A one-dimensional k-component Fibonacci structure, with k different intervals, is the natural extension of the standard Fibonacci structure with two intervals. We prove that the structures with k≤5 are quasiperiodic, and the projection method can be applied to deal with the pattern and indexing problem of its x-ray-diffraction spectrum. For k>5, the resulting structures are no longer quasiperiodic, but they are still ordering. The analytically obtained results have been compared to experimental results for Ta-Al three-component Fibonacci superlattice structures and to numerical calculations. © 1993 The American Physical Society.

Hu A.;Wen Z. X.;Jiang S. S.;Tong W. T.;Peng R. W.;Feng D.

Physical Review B

1993

In situ observation of the ferroelastic phase transition in Er-doped lanthanum pentaphosphate has been carried out by real time white-beam synchrotron radiation x-ray topography. The ferroelastic domain walls are found to vanish and reappear with characteristics of a classical second-order transition on topographs on cycling the sample between room temperature and above the transition temperature. However, fluctuations of the number of domain walls with temperature approaching the Curie point are revealed for the first time and shown to be reversible. Discussions on these interesting phenomena are presented.

Hu Z. W.;Jiang S. S.;Huang P. Q.;Huang X. R.;Feng D.;Wang J. Y.;Li L. X.

Applied Physics Letters

1994

C60 powder, pellets and single crystals were oxygenated at 0.11 kbar and then studied with MAS ¹³C NMR, DSC and XRD. In agreement with reports by other authors, powder samples exhibited minor NMR resonances, indicative of blocking of fullerene rotation by interstitial oxygen, the distribution of which had yet to attain the equilibrium state. Also, as reported by others, DSC showed two endothermic peaks near 260 K, and both, we found, corresponded to a discontinuous change in the lattice parameter. The peak on the low-temperature side moved up in temperature with elapsed time. Pellets, in which presumably oxygen diffused easily, displayed only one peak but shifted in the same manner. Single crystals, in contrast, had only the higher-temperature "immobile" peak. We suggest that the shifting endotherm originates from the transition of oxygen-intercalated C60 to a merohedral disordered phase, in which the rotation of fullerene molecules is partially impeded by oxygen. A phenomenological model is proposed for this transition.

Gu Min;Wang Yening;Zhang Weiyi;Hu Chen;Yan Feng;Feng Duan;Tang Tong B.

Physics Letters Section A General Atomic and Solid State Physics

1996

The in-plane uniaxial anisotropy and perpendicular anisotropy of sputtered Co/Ag(111) multilayers have been investigated by magnetic measurements and the in-plane ferromagnetic resonance (FMR) technique. The data-fitting analysis for the FMR experimental results about the angular dependence of the resonance field shows that the in-plane anisotropy cannot be fully described by only using the first-order term, and the second-order term must be included. Furthermore, the interface-induced anisotropy has been obtained by FMR. Both ferromagnetic and antiferromagnetic couplings have been revealed by hysteresis loop measurement. Specifically, a spin-flip phase transition has been observed in the sputtered Co/Ag(111) multilayers, which is attributed to the effects of the AF-coupling and in-plane uniaxial anisotropy. © 1995 American Institute of Physics.

Feng J. W.;Kang S. S.;Pan F. M.;Jin G. J.;Lu M.;Hu A.;Jiang S. S.;Feng D.

Journal of Applied Physics

1995

We study in this paper the diffraction spectrum (Fourier transform) of a one-dimensional k-component Fibonacci structure (KCFS), which contains k different intervals and can be generated by a substitution rule. Theoretical and numerical calculations based on the geometrical models for atomic KCFS have been made. The structures with 1

Peng R. W.;Wang Mu;Hu An;Jiang S. S.;Jin G. J.;Feng Duan

Physical Review B

1995

We present an absolute measurement of a two-photon absorption (TPA) coefficient of C 60 thin film at 633 nm. Large values of β≊4.4 cm/W were determined. A nearly resonant TPA transition around the 3.76 eV absorption region was discussed.

Han Y. N.;Zhang W. J.;Gao X. M.;Cui Y. B.;Xia Y. X.;Gu G.;Zang W. C.;Yang P.;Du Y. W.;Feng D.

Applied Physics Letters

1993

Nanocrystalline Ge:H films were deposited on the anode of a conventional plasma-enhanced chemical vapor deposition system using highly H2-diluted GeH4 as source gas. The structural changes with substrate temperature, hydrogen dilution, and rf power were investigated by x-ray diffraction and Raman scattering. The hydrogen content and H bonding configuration were determined by infrared absorption spectroscopy. It was found that increased rf power mainly favors nucleation of grains while increased H2 dilution mainly favors the subsequent growth of grains. Transitions from an amorphous to a crystalline and then back to an amorphous phase are observed as the substrate temperature is increased. The amorphous phase at high temperatures and variations in the preferred crystallite orientations are explained by changes in the diffusion length of adsorbed precursors due to changing hydrogen coverage on the growing surface. © 1998 American Institute of Physics.

Poulsen Per R.;Wang Mingxiang;Xu Jun;Li Wei;Chen Kunji;Wang Guanghou;Feng Duan

Journal of Applied Physics

1998

By means of a conventional Raman scattering technique, Raman spectra of proton-exchanged LiNbO3 (PELN) and LiTaO3 (PELT) crystals were examined as a function of PE time. The experimental result was that the relative intensities IE(TO)/IA1(TO) reach maxima and minima in PELN and PELT with about 12 and 8 h proton treatment, respectively, when y-surface cracks are visible. This phenomenon, together with the different extraordinary index changes reported previously, reflects the microstructural difference between PELN and PELT. This difference mainly arises from both the different displacements of positive ions along the optical z axis in bulk and the different proton distributions in the exchange layer due to PE.

Wu Xing-Long;Yan Feng;Zhang Ming-Sheng;Jiang Shu-Sheng;Feng Duan

Journal of Physics Condensed Matter

1996

Raman spectra of LiNbO3 crystals with different proton-exchange time were examined. E(TO) and A1(TO) modes appear in the A 1- and E-symmetry spectra, respectively, and their intensities show a dependence on exchange time. We attribute these results to both the internal strains resulting from order-disorder distribution of protons in the sample and the enhanced photorefractive effect. In addition, in the E-symmetry spectra the softening of A1(TO) mode at 630 cm^-1 was found about 4%. The phenomenon arises from the existence of ferroelectric and paraelectric phases in the protonated sample at room temperature. © 1995 American Institute of Physics.

Wu Xinglong;Zhang Ming-Sheng;Yan Feng;Feng Duan

Journal of Applied Physics

1995

We have examined the Raman spectra of violet and infrared emitting Ge⁺-implanted SiO2 films with special emphasis upon annealing temperature (AT) dependence of Raman scattering. We found that the complete spectrum mainly consists of three bands at 220-280, 300, and 430 cm^-1, corresponding to scattering of Ge-related components, Ge nanocrystallites, and localized Si-Si optical phonons in the Ge neighborhoods, respectively. The Ge crystalline band shows an obvious AT dependence. The theoretical result from the phonon confinement model can predict its linewidth change with AT, but cannot explain its constant peak frequency. Based on the experimental result from x-ray diffraction, we attributed the discrepancy mainly to the compressive stress exerted on Ge nanocrystallites, which leads to the upshift of Ge crystallite peak thereby basically compensating the downshift caused by the confinement on phonon frequency. © 1997 American Institute of Physics.

Wu X. L.;Gao T.;Bao X. M.;Yan F.;Jiang S. S.;Feng D.

Journal of Applied Physics

1997