Yen-Ru Lee

Polarization-resolved output analysis of X-ray multiple-wave interaction

The polarization suppression of the interfering components in X-ray multiple-wave interaction is observed for the first time by using a polarization analyzer with an arbitrary inclination of the diffraction plane with respect to that of the investigated crystal. The condition for total suppression of the multiple-wave interaction outside the investigated crystals by a polarization analyzer is derived theoretically from the modified Born approximation. By means of the partial suppression of the strong interfering component, the increase in the visibility of multiple-wave interference is experimentally and theoretically demonstrated. The proposed experimental polarization-resolved technique provides an operational way to enhance the visibility of X-ray multiple-wave interaction outside the investigated crystals for direct phase determination.

Characterization of ordered mesoporous films on silicon (001) surface using X‐ray and electron diffraction

A continuous silica film with well aligned mesochannels parallel to the Si(001) surface was found to be formed through sol–gel dip-coating of a silica precursor with nonionic ethylene oxide surfactant. Two two-dimensional mesoporous structures in centered and non-centered rectangular symmetries and with the short axes of elongated ellipsoidal pores normal to the surface were observed by X-ray and electron diffraction. Detailed transmission electron microscopy investigations were employed to view the direction dependence of the channel or pore packing in the continuous film.

Direct measurement of spatial distortions of charge density waves in K0.3MoO3

Using x-ray scattering and multiple diffraction on a charge density wave (CDW) material, K0.3MoO3, under applied voltages, we demonstrate that the occurrence of nonlinear conductivity caused by the periodic media is through the internal deformation of the CDW lattice, i.e., a phase jump of 2π, as the applied voltage exceeds the threshold. From the evolution of the measured peak width of satellite reflections as a function of the field strength, we also report that the CDW lattice can be driven to move and undergo a dynamic phase transition from the disordered pinning state to ordered moving solid state and then to disordered moving liquid.

X-ray multiple-wave coherent interaction in a quasi-two-dimensional material NbSe2-2H.

The first observation of the X-ray multiple-wave interaction in an incommensurate charge-density-wave (CDW) modulated structure at low temperatures is reported for an example of a quasi-two-dimensional material, NbSe(2)-2H. Via the coherent interaction between the X-ray waves propagating in the CDW-modulated structure and the host structure, the phase-dependent intensity variations of a CDW reflection were detected. In accord with a centrosymmetric structure, the phases of the structure-factor triplets of two CDW reflections and a Bragg reflection of the host structure were determined to be either 0 or 180 degrees, and not to vary with temperature. Relative phase differences of the two CDW reflections are also deduced.

Phase-dependent polarization aspects of three-wave X-ray diffraction: an iterative Born approximation

The iterative Born approximation is derived for three-wave dynamical X-ray diffraction. Dependence of the three-wave diffraction profiles of the diffracted wave on the polarization state of a linearly polarized incident wave is theoretically and experimentally investigated. General conditions of the phase sensitivity as well as the asymmetry of diffraction profiles are obtained from this approximation and compared with direct dynamical calculations. Reasonable qualitative agreement between the results obtained from this iterative approach and the exact dynamical calculation is shown. A new feature of reversing asymmetry of an intensity profile with respect to phase change is theoretically predicted.

Two-leg t − J ladder: A mean-field description

Two-leg t-J ladders are investigated in the framework of a combination of the phase string formulation and bond-operator representation. We develope a mean-field theory in the strong rung interaction regime, i.e.

Qantitative determination of phase for macromolecular crystals using multiple diffraction methods and dynamical theory

J_{\perp}\gg J, t

Direct Observation of Resonance Fringes in X-ray Cavity: A Diffraction Experiment

, which provides a unified description of the undoped insulating phase and the low doping phase --- the so-called C1S0 phase. Both of them are characterized by the resonating-valence-bond (RVB) order parameter, with gap opened up in all spin excitations. The ground state of the doped phase is intrinsically a superconductor with a d-wave symmetry, which is driven by the RVB correlations. The ground-state energy is in good agreement with numerical results. Phase separation is shown to occur beyond some critical value of J/t for given doping concentration. We also show that the spin gap in the doped phase is determined by quasi-particle-like excitations. The local structure of hole pairs as well as the spectra of various spin and charge modes are analyzed in comparison with other approaches.

Substrate-mediated multiwave resonance grazing incidence x-ray diffraction in thin films: A method for direct phase determination

Abstract Multiple diffraction techniques for quantitative phase determination of macromolecular crystals are briefly described and overviewed. The modified second-order iterative approximation [Chang, S. L.; Tang, M. T.: Acta Cryst. A44 (1988) 1065] is employed to derive analytic expressions for the phase sensitivity of multiple diffraction and the visibility of multiple diffraction line profiles. Calculated visibility and sensitivity of three-beam cases of the protein, aldose reductase, are illustrated. The functions used for intensity profile fitting in the quantitative phase determination procedure are also modified accordingly. This calculation provides an effective way of choosing appropriate reflections for experimentally generating useful three-beam diffractions for phase analysis. Other practical issues are also addressed.

Direct observation of charge ordering in magnetite using resonant multiwave x-ray diffraction.

C431 P.15.01.1 Acta Cryst. (2005). A61, C431 Direct Observation of Resonance Fringes in X-ray Cavity: A Diffraction Experiment Shih-Lin Chang, Yuriy P. Stetsko, Mau-Tsu Tang, Yen-Ru Lee, Wen-Hsien Sun, Hsueh-Hung Wu, Makina Yabashi, Tetsuya Ishikawa, Department of Physics, National Tsing Hua University, Taiwan, R.O.C.. National Synchrotron Radiation Research Center Taiwan, R.O.C.. Spring-8/JASRI, Japan. Spring-8/RIKEN,Japan. Email: slchang@phys.nthu.edu.tw