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We report the use of an electrostatic MEMS-based device to produce high quality electron vortex beams with more than 1000 quanta of orbital angular momentum (OAM). Diffraction and off-axis electron holography experiments are used to show that the diameter of the vortex in the diffraction plane increases linearly with OAM, thereby allowing the angular momentum content of the vortex to be calibrated. The realization of electron vortex beams with even larger values of OAM is currently limited by the breakdown voltage of the device. Potential solutions to overcome this problem are discussed., 9 pages, 4 images

Potassium sulfate (K2SO4) is a very important compound, mostly used as nutrient for plant growth. Potassium sulfate production can be accomplished through the Mannheim process. For potassium bearing silicate minerals, such as glauconite, one alternative is acid leaching followed by selective precipitation and thermal decomposition of potassium alum (KAl(SO4)2). This chemical process is responsible for the formation of soluble K2SO4 and insoluble Al2O3, which can be later separated after solubilization in water and filtration. In this pyrometallurgical reaction, the temperature control is very important. Through the addition of a reducing agent, the decomposition temperature could be significantly reduced. In the present work, the thermal behavior of synthetic samples of hydrated potassium alum (KAl(SO4)2·12H2O) is appreciated through thermogravimetric analysis (TGA), both in the absence as well as in the presence of a reducing agent (charcoal) under inert atmosphere (nitrogen) and dynamic analysis. The addition of a stoichiometric amount of the reducing agent stimulated considerably the decomposition, which started at a lower temperature in comparison with the pure alum sample. Based on the XRD characterization of selected samples, it is suggested that the decomposition process should happen in at least two stages, with Al2(SO4)3 as one of the intermediate reagents. After full decomposition, only Al2O3 and K2SO4 have been identified, as expected based on thermodynamic simulations. Finally, it was demonstrated that the K2SO4 formed could be totally transferred to aqueous solution after a solubilization carried out at 363 K for two hours; the remaining solid was characterized as pure aluminum oxide (Al2O3). Keywords: Potassium alum, Thermal decomposition, TGA, Charcoal, K2SO4, Al2O3

With increasing environmental concerns, much effort has been spent in research regarding development of sustainable processes for production of fuels and chemical products. In this context, hydrothermal liquefaction (HTL) has gained increasing attention, as a possible route for the chemical transformation of organic raw-materials, some sort of biomass, for example, into liquid oils at temperatures usually below 400°C, under moderate to high pressures (5 - 25 MPa), usually in the presence of a suitable catalyst. In the present work the thermogravimetric (TG) behavior under inert atmosphere of pure green coconut fiber and mixtures thereof with a spinel phase (Fe2CoO4), acting as catalyst has been studied. Spinel samples have been produced at 1000°C and different calcination times (3h, 6h and 9h). Both raw and synthesized materials were characterized through different techniques, such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and Infrared Absorption Spectroscopy (FTIR). According to the TG data, the catalyst produced during a calcination time of 9h showed a superior behavior regarding the lignin full thermal decomposition, which developed without fixed carbon formation. The results further suggest that the mixing process has a significant effect over the measured degradation kinetics, as it has a direct influence over the contact between catalyst and fibers. The kinetic modelling applied to the dynamic TG signal allowed a quantitative representation of the experimental data. The global process activation energy and order have proven to be respectively, 85.291 kJ / mol and 0.1227.

