A low electric field applied during film deposition has a significant influence on the orientation of ferroelectric thin films prepared by pulsed laser deposition. C-axis oriented growth of LiNbO3 films was demonstrated on fused silica with the aid of a low bias voltage Vb = 0-120 V, and complete c-axis orientation was achieved at Vb = 110 V. In contrast, the electric field cannot induce c-axis orientation of LiTaO3 films. Theoretical analysis suggests that the electrostatic energy provides an extra driving force for the c-axis oriented growth of the ferroelectric films if the permittivity components satisfy ε33/ε11 ≥ 2, as in LiNbO3 film, but not if ε33/ε11 > 2 at the deposition temperature, as in LiTaO3 film. © 1996 American Institute of Physics.

Hu W. S.;Liu Z. G.;Feng D.

Journal of Applied Physics

1996

We study the magnetostatic modes in a Fibonacci multilayer consisting of alternating magnetic and nonmagnetic layers. The constant of motion, depending on both the in-plane wave vector and the frequency of the mode, is explicitly obtained and used to describe general features of the frequency spectra. Furthermore, spin wave spectra and precession amplitudes of magnetization for a finite Fibonacci multilayer are numerically calculated by the transfer matrix method. For a given in-plane wave vector, the distribution of frequency exhibits a triadic Cantor structure with large gaps in the low-frequency region, small gaps in the high-frquency region, and many ''isolated'' modes in the gaps. The gaps strongly depend on the in-plane wave vector and the thicknesses of the magnetic and nonmagnetic layers. We find three types of states in the quasiperiodic direction: extended states in the high-frequency region near the upper band edge, critical states in the triadic subbands, and surface states in gaps. Besides the conventional Damon-Eshbach surface mode localized at two opposite surfaces of the multilayer for positive and negative wave vectors, respectively, another kind of surface modes are discovered. When the wave vector is reversed, these modes are still localized at the same sides of the multilayer. © 1995 The American Physical Society.

Feng J. W.;Jin G. J.;Hu A.;Kang S. S.;Jiang S. S.;Feng D.

Physical Review B

1995

A new class of quasiperiodic superlattice structures called three-component Fibonacci structures has been studied both theoretically and experimentally. These structures with the characteristic irrational intervals A, B, and C can be produced by the substitution rule AAC, CB, and BA. The projection method is applied to deal with the pattern and index of their diffraction spectrum. The analytical results are compared with the experimental one from three-component Fibonacci Ta/Al superlattices. The experimental results are in good agreement with the numerical calculations using the model for compositionally modulated multilayers. Some possible applications of these structures are discussed. © 1992 The American Physical Society.

Peng R. W.;Hu A.;Jiang S. S.;Zhang C. S.;Feng D.

Physical Review B

1992

We present the studies of the interface optical phonons in k-component Fibonacci (KCF) dielectric multilyaers, in which k different incommensurate intervals are arranged according to a substitution rule. In the dielectric continuum approximation, the dispersion relations and the frequency spectra are obtained by the transfer-matrix method. Free-boundary and periodic-boundary conditions are taken into account. With the free-boundary condition, the dispersion relations of the interface optical phonons in the KCF multilayers are demonstrated to possess two bands of dual structures. For the KCF multilayers with (Formula presented) each subband is a self-similar structure and contains (Formula presented) filial generations; for the KCF multilayers with (Formula presented) the sub-bands do not show self-similarity, but they still have the hierarchical characteristic (where k is the number of different incommensurate intervals). In the case of the periodic-boundary condition, the frequency span of interface optical phonons in the KCF multilayers is singularly continuous and the frequency spectra are analyzed by a multifractal concept. A dimensional spectrum of singularities associated with the frequency spectrum, (Formula presented) demonstrates that in the KCF multilayers the interface optical phonons distribution presents a genuine multifractality. It is also shown that by increasing the number of different incommensurate intervals in KCF multilayers, the fractal dimension of the corresponding support decreases. © 1999 The American Physical Society.

Peng R. W.;Jin G. J.;Wang Mu;Hu A.;Jiang S. S.;Feng D.

Physical Review B Condensed Matter and Materials Physics

1999

Structural properties of alternating nanocrystalline silicon/amorphous silicon multilayers with visible light emission at room temperature were examined by means of x-ray diffraction. According to the linewidths and intensities of the diffraction peaks in the low- and high-angle ranges, we have determined the effective interface thickness, the mean crystallite sizes, and the internal strains, which are closely related to the photoluminescence in this material. In addition, the existence of the voids or holes was also observed, indicating that the improved electrical properties of this kind of hydrogenated nanocrystalline materials are due to the inhomogeneous structure of the material. © 1997 American Institute of Physics.

