This article introduces the use of in situ high-resolution transmission electron microscopy (HRTEM) techniques for the study and development of nanomaterials and their properties. Specifically, it shows how in situ HRTEM (and TEM) can be used to understand diverse phenomena at the nanoscale, such as the behavior of alloy phase formation in isolated nanometer-sized particles, the mechanical and transport properties of carbon nanotubes and nanowires, and the dynamic behavior of interphase boundaries at the atomic level. Current limitations and future potential advances in in situ HRTEM of nanomaterials are also discussed.

Crystalline tungsten suboxide nanowires were grown on silicon substrates by thermal evaporation of tungsten powder in a flow of argon gas without any catalyst. With different growth temperatures, two kinds of tungsten suboxide nanowires (W18O49 and W20O58) were obtained. The structures, morphologies, and compositions of these two nanowires were characterized by scanning electron microscopy (SEM), electron probe microanalyzer (EPMA), x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), x-ray photoelectron spectroscopy (XPS), and Raman techniques. The results show that XRD and TEM are not good characterization techniques for identifying W18O49 and W20O58 nanowires; however, Raman spectroscopy (RS) is a powerful tool to distinguish the difference between them. This is due to the notable molecular bond contributing to the vibrational frequency.

The electrical conductivities of Cu–3at.%Ti alloys aged at 773 K in a hydrogen atmosphere were investigated as a function of aging time. The electrical conductivity of the quenched alloy, 5.2% International Annealed Copper Standard (IACS), improved with aging time to 66% IACS after 48 h. This was mainly caused by the dilution of the Cu–Ti solid solution in the alloy, which is supported by the fact that the lattice parameter of the face-centered cubic (fcc) phase approaches that of pure Cu by aging in a hydrogen atmosphere.

The electric-pulse–induced resistance switching of the Ag–La0.7Ca03MnO3(LCMO)–Pt heterostructures was studied. The multilevel resistance switching (MLRS), in which several resistance states can be obtained, was observed in the switching from high to low resistance state (HRS → LRS) by applying electric pulse with various pulse voltages. The threshold pulse voltages of MLRS are related to the initial resistance values as well as the switching directions. On the other hand, the resistance switching behavior from low to high resistance states (LRS → HRS) shows unobvious MLRS. According to the resistance switching behavior in serial and parallel modes, MLRS was explained by the parallel effect of multifilament forming/rupture in the Ag–LCMO interface layer. The present results suggest a possible application of Ag–LCMO–Pt heterostructures as multilevel memory devices.

Magnesium alloys are potential biodegradable biomaterials in hard tissue implants. However, the fast degradation rate in the biological environment has hampered widespread applications. We propose to use a ZrO2 coating in conjunction with a Zr transition layer to improve the corrosion resistance of AZ91 magnesium alloy. X-ray photoelectron spectroscopy discloses that the coating is composed of ZrO2. The Vickers hardness measurement demonstrates that the surface hardness of the alloy is significantly enhanced. The electrochemical behavior of the coated sample is systematically evaluated by means of potentiodynamic polarization, open-circuit potential evolution, and electrochemical impedance spectroscopy. The electrochemical results indicate that the corrosion resistance of the coated alloy is enhanced significantly, and the electrode-controlled processes in a coated alloy–solution system are discussed.

Hydrogenation and dehydrogenation of metal hydrides are of great interest because of their potential in on-board applications for hydrogen vehicles. This paper aims to study hydrogen diffusion in metal hydrides, which is generally considered to be a controlling factor of hydrogenation/dehydrogenation. The present work first calculated temperature-dependent hydrogen diffusion coefficients by a theoretical model incorporated with experimental data in a Mg-based system and accordingly the activation energy. The grain size effect on diffusion in nanoscale was also investigated.

We have studied grain-growth and texture development in polycrystalline lithium fluoride thin films using dark-field transmission electron microscopy. We demonstrate that we can isolate the size distribution of 〈111〉 surface normal grains from the overall size distribution, based on simple and plausible assumptions about the texture. The {111} texture formation and surface morphology were also observed by x-ray diffraction and atomic force microscopy, respectively. The grain-size distributions become clearly bimodal as the annealing time increases, and we deduce that the short-time size distributions are also a sum of two overlapping peaks. The smaller grain-size peak in the distribution corresponds to the {111}-oriented grains, which do not grow significantly, while all other grains increase in size with annealing time. A novel feature of the LiF films is that the {111} texture component strengthens with annealing, despite the absence of growth for these grains, through the continued nucleation of new grains.

