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Packaging insulation materials with high thermal conductivity and excellent dielectric properties are favorable to meet the high demand and rapid development of third generation power semiconductors. In this study, we propose to improve the thermal conductivity of epoxy resin (EP) by incorporating a three-dimensional boron nitride thermally conductive network. Detailedly, polyurethane foam (PU) was used as a supporter, and boron nitride nanosheets (BNNSs) were loaded onto the PU supporter through chemical bonding (BNNS@PU). After immersing BNNS@PU into the EP resin, EP-based thermally conductive composites were prepared by vacuum-assisted impregnation. Fourier transform infrared spectrometer and scanning electron microscope were used to characterize the chemical bonding and morphological structure of BNNS@PU, respectively. The content of BNNS in BNNS@PU/EP composites was quantitatively analyzed by TGA. The results show that the thermal conductivity of the BNNS@PU/EP composites reaches 0.521 W/m K with an enhancement rate η of 30.89 at an ultra-low BNNS filler content (5.93 wt. %). Additionally, the BNNS@PU/EP composites have excellent dielectric properties with the frequency range from 101 to 106 Hz. This paper provides an interesting idea for developing high thermal conductivity insulating materials used for power semiconductor packaging. [ABSTRACT FROM AUTHOR]

Over the last two decades, Electron Energy Loss Spectroscopy (EELS) imaging with a scanning transmission electron microscope has emerged as a technique of choice for visualizing complex chemical, electronic, plasmonic, and phononic phenomena in complex materials and structures. The availability of the EELS data necessitates the development of methods to analyze multidimensional data sets with complex spatial and energy structures. Traditionally, the analysis of these data sets has been based on analysis of individual spectra, one at a time, whereas the spatial structure and correlations between individual spatial pixels containing the relevant information of the physics of underpinning processes have generally been ignored and analyzed only via the visualization as 2D maps. Here, we develop a machine learning-based approach and workflows for the analysis of spatial structures in 3D EELS data sets using a combination of dimensionality reduction and multichannel rotationally invariant variational autoencoders. This approach is illustrated for the analysis of both the plasmonic phenomena in a system of nanowires and in the core excitations in functional oxides using low loss and core-loss EELS, respectively. The code developed in this manuscript is open sourced and freely available and provided as a Jupyter notebook for the interested reader. [ABSTRACT FROM AUTHOR]

Low-energy ion beam irradiation, combined with the introduction of impurities, presents a promising approach for nanopatterning silicon (Si) surfaces. In this research, we investigate the surface evolution of Si (100) surfaces irradiated by 75 eV helium (He) plasma, in the presence of tantalum (Ta), traditionally regarded as an impurity incapable of initiating pattern formation, as evidenced in prior studies. The Ta impurities are pre-deposited onto the Si surfaces using the magnetron sputtering method, which offers a more controlled and quantifiable approach compared with the conventional co-deposition route. After irradiation at 800 K, dense cone arrays are produced on the Si surface. The growth of the cones is explored for fluence spanning (1–10) × 1025 m−2. The cross-sectional scanning electron microscope images indicate that the cone lengths and base width are well characterized by t1/2 dependence. The kinetics of the cone growth follow Fick's law, characterized by an effective diffusive mechanism with the coefficients of diffusion: D = 6.49 ± 0.83 × 10−16 m−2 s−1. Transmission electron microscope observations reveal that the cone has distinct inner and outer parts with different microstructures and a clear interface. The growth mechanism of these cones is elucidated as a composite process involving preferential sputtering, the destabilizing influence of He bubbles, and the migration of adatoms. [ABSTRACT FROM AUTHOR]

The scanning electron microscope (SEM) recordings of dynamic nano-electromechanical systems (NEMS) are difficult to analyze due to the noise caused by low frame rate, insufficient resolution, and blurriness induced by applied electric potentials. Here, we develop an image processing platform enhanced by the physics of the underlying system to track the motion of buckling NEMS structures in the presence of high noise levels. The algorithm is composed of an image filter, two data filters, and a nonlinear regression model, which utilizes the expected form of the physical solution. The method was applied to the recordings of a NEMS beam about 150 nm wide, undergoing intra- and inter-well post-buckling states with a transition rate of approximately 0.5 Hz. The algorithm can track the dynamical motion of the NEMS and capture the dependency of deflection amplitude on the compressive force on the beam. With the help of the proposed algorithm, the transition from inter-well to intra-well motion is clearly resolved for buckling NEMS imaged under SEM. [ABSTRACT FROM AUTHOR]

A non-destructive method for detecting sub-micrometer-sized micropipes on an entire wafer surface is investigated. Since it is difficult to detect sub-micrometer-sized micropipes due to their small core size, a non-destructively and accurately detecting method is required. To solve the issue, we focus on a characteristic depression generated around micropipes, namely, line-shaped depressions. In this paper, the location of line-shaped depressions is identified by using optical inspection, and the line-shaped depressions are distinguished whether micropipes exhibit line-shaped depression or not by using mirror electron microscope observation as high-resolution inspection. The accuracy of the distinction results is confirmed by scanning electron microscope observation, and electrical characteristics of the P–N diode are fabricated using the inspected wafer. Furthermore, the sub-micrometer-sized micropipes are observed at the sites of leakage current identified by emission microscopy. Additionally, device simulation of the blocking-voltage characteristics of P–N diodes suggests that the increase in leakage current depends on the electric field at the sub-micrometer-sized micropipes, regardless of their core size. [ABSTRACT FROM AUTHOR]

Gastropods forage with their radula, a thin chitinous membrane with embedded teeth, which scratch across the substrate to lose food particles. During this interaction, the risk of loosening particles is obvious without having a specialized mechanism holding them on the tooth surface. As mucus secretions are essential in molluscan life cycles and the locomotion and attachment gels are known to have an instant high adhesion, we have hypothesized that the saliva could support particle retention during feeding. As adhesion of snail saliva was not studied before, we present here an experimental setup to test its particle-binding capacity using a large land snail (Lissachatina fulica, Stylommatophora, Heterobranchia). This experiment was also applied to the gels produced by the snail foot for comparison and can be potentially applied to various fluids present at a small volume in the future. We found, that the saliva has high particle retention capacity that is comparable to the foot glue of the snail. To gain some insight into the properties of the saliva, we additionally studied it in the scanning electron microscope, estimated its viscosity in a de-wetting experiment, and investigated its elemental composition using energy dispersive X-ray spectroscopy reveling higher contents of Ca, Zn and other potential cross-linkers similar to those found in the glue. [ABSTRACT FROM AUTHOR]

In recent years, precision and accuracy for a more precise critical dimension (CD) control have been required in CD measurement technology. CD distortion between the measurement by a critical dimension scanning electron microscope (CD-SEM) and a reference tool is the most important factor for a more accurate CD measurement. CD bias varies by a CD-SEM and a pattern condition. Therefore, it is urgently needed to identify, characterize, and quantify those parameters that may or may not affect the CD measurement by a CD-SEM. The sensitivity of the Monte Carlo simulated CD-SEM images with multiple physical modeling components has been studied previously. In this study, we demonstrate that the work function and elastic scattering potential models have a significant impact on secondary electron emission intensity, but their influence on the shape of the linescan profile is small, and other factors like the optical energy loss function and dielectric function models have even smaller effects. We have evaluated the uncertainty in the linescan profiles of Si line structures with different sidewall angles due to several different physical factors. It is found that when the CD is evaluated by a peak/valley method, the uncertainty of the CD is negligible. Therefore, it is concluded that the CD value and its related uncertainty are not critically related to the physical factors of the present Monte Carlo simulation model but rely dominantly on the line structure and electron beam parameters. [ABSTRACT FROM AUTHOR]

