Ning-Ning Liu

Nonlinear optical properties of self-organized complex oxide Ce : BaTiO3 quantum dots grown by pulsed laser deposition

Ordered self-organized complex oxide Ce:BaTiO3 quantum dots shaped as a pyramid with a square base were fabricated by pulsed laser deposition. The density of the quantum dots was about 140 μm−2. The nonlinear optical properties were determined by the single beam Z scan method at a wavelength of 0.532 μm with a laser duration of 10 ns. The nonlinear refractive indices of the wetting layer and the self-organized ordered quantum dots were 8.87×10−8 and 6.39×10−7 esu, respectively. The mechanisms of the nonlinear effect enhancement for these low-dimensional structures are discussed.

Fabrication and characteristics of CeO2 films on Si(1 0 0) substrates by pulsed laser deposition

A detailed investigation about the dependence of film orientation on deposition temperature and ambient oxygen pressure has been carried out for CeO2 films on Si(1 0 0) substrates using pulsed laser deposition. It has been found that the CeO2 film orientation varies with increasing oxygen pressure at 750 degrees C deposition temperature. In addition, the recovery of preferential orientation of CeO2 films grown at 20 Pa ambient oxygen pressure with increasing deposition temperature has also been found for the first time. X-ray photoelectron spectroscopy (XPS) measurements confirm that stoichiometric CeO2 films can be grown at lower oxygen pressure(similar to 5 x 10(-3) Pa). HRTEM result also indicates that the CeO2 films grown at low oxygen pressure are of high crystallinity

Third-order optical nonlinear properties of amorphous Si/SiO2 superlattices fabricated by magnetron sputtering

Abstract The nonlinear optical response of amorphous Si/SiO2 superlattices fabricated by magnetron sputtering are studied using the Z-scan technique. The real and imaginary parts of the third-order optical nonlinearity χ(3) have been measured at 532 nm and found to be 6.392×10−7 esu and −9.814×10−7 esu, respectively. The results indicate an enhancement over crystalline silicon and porous silicon, which may be attractive for potential application in electro-optic devices.

Curie temperature for a finite alternating ferroelectric superlattice

We examine the critical behavior of a finite alternating ferroelectric superlattice based on the transverse Ising model. By the transfer matrix method we derive analytical equations for the Curie temperature of the superlattice. Numerical results are obtained for the dependence of the Curie temperature on the thickness and exchange constants of the superlattice. The effect of transverse field on the Curie temperature is also investigated.

Curie temperature for an alternating magnetic superlattice

Abstract We examine the critical behavior of a magnetic superlattice which is made up of two magnetic materials, A and B. By transfer matrix method we derive the analytical equations for Curie temperature of the superlattice which alternates as ABAB…AB or ABA…BA. Numerical results are obtained for the dependence of Curie temperature on the thickness and exchange constants of the superlattice. The effects of the surface modification are also studied numerically.

Pressure Behavior of Deep Centers in ZnSxTe1—x Alloys

We have measured photoluminescence of ZnSxTe1-x alloys (x > 0.7) at 300 K and under hydrostatic pressure up to 7 GPa. The spectra contain only a broad emission band under excitation of the 406.7 nm line. Its pressure coefficients are 47, 62 and 45 meV/GPa for x = 0.98, 0.92 and 0.79 samples, which are about 26%, 7% and 38% smaller than that of the band gap in the corresponding alloys. The Stokes shifts between emission and absorption of the bands were calculated by fitting the pressure dependence of the emission intensity, being 0.29, 0.48 and 0.13 eV for the three samples, respectively. The small pressure coefficient and large Stokes shift indicate that the emission band observed in our samples may correspond to the Te isoelectronic center in the ZnSxTe1-x alloy.

Phase transitions in a transverse spin- Ising ferroelectric superlattice

Within the framework of the mean-field theory, we study the phase transitions of transverse spin-1/2 Ising ferroelectric superlattices formed from two alternating materials. By the transfer matrix method, we derive a nonlinear equation for the phase transition temperature of the superlattice with arbitrary layer-number in one period and arbitrary exchange constants. The dependence of the transition temperature on the layer-number and the interface exchange constant was calculated numerically

Phase transition properties of a finite ferroelectric superlattice from the transverse Ising model.

We consider a finite ferroelectric superlattice in which the elementary unit cell is made up of 1 atomic layers of type A and n atomic layers of type B. Based on the transverse Ising model we examine the phase transition properties of the ferroelectric superlattice. Using the transfer matrix method we derive the equation for the Curie temperature of the superlattice. Numerical results are given for the dependence of the Curie temperature on the thickness and exchange constants of the superlattice.

Self-organized growth of complex oxide Ce : BaTiO3 nano-islands on (1 0 0)MgO by pulsed laser ablation

Pulsed laser ablation epitaxial Stransky-Krastanow growth of self-organized complex oxide Ce:BaTiO3 islands on MgO(1 0 0) substrates is demonstrated. The lattice mismatch of Ce: BaTiO3/MgO heterostructure leads to a strain-driven distribution of nanoscale Ce : BaTiO3 islands on the top of a two-dimensionally grown wetting layer. Atomic force microscopy, X-ray diffraction and X-ray energy dispersive spectrometer are used to determine the structure of the wetting layer and morphological dimensions and the composition of the islands. The square base pyramidal complex oxide islands are observed. The density of the islands, their average dimension, height, and aspect ratio turn out to be about 140 mu m(-2), 87.9 nm, 9.6 nm, and 0.15, respectively, for our experimental condition. Furthermore, the difference of the critical thickness between the complex oxide and semiconductor with similar lattice mismatch and their mechanism are discussed