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Evolution of precipitates in aluminum 6061 alloy, quenched after 2 h hold at 550oC (super-saturated solid solution state – SSSS) and aged at 145oC (for up to 960 min), was studied by routine, ex-situ, transmission electron microscopy (TEM). In parallel, initial stages of the precipitation hardening process (after few-minute ageing) were studied by in-situ TEM. It was An appearance of short-living (~8 min) loose, disordered, spherical ~6 nm in diameter precipitates was captured. These precipitates rearranged after relatively long interval of time (~100 min, corresponding to 240 min ageing in the ex-situ tests) into long-range ordered rod-like Guinier–Preston (GP) zones (presuming GPI). The dimensions of the latter, 20 nm×2.1 nm, was determined based on the ex-situ TEM images.-Longer, 960 min, ageing results in GPI → GPII transformation accompanied by an increase of dimensions and strength of the rod-like precipitates. Determined geometrical parameters are in a reasonable agreement with corresponding parameters assessed previously using shock-wave technique. This fact implies that shock-wave technique can be considered as a useful tool for studying dislocation/defect interactions in a wide variety of strengthened alloys.

We report spin-resolved hard X-ray photoelectron spectroscopy (spin-HAXPES) for a buried Fe thin film in the valence band region. For the spin-HAXPES experiments, we developed an ultracompact built-in Mott-type spin-filter in a sample carrier, which enabled us to use the merit of two-dimensional (2D) multi-channel detector in a recent photoelectron analyser without modifying an apparatus for HAXPES. The effective Sherman function and the single-channel figure of merit (FOM) of the spin-filter were assessed to be −0.07 and 2.0 × 10−4, respectively. By utilizing the 2D detector of the photoelectron analyser, the effective FOM increased by a factor of ~4 × 104 compared to the case when only 1 channel of the 2D detector was used. We have applied spin-HAXPES to MgO(2 nm)/Fe(50 nm)/MgO(001) structures. The spin-HAXPES experiments revealed the majority and minority spin electronic states and the spin polarisation of the buried Fe thin film. Due to the large photoionization cross-section of the 4s orbital of Fe in HAXPES, the spin-resolved spectra mainly reflected the Fe 3d and 4s states. The observed spin-HAXPES and spin polarisation spectral shapes agreed well with the calculated spin-resolved cross-section weighted densities of states and spin polarisation spectra. In contrast, a small discrepancy in the energy scale was recognised due to the electron correlation effects. These results suggest that the electron correlation effects are important in the electronic structure of bulk Fe, and spin-HAXPES is useful for detecting genuine spin-resolved valence band electronic structures of buried magnetic materials., Graphical abstract

Pinning of a three-phase contact line at the nanoscale cannot be explained by conventional macroscale theories and thus requires an experimental insight to understand this phenomenon. We performed in-situ transmission electron microscopy observation of the three-phase contact lines of bubbles inside graphene liquid cells to experimentally investigate the causes of nanoscale pinning. In our observations, the three-phase contact line was not affected by the 0.6 nm-thick inhomogeneity of the graphene surface, but thicker metal nanoparticles with diameters of 2-10 nm and nanoflakes caused pinning of the gas-liquid interface. Notably, we found that flake-like objects can cause pinning that prevents the bubble overcome the flake object in a noncontact state, with a 2 nm-thick liquid film between them and the bubble. This phenomenon can be explained by the repulsive force obtained using the Derjaguin, Landau, Verwey, and Overbeek theory. We also observed that the flake temporally prevented the gas-liquid interface moving away from the flake. We discussed the physical mechanism of the attractive force-like phenomenon by considering the nanoconfinement effect of the liquid sandwiched by two graphene sheets and the hydration layer formed near the solid surface.

Several studies available in technical literature highlight that small variations in pearlite interlamellar spacing and colony average size promote significant changes in the mechanical properties of eutectoid steels. Therefore, the quantitative characterization of these parameters aiming to establish, or to predict, microstructure-property relationships is of great importance. However, the characterization techniques currently available for revealing pearlite colonies are complex, laborious and often require the use of high-cost resources. In this context, this work presents results about the development of an oxidation contrast method capable to reveal pearlite colonies for direct observation by optical microscopy. The developed method was applied to three different eutectoid steels and the average sizes of pearlite colonies were measured. The results obtained using the proposed technique were compared with those determined applying a usual method described in the literature. It was concluded that the proposed contrast method is effective and, once standardized among users, it can be a representative way for determining the average size of pearlite colonies.