We report on the metrological characterization of the emission from a germanium-vacancy center in diamond under a microfabricated solid immersion lens in a confocal laser-scanning microscope setup. Ge ions were implanted into a synthetic diamond at 3 MeV, and germanium-vacancy centers were then formed by subsequent annealing. Afterward, solid immersion lenses were fabricated in a focused ion beam scanning electron microscope. The photoluminescence was investigated at room temperature in terms of the spectral distribution, the excited state lifetime, the second-order correlation function, and the saturation behavior, proving simultaneous high single-photon purity and high brightness. Two methods were exploited to minimize the residual multi-photon probability: spectral filtering and temporal filtering. According to these results, we assume that Raman scattered photons and emission from neighboring color centers play an important role in the residual multi-photon emission probability. The system efficiency of the single-photon source was investigated and found to be in accordance with the value calculated from all sources of loss in the setup. The branching ratio of the germanium-vacancy center for the decay into the ground state and into metastable state was calculated. The results enable the usage of the single-photon source in future quantum radiometric experiments. [ABSTRACT FROM AUTHOR]

This study elucidates the thermal-induced bandgap broadening (TBB) phenomenon in copolymer organic semiconductors (OSCs). From the perspective of device physics, the diketopyrrolopyrrole-based copolymer was employed as the semiconductor layer to fabricate a back-to-back Schottky junction structure. Characterization through the analysis of I–V curves enables the qualitative exploration of the correlation between bandgap and temperature in copolymer OSCs. Then, technology computer-aided design was utilized to explore the influence of thermal-induced bandgap broadening on the back-to-back Schottky I–V curves. Subsequently, the variable temperature UV-VIS-NIR absorption spectra of the copolymer OSCs were analyzed, providing quantitative evidence of the thermal-induced bandgap broadening phenomenon and confirming its recoverability. Through the research of the Schottky junction and absorption spectra, we verified the consistency of the TBB phenomenon in both the electrical and optical bandgaps. From the scanning electron microscope images of the copolymer OSC films, it is found that the thermal-induced bandgap broadening phenomenon is mainly caused by thermal expansion and increased disorder of copolymer molecules. This study highlights a physical phenomenon of copolymer OSCs that is different from most inorganic semiconductors, and such insight offers a theoretical perspective for the application and thermal stability investigation of copolymer devices under high temperature conditions. [ABSTRACT FROM AUTHOR]

Strain engineering is an alternative to chemical modification in manipulating functionalities of materials. Here, we report the lattice strain could relax the abrupt phase transition of (Ni1−xFex)1−δS and lead to an excellent negative thermal expansion (NTE) effect. The high-resolution scanning transmission electron microscope and extended x-ray absorption fine structure unambiguously demonstrate that parallel Ni3S4-type nanosheets could be introduced into the matrix lattice by increasing the δ value. By forming the Ni(Fe)-S-Ni(Fe) bonds, the (1–11) plane of nanosheets epitaxially grows on the (002) plane of the hexagonal matrix. Those bonds are strong enough to bear the large lattice mismatch along the interface as the phase transition occurs. As the concentration of nanosheets increases, the weak and inhomogeneous strain in matrix lattice becomes strong and uniform, expanding the NTE window in different ways. This result opens an unconventional avenue for designing NTE materials and extends the research scope of lattice strain as well. [ABSTRACT FROM AUTHOR]

The FurnaSEM microfurnace was installed in the chamber of a scanning electron microscope to carry out in situ experiments at high temperatures and test its limits. The microfurnace was used in combination with different types of detectors (Everhart–Thornley for the collection of secondary electrons in a high vacuum, gas secondary electron detector for the specific collection of secondary electrons in the presence of gas, and Karmen© detector for the collection of backscattered electrons at high temperature). Experiments carried out on various samples (metal alloys and ceramics) show that the microfurnace operates in both high-vacuum and low-vacuum modes. Temperature ramp rates during temperature cycles applied to the sample range from 1 to 120 °C/min (temperature rise) and 1 to 480 °C/min (controlled and natural cooling). The maximum temperature at which images were recorded up to 25 k × magnification was 1340 °C, with a residual air atmosphere of 120 Pa. The choice of a flat furnace with the sample placed directly above it has enabled innovative experiments to be carried out, such as low-voltage imaging (using a shorter working distance—up to 10 mm—than is possible with conventional furnaces), 3D imaging (by tilting the stage by up to 10°), and high-temperature backscattered electron imaging (using a dedicated detector). [ABSTRACT FROM AUTHOR]

When conducting in situ experiments at high temperatures in a scanning electron microscope using microfurnaces, controlling the temperature of a sample of a few mm3 placed in the hot zone of the furnace can be a complex task. In most cases, the temperature of the sample is estimated by means of a thermocouple placed in the hot body of the furnace, and the assumption made is that the temperature of the furnace is the temperature of the sample. In this work, a detailed understanding of the thermal response of the sample placed in the hot zone of the furnace is proposed. Temperature differences due to contact resistance between the furnace surface and the sample, the nature of the sample, and the sample geometry are calculated with a numerical model and measured experimentally on a dedicated test bench. Three technical solutions (bonding, sandwiching, and mini-crucible) for limiting temperature differences between the furnace surface and sample are proposed and validated by numerical calculations and experimental measurements. [ABSTRACT FROM AUTHOR]

The development of a new heating system dedicated to in situ scanning electron microscope (SEM) experimentation at high temperatures is reported. This system, called FurnaSEM, is a compact microfurnace, enabling heat treatments up to 1300 °C. The choice of materials for the microfurnace is explained. The design of the microfurnace is optimized by iterations of numerical simulations, and the thermal characteristics of the microfurnace are calculated numerically. The numerical results obtained are compared with the thermal characteristics of a manufactured microfurnace, measured on a specially developed dedicated test bench. This test bench includes a working chamber simulating a SEM chamber equipped with a thermal camera. The results obtained during various qualification tests enabled us to determine the main technical characteristics of the FurnaSEM microfurnace: temperature profiles on the sample support surface, energy consumption at high temperatures, and the range of achievable thermal cycles. [ABSTRACT FROM AUTHOR]

Because of their full compatibility with CMOS technology, HfO2-based ferroelectrics, and especially Hf0.5Zr0.5O2 (HZO), attract a lot of attention. However, the overwhelming majority of measurement techniques provides only information about the cumulative electrical response of many domains of HZO, i.e., at the macroscopic level. So far, only piezoresponse force microscopy technique was applied to visualize distinct ferroelectric domains in HZO and to analyze the local switching behavior in the microscopic level. This work introduces the possibility of using electron beam-induced current (EBIC) technique in the scanning electron microscope to visualize the gradual polarization reversal of HZO and to obtain the local polarization dynamics. We show that although the local EBIC signal is affected by surrounding domains, studying the variations in the ferroelectric response of individual domains as well as the spread of the local stiffness and local imprint is possible by this method. Besides, we show the connection between the EBIC current and an electric field across passive non-ferroelectric layers at interfaces between HZO and metal electrodes, which opens up additional opportunities to use the EBIC technique for investigations of interface-dependent properties of HZO ferroelectrics in the future. [ABSTRACT FROM AUTHOR]

