Abstract: In the last few decades, nanostructuring has driven significant attention towards the development of novel metallic materials with advanced mechanical properties. Nanocrystalline (nc) metals are a class of nanostructured materials with grain sizes smaller than about 100 nm. These exhibit outstanding mechanical strength and fatigue properties compared to their coarse-grained (cg) counterparts. These are promising candidates for application as structural or functional materials. Nc metals in the form of thin films are employed as hard coatings on bulk components, structural components, and conductive layers in various micro-/nanoscale devices. These structural components and devices are often subjected to cyclic stresses or fatigue loading. Under these cyclic stresses, nc metals tend to exhibit the Bauschinger effect (BE). The strength loss during the BE is of great importance concerning the strength-ductility trade-off in nc metals. Furthermore, contact surfaces of the engineering components in service often undergo relative motion and are subject to both friction and wear. These extreme loading conditions demand nc metals with tailored interfacial characteristics for improved tribological performance. Aiming at ensuring high reliability and mechanical robustness for optimum performance of these components, there has been a strong motivation for understanding the mechanical properties and governing deformation mechanisms in nc metallic materials. This thesis aimed at in-depth investigation of microstructures at micro-/nanoscales using state-of-the-art in situ and ex situ transmission electron microscopy (TEM) to develop a closer link between the deformation structure and underlying deformation mechanisms in some nc metallic materials. The thesis has primarily focused on the in situ TEM nanomechanics of the BE and rotational deformation of grains in nc palladium thin films. A sputtered thin film of nc Pd was deformed inside TEM by cyclic loading-unloading experiments and the evolving microstructure was studied in real-time under different TEM imaging modes. The stress-strain response of the film exhibited a characteristic non-linear unloading behavior confirming the BE in the film. The corresponding bright-field TEM imaging revealed evidence of partially reversible dislocation activity. Towards a quantitative understanding of the deformation structure in real-time, in situ nanomechanical testing was coupled with precession-assisted automated crystal orientation mapping in scanning TEM (ACOM-STEM). Global ACOM-STEM analysis offered crystal orientation of a large number of grains at different states of deformation and confirmed partially reversible rotations of nanosized grains fitting to the observed BE during loading and unloading. Analysis of intragranular rotations showed substantial changes in the sub-structure within most of these grains indicating a dominant role of dislocation-based processes in driving these rotations. Globally, an unusually random evolution of texture was seen that demonstrated the influence of deformation heterogeneity and grain interactions on the resulting texture characteristics in nc metals. In the quest of understanding the grain interactions, local investigations based on annular dark-field STEM imaging during loading-unloading showed reversible changes in the contrast of grains with sets of adjoining grains exhibiting a unique cooperative rotation. Local analysis of the density of geometrically necessary dislocations (GNDs) showed the formation of dislocation pile-up at grain boundaries due to the generation of back-stresses during unloading. Critical observations of the evolution of GND density offered greater insights into the mechanism of cooperative grain rotations and these rotations were related to grain structure and grain boundary characteristics. In addition to understanding the influence of grain structure and grain boundaries, the thesis has further investigated the role of heterointerfaces in sputtered Au-Cu and Cu-Cr nanocrystalline multilayered composites (NMCs) deformed under cyclic sliding contact. The microstructural evolution in the NMCs was investigated at different deformation states by classical TEM imaging, ACOM-STEM as well as energy-filtered TEM (EFTEM). Au-Cu NMC with an initial high density of twin boundaries deformed by stress-driven detwinning with a concurrent change in grain structure in both Au and Cu. The formation of a vortex structure was observed due to plastic flow instabilities at Au-Cu interfaces that led to codeformation and mechanical intermixing. Cu-Cr NMC showed a preferential grain growth in Cu layers whereas no noticeable change in the grain sizes was seen in Cr layers. The phase maps revealed sharp interfaces between Cu and Cr layers indicating no intermixing between the immiscible phases. EFTEM results exposed the cracking processes in Cr layers with a concurrent migration of Cu in the cracks. Overall, the thesis has attempted to analyze the competing deformation processes and relate these with the microstructural heterogeneity in terms of grain structure and GB and interfacial characteristics in nc metallic materials.

