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Current and future capabilities of X-ray spectromicroscopy are discussed based on coherence-limited imaging methods which will benefit from the dramatic increase in brightness expected from a diffraction-limited storage ring (DLSR). The methods discussed include advanced coherent diffraction techniques and nanoprobe-based real-space imaging using Fresnel zone plates or other diffractive optics whose performance is affected by the degree of coherence. The capabilities of current systems, improvements which can be expected, and some of the important scientific themes which will be impacted are described, with focus on energy materials applications. Potential performance improvements of these techniques based on anticipated DLSR performance are estimated. Several examples of energy sciences research problems which are out of reach of current instrumentation, but which might be solved with the enhanced DLSR performance, are discussed.

The molecular packing in a polymer: fullerene bimolecular crystal is determined using X-ray diffraction (XRD), molecular mechanics (MM) and molecular dynamics (MD) simulations, 2D solid-state NMR spectroscopy, and IR absorption spectroscopy. The conformation of the electron-donating polymer is significantly disrupted by the incorporation of the electron-accepting fullerene molecules, which introduce twists and bends along the polymer backbone and 1D electron-conducting fullerene channels., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Anomalous small angle X-ray scattering (ASAXS) is shown to be an ideal technique to investigate the particle size and particle composition dynamics of carbon-supported alloy nanoparticle electrocatalysts at the atomic scale. In this technique, SAXS data are obtained at different X-ray energies close to a metal absorption edge, where the metal scattering strength changes, providing element specificity. ASAXS is used to, first, establish relationships between annealing temperature and the resulting particle size distribution for Pt25Cu75 alloy nanoparticle electrocatalyst precursors. The Pt specific ASAXS profiles were fitted with log-normal distributions. High annealing temperatures during alloy synthesis caused a significant shift in the alloy particle size distribution towards larger particle diameters. Second, ASAXS was used to characterize electrochemical Cu dissolution and dealloying processes of a carbon-supported Pt25Cu75 electrocatalyst precursor in acidic electrolytes. By performing ASAXS at both the Pt and Cu absorption edges, the unique power of this technique is demonstrated for probing composition dynamics at the atomic scale. These ASAXS measurements provided detailed information on the changes in the size distribution function of the Pt atoms and Cu atoms. A shift in the Cu scattering profile towards larger scattering vectors indicated the removal of Cu atoms from the alloy particle surface suggesting the formation of a Pt enriched Pt shell surrounding a Pt-Cu core. Together with XRD and TEM, ASAXS is proposed to play an increasingly important role in the mechanistic study of degradation phenomena of alloy nanoparticle electrocatalysts at the atomic scale.

The primary cell wall is highly hydrated in its native state, yet many structural studies have been conducted on dried samples. Here, we use grazing-incidence wide-angle X-ray scattering (GIWAXS) with a humidity chamber, which enhances scattering and the signal-to-noise ratio while keeping outer onion epidermal peels hydrated, to examine cell wall properties. GIWAXS of hydrated and dried onion reveals that the cellulose ([Formula: see text]) lattice spacing decreases slightly upon drying, while the (200) lattice parameters are unchanged. Additionally, the ([Formula: see text]) diffraction intensity increases relative to (200). Density functional theory models of hydrated and dry cellulose microfibrils corroborate changes in crystalline properties upon drying. GIWAXS also reveals a peak that we attribute to pectin chain aggregation. We speculate that dehydration perturbs the hydrogen bonding network within cellulose crystals and collapses the pectin network without affecting the lateral distribution of pectin chain aggregates.

We report x-ray-diffraction measurements of the microstructural origin of circumferential magnetic anisotropy [or orientation ratio (OR), the ratio of the remanent magnetization along the circumferential and radial directions] in textured magnetic recording disks. We study a series of CoPtCrB magnetic media with CrX underlayers with varying OR and quantify the anisotropic strain in the CrX underlayer and the c-axis alignment in the hexagonal-close-packed media. Our data show that the c-axis alignment results from the anisotropic strain in the underlayer and suggest that the OR comes predominately from the media c-axis alignment. [ABSTRACT FROM AUTHOR]

Focuses on a study that investigated structural depth profiling of iron oxide thin films using grazing incidence asymmetric Bragg x-ray diffraction. Information on grazing incidence asymmetric Bragg diffraction; Details of the experiment; Results; Discussion.

