An extended version of self-consistent field (SCF) theory that was recently introduced by the authors [Li et al., J. Chem. Phys.137, 024906, (2012)] is used to study the phase behavior of a polymer blend with reversible crosslinks. The system consists of symmetric AB diblock copolymers and homopolymers of type A and B. We consider reversible crosslinks that can form between the diblock copolymers with a crosslink strength z and crosslink weights ωA and ωB for monomers of type A and B, respectively. Crosslinks between homopolymers are disabled. We present a phase diagram as a function of the A fraction of homopolymers $\phi _{\rm{\alpha }}^{{\rm{rel}}}$, the crosslink strength z, and the crosslink asymmetry ∆ω = ωA − ωB. A hexagonal phase is found for suitably large $\phi _{\rm{\alpha }}^{{\rm{rel}}}$, and suitably small z and $\left| {\Delta {\rm{\omega }}} \right|$. Otherwise the system forms a lamellar phase. A deeper insight into the phase behavior is gained from analyzing the free energy contributions in the hexagonal and the lamellar phase with the help of the capabilities of the extended SCF theory developed by us.

Grain size influences the mechanical strength of materials. In polycrystalline materials, strength increases with decreasing average grain size (for grains larger than 100 nm). This well-known Hall–Petch relationship typifies a strengthening mechanism, in which dislocation motion is impeded by grain boundaries. As grains become smaller, higher stresses are required to deform them. However, this formalism only considers the role of the “average” size of grains. Heterogeneous materials, however, have a broad “distribution” of grain sizes. Here we show that materials with narrowed grain size distributions have mechanical properties that differ from Hall–Petch predictions. Narrower distributions show increased strength, as their homogeneously sized grains yield at higher loads than the large grains in materials with broader grain size distributions. Plastic deformation depends on the coarsest grains, which yield first. These results suggest new routes for tailoring material properties.

This paper reviews the recent development of surface-reaction-limited pulsed chemical vapor deposition (SPCVD) technique for the growth of TiO2 one-dimensional nanostructures. SPCVD uses separated TiCl4 and H2O precursor pulses, and the anisotropic growth of TiO2 crystals is attributed to the combined effects of surface recombination and HCl restructuring at high temperature during elongated purging time. Therefore, the crystal growth is effectively decoupled from precursor vapor concentration, which allows uniform growth of TiO2 nanorods (NRs) inside highly confined spaces. The phase of TiO2 NRs can be tuned from anatase to rutile by raising the deposition temperature. Au catalysts are able to enhance the growth rate and led to bifurcated nanowire (NW) morphology. A high density three-dimensional (3D) NW architecture was created by SPCVD growing TiO2NRs inside dense Si NW forests. Such 3D structures offer both large surface area and excellent charge transport property, which substantially improved the efficiency of photoelectrochemical devices.

Recently, the {10-12} twin variants activated during dynamic plastic deformation (DPD) of Mg alloy have been investigated by analyzing their Schmid factors (SFs), and their contributions to deformation have been calculated. During DPD of Mg–3%Al–1%Zn alloy, different {10-12} variants are generated relative to their SFs when initial grains have defined orientations with one a-axis of the crystal lattice at roughly 0 or 30° from the compression direction. The volume fraction of twins deeply influences the strain accommodated by twinning. The {10-12} variant pair with the maximum SF accommodated about 90% of the twinning strain. Its high volume fraction indicated that both nucleation and growth mechanisms played important roles in the strain accommodation. Other {10-12} variants had a lower volume fraction and accommodated twinning strain mainly by twin nucleation and made a lesser contribution to the total deformation.