Abstract: Three series of poly(butylene succinate) (PBSu) nanocomposites containing 0.5, 1 and 2.5 wt% strontium hydroxyapatite [Sr-5(PO4)(3)OH] nanorods (SrHAp nrds) were prepared by in situ polymerisation. The structural effects of Sr-5(PO4)(3)OH nanorods, for the different concentrations, inside the polymeric matrix (PBSu), were studied through high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). HAADF-STEM measurements revealed that the SrHAp nanorods at low concentrations are dispersed inside the polymeric PBSu matrix while in 1 wt% some aggregates are formed. These aggregations affect the mechanical properties giving an enhancement for the concentration of 0.5 wt% SrHAp nrds in tensile strength, while a reduction is recorded for higher loadings of the nanofiller. Studies on enzymatic hydrolysis revealed that all nanocomposites present higher hydrolysis rates than neat PBSu, indicating that nanorods accelerate the hydrolysis degradation process. In vitro bioactivity tests prove that SrHAp nrds promote the formation of hydroxyapatite on the PBSu surface. All nanocomposites were tested also in relevant cell culture using osteoblast-like cells (MG-63) to demonstrate their biocompatibility showing SrHAp nanorods support cell attachment.

Abstract: Additives in semiconductor metal oxides are commonly used to improve sensing behavior of gas sensors. Due to complicated effects of additives on the materials microstructure, adsorption sites and reactivity to target gases the sensing mechanism with modified metal oxides is a matter of thorough research. Herein, we establish the promoting effect of nanocrystalline zinc oxide modification by 1-7 at.% of indium on the sensitivity to CO gas due to improved nanostructure dispersion and concentration of active sites. The sensing materials were synthesized via an aqueous coprecipitation route. Materials composition, particle size and BET area were evaluated using X-ray diffraction, nitrogen adsorption isotherms, high-resolution electron microscopy techniques and EDX-mapping. Surface species of chemisorbed oxygen, OH-groups, and acid sites were characterized by probe molecule techniques and infrared spectroscopy. It was found that particle size of zinc oxide decreased and the BET area increased with the amount of indium oxide. The additive was observed as amorphous indium oxide segregated on agglomerated ZnO nanocrystals. The measured concentration of surface species was higher on In2O3-modified zinc oxide. With the increase of indium oxide content, the sensor response of ZnO/In2O3 to CO was improved. Using in situ infrared spectroscopy, it was shown that oxidation of CO molecules was enhanced on the modified zinc oxide surface. The effect of modifier was attributed to promotion of surface OH-groups and enhancement of CO oxidation on the segregated indium ions, as suggested by DFT in previous work.

Abstract: The structural and magnetic properties of LaMnO₃/LaFeO₃(LMO/LFO) heterostructures are characterized using a combination of scanning transmission electron microscopy, electron energy-loss spectroscopy, bulk magnetometry, and resonant x-ray reflectivity. Unlike the relatively abrupt interface when LMO is deposited on top of LFO, the interface with reversed growth order shows significant cation intermixing of Mn³⁺and Fe³⁺, spreading ∼8 unit cells across the interface. The asymmetric interfacial chemical profiles result in distinct magnetic properties. The bilayer with abrupt interface shows a single magnetic hysteresis loop with strongly enhanced coercivity, as compared to the LMO plain film. However, the bilayer with intermixed interface shows a step-like hysteresis loop, associated with the separate switching of the “clean” and intermixed LMO sublayers. Our study illustrates the key role of interfacial chemical profile in determining the functional properties of oxide heterostructures.