The challenge of continuous printing in high-efficiency large-area organic solar cells is a key limiting factor for their widespread adoption. A materials design concept for achieving large-area, solution-coated all-polymer bulk heterojunction solar cells with stable phase separation morphology between the donor and acceptor is presented. The key concept lies in inhibiting strong crystallization of donor and acceptor polymers, thus forming intermixed, low crystallinity, and mostly amorphous blends. Based on experiments using donors and acceptors with different degree of crystallinity, the results show that microphase separated donor and acceptor domain sizes are inversely proportional to the crystallinity of the conjugated polymers. This methodology of using low crystallinity donors and acceptors has the added benefit of forming a consistent and robust morphology that is insensitive to different processing conditions, allowing one to easily scale up the printing process from a small-scale solution shearing coater to a large-scale continuous roll-to-roll (R2R) printer. Large-area all-polymer solar cells are continuously roll-to-roll slot die printed with power conversion efficiencies of 5%, with combined cell area up to 10 cm2. This is among the highest efficiencies realized with R2R-coated active layer organic materials on flexible substrate. [ABSTRACT FROM AUTHOR]

Recent improvements in solution-coated organic semiconductors (OSCs) evidence their high potential for cost-efficient organic electronics and sensors. Molecular packing structure determines the charge transport property of molecular solids. However, it remains challenging to control the molecular packing structure for a given OSC. Here, the application of alternating electric fields is reported to fine-tune the crystal packing of OSC solution-shearing coated at ambient conditions. First, a theoretical model based on dielectrophoresis is developed to guide the selection of the optimal conditions (frequency and amplitude) of the electric field applied through the solution-shearing blade during coating of OSC thin films. Next, electric field-induced polymorphism is demonstrated for OSCs with both herringbone and 2D brick-wall packing motifs in 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene and 6,13-bis(triisopropylsilylethynyl) pentacene, respectively. Favorable molecular packing can be accessible in some cases, resulting in higher charge carrier mobilities. This work provides a new approach to tune the properties of solution-coated OSCs in functional devices for high-performance printed electronics. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries may become an alternative to the widespread lithium-ion technology due to cost and kinetic advantages provided that cyclability is improved. For this purpose, the interplay between electrochemical and structural processes is key and is demonstrated in this work for Na2.46V6O16 (NVO) and Li2.55V6O16 employing operando synchrotron X-ray diffraction. When NVO is cycled between 4.0 and 1.6 V, Na-ions reversibly occupy two crystallographic sites, which results in remarkable cyclability. Upon discharge to 1.0 V, however, Na-ions occupy also interstitial sites, inducing irreversible structural change with some loss of crystallinity concomitant with a decrease in capacity. Capacity fading increases with the ionic radius of the alkali ions (K+ > Na+ > Li+), suggesting that smaller ions stabilize the structure. This correlation of structural variation and electrochemical performance suggests a route toward improving cycling stability of a sodium-ion battery. Its essence is a minor Li+-retention in the A2+ xV6O16 structure. Even though the majority of Li-ions are replaced by the abundant Na+, the residual Li-ions (≈10%) are sufficient to stabilize the layered structure, diminishing the irreversible structural damage. These results pave the way for further exploitation of the role of small ions in lattice stabilization that increases cycling performance. [ABSTRACT FROM AUTHOR]

Operando X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) studies of Ge anodes are carried out to understand the effect of cycling rate on Ge phase transformation during charge/discharge process and to relate that effect to capacity. It is discovered that the formation of crystalline Li15Ge4 (c-Li15Ge4) during lithiation is suppressed beyond a certain cycling rate. A very stable and reversible high capacity of ≈1800 mAh g−1 can be attained up to 100 cycles at a slow C-rate of C/21 when there is complete conversion of Ge anode into c-Li15Ge4. When the C-rate is increased to ≈C/10, the lithiation reaction is more heterogeneous and a relatively high capacity of ≈1000 mAh g−1 is achieved with poorer electrochemical reversibility. An increase in C-rate to C/5 and higher reduces the capacity (≈500 mAh g−1) due to an impeded transformation from amorphous Li xGe to c-Li15Ge4, and yet improves the electrochemical reversibility. A proposed mechanism is presented to explain the C-rate dependent phase transformations and the relationship of these to capacity fading. The operando XRD and XAS results provide new insights into the relationship between structural changes in Ge and battery capacity, which are important for guiding better design of high-capacity anodes. [ABSTRACT FROM AUTHOR]

