X-ray dynamical diffraction in amino acid crystals: a step towards improving structural resolution of biological molecules via physical phase measurements

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPIn this work, experimental and data analysis procedures were developed and applied for studying amino acid crystals by means of X-ray phase measurements. The results clearly demonstrated the sensitivity of invariant triplet phases to electronic charge distribution in D-alanine crystals, providing useful information for molecular dynamics studies of intermolecular forces. The feasibility of using phase measurements to investigate radiation damage mechanisms is also discussed on experimental and theoretical grounds.50689700CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP306982/2012-9452031/2015-02012/01367-212/15858-814/08819-114/21284-016/11812-4Acknowledgments are due to the Brazilian funding agencies CNPq (grant Nos. 306982/2012-9 and 452031/20150) and FAPESP (grant Nos. 2012/01367-2, 12/15858-8, 14/08819-1, 14/21284-0 and 16/11812-4), Diamond Light Source (proposal MT11922), and the Brazilian Synchrotron Light Source (proposals 17063, 18011 and 19018). We also thank Professor Lisandro P. Cardoso, Dr Steven Collins and Dr José Brandão-Neto for helpful discussions

Two-dimensional ferromagnetic extension of a topological insulator

Inducing a magnetic gap at the Dirac point of the topological surface state (TSS) in a 3D topological insulator (TI) is a route to dissipationless charge and spin currents. Ideally, magnetic order is present only at the surface and not in the bulk, e.g. through proximity of a ferromagnetic (FM) layer. However, such a proximity-induced Dirac mass gap has not been observed, likely due to insufficient overlap of TSS and the FM subsystem. Here, we take a different approach, namely FM extension, using a thin film of the 3D TI Bi$_2$Te$_3$, interfaced with a monolayer of the lattice-matched van der Waals ferromagnet MnBi$_2$Te$_4$. Robust 2D ferromagnetism with out-of-plane anisotropy and a critical temperature of $\text{T}_\text{c}\approx$~15 K is demonstrated by X-ray magnetic dichroism and electrical transport measurements. Using angle-resolved photoelectron spectroscopy, we observe the opening of a sizable magnetic gap in the 2D FM phase, while the surface remains gapless in the paramagnetic phase above T$_c$. This sizable gap indicates a relocation of the TSS to the FM ordered Mn moments near the surface, which leads to a large mutual overlap.Comment: 6 pages, 3 figure

Two-dimensional ferromagnetic extension of a topological insulator

Inducing a magnetic gap at the Dirac point of the topological surface state (TSS) in a three-dimensional (3D) topological insulator (TI) is a route to dissipationless charge and spin currents. Ideally, magnetic order is present only at the surface, as through proximity of a ferromagnetic (FM) layer. However, experimental evidence of such a proximity-induced Dirac mass gap is missing, likely due to an insufficient overlap of TSS and the FM subsystem. Here, we take a different approach, namely ferromagnetic extension (FME), using a thin film of the 3D TI Bi2Te3, interfaced with a monolayer of the lattice-matched van der Waals ferromagnet MnBi2Te4. Robust 2D ferromagnetism with out-of-plane anisotropy and a critical temperature of Tc≈15 K is demonstrated by x-ray magnetic dichroism and electrical transport measurements. Using angle-resolved photoelectron spectroscopy, we observe the opening of a sizable magnetic gap in the 2D FM phase, while the surface remains gapless in the paramagnetic phase above Tc. Ferromagnetic extension paves the way to explore the interplay of strictly 2D magnetism and topological surface states, providing perspectives for realizing robust quantum anomalous Hall and chiral Majorana states

Two-dimensional ferromagnetic extension of a topological insulator

Inducing a magnetic gap at the Dirac point of the topological surface state (TSS) in a three-dimensional (3D) topological insulator (TI) is a route to dissipationless charge and spin currents. Ideally, magnetic order is present only at the surface, as through proximity of a ferromagnetic (FM) layer. However, experimental evidence of such a proximity-induced Dirac mass gap is missing, likely due to an insufficient overlap of TSS and the FM subsystem. Here, we take a different approach, namely ferromagnetic extension (FME), using a thin film of the 3D TI Bi2Te3, interfaced with a monolayer of the lattice-matched van der Waals ferromagnet MnBi2Te4. Robust 2D ferromagnetism with out-of-plane anisotropy and a critical temperature of Tc ≈ 15 K is demonstrated by x-ray magnetic dichroism and electrical transport measurements. Using angle-resolved photoelectron spectroscopy, we observe the opening of a sizable magnetic gap in the 2D FM phase, while the surface remains gapless in the paramagnetic phase above Tc. Ferromagnetic extension paves the way to explore the interplay of strictly 2D magnetism and topological surface states, providing perspectives for realizing robust quantum anomalous Hall and chiral Majorana states.</p

Hybrid and effective satellites for studying superlattices

Abstract Observation of new synchrotron X-ray scattering processes in semiconductor superlattice structures are reported. They are analogous to the three-beam diffraction in single crystal; however, the basic difference is that in these new processes superlattice-satellite reflections came to play. They give rise to effective-satellite reflections (superlattice -superlattice coupling) and hybrid-satellite reflections (substratesuperlattice coupling). These sort of reflections are features that depend on the rotation of the sample around the surface-normal direction, i.e. an azimuthal or f rotation. Their positions in f are very sensitive to the in-plane projection of the reciprocal space, but while the effectivesatellite reflections are sensitive to the superlattice parameters, the positions of the hybrid-satellite reflections depend mostly on the substrate ones. The selective sensitivity of these two sort of reflections is the physical fact that can be used as a new tool for studying superlattices.

Proper usage of Scherrer's and Guinier's formulas in X-ray analysis of size distribution in systems of monocrystalline CeO2 nanoparticles

In nowadays, X-ray diffraction and scattering phenomena are widely used as analytical tools in the optimization and control of nanomaterial synthesizing processes. In systems of monocrystalline nanoparticles with size distribution, the physical meaning of size values as determined by using X-ray methods is still controvertial. To answer such fundamental issue, series of virtual nanoparticles with sizes ranging from 1 nm to 90 nm were generated and their exact scattering power computed via pair distance distribution function. Composed X-ray diffraction and scattering patterns from systems of virtual nanoparticles demonstrated that diffraction and scattering phenomena see the size distributions with different weightings. Therefore, combining both phenomena leads to the determination of size distribution in the systems. In practice, X-ray diffraction and small-angle scattering experiments were applied to solve the size distributions in a series of samples of cubic ceria nanoparticles, revealing a systematic size dispersion as a function of synthesis parameters.Comment: 18 pages, 18 figure