Using the thermal oxidation of iron, we show that the growth morphologies of one-dimensional nanostructures of hematite (α-Fe2O3) can be tuned by varying the oxygen gas pressure. It is found that the oxidation at the oxygen gas pressures of ∼0.1 Torr is dominated by the growth of hematite nanobelts, whereas oxidation at pressure near 200 Torr is dominated by the growth of hematite nanowires. Detailed transmission electron microscopy study shows that both the nanobelts and nanowires grow along the direction with a bicrystal structure. It is shown that nanowires are rooted on Fe2O3 grains, whereas nanobelts are originated from the boundaries of Fe2O3 grains. Our results show that oxygen gas pressure can be used to manipulate the Fe2O3/Fe3O4 interfacial reaction, thereby tailoring the oxide growth morphologies via the stress-driven diffusion.

Multiwalled carbon nanotube (MWCNT)-reinforced copper (Cu) nanocomposite coatings were consolidated using kinetic spraying. Nanocomposite particles colliding with supersonic velocity led to severe plastic deformation and deposition and resulted in bimodal structural evolution by grain refinement and work hardening. These microstructural factors contributed to the remarkable strengthening of the nanocomposites in conjunction with Orowan looping of MWCNTs. In this study, the microstructural and physical metallurgical analyses were performed to understand the strengthening mechanisms of MWCNT/Cu nanocomposites consolidated by kinetic spraying.

In this article, we investigated the effect of Sn grain structure on the electromigration (EM) reliability of Sn–2.5Ag (wt%) solder joints used in flip-chip packages. The electron backscattering diffraction technique was applied to characterize the Sn grain size and orientation of the solder joints. Failure analyses on Sn–2.5Ag solder joints after EM tests showed that the Sn grain structure was important in controlling the kinetics of the intermetallic compound growth and void formation under EM. Further microstructural analysis revealed that the grain sizes and orientations of the solder joints after multiple solder reflows were statistically different from those with a single solder reflow and resulted in an improved EM reliability. Thermal annealing effect was also investigated to separate the thermal effect from the EM-induced effect. Results obtained in this study demonstrated that EM reliability of Pb-free solder joints could be improved by optimization of the Sn grain structure.

Crystalline pentagonal nano- and microrods (PRs) and pentagonal nano- and microparticles (PPs) with 5-fold symmetry are studied. Structure of PRs and PPs and their elastic distortions are characterized in the framework of the disclination approach. Relaxation of mechanical stresses due to disclinations causes structural transformations in PRs and PPs. Experimental evidence of such transformations, namely, the appearance of internal cavities and pores, and growth of whiskers in copper PRs and PPs grown in the process of electrodeposition is demonstrated. A brief review of existing models of stress relaxation in PRs and PPs is presented. We discuss a new model of nanowhisker growth based on the nucleation of two dislocation loops of opposite signs near the surface of the crystal with disclination. As a result, vacancy-type dislocation loop remains in the material and serves as a nucleus for cavity, while the interstitial loop comes to the free surface and contributes to whisker growth.

In this research, we performed experimental investigations of the influence of copper presence on hardness of arsenic triselenide (As2Se3)–arsenic triiodide (AsI3) pseudobinary glasses. The samples belong to the group of chalcogenide glasses, that, when compared with oxide glasses, can be synthesized much more easily in a wide variety of compositions, allowing also fine-tuning of their properties. Here, presence of iodine (I) facilitates glass formation, whereas addition of copper (Cu) creates possibility for interesting optoelectronic properties. As it is important to study mechanical properties of materials with respect to their fabrication and manipulation, we report results of instrumented indentation testing (IIT) of bulk samples of Cux[(As2Se3)0.9(AsI3)0.1]100−x with x = 5, 10, 20, and 25 at.% of Cu. This technique enables fast determination of indentation hardness, hardness value according to Vickers and indentation modulus directly from the indentation load–displacement curves. It was shown that all these parameters increase linearly with the increase of copper content. Improvement of the mechanical properties justifies the addition of Cu into the glass matrix.

