Abstract: Ni thin films sputter-deposited at room temperature with varying Ar pressures were investigated with automated crystal orientation mapping in a transmission electron microscope to uncover the mechanisms controlling the internal stress build-up recorded in-situ during deposition. Large grains were found to induce behaviour similar to a stress-free nucleation layer. The measurements of grain size in most of the Ni thin films are in agreement with the island coalescence model. Low internal stress was observed at low Ar pressure and was explained by the presence of large grains. Relaxation of high internal stress was also noticed at the highest Ar pressure, which was attributed to a decrease of Σ3 twin boundary density due to a low deposition rate. The results provide insightful information to better understand the relationship between structural boundaries and the evolution of internal stress upon deposition of thin films.

Abstract: Occupancy of different structural positions in a crystal lattice often seems to play a key role in material prop-erties. Several experimental techniques have been developed to uncover this issue, all of them being mostly bulk sensitive. However, many materials including topological insulators (TIs), which are among the most intriguing modern materials, are intended to be used in devices as thin films, for which the sublattice occupancy may differ from the bulk. One of the possible approaches to occupancy analysis is X-ray Photoelectron Diffraction (XPD), a structural method in surface science with chemical sensitivity. We applied this method in a case study of Sb2(Te1-xSex)3 mixed crystals, which belong to prototypical TIs. We used high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) as a reference method to verify our analysis. We revealed that the XPD data for vacuum cleaved bulk crystals are in excellent agreement with the reference ones. Also, we demonstrate that the anion occupancy near a naturally formed surface can be rather different from that of the bulk. The present results are relevant for a wide range of compositions where the system remains a topological phase, as we ultimately show by probing the transiently occupied topological surface state above the Fermi level by ultrafast photoemission.

Abstract: Atomic layer deposition (ALD) is a vapor based technique which allows to deposit uniform, conformal films with a thickness control at the atomic scale. In this research, Al 2 O 3 coatings were deposited on micrometer-sized Fe and Cu powder (particles) using the thermal trimethylaluminum (TMA)/ water (H 2 O) process in a rotary pump-type ALD reactor. Rotation of the powder during deposition was required to obtain a pinhole-free ALD coating. The protective nature of the coating was evaluated by quantifying its effectiveness in protecting the metal particles during oxidative annealing treatments. The Al 2 O 3 coated powders were annealed in ambient air while in-situ thermogravimetric analysis (TGA) and in-situ x-ray diffraction (XRD) data were acquired. The thermal stability of a series of Cu and Fe powder with different Al 2 O 3 thicknesses were determined with TGA. In both samples a clear shift in oxidation temperature is visible. For Cu and Fe powder coated with 25 nm Al 2 O 3 , we observed an increase of the oxidation temperature with 300-400°C. For the Cu powder a thin film of only 8 nm is required to obtain an initial increase in oxidation temperature of 200°C. In contrast, for Fe powder a thicker coating of 25 nm is required. In both cases, the oxidation temperature increases with increasing thickness of the Al 2 O 3 coating. These results illustrate that the Al 2 O 3 thin film, deposited by the thermal ALD process (TMA/H 2 O) can be an efficient and pinhole-free barrier layer for micrometer-sized powder particles, provided that the powder is properly agitated during the process to ensure sufficient vapour-solid interaction.

Abstract: Apart from the most studied tin-oxide compounds, SnO and SnO2, intermediate states have been claimed to exist for more than a hundred years. In addition to the known homologous series (Seko et al., Phys. Rev. Lett. 100, 045702 (2008)), we here predict the existence of several new compounds with an O concentration between 50 % (SnO) and 67 % (SnO2). All these intermediate compounds are constructed from removing one or more (101) oxygen layers of SnO2. Since the van der Waals (vdW) interaction is known to be important for the Sn-Sn interlayer distances, we use a vdW-corrected functional, and compare these results with results obtained with PBE and hybrid functionals. We present the electronic properties of the intermediate structures and we observe a decrease of the band gap when (i) the O concentration increases and (ii) more SnO-like units are present for a given concentration. The contribution of the different atoms to the valence and conduction band is also investigated.