Focussed ion beam - scanning electron microscope (FIB-SEM) 3D examination was conducted on three standard UO2 and one Cr doped UO2 high burn-up pressurized water reactor (PWR) fuel samples. This work complemented other microanalysis examination, including an electron backscattered diffraction (EBSD) work on the polished surface. A parallel article giving the EBSD results was submitted simultaneously. Together, they found, in all the central area of these high burn-up samples: (i) a restructuring of the initial grains into smaller sub-grains forming low angle boundaries and with crystal orientations around that of their parent grains; and (ii) intragranular bubbles mostly situated on these low angle boundaries. The FIB-SEM 3D examination showed how such inter-sub-grain bubbles start as small compact but also small lenticular bubbles, similar to typical small intergranular lenticular bubbles. With increasing burn-up, these lenticular bubbles get thicker and locally interlink to form more complex bubbles. However, no long distance networks, between the sub-grains or between the original grains, were found. Such networks could have been a path for part of the fission gases to reach the grain boundaries, the grain edges (the intersection line of three grain boundaries), and the rod free volumes. These FIB-SEM 3D examinations brought details on the intragranular and intergranular bubbles situation for each studied volume. The distribution of the intragranular bubbles according to their sizes and shapes was exposed. The central restructuring, studied in this work, is likely to play a role in the increase of the fission gas release fractions at high burn-up. This work is an incentive to study further this restructuring and the bubbles formed, combining different approaches. [ABSTRACT FROM AUTHOR]

Measurements of transport phenomena are constantly plagued by contact resistance, prohibiting the sample's intrinsic electrical or thermal conductivity from being accurately determined. This predicament is particularly severe in thermal transport measurements due to the inability to meet similar impedance requirements for a four-probe method used in electrical resistance measurements. Here, we invent a three-probe measurement method that makes an accurate determination of thermal conductivity possible for nanomaterials. Incorporating electron beam heating provided by a scanning electron microscope (SEM) on a diffusive thermal conductor not only quantifies the thermal contact resistance, which may introduce an error of more than 270% to a sample's thermal conductivity, but also eliminates several device uncertainties that may contribute an additional 17% error in a measurement. The method also enables local temperature measurements, revealing nanoscale structural variations unfound by SEM. The high accuracy of the technique would make standardization of nanoscale thermal transport measurement possible. [ABSTRACT FROM AUTHOR]

Lead-free antiferroelectric AgNbO3 ceramics have garnered extensive attention due to their rapid charge/discharge capabilities and environmentally friendly nature, holding immense potential for energy storage applications. However, the practical utilization of AgNbO3 has been hindered by its low energy storage density. This study employed an A/B-site co-doping strategy, which yielded positive effects on the energy performance of AgNbO3 ceramics. By modifying the A/B-sites with equivalent amounts of Bi3+ and Y3+ ions, enhanced maximum polarization, improved breakdown field, and slimmer hysteresis loops were simultaneously achieved, as the combined effects of refined grain size, wider optical bandgap, and randomly distributed antiferroelectric nanodomains, which were verified through the scanning electron microscope, transmission electron microscope, and ultraviolet–visible spectrum. As a consequence, a high energy storage density of 5.40 J/cm3 accompanied by an energy storage efficiency of 56.5% was achieved in the Ag0.97Bi0.01Nb0.994Y0.01O3 ceramic under a relatively low electric field of 190 kV/cm. This study underscores the effectiveness of A/B-site aliovalent co-doping as a viable strategy for developing high-performance ceramic capacitors for energy storage applications. [ABSTRACT FROM AUTHOR]

The primary goal of this study is to examine the impact of sodium hydroxide (NaOH)/alkali-activated fly ash on the fresh properties and mechanical properties of self-compacting concrete (SCC). The fresh properties, known as the workability of SCC characteristics, were determined using the U-box, V-funnel, J-ring, and L-box tests. The M30 grade SCC containing superplasticizer of 0.86 wt. % of cement is replaced with 10%, 15%, 20%, 25%, 30%, and 40% of alkali-activated fly ash. On days 7, 14, and 28 after curing, the compressive strength and the splitting tensile strength of the SCC were examined. The study was further extended to evaluate the behavior of reinforced concrete beams containing fly ash and ground granulated blast furnace slag, whose size was 1200 × 100 × 150 mm3, under flexure loading. Based on the test results, it was found that the increase in the replacement of cement with alkali-activated fly ash increased the workability in the SCC. With the addition of superplasticizers, the SCC gained much more workability than conventional concrete containing no superplasticizer. The mechanical properties of 10% and 15% activated fly ash in Portland cement provided the maximum strength for the SCC at different ages of curing. The maximum first crack load and maximum ultimate flexure loading of the reinforced concrete beam containing 10% activated fly ash by weight of cement were greater than those of the control concrete beam. The microstructural scanning electron microscope observations confirmed that the alkali-activated fly ash increased the strength properties of the self-compacting concrete. [ABSTRACT FROM AUTHOR]

The use of aluminum alloys in automobiles is expanding, and the potential for additional increases is significant. Further growth will be determined by improvements in material qualities for existing applications or the discovery of new applications. Alloy A-356 (LM25) is commonly employed for high-quality alloy wheel rims in various motor vehicles, constituting 40% of global car usage. This study introduces 0.2% Cu into the Al–Si–Mg alloy system to enhance the mechanical properties. The alloy blend is cast into a metal mold, subjected to a 4-h cure at 540 °C, quenched with water, and precipitation hardened for 12 h at 1800 °C. Optical and scanning electron microscopes are utilized to analyze the alkali microstructure. The mechanical properties of alloyed and unalloyed castings, including hardness and tensile test results, are examined in untreated and heat-treated states. Fracture surfaces of tensile specimens are scrutinized. Intermetallic compounds formed during solidification are studied using scanning electron microscopy and x-ray diffraction analysis. The tensile strength under unalloyed (LM25) and alloyed (LM25 + 0.2 wt. % Cu) conditions before and after heat treatment [(72, 165.4 and 88.3, 237.1) and (78, 179.6 and 98, 252.9, respectively)] shows a significant increase. [ABSTRACT FROM AUTHOR]