Abstract: Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive cancers with a low response to treatment and a five-year survival rate below 5%. The ineffectiveness of treatment is partly because of an immunosuppressive tumor microenvironment, which comprises tumor-supportive pancreatic stellate cells (PSCs). Therefore, new therapeutic strategies are needed to tackle both the immunosuppressive PSC and pancreatic cancer cells (PCCs). Recently, physical cold atmospheric plasma consisting of reactive oxygen and nitrogen species has emerged as a novel treatment option for cancer. In this study, we investigated the cytotoxicity of plasma-treated phosphate-buffered saline (pPBS) using three PSC lines and four PCC lines and examined the immunogenicity of the induced cell death. We observed a decrease in the viability of PSC and PCC after pPBS treatment, with a higher efficacy in the latter. Two PCC lines expressed and released damage-associated molecular patterns characteristic of the induction of immunogenic cell death (ICD). In addition, pPBS-treated PCC were highly phagocytosed by dendritic cells (DCs), resulting in the maturation of DC. This indicates the high potential of pPBS to trigger ICD. In contrast, pPBS induced no ICD in PSC. In general, pPBS treatment of PCCs and PSCs created a more immunostimulatory secretion profile (higher TNF-α and IFN-γ, lower TGF-β) in coculture with DC. Altogether, these data show that plasma treatment via pPBS has the potential to induce ICD in PCCs and to reduce the immunosuppressive tumor microenvironment created by PSCs. Therefore, these data provide a strong experimental basis for further in vivo validation, which might potentially open the way for more successful combination strategies with immunotherapy for PDAC.

Abstract: The development of coatings with tunable performances is critical to meet a wide range of technological applications each one with different requirements. Using the plasma-enhanced chemical vapor deposition (PECVD) process, scientists can create hydrogenated amorphous carbon coatings doped with metal (a-C:H:Me) with a broad range of mechanical properties, varying from those resembling polymers to ones resembling diamond. These diverse properties, without clear relations between the different families, make the material selection and optimization difficult but also very rich. An innovative approach is proposed here based on projected performance indices related to fracture energy, strength, and stiffness in order to classify and optimize a-C:H:Me coatings. Four different a-C:H:Cr coatings deposited by PECVD with Ar/C2H2 discharge under different bias voltage and pressures are investigated. A path is found to produce coatings with a selective critical energy release rate between 5–125 J/m2 without compromising yield strength (1.6–2.7 GPa) and elastic limit (≈0.05). Finally, fine-tuned coatings are categorized to meet desired applications under different testing conditions.

Abstract: Crystal structure prediction is the holy grail of crystal engineering and is key to its ambition of driving the formation of solids based on the selection of their molecular constituents. However, this noble quest is hampered by the limited predictability of the incorporation of solvent molecules, first and foremost the ubiquitous water. In this context, we herein report the structure of four methylene blue cyanometallate phases, where anions with various shapes and charges influence the packing motif and lead to the formation of differently hydrated structures. Importantly, water molecules are observed to play various roles as isolated fillings, dimers, or an infinite network with up to 13 water molecules per repeating unit. Each crystal structure has been determined by single-crystal X-ray diffraction and evaluated with the aid of Hirshfeld surface analysis, focussing on the role of water molecules and the hierarchy of different classes of interactions in the overall supramolecular landscape of the crystals. Finally, the collected pieces of evidence are matched together to highlight the leading role of MB stacking and to derive an explanation for the observed hydration diversity based on the structural role of water molecules in the crystal architecture.

Abstract: We report on cooperative grain rotation accompanied by a strong Bauschinger effect in nanocrystalline (nc) palladium thin film. A thin film of nc Pd was subjected to cyclic loading-unloading using in situ TEM nanomechanics, and the evolving microstructural characteristics were investigated with ADF-STEM imaging and quantitative ACOM-STEM analysis. ADF-STEM imaging revealed a partially reversible rotation of nanosized grains with a strong out-of-plane component during cyclic loading-unloading experiments. Sets of neighboring grains were shown to rotate cooperatively, one after the other, with increasing/decreasing strain. ACOM-STEM in conjunction with these experiments provided information on the crystallographic orientation of the rotating grains at different strain levels. Local Nye tensor analysis showed significantly different geometrically necessary dislocation (GND) density evolution within grains in close proximity, confirming a locally heterogeneous deformation response. The GND density analysis revealed the formation of dislocation pile-ups at grain boundaries (GBs), indicating the generation of back stresses during unloading. A statistical analysis of the orientation changes of individual grains showed the rotation of most grains without global texture development, which fits to both dislocation- and GB sliding-based mechanisms. Overall, our quantitative in situ experimental approach explores the roles of these different deformation mechanisms operating in nanocrystalline metals during cyclic loading.

