Grazing Incidence Synchrotron X-ray Diffraction Research Articles

Identifying heating rate dependent oxidation reactions on a nickel-based superalloy using synchrotron diffraction

Synchrotron grazing incidence X-ray diffraction has been used to newly reveal the heating rate dependent oxidation reactions that develop on a polycrystalline nickel-based superalloy. A continuous layer of precursor oxide was shown to form during the heating stage. Their approximate growth rates, their effect on local surface compositions of the alloy substrate, and their degree of interface planarity are considered critical in determining subsequent oxidation reactions when held for extended thermal exposures. The precursor oxides were predominantly nickel or cobalt based (NiO/CoO and Co3O4/NiCo2O4). Following the fastest heating rates (40 °C min−1 and above), the stable Cr2O3 phase formed, inhibiting Ni or Co diffusion to the surface. At slower heating rates (10–20 °C min−1), no evidence of the stable Cr2O3 was found, even after 200 h at elevated thermal exposure, instead continued growth of the precursor oxides was observed. Heating at 5 °C min−1 gave rise to an intriguing zone where sufficient precursor and favourable kinetics enabled the formation of a spinel, NiCr2O4, surface layer. Cross sections observed with electron microscopy confirmed this to be planar and continuous. Heating at the slowest tested 2 °C min−1 contrarily gives a non-protective surface layer comprising an outwardly growing NiO/CoO precursor oxide on top of an inwardly growing mixed oxide. The quantities, interfacial morphologies of oxides of the precursor oxide grown and the possible thermodynamic reactions that lead to their formation are discussed.

Influence of Iodine Doping on the Structure, Morphology, and Physical Properties of Manganese Phthalocyanine Thin Films

Doping with halide ions is a popular method to alter the properties of metal phthalocyanines (MPcs), particularly magnetic and electrical nature of organic semiconductors for applications in spintronic or electronic devices. Doping can cause a structural rearrangement in MPc packing, and the physical properties may be correlated with molecular packing. Films of a planar and magnetic MPc, manganese(II)phthalocyanine (MnPc), are chosen for iodine doping study. The optical, magnetic, and electrical properties of pristine- and iodine-doped MnPc thin films are investigated and can be directly associated with their molecular structure. Two-dimensional grazing incidence synchrotron X-ray diffraction reveals structural disorder in MnPc films upon iodine infusion induced by the reorientation of ordered, edge-on molecular configuration to tilted and face-on configurations in a random fashion. The film morphology changes accordingly, where in the uniform crystallites reorganize in a disordered manner. The ferromagne...

Active-Phase Formation and Stability of Gd/Pt(111) Electrocatalysts for Oxygen Reduction: An In Situ Grazing Incidence X-Ray Diffraction Study.

Alloys of platinum and gadolinium present significant activity enhancement over pure Pt for the oxygen reduction reaction (ORR), both in the form of extended electrode surfaces and nanoparticulate catalysts. The active phase consists of a compressed Pt overlayer formed on Pt5 Gd electrodes upon exposure to the electrolyte by acid leaching. Here, we investigate the formation, strain and correlation lengths of the active Pt overlayer by using in situ synchrotron grazing incidence X-ray diffraction on Gd/Pt(111) single-crystalline electrodes. The overlayer forms upon exposure to electrolyte under open circuit conditions; the compressive strain relaxes slightly upon repeated electrochemical cycling in the potential range 0.6 to 1.0 V versus the reversible hydrogen electrode (RHE). In addition, the strain relaxes strongly when exposing the electrode to 1.2 V versus RHE, and the thickness of the crystalline portion of the overlayer increases with potential above 1.3 V versus RHE.

In-situ synchrotron GIXRD study of passive film evolution on duplex stainless steel in corrosive environment

This paper presents new findings about the passive film formed on super duplex stainless steel in ambient air and corrosive environments, studied by synchrotron grazing-incidence X-ray diffraction (GIXRD). The passive film, formed in air, was seen to be a nano-crystalline mixed-oxide. Electrochemical polarisation to the passive region in aqueous 1 M NaCl at room temperature resulted in an increase of the passive film thickness, preferential dissolution of Fe, and partial loss of crystallinity. After termination of polarization to the transpassive regime, reformation of the mixed-oxides was observed, showing a thicker, semi-crystalline, and more defective nature (more vacancies) with further new oxides/hydroxides.

