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ZnO quantum dots ͑QDs͒ of controlled sizes have been fabricated by a simple sol-gel method. The blueshift of room-temperature photoluminescence measurement from free exciton transition are observed decreasing with the QD size that is ascribed to the quantum confinement effect. From the resonant Raman scattering, the coupling strength between electron and longitudinal optical phonon, deduced from the ratio of the second-to the first-order Raman scattering intensity, diminishes with reducing the ZnO QD diameter. The size dependence of electron-phonon coupling is principally a result of the Fröhlich interaction.

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Both band gap engineering and spatial confinement of optical phonon were observed depending upon the size of ZnO quantum dots at room temperature. Size-dependent blueshifts of photoluminescence and absorption spectra reveal the quantum confinement effect. The measured Raman spectral shift and asymmetry for the E2(high) mode caused by localization of optical phonons agree well with that calculated by using the modified spatial correlation model.

With femtosecond pulse excitation at the wavelength near 800nm, we observed three upconverted emission peaks from ZnO nanowires. The ultraviolet peak at about 385nm and the green emission band centered at about 515nm were attributed to the near band edge emission and defect level emission, respectively, while the intermediate peak was assigned to the second harmonic generation. From the quadratic dependence of the emission intensity on the excitation pulse energy, it is confirmed that the 385nm photoluminescence was mainly generated via two-photon absorption in ZnO nanowires under very intense light-matter interaction.

Self-assembled secondary ZnO nanoparticles, recognized with the agglomeration of crystalline subcrystals, are successfully synthesized by a simple sol-gel method. TEM images display that one artificial cluster behaves in a single-crystal-like wurtzite structure because subcrystals coagulate as the same crystal orientation. Moreover, from the resonant Raman scattering, the as-grown sample exhibits phonon red shift; meanwhile, the coupling strength between electron and longitudinal optical phonon, determined by the ratio of secondto first-order Raman scattering cross sections, diminishes compared with the samples after postannealing at 350 and 500°C. The size dependence of electron-phonon coupling is principally as a result of the Fröhlich interaction.

We report a simple method for fabricating heterostructured ZnMgO nanowires by annealing the preformed ZnO / MgO core-shell structure. Photoluminescence from the alloy nanowires shows strong near-band-edge ͑NBE͒ emission, reflecting good material quality. A blueshift of the NBE emission at room temperature after the annealing treatment is attributed to the diffusion of Mg from the shell into the core ZnO of the nanowires to form a ternary ZnMgO alloy. Band gap engineering and stimulated emissions of ZnMgO nanowires with different Mg doping concentrations are also demonstrated.

Sn/Cu solder joints serve as electrical pathways and mechanical supports in microelectronic packaging. This study demonstrates that the Cu plating formula has a strong effect on the incorporation of impurities in the Cu deposit and, consequently, affects the microstructural evolution of the Sn/Cu interface. An additive formula with polyethylene glycol (PEG) and chloride ions (Cl−) results in a high-level incorporation of impurities (carbon, oxygen, sulfur, and chlorine) in the Cu deposit. Segregation of impurities to the Sn/Cu interface occurs during thermal aging, which induces the formation of voids and Cu-impurity compounds (CuO, Cu2O, and CuS2) embedded in the Cu6Sn5 and Cu3Sn phase layers, forming an unusual alternating layer structure that is structurally loose and unstable. The addition of bis(3-sulfopropyl) disulfide (SPS) along with PEG and Cl− helps restore the microstructural integrity of the Sn/Cu interface by suppressing the incorporation of impurities. This suppression strongly depends upon the SPS concentration and the PEG molecular weight. The aging temperature also has a significant effect on the microstructural evolution of the Sn/Cu interface, which is determined by the change of the dominant diffusion species.