Bulk metallic glass forms when liquid metal alloys solidify without crystallization. In the search for iron-based bulk glass-forming alloys of the metal–metalloid type (Fe–B- and Fe–C-based), crystals based on the structural prototype C6Cr23 often preempt the amorphous phase. Destabilizing this competing crystal structure could enhance glass formability. We carried out first-principles total energy calculations of enthalpy of formation to identify third elements that can effectively destabilize C6Cr23. Yttrium appears optimal among transition metals, and rare earths also are suitable. Atomic size is the dominant factor.

Stoichiometric and magnesium-substituted synthetic hydroxyapatite (HA) powders with different Mg contents were characterized by Raman and cathodoluminescence (CL) spectroscopies. The substitution of Ca ions by Mg is presently of great interest because it may improve activity in the first stage of the bone remodeling process. In this paper, we show new evidence that CL spectroscopy has the capability to detect the presence of crystal defects, related to the presence of magnesium substituting calcium in Mg-doped HA powders. The dependence of CL spectra of stoichiometric and magnesium-doped HA powders on their chemical composition was studied, and the results are compared with Raman analysis and data previously collected by other analytical tools. All the investigated powders showed five distinct CL bands; moreover, in magnesium-doped HA, an additional band at higher energy was found. The intensity ratios between selected CL bands showed some relationships with the powder crystallinity and the estimated amount of magnesium both in the HA lattice and in the amorphous surface layer; moreover the band observed only in magnesium-substituted powders could be directly related to the amount of magnesium entered into the HA lattice. Such results can contribute to improve the knowledge of the crystallographic structure of Mg-substituted hydroxyapatite.

The interfacial reactions between solders and under bump metallization (UBM) have been of great interest recently in flip chip technology. Intermetallic compounds (IMCs), i.e., (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4, usually formed between solders and UBM. To fully understand the interfacial reactions and phase transformation phenomenon, a suitable phase diagram concerning solders, IMCs, and UBM materials is required. In particular, a Sn-rich phase region in the Sn–Cu–Ni ternary diagram is very critical in determining the concentration tendency of x and y values in (Ni1−x,Cux)3Sn4 and (Cu1−y,Niy)6Sn5 compounds. In this study, ternary Sn–Cu–Ni alloys were prepared and annealed at 240 °C. Three equilibrium phases, Sn, Ni3Sn4, and Cu6Sn5, were identified by x-ray diffraction analysis and also showed in backscattered electron imaging. Using electron probe microanalysis quantitative analysis, three acme compositions of the ternary region in the Sn–Cu–Ni isotherm near the Sn-rich corner were determined as 98.5 at.% Sn, (Ni0.80, Cu0.20)3Sn4 and (Cu0.59,Ni0.41)6Sn5. In addition, the solubility of Cu and Ni in (Ni,Cu)3Sn4 and (Cu,Ni)6Sn5 compounds was evaluated. Finally, the isothermal section of the ternary Sn–Cu–Ni system at 240 °C was proposed on the basis of experimental results in this study.

The nucleation and growth of Cu2O islands due to Cu(100) oxidation at temperatures from 200 to 350 °C have been observed by in situ ultra-high-vacuum transmission electron microscopy. For this temperature range, epitaxial Cu2O islands form a triangular shape with rounded edges when Cu(100) is exposed to dry oxygen at 5 × 10−4 Torr in situ. Our initial analysis on the nucleation and growth of these three-dimensional Cu2O islands agrees well with the heteroepitaxial model of surface diffusion of oxygen.

The electromigration behavior of the high-lead and eutectic SnPb composite solder bumps was investigated at 150 °C with 5 × 103 A/cm2 current stressing for up to 1711 h. The diameter of the bumps was about 125 μm. The underbump metallization (UBM) on the chip side was sputtered Al/Ni(V)/Cu thin films, and the Cu pad on the board side was plated with electroless Ni/Au. It was observed that damages occurred in the joints in a downward electron flow (from chip side to the substrate side), while those joints having the opposite current polarity showed only minor changes. In the case of downward electron flow, electromigration damages were observed in the UBM and solder bumps. The vanadium in Ni(V) layer was broken under current stressing of 1711 h while it was still intact after current stressing of 1000 h. The electron probe microanalyzer (EPMA) elemental mapping clearly shows that the Al atoms in the trace migrated through the UBM into the solder bump during current stressing. Voids were found in the solder bump near the UBM/solder interface. The Sn-rich phases of the solder bumps showed gradual streaking and reorientation upon current stressing. This resulted in the formation of uniaxial Sn-rich phases in the middle of the solder bump, while the columnar and fibrous Sn-rich phases were formed in the surrounding regions. The formation mechanism of electromigration-induced damage to the UBM structure and solder bump were discussed.

