This study investigates thermally induced structural damages to amorphous plasma-enhanced chemical vapor deposition (PECVD) SiNx thin films at elevated temperatures, including chemical structure, microstructure, and physical integrity. The films were synthesized by means of PECVD method. Heating to elevated temperatures in air was found to cause multiple forms of chemical, structural, and physical damages. Chemically the films were found to oxidize and lose their nitrogen and hydrogen contents. Structurally the amorphous SiNx matrix was found to convert partially into SiO2 as a result of oxidation and to crystallize into Si3N4 crystallites. The physical damages include pinholes, circular “penny” cracks, random “dry mud” cracks, and spalling. The types of the damages were observed in different temperature regimes. The formation of the penny cracks is attributed to excessive compressive stresses created in the film by oxidation, which is associated with a large volume expansion. The formation of the random cracks is attributed to tensile stresses caused by crystallization, which is associated with a large volume contraction. Such damages limit the suitable application conditions for devices made of these films.

In the present work, Fe3O4 nanospheres, sponges, and urchins were prepared. Investigation of static magnetic and microwave electromagnetic (EM) characteristics of polymorphic Fe3O4 nanomaterials showed that morphology plays a crucial role in determining the resulting properties. Compared with Fe3O4 nanospheres and urchins, enhanced saturation magnetization and coercivity were observed in Fe3O4 sponges composed of ordered nanofibers. Enhancement of saturation magnetization and coercivity are associated with increased magnetic interactions and shape anisotropy, respectively. The Fe3O4 sponges and urchins produced reflection loss (RL) values of −35.77 dB at 8.0 GHz and −43.23 dB at 16.8 GHz, respectively. The excellent microwave absorption performance is ascribed to their unique morphologies. Such morphologies resulted in reinforced EM parameters and multiresonant behavior.

(Pb0.87−0.07xBa0.10+0.07x)La0.02(Zr0.7Sn0.15Ti0.15)O3 ceramics with 0 ≤ x ≤1 were prepared by conventional solid-state reaction process, and their dielectric and electric field–induced pyroelectric properties were systemically investigated. Compared with conventional pyroelectric materials, (Pb0.87−0.07xBa0.10+0.07x)La0.02(Zr0.7Sn0.15Ti0.15)O3 ceramics exhibited higher pyroelectric coefficient and figure of merit, which are beneficial for the development of pyroelectric devices. The specimens with x = 0.65 showed good pyroelectric properties for practical applications. When a 500 V/mm dc bias field was applied, they showed the maximum pyroelectric coefficient of 12,200 μC/m2K and the figure of merit of 106 × 10−5 Pa−0.5 at 45 °C, which are larger than those observed from conventional pyroelectric materials. Improvement of pyroelectric property is beneficial for the development of infrared detectors.

Following our recent report demonstrating the significance of the nearest-neighbor unlike atom-pair bond in metallic alloys, an equation for the energy of such a bond is presented in this study. The success of empirically derived Miedema’s equation in predicting the signs of the heats of formation of metallic alloys is explained. The negative contribution to the energy stems from the ionicity in the bond. The charge transfer on the bond, suggested by Pauling to establish electroneutrality, contributes the positive term which is quantified in this study. The value of Miedema’s empirically derived constant (Q/P)1/2 and the origin of the R/P term follow from the present model. It is shown that the energy of the atom-pair bond, calculated using the model, in the compounds of MgCu2 structure type are directly correlated to the experimental heats of formation of the compounds, and this fact enables the prediction of the heats of formation values for new compounds of the same structure type.

A Mn3O4/graphene hybrid material is fabricated using a facile and simple in-situ reduction process and shown to be a promising anode for lithium rechargeable batteries. The hybrid material retains a high capacity with a good cycle life of up to 990 mAh g−1 after 30 cycles. The excellent electrochemical performance is attributable to the unique nanostructure of the hybrid material. Highly crystalline Mn3O4 particles (20–30 nm) are uniformly dispersed on graphene whose high electronic conductivity and high surface area provide a conductive percolating network throughout the electrode in the hybrid material. The conductive graphene networks enhance an electron transfer in the electrode and promote the electrochemical activity of the crystalline Mn3O4.

The decomposition mechanism of block copolymer templates inside as-synthesized mesostructured solids has been systematically studied using solid-state 1H magic angle spinning nuclear magnetic resonance spectroscopy, thermogravimetric analysis, and high-vacuum Fourier transform infrared spectrometry. It is shown that there exists hydrogen-bonding interaction between silanols and block copolymers at the inorganic–organic interface in the self-assembled as-synthesized mesostructured solids, which plays an important role in protecting the surfactants against decomposition during the high-temperature hydrothermal treatment process. Increasing silanol concentration can enhance the hydrogen-bonding interaction and thus shows better “protection” effect. Moreover, the thermal decomposition of the block copolymer in as-synthesized mesostructured solids in air commences at higher temperatures compared with that in acidic solution or in air, providing further evidence in support of the silanol protection mechanism.