Abstract: We present the in situ synthesis of Pt nanoparticles within MIL-101-Cr (MIL = Materials Institute Lavoisier) by means of atomic layer deposition (ALD). The obtained Pt@MIL-101 materials were characterized by means of N2 adsorption and X-ray powder diffraction (XRPD) measurements, showing that the structure of the metal organic framework was well preserved during the ALD deposition. X-ray fluorescence (XRF) and transmission electron microscopy (TEM) analysis confirmed the deposition of highly dispersed Pt nanoparticles with sizes determined by the MIL-101-Cr pore sizes and with an increased Pt loading for an increasing number of ALD cycles. The Pt@MIL-101 material was examined as catalyst in the hydrogenation of different linear and cyclic olefins at room temperature, showing full conversion for each substrate. Moreover, even under solvent free conditions, full conversion of the substrate was observed. A high concentration test has been performed showing that the Pt@MIL-101 is stable for a long reaction time without loss of activity, crystallinity and with very low Pt leaching.

Abstract: In this study, we applied cluster beam deposition (CBD) as a new approach for fabricating efficient plasmon-based photocatalytic materials. Au nanoclusters (AuNCs) produced in the gas phase were deposited on TiO2 P25-coated silicon wafers with coverage ranging from 2 to 8 atomic monolayer (ML) equivalents. Scanning Electron Microscopy (SEM) images of the AuNCs modified TiO2 P25 films show that the surface is uniformly covered by the AuNCs that remain isolated at low coverage (2 ML, 4 ML) and aggregate at higher coverage (8 ML). A clear relationship between AuNCs coverage and photocatalytic activity towards stearic acid photo-oxidation was measured, both under ultraviolet and green light illumination. TiO2 P25 covered with 4 ML AuNCs showed the best stearic acid photo-oxidation performance under green light illumination (Formal Quantum Efficiency 1.6 x 10-6 over a period of 93 h). These results demonstrate the large potential of gas-phase AuNCs beam deposition technology for the fabrication of visible light active plasmonic photocatalysts.

Abstract: To obtain a nanocrystalline SnO2 matrix and mono- and bimetallic nanocomposites SnO2/Pd, SnO2/Pt, and SnO2/PtPd, a flame spray pyrolysis with subsequent impregnation was used. The materials were characterized using X-ray diffraction (XRD), a single-point BET method, transmission electron microscopy (TEM), and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with energy dispersive X-ray (EDX) mapping. The electronic state of the metals in mono- and bimetallic clusters was determined using X-ray photoelectron spectroscopy (XPS). The active surface sites were investigated using the Fourier Transform infrared spectroscopy (FTIR) and thermo-programmed reduction with hydrogen (TPR-H-2) methods. The sensor response of blank SnO2 and nanocomposites had a carbon monoxide (CO) level of 6.7 ppm and was determined in the temperature range 60-300 degrees C in dry (Relative Humidity (RH) = 0%) and humid (RH = 20%) air. The sensor properties of the mono- and bimetallic nanocomposites were analyzed on the basis of information on the electronic state, the distribution of modifiers in SnO2 matrix, and active surface centers. For SnO2/PtPd, the combined effect of the modifiers on the electrophysical properties of SnO2 explained the inversion of sensor response from n- to p-types observed in dry conditions.