ISPOR Asia Pacific 2018；2018.9.8-11；Tokyo, Japan

Magnetic shape memory materials show outstanding and multifunctional properties (e.g. "giant" magnetomechanical, magnetocaloric, barocaloric), originating from the occurrence of both a martensitic transformation and magnetic order. Thin films and nanostructures of these materials have a great potential for different applications, such as micro- or nano-actuators, energy harvesters, valves and solid-state microrefrigerators [1]. We have demonstrated that the microstructure and magnetic properties of Ni-Mn-Ga thin films can be engineered by properly choosing substrate, growth conditions [2] and post-growth treatments. The films have been epitaxially grown on MgO(100) or on Cr/MgO(100) by RF sputtering, with thicknesses up to 200 nm. We have examined the relation between microstructure and magnetization process, simulating magnetization processes in films with different orientation and spatial organization of the martensitic twin variants. The micromagnetic simulations show a good agreement with the experimental results. Starting from the films grown on Cr/MgO, we have also realized Ni-Mn-Ga nanodots (d=160, 650 nm) by polystyrene-nanosphere lithography, and freestanding nanodisks, by subsequently removing the Cr underlayer via chemical etching. The microstructure and magnetic configuration of the nanostructures are influenced by the lateral confinement and release from the substrate. Furthermore, by varying temperature and applying a magnetic field to the free-standing nanodisks, we have obtained important microstructural changes, enabling different actuation modes [3]. [1] A. Backen et al., Adv. Eng. Mater. 14, 696-709 (2012) [2]P. Ranzieri et al., Adv. Mater. 27, 4760 (2015) [3]M. Campanini et al., Small 2018, 1803027

Magnetic shape memory alloys have a great potential for micro- and nano-actuators and energy harvesters, thanks their outstanding magnetomechanical properties. We will show that the microstructure and magnetic properties of Ni-Mn-Ga thin films can be engineered by properly choosing the substrate and growth conditions. The films were epitaxially grown on Cr/MgO(100) by r.f. sputtering, with thicknesses up to 200 nm. We then realized Ni-Mn-Ga nanodots (d=160, 650 nm) by polystyrene-nanosphere lithography and freestanding nanodisks by subsequently removing the Cr underlayer via chemical etching. The microstructure and magnetic configuration of the nanostructures are influenced by the lateral confinement and release from the substrate. Furthermore, by varying temperature and applying a magnetic field to the free-standing nanodisks, we have obtained important microstructural changes, enabling different actuation modes. We have also examined the relation between microstructure and magnetization process, simulating magnetization processes in systems with different orientation and spatial organization of the martensitic twin variants. The micromagnetic simulations show a good agreement with the experimental results.

InAs nanowires have been grown by molecular beam epitaxy using Mn as growth catalyst. Nanowires (NWs) have been obtained on SiO2 and oxidized GaAs for growth temperatures in the range of 370-410 degrees C. The growth temperature is found to be the same as that of the growth of Au-catalyzed InAs wires. These results suggest that the InAs NWs grow with the Mn nanoparticle in the solid phase and allow some comparison with the existing models for Au-catalyzed nanowires. The morphology and the lattice structure were investigated by electron microscopy techniques. The lattice of the wire body is found to be mainly wurtzite InAs. Mn K-edge x-ray absorption fine structure was used to determine the local environment of the Mn atoms: The authors found that most of the Mn atoms are found in a hexagonal MnAs phase. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3385892]

Asymmetric binary nanocrystals (BNCs), comprising one c-axis elongated anatase TiO2 section and one gamma-Fe2O3 spherical domain attached together, are synthesized by heterogeneous nucleation of iron oxide onto the longitudinal facets of TiO2 nanorods in a ternary surfactant mixture. The topologically controlled composition of the BNCs is ascertained by a combination of powder X-ray diffraction, Raman and Mössbauer spectroscopy, high-angle annular dark-field imaging, and high-resolution transmission electron microscopy lattice fringe mapping, while their size-dependent magnetic behavior is demonstrated by ac susceptibility measurements. The heteroepitaxial growth proceeds through a mechanism never observed before for colloidal nanoheterostructures: the two domains share a restricted and locally curved junction region, which accommodates efficiently the interfacial strain and retards the formation of misfit dislocations. It is believed that these BNCs, which combine the properties of two technologically relevant oxide materials, can pave the way to reinforced applications in several fields of nanoscience, such as in photocatalysis, in malignant cell treatments, and in nanocrystal assembly.

Magnetic nanoparticles are considered key nanomaterials for future information storage, energy and biomedical and pharmaceutical applications. In particular in the biomedicine, they are suitable for both diagnostics, therapeutics and delivery. They are proposed as contrast agents to enhance the magnetic resonance imaging signal, while in the field of therapeutics, they can be used as magnetic vectors in drug delivery and/or as heat mediators in hyperthermia treatment. In this last application, the apoptosis of cancer cells is produced by the local increase of the temperature thanks to the heating of the magnetic nanoparticles contained in the cells under a oscillating magnetic fields. The physic-chemical mechanisms and effects that give rise to the magnetic energy losses are under study. One of the most discussed questions is the role of the interparticle interactions induced by the different aggregation levels, which can be different in the laboratory conditions and into the cells.

