X-ray standing wave and reflectometric characterization of multilayer structures

Microstructural characterization of synthetic periodic multilayers by x-ray standing waves have been presented. It has been shown that the analysis of multilayers by combined x-ray reflectometry (XRR) and x-ray standing wave (XSW) techniques can overcome the deficiencies of the individual techniques in microstructural analysis. While interface roughnesses are more accurately determined by the XRR technique, layer composition is more accurately determined by the XSW technique where an element is directly identified by its characteristic emission. These aspects have been explained with an example of a 20 period Pt/C multilayer. The composition of the C-layers due to Pt dissolution in the C-layers, Pt$_{x}$C$_{1-x}$, has been determined by the XSW technique. In the XSW analysis when the whole amount of Pt present in the C-layers is assumed to be within the broadened interface, it l eads to larger interface roughness values, inconsistent with those determined by the XRR technique. Constraining the interface roughness values to those determined by the XRR technique, requires an additional amount of dissolved Pt in the C-layers to expl ain the Pt fluorescence yield excited by the standing wave field. This analysis provides the average composition Pt$_{x}$C$_{1-x}$ of the C-layers .Comment: 12 pages RevTex, 10 eps figures embedde

A Resonant X-ray Scattering Study of Octahedral Tilt Ordering in LaMnO3_3 and Pr1−x_{1-x}Cax_xMnO3_3

We report an x-ray scattering study of octahedral tilt ordering in the manganite series Pr$_{1-x}$Ca$_x$MnO$_3$ with x=0.4 and 0.25 and in LaMnO$_3$. The sensitivity to tilt ordering is achieved by tuning the incident x-ray energy to the L$_I$, L$_{II}$ and L$_{III}$ absorption edges of Pr and La, respectively. The resulting energy-dependent profiles are characterized by a dipole-resonant peak and higher energy fine structure. The polarization dependence is predominantly $\sigma$-to-$\pi$ and the azimuthal dependence follows a sin-squared behavior. These results are similar to those obtained in recent x-ray scattering studies of orbital ordering carried out in these same materials at the Mn K edge. They lead to a description of the cross-section in terms of Templeton scattering in which the tilt ordering breaks the symmetry at the rare earth site. The most interesting result of the present work is our observation that octahedral tilt ordering persists above the orbital ordering transition temperatures in all three samples. Indeed, we identify separate structural transitions which may be associated with the onset of orbital and tilt ordering, respectively, and characterize the loss of tilt ordering versus temperature in LaMnO$_3$.Comment: 24 pages, 8 figure

Greedy Shortest Common Superstring Approximation in Compact Space

Given a set of strings, the shortest common superstring problem is to find the shortest possible string that contains all the input strings. The problem is NP-hard, but a lot of work has gone into designing approximation algorithms for solving the problem. We present the first time and space efficient implementation of the classic greedy heuristic which merges strings in decreasing order of overlap length. Our implementation works in O(n log σ) time and bits of space, where n is the total length of the input strings in characters, and σσ is the size of the alphabet. After index construction, a practical implementation of our algorithm uses roughly 5n log σ bits of space and reasonable time for a real dataset that consists of DNA fragments.Peer reviewe

Inert coupling of IRDye800CW to monoclonal antibodies for clinical optical imaging of tumor targets

Imaging- and therapeutic targets in neoplastic and musculoskeletal inflammatory diseas

Location of Ti Atoms Diffused into Nearly Perfect Crystals of LiNbO3\mathrm{LiNbO_3} : An X-Ray Standing-Wave Study

The lattice position of Ti atoms diffused into less than perfect single crystals of congruently grown LiNbO3 was investigated by means of X-ray standing-wave experiments in which distances between Ti atoms and diffraction planes associated with the (0, 1, bar 4),(1, bar 1, bar 4),(bar 1, 0, bar 4) and (0, 0, bar 6) reflections were determined and triangulated to identity the Ti position. The current results indicate that it is the (vacant) Li site where Ti atoms are accommodated in the LiNbO3 structure

Kossel diffraction and X-ray standing waves : two birds of one feather

By virtue of the optical reciprocity theorem, Bragg-case Kossel diffraction in perfect crystals can be viewed as the reverse process of x-ray standing waves (XSW) in the sense that the location of the source of radiation and the point of detection are merely interchanged between the two. A method can then be devised to determine atomic positions in a crystal lattice by analyzing the profile of angularly resolved Kossel lines, yielding equivalent information as an analogous XSW experiment would. Technical aspects of this novel method are discussed and first experimental results involving Ge and Er:LiNbO3 single crystal samples are presented, indicating that the equivalence between Kossel diffraction and XSW is indeed realized

X-ray standing wave and ion scattering studies on Au-implanted LiNbO3(0001)\mathrm{LiNbO_3(0001)} single crystals

X-ray standing wave and combined Rutherford backscattering spectrometry and channeling experiments have been performed on Au-implanted and annealed (0001)-oriented LiNbO3 single crystals. At an ion dose of ⋍ 1 × 1015 cm−2 confined in a 117 nm thick (FWHM) layer, resulting in a AuNb ratio of ≅ 5 × 10−3, no significant cluster formation has been observed. Most of the Au atoms have been found to lie on the c-axis of the LiNbO3 structure. However, they do not occupy a single lattice site. Rather they appear to be distributed over several sites on the [0001] atomic strings, which contain Nb, Li and structural vacancy sites. A small fraction (∼ ca. 20%) of the Au atoms appear to be displaced from the threefold symmetry axis - most likely at tetrahedral sites. The possibility of this fraction of Au atoms existing as small clusters like dimers or trimers cannot be ruled out