Reflow behavior of a Sn–8.5Zn–0.5Ag–0.01Al–0.1Ga (five-element) solder on the Ni/Cu substrate was investigated under different heating rates. Reflowed samples show decreased Zn and increased AgZn3 in the solder with a reduction in the heating rate. The Zn at the solder/substrate interface was found to be much lower than that in the Sn–Zn solder systems. Cu was observed to be diffused through the electroplated Ni layer and noticed only with the Ag–Zn compound in the solder. Ga was spotted at the interface in the Ag–Zn matrix, whereas Al was detected with the Zn at the interface. Small intermetallic compound (IMC) layer was formed at the interface; however, its amount enhanced with the reduction in the heating rate. Present study relates the reflow behavior of the five-element solder with the reactivity of different elements in the system and its influence on the formation of IMCs in the solder and at the solder/substrate interface.

A Zn2SnO4/graphene (Zn2SnO4/G) hybrid was prepared by a facile one-pot hydrothermal route using SnCl4·5H2O, ZnSO4·7H2O, and graphite oxide as the precursors and NaOH as the mineralizer. Microsized Zn2SnO4 crystals with an octahedral shape are firmly confined by the graphene sheets, forming a unique hybrid structure. The confining effect of graphene leads to a more homogeneous size distribution of Zn2SnO4 crystals in Zn2SnO4/G than in bare Zn2SnO4. The introduction of graphene also brings an improved Li-storage performance for Zn2SnO4 due to the combined buffering, conducting, and confining effects of graphene. After being cycled at 200 mA/g for 50 times, Zn2SnO4/G can still keep a charge capacity of 326 mAh/g, while for bare Zn2SnO4, its charge capacity drops to only 100 mAh/g after the same cycles.

Methods for identifying the hardening behavior of solids described by power law through indentation testing have been well developed. However, many important engineering materials deviate from the power law description significantly. After fitting the uniaxial curves of several typical materials, the three-parameter relationship proposed by Voce [E. Voce, J. Inst. Met.74, 537–562 (1948)] is chosen to describe the hardening behavior for its fitting performance and inherent simplicity. Based on the Voce law, an efficient method is formulated to extract the hardening data from a single spherical indentation curve. Improved identifying performance is manifested by applying the method to four metallic materials. It is validated that the present method has the ability to effectively identify the plastic properties of materials through spherical indentation testing.

Electro-optical films composed of liquid crystal (LC) microdroplets encapsulated in an organically modified xerogel matrix were prepared by combined sol-gel and phase separation methods. The incorporation of a titanium alkoxide in the synthesis process as a co-precursor to silicon alkoxides was achieved without any destructive influence on the macroscopic LC phase separation. The consequent increase in the refractive index of the matrix satisfied the important criteria for high-performance films. The prepared films exhibit an outstanding 75.9% change in transmittance as an electric field is applied. An original setup was developed that enables the measurement of the film transmittance versus applied voltage at different temperatures over the full visible and near-infrared (near-IR) spectral range. For the first time, the relationship between these important characteristics (i.e., change in transmittance versus wave length versus temperature) was measured for a xerogel-dispersed LC composite film. The maximum of the curve increased and moved from the IR to the midvisible range with increasing temperature, achieving its maximum at 25.2 °C and 551 nm.

The surface enthalpy of yttria-stabilized hafnia (YSH) (YxHf1 − xO2 − x/2) with different compositions was directly measured by a combination of high-temperature oxide-melt solution calorimetry and water adsorption calorimetry. The surface enthalpies for hydrated surfaces are 0.27 ± 0.06 J/m2 for x = 0.1, 0.77 ± 0.09 J/m2 for x = 0.17, and 1.30 ± 0.09 J/m2 for x = 0.24; and those for anhydrous surfaces are 0.51 ± 0.06, 1.08 ± 0.13, and 1.76 ± 0.09 J/m2 respectively. The enthalpies of both hydrated and anhydrous surfaces increase approximately linearly (R2 > 0.93) with increasing yttrium concentration. The surface enthalpies of Y0.1Hf0.9O1.95 were used to approximate those for pure anhydrous cubic hafnia. Combining the data relating to surface energies for monoclinic hafnia from our previous work and estimated data for tetragonal hafnia, a tentative stability map of HfO2 polymorphs as a function of surface area (SA) was constructed.