Au-catalyzed InxGa1-xAs nanowires (NWs) and InxGa1-xAs/GaAs core-shell NWs were grown by molecular beam epitaxy on (1 1 1)B GaAs. The effects of In content, growth temperature, and V/III elemental flux ratios on NW morphology have been investigated. The structure of the NWs has been characterized by SEM and transmission electron microscopy and their optical properties by low-temperature photoluminescence.

Ferromagnetic martensitic NiMnGa Heusler alloys are promising materials potentially exploitable for the fabrication of microdevices based on novel actuation mechanisms [1]. In bulk materials, giant strains obtainable by magnetomechanical effects based on the twin variant reorientation induced by a magnetic field (MIR), are higher than typical magnetostriction and state-of-the-art piezoelectric values [2]. Moreover, the coupling between magnetic and structural degrees of freedom leads to several multifunctional properties (e.g. "giant" magnetomechanical, magnetocaloric) [3]. Low-dimensional materials, mainly thin films, have recently attracted much interest for the promising applications. With respect to the bulk materials, they offer the further possibility of tuning properties by thickness [4] and by the choice of suitable substrates and underlayers [5]. The present paper is aimed at deepening these effects, also extending the study to laterally confined substrate-constrained and free-standing nanostructures.

At present the most interesting technology for the preparation of advanced opto-electronic devices seems to be the one based on semiconductor nanowires (NWs). Because of their high aspect ratio the NWs are the best candidates for the combination of highly mismatched semiconductors while maintaining good crystal quality. In particular, thanks to strain relaxation at the NW sidewalls, a reduction of the misfit dislocation density is possible, which is highly beneficial for device applications. In this regard interface sharpness is also a critical issue, especially for InAs/GaAs. In this work we present a study of the structure and strain relaxation in InAs/GaAs axial nanostructures in self-assisted NWs grown by MBE on (111) Si substrates. The growth was performed without the use of any catalyst. The top InAs segment is grown on the bottom self-assisted GaAs part of the NW via a two-step process by supplying In and As separately. The samples have been studied by High Resolution TEM (HR-TEM) as well as Scanning TEM (STEM) with a HAADF (High Angle Annular Dark Field) detector. HR-TEM showed that the InAs/GaAs is sharp at the atomic level, a result that has never been reported in the literature for MBE grown InAs/GaAs NWs. By STEM-HAADF the chemical transition between GaAs and InAs was seen to occur abruptly over a distance of 1.5 nm across the interface. The strain relaxation and related misfit dislocation (MD) generation were investigated by mapping the strain distribution obtained by processing HR-TEM images of the interface by the Geometrical Phase Analysis (GPA) method. MDs were detected as expected due to the size of about 70 nm of the NWs. However, their mutual distance increases radially on going from the NW center towards the sidewalls confirming that the strain was partially relaxed elastically at the sidewalls thus decreasing the formation probability of the MDs, i.e. their density. The latter experimental results have been compared with FEM (Finite Element Method) calculations with excellent agreement.

Monodispersed Fe3O4 nanoparticles with comparable size distributions have been synthesized by two different synthesis routes, co-precipitation and thermal decomposition. Thanks to the different steric stabilizations, the described samples can be considered as a model system to investigate the effects of magnetic dipolar interactions on the aggregation states of the nanoparticles. Moreover, the presence of magnetic dipolar interactions can strongly affect the nanoparticle efficiency as a hyperthermic mediator. In this paper, we present a novel way to visualize and map the magnetic dipolar interactions in different kinds of nanoparticle aggregates by the use of Lorentz microscopy, an easy and reliable in-line electron holographic technique. By exploiting Lorentz microscopy, which is complementary to the magnetic measurements, it is possible to correlate the interaction degrees of magnetic nanoparticles with their magnetic behaviors. In particular, we demonstrate that Lorentz microscopy is successful in visualizing the magnetic configurations stabilized by dipolar interactions, thus paving the way to the comprehension of the power loss mechanisms for different nanoparticle aggregates.