Abstract: Indium oxide based transparent conductive oxides (TCOs) are promising contact layers in solar cells due to their outstanding electrical and optical properties. However, when applied in Cu(In,Ga)Se-2 or Si-hetero-junction solar cells the specific roughness of the material beneath can affect the growth and the properties of the TCO. We investigated the electrical properties of hydrogen doped and hydrogen-tungsten co-doped indium oxides grown on rough Cu(In,Ga)Se-2 samples as well as on textured and planar glass. At sharp ridges and V-shaped valleys crack-shaped voids form inside the indium oxide films, which limit the effective electron mobility of the In2O3:H and In2O3:H,W thin films. This was found for films deposited by magnetron sputtering and reactive plasma deposition at several deposition parameters, before as well as after annealing and solid phase crystallization. This suggests universal behavior that will have a wide impact on solar cell devices.

Abstract: The development of sensor materials of which gas sensitivity activates under light illumination is of great importance for the design of portable gas analyzers with low power consumption. In the present work a ZnO/CsPbBr3 nanocomposite based on nanocrystalline ZnO and colloidal cubic-shaped perovskite CsPbBr3 nanocrystals (NCs) capped by oleic acide and oleylamine was synthesized. The individual materials and obtained nanocomposite are characterized by x-ray diffraction, low-temperature nitrogen adsorption, x-ray photoelectron spectroscopy, high angle annular dark field scanning transmission electron microscopy with energy-dispersive Xray spectroscopy mapping and UV-vis absorption spectroscopy. The spectral dependence of the photoconductivity of the ZnO/CsPbBr3 nanocomposite reveals a well-defined peak that strongly correlates with the its optical absorption spectrum. The nanocomposite ZnO/CsPbBr3 shows enhanced photoresponse under visible light illumination (lambda(max) = 470 nm, 8 mW/cm(2)) in air, oxygen and argone, compared with pure nanocrystalline ZnO. Under periodic illumination in the temperature range of 25-100 degrees C, the ZnO/CsPbBr3 nanocomposite shows a sensor response to 0.5-3.0 ppm NO2, unlike pure nanocrystalline ZnO matrix, which demonstrates sensor sensitivity to NO2 under the same conditions above 100 degrees C. The effects of humidity on the sensor signal and photoresponse are also discussed.

Abstract: Nanostructures p-CoOx/n-SnO2 based on tin oxide nanowires have been prepared by two step CVD technique and characterized in detail by XRD, XRF, XPS, HAADF-STEM imaging and EDX-STEM mapping. Depending on the temperature of decomposition of cobalt complex during the second step of CVD synthesis of nanostructures cobalt oxide forms a coating and/or isolated nanoparticles on SnO2 nanowire surface. It was found that cobalt presents in +2 and +3 oxidation states. The measurements of gas sensor properties have been carried out during exposure to CO (14 ppm), NH3 (21 ppm), and H2S (2 ppm) in dry air. The opposite trends were observed in the effect of cobalt oxide on the SnO2 gas sensitivity when detecting CO or NH3 in comparison to H2S. The decrease of sensor signal toward CO and NH3 was attributed to high catalytic activity of Co3O4 in oxidation of these gases. Contrary, the significant increase of sensor signal in the presence of H2S was attributed to the formation of metallic cobalt sulfide and removal of the barrier between p-CoOx and n-SnO2. This effect provides an excellent selectivity of p-CoOx/n-SnO2 nanostructures in H2S detection.

