NEXAFS Sensitivity to Bond Lengths in Complex Molecular Materials: A Study of Crystalline Saccharides

High-spatial resolution functional chemistry of nitrogen compounds in the observed UK meteorite fall Winchcombe

Organic matter in extraterrestrial samples is a complex material that might have played an important role in the delivery of prebiotic molecules to the early Earth. We report here on the identification of nitrogen-containing compounds such as amino acids and N-heterocycles within the recent observed meteorite fall Winchcombe by high-spatial resolution spectroscopy techniques. Although nitrogen contents of Winchcombe organic matter are low (N/C ~ 1-3%), we were able to detect the presence of these compounds using a low-noise direct electron detector. These biologically relevant molecules have therefore been tentatively found within a fresh, minimally processed meteorite sample by high spatial resolution techniques conserving the overall petrographic context. Carbon functional chemistry investigations show that sizes of aromatic domains are small and that abundances of carboxylic functional groups are low. Our observations demonstrate that Winchcombe represents an important addition to the collection of carbonaceous chondrites and still preserves pristine extraterrestrial organic matter.

All-Water Etching-Free Electron Beam Lithography for On-Chip Nanomaterials

Electron beam lithography uses an accelerated electron beam to fabricate patterning on an electron-beam-sensitive resist but requires complex dry etching or lift-off processes to transfer the pattern to the substrate or film on the substrate. In this study, etching-free electron beam lithography is developed to directly write a pattern of various materials in all-water processes, achieving the desired semiconductor nanopatterns on a silicon wafer. Introduced sugars are copolymerized with metal ions-coordinated polyethylenimine under the action of electron beams. The all-water process and thermal treatment result in nanomaterials with satisfactory electronic properties, indicating that diverse on-chip semiconductors (e.g., metal oxides, sulfides, and nitrides) can be directly printed on-chip by an aqueous solution system. As a demonstration, zinc oxide patterns can be achieved with a line width of 18 nm and a mobility of 3.94 cm² V^-1 s^-1. This etching-free electron beam lithography strategy provides an efficient alternative for micro/nanofabrication and chip manufacturing.

Extracting structural insights from soft X-ray scattering of biological assemblies

Resonant soft X-ray scattering (RSoXS), a technique that combines X-ray absorption spectroscopy and X-ray scattering, can probe the nano- and meso-scale structure of biological assemblies with chemical specificity. RSoXS experiments yield scattering data collected at several photon energies, for example across an elemental absorption edge of interest. Collecting a near-edge X-ray absorption fine structure (NEXAFS) spectrum complements RSoXS experiments and determines X-ray energies that are best suited for RSoXS measurements. The analysis of RSoXS data is similar in many ways to analysis of small angle X-ray scattering using hard X-rays, with an added dimension that includes an X-ray energy dependence. This chapter discusses procedures for predicting scattering contrast and thereby identifying energies suitable for RSoXS measurements using NEXAFS spectra, analyses of 2D RSoXS images through integration into 1D profiles, and strategies for elucidating the origin of RSoXS scattering features. It also discusses existing and potential methods for interpretation of RSoXS data to gain detailed structural insights into biological systems.

Determination of H-Atom Positions in Organic Crystal Structures by NEXAFS Combined with Density Functional Theory: a Study of Two-Component Systems Containing Isonicotinamide

It is important to be able to identify the precise position of H-atoms in hydrogen bonding interactions to fully understand the effects on the structure and properties of organic crystals. Using a combination of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and density functional theory (DFT) quantum chemistry calculations, we demonstrate the sensitivity of core-level X-ray spectroscopy to the precise H-atom position within a donor-proton-acceptor system. Exploiting this sensitivity, we then combine the predictive power of DFT with the experimental NEXAFS, confirming the H-atom position identified using single-crystal X-ray diffraction (XRD) techniques more easily than using other H-atom sensitive techniques, such as neutron diffraction. This proof of principle experiment confirms the H-atom positions in structures obtained from XRD, providing evidence for the potential use of NEXAFS as a more accurate and easier method of locating H-atoms within organic crystals.

X-ray Raman scattering for bulk chemical and structural insight into green carbon

X-ray Raman scattering (XRS) spectroscopy is an emerging inelastic scattering technique which uses hard X-rays to study the X-ray absorption edges of low-Z elements (e.g. C, N, O) in bulk. This study applies XRS spectroscopy to pyrolysis and hydrothermal carbons. These materials are thermochemically-produced carbon from renewable resources and represent a route for the sustainable production of carbon materials for many applications. Results confirm local structural differences between biomass-derived (Oak, Quercus Ilex) pyrolysis and hydrothermal carbon. In comparison with NEXAFS, XRS spectroscopy has been shown to be more resilient to experimental artefacts such as self-absorption. Density functional theory XRS calculations of potential structural sub-units confirm that hydrothermal carbon is a highly disordered carbon material formed principally of furan units linked by the α carbon atoms. Comparison of two pyrolysis temperatures (450 °C and 650 °C) shows the development of an increasingly condensed carbon structure. Based on our results, we have proposed a semi-quantitative route to pyrolysis condensation.

