In situ observation of nanograin rotation and deformation in nacre

Nacre is a natural nanocomposite material with superior mechanical strength and toughness. What roles do the nanoscale structures play in the inelasticity and toughening of nacre? Can we learn from this to produce nacre-like nanocomposites? Here we report in situ dynamic atomic force microscope observations of nacre with aragonite nanograins (nanoparticles) of an average grain size of 32 nm, which show that nanograin rotation and deformation are the two prominent mechanisms contributing to energy dissipation in nacre. The biopolymer spacing between the nanograins facilitates the grain rotation process. The aragonite nanograins in nacre are not brittle but deformable.     

In situ TEM observation of spontaneous alloying in nanometer-sized particles

The alloying behaviour in nanometer (nm)-sized particles was studied by transmission electron microscopy (TEM). When solute atoms are vapour-deposited onto nm-sized particles at room temperature, rapid dissolution of solute atoms into particles occur, and solid solution or compound particles are successfully formed. Such spontaneous alloying occurs even between nm-sized particles of different elements. Our results can be summarized as: (i) spontaneous alloying takes place via a solid-state process, (ii) spontaneous alloying becomes more difficult with increasing particle size, (iii) spontaneous alloying is not an artifact originating from the temperature rise in particles which might be induced by heat of condensation and (iv) remarkable enhancement of solubility is observed in nm-sized compound particles.     

In situ observation of electrode melting in multilayer ceramic capacitors

In the usage of multilayer ceramic capacitors, we are concerned with the intrinsic dielectric properties of the ceramic and its long-term stability/reliability under external stresses in service conditions. Of equal importance to long-term reliability is the short-term survivability under current (power)-surge conditions. It differs from the ability to withstand voltage surge, which is determined by the dielectric strength of the ceramic. In this paper, we present some observations on sectioned and polished multilayer ceramic capacitors, which were subjected to controlled current-surge test conditions. Capacitors from several vendors were examined. The samples were examinedin situ under an optical microscope while current pulses of varying magnitude were applied at a constant voltage. Subsequently some samples were further examined by scanning electron microscopy. The failure mechanism appeared to be the heat-induced local melting of internal electrodes, which might then lead to a blow-out or charring of the capacitor. In less severe cases, we observed local melting and crack formation in the surrounding ceramic as well. The primary change in capacitor properties was in the degradation of the insulation resistance. In severe cases, this also led to an increase in the dissipation factor.     

In situ observation of oscillatory growth of bismuth nanoparticles

We study the growth of Bi nanoparticles in an engineered precursor-scarce environment in a liquid cell at an elevated temperature (180 °C) using transmission electron microscopy. Observation reveals dynamics of oscillatory growth of individual nanoparticles, pairwise Ostwald ripening and anti-Ostwald ripening and a global collective oscillation. The experimental results suggest a mass-transport zone is present around each particle, which couples to the observed growth kinetics. This study shed light on a new route for system engineering to reverse particle coursing by Ostwald ripening.     

In situ TEM observations of irradiation-induced phase change in tungsten

Electron irradiation-induced phase change in tungsten was examined by in situ high resolution electron microscopy. In samples prepared by a chemical polishing technique using a NaOH aqueous solution, an α to β phase change was induced under 200 keV electron irradiation at 773 K. It is suggested that sodium atoms deposited on the tungsten sample from the solution, rather than oxygen atoms, may play an essential catalytic role in inducing the phase change.     

In situ observation of cement particle growth during setting

The evolution of the cement paste microstructure is a complex phenomenon, which governs the setting of concrete. During setting, cement particles tend to flocculate and agglomerate due to their surface charges, attraction forces and variety of other reasons. However, it is still unclear how these developments in cement paste microstructure influence the setting of concrete. In order to better understanding the correlation between cement paste microstructure development and corresponding concrete behavior during setting, in situ observations on cement particles behaviors are essential. In this study, in situ observations on microstructure development of fresh pastes were made on three different cement pastes by using a newly developed Quantomix WETSEM? capsuling system in a conventional scanning electron microscope. Further, by employing image analysis techniques on the captured images, microstructure changes of these cement pastes were investigated quantitatively. During the study single and multiple particle growth, hydration rate of different cement particles, and total solids growth in association with various solid concentrations and corresponding heat of hydration were studied quantitatively and as well as qualitatively. The purpose of this quantitative study is to investigate the feasibility of using such a new technology to evaluate the factors influencing the cement paste microstructure evolutions during setting.     