The continuation of Moore's law requires new materials at both extremes of the dielectric permittivity spectrum and an increased understanding of the fundamental mechanisms limiting their electrical reliability. To address the latter, reflection electron energy loss spectroscopy has been utilized to measure the band gap of various oxide-based low and high dielectric constant (k) materials of interest to the semiconductor industry. In situ Ar+ sputtering has been additionally utilized to simulate process-induced defect states that are believed to contribute to electrical leakage, time-dependent dielectric breakdown, charge trapping, and other fixed-charge reliability issues in nano-electronic devices. It is observed that Ar+ sputtering predominantly generates surface oxygen vacancy defects in the upper portion of the band gap for both low and high-k dielectric materials. These results are in agreement with numerous theoretical investigations of defects in low and high-k dielectric materials and models for mechanisms that limit their reliability.

The microstructure evolution and mechanical responses are investigated in uniaxial tensile test performed on AZ31 magnesium alloy sheets processed by the flat extrusion container. A novel emphasis based on the texture was used to estimate the relative magnitude of hardening effects related to the deformation twinning. The anisotropic behavior of the sheets is sensitive to the orientation of the crystals with respect to the loading direction. This is ascribed to the effect of the initial texture and the activation of their relative critical resolved shear stresses on slip and twinning. The increased accumulated hardening increases the twin nucleation stress. The deformation twinning significantly induces an asymmetry in the yield behavior. Moreover, it remarkably prolongs the slope of the stage II in the working hardening curve. An accepted notion is proposed that the preferential activity of deformation twinning exerts a significant effect on mechanical anisotropy during tension.

Ceramic volumetric composites xLa0.7Pb0.3MnO3–(1−x)PbTiO3 (x = 0.18 and 0.85) were prepared. X-ray investigations have shown that rather low sintering temperature (800 °C) has allowed us to avoid the reaction and interdiffusion between two initial phases. Heat capacity, thermal expansion, and intensive magnetocaloric effect were measured in a wide temperature range. The sample composition has a low influence on temperatures of the ferromagnetic and ferroelectric phase transitions in composites. Electro- and barocaloric effects were determined by analysis in the framework of thermodynamic theory, electric equation of state, Maxwell relationships, and entropy–temperature–pressure phase diagram. Multicaloric efficiency of composites is discussed and compared with that of initial La0.7Pb0.3MnO3 and PbTiO3 compounds. Variation of a relationship between components can significantly increase both barocaloric and magnetocaloric efficiency of compositional material due to the mechanical stress appearing between grains of different ferroic phases under magnetic field.

We report the results of the systematic investigation into correlations between energetics and hexagonal stacking configurations for carbon, silicon, SiC, BN, AlN, GaN, and InN polytypes with sp3-bonded networks. The atomistic geometry, energetics, and electronic structure for these compounds with up to the periodic stacking length of L = 8 have been carefully calculated based on the density functional theory within the generalized gradient approximation (GGA). Using the Axial Next-Nearest-Neighbor Ising model extracted from the GGA calculations, we have also studied the energetics for more than 6 million kinds of nonequivalent stacking polytypes with up to L = 30, whose configurations have been deduced by the efficient polytype generation algorithm [E. Estevez-Rams and J. Martinez-Mojicar, Acta Crystallogr., Sect. A: Found. Crystallogr. 64, 529 (2008)], and illustrated some trends of structural and energetic properties for these compounds.

Solidification of undercooled Ni–3.3 wt% B alloy melt was investigated by glass fluxing. If ΔTe < 140 ± 10 K, two recalescences appear, indicating that stable eutectic reaction occurs; if ΔTe ≥ 140 ± 10 K, three recalescences can be observed, indicating that metastable eutectic reaction occurs. Analysis indicates that the phase fractions of the as-solidified structure can be predicted by the recalescence delay times in the cooling curves. High-speed video images show that the solidification interface of primary solidification changes from single dendritic shape to spherical shape with increasing ΔTp; the interface of eutectic solidification changes from many small “dendrites” to a single large one with increasing ΔTe; the interface of residual liquid solidification changes from many small rings to a single large one with increasing ΔTr. The growth velocity of eutectic solidification suggests a coupled growth at small and moderate undercoolings and decoupled growth at large undercooling, whereas that of residual liquid solidification cannot be interpreted by the available models.

