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Surface monolayers assembled on a liquid sub-phase represent a class of systems that is of great interest for studies of phase transitions in quasi-2D systems, chemical self-assembly, surfactant behavior, and biologically relevant monolayers and membranes. X-ray scattering is ideal for studying structural, dynamic, and mechanical properties of these surface monolayers at nanoscale due to the penetrating ability and short wavelength of x-rays. We show here that grazing incidence x-ray off-specular scattering (GIXOS) provides rapid access to in-plane and out-of-plane nanoscale structure, surface fluctuating modes, and potentially bending stiffness. We show that analysis of GIXOS data is highly sensitive to resolution effects. We further present detailed analysis of GIXOS from phospholipid 1,2-dipalmitoyl-phosphatidyl-choline C40H80NO8P (DPPC) and obtain quantitative, angstrom-resolution details of electron density profile normal to the surface that is comparable to those that are obtained from specular x-ray reflectivity measurements. We compare these GIXOS results to x-ray reflectivity measurements performed on the same samples. While electron density and main structural characteristics (such as monolayer thickness) obtained by GIXOS agree with x-ray reflectivity results, the interfaces of GIXOS-derived density profiles are found to be systematically sharper than those obtained with x-ray reflectivity. The possible reasons for these differences are discussed. [ABSTRACT FROM AUTHOR]

We demonstrate, to our knowledge, the first bright circularly polarized high-harmonic beams in the soft X-ray region of the electromagnetic spectrum, and use them to implement X-ray magnetic circular dichroism measurements in a tabletop-scale setup. Using counterrotating circularly polarized laser fields at 1.3 and 0.79 µm, we generate circularly polarized harmonics with photon energies exceeding 160 eV. The harmonic spectra emerge as a sequence of closely spaced pairs of left and right circularly polarized peaks, with energies determined by conservation of energy and spin angular momentum. We explain the single-atom and macroscopic physics by identifying the dominant electron quantum trajectories and optimal phase-matching conditions. The first advanced phase-matched propagation simulations for circularly polarized harmonics reveal the influence of the finite phase-matching temporal window on the spectrum, as well as the unique polarization-shaped attosecond pulse train. Finally, we use, to our knowledge, the first tabletop X-ray magnetic circular dichroism measurements at the N4,5 absorption edges of Gd to validate the high degree of circularity, brightness, and stability of this light source. These results demonstrate the feasibility of manipulating the polarization, spectrum, and temporal shape of high harmonics in the soft X-ray region by manipulating the driving laser waveform. [ABSTRACT FROM AUTHOR]

Using high-resolution x-ray scattering and x-ray photon correlation spectroscopy (XPCS), we have investigated the structure and dynamics of charge density wave (CDW) dynamics in pure and titanium-doped 1T-TaS2. Time-averaged scattering measurements of pure and doped samples reveal that 1T-TaS2 is a weakly pinned two-dimensional CDW system. Using XPCS, we find that after long anneals the CDW domain structure in the incommensurate phase is pinned and stable against spontaneous fluctuations thus rejecting phasons as spontaneous excitations in higher-dimensional CDW systems. By examining the dynamics of deeply quenched samples upon heating, we find that metastable CDW configurations collectively rearrange in a nonequilibrium manner. For nominally pure samples, we determine an energy barrier to relaxation of 4600 K that is considerably greater than that found for lower-dimensional CDWs. [ABSTRACT FROM AUTHOR]

Here, we photoinduce and directly observe with x-ray scattering an ultrafast enhancement of the structural long-range order in the archetypal Mott system V2O3. Despite the ultrafast increase in crystal symmetry, the change of unit cell volume occurs an order of magnitude slower and coincides with the insulator-to-metal transition. The decoupling between the two structural responses in the time domain highlights the existence of a transient photoinduced precursor phase, which is distinct from the two structural phases present in equilibrium. X-ray nanoscopy reveals that acoustic phonons trapped in nanoscale twin domains govern the dynamics of the ultrafast transition into the precursor phase, while nucleation and growth of metallic domains dictate the duration of the slower transition into the metallic phase. The enhancement of the long-range order before completion of the electronic transition demonstrates the critical role the nonequilibrium structural phases play during electronic phase transitions in correlated electrons systems. [ABSTRACT FROM AUTHOR]

The X-ray Bragg coherent diffractive imaging (CDI) technique assumes that the structure factor holds constant over the measured crystal. This approximation breaks down for materials exhibiting variations in the unit-cell configuration, such as piezo- and ferroelectrics. In that case, the strain field cannot be reliably determined from the reconstruction because the lattice deformation and the structure factor contribute concomitantly. Proposed here is a solution to this problem achieved by combining Bragg CDI and the multiwavelength anomalous diffraction approach that measures a Friedel pair of reflections at two different photon energies near an absorption edge. Comparing the obtained reconstructions with a parametric model that includes calculating the scattering amplitude as a function of wavelength and the unit-cell configuration, the contributions of the lattice deformation and the structure factor are separated. Simulations of the ferroelectric material BaTiO 3 demonstrate the possibility of simultaneous probing of the strain and displacement of the Ti atoms. The proposed method opens up an opportunity to apply coherent X-ray diffraction for nanoscale-resolved 3D mapping of polarization domains in micro- and nanocrystals.