X-ray diffraction @ elettra synchrotron: atomic insight of your biomedical target

Crystallography is an invaluable tool to understand atomic structure. The knowledge at atomic scale of small and large molecules is crucial for many biomedical and biotechnological applications, ranging from drug design and optimization to enzyme functional studies and engineering. The physical properties of the solid state seen in crystals and powders of both drugs and pharmaceutical excipients are of interest because the nature of the crystalline form of a drug substance, due to polymorphism, may affect both the production and formulation as well as its stability in the solid state, its solution properties and its absorption. We offer a comprehensive access to state of the art X-ray diffraction tools and methodologies, supporting all the steps, from sample preparation to 3D structure analysis

Manipulating electronic states at oxide interfaces using focused micro X-rays from standard lab-sources

Recently, x-ray illumination, using synchrotron radiation, has been used to manipulate defects, stimulate self-organization and to probe their structure. Here we explore a method of defect-engineering low-dimensional systems using focused laboratory-scale X-ray sources. We demonstrate an irreversible change in the conducting properties of the 2-dimensional electron gas at the interface between the complex oxide materials LaAlO3 and SrTiO3 by X-ray irradiation. The electrical resistance is monitored during exposure as the irradiated regions are driven into a high resistance state. Our results suggest attention shall be paid on electronic structure modification in X-ray spectroscopic studies and highlight large-area defect manipulation and direct device patterning as possible new fields of application for focused laboratory X-ray sources.Comment: 12 pages, 4 figure

The high-pressure diffraction beamline XPRESS at Elettra

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In-Plane Band Gap Engineering by Hydrogenation of Dilute Nitride Semiconductors

We present two different methods to pattern the band gap of dilute nitrides in their growth plane by exploiting the unique capability of H to passivate N in these materials. By deposition of metallic masks on and subsequent H irradiation of GaAs1-xNx, we artificially create zones of the crystal having the band gap of untreated GaAs1-XNX well surrounded by GaAs-like barriers. Alternatively, by focusing an energetic e--beam on the surface of hydrogenated GaAs1-xN x we displace H atoms from their N passivation sites, thus leading to a controlled decrease in the crystal band gap in the spatial region where the e--beam is steered. © 2007 American Institute of Physics

Influence of N-cluster states on the gyromagnetic factor of electrons in GaAs1-xNx

The effective gyromagnetic factor of electrons, g(e)(*), has been determined by Zeeman splitting measurements in a large number of GaAs1-xNx/GaAs (x < 0.7%) samples. Upon N incorporation, g(e)(*) shows first a sign reversal with respect to that of GaAs, then increases abruptly for a nitrogen concentration of order of 0.04%, and finally displays a nonmonotonic dependence on composition for higher x values. This behavior is well reproduced by a modified k center dot p model taking into account a nonmonotonic loss of Gamma character of the conduction band minimum due to multiple crossings between the redshifting conduction band edge and N-cluster states

Photoluminescence under magnetic field and hydrostatic pressure in GaAs1−xNx for probing the compositional dependence of carrier effective mass and gyromagnetic ratio

The influence of nitrogen cluster states on the conduction band (CB) structure of GaAs1-xNx is probed by measuring the effective mass and gyromagnetic ratio of electrons for x < 0.7%. An unusual compositional dependence of these two important CB parameters is found. Such behaviors are well reproduced by a modified k·p model taking into account a non-monotonic loss of γ character of the CB minimum due to multiple crossings between the red-shifting conduction band edge and N cluster states. As well, sudden variations in the electron mass can be externally induced by applying a hydrostatic pressure, which brings the upward moving CB edge into interaction with N states, which at ambient pressure are resonant with the GaAs1-xNx CB continuum. © 2007 American Institute of Physics

The Unexpected Helical Supramolecular Assembly of a Simple Achiral Acetamide Tecton Generates Selective Water Channels

International audienceAchiral 2-hydroxy-N-(diphenylmethyl)acetamide (HNDPA) crystallizes in the P61 chiral space group as a hydrate, building up permeable chiral crystalline helical water channels. The crystallization driven chiral self-resolution process is highly robust, with the same air stable crystalline form readily obtained from a variety of conditions. Interestingly, the HNDPA supramolecular helix inner pore is filled by a helical water wire. The whole edifice is mainly stabilized by robust hydrogen bonds involving the HNDPA amide bonds and CH…π interactions between the HNDPA phenyl groups. The crystalline structure shows a breathing behavior, with completely reversible release and reuptake of water inside the chiral channel, under ambient conditions. Importantly, the HNDPA channel is able to transport water very efficiently and selectively in biomimetic conditions. With a permeability per channel of 3.3 million water molecules per second in large unilamellar vesicles (LUV) and a total selectivity against NaCl, the HNDPA channel is a very promising functional nanomaterial for future applications

Interaction between conduction band edge and nitrogen states probed by carrier effective mass measurements in GaAs1-xNx

The electron effective mass, me, has been determined by magneto-photoluminescence in as-grown and hydrogenated GaAs1-xNx samples for a wide range of nitrogen concentrations (from x<0.01% to x=1.78%). A modified k?p model, which takes into account hybridization effects between N cluster states and the conduction band edge, reproduces quantitatively the experimental me values up to x ? 0.6%. Experimental and theoretical evidence is provided of the N complexes responsible for the non-monotonic and initially puzzling compositional dependence of the electron mass

The Unexpected Helical Supramolecular Assembly of a Simple Achiral Acetamide Tecton Generates Selective Water Channels

Cover profile for 10.1002/chem.202200383International audienc