Abstract: Colloidal nanoparticles (NPs) including nanowires and nanosheets made by chemical methods involve many organic ligands. When the structure of NPs is investigated via transmission electron microscopy (TEM), the organic ligands act as a source for e-beam induced deposition and this causes substantial build-up of carbon layers in the investigated areas, which is typically referred to as “contamination” in the eld of electron mi- croscopy. This contamination is often more severe for scanning TEM, a technique that is based on a focused electron beam and hence higher electron dose rate. In this paper, we report a simple and effective method to clean drop-cast TEM grids that contain NPs with ligands. Using a combination of activated carbon and ethanol, this method effectively reduces the amount of ligands on TEM grids, and therefore greatly improves the quality of electron microscopy images and subsequent analytical measurements. This ef cient and facile method can be helpful during electron microscopy investigation of different kinds of nanomaterials that suffer from ligand- induced contamination.

Abstract: Highly ordered SBA-15-type ethane-bridged PMOs have been obtained by employing H3PO4 as acid to tune the pH in the presence of copolymer surfactant P123. The effects of the acidity and the addition of inorganic salt on the formation of the mesostructure are investigated. It is found that, compared with HCl, the polyprotic weak acid H3PO4 is preferable for the synthesis of highly ordered SBA-15-type ethane-bridged PMOs with larger pore size and surface areas under mild acidic conditions. Moreover, taking the advantages of the mild acidic condition, vanadium-containing SBA-15-type ethane-bridged PMOs were successfully prepared through a direct synthesis approach. The XRD, N2-sorption, UVVis and CW-EPR studies of the V-PMO show that part of the vanadium species are present in polymeric (VOV)n clusters, while part of the vanadium centers are well-dispersed and immobilized on the inner surface of the mesopores.

Abstract: A two-step procedure was applied to prepare bimetallic Ag-Ni glassy carbon supported catalysts (Ag-Ni/GC). First Ni layers were prepared by means of electrodeposition in an aqueous deaerated nickel chloride + nickel sulfamate + boric acid solution. Second, the partial replacement of Ni layers by Ag was achieved upon immersion of the latter in solutions containing silver nitrate. Three different pretreatment protocols were used after preparation of the Ag/Ni deposits; as prepared, cathodised in alkali and scanned in acid. After the pretreatment the surface was characterised by means of spectroscopy techniques (scanning electron microscopy and energy dispersive x-ray) and electrochemically in an alkali NaOH solution through cyclic voltammetry (CV). Afterwards the modified electrodes were tested for the reduction of benzylbromide in acetonitrile solutions by using CV and were found to show improved activity compared to bulk Ag electrode. The highest activity towards benzylbromide reduction was observed for pre-cathodised Ag-Ni electrodes. A final stage of the research focuses on the development of a practical Ag/Ni foam catalyst for the reduction of benzylbromide. Due to the high electrochemical active surface area of Ag/Ni foam, a higher conversion of benzyl bromide was obtained in comparison with bulk Ag.

Abstract: The problem of the epitaxial growth of the high temperature superconducting R1+xBa2xCu3O7δ (R = Y or rare earth except Ce and Tb) films has been addressed. Using in situ ultra high vacuum Scanning Tunneling Microscopy (UHV-STM) we have studied the role of cationic substitution and substrate mismatch on the growth mode of stoichiometric and Nd-rich Nd1+xBa2xCu3O7δ thin films. The results are compared to the growth of Y1Ba2Cu3O7δ, Dy1Ba2Cu3O7δ and Gd1Ba2Cu3O7δ epitaxial films. Two main phenomena are investigated: a) the first stage of the direct nucleation on the substrate and b) the crossover between 2D and 3D growth upon increasing the film thickness. At the first stage of the growth, pseudo-cubic perovskite (Re,Ba)CuO3 nuclei are formed. While they disappear after the growth of a few nm in stoichiometric films, they persist on the surface of Nd-rich films of up to 110 nm thickness. Stoichiometric R1+xBa2xCu3O7δ films exhibit a rough morphology with increasing thickness due to island growth mode, whereas Nd-rich films remain smooth and continue to grow layer by layer. It is proposed that linear defects (like anti-phase boundaries), which are formed due to the misalignment of growth fronts, are the source of screw dislocations in stoichiometric films. In Nd-rich films, linear defects are eliminated through the insertion of (Nd,Ba)CuO3 extra layers without introduction of any screw dislocations.