Integrating carbon nanotubes (CNTs) into a polymer matrix can significantly modify its physical properties, providing that the challenges associated with CNT dispersion are successfully resolved. In this work, we investigate the enhancement of the dielectric properties of silicone when multiwall carbon nanotubes (MWCNTs) are introduced to its polymer matrix as a filler in the frequency range from 0.5 to 20 GHz. An optimized procedure is used to prepare nanocomposites with MWCNTs concentrations by weight of 0%, 0.5%, 1.0%, 1.5%, and 2.0%. The investigated dielectric properties for the prepared nanocomposites are the real dielectric constant ɛ′, the imaginary dielectric constant ɛ″, the loss tangent tan δ, and the AC conductivity σAC. The dispersion of the MWCNTs in the silicone matrix is confirmed using the Fourier-transform infrared (FTIR) spectroscopy and the scanning electron microscope. This study shows that the dielectric properties of the nanocomposite are enhanced as the MWCNT's concentration is increased over the entire frequency range. For example, the enhancement in ɛ′ value was from 3.2 up to 21.6 at 0.5 GHz and from 2.5 to 10.6 at 20 GHz as the concentration increased from 0% to 2.0%. For the ɛ″ value, the enhancement was from less than 0.1 to 8.6 at 0.5 GHz and to 2.0 at 20 GHz, respectively. Based on the obtained tanδ values, the nanocomposites with MWCNTs of 0.5% and 1.0% can be classified as low-loss dielectrics, while the other nanocomposites with MWCNTs of 1.5% and 2.0% are classified as lossy dielectrics. [ABSTRACT FROM AUTHOR]

The damage impact of mechanical shocks on stator bar insulation is a key factor in high-voltage motor accidents. This study conducted electrical aging acceleration and breakdown experiments on damaged stator insulating materials to understand failure causes and evaluation methods. The relationship between sample defect area and depth and electrical properties was analyzed, along with the morphology of the damaged surface using a scanning electron microscope. Results show that the defect area correlates with impact mode but does not directly impact electrical performance. Effective insulation thickness is positively linked to electrical performance. This study serves as a valuable reference for evaluating mechanical impact faults in high-voltage motors. [ABSTRACT FROM AUTHOR]

By applying ultrasonic treatment to ZL205A aluminum alloy melt containing different Cd contents and then using a tensile test, a scanning electron microscope experiment, and a metallographic experiment, the influence of ultrasonic treatment to ZL205A aluminum alloy melt on the properties of aluminum–copper alloy with different Cd contents in the liquid phase high-temperature region was studied. The effect of ultrasonic treatment on the solidification structure of ZL205A aluminum alloy was investigated. The results showed that there was no significant difference in the form of Cd and the solid solution rate of the aluminum alloy with different Cd contents in ultrasonic-assisted casting. However, the effect of ultrasonic waves on the high-temperature liquid phase of the melt of ZL205A aluminum alloy can effectively reduce the porosity defects in the solidification structure of the casting, refine the solidification structure, and make the structure more uniform. The ultrasonic cavitation effect can promote the formation and uniform distribution of Al–3Ti and improve the nucleation rate, and the effect can continue after heat treatment. This can solve the problem that increasing Cd content in ZL205A greatly reduces the toughness of castings while increasing the strength. The sample with a Cd content of 0.20% and with ultrasonic treatment has the highest strength, the average tensile strength is 475.5 MPa, and the yield strength is 381.75 MPa. However, compared with the conventional casting samples with the same Cd content, the decrease in elongation was significantly reduced. [ABSTRACT FROM AUTHOR]

We reported here on the fabrication and characterization of a smart titanium alloy bolt based on a high-frequency piezoelectric thin-film sensor. The thin-film sensor was directly deposited on a titanium alloy bolt head with radio frequency magnetron sputtering and characterized by a scanning electron microscope and an atomic force microscope. The ultrasonic characteristics of the smart bolt, which include a pure and broad frequency spectrum peaked at 14.81 MHz, high measurement accuracy below 3%, and high repeatability free from some interference from bolt detection position change, were fully characterized. No obvious frequency shift was observed with the increase in axial preload. Based on the mono-wave method [TOF (time of flight) of longitudinal mode wave], TOF change increased linearly with preload force in the range of 0–20 kN. With the increase in temperature from 22 to 150 °C, the TOF linearly increases while the longitudinal wave velocity linearly decreases. The results indicate the prepared smart titanium alloy bolt is suitable as a smart aviation and automotive fastener. [ABSTRACT FROM AUTHOR]

In this study, basalt fibers (BFs) and nano-silica (NS) were innovatively combined to reinforce recycled aggregate concrete (RAC) to prepare recycled aggregate concrete (named NBRAC) with better mechanical and microstructural properties as an alternative to ordinary concrete. Different NBRAC specimens were prepared by adjusting the contents of NS and BF; the damage mechanism and mechanical properties of NBRAC were investigated; and the compressive, split tensile, and flexural strengths of NBRAC were evaluated. The microstructure of NBRAC was analyzed by scanning electron microscopy observation. The results showed that the densification of NBRAC was improved under the condition of 50% RA substitution rate and that its compressive, split tensile, and flexural strengths were increased by 6.8%, 16.3%, and 32.7%, respectively, compared with that of natural concrete, which proved that the method was feasible for the preparation of high-performance RAC. Scanning electron microscope image analysis confirmed the improvement effects of NS and BF on RAC, and combined with the experimental data, a composite explanation for the improvement effects of NS and BF on RAC was proposed for the first time. [ABSTRACT FROM AUTHOR]

The use of slag-based alkali-activated concrete (AAC) could effectively address the issues of resource extraction and carbon emissions caused by traditional Portland cement. In this study, the effects of the fly ash content, water–binder ratio, and alkali activation modulus on the early mechanical properties of AAC were investigated. A total of 105 cube specimens (35 sets) were designed and subjected to compressive strength tests, scanning electron microscope tests, and x-ray diffraction composition analysis. The results indicated that excellent early strength was observed in AAC, with a compressive strength reaching ∼90% of the 28th day strength before 14 days. An increase in the fly ash content and a decrease in the water–binder ratio significantly improved the compressive strength within the same age period. The impact of a lower alkaline activation modulus on strength was found to be insignificant. Based on the experimental results, a calculation method and a constitutive model for early strength were proposed, and the theoretical values exhibited a high level of agreement with the measured values. [ABSTRACT FROM AUTHOR]

This paper presents a novel piezoelectric-driven nanoindentation system for a scanning electron microscope (SEM) with an improved analog compensation (IAC) method. This system mainly consists of a piezoelectric-driven indenter head, a rectangle-shaped transducer, and a nanopositioner module. Compared with the state-of-the-art piezoelectric-driven nanoindentation system with a circle-shaped transducer, the proposed nanoindentation system is capable of multi-direction operation inside a SEM with a rectangle-shaped transducer. Self-matched semiconductor strain gauges are selected as the position sensor for the piezoelectric-actuator. The Wheatstone bridge output voltage cannot achieve a zero temperature coefficient because the temperature coefficients of self-matched semiconductor strain gauge pairs become significantly different from each other after installation in practice. An IAC method is proposed to compensate the temperature coefficients further. Compared with the existing analog compensation method, the IAC method solves the problem of amplifier saturation and improves the sensitivity of the self-matched semiconductor strain gauge pairs position sensor by 27%. The multi-direction operation results inside a standard SEM HITACHI SU5000 validate the advantage of the developed nanoindentation system. [ABSTRACT FROM AUTHOR]

