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Abstract: For the comprehensive characterization of nanoparticles cross-sectional investigation on the atomic scale by analytical and high-resolution transmission electron microscopy (TEM) is indispensable. Cross-sectioning is especially important for anisotropic nanoparticles to gain information on structure and chemistry along all important projections. We present a focused ion beam (FIB) method for site- and orientation-specific cross-sectioning of arbitrary nanoparticles that are dispersed on a substrate. By adopting a shadow geometry originally developed for thin sensitive films'' protection of the specimen by a platinum layer is avoided. This enables simultaneous observation (from the front side) by the electron beam and ion-beam sectioning (from the back side of the supporting substrate) of individually selected particles with excellent accuracy on the nanometer scale. The feasibility and general applicability of the method is demonstrated by site-specific sectioning and cross-section HRTEM investigation of two types of anisotropic nanostructures: silver nanorods with five-fold twin structure and Janus-type silver patchy particles. [Copyright &y& Elsevier]

Abstract: High-quality samples are indispensable for every reliable transmission electron microscopy (TEM) investigation. In order to predict optimized parameters for the final Ar+-ion milling preparation step, topographical changes of symmetrical cross-section samples by the sputtering process were modeled by two-dimensional Monte-Carlo simulations. Due to its well-known sputtering yield of Ar+-ions and its easiness in mechanical preparation Si was used as model system. The simulations are based on a modified parameterized description of the sputtering yield of Ar+-ions on Si summarized from literature. The formation of a wedge-shaped profile, as commonly observed during double-sector ion milling of cross-section samples, was reproduced by the simulations, independent of the sputtering angle. Moreover, the preparation of wide, plane parallel sample areas by alternating single-sector ion milling is predicted by the simulations. These findings were validated by a systematic ion-milling study (single-sector vs. double-sector milling at various sputtering angles) using Si cross-section samples as well as two other material-science examples. The presented systematic single-sector ion-milling procedure is applicable for most Ar+-ion mills, which allow simultaneous milling from both sides of a TEM sample (top and bottom) in an azimuthally restricted sector perpendicular to the central epoxy line of that cross-sectional TEM sample. The procedure is based on the alternating milling of the two halves of the TEM sample instead of double-sector milling of the whole sample. Furthermore, various other practical aspects are issued like the dependency of the topographical quality of the final sample on parameters like epoxy thickness and incident angle. [Copyright &y& Elsevier]

Abstract: Aluminium/alumina composites based on ceramic preforms prepared via freeze-casting are examined. Domains composed of alternating but also interpenetrating ceramic and metallic lamellae are observed. Single-domain samples were extracted from composites processed under different conditions. In situ scanning electron microscopy analyses were carried out to investigate the damage evolution under compressive load. The composite is strong and brittle when loaded along directions parallel to the freezing direction. When compressed in other directions, the behavior is controlled by the soft metal. The plastic anisotropy is less pronounced than theoretical predictions for laminates, which is explained by the presence of bridges between the ceramic lamellae. Coating the preform with Cu or Cu2O prior to melt infiltration reduces the compressive strengths of the composites. Transmission electron microscopy analysis shows that even in the case of a Cu coating a Cu2O layer is formed during processing, weakening the interface and preventing the dissolution of Cu in the aluminium alloy. [Copyright &y& Elsevier]