International audience; ZnSe nanowires with a dominant wurtzite structure have been grown at low temperature (300 degrees C) by molecular beam epitaxy assisted by solid Au nanoparticles. The nanowires emission is polarized perpendicularly to their axis in agreement with the wurtzite selection rules. Alternations of wurtzite and zinc-blende regions have been observed by transmission electron microscopy, and their impact on the nanowires optical properties has been studied by microphotoluminescence. The nanowires show a dominant intense near-band-edge emission as well as the ZnSe wurtzite free exciton line. A type II band alignment between zinc-blende and wurtzite ZnSe is evidenced by time-resolved photoluminescence. From this measurement, we deduce values for the conduction and valence band offsets of 98 and 50 meV, respectively. (C) 2015 AIP Publishing LLC.

We present an EXAFS study of the Mn atomic environment in Mn-doped GaAs nanowires. Mn doping has been obtained either via the diffusion of the Mn used as seed for the nanowire growth or by providing Mn during the growth of Au-induced wires. As a general finding, we observe that Mn forms chemical bonds with As but is not incorporated in a substitutional site. In Mn-induced GaAs wires, Mn is mostly found bonded to As in a rather disordered environment and with a stretched bond length, reminiscent of that exhibited by MnAs phases. In Au-seeded nanowires, along with stretched Mn-As coordination we have found the presence of Mn in a Mn-Au intermetallic compound., This is an author-created, un-copyedited version of an article accepted for publication in Semiconductor Science and Technology. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The definitive publisher-authenticated version is available online at doi:10.1088/0268-1242/27/8/085001

We performed a comparative investigation of interface structure and composition in pseudomorphic ZnSe∕GaAs(001) heterostructures grown using interface fabrication procedures that produce epilayers with minimum stacking fault densities (below 104cm−2). We detected in all cases a 1nm thick intermixed region at the interface that is depleted of As and is comprised of a (Zn,Ga)As alloy with zincblende structure. No ZnAs formation was found in any of the interfaces examined. Our results imply that Ga-Se reactions at the ZnSe∕GaAs interface do not necessarily lead to nucleation of high densities of stacking faults and that ZnAs formation plays no role in the observed reduction of the native defect density.

Self-catalyzed GaAs nanowire growth was obtained by molecular beam epitaxy on GaAs(001) substrates after predeposition of subnanometer-thick Si layers. Two substrate preparation methods are presented, the first based on the epitaxial growth of Si on GaAs and subsequent exposure to atmosphere, and the second on the direct deposition of Si on epiready GaAs substrates. X-ray photoemission spectroscopy shows that both methods result in a thin Si oxide layer that promotes the growth of GaAs nanowires aligned along the h111i direction. High densities of nanowires were obtained at substrate temperatures between 620 and 680 C. Systematic electron microscopy studies indicate that nanowire growth is associated with the formation of Ga nanoparticles on the substrate surface, which act as a catalyst in the vapor-liquid-solid growth mechanism frame. The majority of the nanowires have a pure zinc-blende structure, and their photoluminescence is dominated by a photoluminescence peak 3 to 5 meV in width and centered at 1.516 to 1517 eV.

We report on the morphological and structural properties of GaAs nanowires nucleated by self-catalyzed vapor-liquid-solid processes by molecular beam epitaxy on Si-treated GaAs substrates. We found that GaAs nanowires display zincblende and/or wurtzite phase depending on the As/Ga abundance ratio at the growth front, that determines the size and supersaturation of the Ga nanoparticles at the nanowire tip. We also found that even when growth conditions lead to the disappearance of such Ga nanoparticles, preferential one-dimensional growth continues through a vapor-solid mechanism. The nanowire portions grown by vapor solid mechanism display zincblend structure.

Cathodoluminescence technique combined with transmission electron microscopy (TEM-CL) has been used to characterize optical properties of dislocations in GaN epilayers. The dislocations act as nonradiative centers with different recombination rates. TEM-CL observation showed that even for the same Burgers vector of a, the dislocations show different electrical activity depending on the direction of dislocation line, i.e., the edge-type dislocation parallel to the c plane is very active, while the screw-type one is less active. The simulation of the CL images gives us the information of parameters such as carrier lifetime and diffusion length. (C) 2003 American Institute of Physics.