The reversible electrochemical insertion of multivalent ions into materials has promising applications in many fields, including batteries, seawater desalination, element purification, and wastewater treatment. However, finding materials that allow for the insertion of multivalent ions with fast kinetics and stable cycling has proven difficult because of strong electrostatic interactions between the highly charged insertion ions and atoms in the host framework. Here, an open framework nanomaterial, copper hexacyanoferrate, in the Prussian Blue family is presented that allows for the reversible insertion of a wide variety of monovalent, divalent, and trivalent ions (such as Rb+, Pb2+, Al3+, and Y3+) in aqueous solution beyond that achieved in previous studies. Electrochemical measurements demonstrate the unprecedented kinetics of multivalent ion insertion associated with this material. Synchrotron X-ray diffraction experiments point toward a novel vacancy-mediated ion insertion mechanism that reduces electrostatic repulsion and helps to facilitate the observed rapid ion insertion. The results suggest a new approach to multi­valent ion insertion that may help to advance the understanding of this complex phenomenon. [ABSTRACT FROM AUTHOR]

The crystallization and electrical characterization of the semiconducting polymer poly(3-hexylthiophene) (P3HT) on a single layer graphene sheet is reported. Grazing incidence X-ray diffraction revealed that P3HT crystallizes with a mixture of face-on and edge-on lamellar orientations on graphene compared to mainly edge-on on a silicon substrate. Moreover, whereas ultrathin (10 nm) P3HT films form well oriented face-on and edge-on lamellae, thicker (50 nm) films form a mosaic of lamellae oriented at different angles from the graphene substrate. This mosaic of crystallites with π-π stacking oriented homogeneously at various angles inside the film favors the creation of a continuous pathway of interconnected crystallites, and results in a strong enhancement in vertical charge transport and charge carrier mobility in the thicker P3HT film. These results provide a better understanding of polythiophene crystallization on graphene, and should help the design of more efficient graphene based organic devices by control of the crystallinity of the semiconducting film. [ABSTRACT FROM AUTHOR]

Rapid thermal processing (RTP) is widely used for processing a variety of materials, including electronics and photovoltaics. Presently, optimization of RTP is done primarily based on ex-situ studies. As a consequence, the precise reaction pathways and phase progression during the RTP remain unclear. More awareness of the reaction pathways would better enable process optimization and foster increased adoption of RTP, which offers numerous advantages for synthesis of a broad range of materials systems. To achieve this, we have designed and developed a RTP instrument that enables real-time collection of X-ray diffraction data with intervals as short as 100 ms, while heating with ramp rates up to 100 °Cs-1, and with a maximum operating temperature of 1200 °C. The system is portable and can be installed on a synchrotron beamline. The unique capabilities of this instrument are demonstrated with in-situ characterization of a Bi2O3-SiO2 glass frit obtained during heating with ramp rates 5 °C s-1 and 100 °C s-1, revealing numerous phase changes. [ABSTRACT FROM AUTHOR]

In this work, crystallization kinetics and aggregate growth of poly(3-ethylhexylthiophene) (P3EHT) thin films are studied as a function of film thickness. X-ray diffraction and optical absorption show that individual aggregates and crystallites grow anisotropically and mostly along only two packing directions: the alkyl stacking and the polymer chain backbone direction. Further, it is also determined that crystallization kinetics is limited by the reorganization of polymer chains and depends strongly on the film thickness and average molecular weight. Time-dependent, field-effect hole mobilities in thin films reveal a percolation threshold for both low and high molecular weight P3EHT. Structural analysis reveals that charge percolation requires bridged aggregates separated by a distance of ≈2-3 nm, which is on the order of the polymer persistence length. These results thus highlight the importance of tie molecules and inter-aggregate distance in supporting charge percolation in semiconducting polymer thin films. The study as a whole also demonstrates that P3EHT is an ideal model system for polythiophenes and should prove to be useful for future investigations into crystallization kinetics. [ABSTRACT FROM AUTHOR]

In this work, the impact of cation disorder on the electrical properties of biaxially textured Co2ZnO4 and Co2NiO4 thin films grown by pulsed laser deposition are investigated using a combination of experiment and theory. Resonant elastic X-ray diffraction along with conductivity measurements both before and after post-deposition annealing show that Co2ZnO4 and Co2NiO4 exhibit opposite changes of the conductivity with cation disorder, which can be traced back to their different ground-state atomic structures, being normal and inverse spinel, respectively. Electronic structure calculations identify a self-doping mechanism as the origin of conductivity. A novel thermodynamic model describes the non-equilibrium cation disorder in terms of an effective temperature. This work offers a way of controlling the conductivity in spinels in a quantitative manner by controlling the cation disorder and a new design principle whereby non-equilibrium growth can be used to create beneficial disorder. [ABSTRACT FROM AUTHOR]