Ductilities generated after four types of creep test are compared: (i) constant load, (ii) constant stress (calculated); (iii) constant stress (from direct observation of the minimum section) and (...

The motion of valence electrons dictates the course of several physical transformations and chemical reactions of great importance in biology and for technological applications. Direct observation ...

Materials defects are very important for enhancing the catalytic functions and applications. However, the surface defects of materials are usually diverse, and their catalytic activity is generally...

Water is one of the most significant causes of lubrication failure. There is little research on the direct observation of the impact of water on lubrication properties. In this study, the influence of water on oil replenishment under different elastohydrodynamic (EHD) lubricating conditions is evaluated using optical interferometry and infrared microscopy, and a dimensionless criterion when water influences the film thickness is proposed. Evidence shows that the scour displacing effect and emulsification of water/oil are the main reasons for the reduction in film thickness. Once a water droplet enters an oil reservoir around the critical contact zone, it hardly moves away. This aggravates starvation, reduces the center film thickness of the contact, and leads to lubrication failure of the mechanical components.

Since manufacturing is transitioning into Pb-free solder development for electronic assembly and packaging, consumer demands for more compact electronics have increased the importance of reliability issues brought about by the increased density of circuitry. Therefore, the role of alloying elements that can be added to common Pb-free solders such as Sn-Cu or Sn-Ag-Cu alloys in enhancing the properties and performance of the solder becomes important. Microstructural analysis along with direct observation in situ synchrotron radiography were used to study the effect of Ni, Zn, Au, In and Sb on the development of phases in Sn-10 wt.%Cu (Sn-10Cu). It was found that adding Ni and Zn to a Sn-10Cu alloy had the greatest impact on the microstructure with the Cu3Sn phase completely absent after these additions were made. Additions of Au and In also resulted in a reduction in the amount of Cu3Sn; however, the effect was not as pronounced. Removing the Cu3Sn phase from Sn-Cu Pb-free solder alloys is a possible approach for the design of more desirable microstructures that translate to better performance in modern electronic packaging.

A series of n-cycloparaphenylenes ([n]CPP, n = 8, 9, and 12) were studied by ultraviolet photoemission, inverse photoemission, ultraviolet-visible absorption, and X-ray photoemission spectroscopy to detect their unique electronic structures. [n]CPP has a cyclic structure in which both ends of n-poly(p-phenylene)s (nP) are connected. The molecular size dependence of the HOMO-LUMO gap of [n]CPP was investigated by direct observation and was found to increase as the molecular size increased. This trend is opposite to that of typical π-conjugated systems. Highly strained molecular structures, especially of small [n]CPPs, significantly impact their electronic structure. Insights into the electronic structure of [n]CPP obtained here will aid the design of electronic functionality of non-planar π-conjugation systems.

Ruddlesden-Popper perovskites possess a rich variety of multiple phases due to their mixed organic cations and variable layer numbers. However, the direct observation of these phases and their optical performance in ultrathin nanosheets, have rarely been reported. Here we demonstrate, through a one-pot CVD synthesis method to incorporate MA(+) and NMA(+) cations into PbI2 simultaneously, that the stackings of Ruddlesden-Popper phases with a distribution of a number of layers n can be produced within a single perovskite nanosheet. As featured by the micro-, time-resolved and temperature-dependent photoluminescence measurements, the optical properties are highly dependent on the nanosheet thickness. The work was financially supported by the National Key R&D Program of China (Grant No. 2020YFA0308900), the National Natural Science Foundation of China (Grant No. 92064010, 61801210, 91833302), the Natural Science Foundation of Jiangsu Province (Grant No. BK20180686), the China postdoctoral Science Foundation (2020M683555), the funding for "Distinguished professors" and "High-level talents in six industries" of Jiangsu Province (Grant No. XYDXX-021), the Fundamental Research Funds for the Central Universities, the Key Research and Development Program of Shaanxi Province (2020GXLH-Z-020, 2020GXLH-Z-027) and the start-up foundation of Northwestern Polytechnical University and Nanjing Tech University.

