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This work presents a hydrothermal-based facile method for synthesizing ZnFe2O4, whose size can be controlled with the concentration of sodium acetate used as a fuel and its physical changes at nanoscales when exposed to two different gases. The structural, morphological, compositional, and electronic properties of the synthesized samples are also presented in this paper. The crystal structure of the synthesized samples was determined using an X-ray Diffractometer (XRD). The results revealed fluctuations in the size, lattice parameter, and strain in the nanoparticles with increasing the concentration of sodium acetate. Field-Emission Scanning Electron Microscopy (FESEM) was used to determine synthesized materials' morphology and particle size. It revealed that the particles possessed approximately spherical morphology whose size decreased significantly with the increasing amount of sodium acetate. Transmission Electron Microscopy (TEM) was utilized to determine the structure, morphology, and elemental distributions in particles at the nanoscale, and it confirmed the findings of XRD and FESEM analyses. The high-resolution TEM (HRTEM) imaging analysis of the nanoparticles in our studied samples revealed that the particles predominantly possessed (001) type facets. X-ray photoelectron spectroscopy (XPS) and core-loss electron energy loss spectroscopy (EELS) showed an increasing fraction of Fe2+ with the decreasing size of the particles in samples. The Brunauer, Emmett, and Tellers (BET) analysis of samples revealed a higher surface area as the particle size decreases. In addition, the determined surface area and pore size values are compared with the literature, and it was found that the synthesized materials are promising for gas-sensing applications. The ab initio calculations of the Density of States (DOS) and Band structure of (001) surface terminating ZnFe2O4 were carried out using Quantum Espresso software to determine the bandgap of the synthesized samples. They were compared to their corresponding experimentally determined bandgap values and showed close agreement. Finally, in-situ TEM measurement was carried out on one of the four studied samples with robust properties using Ar and CO2 as reference and target gases, respectively. It is concluded from the presented study that the size reduction of the ZnFe2O4 nanoparticles (NPs) tunes the bandgap and provides more active sites due to a higher concentration of oxygen vacancies. The in-situ TEM showed us a nanoscale observation of the change in one of the crystal structure parameters. The d spacing of ZnFe2O4 NPs showed a noticeable fluctuation, reaching more than 5% upon exposure to CO2 and Ar gases. [ABSTRACT FROM AUTHOR]

Transmission electron microcopy (TEM) analysis of liquid metals, especially mercury (Hg), is difficult to carry out because their specimen preparation poses a daunting task due to the unique surface properties of these metals. This paper reports a cryoTEM study on Hg using a novel specimen preparation technique. Hg metal is mixed with water using sonication and quenched in liquid ethane cryogen. This technique permits research into the morphological, phase and structural properties of Hg at nanoscale dimensions. [ABSTRACT FROM AUTHOR]

This study demonstrated the deposition of size-controlled gold (Au) nanoclusters via direct-current magnetron sputtering and inert gas condensation techniques. The impact of different source parameters, namely, sputtering discharge power, inert gas flow rate, and aggregation length on Au nanoclusters' size and yield was investigated. Au nanoclusters' size and size uniformity were confirmed via transmission electron microscopy. In general, Au nanoclusters' average diameter increased by increasing all source parameters, producing monodispersed nanoclusters of an average size range of 1.7 ± 0.1 nm to 9.1 ± 0.1 nm. Among all source parameters, inert gas flow rate exhibited a strong impact on nanoclusters' average size, while sputtering discharge power showed great influence on Au nanoclusters' yield. Results suggest that Au nanoclusters nucleate via a three-body collision mechanism and grow through a two-body collision mechanism, wherein the nanocluster embryos grow in size due to atomic condensation. Ultimately, the usefulness of the produced Au nanoclusters as catalysts for a vapor–liquid–solid technique was put to test to synthesize the phase change material germanium telluride nanowires. [ABSTRACT FROM AUTHOR]

Abstract: TiO2 nanoparticles (NPs) were prepared using flame synthesis and then characterized using transmission electron microscopy. We found that the flame method yields both crystalline TiO2 and amorphous TiO2 NPs. TEM analysis revealed that only the crystalline TiO2 NPs were coated with carbon. Based on this observation, we proposed a growth model for the diffusion and precipitation of carbon atoms in TiO2 NPs. The optical properties of TiO2 NPs were investigated by performing valence electron energy loss spectrometry analysis. We observed that carbon-coated TiO2 NPs have higher absorption in the visible range due to their lower band-gap energy. [Copyright &y& Elsevier]