Materials research studies are dealing with a large number of images, which can now be facilitated via image-based machine learning techniques. In this article, we review recent progress of machine learning-driven image recognition and analysis for the materials and chemical domains. First, the image-based machine learning that facilitates the property prediction of chemicals or materials is discussed. Second, the analysis of nanoscale images including those from a scanning electron microscope and a transmission electron microscope is discussed, which is followed by the discussion about the identification of molecular structures via image recognition. Subsequently, the image-based machine learning works to identify and classify various practical materials such as metal, ceramics, and polymers are provided, and the image recognition for a range of real-scenario device applications such as solar cells is provided in detail. Finally, suggestions and future outlook for image-based machine learning for classification and prediction tasks in the materials and chemical science are presented. This article highlights the importance of the integration of the image-based machine learning method into materials and chemical science and calls for a large-scale deployment of image-based machine learning methods for prediction and classification of images in materials and chemical science. [ABSTRACT FROM AUTHOR]

The fluid transport in porous media is a critical property for oil and gas exploitation, construction engineering, and environmental protection. It is profoundly influenced by pore geometry and mineral properties. Currently, the Kozeny–Carman equation serves as the permeability prediction equation for porous media, established on the circular pores model. However, it fails to fully account for the impact of pore shape and mineral properties of the soil, leading to significant deviations between predicted and measured soil permeability results. In this paper, based on scanning electron microscope image and mercury intrusion porosimetry, the pores were divided into circular pores and narrow slit pores according to the ratios of pore area and circumference. Then, the quantitative expression of the two types of pores and their connectivity and tortuosity were given, and the circular and narrow slit composite pore model was used to describe the soil pore. Subsequently, the electrostatic potential of pore water was calculated by the Poisson–Boltzmann equation to consider the adsorption effect of minerals on pore water. Combined with the Navier–Stokes equation, the permeability prediction equation considering pore geometry, pore connectivity, and tortuosity and mineral properties was established. Finally, the experimental results illustrated that the theoretical prediction results were in good agreement with the experimental results. The proposed permeability prediction equation proves valuable for assessing and predicting the fluid transport in porous media. [ABSTRACT FROM AUTHOR]

Lithium batteries are promising techniques for renewable energy storage attributing to their excellent cycle performance, relatively low cost, and guaranteed safety performance. The performance of the LiFePO4 (LFP) battery directly determines the stability and safety of energy storage power station operation, and the properties of the internal electrode materials are the core and key to determine the quality of the battery. In this work, two kinds of commercial LFP batteries were studied by analyzing the electrical properties and material properties of the electrodes. After performing the rate and cycle performance tests of the battery cell, differential scanning calorimetry, scanning electron microscope, x-ray diffraction, and inductively coupled plasma were used to explore the performance of electrode materials to establish the correlation between the battery performance and the electrochemical reaction law of the internal materials and further to judge the influence of the key material properties on the battery performance. This work opens up an avenue for technical supervision of energy storage power stations. [ABSTRACT FROM AUTHOR]

Laminar-type spherical diffraction gratings overcoated with carbon-based materials were designed, fabricated, and evaluated for the purpose of enhancing the analytical sensitivity of the flat-field spectrograph in a vacuum ultraviolet region of 35–110 eV. As the design benchmark for numerical calculations, diffraction efficiency (DE) and spectral flux, which are defined by the product of the DE and numerical aperture and correlate with the analytical sensitivity of the spectrograph, were used. To simplify the feasibility study on the overcoating effects, we assumed a laminar-type grating having a grating constant of 1/1000 mm and coated with a Au layer of 30.0 nm thickness and an incidence angle of 84.0°. The optimized groove depth and duty ratio were 30.0 nm and 0.3, respectively. In addition, the optimum thicknesses of the overcoating layer were 44, 46, 24, and 30 nm for B4C, C, diamond-like-carbon, and SiC, respectively. Based on these results, we have fabricated a varied-line-spacing holographic grating overcoated with B4C with a thickness of 47 nm. For the experimental evaluation, we used the light source of Mg-L and Al-L emissions excited by the electron beam generated from an electron microscope, an objective flat-field spectrograph, and a CCD imaging detector. The experimental results showed that the spectrograph employing a new grating overcoated with the B4C layer indicated almost the same spectral resolution and 2.9–4.2 times higher analytical sensitivity compared with those obtained with a previously designed Au-coated grating having a grating constant of 1/1200 mm and used at an incidence of 86.0°. [ABSTRACT FROM AUTHOR]

Accurate simulations of the shock response of heterogeneous energetic (HE) materials require closure models, which account for energy localization in the micro-structure. In a multi-scale framework, closure is provided by reaction rate models that account for ignition and growth of hotspots, allowing for prediction of the overall macro-scale sensitivity of a HE material. In the present meso-informed ignition and growth (MES-IG) model, the reaction rate is expressed as a function of shock pressure and morphology of the void field in a pressed energetic material. In MES-IG, the void morphology is quantified in terms of a limited number of parameters: viz., overall porosity, void size, and shape (aspect ratio and orientation). In this paper, we quantify the effects of arbitrary variations in void shapes on meso-scale energy deposition rates. A collection of voids of arbitrary shapes is extracted from scanning electron microscope (SEM) images of real, pressed HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) samples and classified into groups based on their similarity in shapes. Direct numerical simulations (DNS) are performed on the highly contorted "real" void shapes, and the calculated hotspot ignition and growth rates are compared with values predicted by the MES-IG. It is found that while the parameterization of complex void morphologies in terms of orientation and aspect ratio gives fairly good agreement between DNS and MES-IG reaction rates, the intricate details of highly complex void shapes impact hotspot characteristics to a significant extent. This work suggests possible improvements for the prediction of reaction rate in the energetic microstructure by adopting a more detailed description of shapes. [ABSTRACT FROM AUTHOR]

Piezoresistance, the change of electrical resistance due to applied mechanical strain, has been characterized for films in tension or bending. However, measuring the compressive piezoresistance of films remains a challenge because the in-plane compression often results in macroscopic buckling and kinking, leading to localization of strain. Here, we overcame this issue via a newly developed method to calculate the compressive piezoresistance of films by measuring the change of resistance in situ under tensile and bending stresses. A linear fit was applied to the experimental tensile piezoresistive response and a quadratic fit was applied to the bending piezoresistive response. The experimental bending response was mathematically decomposed into its tensile and compressive components. The compressive response was then isolated by subtracting the tensile response from the bending response. In this study, the method is applied to reduced graphene oxide (rGO) film specimens. For rGO films, the compressive piezoresistance was found to be much greater than the tensile piezoresistance. Scanning electron microscope images revealed that extensive damage occurred on the compressive side of the bending specimen, resulting in a large increase in resistivity. We anticipate that our study will be adapted to applications that require mechanically reliable, flexible, and highly conductive materials, such as flexible electronics and structural energy and power. [ABSTRACT FROM AUTHOR]

We have demonstrated that intense 7-fs, ∼810-nm laser pulses can produce a much finer periodic nanostructure on a diamond-like carbon film through ablation in air than that formed with intense 100-fs, ∼800-nm laser pulses. The minimum period size is ∼60 nm, corresponding to ∼1/13 of the center wavelength. To understand the physical mechanism responsible for the finer nanostructuring, we have observed a bonding structural change in the nanostructure with micro-Raman spectroscopy and a scanning transmission electron microscope. It has been found that the modified layer thickness with the 7-fs pulses is much thinner than that with the 100-fs pulses. The results show that the 7-fs pulses create a few-nm-thick layer with high-density electrons and excite short-range surface plasmon polaritons, which have a large wave number around the layer and induce the plasmonic near-field nanoablation. The period size estimated by using a model target reproduces well the observed size of nanostructures. [ABSTRACT FROM AUTHOR]