Single-atom (SA) decoration represents the forefront of technological advancements in heterogeneous catalysis, harnessing the exceptional performance of catalysts at the atomic level. However, the high surface energy of isolated atoms often leads to agglomeration, resulting in the formation of nanoparticles. To address this challenge, trapping single atoms within surface defects has emerged as an effective strategy for atom immobilization. Conventional defect engineering techniques, such as high-temperature thermal reduction, suffer from adverse effects, such as sintering of the support material. In this study, we introduce a novel and facile room-temperature sonochemical method to induce well-defined atomic-scale defects on the surface of highly active TiO 2 nanosheets, predominantly exposing the (001) facet. By introducing a highly diluted Pt precursor to the ultrasonicated nanosheet slurry, isolated Pt atoms were selectively trapped within freshly formed defects. Remarkably, the resulting Pt single atom decorated samples exhibit a striking 100-fold increase in photocatalytic H 2 evolution compared to pristine TiO 2 nanosheets. Notably, we demonstrate that the density of the generated defects and the loading of Pt single atoms can be precisely tailored by adjusting the sonication time. Atomic-scale characterization, complemented by density functional theory (DFT) calculations, provides compelling evidence of the strong bonding between Pt single atoms and the defects generated via sonochemical treatment. Our findings offer a promising approach for defect engineering and SA decoration on a larger scale, underscoring the significant potential of this room-temperature technique for heterogeneous catalysis. [Display omitted] • The suggested room-temperature sonochemical method traps single atoms. • The Pt single-atom on 2d TiO 2 exhibited a 100-fold increase in H 2 evolution. • The sonication time controls the Pt single-atom loading and defect density. • DFT calculations proved the strong bonding between single-atoms and defects. [ABSTRACT FROM AUTHOR]

[Display omitted] • Focused study aiming at technological parameters of corroded Mediaeval Zwischgold. • Gold layer in a nanoscale thickness range of 20–50 nm, with the peak at 30 nm. • Full foil thickness (50–260 nm) obtained from EDX derived Ag/Au weight ratio. • Ultra-high-resolution SEM measurements, supported by STEM and RBS. • Scientific evidence for paleness of Zwischgold. A special gilding material called Zwischgold has been frequently observed in medieval gilded artefacts. As a bilayer metal leaf made from gold and silver, it exhibits similar but slightly paler golden colour tone compared to pure gold. Zwischgold surface can be darkened quickly due to the corrosion of its silver base. Despite its frequent mentions in medieval guild statutes, the production of Zwischgold and its important technological parameters have been under a veil of secrecy since the Middle Ages. Here, we examine the thicknesses and materials proportions of medieval Zwischgold, through high-resolution scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM-EDX) on a large number of samples taken from late medieval gilded sculptures. We observe that medieval Zwischgold contains ultra-thin gold layers in a thickness range of ca. 20–50 nm, indicating the employment of high-precision technologies in manufacturing of delicate art materials in the late medieval period. It further clarifies some ambiguity in gilding history, regarding the colour appearance of medieval Zwischgold. As supportive data, Rutherford backscattering spectrometry (RBS) and scanning transmission electron microscopy (STEM) were applied, in order to confirm the precision and accuracy of the sample preparation and the SEM analysis. [ABSTRACT FROM AUTHOR]

The correlation between the choice of reference material and model utilized in determining fracture toughness from indentation-induced radial cracks was critically investigated with six commonly used reference materials. Initially, the empirical constants in Anstis's and Laugier's equations were calculated, compared and analyzed. According to the values of the constants, the reference materials were categorized into three groups. This classification was further verified by evaluating the corresponding constants of 13 additional equations. To account for the classification, FIB technique was employed to examine the crack morphology in the reference materials – Si (100) features an almost Half-penny-shaped crack while the cracks in SiC (0001) display nearly as a rectangle, both far from the assumptions employed by the models. Subsequently, an improved and more reliable procedure to determine fracture toughness is proposed. Finally, with this procedure, the fracture toughness of a diamond/SiC composite film is determined to be 11.1 ± 1.1 MPa m1/2. [ABSTRACT FROM AUTHOR]

In the current paper, mesocrystals are used as effective precursors to design nanoreactors with different kinds of enclosed porosity. The thermal treatment of hematite mesocrystalline nanoparticles is investigated as a post-processing tool for the engineering of internal organization of hierarchical structures. The porosity of starting materials and of particles thermally treated at different temperatures is investigated by transmission electron microscopy, nitrogen sorption and 360° electron tomography. Virtual Capillary Condensation and Maximum Sphere Inscription are used as independent approaches for the quantitative assessment of internal porosity. The combination of experimental evidences and simulations provides a deep understanding of the internal topology of nanoreactors upon thermal treatment of mesocrystalline particles. This new design strategy may pave the way for exploring the use of the post-treated mesocrystals as carriers to encapsulate materials for optoelectronic applications. [ABSTRACT FROM AUTHOR]