Abstract: A multi-element diffusion flame burner (MEDB) is useful in the study of flame synthesis of nanomaterials. Here, the growth of pure anatase and carbon-coated titanium dioxide (TiO2) using an MEDB is demonstrated. Hydrogen (H2), oxygen (O2), and argon (Ar) are utilized to establish the flame, whereas titanium tetraisopropoxide is used as the precursor for TiO2. The nanoparticles are characterized using high-resolution transmission electron microscopy, with elemental mapping (of C, O, and Ti), X-ray diffraction, Raman spectroscopy, and thermogravimetric analysis. The growth of pure anatase TiO2 nanoparticles occurs when Ar and H2 are used as the precursor carrier gas, while the growth of carbon-coated nanoparticles ensues when Ar and ethylene (C2H4) are used as the precursor carrier gas. A uniform coating of 3–5nm of carbon is observed around TiO2 particles. The growth of highly crystalline TiO2 nanoparticles is dependent on the gas flow rate of the precursor carrier and amorphous particles are observed at high flow rates. Carbon coating occurs only on crystalline nanoparticles, suggesting a possible growth mechanism of carbon-coated TiO2 nanoparticles. [Copyright &y& Elsevier]

• We study the effect of Si/Al ratio in Zeolite-Y on heptane hydrocracking • The effect of bi-metallicity (Ni-W) was also examined. • Bimetallicity resulted in enhanced metal dispersion and larger BET surface area. • Ni-W/Zeolite-Y catalysts were more catalytically active than Ni/Zeolite-Y. • Hydrocracking over Zeolites with high Si/Al ratio was more stable with time. This study investigated the effect of the SiO 2 /Al 2 O 3 ratio in the range of 5-80 in zeolite Y (ZY) as a support for the bi-functional reaction of heptane hydrocracking. Bi-metallicity impact, through the addition of W on Ni in the supported metal catalysts was also examined. The catalytic activity was assessed at 350°C and 400°C in order to deduce an optimized composition of the catalyst in terms of metal composition and Si/Al ratio. The results were correlated to the catalysts' surface and bulk properties, the latter after employing a number of material characterization techniques. It was shown that Ni-W bimetallic catalysts demonstrated better catalytic activity (conversion, 78% to 91%) than Ni-based monometallic counterpart catalysts (conversion, 74.2% to 82.7%), with NiO-WO 3 -ZY30 (SiO 2 /Al 2 O 3 ratio equal to 30) exhibiting the highest conversion. This was attributed to the bimetallic's enhanced metal dispersion and smaller particle size, evaluated using temperature-programmed desorption (TPD) of H 2 and high-resolution transmission electron microscopy (HR-TEM) imaging. The stronger acidity, as quantified by total acidity calculations, of zeolite Y having higher Si/Al ratio, and their balanced ratio of micro- and meso-porosity played a vital role in their catalytic performance. This study provides useful design guidelines on how to adjust both the Si/Al ratio in the zeolite Y support and the catalyst's bimetallicity for enhanced hydrocracking performance. [Display omitted] [ABSTRACT FROM AUTHOR]

• An easy approach to prepare plan-view TEM sample using FIB lift-out approach. • Plan view study of layered 2D materials. • HRTEM and SADP of misfit compound SnTiS 3 (SnS-TiS 2). • Plan-view imaging of vertically grown MoS 2 and graphene sheets (3D graphene). Plan-view transmission electron microscopy (TEM) or electron diffraction imaging of a bulk or 2D material can provide detailed information about the structural or atomic arrangement in the material. A systematic and easily implementable approach to preparing site-specific plan-view TEM samples for 2D thin film materials using FIB is discussed that could be routinely used. The methodology has been successfully applied to prepare samples from 2D materials such as, MoS 2 thin film, vertically oriented graphene film (VG), as well as heterostructure material SnTiS 3. It is worth mentioning that in contrast to planar conventional graphene, VG grows vertically from the substrate and takes nanosheet arrays. Samples prepared using this methodology provide a simple, faster, and precise course in obtaining valuable structural information. The top-view imaging offers various information about the growth nature of the materials suggesting the efficiency of the sample preparation process. [ABSTRACT FROM AUTHOR]