Using X-ray diffraction-based pole figures, we present quantitative analysis of the microstructure of poly(3-hexylthiophene) thin films of varying thicknesses, which allows us to determine the crystallinity and microstructure at the semiconductor-dielectric interface. We find that the interface is approximately one fourth as crystalline as the bulk of the material. Furthermore, the use of a self-assembled monolayer (SAM) enhances the density of interface-nucleated crystallites by a factor of ∼20. Charge transport measurements as a function of film thickness correlate with interface crystallinity. Hence, we establish the crucial role of SAMs as nucleating agents for increasing carrier mobility in field-effect devices. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 [ABSTRACT FROM AUTHOR]

Sputter-deposited W films with nominal thicknesses between 5 and 180 nm were prepared by varying the base pressure prior to film deposition and by including or not including sputtered SiO2 encapsulation layers. X-ray and electron diffraction studies showed that single phase, polycrystalline α-W could be achieved in as-deposited films as thin as 5 nm. The stress state in the as-deposited films was found to be inhomogeneous. Annealing resulted in stress relaxation and reduction of resistivity for all films, except the thinnest, unencapsulated film, which agglomerated. In-plane film grain sizes measured for a subset of the annealed films with thicknesses between 5 and 180 nm surprisingly showed a near constant value (101-116 nm), independent of film thickness. Thick-film (≥120 nm) resistivity values as low as 8.6 μΩ cm at 301 K were obtained after annealing at 850 °C for 2 h. Film resistivities were found to increase with decreasing film thicknesses below 120 nm, even for films which are fully A2 α-W with no metastable, A15 β-W evident. [ABSTRACT FROM AUTHOR]

The article provides a comprehensive description of the free computer analysis program SAXSMorph designed for generating three-dimensional (3D) representative morphologies for two-phase systems with the use of small-angle X-ray and neutron scattering data.

The surface onto which polymeric semiconductors are cast from solution plays an important role in determining the electrical transport properties of the polymeric thin film. The authors use synchrotron-based x-ray diffraction to show that even moderate roughness (rms∼5 Å) can affect the texture of semicrystalline poly(thiophene) thin films. Moreover, the authors use a novel optical characterization technique (surface plasmon resonance spectroscopy) to characterize the appearance of electronic states in the bandgap of thin films (∼20 nm) of regioregular poly(thiophene). Such states may be due to the heterointerface between the thin Au substrate and the polymer. [ABSTRACT FROM AUTHOR]

Grazing-incidence X-ray diffraction and rocking scans have quantified the structure of poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester in the active layers of organic solar cells. Our study reveals that the device JSCcorrelates with the local structural development of pure PCBM and, to second order, the extent of out-of-plane P3HT π-stacking. [ABSTRACT FROM AUTHOR]

We report on the electrical resistance and microstructure of sputter deposited copper thin films grown in an oxygen containing ion-beam sputtering atmosphere. For films thinner than 5 nm, 6%–10% oxygen causes a minimum in film resistivity, while for thicker films, there is a monotonic increase in resistivity. X-ray reflectivity measurements show significantly smoother films for these oxygen flow rates. X-ray diffraction shows that the oxygen doping causes a refinement of the copper grain size and the formation of cuprous oxide. We suggest that the formation of cuprous oxide limits copper grain growth, which causes smoother interfaces, and thus reduces resistivity by increasing specular scattering of electrons at interfaces. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Organic-inorganic hybrid halide perovskites are one of the most promising emerging photovoltaic materials due to their high efficiency and potentially low processing cost. Here, we present a well-controlled, manufacturing relevant annealing method, radiative thermal annealing, for the methylammonium lead triiodide (MAPbI3) films formed by a solvent engineering process, with dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) as solvent and diethyl ether as the antisolvent. Radiative thermal annealing can produce high quality perovskite films, evidenced by high efficiency solar cell devices (~18% power conversion efficiency), in a shorter time than the widely used hot plate annealing. Using in situ X-ray diffraction during the radiative annealing, we show that the role of the antisolvent is not to form an important intermediate compound (a PbI2-MAI-DMSO complex) by washing of the main solvent (DMF), but to achieve a pinhole free, uniform film of MAPbI3 with minimal intermediate compound. Importantly, we show that having a PbI2-MAI-DMSO intermediate compound does not guarantee a high quality (pinhole free) perovskite film. We directly show that humidity induces MAPbI3 to decompose into PbI2 more rapidly and, as such, negatively impacts the reproducibility of the device performance. The study is extended to reveal the effect of annealing temperature profile and deposition substrate to demonstrate the complexity of perovskite processing parameters. This coupled experimental approach allows a better understanding of the effect of processing protocols, including antisolvent, humidity, and annealing profile, on MAPbI3 film quality and the resultant solar cell performance. [ABSTRACT FROM AUTHOR]