Stabilization of the Metastable Form I of Piracetam by Crystallization on Silicon Oxide Surfaces

The crystallization of the nootropic drug piracetam in spin-coated thin layers on silicon oxide surfaces was analyzed by optical microscopy, as well as powder and synchrotron grazing-incidence X-ray diffraction. We observed the crystal structure formed to depend on the concentration of the solution used in the preparation of the samples and identified either the polymorphic form I (for concentrations 0.147 mol·dm–3). Although significant dewetting of the materials occurred over time, the transformation of form I, which is metastable at room temperature, to the more thermodynamically stable forms II or III was not observed, even at the long-term (9 months). Even when subject to prolonged solvent-vapor annealing, dewetting but no alteration of the polymorphic form occurred. Our results suggest that the metastable piracetam form I is stabilized upon crystallization from solution in thin films, which might generally pave the way to stabilizing metastable forms of drugs of inc...

Grazing incidence synchrotron X-ray diffraction of marbles consolidated with diammonium hydrogen phosphate treatments: non-destructive probing of buried minerals

Diammonium hydrogen phosphate (DAP)-based consolidating treatments react with carbonatic stones and form calcium phosphates phases, whose composition depends on the availability of free calcium ions. In this work, an innovative non-destructive approach based on grazing incidence X-ray diffraction (GIXRD) with synchrotron radiation (SR) is used to investigate DAP-treated Carrara marble specimens and to study the influence of the substrate composition on the crystallization of calcium phosphate phases. The outcomes indicate that the presence of compositional micro-heterogeneity of Carrara marble favours the formation of specific phases. Dicalcium phosphate dihydrate, a calcium phosphate with a low Ca/P molar ratio, is formed on carbonatic phases with a low Ca amount, such as dolomite grains and Mg-containing veins. Furthermore, this study highlights the potentialities of SR-GIXRD as a powerful non-destructive tool for the diagnostic of Cultural Heritage objects since it allows investigating the conservation history of stone materials and their interaction with the environment.

Enhanced Ordering in Monolayers Containing Glycosphingolipids: Impact of Carbohydrate Structure

The influence of carbohydrate structure on the ordering of glycosphingolipids (GSLs) and surrounding phospholipids was investigated in monolayers at the air-water interface. Binary mixtures composed of GSLs, chosen to span a range of carbohydrate complexity, and zwitterionic dipalmitoylphosphatidylcholine phospholipid, were studied. X-ray reflectivity was used to measure the out-of-plane structure of the monolayers and characterize the extension and conformation of the GSL carbohydrates. Using synchrotron grazing incidence x-ray diffraction, the in-plane packing of the lipid acyl chains and the area per molecule within ordered domains were characterized at different mole ratios of the two components. Our findings indicate that GSL-containing mixtures, regardless of the carbohydrate size, enhance the ordering of the surrounding lipids, resulting in a larger fraction of ordered phase of the monolayer and greater dimensions of the ordered domains. Reduction of the averaged area per molecule within the ordered domains was also observed but only in the cases where there was a size mismatch between the phospholipid headgroups and GSL components, suggesting that the condensation mechanism involves the relief of steric interactions between headgroups in mixtures.

What's underneath? A non-destructive depth profile of painted stratigraphies by synchrotron grazing incidence X-ray diffraction.

Many works of art are complex systems consisting of a core completed by the overlapping of several painted layers. In this work, we apply an innovative method based on grazing incidence X-ray diffraction (GIXRD) with synchrotron radiation (SR) to investigate polychrome stratigraphies with a completely non-destructive approach. The SR-GIXRD measurements provided direct and unambiguous compositional and stratigraphic information of the crystalline species lying in different layers. The investigations performed on a small fragment sampled from a painted terracotta statue allowed the identification of pigments, fillers, aggregates of the matrix and newly formed decay salts in micrometric-thin paint layers. Furthermore, the great potentiality of this study is the feasibility of depth profile investigations on multi-layered painted samples from cultural heritage objects without resorting to cross sectional analyses. Currently, the method is non-destructive but it can be potentially non-invasive in situations where small moveable artworks can be placed into the measurement chamber of the SR-XRD beamlines. The overall study paves the way to a new scenario of artwork investigations, shedding light on new unexplored approaches for non-destructive studies of cultural heritage objects, their conservation history and their interaction with the environment.

Graphene induced electrical percolation enables more efficient charge transport at a hybrid organic semiconductor/graphene interface.