Abstract: Submicron-sized quasicrystalline particles were obtained in an Al-Zn-Mg-Cu alloy produced by traditional melting. These particles consist of an Al-Fe-Ni core and a Mg-Cu-Zn shell and were found to be stable and embedded randomly in the Al matrix. The diffraction patterns of these core-shell particles reveal a decagonal core and an icosahedral shell with, respectively, ten- and five-fold axes aligned. High resolution scanning transmission electron microscopy of the Mg-Cu-Zn shell confirms the five-fold symmetry atomic arrangement and the icosahedral structure. It can therefore be concluded that Fe and Ni impurities play an important role in mediating the formation of such an unusual ternary core-shell quasicrystalline particle. These findings provide some novel insights in the formation of quasicrystals in traditional industrial Al alloys.

Abstract: In this work, we report an anomalous phenomenon on superelastic cycling of NiTi shape memory alloys when deforming at the temperature close to the border of superelastic window. New unexpected effects are found-(i) critical stress for inducing martensite transformation during the second loading cycle is higher than that of the first cycle; ( ii ) the plateau stress of the second cycle decreases to the original level when the strain overcomes the limit of the first cycle; ( iii ) transition from good superelasticity in the first cycle to fully irreversible strain in the second. We propose that defects generated during the first superelastic cycle close to the border of superelastic window impede following stress-induced martensitic transformations, leading to the increase of critical stress beyond yield stress of the B2 matrix, and thus functional fatigue of NiTi alloys. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Abstract: Organic photovoltaic (OPV) devices are on the verge of commercialization being long-term stability a key challenge. Morphology evolution during lifetime has been suggested to be one of the main pathways accounting for performance degradation. There is however a lack of certainty on how specifically the morphology evolution relates to individual electrical parameters on operating devices. In this work a case study is created based on a thermodynamically unstable organic active layer which is monitored over a period of one year under non-accelerated degradation conditions. The morphology evolution is revealed by compositional analysis of ultrathin cross-sections using nanoscale imaging in scanning transmission electron microscopy (STEM) coupled with electron energy-loss spectroscopy (EELS). Additionally, devices are electrically monitored in real-time using the non-destructive electrical techniques capacitance-voltage (C-V) and Impedance Spectroscopy (IS). By comparison of imaging and electrical techniques the relationship between nanoscale morphology and individual electrical parameters of device operation can be conclusively discerned. It is ultimately observed how the change in the cathode contact properties occurring after the migration of fullerene molecules explains the improvement in the overall device performance. (C) 2014 Elsevier B.V. All rights reserved.

Abstract: The development of a stable, efficient and economic catalyst for hydrogen evolution reaction (HER) of water splitting is one of the most hopeful approaches to confront the environmental and energy crisis. A two-step method is employed to obtain metal clusters (Ru, N, Pd etc.) combining single cobalt atoms anchored on nitrogen-doped carbon (Ru/Pt/Pd@Co-SAs/N-C). Based on the synergistic effect between Ru clusters and single cobalt atoms, Ru@Co-SAs/N-C exhibits an outstanding HER electrocatalytic activity. Specifically, Ru@Co-SAs/N-C only needs 7 mV overpotential at 10 mA cm(-2) in 1 M KOH solution, which is much better than commercial 20 wt% PVC (40 mV) catalyst. Density functional theory (DFT) calculations further reveal the synergy effect between surface Ru nanoclusters and Co-SAs/N-C toward hydrogen adsorption for HER. Additionally, Ru@CoSAs/N-C also exhibits excellent catalytic ability and durability under acidic and neutral media. The present study opens a new avenue towards the design of metal clusters/single cobalt atoms heterostructures with outstanding performance toward HER and beyond.

Abstract: Hierarchical semiconductors are the most important photocatalysts, especially for visible light-induced hydrogen production from water splitting. We demonstrate herein a hierarchical electrostatic assembly approach to hierarchical CdS/m-TiO2/G ternary photocatalyst, which exhibits high photoactivity and excellent photostability (more than twice the activity of pure CdS while 82% of initial photoactivity remained after 15 recycles during 80 h irradiation). The ternary nanojunction effect of the photocatalyst has been investigated from orbitals hybrid, bonding energy to atom-stress distortion and nano-interface fusion. And a coherent separation mechanism of charge carriers in the ternary system has been proposed at an atomic/nanoscale. This work offers a promising way to inhibit the photocorrosion of CdS and, more importantly, provide new insights for the design of ternary nanostructured photocatalysts with an ideal heterojunction.

