Ni-based under-bump metallization (UBM) has attracted wide attention due to its low reaction rate with Sn, compared with Cu and Cu alloy. In this study, the interfacial reactions between eutectic Sn–3.5Ag solder and Ni-based UBM, including electroplated Ni (EP-Ni) and electroless Ni (EL-Ni) are investigated. Morphology and growth kinetics of Ni3Sn4 intermetallic compounds are studied at different reflow temperatures and durations. The growth rate and the growth activation energy of Ni3Sn4 were measured for the two sets of samples. The activation energies are measured to be 25 kJ/mol and 38 kJ/mol for the Ni3Sn4 growth on EP-Ni and EL-Ni, respectively. The Ni3Sn4 on EP-Ni UBMs shows a slower growth rate and the Ni3Sn4/solder interface is void free even after 20-min reflow at 240 °C. On the other hand, the interface of Ni3Sn4/EL-Ni has a lot of microvoids after reflowing at 240 °C for 20 min.

Surface-functionalized magnetic nanoparticles were prepared by a facile one-pot solvothermal method in ethylene glycol solution. Zeta value, size, and magnetic properties could be well tuned by introducing different functional group molecules. Characterizations, including transmission electronic microscopy, scanning electronic microscopy, thermogravimetric analysis, x-ray powder diffraction and vibrating sample magnetometer, and Fourier transform infrared spectrophotometer demonstrated the efficiency of this simple and general synthesis strategy. The hydrophilic magnetic nanoparticles with various surface functional groups and zeta values were evidenced as excellent candidates for bioseparation by extracting DNA molecules from a model mixture of cell fractures.

Li+ for Na+ ion-exchange-induced phase separation in borosilicate glass was investigated. A glass with a composition, 70SiO2·15B2O3·15Na2O, was prepared. The glass was transparent, and macroscopically no phase separation was observed because the immiscibility temperature for the composition was lower than the glass transition temperature. Substitution of Li+ for Na+ at the surface domain of the glass induced phase separation in the domain and subsequent heat treatment evolved interconnected silica-rich and alkali borate-rich phases through the phase separation. However, the parts in which ion exchange did not occur kept homogeneous and transparent. This phenomenon is explainable by the fact that the immiscibility temperature for the Li+-substituted composition of the original glass elevated up to a temperature higher than the ion exchange and heat treatment temperatures. The borate-rich phases leached by acid treatment for the phase-separated glass. Through these processes, we obtained monolithic glasses consisting of porous domains, and homogeneous and transparent parts.

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.

The oxidation behavior of Cu50Zr50 and Cu46Zr46Al8 glasses during continuous heating up to 1073 K has been investigated, with special emphasis on the oxidation resistance in the supercooled liquid (SCL) state. For Cu50Zr50, the oxide layer mostly consists of monoclinic ZrO2 (m-ZrO2), while for Cu46Zr46Al8, the oxide layer consists of two different layers: an outer layer consisting of tetragonal ZrO2 (t-ZrO2) + Al2O3 + metallic Cu (oxidation product from the SCL state of the glass matrix) and inner layer comprised of m-ZrO2 + metallic Cu islands (oxidation product from the crystallized matrix). Cu-enriched regions consisting of Cu51Zr14 (in Cu50Zr50) or AlCu2Zr + Cu70Zr15Al15 + Cu51Zr14 (in Cu46Zr46Al8) are present below the oxide layer. The present study shows that the addition of Al (8 at.%) in Cu50Zr50 results in a significant deterioration of the oxidation resistance in the SCL state since the solutionizing of Al in t-ZrO2 leads to a higher oxygen ion vacancy concentration, thus providing a higher activity of oxygen ions.

We studied the correlation between shear-induced crystallization and rheological behavior of syndiotactic polystyrene. It was found that after applying a steady shear flow around the nominal melting temperature (Tm = 270 °C), crystal growth rate was accelerated compared with the quiescent state and a morphology of oriented lamellae (kebabs) was observed. On the other hand, no obvious morphological change was observed when applying a shear flow with relatively slow shear rate. We discussed a possibility that the difference of crystal growth rate and morphology could be attributed to the competition between shear rate and relaxation time such as reptation time. Our rheological results suggested that when the imposed shear rate is close to the reciprocal of reptation time, oriented lamellae (kebabs) are observed but extended-chain crystals (shishs) cannot be formed since the chain segments between adjacent entanglements remain unstretched.

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.