Biofunctionalization of TiO2 Surfaces with Self-Assembling Layers of Oligopeptides Covalently Grafted to Chitosan

In the field of tissue engineering, a promising approach to obtain a bioactive, biomimetic, and antibiotic implant is the functionalization of a "classical" biocompatible material, for example, titanium, with appropriate biomolecules. For this purpose, we propose preparing self-assembling films of multiple components, allowing the mixing of different biofunctionalities "on demand". Self-assembling peptides (SAPs) are synthetic materials characterized by the ability to self-organize in nanostructures both in aqueous solution and as thin or thick films. Moreover, ordered layers of SAPs adhere on titanium surface as a scaffold coating to mimic the extracellular matrix. Chitosan is a versatile hydrophilic polysaccharide derived from chitin, with a broad antimicrobial spectrum to which Gram-negative and Gram-positive bacteria and fungi are highly susceptible, and is already known in the literature for the ability of its derivatives to firmly graft titanium alloys and show protective effects against some bacterial species, either alone or in combination with other antimicrobial substances such as antibiotics or antimicrobial peptides. In this context, we functionalized titanium surfaces with chitosan grafted to EAK16-II (a SAP), obtaining layer-by-layer structures of different degrees of order, depending on the preparative stoichiometry and path. The chemical composition, molecular structure, and arrangement of the obtained biofunctionalized surfaces were investigated by surface-sensitive techniques such as reflection-absorption infrared spectroscopy (RAIRS) and state-of-the-art synchrotron radiation-induced spectroscopies as X-ray photoemission spectroscopy (SR-XPS), and near-edge X-ray absorption fine structure (NEXAFS). Furthermore, was demonstrated that surfaces coated with EAK and Chit-EAK can support hNPs cell attachment and growth.

Resonant soft X-ray scattering reveals cellulose microfibril spacing in plant primary cell walls

Cellulose microfibrils are crucial for many of the remarkable mechanical properties of primary cell walls. Nevertheless, many structural features of cellulose microfibril organization in cell walls are not yet fully described. Microscopy techniques provide direct visualization of cell wall organization, and quantification of some aspects of wall microstructure is possible through image processing. Complementary to microscopy techniques, scattering yields structural information in reciprocal space over large sample areas. Using the onion epidermal wall as a model system, we introduce resonant soft X-ray scattering (RSoXS) to directly quantify the average interfibril spacing. Tuning the X-ray energy to the calcium L-edge enhances the contrast between cellulose and pectin due to the localization of calcium ions to homogalacturonan in the pectin matrix. As a consequence, RSoXS profiles reveal an average center-to-center distance between cellulose microfibrils or microfibril bundles of about 20 nm.

Single-Shot near Edge X-ray Fine Structure (NEXAFS) Spectroscopy Using a Laboratory Laser-Plasma Light Source

We present a proof of principle experiment on single-shot near edge soft X-ray fine structure (NEXAFS) spectroscopy with the use of a laboratory laser-plasma light source. The source is based on a plasma created as a result of the interaction of a nanosecond laser pulse with a double stream gas puff target. The laser-plasma source was optimized for efficient soft X-ray (SXR) emission from the krypton/helium target in the wavelength range from 2 nm to 5 nm. This emission was used to acquire simultaneously emission and absorption spectra of soft X-ray light from the source and from the investigated sample using a grazing incidence grating spectrometer. NEXAFS measurements in a transmission mode revealed the spectral features near the carbon K-α absorption edge of thin polyethylene terephthalate (PET) film and L-ascorbic acid in a single-shot. From these features, the composition of the PET sample was successfully obtained. The NEXAFS spectrum of the L-ascorbic acid obtained in a single-shot exposure was also compared to the spectrum obtained a multi-shot exposure and to numerical simulations showing good agreement. In the paper, the detailed information about the source, the spectroscopy system, the absorption spectra measurements and the results of the studies are presented and discussed.

Compact system for near edge X-ray fine structure (NEXAFS) spectroscopy using a laser-plasma light source

We present a compact laboratory system for near edge soft X-ray fine structure (NEXAFS) spectroscopy that was developed using a laser-plasma light source. The source is based on a double stream gas puff target. The plasma is formed by the interaction of a laser beam with the double stream gas puff target approach. The laser plasma source was optimized for efficient soft X-ray emission from a krypton/helium target in the range of 1.5 to 5 nm wavelength. This emission is used to acquire simultaneously the emission and absorption spectra of soft X-ray light from the source and from the investigated sample using a grazing incidence spectrometer. The measurements in the transmission mode reveal the features near the carbon K-α absorption edge of thin PET film. From those features, the composition of the sample was successfully obtained. The data are in agreement with synchrotron measurements. In the paper, the detailed information about the source, its optimization, the system, spectral measurements and the results are presented and discussed.

X-ray Raman scattering: a new in situ probe of molecular structure during nucleation and crystallization from liquid solutions

X-ray Raman scattering (XRS) has been used for in situ probing of solute molecule speciation in solution during cooling crystallization.