Abstract: This work is focused on synthesis and characterization of targeted magnetic nanoparticles as magnetic resonance imaging (MRI) agents for in vivo visualization of gliomas. Ferric oxide (Fe3O4) cores were synthesized by thermal decomposition and coated with bovine serum albumin (BSA) to form nanoparticles with D-eff of 53 +/- 9 nm. The BSA was further cross-linked to improve colloidal stability. Monoclonal antibodies against vascular endothelial growth factor (mAbVEGF) were covalently conjugated to BSA through a polyethyleneglycol linker. Here we demonstrate that 1) BSA coated nanoparticles are stable and non-toxic to different cells at concentration up to 2.5 mg/mL; 2) conjugation of monoclonal antibodies to nanoparticles promotes their binding to VEGF-positive glioma C6 cells in vitro; 3) targeted nanoparticles are effective in MRI visualization of the intracranial glioma. Thus, mAbVEGF-targeted BSA-coated magnetic nanoparticles are promising MRI contrast agents for glioma visualization. (C) 2015 Elsevier Inc. All rights reserved.

Abstract: Herein, we describe for the first time the synthesis of the highly porous Hf-tetracarboxylate porphyrin-based metal-organic framework (MOF) (Hf)PCN-224(M) (M = H2, Co2+). (Hf)PCN-224(H2) was easily and efficiently prepared following a simple microwave-assisted procedure with good yields (56–67%; space-time yields: 1100–1270 kg m−3·day−1), high crystallinity and phase purity by using trifluoromethanesulfonic acid and benzoic acid as modulators in less than 30 min. By simply introducing a preliminary step (10 min), 5,10,15,20-(tetra-4-carboxyphenyl)porphyrin linker (TCPP) was quantitatively metalated with Co2+ without additional purification and/or time consuming protection/deprotection steps to further obtain (Hf)PCN-224(Co). (Hf)PCN-224(Co) was then tested as catalyst in CO2 cycloaddition reaction with different epoxides to yield cyclic carbonates, showing the best catalytic performance described to date compared to other PCNs, under mild conditions (1 bar CO2, room temperature, 18–24 h). Twelve epoxides were tested, obtaining from moderate to excellent conversions (35–96%). Moreover, this reaction was gram scaled-up (x50) without significant loss of yield to cyclic carbonates. (Hf)PCN-224(Co) maintained its integrity and crystallinity even after 8 consecutive runs, and poisoning was efficiently reverted by a simple thermal treatment (175 °C, 6 h), fully recovering the initial catalytic activity.

Abstract: It is generally believed that β00 precipitates, rather than β0 precipitates, are the major strengthening precipitates in
aged Al–Mg–Si alloys. The reason for this difference is not well understood. To clarify this, two samples of the
same Al–Mg–Si alloy but with different aging states were prepared. The under-aged sample only contains nanoprecipitates
of the β00 type, while the peak-aged one contains nearly equal volumes of β00 and β0 precipitates. We
have, for the first time, separated the strengthening effect of the contribution from βʺ and βʹ precipitates,
respectively, by an indirect approach based on high-precision measurements of volume fractions, number densities,
sizes, proportions of the precipitates, their lattice strains, the composition and grain size of the matrix. The
β0 precipitates, which take 45.6% of the total precipitate volume in the peak-aged sample, contribute to the entire
precipitation strengthening by only 31.6%. The main reason why they are less useful compared to β00 precipitates
has been found to be associated with their smaller lattice strains relative to the matrix, which is 0.99% versus
2.10% (for β00 ).