We have investigated the different mechanisms of photoluminescence ͑PL͒ of silicon nanocrystals due to the quantum confinement effect ͑QCE͒ and interface states. Si nanocrystals were formed by pulsed-laser deposition in inert argon and reactive oxygen gas. The collisions between the ejected species greatly influence the morphology of the Si nanocrystals and cause a transition from a film structure to a porous cauliflowerlike structure, as the ambient gas pressure increases from 1 mTorr to 1 Torr. The oxygen content of the Si nanocrystals increases with increasing O 2 ambient pressure, and nearly SiO 2 stoichiometry is obtained when the O 2 pressure is higher than 100 mTorr. Broad PL spectra are observed from Si nanocrystals. The peak position and intensity of the PL band at 1.8 -2.1 eV vary with ambient gas pressure, while intensity changes and blueshifts are observed after oxidation and annealing. The PL band at 2.55 eV shows vibronic structures with periodic spacing of 97Ϯ9 meV, while no peak shift is found before and after oxidation and annealing. Raman and transmission electron microscope measurements show consistent results in crystal size while more accurate atomic force microscope measurements reveal a smaller crystal size. X-ray diffraction reveals a polycrystal structure in the Si nanocrystals and the crystallinity improves after annealing. Combined with the PL spectra of Si nanocrystals obtained by crumbling electrochemically etched porous Si layer, the results clearly demonstrate that the PL band at 1.8 -2.1 eV is due to the QCE in the Si nanocrystal core, while the PL band at 2.55 eV is related to localized surface states at the SiO x /Si interface.

Thin films of HfO2 high-k dielectric have been prepared by pulsed-laser deposition at various substrate temperatures and pressures. X-ray diffraction, atomic force microscopy, secondary ion mass spectroscopy and ellipsometry were used to characterize the deposited films. Experimental results show that substrate temperature has little effect on the stoichiometry, while deposition pressure plays an important role in determining the ratio of Hf and O. It is also found that the optical properties of the HfO2 thin films have strong dependence on both the deposition temperature and pressure. The electrical properties of HfO2 metal–insulator–metal (MIM) capacitors were investigated at various deposition temperatures. It is shown that the HfO2 (56 nm) MIM capacitor fabricated at 200 °C shows an overall high performance, such as a high capacitance density of ∼3.0 fF/μm2, a low leakage current of 2×10−9 A/cm2 at 3 V, low-voltage coefficients of capacitance, and good-frequency dispersion properties. All of these indicate that the HfO2 MIM capacitors are very suitable for use in Si analog circuit applications.

Magnetic properties of vortex nucleation, annihilation, and switching field distribution (SFD) in NiFe disk arrays, where the elements are with 300nm diameter and different degrees of asymmetry, were investigated through measurements and simulations of hysteresis loop. The nucleation and annihilation of vortex state show strong dependences on the asymmetry. More interestingly, the width of SFD, the crucial factor for high-density storage application, oscillating with the degree of asymmetry is observed. The simulation results agree well with the experimental data.

Silicon oxide ͑SiO x ͒ nanostructured films have been formed by pulsed-laser deposition of Si in oxygen at different substrate temperatures, in order to study the structures and optical properties related to quantum confinement effects. After laser ablation, the single-crystal Si(100) target is converted to a polycrystal structure and shows weak photoluminescence (PL). The as-deposited SiO x nanostructured films show large particles (i.e., droplets) on a uniform background film. The droplets with weak PL emission have the same high crystallinity as the Si(100) target. Strong PL is observed from the amorphouslike background films rather than from the crystalline droplets. As substrate temperatures increase from room temperature ͑23°C͒ to 800°C, the PL band continually redshifts from 1.9 to 1.6 eV and the optical band gap decreases from 2.9 to 2.1 eV due to the increased Si concentration in the films. After high-vacuum annealing at 800°C, both the PL and optical absorption are enhanced. The optical band gap also decreases after annealing. Combined with the progressive PL redshifts of the SiO x films with increasing Si concentration by plasma-enhanced chemical vapor deposition, the results support the quantum confinement theory.

Effect of antiferromagnet on superconductivity has been investigated in IrMn/Nb bilayers. Significant suppression of both transition temperature (Tc) and lower critical field (Hc1) of Nb is found in IrMn/Nb bilayers as compared to a single layer Nb of same thickness; the suppression effect is even stronger than that of a ferromagnet in NiFe/Nb bilayers. The addition of an insulating MgO layer at the IrMn-Nb interface nearly restores Tc to that of the single layer Nb, but Hc1 still remains suppressed. These results suggest that, in addition to proximity effect and magnetic impurity scattering, magnetostatic interaction also plays a role in suppressing superconductivity of Nb in IrMn/Nb bilayers. In addition to reduced Tc and Hc1, the IrMn layer also induces broadening in the transition temperature of Nb, which can be accounted for by a finite distribution of stray field from IrMn.