Irreversible structural transformation in intercalation-type cathode materials, which has been frequently observed, has been perceived as a principal cause of capacity fading and voltage decay in (...

The atomic arrangement of the Si(110)-(16×2) reconstruction was directly observed using noncontact atomic force microscopy (NC-AFM) at 78 K. The pentagonal structure, which is the most important building block of the reconstruction, was concluded to consist of five atoms, while only four or five spots (depending on tip bias) have been reported with scanning tunneling microscopy (STM). Single atoms were determined to exist near step edges between upper and lower terraces, which have not been reported using STM. These findings are key evidence for establishing an atomic model of the Si(110)-(16×2) reconstruction, which indeed has a complex structure.

In recent years, the importance of analyzing excited triplet states has increased dramatically because of their relevance in the design and development of photofunctional molecules. Since the secon...

We have comprehensively investigated asymmetric magnetization reversal behaviors of (x-A Co/7.7 A Pt)5 multilayers (x = 3.1 and 4.7) with perpendicular magnetic anisotropy. Our direct observation of magnetic domain structures by means of magneto-optical microscopy reveals that the asymmetry arises both from nucleation and wall-motion processes. An asymmetric nucleation behavior is observed, which could be originated from the preexisting non-reversed domains which might have a reproducible or random spatial distribution, controllable by tuning the field profile. An asymmetric wall-motion behavior stemming from asymmetric stripe domain evolution is also observed.

Photoelectrochemical (PEC) water splitting devices using semiconductors and electrocatalysts rely on heterogeneous interfaces that drive charge separation, thus determining potential gradients that...

While controlled dielectric breakdown (CBD) emerged as a promising method for accessible solid-state nanopore fabrication, there are still significant challenges in understanding the fabrication dy...

Herein, we present a detailed investigation of the electrochemically triggered formation and dissolution processes of α- and β-sulfur crystals on a monolithic carbon cathode using operando high-res...

Battery explosion incidents hinder the development and application of Li-ion batteries. This paper describes the use of nondestructive computed tomography (CT) to analyze cylindrical Li-ion battery samples that underwent thermal runaway and exploded. Unlike destructive analysis methods, which can lead to a loss of battery structural information, CT scan allows direct observation of a battery’s internal structure without disassembly. In this study, two case studies of 20700 and 18650 batteries show that sidewall and bottom case rupture was caused by blockage of the battery vent region, which prevented the release of the generated gas. This work demonstrates the ability of CT for post-mortem incident analysis and the limitations of current vent design, and also gives insight to a safety issue with some cylindrical batteries.

Fixed bed gasifiers are frequently used for biomass gasification as they have a relatively high efficiency for the conversion biomass to syngas, on a small scale. The distribution of solid particles inside a fixed bed gasifier is usually heterogeneous. This distribution is unknown as the currently used reactions cause the particles to continuously change states. A novel gasifier has been designed to investigate the distribution of these particles inside the gasifier. An opening system at the bottom of the gasifier was equipped to collect particles, without affecting the shapes and positions of the particles remaining inside the gasifier after quenching, at any given point of operation. Because only the bottom of the reactor is opened, the distribution of particles inside the gasifier can be known without the need for transportation, tilting, or splitting of the reactor itself. The gasification performance of this novel gasification system was investigated by varying the distribution of different particles inside the gasifier. Different phenomena, such as product gas distribution were observed during the operation of the gasifier. These phenomena were confirmed by direct observation, using the novel collection/visualization system for solid particles inside the gasifier.