The development of a p-type transparentconducting oxide (p-TCO)requires the deliberate design of a wide band gap and high hole conductivity.Using high-throughput theoretical screening, Cr2MnO4was earlier predicted to be a p-TCO when doped with lithium.This constitutes a new class of p-TCO, one based on a tetrahedrallycoordinated d5cation. In this study, we examine and experimentallyvalidate a few central properties of this system. Combined neutrondiffraction and anomalous X-ray diffraction experiments give siteoccupancy that supports the theoretical prediction that lithium occupiesthe tetrahedral (Mn) site. The lattice parameter of the spinel decreaseswith lithium content to a solubility limit of [Li]/([Li] + [Mn]) ∼9.5%. Diffuse reflectance spectroscopy measurements show that at higherdoping levels the transparency is diminished, which is attributedto both the presence of octahedral Mn and the increased hole content.Room-temperature electrical measurements of doped samples reveal anincrease in conductivity of several orders of magnitude as comparedto that of undoped samples, and high-temperature measurements showthat Cr2MnO4is a band conductor, as predictedby theory. The overall agreement between theory and experiment illustratesthe advantages of a theory-driven approach to materials design. [ABSTRACT FROM AUTHOR]

Vanadium and its surface oxides were studied as a potential nitrogen-selective membrane material for indirect carbon capture from coal or natural gas power plants. The effects of minor flue gas components (SO2, NO, NO2, H2O, and O2) on vanadium at 500-600 °C were investigated by thermochemical exposure in combination with X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and in situ X-ray diffraction (XRD). The results showed that SO2, NO, and NO2 are unlikely to have adsorbed on the surface vanadium oxides at 600 °C after exposure for up to 10 h, although NO and NO2 may have exhibited oxidizing effects (e.g., exposure to 250 ppmv NO/N2 resulted in an 2.4 times increase in surface V2O5 compared to exposure to just N2). We hypothesize that decomposition of surface vanadium oxides and diffusion of surface oxygen into the metal bulk are both important mechanisms affecting the composition and morphology of the vanadium membrane. The results and hypothesis suggest that the carbon capture performance of the vanadium membrane can potentially be strengthened by material and process improvements such as alloying, operating temperature reduction, and flue gas treatment. [ABSTRACT FROM AUTHOR]

The morphology of the bulk heterojunction absorber layer in an organic photovoltaic (OPV) device has a profound effect on the electrical properties and efficiency of the device. Previous work has consistently demonstrated that the solubilizing side-chains of the donor material affect these properties and device performance in a non-trivial way. Here, using Time-Resolved Microwave Conductivity (TRMC), we show by direct measurements of carrier lifetimes that the choice of side chains can also make a substantial difference in photocarrier dynamics. We have previously demonstrated a correlation between peak photoconductance measured by TRMC and device efficiencies; here, we demonstrate that TRMC photocarrier dynamics have an important bearing on device performance in a case study of devices made from donor materials with linear vs. branched side-chains and with variable active layer thicknesses. We use Grazing-Incidence Wide Angle X-ray Scattering to elucidate the cause of the different carrier lifetimes as a function of different aggregation behavior in the polymers. Ultimately, the results help establish TRMC as a technique for screening OPV donor materials whose devices maintain performance in thick active layers (>250 nm) designed to improve light harvesting, film reproducibility, and ease of processing. [ABSTRACT FROM AUTHOR]

Lithium-ionbatteries using germanium as the anode material areattracting attention because of their high-capacity, higher conductivity,and lithium-ion diffusivity relative to silicon. Despite recent studieson Ge electrode reactions, there is still limited understanding ofthe reaction mechanisms governing crystalline Ge and the transformationsinto intermediate amorphous phases that form during the electrochemicalcharge and discharge process. In this work, we carry out in operandoX-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) studieson Ge anodes during the initial cycles to better understand theseprocesses. These two probes track both crystalline (XRD) and amorphous(XAS) phase transformations with potential, which allows detailedinformation on the Ge anode to be obtained. We find that crystallineGe lithiates inhomogeneously, first forming amorphous Li9Ge4during the beginning stage of lithiation, followedby the conversion of the remaining crystalline Ge to amorphous Ge.The lithiation of amorphous Ge then forms amorphous LixGe, which are then further lithiated to form crystallineLi15Ge4. During delithiation, crystalline Li15Ge4transforms directly into a heterogeneous mixof amorphous LixGe, which eventually formamorphous Ge, and interestingly, no amorphous Li9Ge4are detected. Both our in operando XRD and XAS results presentnew insights into the reaction mechanism of Ge as anodes in LIBs,and demonstrate the importance of correlating electrochemical resultswith in operando studies. [ABSTRACT FROM AUTHOR]