Abstract: <script type='text/javascript'>document.write(unpmarked('HAADF-STEM tomography is a common technique for characterizing the three-dimensional morphology of nanomaterials. In conventional tomographic reconstruction algorithms, the image intensity is assumed to be a linear projection of a physical property of the specimen. However, this assumption of linearity is not completely valid due to the nonlinear damping of signal intensities. The nonlinear damping effects increase w.r.t the specimen thickness and lead to so-called \u0022cupping artifacts\u0022, due to a mismatch with the linear model used in the reconstruction algorithm. Moreover, nonlinear damping effects can strongly limit the applicability of advanced reconstruction approaches such as Total Variation Minimization and discrete tomography. In this paper, we propose an algorithm for automatically correcting the nonlinear effects and the subsequent cupping artifacts. It is applicable to samples in which chemical compositions can be segmented based on image gray levels. The correction is realized by iteratively estimating the nonlinear relationship between projection intensity and sample thickness, based on which the projections are linearized. The correction and reconstruction algorithms are tested on simulated and experimental data. (C) 2017 Elsevier B.V. All rights reserved.'));

Abstract: In this report, the possibility of Pt catalytic activity for the dissociation of hydrogen molecules and subsequent hydrogen adsorption on sucrose templated carbon at ambient temperature has been studied. In order to investigate Pt catalytic effect for hydrogen storage solely, 6.8 wt.% Pt-doped (Pt/TC) and pure templated carbon (TC) possessing almost identical specific surface area (SSA) and pore volume (Vp) have been successfully synthesized. Since both Pt/TC and TC shares for their textural properties (e.g. SSA and Vp), any difference of hydrogen adsorption characteristic and storage capacity can be ascribed to the presence of Pt nanoparticles. Both samples are characterized by various techniques such as powder Xray diffraction, ICP-OES, Raman spectroscopy, transmission electron microscopy, cryogenic thermal desorption spectroscopy, low-pressure high-resolution hydrogen and nitrogen BET and high-pressure hydrogen adsorption isotherms in a Sieverts' apparatus. By applying hydrogen and deuterium isotope mixture, cryogenic thermal desorption spectroscopy point to a Pt catalytic activity for the dissociation of hydrogen molecules. Furthermore, the hydrogen adsorption isotherms at RT indicate an enhancement of the initial hydrogen adsorption kinetics in Pt-doped system. However, the hydrogen storage capacity of Pt/TC exhibits a negligible enhancement with a strong hysteresis, suggesting no connection between the spillover effect and a feasible hydrogen storage enhancement. (C) 2013 Elsevier Inc. All rights reserved.

Abstract: In this study the effects of the heating rate and heating time on the formation of crystal-like benzene bridged periodic mesoporous organosilicas (PMOs) are investigated. The time needed to heat up an autoclave during the hydrothermal treatment has shown to be crucial in the synthesis of PMOs, while the total duration of heating gave rise to only minor differences. By choosing a smart heating profile, superior PMO materials can be obtained in a short time. Different heating profiles in a range from one minute to one hour are adopted by microwave equipment and compared with conventional heating methods. The heating rate has a large influence on the porosity characteristics and the uniformity of the obtained particles. Moreover, two new alternative synthetic strategies to adopt the smart heating profile are presented, in order to give some possible solutions for the expensive microwave equipment.

Abstract: A three-dimensional (3D) chemical characterization of nanomaterials can be obtained using tomography based on high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) or energy dispersive X-ray spectroscopy (EDS) STEM. These two complementary techniques have both advantages and disadvantages. The Z-contrast images have good image quality but lack robustness in the compositional analysis, while the elemental maps give more element-specific information, but at a low signal-to-noise ratio and a longer exposure time. Our aim is to combine these two types of complementary information in one single tomographic reconstruction process. Therefore, an imaging model is proposed combining both HAADF-STEM
and EDS-STEM. Based on this model, the elemental distributions can be reconstructed using both types of information simultaneously during the reconstruction process. The performance of the new technique is evaluated using simulated data and real experimental data. The results demonstrate that combining two imaging modalities leads to tomographic reconstructions with suppressed noise and enhanced contrast.

Abstract: High-resolution transmission electron microscopy (TEM) of organic crystals, such as Lead Phthalocyanine (PbPc), is very challenging since these materials are prone to electron beam damage leading to the breakdown of the crystal structure during investigation. Quantification of the damage is imperative to enable high-resolution imaging of PbPc crystals with minimum structural changes. In this work, we performed a detailed electron diffraction study to quantitatively measure degradation of PbPc crystals upon electron beam irradiation. Our study is based on the quantification of the fading intensity of the spots in the electron diffraction patterns. At various incident dose rates (e/Å2/s) and acceleration voltages, we experimentally extracted the decay rate (1/s), which directly correlates with the rate of beam damage. In this manner, a value for the critical dose (e/Å2) could be determined, which can be used as a measure to quantify beam damage. Using the same methodology, we explored the influence of cryogenic temperatures, graphene TEM substrates, and graphene encapsulation in prolonging the lifetime of the PbPc crystal structure during TEM investigation. The knowledge obtained by diffraction experiments is then translated to real space high-resolution TEM imaging of PbPc.