Recently, attention has been directed toward understanding the dynamics and relaxation kinetics of block copolymer micelles, including mechanisms such as micelle fragmentation and fusion. The few prior studies on block copolymer micelle fragmentation relied on ensemble averaging techniques such as small-angle X-ray scattering and dynamic light scattering; some individual particles were imaged by ex situ transmission electron microscopy. Here we report the direct observation of fragmentation for three molecular weights of 1,2-polybutadiene

High-temperature scanning electron microscopy allows the direct study of the temperature behavior of materials. Using a newly developed heating stage, tilted images series were recorded at high temperature and 3D images of the sample surface were reconstructed. By combining 3D images recorded at different temperatures, the variations of material roughness can be accurately described and associated with local changes in the topography of the sample surface.

Patterns on sand generated by blowing winds are one of the most commonly seen phenomena driven by such a self-organization process, as has been observed at the nanoscale after ion irradiation. The origins of this effect have been under debate for decades. Now, a new methodology allows to simulate directly the ripple formation by high-fluence ion-irradiation. Since this approach does not pre-assume a mechanism to trigger self-organization, it can provide answers to the origin of the ripple formation mechanism. The surface atom displacement and a pile-up effect are the driving force of ripple formation, analogously to the macroscopic one. IMPACT STATEMENT The presented model allows to follow the ripple formation and propagation in different steps, at the atomic level, for the first time under low irradiation energies.

The direct observation of temperature changes in (Pb,La)(Zr,Ti)O3 (PLZT) (4/90/10), (8/80/20), and (8/70/30) ceramics during cycle of applying and removing electric field were utilized to evaluate ...

The origin of the increased efficiency of perovskite solar cells by controlling environmental humidity was investigated using conductive atomic force microscopy (C-AFM) and friction force microscop...

A wet cotton rag becomes stiff after natural drying. We propose a model for this hardening phenomenon, which explains that the stiffness of cotton is caused by a cross-linked network between single fibers, mediated by capillary adhesion of bound water on the surface of cellulose. Here, with the aid of atomic force microscopy and atomic force microscopy-infrared spectroscopy, we reveal the existence of the bound water on the surface of a cotton single fiber under naturally dried conditions. We also find that the hydrogen bonding state of the bound water is distinct from that of the bulk water. Two stretching modes of OH groups are clearly decoupled from each other, which arise from the effects of the air-water (hydrophobic) and water-cellulose (hydrophilic) interfaces. This suggests a possible link between the microscopic nature of the bound water and the macroscopic mechanical behavior of cotton fabrics.

In micro EDM, the discharge is significantly influenced by the bubble behavior. The depth-dependent characteristics of bubble behavior play a key role on the dielectric exchange and debris exhaust. However, the difficulty of direct observation on the narrow gap area is a big obstacle in clarifying the bubble behavior in the gap area. In this paper, a method is put forward to both directly observe the behavior of bubble in the interelectrode gap area and the behavior of bubble escaping from the micro hole based on the self-designed SiC sandwich workpiece in the micro hole drilling with EDM. The aim is to comprehensively investigate the bubble behavior by combining the observation of bubbles in the interelectrode gap area with the bubbles escaping from the micro hole. The observation was performed by a high-speed camera at high frame rate. Depending on the proposed methods, the influence of bubble behavior on the micro hole drilling with EDM is comprehensively analyzed.

Efficient thermal insulation at high temperatures poses stringent requirements on suitable materials. Low density, porous inorganic structures with pore sizes in the sub-micrometer range are of particular interest for such materials to control heat conduction. Simultaneously, thermal radiation has to be suppressed, which depends on the optical properties of the constituents. Here, the authors demonstrate a direct observation of the transition from a conduction dominated to a radiation dominated thermal transport mechanism for the case of particulate silica materials at temperatures reaching up to 925 °C. A detailed analysis of the radiative transport through bulk silica as well as solid and hollow silica particles is provided. Optical transparency at high temperatures is the driving force, whereas surface wave modes barely contribute, particularly in case of the insulating particle packings. The existing analytical framework of laser flash analysis is extended to qualitatively describe the radiative and conductive heat transport by two independent diffusive transport models. The analysis provides a better understanding of the challenges to fabricate and analyze efficient thermal insulation materials at high operating temperatures, where multiple heat transport mechanisms need to be controlled.

The Yb valence state of YbInCu4 was measured at 300 and 13 K under pressure by high-resolution x-ray absorption spectroscopy (XAS). The electronic structure of Cu was also measured by XAS at the Cu...