With the recent advances in instrumentation pushing the limits of in situ transmission electron microscopy, the question of local sample temperature comes into focus again. In this work the applicability of parallel beam electron diffraction to locally measure and monitor the sample temperature in TEM is assessed, with applications for in situ heating experiments in mind. With Au nanoparticles applied to the sample surface, temperature is measured in the range from RT to 890 ° C by evaluating the change in scattering angle upon thermal expansion. Repeated measurements at constant temperature reveal a statistical precision of the method as good as 2.8 K . The applicability to locally measure the temperature is demonstrated mapping the temperature gradient across a heating chip. Owing to instantaneous response of thermal expansion to temperature changes, the method is well suited for monitoring even quick temperature changes, as demonstrated by quenching experiments. In order to enable extensive in situ studies, an evaluation method capable of processing large datasets with high precision is developed. Beam parallelity is identified as crucial experimental prerequisite and a routine is established, optimizing the microscope alignment in terms of beam parallelity. Apart from establishing a procedure for local temperature measurement, the present work demonstrates the unique capabilities of MEMS-based in situ heating equipment. [ABSTRACT FROM AUTHOR]

Fundamental understanding of (electro-)chemical processes occurring in batteries down to an atomic level is essential to further improve the performance of commercialized battery technologies and to establish novel cell chemistries. Transmission electron microscopy techniques are well-suited for highly localized structural and chemical analysis, but many electrode materials and their corresponding electrode/electrolyte interfaces and interphases are sensitive towards ambient conditions and/or the high energy electron beam. This necessitates cryogenic cooling of the specimen during sample preparation, transfer, and/or imaging. Here, we highlight the major experimental workflows derived from sample-specific requirements, which vary in complexity and infrastructural requirements. The purpose of this Perspective is to give a comprehensive guideline on both the opportunities and requirements of cryogenic (transmission) electron microscopy to analyze materials/phenomenon-specific questions relevant to battery research. [Display omitted] • Cryo-TEM for battery materials and interfaces sensitive towards the electron beam. • Detailed descriptions of sample-specific preparation and transfer workflows. • Overview of state-of-the-art cryo-TEM techniques used in battery research. • Outlook on future developments and opportunities in the field. [ABSTRACT FROM AUTHOR]

The transition of a thin film into an energetically favorable set of particles at temperatures below the melting point of the bulk material is known as solid-state dewetting. In this work the dewetting behavior of 16 nm thick discontinuous Au thin films on amorphous silicon nitride membranes is quantitatively studied by complementary in situ transmission electron microscopy techniques taking advantage of the unique capabilities of a chip-based heating system. The combination of dedicated imaging and diffraction techniques is used to investigate the interplay of grain growth and texture evolution with the process of dewetting. The results show an initial coarsening of the microstructure preceding the other processes. Texture evolution is highly correlated to material retraction and agglomeration during the following dewetting process. In-plane grain rotation has been observed, acting as an additional mechanism for orientation changes. From a methodological perspective this work demonstrates the capabilities of today’s transmission electron microscopy in combination with state-of-the-art in situ instrumentation. In particular the combination of complementary information from different dedicated techniques in one and the same setup is demonstrated to be highly beneficial. [ABSTRACT FROM AUTHOR]