Because of their preferential two-dimensional layer-by-layer growth in thin films, 5,5′bis(4-alkylphenyl)-2,2′-bithiophenes (P2TPs) are model compounds for studying the effects of systematic chemical structure variations on thin-film structure and morphology, which in turn, impact the charge transport in organic field-effect transistors. For the first time, we observed, by grazing incidence X-ray diffraction (GIXD), a strong change in molecular tilt angle in a monolayer of P2TP, depending on whether the alkyl chain on the P2TP molecules was of odd or even length. The monolayers were deposited on densely packed ultrasmooth self-assembled alkane silane modified SiO2 surfaces. Our work shows that a subtle change in molecular structure can have a significant impact on the molecular packing structure in thin film, which in turn, will have a strong impact on charge transport of organic semiconductors. This was verified by quantum-chemical calculations that predict a corresponding odd-even effect in the strength of the intermolecular electronic coupling. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the chemical and structural properties of solution-processed thin films of P3HT blended with p-type dopant F4TCNQ. The maximum in-plane electrical conductivity of doped films is observed at a molar doping fraction of 0.17, in agreement with the binding mechanism of F4TCNQ:P3HT complexes. Through the use of X-ray diffraction, a previously unreported crystalline phase is observed for P3HT films doped above a critical threshold concentration. This crystalline phase involves the incorporation of F4TCNQ molecules into ordered polymer regions and ultimately improves charge dissociation, leading to higher carrier density in thin film. Finally, optical absorption and X-ray diffraction reveal that the chemical state of P3HT in solution has a dramatic impact on the electrical and structural properties of the blended films. [Copyright &y& Elsevier]

We synthesized CuInS2nanoparticles containingup to20% Fe, Zn, and Ga to study alloying in photovoltaic absorber materialswith anomalous X-ray diffraction. The colloidal synthesis allowedfor detailed analysis of complex quaternary compounds. Anomalous X-raydiffraction (AXRD) was used to clarify the elemental distributionbetween phases. Additionally, optical spectroscopy and X-ray diffractionwere used to probe the band gap and crystal phase, respectively. Substitutionof Zn into wurtzite CuInS2produced a controllable increasein the optical band gap, whereas Ga did not substitute into wurtziteCuInS2, producing no band gap change. Secondary phase precipitationof a chalcopyrite phase was observed with Fe substitution, along witha decrease of the optical band gap. This work demonstrates progressin compositional and structural analysis of quaternary chalcogenidematerials using AXRD. [ABSTRACT FROM AUTHOR]

The structure of copper phthalocyanine (CuPc) thin films (5—100 nm) deposited on single-crystal ZnO(1100) substrates by organic molecular beam deposition was determined from grazing-incidence X-ray diffraction reciprocal space maps. The crystal structure was identified as the metastable polymorph α-CuPc, but the molecular stacking was found to vary depending on the film thickness: for thin films, a herringbone arrangement was observed, whereas for films thicker than 10 nm, coexistence of both the herringbone and brickstone arrangements was found. We propose a modified structure for the herringbone phase with a larger monoclinic β angle, which leads to intrastack Cu-Cu distances closer to those in the brickstone phase. This structural basis enables an understanding of the functional properties (e.g., light absorption and charge transport) of (opto)electronic devices fabricated from CuPc/ZnO hybrid systems. [ABSTRACT FROM AUTHOR]

Rechargeable lithium-sulfur (Li-S) batteries hold great potential for high-performance energy storage systems because they have a high theoretical specific energy, low cost, and are eco-friendly. However, the structural and morphological changes during electrochemical reactions are still not well understood. In this Article, these changes in Li-S batteries are studied in operando by X-ray diffraction and transmission X-ray microscopy. We show recrystallization of sulfur by the end of the charge cycle is dependent on the preparation technique of the sulfur cathode. On the other hand, it was found that crystalline Li2S does not form at the end of discharge for all sulfur cathodes studied. Furthermore, during cycling the bulk of soluble polysulfides remains trapped within the cathode matrix. Our results differ from previous ex situ results. This highlights the importance of in operando studies and suggests possible strategies to improve cycle life. [ABSTRACT FROM AUTHOR]