Hydrogels are promising materials for several applications, including cell scaffolds and artificial load-bearing substitutes (cartilages, ligaments, tendons, etc.). Direct observation of the nanoscale polymer network of hydrogels is essential in understanding its properties. However, imaging of individual network strands at the molecular level is not achieved yet due to the lack of suitable methods. Herein, for the first time, we developed a novel mineral-staining method and network fixation method for transmission electron microscopy observation to visualize the hydrogel network in its unperturbed conformation with nanometer resolution. Surface network observation indicates that the length of surface dangling chains, which play a major role in friction and wetting, can be estimated from the gel mesh size. Moreover, bulk observations reveals a hierarchical formation mechanism of gel heterogeneity. These observations have the great potential to advance gel science by providing comprehensive perspective that link bulk gel properties with nanoscale.

α-RuCl3, with abundant studies in its bulk phase, has shown the promising potential to approach the two-dimensional Kitaev honeycomb model and to realize the consequential quantum spin liquids. In this material, some ingredients spark off the hunting of quantum spin liquid states: the localized magnetic moments on each Ru3+ ion guaranteed by the Mottness, the Kitaev-type interaction originating from the superexchange path over the p-d bonds, and the nearly two-dimensional nature of the van der Waals coupled honeycomb layers. Here, we worked out the growth art of α-RuCl3 monolayer on highly oriented pyrolytic graphite substrate for the first time, and then studied its electronic structure, particularly the delicate orbital occupations. Through scanning tunneling microscopy and spectroscopy study, the bonding configurations are justified by the features of pronounced t2g-pπ and eg-pσ hybridization, and the Mott nature is unveiled by an ~ 0.6 eV full gap at the Fermi level located in the t2g-pπ level. Our experimental results agree well with the density functional theory calculations of the monolayer system. In accordance with previous theoretical research, the epitaxial monolayer α-RuCl3 system holds high tunability comparing to its bulk phase and provides a novel platform to explore the Kitaev physics.

Polymorphism makes it possible to clarify the relationship between emission property and crystal structure. However, based on the exact molecular conformation in tetraphenylethene polymorphisms, it is still challenging to evaluate the difference of intramolecular coplanarity without the support of calculation because of the complex combination of four different torsion angles between four peripheral benzenes and the central ethylene plane. Here, by using a di-formyl-functionalized tetraphenylethene derivative, two ideal polymorphisms with a consistent trend of the corresponding torsion angles have been obtained. For the first time, we explicitly demonstrated that intramolecular coplanarity is the underlying cause of the polymorphism-dependent emission of tetraphenylethene derivatives.

Direct high-speed micro-video records prove the existence of highly overheated zones at the contacts of powder particles during short (~ 1 ms) electric current pulses. The value of overheating can exceed 1600 degrees and lead to the formation of liquid-phase sintering necks, the dimensions of which are well correlated with the size of the overheated zones. The micro-uniformity of the temperature field in the electric pulse heating allow understanding the unusually high consolidation rates of powder materials observed in spark plasma sintering.

Despite the important role of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) binders in graphite electrodes for Li-ion batteries, the direct analysis of these binders remains challenging, particularly at very low concentrations as in practical graphite anodes. In this paper, we report the systematic investigation of the physiochemical behavior of the CMC and SBR binders and direct observations of their distributions in practical graphite electrodes. The key to this unprecedented capability is combining the advantages of several analytic techniques, including laser-ablation laser-induced break-down spectroscopy, time of flight secondary ion mass spectrometry, and a surface and interfacial cutting analysis system. By correlating the vertical distribution with the adsorption behaviors of the CMC, our study reveals that the CMC migration toward the surface during the drying process depends on the degree of cross-linked binder-graphite network generation, which is determined by the surface property of graphite and CMC materials. The suggested analytical techniques enable the independent tracing of CMC and SBR, disclosing the different vertical distribution of SBR from that of the CMC binder in our practical graphite anodes. This achievement provides additional opportunity to analyze the correlation between the binder distribution and mechanical properties of the electrodes.