SnTe is an important material because of its applications in mid-infrared photo-detectors. In the present work, the effects of film thickness on scaling law and surface properties (i.e., morphologies and optical properties) of SnTe thin films have been investigated. SnTe thin films of different thicknesses are prepared by means of e-beam evaporation technique. The surface morphology of each film is analyzed by atomic force microscopy (AFM) as well as a scanning electron microscope. The crystallinity of the films is found to increase with increasing film thickness, as confirmed by x-ray diffraction and Raman measurements. Fractal analysis is performed on AFM images to investigate the irregularity of surfaces. It is found that the surface of the thicker sample is rougher than the thinner sample. The autocorrelation function is applied to investigate the self-affine fractal nature of surfaces. The average roughness, interface width, lateral correlation length, local surface slope, and fractal dimension increased with film thickness. The values of roughness exponent, growth exponent, dynamic exponent, and steepening exponent are calculated and found to be α = 0.76 - 0.96 , β = 0.75 , z = 1.92 , and λ = 0.35 - 0.25 , respectively. The scaling exponents together with the other parameters such as the local surface slope indicate that the growth is quasi-3D island/mound type with rapid surface roughening behavior and obeys anomalous scaling. The multiple scattering cross sections of light together with Fourier transform infrared spectroscopy data analyses suggest that the higher crystalline film with a smaller number of defects is infrared-sensitive and may be more suitable for advanced mid-infrared detector applications. [ABSTRACT FROM AUTHOR]

A process for growing gallium nitride (GaN) vertical p–i–n homojunctions on (111) silicon substrates using metalorganic chemical vapor deposition was developed, and a triple mesa etch technique was used to fabricate efficient betavoltaic energy converters. Monte Carlo simulation platform CASINO was used to model beta radiation penetration into GaN to aid device design. The resulting devices were tested under irradiation from a scanning electron microscope electron beam (e-beam) tuned to imitate the energies of the 63Ni beta emission spectrum. Based on current–voltage measurements taken under e-beam illumination, a maximum open-circuit voltage of ∼ 412 mV and a maximum short-circuit current density of ∼ 407 nA/cm2 were measured. A high fill factor of ∼ 0.77 and power conversion efficiency of ∼ 6.6 % were obtained. Additionally, the proposed triple mesa etch technique used to create these betavoltaics has the potential for further use in fabricating many types of electronic devices using a wide variety of material platforms. [ABSTRACT FROM AUTHOR]

Perovskite La2Ti2O7 nanocrystalline powder was obtained through the shock synthesis method. In the study, La2O3 and TiO2 powders were mixed through ball milling and, subsequently, shocked by a flyer at a velocity of 3.2 km/s. After shock treatment, the sample was recovered and characterized via various techniques, such as x-ray diffraction, Raman, scanning electron microscope, transmission electron microscope, and ultraviolet-visible diffuse reflection spectrum analysis, to find the presence of La2Ti2O7 nanocrystalline powder with an average grain size of approximately 30 nm in the recovered samples with different yields. Moreover, the results further confirm that the high shock temperature and long ball milling treatment induce higher activation of precursors to improve the La2Ti2O7 content in the recovered samples. By adjusting the relative density of precursor and the ball milling period, pure La2Ti2O7 nanocrystalline powder was obtained. The formation mechanism of La2Ti2O7 was carefully illustrated. This study presents a new method to synthesize La2Ti2O7 nanocrystalline powder by detonation-driven flyer impact. [ABSTRACT FROM AUTHOR]

Glass-ceramics containing oriented Sr2TiSi2O8 fresnoite crystallites were explored for piezocatalysis induced dye degradation capability. The parent glass of the 2SrO–1TiO2–3.3SiO2–0.2K2O–0.1Al2O3 (components are indicated by molar ratio) composition was manufactured using the well-known melt-quench method. The two-parent glass samples were separately heat-treated at the crystallization temperature of 850 and 1000 °C/3 h for obtaining varying amounts of Sr2TiSi2O8 crystallites in the glass matrix. The presence of Sr2TiSi2O8 crystallites on the surface of both glass-ceramics was confirmed using x-ray diffraction. The micrographs obtained from the scanning electron microscope evidenced the presence of more numbers along with the greater sizes of Sr2TiSi2O8 crystallites on the surface of the 1000 °C/3 h sample in comparison to the 850 °C/3 h sample. These glass-ceramics were piezoelectric, as the 1000 °C/3 h sample showed a maximum d33 value of 10 pC/N after sufficient polishing. This non-ferroelectric piezoelectricity was induced due to the oriented crystallization of Sr2TiSi2O8 crystallites in the glass-ceramics. The transparency was decreased in this order: parent glass>850 °C/3 h sample>1000 °C/3 h sample. During the piezocatalytic dye degradation experiment, the degradation of methylene blue dye was found to be 71% and 83% within 300 min under ultrasonication energy using 850 and 1000 °C/3 h glass-ceramics, respectively. The hydroxyl radical ( OH ˙ ) was identified as the main active species behind the piezocatalytic dye degradation using glass-ceramics. Hence, this work showed that glass-ceramics can be used for the water-cleaning application using vibrational energy. [ABSTRACT FROM AUTHOR]

The ferroelectric Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZTO) ceramic particles were immobilized in a polymer matrix of polyvinylidene difluoride (PVDF) in order to fabricate flexible and stable composite films for the treatment of water using the piezocatalysis process. The content of BCZTO in BCZTO/PVDF composite films was 0, 5, and 10 wt. % of PVDF. The presence of the BCZTO phase in PVDF composites was confirmed using x-ray diffraction, Raman spectroscopy, and a scanning electron microscope. Piezocatalytic activity of BCZTO/PVDF composite films was investigated by monitoring the degradation of various organic dyes, pharmaceuticals, and bacteria present in the water. The highest values of dye degradation were achieved in 10 wt. % BCZTO/PVDF composite films, where the model dyes named methylene blue, Rhodamine B, and methyl orange dyes were degraded by ∼91%, ∼86%, and 90% after the sonication for 180 min, respectively. The dye degradation performance using piezocatalysis was found to be repeatable and consistent for up to five cycles. Hydroxyl radical (⋅OH) was identified to be the main reactive species behind piezocatalytic dye degradation. An increment in dye degradation performance was observed with an increment in the power of the ultrasonicator during piezocatalysis. In addition, 10 wt. % BCZTO/PVDF composite films displayed 59% and 50% degradation of pharmaceutical antibiotics named tetracycline and ciprofloxacin, respectively, within 180 min of sonication, respectively. Also, more than 99.99% E. coli bacteria were inactivated using 10 wt. % BCZTO/PVDF composite films under 180 min of sonication treatment and showed a bacterial log reduction of 3.4. These promising results indicate the 10 wt. % BCZTO/PVDF composite film as a potential candidate for the treatment of water using piezocatalysis technology. [ABSTRACT FROM AUTHOR]