Abstract: Among lithium battery cathode materials, Li1.2Ni0.13Mn0.54Co0.13O2 (LR-NMC) has a high theoretical capacity, but suffers from voltage and capacity fade during cycling. This is partially ascribed to transition metal cation migration, which involves the local transformation of the honeycomb layered structure to spinel-like nano-domains. Determination of the honeycomb layered/spinel phase ratio from powder X-ray diffraction data is hindered by the nanoscale of the functional material and the domains, diverse types of twinning, stacking faults, and the possible presence of the rock salt phase. Determining the phase ratio from transmission electron microscopy imaging can only be done for thin regions near the surfaces of the crystals, and the intense beam that is needed for imaging induces the same transformation to spinel as cycling does. In this article, it is demonstrated that the low electron dose sufficient for electron diffraction allows the collection of data without inducing a phase transformation. Using calculated electron diffraction patterns, we demonstrate that it is possible to determine the volume ratio of the different phases in the particles using a pair-wise comparison of the intensities of the reflections. Using this method, the volume ratio of spinel structure to honeycomb layered structure is determined for a submicron sized crystal from experimental three-dimensional electron diffraction (3D ED) and precession electron diffraction (PED) data. Both twinning and the possible presence of the rock salt phase are taken into account. After 150 charge-discharge cycles, 4% of the volume in LR-NMC particles was transformed irreversibly from the honeycomb layered structure to the spinel structure. The proposed method would be applicable to other multi-phase materials as well.

Abstract: Recent advances in near-edge X-ray-absorption fine-structure spectroscopy coupled with transmission X-ray microscopy (NEXAFS-TXM) allow large-area mapping investigations of individual nano-objects with spectral resolution up to E/Delta E = 104 and spatial resolution approaching 10 nm. While the state-of-the-art spatial resolution of X-ray microscopy is limited by nanostructuring process constrains of the objective zone plate, we show here that it is possible to overcome this through close coupling with high-level theoretical modelling. Taking the example of isolated bundles of hydrothermally prepared sodium titanate nanotubes ((Na,H)TiNTs) we are able to unravel the complex nanoscale structure from the NEXAFS-TXM data using multichannel multiple-scattering calculations, to the extent of being able to associate specific spectral features in the O K-edge and Ti L-edge with oxygen atoms in distinct sites within the lattice. These can even be distinguished from the contribution of different hydroxyl groups to the electronic structure of the (Na,H)TiNTs.

Abstract: Recently, a new simple and fast method for the synthesis of InP quantum dots by using phosphine as phosphorous precursor and myristic acid as surface stabilizer was reported. Purification after synthesis is necessary to obtain samples with good optical properties. Two methods of purification were compared and the surface processes which occur during purification were studied. Traditional precipitation with acetone is accompanied by a small increase in photoluminescence. It occurs that during the purification the hydrolysis of the indium precursor takes place, which leads to a better surface passivation. The electrophoretic purification technique does not increase luminescence efficiency but yields very pure quantum dots in only a few minutes. Additionally, the formation of In(OH)(3) during the low temperature synthesis was explained. Purification of quantum dots is a very significant part of post-synthetical treatment that determines the properties of the material. But this subject is not sufficiently discussed in the literature. The paper is devoted to the processes that occur at the surface of quantum dots during purification. A new method of purification, electrophoresis, is investigated and described in particular.

Abstract: A major revolution for electron microscopy in the past decade is the introduction of aberration correction, which enables one to increase both the spatial resolution and the energy resolution to the optical limit. Aberration correction has contributed significantly to the imaging at low operating voltages. This is crucial for carbon-based nanomaterials which are sensitive to electron irradiation. The research of carbon nanomaterials and nanohybrids, in particular the fundamental understanding of defects and interfaces, can now be carried out in unprecedented detail by aberration-corrected transmission electron microscopy (AC-TEM). This review discusses new possibilities and limits of AC-TEM at low voltage, including the structural imaging at atomic resolution, in three dimensions and spectroscopic investigation of chemistry and bonding. In situ TEM of carbon-based nanomaterials is discussed and illustrated through recent reports with particular emphasis on the underlying physics of interactions between electrons and carbon atoms.