Non-conductive adhesive (NCA) flip chip interconnects are emerging as attractive alternatives to lead or lead-free solder interconnects due to their environmental friendliness, lower processing temperatures, and extendability to fine pitch applications. The electrical connectivity of a NCA interconnect relies solely on the pure mechanical contact between the integrated circuit bump and the substrate pad; the electrical conductivity of the contact depends on the mechanical contact pressure, which in turns depends to a large extend on cure shrinkage characteristic of the NCA. In addition, to reduce the cost and increase the output, NCA is usually ramped up to 200 °C and cured for 1 min during the assembly process. However, fast cure reaction poses a great challenge for the accurate measurement of cure shrinkage. In this paper, to precisely determine the cure shrinkage at high temperature, cure shrinkage was first measured at lower temperatures with slow reaction rate by means of thermomechanical analyzer and then extrapolated to high temperatures. With the increase of cure temperature, the maximum of degree of cure will increase, but the maximum cure shrinkage reduces due to the expansion of materials at higher cure temperature. Furthermore, the slopes of the linear relationship between the cure shrinkage and the degree of cure at different cure temperatures after gelation were found to be similar and independent of the cure temperature. The cure shrinkage from gel-point to complete curing was determined to be 4.275%.

Copper(I) chloride and bromide nanoparticle-dispersed glasses were prepared by means of a conventional copper staining. The staining was performed by the following process: copper stain was applied on the surfaces of Cl−- or Br−-ion-containing borosilicate glasses, and the glasses were heat-treated at 510 °C for various times. Typical exciton bands observed in the absorption spectra of the glasses after the heat treatment indicated that CuCl and CuBr particles were formed in the surface region of the glasses. The average sizes of the CuCl and CuBr particles in the glasses heat-treated for 48 h were estimated at 4.8 and 2.7 nm, respectively. The nanoparticles were also characterized by x-ray diffraction and transmission electron microscopy. Depth profiles of Cu and CuBr concentration in the glass heat-treated for 48 h were measured. Copper decreased in concentration monotonously with depth, reaching up to 60 μm, while the CuBr concentration had a maximum at about 25 μm in depth.

Preferential Pb electromigration (EM) in eutectic Sn–Pb molten solder was characterized by examining Pb segregation at the anode of the solder on a thin stripe of Cu metallization. The eutectic Sn–Pb molten solder stressed at current densities of 103−104 A/cm2 was found to form columnar Pb-rich phase (α) at the anode side and Pb deficiency at the cathode side. The columnar α-phase grew in the direction parallel to the electron flow, and its growth rate increased proportionally with the current density applied through the molten solder. By measuring the growth rate of the columnar α-phase, we calculated the Pb effective charge number of EM in the eutectic Sn–Pb molten solder to be 2.7, which is one order of magnitude lower than the reported value of 47 for self-electromigration in bulk Pb. The mechanism for the EM-induced Pb segregation in Sn–Pb solder was also explored.

A five-step indentation scheme is proposed to extract the elastic and viscoelastic properties of polymeric materials using a sharp indenter. In the formulation, analytical solutions to the elastic-viscoelastic deformation based on the concept of “effective indenters” proposed by both Pharr and Bolshakov [Understanding nanoindentation unloading curves. J. Mater. Res.17, 2660 (2002)] and Sakai [Elastic recovery in the unloading process of pyramidal microindentation. J. Mater. Res.18, 1631 (2003)] were derived. Indentation experiments on polymethylmethacrylate following the five-step scheme were performed. The elastic-viscoelastic parameters were extracted by fitting the solution based on Sakai’s effective indenter to the experimental results using a genetic algorithm. It was found that the solution based on Sakai's effective indenter was able to correctly extract the elastic properties. Based on this prediction and the experimental results, Pharr and Bolshakov's effective indenter profile could be determined. The extracted elastic-viscoelastic parameters using the solution based on Pharr and Bolshakov's effective indenter were independent of the reloading levels.

This study presents the effect of different nanoscale RE211 additions—Y2BaCuO5 (nmY211), Sm2BaCuO5 (nmSm211), and Nd4Ba2Cu2O10 (nmNd422)—on the nano-scale compositional fluctuation and associated pinning mechanism of the melt-textured growth (MTG) Sm–Ba–Cu–O [SmBCO, of which the composition is Sm123 (Sm1Ba2Cu3Oy) + 25 wt% Sm211 (Sm2BaCuO5)] superconducting bulk materials. The superconductivity and microstructure results indicated that in samples with the addition of these nano-sized particles, nanoscale compositional fluctuations form during the peritectic transformation of melt-growth process, which cause Tc variation on a nanoscale and result in the formation of δTc pinning centers at high magnetic field. The compositional fluctuation regions (δTc pinning centers) are altered by the difference in peritectic temperature, the solubility in the liquid phase, and the ion radius. The direct current transport R-T properties elucidate the change of flux pinning behavior. In addition, the different influence on microstructure and superconductivity between the two methods: mixing rare-earth elements in nanoscale RE211 or in the homogeneous mixed precursor powders [e.g., (Nd, Eu, Gd)–Ba–Cu–O (NEG)] is also discussed.