Simulations and analysis of self-assembly of CdTe nanoparticles into wires and sheets

Recent experiments have reported the self-assembly of TGA- and DMAET-stabilized CdTe nanoparticles (NPs) into wires and sheets, respectively, depending upon the stabilizer used. We develop a mesoscale model based on quantum mechanical calculations and perform Monte Carlo simulations of these NPs to elucidate the conditions under which these two structures will form. We show that consideration of NP shape, directional attraction, and electrostatic interactions is key to determining the anisotropy of the NP-NP interaction and final self-assembled structures.     

In situ observation of reversible rippling in multi-walled boron nitride nanotubes

The recent observation of high flexibility in buckled boron nitride nanotubes (BNNTs) contradicts the pre-existing belief about BN nanotube brittleness due to the partially ionic character of bonding between the B and N atoms. However, the underlying mechanisms and relationships within the nanotube remained unexplored. This study reports for the first time the buckling mechanism in multi-walled BNNTs upon severe mechanical deformation. Individual BNNTs were deformed inside a transmission electron microscope (TEM) equipped with an in situ atomic force microscopy holder. High-resolution TEM images revealed that bent BNNTs form multiple rippling upon buckling. The critical strain to form the first ripple was measured as 4.1% and the buckling process was reversible up to 26% strain. As opposed to carbon nanotubes, the BNNTs buckled into V-shaped ripples rather than smooth wavy shapes. The rippling wavelength was quantified in terms of the outer diameter and thickness of the nanotubes. The BNNTs showed a larger rippling wavelength compared to that of CNTs with the same number of walls. This difference was explained by the tendency of BN structures to reduce the number of thermodynamically unfavorable B-B and N-N bonds at the sharp corners in the rippling regions. The BNNTs' structure also exhibited a higher fracture strain compared to their counterpart.     

In situ SEM observation of column-like and foam-like CNT array nanoindentation

Quantitative nanoindentation of nominally 7.5 and 600 μm tall vertically aligned carbon nanotube (VACNT) arrays is observed in situ within an SEM chamber. The 7.5 μm array consists of highly aligned and weakly interacting CNTs and deflects similarly to classically defined cylindrical columns, with deformation geometry and critical buckling force well estimated using the Euler-Bernoulli theory. The 600 μm array has a highly entangled foam-like morphology and exhibits sequential buckle formation upon loading, with a buckle first forming near the array bottom at approximately 2% strain, followed by accumulating coordinated buckling at the top surface at strains exceeding 5%.     

In situ observation and measurement of the SAW thin-film acoustoelectric effect

The thin-film acoustoelectric effect in SAW devices describes the interaction of electrical energy between a SAW in a piezoelectric medium and a thin film in the wave's propagation path. The real-time observation of the thin-film acoustoelectric interaction is useful in the design and characterization of SAW sensors (i.e., temperature, humidity, viscosity, voltage, current, Hall effects, etc.). An in situ test fixture was designed to be mechanically, thermally, and electrically stable. Data acquisition software and an electron beam evaporation system were configured for real-time thin-film characterization during film growth. Data have been observed for more than 20 SAW devices and over a wide range of frequencies (i.e., 62 MHz to 1 GHz). The results suggest that the use of the in situ procedure yielded good agreement between theoretical predictions and the measured data, which demonstrates a method for the characterization of a SAW H(2)-gas sensor in real-time.     

In situ observation of electrochemical Ostwald ripening during sodium deposition

Sodium(Na)metal batteries(SMBs)using Na anode are potential"beyond lithium"electrochemical technology for future energy storage applications.However,uncontrolla...     

In situ observation of quasimelting of diamond and reversible graphite-diamond phase transformations

Because of technique difficulties in achieving the extreme high-pressure and high-temperature (HPHT) simultaneously, direct observation of the structures of carbon at extreme HPHT conditions has not been possible. Banhart and Ajayan discovered remarkably that carbon onions can act as nanoscopic pressure cells to generate high pressures. By heating carbon onions to approximately 700 degrees C and under electron beam irradiation, the graphite-to-diamond transformation was observed in situ by transmission electron microscopy (TEM). However, the highest achievable temperature in a TEM heating holder is less than 1000 degrees C. Here we report that, by using carbon nanotubes as heaters and carbon onions as high-pressure cells, temperatures higher than 2000 degrees C and pressures higher than 40 GPa were achieved simultaneously in carbon onions. At such HPHT conditions and facilitated by electron beam irradiation, the diamond formed in the carbon onion cores frequently changed its shape, size, orientation, and internal structure and moved like a fluid, implying that it was in a quasimelting state. The fluctuation between the solid phase of diamond and the fluid/amorphous phase of diamond-like carbon, and the changes of the shape, size, and orientation of the solid diamond, were attributed to the dynamic crystallization of diamond crystal from the quasimolten state and the dynamic graphite-diamond phase transformations. Our discovery offers unprecedented opportunities to studying the nanostructures of carbon at extreme conditions in situ and at an atomic scale.     