This article describes the multifunctional applications of TiO2. It substantiates the universality of the anodization process to grow well-ordered TiOxnanotube (T–NT) of hollow cylindrical shape on a variety of planar and nonplanar substrates. It highlights an approach to effectively bring down the cost of anodization via utilization of a small volume of electrolyte. The multifunctionality of these nanostructures is highlighted through representative examples that illustrate wide ranging optical, electronic, and catalytic properties. Combining the T–NT with other materials such as metals and photoactive additives to form composite nanostructures has been shown to benefit photocatalysis, photovoltaics, biological processes, and environment-related applications. This article also demonstrates the applicability of T–NT as an agent to produce dissolved oxygen in simulated blood—an application that can assist in the development of artificial lungs. Key results from the research group, collaborations, and recent articles are highlighted.

“Nanostructured” germanium (Ge; also known as “voided,” “porous,” “nanoporous,” “cratered,” and “honeycomb” Ge) created via ion beam modification has been studied for many years. This work reviews the progress made in studying and characterizing the nanostructured morphology, particularly via the use of experimental techniques such as scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. Specifically, the empirical observations of the structural evolution of Ge as a function of ion beam modification conditions are discussed with added emphasis placed on quantification of the microstructure. The experimental observations and microstructure quantification are further discussed in terms of the implications for proposed formation mechanisms of the nanostructured morphology. Potential uses of the nanostructured morphology in chemical sensor and energy storage applications and suggested future lines of research to further the fundamental understanding of nanostructuring in Ge using ion beam modification are also presented.

The graded composition buffer layers are very commonly used in the semiconductor triple-junction solar cell device. To grow a strain-free 1.0-eV In0.3Ga0.7As thin film on a GaAs substrate, a total of 2.2% misfit strain must be relaxed through well-designed buffer layer structures. In this work, a phase-field model of a multilayered system is developed to probe the roughness of top surface morphology and predict optimal buffer layer thickness. Our simulation shows time evolution of the thin film morphology and the root-mean-square roughness of the surface with different buffer layer thickness designs. The strain distribution is investigated to explain the surface morphology evolution with the effect of the buffer layer. The simulation results show that the buffer layer thickness is a key parameter that affects the quality of the In0.3Ga0.7As epilayers. The simulation results can be effective in improving the design of graded buffer layers.

The magnetic anisotropy energy (MAE) of the bulk hcp Co under mechanical deformation is calculated by ab initio density functional theory (DFT) calculations based on the projector augmented wave method. We present a thorough investigation with respect to the choice of exchange-correlation functionals. The generalized gradient approximation (GGA) succeeds in predicting the easy axis of magnetization but underestimates the MAE in comparison to the experimental value, whereas the local density approximation gives a wrong magnetic easy axis. The DFT+U method offers an alternative to increase the MAE value. Unfortunately, as the MAE reaches the experimental value, strong distortions of the lattice parameters are observed. Our results with GGA suggest that a simultaneous reduction of the c/a ratio and increase of the lateral lattice parameter a will strongly enhance the MAE of the material, as observed experimentally. We also found that the MAE in hcp Co is reduced by shear strain.

We have developed a reactive force field within the ReaxFF framework to accurately describe reactions involving aluminum–molybdenum alloy, which are part parameters of Al–O–Mo ternary system metastable intermolecular composites. The parameters are optimized from a training set, whose data come from density functional theory (DFT) calculations and experimental value, such as heat of formation, geometry data, and equation of states, which are reproduced well by ReaxFF. Body-centered cubic molybdenum’s surface energy, vacancy formation, and two transformational paths, Bain and trigonal paths are calculated to validate the ReaxFF ability describing the defects and deformations. Some structures’ elastic constant and phonon are calculated by DFT and ReaxFF to predict the structures’ mechanics and kinetic stability. All those results indicate that the fitted parameters can describe the energy difference of various structures under various circumstances and generally represent the diffusion property but cannot reproduce the elasticity and phonon spectra so well.