Abstract: It is very challenging to measure the chemical composition of hetero nanostructures in a reliable and quantitative manner. Here, we propose a novel and straightforward approach that can be used to quantify energy dispersive X-ray spectra acquired in a transmission electron microscope. Our method is based on a combination of electron tomography and the so-called ζ-factor technique. We will demonstrate the reliability of our approach as well as its applicability by investigating Au-Ag and Au-Pt hetero nanostructures. Given its simplicity, we expect that the method could become a new standard in the field of chemical characterization using electron microscopy.

Abstract: Supported carbon nanosheets and carbon nanotubes served as sacrificial templates for preparing spacious TiO2 photocatalytic thin films. Amorphous TiO2 was deposited conformally on the carbonaceous template material by atomic layer deposition (ALD). Upon calcination at 550 °C, the carbon template was oxidatively removed and the as-deposited continuous amorphous TiO2 layers transformed into interlinked anatase nanoparticles with an overall morphology commensurate to the original template structure. The effect of type of template, number of ALD cycles and gas residence time of pollutant on the photocatalytic activity, as well as the stability of the photocatalytic performance of these thin films was investigated. The TiO2 films exhibited excellent photocatalytic activity toward photocatalytic degradation of acetaldehyde in air as a model reaction for photocatalytic indoor air pollution abatement. Optimized films outperformed a reference film of commercial PC500.

Abstract: Gold nanoparticles are studied extensively due to their unique optical and catalytical properties. Their exact shape determines the properties and thereby the possible applications. Electron tomography is therefore often used to examine the three-dimensional (3D) shape of nanoparticles. However, since the acquisition of the experimental tilt series and the 3D reconstructions are very time consuming, it is difficult to obtain statistical results concerning the 3D shape of nanoparticles. Here, we propose a new approach for electron tomography that is based on artificial neural networks. The use of a new reconstruction approach enables us to reduce the number of projection images with a factor of 5 or more. The decrease in acquisition time of the tilt series and use of an efficient reconstruction algorithm allows us to examine a large amount of nanoparticles in order to retrieve statistical results concerning the 3D shape.

Abstract: The effect of thermal treatment and mechanical stress on the structural and photocatalytic properties of eight different (synthetic and commercial) photocatalysts has been thoroughly investigated. Different mesoporous Ti-based materials were prepared via surfactant based synthesis routes (e.g. Pluronic 123, CTMABr = Cetyltrimethylammonium bromide) or via template-free synthesis routes (e.g. trititanate nanotubes). Also, the stabilizing effect of the NaOH/NH4OH post-treatment on the templated mesoporous materials and their photocatalytic activity was investigated. Furthermore, the thermal and mechanical properties of commercially available titanium dioxides such as P25 Evonik® and Millenium PC500® were studied. The various photocatalysts were analyzed with N2-sorption, X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) to obtain information concerning the specific surface area, pore volume, crystal structure, morphology, phase transitions, etc. In general, results show that the NaOH post-treatment leads to an increased control of the crystallization process during calcination resulting in a higher thermal stability, but at the same time diminishes the photocatalytic activity. Mesoporous materials in which pre-synthesized nanoparticles are used as titania source have the best mechanical stability whereas the mechanical stability of the nanotubes is the most limited. At increased temperatures and pressures, the tested commercial titanium dioxides lose their superior photocatalytic activity caused by a decreased accessibility of the active sites. The observed changes in adsorption capacities and photocatalytic activities cannot be assigned to one single phenomenon. In this respect, it shows the need to define a general/standard method to compare different photocatalysts. Furthermore, it is shown that the photocatalytic properties do not necessarily deteriorate under thermal stress, but can be improved due to crystallization, even though the initial material is (partially) destroyed. It is shown that the usefulness of a specific type of photocatalyst strongly depends on the application and the temperature/pressure to which it needs to resist.

Abstract: In electron tomography, the fidelity of the 3D reconstruction strongly depends on the employed reconstruction algorithm. In this paper, the properties of SIRT, TVM and DART reconstructions are studied with respect to having only a limited number of electrons available for imaging and applying different angular sampling schemes. A well-defined realistic model is generated, which consists of tubular domains within a matrix having slab-geometry. Subsequently, the electron tomography workflow is simulated from calculated tilt-series over experimental effects to reconstruction. In comparison with the model, the fidelity of each reconstruction method is evaluated qualitatively and quantitatively based on global and local edge profiles and resolvable distance between particles. Results show that the performance of all reconstruction methods declines with the total electron dose. Overall, SIRT algorithm is the most stable method and insensitive to changes in angular sampling. TVM algorithm yields significantly sharper edges in the reconstruction, but the edge positions are strongly influenced by the tilt scheme and the tubular objects become thinned. The DART algorithm markedly suppresses the elongation artifacts along the beam direction and moreover segments the reconstruction which can be considered a significant advantage for quantification. Finally, no advantage of TVM and DART to deal better with fewer projections was observed.