In situ observation of synthesized nanoparticles in ultra-dilute aerosols via X-ray scattering

In-air epitaxy of nanostructures (Aerotaxy) has recently emerged as a viable route for fast, large-scale production. In this study, we use small-angle X-ray scattering to perform direct in-flight characterizations of the first step of this process, i.e., the engineered formation of Au and Pt aerosol nanoparticles by spark generation in a flow of N₂ gas. This represents a particular challenge for characterization because the particle density can be extremely low in controlled production. The particles produced are examined during production at operational pressures close to atmospheric conditions and exhibit a lognormal size distribution ranging from 5–100 nm. The Au and Pt particle production and detection are compared. We observe and characterize the nanoparticles at different stages of synthesis and extract the corresponding dominant physical properties, including the average particle diameter and sphericity, as influenced by particle sintering and the presence of aggregates. We observe highly sorted and sintered spherical Au nanoparticles at ultra-dilute concentrations (< 5 × 10⁵ particles/cm³) corresponding to a volume fraction below 3 × 10^–10, which is orders of magnitude below that of previously measured aerosols. We independently confirm an average particle radius of 25 nm via Guinier and Kratky plot analysis. Our study indicates that with high-intensity synchrotron beams and careful consideration of background removal, size and shape information can be obtained for extremely low particle concentrations with industrially relevant narrow size distributions.

     

In situ observation of temperature-dependent atomistic and mesoscale oxidation mechanisms of aluminum nanoparticles

Oxidation is a universal process causing metals’ corrosion and degradation. While intensive researches have been conducted for decades, the detailed atomistic and mesoscale mechanisms of metal oxidation are still not well understood. Here using in situ environmental transmission electron microscopy (E-TEM) with atomic resolution, we revealed systematically the oxidation mechanisms of aluminum from ambient temperature to ~ 600 °C. It was found that an amorphous oxide layer formed readily once Al was exposed to air at room temperature. At ~ 150 °C, triangle-shaped Al2O3 lamellas grew selectively on gas/solid (oxygen/amorphous oxide layer) interface, however, the thickness of the oxide layer slowly increased mainly due to the inward diffusion of oxygen. As the temperature further increased, partial amorphous-to-crystallization transition was observed on the amorphous oxide film, resulting in the formation of highly dense nano-cracks in the oxide layer. At ~ 600 °C, fast oxidation process was observed. Lamellas grew into terraces on the oxide/gas interface, indicating that the high temperature oxidation is controlled by the outward diffusion of Al. Single or double/multi-layers of oxide nucleated at the corners of the terraces, forming dense γ’-Al₂O₃, which is a metastable oxide structure but may be stabilized at nanoscale.

     

In situ speckle observation of Tyrano/BMAS composites in shear strength measurements

Strain profiles of specimens during interlaminar shear strength tests, short beam and double-notched compression, were measured by a speckle interference method using Tyrano^TR-related fiber-reinforced BaO–MgO–Al₂O₃–SiO₂ glass matrix composites with different surface finished fibers. The speckle interference method could detect changes in shear strain during the tests before the initiation of crack(s). Crack initiation could be detected earlier/easier by the speckle interference method than by video monitoring in both tests. Surface finish affected the shear strain profiles in the specimens. Sliding at the interface seemed to be detected in the composites reinforced with Tyrano fiber having a carbon layer. The speckle interference method is useful for measuring strains over wide areas of the specimens.     

In vitro and in vivo toxicity of CdTe nanoparticles

Cadmium telluride (CdTe) nanoparticles exhibit strong and stable fluorescence that is attractive for many applications such as biological probing and solid state lighting. The evaluation of nanoparticle toxicity is important for realizing these practical applications. However, no systematic studies of CdTe nanoparticle toxicity have been reported. We investigated and compared the size- and concentration-dependent cytotoxicity of CdTe nanoparticles in human hepatoma HepG2 cells using the MTT assay. CdTe nanoparticles elicited cytotoxicity in a concentration- and size-dependent manner, with smaller-sized particles exhibiting somewhat higher potency. Lesser cytotoxicity of partially purified CdTe-Red particles (following methanol precipitation and resuspension) suggested that free cadmium ions may contribute to cytotoxicity. We also evaluated the acute toxicity of CdTe-Red particles following intravenous exposure in male rats (2 micromol/kg). Few signs of functional toxicity or clinical (urinary or blood) changes were noted. Interestingly, motor activity was transiently reduced (2 hours after treatment) and then significantly increased at a later timepoint (24 hours after dosing). These studies provide a framework for further characterizing the in vitro and in vivo toxic potential of different types of CdTe nanoparticles and suggest that the nervous system may be targeted by these nanoparticles under some conditions.