Self-assembly of semiconducting polymer chains during crystallization from a liquid or melt dictates to a large degree the electronic properties of the resulting solid film. However, it is still unclear how charge transport pathways are created during crystallization. Here, we performed complementary in situ electrical measurements and synchrotron grazing incidence X-ray diffraction (GIXD), during slow cooling from the melt of highly regio-regular poly(3-hexylthiophene) (P3HT) films deposited on both graphene and on silicon. Two different charge transport mechanisms were identified, and were correlated to the difference in crystallites' orientations and overall amount of crystallites in the films on each surface as molecular self-assembly proceeded. On silicon, a weak charge transport was enabled as soon as the first edge-on lamellae formed, and further increased with the higher amount of crystallites (predominantly edge-on and randomly oriented lamellae) during cooling. On graphene however, the current remained low until a minimum amount of crystallites was reached, at which point interconnection of conducting units (face-on, randomly oriented lamellae and tie-chains) formed percolated conducting pathways across the film. This lead to a sudden rapid increase in current by ≈10 fold, and strongly enhanced charge transport, despite a much lower amount of crystallites than on silicon.

Role of the X and n factors in ion-irradiation induced phase transformations of Mn+1AXn phases

Phase transitions induced in hcp Mn+1AXn phases (Ti2AlN, Ti2AlC, and Ti4AlN3) by 1 MeV Au+ ion irradiation were investigated, over a series of ion fluences ranging from 1 × 1014 to 2 × 1016 ions cm−2, by transmission electron microscopy (TEM) and synchrotron grazing incidence X-ray diffraction (GIXRD). Irradiation-induced structural evolutions were observed using high-resolution TEM (HRTEM) imaging and selected area electron diffraction (SAED). Based on phase contrast imaging and electron diffraction pattern (EDP) simulations, the atomic-scale mechanisms for the phase transitions were determined. Transformations of the initial hcp phases to the intermediate γ-phases and fcc phases were driven by the formation of Ti/Al antisite defects and extended stacking faults induced by ion irradiation. By comparing the transformation behavior of Ti2AlN with that of Ti2AlC and Ti4AlN3 under the same irradiation conditions, using both the experimental data and first-principles calculations, the role of the X and n parameters in the radiation responses of Mn+1AXn phases were elucidated. The susceptibilities of materials in this Ti-Al-X (X = C, N) system to irradiation-induced phase transitions were determined with respect to the bonding characteristics and compositions of these MAX phases. Ti2AlC is slightly less susceptible to the radiation-induced phase transformation than Ti2AlN, which is attributed to the stronger Ti-Al bond covalency in Ti2AlN. Ti4AlN3 is more resistant to radiation-induced phase transformations than is Ti2AlN, due to the lower Al content and lower anion vacancy ratio in the irradiation-induced solid solution phases.

Structural Characterization of Self-Organized Mono- and Multilayers of Partly Fluorinated Polydialkoxyphosphazenes at the Air/Water Interface

We report studies of the collapse of monolayers of mesomorphic poly[ bis -(2,2,3,3,4,4,5,5-octafluo-ropentoxy)phosphazene] and poly[ bis -(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptoxy)phosphazene]. The structure of the films has been examined at different stages of the collapse process by synchrotron grazing incidence X-ray diffraction. Surface pressure–surface area isotherms show that these films undergo a stepwise collapse with formation of multilayers. Grazing incidence X-ray diffraction reveals only one diffraction peak for the monolayer as well as for multilayers of the two polymers studied, which corresponds to an in-plane interchain spacing d = 15.2±0.1°A and 17.6±0.5°A, respectively. The in-plane correlation length ξ xy reaches ca . 500 A for PFP-C5 (33 macromolecules) and ca . 400 A for PFP-C7 (23 macromolecules), implying a certain mesoscale order similar to a quasi-long-range one.

Nanoporous MoS2 as an Electrode Material Exhibiting High Levels of Pseudocapacitive Charge Storage with Both Li and Na-Ions