Ice templating is able to do much more than macroporous, cellular materials. The underlying phenomenon—the freezing of colloids—is ubiquitous, at a unique intersection of a variety of fields and domains, from materials science to physics, chemistry, biology, food engineering, and mathematics. In this review, I walk through the seemingly divergent domains in which the occurrence of freezing colloids can benefit from the work on ice templating, or which may provide additional understanding or inspiration for further development in materials science. This review does not intend to be extensive, but rather to illustrate the richness of this phenomenon and the obvious benefits of a pluridisciplinary approach for us as materials scientists, and for other scientists working in areas well outside the realms of materials science.

The intermetallic materials digold bismuthide, gold diantimonide, and gold ditelluride were chemically synthesized with a bottom-up wet chemical approach, which has not been achieved before. These gold-based materials display a nano- to microparticle grain size and a well-defined composition-based structure. True intermetallic nanoparticle-based materials have traditionally proven challenging to obtain via wet chemical approaches, making the materials created here significant from a fundamental synthesis standpoint. The knowledge gained by developing reliable synthesis approaches toward intermetallic nanoparticles may be used to develop new materials and enhance the understanding of how to refine the characteristics and enhanced properties of emerging nanoparticle semiconductor materials in advanced applications such as for thermoelectrics.

Potential applications of the molecularly imprinted polymers (MIPs) demand physical configurations in different size ranges. Nowadays, research on MIPs is focused on the development of new or improved morphologies, which involves control and modification of the different parameters during the synthesis. In this study, the effect of different synthesis conditions on the particle size and morphology is investigated. Carbamazepine-imprinted polymers were prepared using precipitation polymerization under various conditions such as: the amounts of cross-linker and functional monomers, initiator, porogen, temperature and time of polymerization. We studied the polymerization conditions to obtain imprinted spherical particles with controllable sizes in the range of 243 nm to 3.4 μm. Scanning electron microscopy and photon correlation spectroscopy were utilized to investigate the morphological characterization. The mole ratio of the functional monomer to the cross-linker was important to obtain smaller uniformly sized particles. In addition, the results showed that the cross-linker in the molecular imprinting synthesis can affect the morphology and composition of the MIPs, which influences the binding affinity.

From bone to dentin to nacre, biomaterials are structurally advanced composites with superior toughness and significant stiffness, based on simple building blocks. Here, using a series of molecular mechanics models with bioinspired topologies, we propose design mechanisms rooted in the simplest mechanical interactions—perfectly brittle linear elastic—which are shown to be sufficient to achieve superior toughness at high stiffness in biological composites. In a two-phase composite system, we show that by adapting the elastic constitutive laws of the matrix phase and by tuning the interactions of the constituents we can realize materials with a large range of combinations of toughness and stiffness. Notably, this can be achieved without changing the fracture energy of the individual composite components. Through a systematic analysis and the development of a simple model, we unveil basic design principles that lead to fundamental insights into the mechanics of natural composites for applications in a range of engineering disciplines.

The nanoindentation fracture behavior of gallium arsenide (GaAs) is examined from two perspectives in two parent papers. The first paper (part I) focuses on in situ nanoindentation within a scanning electron microscope (SEM) and on fractographic observations of cleaved cross-sections of indented regions to investigate the crack field under various indenter geometries. In the second parent paper (part II), cathodoluminescence and transmission electron microscopy are used to investigate the relationship between dislocation and crack fields. The combination of instrumented in situ scanning electron microscopy nanoindentations and cleavage cross-sectioning allows us to establish a detailed map of cracking in the indented region and cracking kinetics for conical and wedge indenter shapes. For wedge nanoindentations, the evolution of the half-penny crack size with the indentation load is interpreted using a simple linear elastic fracture model based on weight functions. Fracture toughness estimates obtained by this technique fall within the range of usual values quoted for GaAs.