Even though the crystal structure of lead telluride (PbTe) has been extensively studied for many years, we discovered that the structure has a strong tendency to form Pb-depleted disks on {001} planes. These disks are around 2–5 nm in diameter and less than 0.5 nm in thickness, with a volume density of around 9 × 1017 cm−3, resulting in lattice strain fields (3–20 nm) on both sides of the disks along their normal directions. Moreover, such disks were also observed in Pb-rich Pb1.3Te, Pb-deficient PbTe1.3, and thallium (Tl)-doped Tl0.01Pb0.99Te and Tl0.02Pb0.98Te crystals. Because of the effects of diffraction contrast imaging by transmission electron microscopy and orientations of the crystals, these native lattice strain fields were incorrectly recognized as precipitates or nanoinclusions in PbTe-based materials. This discovery provides new insight into the formation mechanism of the precipitates or nanoinclusions in PbTe-based materials.

For evaluating the effects of ultrafine nanograins (UFNGs) on the fracture toughness of conventional nanocrystalline (nc) materials, we developed a composite model composed of UFNGs (with a grain size d between 2 and 4 nm) evenly distributed in the conventional nc matrix (20 nm ≤ d ≤ 100 nm). The UFNGs could be treated as a part of triple junctions, denoted as super triple junctions. In the framework of our model, stress concentration near crack tip initiates intergrain sliding that leads to the generation of edge dislocations at super triple junctions. The dependence of critical crack intensity factors on grain size was calculated. It was demonstrated that the existence of the UFNGs approximately doubles the critical crack intensity factors.

Titanium oxide matrix was prepared by sol-gel adding fluoxetine [Prozac (C17H18NF3O)] during the reaction of gelation. This nanostructured material was studied by Fourier transform infrared (FTIR) spectroscopy, N2 adsorption, and x-ray diffraction to detect the interaction between the drug and the matrix. The complex nature of FTIR signals for the matrix and the drug did not allow observation of the interactions; however, using the density functional theory formalism, two stable complexes are suggested to be formed on the drug–matrix system. Both complexes are formed through H bond interactions involving the amine group in fluoxetine and the hydroxylated sites in titanium xerogel. They were found to be energetically stable and independent of the titanium model core cluster used in the calculations.

Lateral ZnO nanowires (NWs) were selectively grown from the edge of a SiO2/Si–Al2O3–SiO2/Si multilayer structure for potential integration into devices using Si processing technology. Microstructural studies demonstrate a two-step growth process in which the tip region, with a diameter of ~10 nm, rapidly grew from the Al2O3 surface and, later, a base growth with a diameter of ~22 nm overgrew the existing narrow ZnO NW, halting further tip growth. Kinetics studies showed that surface diffusion on the alumina seed surface determined ZnO NW growth rate.

There are many challenges associated with adapting traditional nanoindentation methods to the study of compliant, hydrated biomaterials. These include issues related to surface detection, tip–sample adhesion, and fluid interactions. This study demonstrates that the nano-Johnson–Kendall–Roberts (JKR) force curve method can be used effectively in both air and water to overcome the challenges of surface detection and adhesion for nanoindentation of a compliant polymer. Indents were performed on poly(dimethyl siloxane) samples in air, water, and a detergent solution, with detergent used to reduce interfacial forces and provide baseline modulus measurements. The results demonstrated that errors due to adhesion dominated errors due to surface detection or fluid interactions and that JKR modeling could compensate for errors due to adhesion. Several JKR curve-fitting techniques were also evaluated, and all were found to result in moduli within 10% of the baseline moduli of the materials, demonstrating the robustness of this technique.

The microstructures of Zr70Cu30 and Zr70Ni30 metallic glasses (MGs) were investigated via the synchrotron radiation techniques combined with the reverse Monte-Carlo simulations. Although Cu and Ni are neighbor elements in the periodic table and their atomic radii are almost the same in length, it is found that atomic- and cluster-scale structural differences occur between these two Zr-based MGs. In particular, the relatively regular clusters caused by the narrow distributions of atomic separations and bond angles are detected in Zr70Cu30. This is the structural origin of the different glass-forming abilities in ZrCu and ZrNi alloys. This work has implications for understanding of the glass-forming mechanism in this class of glassy materials.

TiO2 nanotube arrays were synthesized by anodic oxidation on a pure titanium substrate in solutions containing 0.175 M NH4F composed of mixtures with different volumetric ratios of DI water and glycerol. According to the results of the current curve recorded during anodization, the time of the first sharp current slope (corresponding to the initial oxide layer formation time) was found to vary from 8 to 171 s depending not only upon the water content in the electrolytes but also upon the voltage. The current curves exhibit oscillation with different amplitudes and periods. In combination with the scanning electron microscope (SEM) images, a growth mechanism, layer-by-layer model, of TiO2 nanotube arrays was presented. Based on this mechanism, many phenomena that appeared during anodization can be reasonably explained. Our results would be helpful for the design of nanoarchitectures in related material systems.