High-density cobalt (Co) nanowires (NWs) were fabricated using porous anodized aluminum oxide as a template. Measurement results show a high magnetic performance for NWs with a coercivity of about 1750 Oe and strong magnetic anisotropy with an easy axis parallel to the NW direction. We have investigated the effect of alternating current (AC) electrodeposition frequency on the magnetic properties of NW samples. We show that understanding the effect of barrier layer is critical for controlling the rate of NW electrodeposition. A circuit model is proposed that accurately describes the role of the barrier and interfacial layers during deposition. Results obtained by simulation of the circuit show an excellent agreement with experimental results for different frequencies and voltages. It is shown that the amount of electrodeposited material can be estimated based on the difference between the anodic and cathodic half cycles in the electrodeposited current. Use of higher frequency leads to more symmetrical half cycles and smaller electrodeposited material.

Through a polyethylene-glycol-assisted hydrothermal method, a series of potassium fluoride (KF)–Yttrium (III) fluoride (YF3) system materials have been synthesized. By controlling the reactant ratios of KF: rare earth ions (RE3+), the hydrothermal temperatures, and the pH values of the prepared solutions, the final products can evolve among the orthorhombic phase of YF3 and/or the tetragonal phase of potassium triyttrium decafluoride (KY3F10) and/or the cubic phase of potassium yttrium tetrafluoride (KYF4). The final products are characterized by the x-ray diffraction (XRD) patterns, the field-emission scanning electron microscopy (FE-SEM) images, the energy-dispersive spectroscopy (EDS) patterns, the photoluminescence (PL) spectra, and the luminescent dynamic decay curves. The XRD patterns of the samples suggest the phase evolution of the final products. The FE-SEM images and the EDS patterns prove that. Europium ion (Eu3+) acting as a probe, its PL spectra and the luminescent decay curves all put together prove the phase evolution of the final products. The research can be extended to study the other KF–REF3 system materials.

Heterogeneous copolymers contain diverse comonomer contents among copolymers, and the extremely diverse case becomes a binary polymer blend. We report a numerical study of crystallization in two series of heterogeneous copolymers that are separated with strong and weak heterogeneities of comonomer distributions, and both of which are composed of crystallizable monomers and noncrystallizable comonomers with various compositions. A comparison of simulation results between these two series of samples demonstrates that, something like a compatibilizer in an incompatible polymer blend, copolymer fractions with intermediate comonomer contents between two compositional extremities depress the prior liquid–liquid demixing on cooling, and hence weaken the subsequent crystallization behaviors. However, we found that in these intermediate fractions, comonomers distribute quite homogeneously on each chain and the amphiphilicity occurs on multiple short sequences, rather than like on a diblock copolymer.

The doping properties and stability of hydrogen in zinc oxide (ZnO) crystals have been investigated by cathodoluminescence (CL) spectroscopy. Hydrogen incorporation was achieved by hydrogen plasma at 200 °C. The ZnO near-band-edge (NBE) peak is dramatically enhanced, while the green emission at 2.4 eV is quenched with increasing hydrogen incorporation. These effects are attributed to hydrogen passivating green luminescence centers, which are most likely negatively charged zinc vacancy defects. E-beam irradiation of H-doped ZnO crystals by an intense electron beam with μW power reverses the hydrogen doping process. This effect is ascribed to the dissociation of H-related defects, formation of “hidden” H2, and electromigration of H+ under the influence of the local trapped charge-induced electric field. These results highlight the potential to modify the local luminescent properties of ZnO by e-beam irradiation.

We report on the absorption, static, and transient luminescence spectra of Sm3+-doped glasses. The dependences between absorption and emission cross sections as well as between luminescence quantum efficiencies and Sm3+ doping concentration are examined. The large stimulated absorption cross section and emission cross section combined with the long fluorescent lifetime make phosphate glasses doped with Sm3+ promising material for visible fiber lasers. Moreover, ΔT(Tx − Tg) of these glasses is about 290 °C, which guarantees their thermal stability against crystallization during the fiber drawing process.

