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With the growing need for sustainable energy technologies, advanced characterization methods become more and more critical for optimizing energy materials and understanding their operation mechanisms. In this review, we focus on the synchrotron-based X-ray imaging technologies and the associated applications in gaining fundamental insights into the physical/chemical properties and reaction mechanisms of energy materials. We will discuss a few major X-ray imaging technologies, including X-ray projection imaging, transmission X-ray microscopy, scanning transmission X-ray microscopy, tender and soft X-ray imaging, and coherent diffraction imaging. Researchers can choose from various X-ray imaging techniques with different working principles based on research goals and sample specifications. With the X-ray imaging techniques, we can obtain the morphology, phase, lattice and strain information of energy materials in both 2D and 3D in an intuitive way. In addition, with the high-penetration X-rays and the high-brilliance synchrotron sources, operando/in-situ experiments can be designed to track the qualitative and quantitative changes of the samples during operation. We expect this review can broaden readers' view on X-ray imaging techniques and inspire new ideas and possibilities in energy materials research. [ABSTRACT FROM AUTHOR]

The formation of epitaxial γ-Al2O3 thin films on 4H-SiC was found to be strongly dependent on the film thickness. An abrupt interface was observed in films up to 200 Å thick with an epitaxial relationship of γ-Al2O3(111)∥4H-SiC(0001) and γ-Al2O3(440)∥4H-SiC(1120). The in-plane alignment between the film and the substrate is nearly complete for γ-Al2O3 films up to 115 Å thick, but quickly diminishes in thicker films. The films are found to be slightly strained laterally in tension; the strain increases with thickness and then decreases in films thicker than 200 Å, indicating strain relaxation which is accompanied by increased misorientation. By controlling the structure of ultrathin Al2O3 films, metal–oxide–semiconductor capacitors with Al2O3 gate dielectrics on 4H-SiC were found to have a very low leakage current density, suggesting suitability of Al2O3 for SiC device integration. [ABSTRACT FROM AUTHOR]

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]

Describes the synthesis, magnetism and structure of CoPtCrB alloys. Formation of fine isolated grains for all Pt concentrations as shown by transmission electron microscopy; Possible cause of the behavior of the anisotropy; Absence of Pt concentration dependence for the stacking fault density.

We describe structural and magnetic measurements of polycrystalline, L1[SUB0] chemically ordered Fe(55-60)Pt(45-40) films as a function of film thickness (from 3 to 13 nm) and growth temperature (270- 370°C). With increasing film thickness, the coercivity increases from about 1 kOe up to 11 kOe (growth at 400°C), while for increasing growth temperature, the coercivity grows from 0.2 to 6 kOe for 4.3 nm thick films and 1.6 to 10 kOe for 8.5 nm thick films. There is a strong, nearly linear correlation between coercivity and the extent of L1[SUB0] chemical order. In all the films there is a mixture of L1[SUB0] and chemically disordered, fcc phases. The grain size in the L1[SUB0] phase increases with both film thickness and growth temperature (increasing chemical order), while in the fcc phase the grain size remains nearly constant and is smaller than in the L1[SUB0] phase. The films all contain twins and stacking faults. The relationship between the coercivity and the film structure is discussed and we give a possible mechanism for the lack of chemical order in the very thin films (lack of nucleation sites for the L1[SUB0] phase). [ABSTRACT FROM AUTHOR]

The mass density profile from thin (∼25 Å) layers of polymer molecules adsorbed on amorphous carbon thin films is determined from measurements of the specular reflectivity of x rays. Important information on the conformation of the polymer molecules is obtained from the density profile (average density as a function of position above the surface). The polymer is a perfluoropolyether (PFPE) with piperonyl end groups and has a molecular weight of 2000–3000 Daltons. Three samples are measured: a nonbonded sample with an approximately 25 Å layer applied by dipping, a bonded sample with the layer applied by dipping but followed by a process to attach the molecule to the carbon, and a cleaned sample which is the nonbonded sample after the polymer had been removed. The density profile of the nonbonded polymer shows that the density within 10 Å of the carbon surface is ∼1.6 gm/cc, which is smaller than the density in the region between 10 and 25 Å (∼1.8 gm/cc). This indicates that the less dense piperonyl end groups are preferentially adsorbed near the carbon surface, which provides a possible explanation of the observation that the addition of the piperonyl end group to PFPE improves adhesion of the polymer to surfaces. The bulk-like density in the region between 10 and 25 Å and the compactness of the layer suggest that the preponderance of molecules have both end groups preferentially adsorbed; consequently, the PFPE chains remain close to the surface. The data from the bonded and nonbonded polymer layers are essentially the same, which indicates the molecular conformation is not strongly affected by the bonding treatment. [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.

We control the anisotropic molecular packing of vapor-deposited glasses of ABH113, a deuterated anthracene derivative with promise for future organic light emitting diode materials, by changing the deposition rate and substrate temperature at which they are prepared. We find that at substrate temperatures from 0.65 Tg to 0.92 Tg, the deposition rate significantly modifies the orientational order in the vapor-deposited glasses as characterized by x-ray scattering and birefringence. Both measures of anisotropic order can be described by a single deposition rate–substrate temperature superposition (RTS). This supports the applicability of the surface equilibration mechanism and generalizes the RTS principle from previous model systems with liquid crystalline order to non-mesogenic organic semiconductors. We find that vapor-deposited glasses of ABH113 have significantly enhanced density and thermal stability compared to their counterparts prepared by liquid-cooling. For organic semiconductors, the results of this study provide an efficient guide for using the deposition rate to prepare stable glasses with controlled molecular packing. [ABSTRACT FROM AUTHOR]

Focuses on a study which investigated the effects of thermal annealing on the magnetic and interface properties of exchange-biased nickel iron/iron manganese thin film couples. Description of the crater edge depth profiles of the deposited and annealed films; Temperature dependence of annealed films; Changes in antiferromagnet in relation to annealing.