Emission from ultrathin quantum wells of different thicknesses is studied. In particular, for structures with doped substrate the unintentional deposition of Cu droplets is used as a probe of electron diffusion inside the material. A large diffusion length (L = 8 ± 3 µm) is found in spite of the presence of quantum dots. In particular, the contribution to the diffusion from re-emission of electrons from quantum dots is evaluated. Copyright © 2003 John Wiley & Sons, Ltd.

Fast epitaxial growth on deeply patterned substrates is a very promising method to get epilayers of high structural quality, as layer cracking and wafer bowing can be avoided (C. V. Falub et al., Science 335, 1330 (2012). This approach is applied here to grow crack-free GaAs microcrystals on Si pillars which is a typical hetero system of interest in the field of the monolithic integration of III-V's on Si. The (001) offcut Si substrate was patterned into square pillars of various size by deep reactive ion etching (DRIE). 2 µm thick GaAs was then deposited by MBE at 580 °C at a rate of 0.5 ML/s with V/III=50. The defect analysis was carried out by TEM, HR-TEM, STEM-ADF (Annular Dark Field) and GPA (Geometrical Phase Analysis). The GaAs deposits were 2 µm high. The anti-phase domains were located only at the interface and their density was drastically limited by the substrate offcut. Threading dislocations (TDs) were present but were confined to the bottom 500 nm of the GaAs as they annihilated each another or bent back to the interface due to mutual interactions. They did not reach the GaAs microcrystal top that will serve as active region in devices. The TDs originated from misfit dislocations of both 60° and edge type. Twins were also present originating at the interface very likely at the offcut substrate steps. Some of them reached the topmost part of GaAs. As no dangling bond is associated with twins, they should not be electrically active in devices.

GaAs nanowires have been grown on SiO2 and GaAs by molecular beam epitaxy using manganese as growth catalyst. Transmission electron microscopy shows that the wires have a wurtzite-type lattice and that alpha-Mn particles are found at the free end of the wires. X-ray absorption fine structure measurements reveal the presence of a significant fraction of Mn-As bonds, suggesting Mn diffusion and incorporation during wire growth. Transport measurements indicate that the wires are p-type, as expected from doping of GaAs with Mn.

The effect of strain, composition and disorder in ADF images is systematically studied as a function of detection angle in order to understand the main contrast mechanisms. We demonstrate that the complex phenomenology in ADF images can be accounted for by accurate simulations and modelling. The advantage of an accurate modelling on the image interpretation will be demonstrated in the case of dislocations, chemical analysis of InGaP/GaAs and most noticeably the measurement of both In and N content in quaternary InGaAsN.

We report the Pd-assisted chemical beam epitaxy growth of zinc blende InAs nanowires which are grown on InAs(111)A substrates by employing Pd octane and hexadecyl thiolates as catalyst precursors. The structural properties of these nanowires are investigated by scanning and transmission electron microscopy. Furthermore, we demostrate the growth of InAs nanowires on patterned substrates by employing the Pd hexadecylthiolate precursors as a direct-write resist in electron beam lithography.

Scanning transmission electron microscopy (STEM) high angle annular dark field (HAADF) imaging is now well established as a powerful tool for studying the structural and chemical properties of solid-state matter at atomic resolution. The HAADF image intensity depends sensitively on the atomic numbers of the elements in the atomic column, and important qualitative chemical information at atomic resolution can be achieved by direct inspection of the HAADF image contrast. Nevertheless, if quantitative information on the chemistry of the specimen is sought for, it becomes necessary to compare the experimental results with HAADF image simulations. Alas a satisfactory comparison between experiment and simulation has been so far quite difficult. In particular a recent article [1] raised the problem of discordance between simulations and experiment in the evaluation of the baseline intensity between intensity atomic positions. For this reason this baseline intensity is subtracted in their quantitative evaluation. Quite likely, this baseline additional intensity is due to incoherent effects on the probe.

Dilute nitrides alloys, as GaAsxN1−x, have been extensively studied in the last few years since the presence of small amounts of N in III–V semiconductors leads to major changes in the physical properties of the host materials. In particular, the strong reduction of band gap induced by N enables important technological applications in the field of active optical devices and microelectronics.