transmission electron microscope [2]. There are reports in the literature on the production of carbon structures in water medium by generating an electric arc to create high temperatures [3,4]. It was found that several metals including gold catalyze carbon onion growth from various precursor species. Multiwalled carbon nanotubes have also been coated with silica (SiO2) [5,6]. It has previously been demonstrated that gold and silver nanoparticles react with halocarbons leading to the complete leaching of the metals along with deposition of carbon in an amorphous form [7]. This method, if used with core–shell nanoparticles such as Au@SiO2 [8] makes possible the deposition of amorphous carbon species inside ceramic nanoshells. The nano dimension of the cavity may force a reaction between the carbon species in the solution phase itself, with or without catalysis by the metals or their ions. With this conjecture, we investigated the metal oxide nanoshells after leaching the metal core of core–shell nanoparticles. Carbon onion structures within silica shells were detected in these experiments. It may be noted that the main objective of this work is not to introduce a new method for the synthesis of carbon onions, but to introduce a new material where carbon onions have been made inside the silica shell. Chloroauric acid and trisodium citrate were purchased from CDH fine chemicals, India. (3-amino) propyl trimethoxysilane (APS) and tetra methoxysilane (TMS) were purchased from Aldrich and were used without additional purification. Ethanol and 2-propanol were purchased from E. Merck. CCl4 was purchased from Ranbaxy Chemicals, India. Triply distilled water was used for all the experiments. Gold nanoparticles of size 15 nm were prepared using the Turkevich reduction method [9]. In order to cover this gold particle with silica, a method adopted by Makarova et al. [10] was followed. Further growth of the silica shell was achieved by following the Stober method [11]. To 50 ml of the gold sol, 0.25 ml of millimolar solution of freshly prepared solution of 3-aminopropyl trimethoxysilane (APS) was added with vigorous stirring. This mixture was allowed to stand for around 15 min for complete complexation. A solution of active silica was prepared by adjusting the pH to 10–11 of a 0.54 wt.% of sodium silicate solution by progressive addition of a cation exchange resin, Dualite C 225–Na 14–52 mesh. Two milliliters of active silica thus prepared was added to 50 ml of the surface modified gold sol. The resulting mixture was allowed to stand for one day so that the active silica polymerizes on the surface of the gold particle to form Au@SiO2. The solution thus obtained was centrifuged for around 1 h and the particles were collected and re-dispersed in about 50 ml of 2propanol. To this solution, around 5 ml of CCl4 solution was added. The reaction between themetal core and CCl4 happens over a period of several days and was studied by UV/Vis spectroscopy in a time dependent manner. It was found that the reaction between the gold nanoparticle and CCl4 is quite slow and the reason for this slow rate may be the thickness of the silica shell. It is reported that silica covering of Au@SiO2 is porous in nature, and gold core is accessible for halocarbons. Earlier studies including ours onAu@SiO2 shows that after leaching the core with CN ion a well-defined shell exists showing that shell is permeable for ions [10] and possibly, molecules. Same way clear shells were seen in the case of mineralization of silver core of Ag@ZrO2 using CCl4 [12]. The plasmon absorption of the Au@SiO2 nanoparticles at 524 nm progressively reduces in intensity as the reaction occurs. Once the reaction is complete, a peak corresponding to Au3þ appears at around 320 nm in the UV/Vis spectrum of the solution. Chlorine is removed as Cl . At this point, the solution is pale yellow in