The relationship between the preparation conditions of MgB2 powder and the performance of the critical current density (Jc) of an applied magnetic field (B) of the final ex situ tape produced from it was investigated. The pelletizing pressure of the precursor is crucially important for improving the Jc-B performance of ex situ tape. The higher the pressure, the greater the resulting Jc of the ex situ MgB2 tape. We have shown that the pelletizing pressure used for the precursor mixture during the powder preparation process affects the phases formed in the MgB2. On the other hand, the heating time used is effective in changing the slope of the Jc-B curve of the final tape. This is thought to be due to a change in the crystallinity of the prepared MgB2 powder. The experimental data gathered here will become the basis for investigating the establishment of a guideline for preparing the starting powder used for the manufacture of ex situ MgB2 tape.

Giant “pop-in” displacements are observed in crystalline silicon and germanium during high-load nanoindentation with a spherical diamond tip. These events are consistent with material removal triggered by lateral cracking during loading, which poses a hazard to microelectromechanical systems (MEMS) operation. We examine the scaling of the pop-in displacements as a function of peak indentation load and demonstrate a correlation with the depth of the plastic contact zone. We argue that giant pop-ins may occur in a broad range of highly brittle materials.

The spatial resolution of the transmission electron microscope makes it an ideal environment in which to continuously track the real-time response of a system to an external stimulus and to discover and quantify the rate-limiting fundamental microscopic processes and mechanisms governing the macroscopic properties. Advances in instrumentation, stage design, recording media, computational power, and image manipulation software are providing new opportunities for not only observing the microscopic mechanisms but also measuring concurrently the macroscopic response. In this article, the capability of this technique as applied to mechanical properties of materials is highlighted.

We report the synthesis of Th1–xMnxO2 (x = 0, 0.001, 0.002, 0.004, and 0.01 wt%) nanoparticles by the urea combustion method using thorium nitrate gel followed by heat treatment at a higher temperature (T). The obtained Th1–xMnxO2 nanocrystals were characterized by x-ray diffraction (XRD), direct-current magnetization (M) measurements and electron paramagnetic resonance (EPR). XRD analysis revealed that Th1–xMnxO2 crystallizes in the cubic structure (Fm3m). M measurements showed ferromagnetic ordering at room temperature for Th0.99Mn0.01O2 samples annealed at 775 K. An intense and broad ferromagnetic resonance (FMR) having linewidth of ∼1200 G, was observed at relatively lower fields in the EPR spectra of Th0.99Mn0.01O2 samples annealed at 775 K, indicating the presence of a ferromagnetic phase at room temperature. EPR measurements were used to estimate the number of spins involved in the ferromagnetic ordering. Out of the total Mn present in Th0.99Mn0.01O2 samples, about 25% of the Mn2+ ions were found to be responsible for the ferromagnetic ordering. In addition to the FMR signal, a weak hyperfine sextet was observed at g = 2.0048 (55Mn, I = 5/2), which corresponds to the −1/2 ↔ +1/2 transition of Mn2+ ions, suggesting its presence at thorium sites (uncoupled spins). X-ray photoelectron spectra indicated that the manganese ions exist mainly as Mn2+, Mn3+, and Mn4+. The room-temperature ferromagnetism may be attributed to the coupling between these Mn2+ ions at thorium sites in ThO2 rather than due to the formation of any metastable secondary phases.

NiCrAlY coatings with and without CrN or CrON interlayer as diffusion barrier were deposited on superalloy DSM11 by arc ion plating (AIP). The oxidation performance of the coating systems was evaluated by isothermal oxidation tests at 1100 °C for 100 h. The element interdiffusion and oxidation behavior of the coating systems were described. It was found that the NiCrAlY coatings provided protective effect for the DSM11 substrate. However, serious interdiffusion between the coatings and substrate resulted in rapid degradation of the coatings. The addition of CrN or CrON interlayer between the coatings and substrate markedly decreased the interdiffusion. CrON interlayer performed better than CrN interlayer, which was attributed to the excellent diffusion barrier ability of Al2O3 layer formed in the interlayer at high temperature. Also, the NiCrAlY/CrON coating system exhibited more effective protection for DSM11 than the NiCrAlY/CrN coating system.