In this study, we demonstrate an enhancement of the measured spin Seebeck coefficient in Fe3O4/Pt bilayer films due to an increase in Fe nanodroplets formed by pulsed laser deposition. Four bilayer films were deposited at the same time from a highly textured target, resulting in a general increase in droplet formation that was confirmed to be Fe rich by scanning electron microscope and transmission electron microscope-dispersive x-ray spectroscopy. Of these four films, there were two distinct groupings with differing density of α-Fe droplets, where the bilayer with higher droplet density exhibited a 64% increase in the measured spin Seebeck coefficient from 38 to 63 nV m/W. [ABSTRACT FROM AUTHOR]

To study the effect of aging on the low-temperature crack resistance of fiber asphalt mixes, three kinds of fibers (lignin fiber, polyester fiber, and basalt fiber) were dry blended into AC-13 asphalt mixes to prepare unaged, asphalt aged (that is, the original asphalt material is subjected to aging treatment), short-term aged, and long-term aged fiber reinforced asphalt mixes. Semicircular bending (SCB) tests and scanning electron microscopy tests were used to analyze and study the effects of aging time and fiber type on the low-temperature properties of asphalt mixtures at an ambient temperature of −5 °C. The SCB test results indicated that: with the deepening of aging, the fracture toughness and fracture energy of the fiber asphalt mixture specimens will tend to decrease, and the aging of the original asphalt has a greater impact on the specimens without fiber; there was great variability in the effect of lignin fibers on the crack resistance of the mix, but it could be a good promoter in unaged asphalt mixes; polyester fiber is the material of choice for improving low-temperature crack resistance in long-term aging pavements; the incorporation of basalt fiber greatly enhances the crack resistance of asphalt mixes and is an excellent material for improving aging asphalt mixes. It is clearly seen by the scanning electron microscope test that with the deepening of aging, the adhesion of asphalt and aggregate gradually deteriorates, and even more so, there is the phenomenon of fine aggregate flaking, and the fiber cannot play an excellent role in reinforcement and crack resistance. [ABSTRACT FROM AUTHOR]

The hole expansion ratio (HER) test is used to determine the stretch-flangeability of materials. Standard HER tests are performed on specimens sized a few tens of centimeters, termed macro-HER tests. This leads to significant material wastage due to the destructive nature of the tests. No information at the microstructure length scale is obtained, and the results suffer from user uncertainty in the identification of the through-thickness crack. This paper presents a novel miniature HER setup (termed micro-HER test), in which miniature specimens are tested inside a scanning electron microscope (SEM). The deformation is imaged from the top using the secondary electron detector installed in the SEM, coupled with the digital image correlation (DIC) technique, allowing for measurement of full field strains at the microstructural scale and identifying their deformation/fracture mechanisms. As a case study, six different steel grades were tested to measure their micro-HER values and compare them with the corresponding macro-HER values. The latter were found to be higher for the more ductile grades of steel. Late detection of through-thickness cracks and thicker samples leading to a higher volume of plastic deformation could contribute to this overestimation of values in macro-HER tests. DIC results from micro-HER tests on a ferrite–martensite (10% volume fraction) dual-phase steel showed high magnitudes of strain localization at the ferrite–martensite interfacial regions, indicating that such interfaces might be hotspots for failure under triaxial stress states. The challenges and errors associated with the measurements are also discussed. [ABSTRACT FROM AUTHOR]

Electric Field Assisted Sintering (EFAS, also referred to as spark plasma sintering) is a powerful technology for the consolidation of powder materials. The high heating rate during the sintering process is critical for minimizing energy consumption, but it can also cause microstructure heterogeneities in sintered parts, such as spatially varied porosity. The examination of localized porosity usually requires the use of a scanning electron microscope with a carefully prepared surface. In this paper, photothermal radiometry is used to measure local thermal diffusivity and extract localized porosity of EFAS-sintered parts by using a percolation-threshold model. Applying this approach, we identified the radial position-dependent porosity variation in EFAS parts, which is likely formed due to the large temperature gradient during the sintering process. This approach has a unique advantage because it can measure samples with minimal or no surface preparation, enabling the possibility of in situ characterization in EFAS with proper system modification. Necessary modifications on the measurement approach for EFAS deployment and in situ characterization are also discussed. [ABSTRACT FROM AUTHOR]

In this study, Au nanoparticles were introduced to functionalize hydrogen-terminated diamond (H-diamond) to optimize surface modification and improve the performance of diamond sensor for trace detection of SARS-CoV-2 N-protein. The Au nanoparticles were obtained by an electron beam evaporation system and annealing. Atom force microscope and scanning electron microscope were utilized to characterize the structure, morphology, and distribution of fabricated Au nanoparticles. The concentration of SARS-CoV-2 N-protein was determined by the investigation of transfer characteristics of a diamond solution gate field effect transistor. Sensitivity of this sensor was obtained as 27.43 mV/lg (N-protein concentration), which was higher than a regular H-diamond sensor. In addition, it had a wider linear detection range of 10−15–10−5 mg/ml and a lower limit of detection of 10−15 mg/ml. Accordingly, the detection performance of diamond sensor has been greatly improved due to the functionalization of Au nanoparticles. [ABSTRACT FROM AUTHOR]

The components and pore structure of shale are complex due to the heterogeneous distribution of organic matter and the complex distributions of the minerals. The digital core, possessing the advantages of being economical and reusable, can be widely used to directly characterize the three dimensional (3D) micro-pore structure and to numerically simulate its physical properties. During construction of a digital shale core, it is a challenge to solve the multicomponent segmentation for the digital shale core, the contradiction between the sample size and image resolution, and the identification of the pore types in the 3D pore space. Therefore, an automatic workflow based on the gray gradient-maximum entropy-3D morphology was developed. The gray gradient-maximum entropy algorithm was used to segment each sub-image of focused ion beam scanning electron microscope images to generate segmented images. On this basis, the pore size distribution was optimized via 3D morphological erosion. Based on the concept of pore clusters, the organic and inorganic pores were identified using the 3D morphological method for the first time. The construction of a multicomponent digital shale core was realized. The 3D micro-pore structure of the organic and inorganic pores was characterized by pore connectivity, heterogeneity, and pore size distribution. The accuracy of the proposed method was verified using low-temperature N2 adsorption experiment data. The results of this study provide new insight into the multicomponent digital shale core construction and lay the foundation for the characterization of the petrophysical properties and micro-/nano-scale fluid flow simulations of shale. [ABSTRACT FROM AUTHOR]

Nanobubble formation by radiolysis of water has been observed in a transmission electron microscope using very high electron dose ratios. Here, surface micro- and nanobubbles were formed in situ in a conventional scanning electron microscope at relatively low magnifications of ∼1000. Bubble formation was observed at a low dose ratio of 1.3 × 1011 electrons/cm2 s, which is 5–7 orders of magnitude smaller than in previous studies using transmission electron microscopes. Our observations suggest that the pressure in the liquid cell is one of the important factors for the formation of bubbles. The contact angles obtained by direct observation of 69 bubbles were 50°–90°, with an average of 69°. These angles are much larger than those of the bubbles previously observed using an atomic force microscope. Despite the large contact angles (and large Laplace pressures), the micro- and nanobubble lifetimes were at least three days. Scanning electron microscopy shows potential as an important analytical tool for micro- and nanobubbles. [ABSTRACT FROM AUTHOR]