Wu X. L.;Tong S.;Liu X. N.;Bao X. M.;Jiang S. S.;Feng D.;Siu G. G.

Applied Physics Letters

1997

Using Zn targets in a 100 Pa oxygen ambient at substrate temperatures of 275-425°C, completely (0001)-textured ZnO thin films have been deposited on (0001)-oriented α-SiO 2 substrates by the pulsed laser reactive ablation technique. The effects of deposition parameters on the microstructures of the films have been analysed. The full-width-at-half-maximum (FWHM) 2θ angle of the (0002) X-ray reflection reached its minimum of 0.320° for the ZnO films grown at substrate temperatures between 325 and 375°C. The films proved to be dense, smooth, transparent and colourless. Thick lamina-like grains were observed in the ZnO films by scanning electron microscopy. The reflective indices of the films vs. wavelength calculated from the measured oscillated optical transmittance were close to those of bulk ZnO crystal. The band gap of the piezoelectric semiconductor ZnO was estimated as 3.28 eV. Favourable optical waveguiding properties of the films have been demonstrated by the observation of sharp m-lines from the transverse electric (TE) modes excited by the prism-coupling method.

Hu W. S.;Liu Z. G.;Sun J.;Guo X. L.;Yang Z. J.;Feng D.;Shi L. J.

Materials Science and Engineering B

1996

Completely (001) textured LiNbO3 films have been fabricated upon thermally oxidized SiO2/Si substrates by in situ application of a low electric field in a pulsed-laser deposition system. The biased voltage was 70-75 V on parallel electrodes separated by 7.0 mm. Li-enriched crystal and ceramic targets were used. The achieved films were nearly stoichiometric and have smooth surfaces. Waveguiding performance of the films was demonstrated by a prism-coupling method. The refractive indices were calculated on the basis of isotropic and anisotropic waveguide theories. A low-light propagation loss of 1.9 dB/cm in the films was achieved. It is expected that the films can be used in integrated-optical devices that require d33, γ33, ε33, and n33 elements. © 1996 Optical Society of America.

Hu W. S.;Liu Z. G.;Lu Y. Q.;Zhu S. N.;Feng D.

Optics Letters

1996

The concentration distributions of Y dopings in LiTaO 3 across the growth striations in as-grown crystals are obtained by means of x-ray energy dispersive spectrum analysis in a scanning transmission electron microscope at room temperature. The results show that it is the concentration gradient of the dopings which determines the configurations of ferroelectric domains. The mechanism for the formation of the periodic laminar ferroelectric domains (PLFDs) is explained theoretically by considering the influence of the distributions of the dopings on the para-ferroelectric phase transitions in LiTaO 3 and LiNbO 3 crystals. It is shown that the coupling between the order parameter and the conjugate external field, which results from the ambipolar diffusion or from the strain-induced polarization mechanism associated with the dopings and their compensated point defects, is just the physical reason for the formation of such PLFDs in these two materials.

Chen Jun;Zhou Qun;Hong Jin-Feng;Wang Wen-Shang;Ming Nai-Ben;Feng Duan;Fang Chen-Gao

Journal of Applied Physics

1989

The microstructures of as-deposited Co-Ag nano-granular films are characterized by X-ray diffraction, transmission electron microscopy and high-resolution electron microscopy. In as-deposited films, there is a strong tendency for phase separation to occur; Co and Ag particles coexist in the films. The average size of Co grains varies with the Co concentration. Ag particles have the preferential lattice orientation <110> and Co particles have lattice orientations <110>, <111>, <112>, and <100> in the direction of the film surface normal. There is a tendency for two connecting grains to have two groups of parallel lattice planes.

Du J. H.;Li Q.;Wang L. C.;Sang H.;Zhang S. Y.;Du Y. W.;Feng D.

Journal of Physics Condensed Matter

1995

Using the Czochralski method we have grown LiNbO3crystals with periodic laminar ferroelectric domains whose half-period nearly corresponds to the coherence length. Quasi-phase-matching for the nonlinear optical coefficient d33has been approximately realized and enhancement of second-harmonic generation relative to conventionally phase-matched crystals of the same length has been observed.

Feng Duan;Ming Nai-Ben;Hong Jing-Fen;Yang Yong-Shun;Zhu Jin-Song;Yang Zhen;Wang Ye-Ning

Applied Physics Letters

1980