We use a systematic approach that combines experimental X-ray diffraction (XRD) and computational modeling based on molecular mechanics and two-dimensional XRD simulations to develop a detailed model of the molecular-scale packing structure of poly(2,5-bis (3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene) (PBTTT-C14) films. Both uniaxially and biaxially aligned films are used in this comparison and lead to an improved understanding of the molecular-scale orientation and crystal structure. We then examine how individual polymer components (i.e., conjugated backbone and alkyl side chains) contribute to the complete diffraction pattern, and how modest changes to a particular component orientation (e.g., backbone or side-chain tilt) influence the diffraction pattern. The effects on the polymer crystal structure of varying the alkyl side-chain length from C12 to C14 and C16 are also studied. The accurate determination of the three-dimensional polymer structure allows us to examine the PBTTT electronic band structure and intermolecular electronic couplings (transfer integrals) as a function of alkyl side-chain length. This combination of theoretical and experimental techniques proves to be an important tool to help establish the relationship between the structural and electronic properties of polymer thin films. [ABSTRACT FROM AUTHOR]

Abstract: We present a comprehensive investigation of morphological changes inside the active layer of an organic solar cell induced by substrate heating during layer deposition by thermal evaporation in ultra-high vacuum. To explore the trends observed in solar cell devices, we apply absorption and photoluminescence spectroscopy, atomic force microscopy, X-ray diffraction, and organic field effect transistor measurements. The material combination we use comprises unsubstituted dicyanovinyl end-capped quaterthiophene (DCV4T) as the donor material mixed with as the acceptor. The solar cell power conversion efficiency decreases with increasing substrate temperature during film deposition due to changes in the crystalline structure of the oligothiophene phase, leading to a decrease in absorption strength. Photoluminescence measurements show that substrate heating increases the amount of phase separation between the donor and acceptor, and topology and structure investigations reveal large aggregates of polycrystalline DCV4T at the surface. However, the fill factor is increased for higher substrate temperatures due to better transport properties. The highest efficiency obtained with this material combination and stack design is 3.0% under AM1.5g illumination. [Copyright &y& Elsevier]

We demonstrate that poly(3,4-dialkylterthiophenes) (P34ATs) have comparable transistor mobilities (0.17 cm² V-1 s-1) and greater environmental stability (less degradation of on/off ratio) than regioregular poly(3-alkylthiophenes) (P3ATs). Unlike poly(3-hexylthiophene) (P3HT), P34ATs do not show a strong and distinct π-π stacking in X-ray diffraction. This suggests that a strong π-π stacking is not always necessary for high charge-carrier mobility and that other potential polymer packing motifs in addition to the edge-on structure (π-π stacking direction parallel to the substrate) can lead to a high carrier mobility. The high charge-carrier mobilities of the hexyl and octyl-substituted P34AT produce power conversion efficiencies of 4.2% in polymer:fullerene bulk heterojunction photovoltaic devices. An enhanced open-circuit voltage (0.716-0.771 eV) in P34AT solar cells relative to P3HT due to increased ionization potentials was observed. [ABSTRACT FROM AUTHOR]

Two cations A and B in A2BO4 spinels appear in precise 2:1 Daltonian ratio ("line compounds") only at very low temperature. More typically, at finite temperature, they tend to become either A rich or B rich. Here we survey the experimentally observed stoichiometry asymmetries and describe the first-principles framework for calculating these. Defect calculations based on first principles are used to calculate the enthalpies of substitution of A atom ΔH(ATd) and B atom ΔH(BOh) and determine their site occupancies leading to (non)-stoichiometry. In Co2ZnO4, the result of the calculation for site occupancy compares well with that measured via anomalous x-ray diffraction. Further, the calculated phase boundary also compares well with that measured via Rietveld refinement of x-ray diffraction data on bulk ceramic sintered samples of Co2ZnO4 and Rh2ZnO4. These results show that Co2ZnO4 is heavily Co nonstoichiometric above 500°C, whereas Rh2ZnO4 is slightly Zn nonstoichiometric. We found that, in general, the calculated ΔH(ATd) is smaller than ΔH(BOh), if the A-rich competing phase is isostructural with the A2BO4 host, for example, A2AO4, whereas B-rich competing phase is not, for example, BO. This observation is used to qualitatively explain nonstoichiometry and solid solutions observed in other spinels. [ABSTRACT FROM AUTHOR]