MoS2 is an attractive high power density energy storage material because of its layered crystal structure consisting of large van der Waals gaps that allow for fast ion diffusion. However, much of the work on MoS2 as an energy storage material has been focused on the high capacity four-electron reaction which irreversibly converts MoS2 into molybdenum metal and lithium sulfide in the first cycle. Subsequent cycles undergo lithium-sulfur redox chemistry leading to poor electrochemical reversibility. In this study, we show that MoS2 can reversibly store alkali ions without the irreversible conversion of the parent material by limiting the electrochemical processes to a one-electron transfer. The MoS2 layered crystal structure is preserved for the one-electron reaction which leads to fast charge transfer kinetics and high electrochemical reversibility. We have prepared mesoporous MoS2 thin films through di-block copolymer templating of molecular molybdenum precursors followed by high temperature sulfurization. This synthesis method yields an ordered three-dimensional mesoporous structure that leads to interconnected nanosized 2H-MoS2 grains that are ideal for fast ion diffusion and good electrolyte accessibility. These mesoporous thin films of MoS2 are examined as pseudocapacitive energy storage devices with high specific capacitances for Li-ions and Na-ions. Pseudocapcitive charge storage is an ideal hybrid between a battery and a capacitor because high power is achieved without significant expense to energy density. This ideal combination is achieved for mesoporous MoS2 through intercalation pseudocapacitance which occurs when ions intercalate into the channels or layers of a redox-active material accompanied by a faradaic charge-transfer, usually with no crystallographic phase change. In this work, we have shown that mesoporous MoS2 effectively stores energy through intercalation pseudocapacitance. When Li-ions are utilized, the material can be charged and discharged in 20 seconds and maintains 81% of the capacity observed for a 2000 second discharge. When mesoporous MoS2 is cycled with the bulkier Na-ion, a 23 second charging time still maintained 69% of the capacity observed for a 2000 second discharge. Detailed electrochemical kinetic analyses was used to quantitatively decouple the diffusion controlled and capacitive controlled charge storage processes. This analysis revealed that Li-ion storage in this material is 91% capacitive and Na-ion storage is 59% capacitive. The ideal nanoscale architecture of mesoporous MoS2 designed for this study leads to ultra-long cycle lifetimes with both Li and Na-ions. We have shown that mesoporous MoS2 can achieve over 10,000 cycles when cycled in a Li-ion electrolyte. Utilizing synchrotron grazing incidence x-ray diffraction techniques we have correlated superior electrochemical kinetics and cycle longevity with an ordered porous structure and textured crystal structure. This study underscores the utility of designing precise nanoscale architectures which allow for the development of new extrinsic pseudocapacitive charge storage materials that behave significantly different from the bulk. Figure 1

Absence of Structural Impact of Noble Nanoparticles on P3HT:PCBM Blends for Plasmon-Enhanced Bulk-Heterojunction Organic Solar Cells Probed by Synchrotron GI-XRD.

The incorporation of noble metal nanoparticles, displaying localized surface plasmon resonance, in the active area of donor-acceptor bulk-heterojunction organic photovoltaic devices is an industrially compatible light trapping strategy, able to guarantee better absorption of the incident photons and give an efficiency improvement between 12% and 38%. In the present work, we investigate the effect of Au and Ag nanoparticles blended with P3HT: PCBM on the P3HT crystallization dynamics by synchrotron grazing incidence X-ray diffraction. We conclude that the presence of (1) 80 nm Au, (2) mix of 5 nm, 50 nm, 80 nm Au, (3) 40 nm Ag, and (4) 10 nm, 40 nm, 60 nm Ag colloidal nanoparticles, at different concentrations below 0.3 wt% for Au and below 0.1% for Ag in P3HT: PCBM blends, does not affect the behaviour of the blends themselves.

Structural Characterization of Self-Organized Mono- and Multilayers of Poly[bis(2,2,3,3-tetrafluoropropoxy)phosphazene] at the Air/Water Interface

The layering transitions of mesomorphic poly[bis(2,2,3,3-tetrafluoropropoxy)phosphazene] induced by compression were found to result in the formation of stable multilayers directly at the air/water interface. This phenomenon is discussed with particular emphasis on its in situ structural characterization by Brewster angle microscopy, infrared spectroscopy, synchrotron grazing incidence X-ray diffraction, and X-ray reflectivity data. Compression of Langmuir monolayer is followed by layer-by-layer growth manifested by pronounced steps in the pressure/area isotherm. Grazing incidence X-ray diffraction reveals only one diffraction peak for the monolayer as well as for multilayers, which corresponds to an interchain spacing d = 12.3 A. The in-plane correlation length ξxy reaches an impressive 345 A for the uncompressed monolayer and 470 A for the tetralayer, implying a certain mesoscale order similar to a quasi-long-range one. After formation of the four-layer thick film the transition into a 3D crystalline tr...

Influence of Confined Polymer Structure on Proton Transport Property in Sulfonated Polyimide Thin Films

The organized structure and proton transport property in sulfonated polyimide (SPI) thin film have been studied, much less is known at the interfacial charge transport during confinement of such materials. The proton conductivity of SPI thin film is correlated well with the highly oriented polymer structures as determined by infrared (IR) p-polarized multiple-angle incidence resolution spectrometry (p-MAIRS) and in situ RH dependent synchrotron grazing incidence X-ray diffraction (GI-XRD). The high proton conductivity of 2.8 × 10−1 S cm−1 at 80°C and 90% RH was achieved in the highly oriented SPI thin film. In contrast, the bulk SPI showed the drop of conductivity value at high relative humidity region, which is due to the significant structural disorder accompanied by the strong interaction between the sulfonic acid side chains and water molecules.