Barium titanate zirconate, Ba(Ti1−xZrx)O3 (0 ≤ x ≤ 0.25), thin films were deposited via the chemical solution deposition (CSD) method directly on copper foils. The films were processed in a reductive atmosphere containing nitrogen, water vapor, and hydrogen gas at 900 °C to preserve the metallic copper substrate during crystallization. Increasing the fraction of BaZrO3 revealed several effects, including an increase in unit cell dimensions, a decrease in both the temperature and value of the maximum permittivity, as well as a decrease in the average grain size of the films. The decrease in the relative permittivity was attributed to a grain size effect as opposed to zirconium substitution. In film compositions containing 25 mol% BaZrO3, the permittivity below Tmax became dispersive, and the ferroelectric transitions became increasingly diffuse. These characteristics suggest relaxor-like behavior. The dielectric tunability of Ba(Ti1−xZrx)O3 was studied at room temperature and at Tmax for each composition. There was little variation in the tunability with measurement temperature; however compositions that were ferroelectric at room temperature saw a decrease in hysteresis at Tmax, and all compositions showed an increase in permittivity.

Adhesion of thin films of epitaxial oxides to nickel-based metallic substrates is important for the successful development of high-temperature superconductor coated conductors. Detachment of epitaxial oxide buffer layers at the oxide/metal interface during either oxide growth or subsequent processing renders the conductor useless. In this study, thermal desorption spectroscopy (TDS) has been used to identify and understand one of the causes of buffer layer detachment, oxidation of carbon at the oxide–metal interface to form carbon monoxide. Results of TDS indicate that on the surface of a bare nickel-based alloy substrate, the rate of carbon oxidation depends on both the supply of carbon from the substrate and the supply of oxygen from the vapor. Sulfur at the surface of the alloy substrate reduces the rate of carbon oxidation. The effectiveness of various treatments of the bare substrate to eliminate CO formation and epitaxial oxide detachment has been demonstrated. TDS provides both a means to evaluate the kinetics of the oxidation reaction and a tool to assess the need and effectiveness of a substrate oxidation treatment.

Highly oriented lead zirconate titanate (PZT) films were fabricated on a platinized silicon substrate using a combination of sol-gel and radio frequency (RF) magnetron sputtering deposition methods. A sol-gel derived PZT layer highly oriented to the (100) plane was deposited as a seed layer, and PZT with the same composition then was deposited on the seed layer by RF-magnetron sputtering. The film deposited on the seed layer showed a strong (100) preferred orientation, while the film deposited without the seed layer showed a (111) preferred orientation. Furthermore, a thick PZT film of up to 4 μm was able to be deposited without cracks by using the seed layer. The piezoelectric property of the (100) oriented film was much better than that of the (111) oriented film.

The mechanical alloying method was used to synthesize a single glassy phase of Co65Ti20W15 alloy powders, using a high-energy ball mill. The glass transition temperature of the end-product, which was obtained after 173 ks of milling time, lies at 786 K, whereas the crystallization takes place at 878 K through a single sharp exothermic peak with an enthalpy change of crystallization of −4.37 kJ/mol. The reduced glass transition temperature was found to be 0.51. This glassy alloy powders exhibit a very large supercooled liquid region (92 K) for a ternary metallic system. The spark plasma sintering method was used to consolidate the glassy powders under an argon gas atmosphere at 843 K with a pressure of 19.6–38.2 MPa. The sample that was consolidated within 180 s maintains its chemically homogeneous glassy structure with a relative density of above 99.6%. Neither the supercooled liquid region nor crystallization temperature was affected by such a rapid consolidation procedure. Thus, the thermal stability of the bulk glassy sample is almost identical with the original glassy powders. The Vickers microhardness of the bulk glassy Co65Ti20W15 reveals high values, ranging between 8.69 and 8.83 GPa. The fabricated bulk glassy alloy shows high compressive strength of 2.44 GPa with a Young’s modulus of 176.81 GPa. Neither yielding stress, nor plastic strain could be detected for this glassy alloy, which its elastic strain is 1.33%.

