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Porous silicon is excited using near-infrared femtosecond pulsed and continuous wave radiation at an average intensity of ∼106 W/cm2 (8×1010 ;W/cm2 peak intensity in pulsed mode). Our results demonstrate the presence of micron-size regions for which the intensity of the photoluminescence has a highly nonlinear threshold, rising by several orders of magnitude near this incident intensity for both the pulsed and continuous wave cases. These results are discussed in terms of stimulated emission from quantum confinement engineered intrinsic Si-Si radiative traps in ultrasmall nanocrystallites, populated following two-photon absorption. © 1999 American Institute of Physics.

Epitaxial growth of Ni(Al)Si0.7Ge0.3 on relaxed Si0.7Ge0.3/Si(100) substrates was achieved via an Al interlayer mediated epitaxy. After annealing, most of the Al atoms from the original 3 nm interlayer diffused toward the surface but the remaining Al atoms in the epitaxial monogermanosilicide distributed uniformly, independent of the annealing temperatures. The incorporation of Al increases the transition temperature from the Ni-rich germanosilicide phase to the monogermanosilicide phase. The reduced Ni diffusion, the increased lattice constant due to substitutional Al, and the increased thermal expansion of monogermanosilicide are assumed to be the main mechanisms enabling the epitaxial growth of the quaternary silicide. [ABSTRACT FROM AUTHOR]

Ultrafast time-resolved differential reflectivity of Bi2Se3 crystals is studied using optical pump-probe spectroscopy. Three distinct relaxation processes are found to contribute to the initial transient reflectivity changes. The deduced relaxation timescale and the sign of the reflectivity change suggest that electron-phonon interactions and defect-induced charge trapping are the underlying mechanisms for the three processes. After the crystal is exposed to air, the relative strength of these processes is altered and becomes strongly dependent on the excitation photon energy. [ABSTRACT FROM AUTHOR]

Bipolar resistance switching behaviors in the M/La0.7Ca0.3MnO3/Pt (M=Pt, Ag, Cu, Al, Ti, and W) junctions were investigated. We found that the switching polarities of the junctions for M=Pt, Ag, and Cu were opposite to those for M=Al, Ti, and W. This phenomenon was attributed to the different Gibbs free energy of the metal oxide formation. Based on Auger electron spectroscopy measurement of the M/La0.7Ca0.3MnO3 interfaces, the switching mechanisms were further discussed in terms of metal electrode redox reaction for M=Al, Ti, and W and oxygen vacancy generation/annihilation in the La0.7Ca0.3MnO3 film for M=Pt, Ag, and Cu, respectively. [ABSTRACT FROM AUTHOR]

Dense hexagonal TmMnO3 ceramics were synthesized by solid-state reaction technique combined with high-pressure treatment which significantly increased the density of ceramic samples. The crystal structure of the hexagonal TmMnO3 oxide was refined by using Rietveld analysis based on powder x-ray diffraction experiment. We observed obvious dielectric peaks through dielectric measurement on the specimen subjected to postannealing in oxygen atmosphere. A ferroelectric-paraelectric transition around 348 °C is identified. Polarization-electric field hysteresis (P-E) loop measurement proved the ferroelectricity of the sample at room temperature. [ABSTRACT FROM AUTHOR]

The authors performed a systematic study of the structural and electrical properties of Nb:TiO2 thin films by varying the substrate temperature (TS) and oxygen partial pressure (PO2). Niobium is found to incorporate easily and substitutionally into titanium lattice site as indicated by its low activation energy. By increasing TS, the carrier concentration (n) increases in the same way that niobium substitution fraction (s) increases, and the mobility increases as the structural quality is improved. With increasing PO2, n decreases dramatically though s does not change considerably. This may indicate that a large number of p-type native defects form, which “kill” the electrons produced by the Nb donors. [ABSTRACT FROM AUTHOR]

