Observation of strong nonlinear interactions in parametric down-conversion of X-rays into ultraviolet radiation.

Nonlinear interactions between X-rays and long wavelength radiation can be used as a powerful atomic-scale probe for light-matter interactions and for properties of valence electrons. However, reported X-ray nonlinear effects were small and their observations required tremendous efforts. Here we report the observation of strong nonlinearities in parametric down-conversion (PDC) of X-rays to long wavelength radiation in gallium arsenide and lithium niobate crystals, with efficiencies about 4 orders of magnitude stronger than the efficiencies measured in any material studied before. Furthermore, we show that the efficiency in the ferroelectric phase of strontium barium niobite is two orders of magnitude stronger than in its paraelectric phase. This observation suggests that the lack of inversion symmetry is the origin for the strong observed nonlinearity. Additionally, we demonstrate the ability to use the effect for the investigation of the spectral response of non-centrosymmetric materials at wavelengths ranging from infrared to soft X-rays.

Patient perceptions of communication with diagnostic radiographers.

INTRODUCTION: The aims of this study were to (1) examine what makes a communication encounter with a diagnostic radiographer effective from the patient's perspective and (2) explore the impact of communication skills on the relationship between a diagnostic radiographer and their patient. METHODS: Semi-structured interviews were conducted with 10 patients immediately after their imaging examination. Completed interviews were analysed using an inductive approach. RESULTS: Five themes were identified in the qualitative data. (1) Introduction and Greeting, (2) Explanation/Instruction, (3) Feeling at ease, (4) Clear communication and (5) Gentle manner. CONCLUSION: These results have identified that effective communication promotes the development of rapport and trust between the radiographer and patient. These findings have implications for practitioners, educators and university programs and should be considered in the development of communication skills training programs for diagnostic radiography students.

Selective probing of magnetic order on Tb and Ir sites in stuffed Tb2Ir2O7  using resonant x-ray scattering.

We study the magnetic structure of the 'stuffed' (Tb-rich) pyrochlore iridate Tb2+x Ir2-x O7-y  (x ∼ 0.18), using resonant elastic x-ray scattering (REXS). In order to disentangle contributions from Tb and Ir magnetic sublattices, experiments were performed at the Ir L 3 and Tb M 5 edges, which provide selective sensitivity to Ir 5d and Tb 4f  magnetic moments, respectively. At the Ir L 3 edge, we found the onset of long-range [Formula: see text] magnetic order below [Formula: see text] K, consistent with the expected signal of all-in all-out (AIAO) magnetic order. Using a single-ion model to calculate REXS cross-sections, we estimate an ordered magnetic moment of [Formula: see text] at 5 K. At the Tb M 5 edge, long-range [Formula: see text] magnetic order appeared below ∼[Formula: see text] K, also consistent with an AIAO magnetic structure on the Tb site. Additional insight into the magnetism of the Tb sublattice is gleaned from measurements at the M 5 edge in applied magnetic fields up to 6 T, which is found to completely suppress the Tb AIAO magnetic order. In zero applied field, the observed gradual onset of the Tb sublattice magnetisation with temperature suggests that it is induced by the magnetic order on the Ir site. The persistence of AIAO magnetic order, despite the greatly reduced ordering temperature and moment size compared to stoichiometric Tb2Ir2O7, for which [Formula: see text] K and [Formula: see text], indicates that stuffing could be a viable means of tuning the strength of electronic correlations, thereby potentially offering a new strategy to achieve topologically non-trivial band crossings in pyrochlore iridates.

A device for the application of uniaxial strain to single crystal samples for use in synchrotron radiation experiments.

We present the design, construction, and testing of a straining device compatible with many different synchrotron radiation techniques, in a wide range of experimental environments (including low temperature, high field and ultra-high vacuum). The device has been tested by X-ray diffraction on single crystal samples of quasi-one-dimensional Cs2Mo6Se6 and K2Mo6Se6, in which microscopic strains up to a Δc/c = 0.12% ± 0.01% change in the c lattice parameters have been achieved. We have also used the device in an inelastic X-ray scattering experiment, to probe the strain-dependent speed of sound ν along the c axis. A reduction Δν/ν of up to -3.8% was obtained at a strain of Δc/c = 0.25% in K2Mo6Se6.

Ab initio calculations of the forbidden Bragg reflections energy spectra in wurtzites versus temperature.

Thermal-motion induced (TMI) scattering is caused by the influence of atomic displacements on electronic states in crystals and strongly depends on temperature. It corresponds to dipole-dipole resonant x-ray scattering, but is usually accompanied by dipole-quadrupole scattering. The phenomenological theory supposes the dipole-quadrupole term to be temperature independent (TI). As a result, the transformation of the energy spectra with temperature observed experimentally in ZnO and GaN corresponds to the interference between the TMI and TI terms. In the present paper the direct confirmation of this theoretical prediction is given. Ab initio molecular dynamics was used to simulate the sets of atomic sites at various temperatures followed by quantum mechanical calculation of resonant Bragg reflection energy spectra. The results of simulation are in excellent coincidence with experimental energy spectra of forbidden reflections and confirm the earlier phenomenological conjecture about the interference between the TI dipole-quadrupole and TMI dipole-dipole contributions to the resonant atomic factor.

Circular dichroism in core level photoemission from an adsorbed chiral molecule.

The results of experimental measurements and theoretical simulations of circular dichroism in the angular dependence (CDAD) of photoemission from atomic core levels of each of the enantiomers of a chiral molecule, alanine, adsorbed on Cu(110) are presented. Measurements in, and out of, substrate mirror planes distinguish CDAD due to the chirality of the sample and the experimental geometry. The effect due to sample chirality is relatively weak, so such measurements may not provide a routine spectral fingerprint of adsorbate chirality.

Bond lengths and bond strengths in weak and strong chemisorption: N2, CO, and CO/H on nickel surfaces.

New chemical-state-specific scanned-energy mode photoelectron diffraction experiments and density functional theory calculations, applied to CO, CO/H, and N2 adsorption on Ni(100), show that chemisorption bond length changes associated with large changes in bond strength are small, but those associated with changes in bond order are much larger, and are similar to those found in molecular systems. Specifically, halving the bond strength of atop CO to Ni increases the Ni-C distance by 0.06 A, but halving the bond order (atop to bridge site) at fixed bond strength causes an increase of 0.16 A.