Magnetic ordering of implanted Mn in HOPG substrates

Currently, significant research efforts are geared towards using carbon-based materials for electronic applications. Here we report the observation of magnetic ordering of implanted Mn in HOPG substrates. Superconducting quantum interference device measurements show higher moments for Mn-doped samples and also the existence of double and inverted hysteresis in both undoped and doped samples. High-resolution transmission electron microscopy shows the presence of nanocrystals in implanted samples. Grazing incidence synchrotron x-ray diffraction studies show the presence of three stable manganese carbides, including antiferromagnetic Mn${}_{23}$C${}_{6}$. X-ray magnetic circular dichroism (XMCD) measurements show ferromagnetic ordering of Mn moments at temperatures below \ensuremath{\sim}100 K. However, a very weak XMCD signal indicates that only about 1$%$ of Mn atoms are ferromagnetically ordered. We conclude that the observed Mn ferromagnetic ordering is caused by uncompensated Mn moments on the surface of antiferromagnetic Mn${}_{23}$C${}_{6}$ nanocrystals that are aligned by the local magnetic field.

Periodic elastic nanodomains in ultrathin tetragonal-like BiFeO3films

We present a synchrotron grazing incidence x-ray diffraction analysis of the domain structure and polar symmetry of highly strained BiFeO${}_{3}$ (BFO) thin films grown on LaAlO${}_{3}$ substrate. We reveal the existence of periodic elastic nanodomains in the pure tetragonal-like BFO ultrathin films down to a thickness of 6 nm. A unique shear strain-accommodation mechanism is disclosed. We further demonstrate that the periodicity of the nanodomains increases with film thickness but deviates from the classical square root law in the ultrathin thickness regime (6--30 nm). Temperature-dependent experiments further reveal the disappearance of periodic modulation above \ensuremath{\sim}90 \ifmmode^\circ\else\textdegree\fi{}C due to a ${M}_{C}$-${M}_{A}$ structural phase transition.

Light emission from thulium silicates and oxides for optical amplifiers on silicon in the extended optical communications band

Films composed of Tm2Si2O7 and Tm2O3 grains formed on SiO2/Si substrates by radio magnetic sputtering and subsequent thermal annealing up to 1250 °C were characterized by synchrotron grazing incidence X-ray diffraction, cross-sectional transmission microscopy, and micro photoluminescence (PL) measurements. The films composed of triclinic (type-B) and monoclinic (type-C) Tm2Si2O7 grains on SiO2/Si and Tm2O3 grains on Si exhibit photoluminescence at the wavelength of about 1620 nm for the silicates and 1630 nm for the oxide, which indicates that they have good potential as light amplifiers on Si in the L and U bands at telecommunications wavelengths.

The correlation between gate dielectric, film growth, and charge transport in organic thin film transistors: the case of vacuum-sublimed tetracene thin films

The complex interplay of dielectric substrate properties, semiconducting film growth, crystal structure, texture, and charge carrier transport is investigated for the case of tetracene films deposited on different dielectrics (polystyrene, parylene C, polymethylmethacrylate, hexamethyldisilazane-treated SiO2, and untreated SiO2). The tetracene hole mobility, measured in the bottom-gate organic thin film transistor (OTFT) configuration, varies over more than one order of magnitude depending upon the dielectric layer used. Atomic force microscopy and synchrotron grazing incidence X-ray diffraction measurements, analyzed with the extended Rietveld method, were used to investigate the influence of film connectivity, crystalline phase, polymorphism, and texture on charge transport. The role of the surface polarity and the processing conditions of the gate dielectric layer are also discussed. Based on our results, we propose guidelines for the selection of a gate dielectric material favorable for charge transport in tetracene films.

Evidence for a crystallite-rich skin on perfluorosulfonate ionomer membranes

Perfluorosulfonate ionomer (PFSI) membranes are widely used in electrochemical applications such as fuel cells, chlor-alkali cells, and actuators/sensors. In this work, the surface crystallization of a solution-cast PFSI membrane is quantitatively characterized for the first time by synchrotron grazing incidence X-ray diffraction (GIXRD) and small angle X-ray scattering (GISAXS). A crystallite-rich skin is observed on the PFSI membrane surface, which is 4 nm thick, possesses a crystallinity which is 40% higher than the bulk, with the crystallites aligned parallel to the membrane surface. An intermediate layer exists between the skin and the bulk. The discovery of a crystallite-rich skin may help to explain the surface properties of PFSI membranes, and facilitate an understanding of the transport properties across the membrane interface.