Uniaxial tensile tests were performed on Cu/Nb multilayered foils to investigate yield strength and grain boundary strengthening in the layered foils at room temperature and in fine-grained Nb at 600 °C. At room temperature, yielding in Cu/Nb multilayered foils is controlled by deformation in both layers, and grain boundary strengthening is observed with a Hall–Petch slope (kRT) of 198 ± 56 MPa·μm1/2 at a strain rate of 10−4 s−1. At 600 °C, yielding in Cu/Nb multilayered foils is controlled by deformation in just the Nb layers. Hall–Petch strengthening is observed over a range of strain rates, but the Hall–Petch slope decreases from 197 ± 71 MPa·μm1/2 for a strain rate of 10−4 s−1 to only 25 ± 40 MPa·μm1/2 for a strain rate of 10−6 s−1. The significant drop in the Hall–Petch slope for Nb with decreasing strain rate indicates a change in the controlling deformation mechanism from dislocation glide to dislocation creep.

Temperature is one of the most important factors affecting the state and behavior of materials. In situ heating transmission electron microscopy (TEM) is a powerful tool for understanding such temperature effects, and recently in situ heating TEM has made significant progress in terms of temperature available and resolution attained. This article briefly describes newly developed specimen-heating holders, which are useful in carrying out in situ heating TEM experiments. It then focuses on three main applications of these specimen holders: solid–solid reactions, solid–liquid reactions (including highresolution observation of a solid–liquid interface, size dependence of the melting temperatures of one-, two- and three-dimensionally reduced systems, size dependence of the contact angle of fine metal liquid, and wetting of Si with liquid Au or Al) and solid–gas reactions. These results illustrate the benefit of in situ heating TEM for providing fundamental information on temperature effects on materials.

Oxygen diffusivities in mullite/zirconia composites were measured by 18O/16O isotope exchange and secondary ion mass spectrometry. They exhibited a wide range of values from 10−21 to 10−10 m2/s at temperatures between 1000 and 1350 °C in the composites with 0 to 80 vol% zirconia. At a fixed temperature, oxygen diffusivities in high-zirconia composites were larger by at least eight orders of magnitude than those in low-zirconia composites. The percolation threshold occurred between 30 and 40 vol% zirconia, where oxygen diffusivities dramatically changed. There was a clear tendency of the activation energies of oxygen diffusion in composites to decrease with increasing zirconia contents. The large oxygen diffusivities in the high-zirconia composites were attributed to the interconnected channels of zirconia from the microstructural aspect.

The electron channeling contrast imaging (ECCI) technique was utilized to investigate atomic step morphologies and dislocation densities in 3C-SiC films grown by chemical vapor deposition (CVD) on Si (001) substrates. ECCI in this study was performed inside a commercial scanning electron microscope using an electron backscatter diffraction (EBSD) system equipped with forescatter diode detectors. This approach allowed simultaneous imaging of atomic steps, verified by atomic force microscopy, and dislocations at the film surface. EBSD analysis verified the orientation and monocrystalline quality of the 3C-SiC films. Dislocation densities in 3C-SiC films were measured locally using ECCI, with qualitative verification by x-ray diffraction. Differences in the dislocation density across a 50 mm diameter 3C-SiC film could be attributed to subtle variations during the carbonization process across the substrate surface.

In situ analyzes of gaseous atmospheres could be performed by FT-IR spectroscopy in order to study the corrosion reactions of actinides. Nevertheless experimental conditions and the nature of studied species have a strong effect on IR absorption laws. Thus a prior calibration of our set-up is required to obtain an accurate estimation of gas concentration. For this purpose, the behavior of several air pure gases has been investigated according to their concentration from IR spectra. Reproducible results revealed subsequent increases of the most significant peak areas with gas pressure and small deviations from Beer Lambert's law. This preliminary work allowed to determine precise absorption laws for each studied pure gas in our in situ experimental conditions. Besides our FT-IR set-up was well suitable to quantitative analysis of gaseous atmosphere during corrosion reactions. Finally the effect of foreign gas will be investigated through more complex air mixtures to obtain a complete calibration network.

Y2O3 thin films deposited by Ion Beam Sputtering (IBS) deposition technique exhibit a particular disordered microstructure. In order to obtain a better knowledge on phase transition mechanisms occurring during irradiation, thin films with different microstructures have been implanted with xenon ions at different energies and different doses. This work established two types of transition (cubic-amorphous or cubic-monoclinic) depending mainly on the ion energy with a possibility to control the damaging kinetic via the pre-existing oxygen disorder.