S. S. Jiang

Annealing temperature dependence of Raman scattering in Ge+-implanted SiO2 films

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.

Charge-oscillation-induced light transmission through subwavelength slits and holes

We present a concrete picture of spoof surface plasmons (SSPs) combined with cavity resonance to clarify the basic mechanism underlying extraordinary light transmission through metal films with subwavelength slits or holes. This picture may indicate a general mechanism of metallic nanostructure optics: When light is incident on a nonplanar conducting surface, the free electrons cannot move homogeneously in response to the incident electric field, i.e., their movement can be impeded at the rough parts, forming inhomogeneous charge distributions. The oscillating charges and dipoles then emit photons (similar to Thomson scattering of x rays by oscillating electrons), and the interference between the photons may give rise to anomalous transmission, reflection, or scattering.

Microstructural variations of YBa2Cu3Oy doped with Ca at high doping level

Abstract We have prepared the Y 1− x Ca x Ba 2 Cu 3 O y with x ≤ compounds by the solid state reaction technique. The superconducting critical temperature was measured. The structural parameters as a function of Ca substitution were obtained through the detailed analysis of the X-ray diffraction for these Ca-doped samples. The variation of the lattice parameters, some meaningful bond lengths, and the microstrain in lattice change with the Ca content have been discussed.

White-beam synchrotron topographic characterization of flux-grown KTiOAsO4

KTiOAsO4 crystals grown from tungstate fluxes have been studied by white‐beam synchrotron radiation topography. It is shown that growth striations are primary planar defects. By anomalous scattering, ferroelectric domains in KTA are investigated and the ratio of ‖F(004)‖2 to ‖F(004)‖2 is calculated. The mechanisms of domain inversion via 2‐fold axis or n‐glide plane are also discussed in terms of the structural characteristics of KTA.

QUANTUM WAVEGUIDE THEORY OF SERIAL STUB STRUCTURES

The electronic behaviors in quantum wires with serial stubs are studied. A general theory of quantum waveguide based on transfer matrix method is developed and is used to treat periodic stub structures, serial stub structures with a defect stub, and Fibonacci stub structures. A number of interesting physical properties in connection with electronic transmission, energy spectra, and charge density distributions in these structures, are found theoretically. In particular, we find that whether there are periodicity and symmetry in the transmission and energy spectra depends on the commensurability of the length parameters. If one length ratio is incommensurate, then the transmission and energy spectra do not exhibit periodicity and symmetry even for periodic stub structures. In particular, the quasiperiodic behaviors are shown in Fibonacci stub structures proposed by us whenever the length parameters are commensurate. The experimental relevance is also addressed briefly.

Mechanochemical effects of grinding on the YBa2Cu3Ox superconductor

Abstract The mechanical grinding effects on the powders of YBa 2 Cu 3 O x superconductor are examined. The grain size, the oxygen content of the powders decrease, and the content of the amorphous phase, the crystal strain increase, with the increasing of grinding time. Except that for amorphous phase, the crystallized phase can be refined by the orthorhombic and tetragonal phases. The refined results show that the diffraction peaks broaden after continuous grinding. This broadening can be explained from the crystal strain and the small grain size due to prolonged grinding. The lattice constants of the refined phases vary with the grinding time.

Structure of La1.85Sr0.15CuO4 doped with Zn in high doping level

Abstract Practically impurity-free ceramic superconductors of La 1.85 Sr 0.15 Cu 1− y Zn n O 4 with 0.00 ≤ y ≤ 0.30 were synthesized. The structure of these Zn-doped samples was characterized by X-ray diffraction studies. Rietveld refinements show that there is a tetragonal-to-orthorhombic phase transition which occurs at about y ≈ 0.15. The bond length between the two apical oxygen atoms in the CuO 6 octahedra for the Zn-doped samples decreases with increasing content of Zn in the tetragonal region, and the tilt angle of the CuO 6 octahedra increasing with content of Zn in the orthorhombic region. The metal-insulator transition is also observed in this Zn-doped systems.

The suppression of magnetoresistance and superconductivity for La2/3Ca1/3MnO3/YBa2Cu3O7−δ bilayers

Abstract The La 2/3 Ca 1/3 MnO 3 (LCMO, t m =300 A)/YBa 2 Cu 3 O 7− δ (YBCO, t s =20–500 A) heterostructural bilayers are prepared by the rf magnetic sputtering technique on SrTiO 3 (STO) substrate at high temperature. Using the four-probe method, the electronic and magnetic transport properties have been investigated with and without magnetic field applied up to 4 T, The superconducting zero resistance temperature increases with the increase of the thickness of YBCO, t s , with t s >85 A. The nature of resistance for LCMO is screened by YBCO with the thickness more than about 250 A, but the magnetoresistance (MR) effect is observed in the bilayers. MR increases with the decrease of the thickness of YBCO. Structural characterizations of the bilayers show that there is interdiffusion appeared in the interface between LCMO and YBCO, and, LCMO and STO.

X-RAY DIFFRACTION STUDY OF ALTERNATING NANOCRYSTALLINE SILICON/AMORPHOUS SILICON MULTILAYERS

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.

X-RAY SMALL-ANGLE REFLECTION AND HIGH-ANGLE DIFFRACTION STUDIES ON Co/Cu MAGNETIC MULTILAYERS

With varying thickness of the spacer near the second oscillatory GMR peak in Co/Cu system, a series of glass/Fe/[Co/Cu]20/Co multilayers are prepared by magnetronsputtering technique. The MR values are relatively small. High angle X-ray diffraction shows that the copper crystallizes in fcc structure with (111) texture and the cobalt crystallizes in hcp structure with (002) preferential orientation. There is a mixed amorphous CoCu layer at the interface due to the diffusion between cobalt and copper, which may decrease the MR value. The thickness, the mass density for each sub-layer and the surfacial and interfacial roughnesses are refined from the X-ray specular reflectivity measurement.