Solid-state dewetting describes the transformation of thin films into a set of particles or droplets at temperatures well below the melting temperature of the bulk. In this work in situ scanning transmission electron microscopy has been used to study the dewetting behavior of discontinuous Au thin films (15 nm and 22 nm thick) on amorphous silicon nitride membranes at temperatures ranging from 300 °C to 600 °C. The combination of microscopic and statistical information enabled not only the qualitative discussion of the observed processes but also the quantification of the kinetics as well as the development of a model of the underlying morphological mechanism. A model-free master curve approach to the temporal evolution of the covered area at different temperatures is used to determine the activation energy of dewetting ( 1.04 ± 0.14 eV for the 15 nm thick film). A closer inspection reveals a multiple power law behavior, which is discussed in the frame of depercolation. Retraction of finger-like structures is found to be the dominant morphological mechanism based on the observed linear relationship between covered area and boundary length. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mesoporous TiO2 layer synthesized using nanocasting techniques. [•] 3D morphology of pore-space analyzed by electron tomography. [•] Pore size distribution observed in reconstructed tomograms matches experimental sorption data. [•] Anisotropic diffusion coefficients evaluated by diffusion flux simulation in 3D medium. [•] Parametric study revealed effects of templated pore size on model reactor performance. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate the capability of hot wall reactor gas phase synthesis to produce germanium (Ge) on silicon (Si) anisotropic particles. A two stage reactor setup is used to produce silicon nanoparticles (SiNPs) of 29.6nm in diameter with a very narrow size distribution and to deposit Ge on them. The gaseous precursors are monosilane (SiH4) and monogermane (GeH4). In a SEM study Ge patch formation on the SiNPs due to Stranski–Krastanov growth is observed. The patch size as well as the number of patches per SiNP is dependent on the process temperature and the GeH4 partial pressure. By varying these parameters it is possible to synthesize Janus-like particles with only one e.g. facetted Ge patch per SiNP, as well as patchy particles carrying an average of four to eight patches. HRTEM analysis shows, that the Ge grows epitaxial and crystalline on the surface of the SiNPs. From geometric phase analysis (GPA) the termination of inserted (220) half planes corresponding to misfit dislocations can be deduced, indicating a largely relaxed lattice in the Ge patches. A continuous tilt of the (111) lattice planes in the Si core below a Ge patch indicates that elastic deformation also contributes to the strain relaxation. [Copyright &y& Elsevier]

Abstract: Objective: Clinical studies reveal that veneer chipping is one major problem associated with zirconia based dental restorations, the underlying mechanisms being still investigated. We semi-quantitatively analyzed the effects of different surface treatments (thermal etching, 35/105μm sandblasting and coarse bur drilling (150μm)) on the microstructure of a zirconia veneered dental ceramic. Methods: The relative monoclinic content on zirconia surfaces was determined using X-ray diffraction (XRD). The microstructure at the zirconia–veneer interface has thereafter been investigated using transmission electron microscopy (TEM). Selected area electron diffraction (SAED) was used to qualitatively assess the depth of the stress-induced phase transformation. Results: Sandblasting or bur drilling significantly roughened the zirconia surface. A reverse transformation of already transformed monoclinic zirconia grains back into the tetragonal polymorph has been observed after thermal veneering treatment. In TEM, the mechanically treated samples revealed a highly damaged area of 1–3μm from the interface. The presence of monoclinic phase in veneered zirconia samples has been observed in SAED up to depths of 4μm (35μm sandblasted), 11μm (105μm sandblasted) and 9μm (150μm diamond drilled) below the interface. Significance: Regardless of the treatment protocol and produced roughness, the veneering ceramic perfectly sealed the zirconia surface. XRD showed an increased amount of monoclinic phase on the surface treated zirconia. However after thermal treatment, the monoclinic phase was re-transformed into the tetragonal polymorph. TEM/SAED analysis has found indication for a greater extend of the monoclinic transformation into the bulk zirconia compared to the treatment related defective zone depth. [Copyright &y& Elsevier]

High-pressure torsion was applied to join two disks of single-phase equiatomic fcc CoCrFeMnNi and bcc HfNbTaTiZr high entropy alloys (HEAs). After 15 revolutions a bulk nanocomposite had developed with alternating nano-lamellae of elongated nanocrystalline CoCrFeMnNi and mixed amorphous-nanocrystalline HfNbTaTiZr, exhibiting complex microstructures with numerous vortex-like regions. While the fcc phase retains a rather homogeneous elemental distribution, the former bcc high entropy alloy experiences a chemical separation towards Ta-rich and Ta-poor phases. The joining of dissimilar HEAs under constrained conditions (cold shut) enables the design of novel HEA-based composites by non-equilibrium processing. [Display omitted] [ABSTRACT FROM AUTHOR]