Abstract: A method for the preparation of NiO and Nb–NiO nanocomposites is developed, based on the slow oxidation of a nickel-rich Nb–Ni gel obtained in citric acid. The resulting materials have higher surface areas than those obtained by the classical evaporation method from nickel nitrate and ammonium niobium oxalate. These consist in NiO nanocrystallites (7–13nm) associated, at Nb contents >3at.%., with an amorphous thin layer (1–2nm) of a niobium-rich mixed oxide with a structure similar to that of NiNb2O6. Unlike bulk nickel oxides, the activity of these nanooxides for low-temperature ethane oxidative dehydrogenation (ODH) has been related to their redox properties. In addition to limiting the size of NiO crystallites, the presence of the Nb-rich phase also inhibits NiO reducibility. At Nb content >5at.%, Nb–NiO composites are thus less active for ethane ODH but more selective, indicating that the Nb-rich phase probably covers part of the unselective, non-stoichiometric, active oxygen species of NiO. This geometric effect is supported by high-resolution transmission electron microscopy observations. The close interaction between NiO and the thin Nb-rich mixed oxide layer, combined with possible restructuration of the nanocomposite under ODH conditions, leads to significant catalyst deactivation at high Nb loadings. Hence, the most efficient ODH catalysts obtained by this method are those containing 3–4at.% Nb, which combine high activity, selectivity, and stability. The impact of the preparation method on the structural and catalytic properties of Nb–NiO nanocomposites suggests that further improvement in NiO-catalyzed ethane ODH can be expected upon optimization of the catalyst. [Copyright &y& Elsevier]

• As-prepared GeTe films deposited at 25 °C were amorphous. • The degree of crystallinity of GeTe films increased when annealing time increased. • The average grain size increased by 60% upon doubling the annealing time. • Upon crystallization, Te-rich tetrahedra formation is favored over Ge-rich tetrahedra. This study investigates the effects of vacuum annealing on the structural and electrical properties of germanium telluride thin films. To this end, GeTe thin films were prepared via DC magnetron sputtering in three sets—as-prepared at 25 °C, as-prepared at 300 °C, and deposited and annealed at 300 °C for different time intervals. Post fabrication, the films were characterized using grazing-incidence X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and four-point probe measurements. The as-prepared films deposited at 25 °C were amorphous, while the remaining film types exhibited crystalline conductivity and comparable sheet-resistance values. However, the observations of this study reveal a gradual increase in the degree of crystallinity and average grain size of the annealed films. The Raman spectroscopy results reveal the increase in film crystallinity to be due to an increase in the concentration of Te-rich tetrahedra at the expense of their Ge-rich equivalents. [Display omitted] [ABSTRACT FROM AUTHOR]

We present a new generation of “true vicinal” functions well-distributed on the inner surface of SBA15: [(≡Si–NH2)(≡Si–OH)] (1) and [(≡Si–NH2)2] (2). From these amine-modified SBA15s, two new well-defined surface organometallic species [(≡Si–NH−)(≡Si–O−)]Zr(CH2tBu)2 (3) and [(≡Si–NH−)2]Zr(CH2tBu)2 (4) have been obtained by reaction with Zr(CH2tBu)4. The surfaces were characterized with 2D multiple-quantum 1H–1H NMR and infrared spectroscopies. Energy-filtered transmission electron microscopy (EFTEM), mass balance, and elemental analysis unambiguously proved that Zr(CH2tBu)4 reacts with these vicinal amine-modified surfaces to give mainly bipodal bis(neopentyl)zirconium complexes (3) and (4), uniformly distributed in the channels of SBA15. (3) and (4) react with hydrogen to give the homologous hydrides (5) and (6). Hydrogenolysis of n-butane catalyzed by these hydrides was carried out at low temperature (100 °C) and low pressure (1 atm). While (6) exhibits a bis(silylamido)zirconium bishydride, [(≡Si–NH−)2]Zr(H)2 (6a) (60%), and a bis(silylamido)silyloxozirconium monohydride, [(≡Si–NH−)2(≡Si–O−)]ZrH (6b) (40%), (5) displays a new surface organometallic complex characterized by an 1H NMR signal at 14.46 ppm. The latter is assigned to a (silylimido)(silyloxo)zirconium monohydride, [(≡Si–N═)(≡Si–O−)]ZrH (5b) (30%), coexistent with a (silylamido)(silyloxo)zirconium bishydride, [(≡Si–NH−)(≡Si–O−)]Zr(H)2 (5a) (45%), and a silylamidobis(silyloxo)zirconium monohydride, [(≡Si–NH−)(≡Si–O−)2]ZrH (5c) (25%). Surprisingly, nitrogen surface ligands possess catalytic properties already encountered with silicon oxide surfaces, but interestingly, catalyst (5) with chelating [N,O] shows better activity than (6) with chelating [N,N]. [ABSTRACT FROM AUTHOR]