Ultra-thin ZrO2 and HfO2 dielectric films grown by atomic layer deposition (ALD) are quite promising materials for gate dielectric applications in future transistors, and they exhibit significantly different as-grown microstructures: polycrystalline and amorphous phases, respectively. However, under the identical deposition conditions, both metal oxides show surprisingly similar capacitance–voltage (C–V) characteristics as a function of film thickness, implying that the identities and densities of fixed charge and bulk trapping charge are similar. Factors other than the film microstructure, such as concentration of impurities incorporated during the film deposition, are believed predominantly to control important C–V characteristics. Only the dielectric constant appears to depend significantly on the identity of the dielectric material. It is found that the dielectric constant of ALD-HfO2 (∼20) is significantly lower than that of ZrO2 (∼30) due to the differences in microstructure and also atomic density of the film. In terms of the leakage current characteristics, the effective potential barrier heights between Pt and these two dielectric films are identical (∼2.3 eV) within the experimental uncertainty. Implications for the electrode/dielectric interface electronic structure are discussed.

An iron nitride sample was irradiated by 2-MeV electrons intermittently for 2100 s with a dose rate of 6.3 × 1024 e.m.−2 s−1 inside a 3-MV high-voltage transmission electron microscope. The electron-stimulated oxidation of Fe4N and Fe2–3N was investigated in situ and ex situ using conventional transmission electron microscopy and high-resolution electron microscopy. It was found that both Fe4N and Fe2–3N nitrides were oxidized by the residual gas in the vacuum chamber to form Fe3O4 oxides. The orientation relationship between Fe4N (γ′) and Fe3O4 (o) was (110)γ′//(220)o, [001]γ′//[001]o, and that between Fe2–3N (ϵ) and Fe3O4 (o) was (110)ϵ//(−220)o, [1–11]ϵ//[001]o. Crystal lattice deformation from iron nitride to iron oxide took place during the dynamic oxidation process. Structural models were proposed to understand the oxide formation, and the models were confirmed by experimental observations. The irradiation effects of Fe4N and Fe2–3N crystals were compared. The results show that Fe4N is more sensitive than Fe2–3N to electron irradiation. These results are important not only for the fabrication of insulating iron oxide film, but also in the field of the surface modification of iron nitride to improve its mechanical properties.

The time-dependent characteristics of incipient plasticity in Ni3Al during nanoindentation in the subcritical load regime were investigated statistically. The waiting time for incipient plasticity to occur at constant load was found to follow a Poisson-like distribution, with the peak shifting toward zero holding time as the load increased and eventually becoming an exponential distribution when the load was close to a critical value. The observed distribution of the strain burst waiting time at loads smaller than the critical value was inconsistent with the picture in which dislocations nucleated homogeneously out of the perfect crystal. The kinetics for the occurrence of strain burst in this case is thought to be governed by the accumulative growth of nucleation precursors.

Three lipophilic L-glutamide derivatives with chromophoric head group were synthesized, and their photo-responsive properties were investigated in organic solution systems. By comparing their spectral behaviors, it was shown that organogels underwent a light blue to purple luminescence change, which was triggered by thermally induced monomeric-to-excimeric phase transition. This switching, based on self-assembly, is supposed to have special advantages in molecular electronics.

A model explaining the variability of oxygen solubility in the transition metals is proposed in this article. It assumes that the energy of solution can be represented as the sum of the work required to embed an oxygen atom in the electron gas of the host lattice, plus the energy generated through the formation of an oxygen anion. The latter term is treated as nearly constant across the transition metal series, leaving the work term to account for the observed variations in oxygen solubility. This work, we argue, can be approximated by the ratio of the number of metal electrons excluded from the region around the oxygen atom to the Fermi energy density of states. In turn, the number of electrons excluded by oxygen is assumed to be proportional to the charge density at the octahedral interstitial site. These assumptions allow us to define a solubility parameter that is easily determined with first-principles methods. This parameter is shown to correlate well with experimental findings regarding oxygen solubility in transition metals. Supported by these findings, we use first principle methods to identify alloying elements likely to reduce the solubility of oxygen in niobium.

Al2O3–Y2O3 powders were synthesized in the range of 25–55% Y2O3 by reverse coprecipitation of nitrate solutions. All starting powders were amorphous and formed primary yttrium aluminum garnet (YAG) upon crystallization. X-ray diffraction detected only garnet in compositions of 30–40% Y2O3 after heat treatment at 1250 °C. Compositions of 45–55% Y2O3 established a metastable YAG + Y4Al2O9 microstructure. The YAG phase field was metastably extended away from its stoichiometry, as indicated by a systematic increase in lattice parameter with Y2O3 content. Although some Al2O3 enrichment was achieved, YAG appears to tolerate greater off-stoichiometry on the Y2O3-rich side. Possible defect structures accommodating the solubility extension were examined. Phase selection results indicate that compositional inhomogeneity is not the only reason behind the appearance of hexagonal YAlO3, which is frequently reported during YAG synthesis.