First-principles calculations on the electronic and magnetic properties of BiNiO3 reveal that the G-type antiferromagnetic structure with the insulating ground state is more stable than other possible configurations. The hybridization of Ni–O and Bi–O leads to the reduction of the spin magnetic moment to 1.67μB in comparison with the Ni2+ d8 configuration of 2μB. The band gap of the antiferromagnetic insulating ground state is predicted to be 0.68 eV. The antiferromagnetic interaction induces the localized spins to be S=1 in the G-antiferromagnetic structure of BiNiO3. [ABSTRACT FROM AUTHOR]

p-type Zn1-xMgxO films doped with N and Al have been deposited by means of introducing Mg into p-type N- and Al-doped ZnO films using ultrasonic spray pyrolysis (USP) method. The structure of the films is confirmed by x-ray diffraction. Hall-effect measurements indicate that the p-type Zn1-xMgxO film shows a low resistivity of 6.4×10-2 Ω cm, high mobility of 11.7 cm2/V s and high carrier concentration of 8.31×1018 cm-3 at room temperature. Furthermore, the optical absorption edge and photoluminescence (PL) peak of p-type Zn1-xMgxO film shift to a shorter wavelength of 356 nm while maintaining excellent electrical performances. The blueshift extent of the film based on p-type ZnO film was not as distinct as compared to that of Zn1-xMgxO film based on pure ZnO film, perhaps owing to the variations in the effectiveness of Mg incorporation in the p-type Zn1-xMgxO film and in the Zn1-xMgxO film. [ABSTRACT FROM AUTHOR]

This paper describes a low-cost soft-lithography method for building large-numerical-aperture microlenses in hybrid sol-gel glass. The fabrication processes comprise three steps, namely fabrication of large numerical aperture microlens array in photoresist as a master, replication of the master in poly-dimethylsiloxane (PDMS) as elastomeric molds and reproduction of the PDMS replica onto the hybrid sol-gel glass as an end structure. Comparing with the direct UV fabrication in the photosensitive sol-gel glass, the proposed method provides a unique advantage in terms of fabrication freedom in shape and thickness of micro-optical elements in the sol-gel glass. This eliminates the difficulties in direct photolithography in sol-gel glass for arbitrary shapes and great thickness due to ever increasing demands. [ABSTRACT FROM AUTHOR]

We present finite-difference time-domain studies for self-collimated beams in photonic crystal structures. Using a pulse propagation technique that eliminates the interference from the boundary of finite photonic crystal structures, we show that the self-collimation phenomena can occur within a relatively wide bandwidth. We also demonstrate near-perfect operation efficiencies over wide frequency ranges in bends and splitters constructed by simply truncating the photonic crystal. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the microstructure and magnetic properties of Sm[sub2](Fe, Si)[sub17]C[subx]/alpha-Fe nanocomposite magnets prepared under high pressure. Coercivity of nanocomposite magnets; Intensity distribution among the Sm[sub2](Fe, Si)[sub17]C[subx] and alpha-Fee peaks in both normal-pressure and high-pressure annealing samples.

The authors performed a systematic study of the structural and electrical properties of Nb:TiO2 thin films by varying the substrate temperature (TS) and oxygen partial pressure (PO2). Niobium is found to incorporate easily and substitutionally into titanium lattice site as indicated by its low activation energy. By increasing TS, the carrier concentration (n) increases in the same way that niobium substitution fraction (s) increases, and the mobility increases as the structural quality is improved. With increasing PO2, n decreases dramatically though s does not change considerably. This may indicate that a large number of p-type native defects form, which “kill” the electrons produced by the Nb donors. [ABSTRACT FROM AUTHOR]

First-principles calculations on the electronic and magnetic properties of BiNiO3 reveal that the G-type antiferromagnetic structure with the insulating ground state is more stable than other possible configurations. The hybridization of Ni–O and Bi–O leads to the reduction of the spin magnetic moment to 1.67μB in comparison with the Ni2+ d8 configuration of 2μB. The band gap of the antiferromagnetic insulating ground state is predicted to be 0.68 eV. The antiferromagnetic interaction induces the localized spins to be S=1 in the G-antiferromagnetic structure of BiNiO3. [ABSTRACT FROM AUTHOR]