A single Cr-rich σ-phase alloy with a composition of Co 17 Cr 46 Fe 16.3 Mn 15.2 Ni 5.5 (at.%) and a tetragonal lattice structure was produced. The tracer diffusion coefficients of Ni and Fe were measured by secondary ion mass spectroscopy using the highly enriched 64Ni and 58Fe natural isotopes. On the homologous temperature scale, Ni and Fe diffuse in the σ phase faster as compared to the corresponding diffusion rates in the equiatomic and face-centered cubic CoCrFeMnNi alloy. In contrast, on the absolute temperature scale, these elements diffuse roughly at the same rates in both materials. Factors influencing element diffusion and phase stability of the σ phase compared to the equiatomic alloy are discussed. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Refractory high entropy alloys (RHEAs) from the Mo–Cr–Ti–Al system exhibit promising strength at elevated temperatures. However, at room temperature they possess a B2-ordered crystal structure and, therefore, exhibit reduced ductility. Guided by thermodynamic calculations, the Al concentration was systematically reduced in MoCrTi- x Al (x = 25, 15, 10, 5, 3 at%) in order to achieve a disordered, solid solution with A2-type crystal structure even at room temperature. The alloys were manufactured by arc melting followed by a homogenization treatment. To evaluate the chemical homogeneity, backscatter electron (BSE) imaging and energy dispersive X-ray spectroscopy (EDS) were performed. Dynamic differential scanning calorimetry (DSC) and selected area diffraction utilizing transmission electron microscopy (TEM-SAD) were performed for the: (i) detection of the characteristic heat signatures of the disorder-order transformations and (ii) determination of the ordering state at room temperature of the synthesized alloys, respectively. In case of MoCrTi–3Al, a single-phase A2 crystal structure without indications of a disorder-order transformation was obtained. Compression tests at temperatures ranging from room temperature up to 800 °C reveal a significant improvement of plastic deformability at room temperature as compared to the formerly investigated equiatomic MoCrTiAl with its B2 crystal structure. • Disordered A2 crystal structures are obtained in MoCrTi- x Al (x = 3, 5 at%). • The A2 crystal structure leads to higher ductility compared to B2 ordered alloys. • Appearance of order is appropriately described by thermodynamic calculations. • PLC effect is detected in all investigated compositions at elevated temperatures. [ABSTRACT FROM AUTHOR]

• The formation of CrTaO 4 after a short incubation period decreased the oxidation kinetics of Ta-containing alloys. • Activation energies for scale growth comparable to those of Cr 2 O 3 and CrTaO 4 forming Ni-based superalloys were found. • The oxygen inward diffusion was found to be rate determining in CrTaO 4 forming alloys. • In Nb-containing alloys, the formation of Nb 2 O 5 caused a porous oxide scale as well as severe oxide spallation. • Ti had a positive effect on the high-temperature oxidation behaviour because it supports the formation of protective CrTaO 4. The high-temperature oxidation mechanism of a series of refractory high entropy alloys: TaMoCrTiAl, NbMoCrTiAl, NbMoCrAl and TaMoCrAl at 1000 °C in air was studied. A complex protective oxide layer consisting of Al 2 O 3 , Cr 2 O 3 and CrTaO 4 oxides was observed for the quinary Ta-containing alloy. The formation of CrTaO 4 in this alloy after a short incubation period decreased the oxidation kinetics from a parabolic to a quartic rate law. Ti was found to support the formation of CrTaO 4. In the Nb-containing alloys, the formation of different Nb 2 O 5 polytypes near the metal/oxide interface caused a highly porous oxide scale and severe oxide spallation. [ABSTRACT FROM AUTHOR]