A hydrogen-containing inorganic clathrale with the nominal composition, K7(H2)3Si46, has been prepared in 98% yield by Ihe reaction of K4Si4 with NH4Br. Rietveld refinement of Ihe powder X-ray diffraction data is consistent with the clathrate type I structure. Elemental analysis and ¹H MAS NMR confirmed the presence of hydrogen in this material. Type I clathrate structure is built up from a Si framework with Iwo types of cages where the guest species, in this case K and H2, can reside: a large cage composed of 24 Si, in which the guest resides in the 6d position, and a smaller one composed of 20 Si, in which the guest occupies the 2a position (cubic space group Pm3n). Potassium occupancy was examined using spherical aberration (Cs) corrected scanning transmission electron microscopy (STEM). The high- angle annular dark-field (HAAD) STEM experimental and simulaled images indicated that the K is deficient in both the 2a and the 6dsites. ¹H and 29Si MAS NMR are consistent with the presence of H2 in a restricted environment and the clathrale I structure, respectively. FTIR and 29Si(¹H) CP MAS NMR results show no evidence for a Si-H bond, suggesting thai hydrogen is present as H2 in interstitial sites. Thermal gravimetry (TG) mass spectrometry (MS) provide additional confirmation of H2 with hydrogen loss at ∼400 °C. [ABSTRACT FROM AUTHOR]

Abstract: The high flux and density of X-rays produced at synchrotrons provide the microelectronics industry with a powerful probe of the structure and behavior of a wide array of solid materials that are being developed for use in devices of the future. They also are of great use in determining why currently-used materials and processes sometimes fail. This paper describes the X20 X-ray beamline facility operated by IBM at the National Synchrotron Light Source, and presents a series of three industry challenges and results that illustrate the variety of techniques used and problems addressed. The value of this research ranges from solving short-term, technically specific problems to increasing our academic understanding of materials in general. Techniques discussed include high-resolution diffraction, time-resolved diffraction, texture measurements, and grazing-incidence diffraction. [Copyright &y& Elsevier]

Metal parts produced by laser powder bed fusion (LPBF) additive manufacturing exhibit characteristic microstructures comparable to those observed in laser welding. The primary cause of this characteristic microstructure is rapid, localized heating and cooling cycles, which result in extreme thermal gradients where material solidification is followed by fast cooling in the solid state. The final microstructure and mechanical performance are also influenced by pore formation caused by melt pool fluid dynamics. Here, we use high speed, in situ X-ray diffraction to probe the kinetics of cooling and solid-solid phase transitions after laser melting in two aerospace titanium alloys: Ti-6Al-4V, an α + β alloy; and Ti-5Al-5V-5Mo-3Cr, a near-β alloy. We complement these diffraction studies with in situ X-ray imaging to probe melt pool dynamics and pore formation. From these two complementary probes, we quantify pore formation during melting and the subsequent microstructural evolution as the material rapidly cools after solidification. These results are critical for understanding defect formation and residual stress development in different titanium alloys under LPBF conditions and can help inform process models to predict final part performance. Unlabelled Image • Direct comparison of materials dynamics in two titanium alloys using in situ X-ray imaging and diffraction during additive manufacturing. • High speed X-ray imaging quantifies fluid dynamics and pore formation during laser melting for both alloys. • In situ X-ray diffraction quantifies cooling rates and residual stress evolution after solidification. • Comparison to thermomechanical modeling provides mechanistic insight into behavior observed by X-ray diffraction. [ABSTRACT FROM AUTHOR]

Abstract: Thin films of SrHfO3 have been grown by MBE on Si (001). Synchrotron X-ray diffraction (XRD) and grazing incidence extended X-ray absorption spectroscopy (GI-EXAFS) were employed to elucidate the epitaxial relationship between the SrHfO3 and Si (001). The SrHfO3 film was unstrained and exhibited a lattice mismatch of 6% with silicon; the orientation was SrHfO3(001)[110] || Si(001)[100]. The SrHfO3 (200) plane demonstrated the expected four fold symmetry with a peak positioned every 90° in the phi scan of X-ray diffraction. Excellent fits of the GI-EXAFS showed that Hf was coordinated to about 6 oxygen atoms at a bonding distance of 2.080Å and about 8 Sr neighbors at 3.53Å. The short range order determined by GI-EXAFS corroborated the long range order determined by XRD, where nearly epitaxial growth, good crystalline quality, low disorder and minimal defects observed make SrHfO3 a viable dielectric candidate in Si based complementary metal-oxide-semiconductor field effect transistors. [Copyright &y& Elsevier]