Microcompression test was applied to determine the Young’s modulus for elastically anisotropic materials for two different orientations of single crystalline Si. Although there is a clear difference in the apparent Young’s moduli for the different orientations, a significant underestimation of Young’s modulus was observed resulting from the substrate deformation as observed in both finite element simulation and experiment. This effect decreases with increasing aspect ratio. To correct the deviation of the apparent Young’s modulus from the theoretical values, a systematic framework of microcompression test is suggested. The modified Sneddon correction using the indentation modulus instead of Young’s modulus successfully yields Young’s moduli of single crystalline silicon in the [100] and [111] directions to within 5.3% and 2.0% deviation, respectively.

To understand the brittleness transition in low-toughness materials, the nucleation and kinetics of dislocations must be measured and modeled. One aspect overlooked is that the apparent activation energy for plasticity is modified at very high stresses. Coupled with state of stress and length scale effects on plasticity, the lowering of the brittle-to-ductile transition (BDT) in such materials can be partially understood. Experimental evidence in silicon single crystals in the length scale regime of 40 nm to 1 mm is presented. It is shown that high stress affects both length scale and temperature-dependent properties of activation volume and activation energy for dislocation nucleation and/or mobility. Nanoparticles and nanopillars of single-crystal silicon demonstrate unexpectedly high fracture toughness at low temperatures under compression. A thermal activation approach can model the three decades of size associated with the factor of three absolute temperature shift in the BDT.

A dislocation–density-based model for slip transmission at variant boundaries and a microstructural failure criterion accounting for variant cleavage planes have been developed to determine optimal variant distributions for significantly improved ductility, through increased slip transmission, and fracture toughness, through increased resistance to crack propagation, in martensitic steels with refined blocks and packets. A crystal plasticity framework, accounting for variant morphologies and orientation relationships that are uniquely inherent to lath martensite, and specialized finite-element methodologies using overlapping elements to represent evolving fracture surfaces are used for a detailed analysis of fracture nucleation and intergranular and transgranular crack growth. The results indicate that the block sizes, variant orientations, and distributions are the key microstructural characteristics for toughening mechanisms, such as crack arrest and deflection, and for desired ductility, delayed crack nucleation, and greater fracture toughness. This approach can be the basis for validated design guidelines for the desired optimal behavior of high-strength and toughness steels.

We developed a polyatomic cluster ion beam system for materials processing, and polyatomic clusters of materials such as alcohol and water were produced by an adiabatic expansion phenomenon. In this article, cluster formation is discussed using thermodynamics and fluid dynamics. To investigate the interactions of polyatomic cluster ions with solid surfaces, various kinds of substrates such as Si(100), SiO2, mica, polymethyl methacrylate, and metals were irradiated by ethanol, methanol, and water cluster ion beams. To be specific, chemical reactions between radicals of polyatomic molecules and surface Si atoms were investigated, and low-irradiation damage as well as high-rate sputtering was carried out on the Si(100) surfaces. Furthermore, materials processing methods including high-rate sputtering, surface modification, and micropatterning were demonstrated with ethanol and water cluster ion beams.

We report herein the crystal growth of ZnO nanoparticles by the foam fractionation method. In this study, the vertical column height of the foam was fixed and the velocity of the sparging air was varied, and the effect of foam flow rate on the synthesis of ZnO was investigated. The obtained ZnO consisted of aggregated platelets and had differing ultraviolet absorbances. The as-synthesized ZnO was hydrophobic because of the interaction between the anionic head groups of sodium dodecyl sulfate (SDS) and the ZnO under the precipitation conditions. The long chain of the SDS molecule was the cause of hydrophobicity. The contact angle of water was in the range of 95–105° for the obtained ZnO/SDS surface. The photocatalytic degradation efficiency of the as-synthesized (ZnO/SDS) and the calcined ZnO was investigated for methylene blue, and the calcined ZnO retained its activity even after three recycles.