Physical aging induced by an exposure of As–Se, As–S, and Ge–Se glasses to the light of different discrete wavelengths is studied using differential scanning calorimetry technique. The value of this effect is compared to the physical aging caused by natural storage in the dark. It is shown that a choice of As or Ge atoms does not influence significantly the spectral dependence of light-assisted physical aging, whereas substitution of Se with S causes drastic changes in the magnitude of the effect. The mechanism of the observed light-induced phenomena is discussed in terms of transient and metastable displacements of network chalcogen atoms.

Graphitic carbon (GC) is prepared using an ion-exchange resin as carbon source at 600 °C. A Co salt is selected as the graphitization catalyst and is pre-exchanged onto the resin during the ion-exchange process. The GC is characterized by transmission electron microscopy, x-ray diffraction, Raman spectroscopy, and thermogravimetry. Analysis of the crystallization shows that graphitization can occur at a temperature of as low as 600 °C, compared to the usual temperature of above 2000 °C in industry and above 1000 °C in literature. Different carbon structures have been found for different pretreatments of the resin and different heat treatment temperatures. This energy-saving method is an important breakthrough for the economic mass production of GC.

The interaction between a dislocation and hydrogen is considered to play an important role in hydrogen-related fractures for metals; it has been experimentally reported that hydrogen affects the dislocation mobility. These studies, however, show different macroscopic softening and/or hardening effects in iron, and the interaction between the dislocation and hydrogen remains unclear. In this study, we investigated the occurrence of interactions between a {112}<111> edge dislocation and a hydrogen atom via the estimation of the stress-dependent energy barriers for the dislocation motion and hydrogen diffusion in alpha iron using atomistic calculations. Our results show the existence of boundary stress conditions: dislocation mobility increment (softening) occurs at a lower applied stress, dislocation mobility decrement (hardening) occurs at an intermediate stress, and no effects occur for the steady motion of a dislocation at a higher stress in this analysis condition.

We report that the hydrogen de/resorption of the 2LiBH4+MgH2 system was modified by introducing Ni nanoparticles. Dehydrogenation analysis revealed that the first-step dehydrogenation, i.e., the decomposition of MgH2, can be significantly promoted by adding a small amount of Ni because of the catalytic effect. However, the improvement of the second-step dehydrogenation, corresponding to the decomposition of LiBH4, needs the addition of a large amount of Ni, resulting in the formation of a Mg–Ni–B ternary alloy. Furthermore, the presence of the Mg–Ni–B ternary alloy allowed an increased reversible H-capacity, in which about 5.3 wt% of hydrogen can be rehydrogenated under 400 °C and 55 bar hydrogen pressure over 10 h, which is higher than that of the pristine 2LiBH4+MgH2 system (4.4 wt%).

Alternating current (AC) electric fields generated by coplanar electrodes are used to externally direct the assembly of submicrometer sized disk-shaped zeolite particles. At the edge of the electrode, zeolite particles assemble in a brushlike structure that forms because of an interplay between an induced dipolar interaction and the drag force due to AC electroosmotic flow. Far from the electrode edge, where the fluid is quiescent, the disk-shaped particles form a nearly hexagonally close-packed structure, similar to suspensions of spherical particles. These results demonstrate a surprising generality of field-directed structures and offer promise for a hierarchical fabrication of nanostructures from zeolites.

Hollow nanoparticles of hexagonal close-packed (hcp)-NaYF4:Yb,Er were synthesized by thermal decomposition of trifluoroacetate precursors at 340 °C via vacancy diffusion, likely due to the Kirkendall effect and Ostwald ripening mechanism. The average outer diameter, inner diameter, and shell thickness of these hollow particles were 14 ± 3 nm, 7 ± 2 nm, and 4 ± 1 nm, respectively. The surface effects on the fluorescence properties of these hollow particles were studied by comparing with that of solid NaYF4:Yb,Er (average size ∼15 ± 3 nm) and solid NaYF4 core/NaYF4:Yb,Er shell (NaYF4 core ∼10 ± 1 nm and NaYF4:Yb,Er shell ∼3 ± 2 nm) nanoparticles containing similar composition of Yb and Er ions. The green, red, and total emission intensities decreased with increasing upconversion active volume-normalized surface area. Surface coatings of undoped NaYF4 on both inner and outer surfaces of the hollow nanoparticles enhanced the total emission intensity by ∼19 and ∼5 times compared with those of the hollow and solid NaYF4:Yb,Er nanoparticles, respectively.

To detect the relatively strong scattering signals of the Raman scattering and the x-ray diffraction (XRD) from CdS and those from the CdS/CdTe interface, an inverted CdTe solar cell structure was prepared and a 35-nm-thick CdS film was deposited on the surface of a CdTe solar cell structure. The Raman and high-resolution XRD scattering spectra allowed us to qualitatively study the interdiffusion and its related reactions at the CdS/CdTe interface. Interdiffusion began to occur at a relatively low temperature of about 350 °C, which coincided with the CdS phase transformation from cubic to hexagonal phase. Substantial interdiffusion of S and Te occurred after heat treatment at a temperature of 550 °C, resulting in formation of S-rich and Te-rich CdSxTe1−x alloy at the CdS/CdTe interface, with S and Te atomic concentration of ∼9% and 11% diffused into the CdTe and the CdS films, respectively.