Electrochemical oxidation of graphite in mixed solutions of H2SO4–H3BO3 with various mass ratios was investigated. The potential correction to concentration in the formation of graphite intercalation compound II stage in the system graphite–H2SO4–H3BO3 was determined and compared with other systems. Boric acid was shown not to be co-intercalated with sulfuric acid into graphite matrix, but to be distributed on the surface of expandable graphite (EXP). The amount of boric acid on EXP depends on concentration of H3BO3 in electrolyte and it ranges from 3.7 to 11.0 wt%. Content of boric oxide formed after thermoshocking is equal to 3–9 wt% in exfoliated graphite (EG). Modification resulted in reducing specific surface area of EG. As the pores in modified EG were blocked by boric oxide, the temperature of oxidation of the EG and graphite foil increased by 200 °C.

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.

Recent advances utilizing forced assembly multilayer coextrusion have led to the development of a new approach to study the structure–property relationships of confined polymer crystallization. Confinement of crystalline polymer materials in layer thicknesses ranging from hundreds to tens of nanometers thick, resulted in multilayer films possessing enhanced gas barrier properties. The enhanced gas barrier has been attributed to nanolayer confinement of the crystalline polymer resulting in a highly ordered intralayer lamellae orientation extending over micron or larger scale areas. Research into the confined crystallization mechanism of the multilayered polymer films has resulted in several material case studies as well as an understanding of the chemical and thermodynamic parameters that control the degree and rate of the confinement in multilayer polymer systems. This review highlights our recent studies on the confinement of poly(ethylene oxide), poly(ε-caprolactone), polypropylene, and poly(vinylidene fluoride) polymers in multilayered films.

The effect of direct current (dc) substrate bias on the promotion of nanocrystallization in Si network has been studied, specifically within He-diluted SiH4 plasma in radio frequency (RF)-plasma-enhanced chemical vapor deposition. In view of organizing nanocrystallinity, controlled transmission of energy to the growing surface is needed and that is obtainable from metastable helium (He*) bombardment and, in particular, ionic helium (He+) bombardment under negative substrate bias. The structural morphology has been adequately regulated to a homogeneous network restraining from an exclusive columnar structure that is coherent to low-temperature growth. Notable improvements in the film quality in terms of enhanced crystallinity with low hydrogen content as well as reduced incubation volume, bulk void, and surface roughness have been demonstrated, even at low substrate temperature and low RF power. Use of appropriate dc substrate-bias has been identified as a supplementary parameter efficiently organizing the growth, making it more device-friendly.

The thermoelectric parameters have been investigated depending on the thickness of the layer of nanostructures IV–VI (PbS, PbSe, PbTe, and SnTe). Based on the theoretical model of quantum well (QW) with infinitely high walls, it is demonstrated that this model explains nonmonotonous behavior of the Seebeck coefficient S with the change of the well width. On the basis of oscillation period Δdexp, we have approached the theoretical d-dependence of the coefficient S to the experimental one and defined the value of the Fermi energy in the corresponding nanostructures. It has been established that the minimum QW width dmin, where the first energy level coincides with the Fermi energy, is equal to the oscillation period of the Seebeck coefficient in this structure.

The photoelectrical properties of highly ordered TiO2 nanotube (TNT) arrays have been systematically and quantitatively studied and found to be closely related to their geometric and crystal structures. The geometric characteristics, including the nanotube diameter and length, were modified by adjusting the anodization potentials and durations, while the crystal structure was modified by thermal annealing at different temperatures. The nanotube array samples with the mixed crystalline phases possess higher photoconversion efficiency than those with the single anatase or rutile phase. The optimal content of rutile phase is about twice of that of anatase phase. In terms of the influence of the geometric structure, the TNT arrays with larger inner diameters and longer tube lengths have better photoelectrical properties. A geometric roughness factor has been applied to describe the combinative effect of the geometric characteristics. The TNT sample with the geometric roughness factor of 125.32 shows the superior photoconversion efficiency of 13.2%. The underlying mechanism has also been discussed in detail.

The standing porous nanoplate-built ZnO hollow microspheres with micro/nanostructure are fabricated based on a modified hydrothermal strategy, using citrate as structural director, and subsequent annealing treatment. The hollow spheres are composed of the vertically standing and cross-linked single crystalline porous nanoplates with the exposed surface of nonpolar (100) planes. Experiments have revealed the structural evolution: the formation of amorphous spheres in the initial reaction stage, followed by surface crystallization and nanoplate outward growth accompanied by inward dissolution of the amorphous spheres. Citrate in the precursor solution plays a dominant role in the formation of such porous ZnO hollow spheres. A model is presented, based on citrate-induced amorphous sphere formation and kinetically controlled dissolution and crystal growth. The model describes the formation of the hollow spheres, thermodynamically and kinetically.