Nanoparticles of manganese cobalt oxide (MnCo2O4) have been prepared with the hydrothermal method, while nanocomposites of MnCo2O4/polypyrrole (MCO/PPy) have been prepared by dispersing MCO nanoparticles in the PPy matrix by an in situ chemical polymerization method. MCO/PPy nanocomposites' structural characterizations were made by x-ray diffraction (XRD) and field-emission scanning electron microscope (FESEM). XRD and FESEM analyses give evidence that MCO nanoparticles are dispersed uniformly, and there is an effect on crystallinity and particle size. The observed shift in the stretching vibrations of Fourier transform infrared spectra for MCO/PPy nanocomposites confirms the interaction between MCO nanoparticles and PPy. Furthermore, the temperature-dependent (300–453 K) DC conductivity measurements of MCO/PPy nanocomposites depict the presence of different conduction mechanisms. The conductivity data are well fitted by the 3D variable range hopping (3D-VRH) model and the band conduction model at low and high temperatures. The characteristic temperature (T0) calculated from the 3D-VRH and the activation energy (Ea) calculated from the band conduction model support the observed highest conductivity for the 10 wt. % MCO/PPy nanocomposite. [ABSTRACT FROM AUTHOR]

Reported here is a comparison of the magnetic, magnetocaloric, and dielectric properties of 50% iron substituted GdCrO3 (GdFe0.5Cr0.5O3) bulk pellet and 960 nm thick film of GdFe0.5Cr0.5O3 (GFCO). The 960 nm film was synthesized on a platinized-silicon substrate by chemical solution deposition and spin-coating methods. The X-ray diffraction scans of the bulk sample and the film as well as the morphology of the film as examined by the field-emission scanning electron microscope indicate phase-pure and polycrystalline nature of these samples. X-ray photoelectron spectroscopy was used to determine the valence states of Gd, Fe, and Cr. The temperature dependence of the dielectric constant from 225 to 700 K shows peaks at TC = 525 K for the bulk and ∼450 K for the film due to ferroelectric to paraelectric transitions, since electric polarization vs electric field hysteresis loops are observed at room temperature. The dielectric studies in the bulk GFCO for T > TC indicate a relaxor-like behavior. The measurements of the magnetization (M) of the samples as a function of temperature (5–350 K) and magnetic field (H) up to 7 T (=70 kOe) depict hysteresis behavior at low temperatures due to the canted antiferromagnetic order of Fe3+/Cr3+ below the Néel temperature of ∼275 K. The M vs H isotherms at various temperatures are used to determine and compare the magnetic entropy change (−ΔS) and relative cooling power (RCP) of the two samples, yielding (−ΔS) = 30.7 J/kg K (18.8 J/kg K) and RCP = 566.5 J/kg (375 J/kg) for the bulk (960 nm film) samples of GFCO at 7 K and 7 T, respectively. The plot of RCP vs T shows that magnetic cooling for this system is most effective for T < 30 K. Comparatively smaller magnitudes of (−ΔS) and RCP for the film vis-à-vis the bulk sample of GFCO scale with its reduced magnetization. This suggests that further improvements in the quality of the films are needed to improve their magnetization and hence their magnetocaloric properties, possibly making them useful for on-chip cooling in miniaturized devices. [ABSTRACT FROM AUTHOR]

The construction of heterojunctions has attracted considerable attention among the various strategies of water-splitting for hydrogen evolution due to their band structure advantages. In this research, we combined chemical vapor deposition and pulsed laser deposition to fabricate MoS2/g-C3N4 heterojunction films on indium-tin oxide glass substrates, and we studied the photoelectrochemical (PEC) performance. The x-ray diffraction, x-ray photoelectron spectroscopy (XPS), and scanning electron microscope characterizations suggested the successful preparation of MoS2/g-C3N4 heterojunction films. In particular, the shifts of the peak positions in the XPS spectra indicated the formation of a strong interaction between the g-C3N4 and MoS2 films. After depositing MoS2 on the g-C3N4 film, the visible-light absorption was enhanced and broadened, the electrical conductivity improved, and the intensity of the photoluminescence peak decreased. As a result, the greater generation, faster transport, and lower recombination rate of electrons and holes caused the heterojunction films to show higher PEC performance. More importantly, the obtained MoS2/g-C3N4 film was confirmed to be an n–n type heterojunction and to have a typical type-II band structure, which could indeed suppress the recombination and promote the separation, transfer, and transport of photogenerated electron–holes. Finally, the obtained MoS2/g-C3N4 film successfully achieved the overall water-splitting and the H2 evolution rate when the visible-light radiation reached 252 µmol/h. [ABSTRACT FROM AUTHOR]

Al-doped ZnO (AZO) is a promising candidate as a transparent conducting electrode. However, the electrical properties of AZO deteriorate greatly after exposing it to excessive heat. This limits the applications of AZO in devices that experience a demanding operation environment. It has been shown that a ZnO cap layer with proper morphology is capable to dramatically improve the thermal stability of AZO. However, the detailed mechanism is not yet clear. A comparison study of the electrical properties of AZO with a ZnO cap layer prepared by magnetron sputtering (MS) at low substrate temperature (70 °C) and chemical vapor deposition (CVD) at high substrate temperature (600 °C) indicates that MS-prepared ZnO is much less effective in protecting AZO from an oxidizing environment under elevated temperature than the CVD-prepared ZnO. The morphology and crystal structures of two types of ZnO/AZO, investigated by a scanning electron microscope and x-ray diffraction, are relatively similar, whereas the atomic structures (e.g., defects) revealed by Raman spectroscopy are rather different. The results suggest that it is difficult to improve the thermal stability of electrical properties of AZO without a proper restructuring process and a ZnO cap layer that could sacrifice its own structural order. The discoveries offer a novel approach to improve the performance of other transparent conducting oxides. [ABSTRACT FROM AUTHOR]

Red phosphors based on BaLaLiTeO6 doped with Eu3+ were prepared by high temperature solid state method. The XRD patterns for the representative samples revealed its single phase structure and the scanning electron microscopes were studied to reveal the morphology and homogeneous distribution of particles with different size. In addition, the density of states and partial density of states of each element revealed that Ba-O and La-O groups are the main factors that determine the optical properties of the BaLaLiTeO6. When emitted by 394 nm near-ultraviolet, all the samples emit bright red light near 618 nm because of 5D0 → 7F2 transition of Eu3+ ions. The optimal doping concentration of Eu3+ in BaLaLiTeO6 is 0.20 and the mechanism of concentration quenching is the dipole-quadrupole interaction. Besides, the temperature-dependent emission spectra of BaLaLiTeO6:0.2Eu3+ red sample were studied systematically and the thermal activation energy of the sample was 0.30 eV, indicating its good thermal stability. The lifetime of Eu3+ ions is in the millisecond level and the CIE chromaticity coordinate of BaLaLiTeO6:0.2Eu3+ is (0.6436, 0.3535) with a high color purity of 99.4%, which is close to the standard of red chromaticity. To sum up, the BaLaLiTeO6:Eu3+ phosphors are the hopeful red component applied in the white light illumination. [ABSTRACT FROM AUTHOR]