Explains x-ray reflectivity measurements on ultrathin amorphous carbon silicon films. Technique for measuring the thickness, density and microscopic surface roughness; Formula for the index of refraction at x-ray energies; Value of the incidence angle of the x-rays.

Solution-processed lead halide perovskite thin-film solar cells have achieved power conversion efficiencies comparable to those obtained with several commercial photovoltaic technologies in a remarkably short period of time. This rapid rise in device efficiency is largely the result of the development of fabrication protocols capable of producing continuous, smooth perovskite films with micrometer-sized grains. Further developments in film fabrication and morphological control are necessary, however, in order for perovskite solar cells to reliably and reproducibly approach their thermodynamic efficiency limit. This Perspective discusses the fabrication of lead halide perovskite thin films, while highlighting the processing--property--performance relationships that have emerged from the literature, and from this knowledge, suggests future research directions. [ABSTRACT FROM AUTHOR]

ABSTRACT An understanding of the structure and properties of polymer electrolyte systems can be crucial to a variety of different applications. The current work performs a study of the composition, structure and properties of poly(ethylene glycol) (PEG)-aromatic polyimide systems incorporating ionic liquids that are relevant to several applications especially fuel cell membranes. Composition was varied through using different aromatic dianhydrides, aromatic diamines and in some cases synthesis solvent. Properties were characterized using Fourier transform infrared spectroscopy, thermal gravimetric analysis, differential scanning calorimetry, small-angle x-ray scattering, electrochemical impedance spectroscopy and cyclic voltammetry. By varying solvent, aromatic regularity and expected rigidity can be tuned, impacting average conductivity by 30%. Varying the aromatic diamine can influence the length scale and amount of aromatic regularity, which can ultimately affect the conductivity by a factor of four. The maximum conductivity reached was 83 mS/cm at 80 °C and 70 %RH. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 509-521 [ABSTRACT FROM AUTHOR]

Electrical vehicles (EVs) are an attractive option for moving towards a CO2 neutral transportation sector, but in order for widespread commercial use of EVs, the cost of electrical energy storage (i.e., batteries) must be reduced and the energy storage capacity must be increased. New, higher performing but Earth abundant electrodes are needed to accomplish this goal. To aid the development of these materials, in situ characterization to understand battery operation and failure is essential. Since electrodes are inherently heterogeneous, with a range of relevant length scales, imaging is a necessary component of the suite of characterization methods. In this Feature Article, the rapidly growing and developing field of X-ray based microscopy (XM) techniques is described and reviewed focusing on in situ and operando adaptations. Further, in situ transmission electron microscopy (TEM) is briefly discussed in this context and its complement to XM is emphasized. Finally, a perspective is given on some emerging X-ray based imaging approaches for energy storage materials. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Ultrathin cross-linked polymer thinfilms are highly desirablematerials because of their important roles in many applications. However,they are difficult and challenging to fabricate. Here we report aone-step process for depositing cross-linked polyurea thin films usinga vapor-phase molecular layer deposition (MLD) technique. 1,4-Diisocyanatobutaneand a series of different multiamines, including diethylenetriamine,triethylenetetramine, and tris(2-aminoethyl)amine, were used to growpolyurea MLD films via urea-coupling reactions. The deposited cross-linkedpolyurea films exhibit characteristic MLD film growth behaviors, suchas constant growth rates, infrared absorption by expected urea modes,and stoichiometric chemical compositions. More importantly, the cross-linkingis shown to be capable of improving the film properties. Based oncross-linking, the thin film density can be increased by approximately50%. In addition, the film decomposition temperature is increasedby about 30 °C, suggesting an enhanced thermal stability of thecross-linked ultrathin polyurea films. [ABSTRACT FROM AUTHOR]

Crystallite orientations, molecular packing disorder, and hole mobility of poly(3-hexylthiophene) thin films that are spin casted from different solvents are studied as a function of film thickness. Grazing incidence x-ray diffraction reveals that films consist of an ultrathin layer of ordered, edge-on oriented aggregates and a more disordered, face-on oriented bulk region. Diffraction and optical absorption spectroscopy elucidate the film-forming process. Field-effect hole mobility provides evidence for interconnecting aggregates as the mechanism for efficient charge transport. [ABSTRACT FROM AUTHOR]

Poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene), PBTTT, is a semiconducting polymer that forms thin film transistors (TFTs) with high field effect mobility on silicon dioxide dielectrics that are treated with alkyltrichlorosilanes (∼0.2 to 0.5 cm²/V s) but forms TFTs with poor mobility on bare silicon dioxide (<0.005 cm²/V s). The microstructure of spin-coated thin films of PB-FFT on these surfaces was studied using synchrotron X-ray diffraction and atomic force microscopy. PBTTT crystallizes with lamellae of π-stacked polymer chains on both surfaces. The crystalline domains are well-oriented relative to the substrate in the as-spun state and become highly oriented and more ordered with thermal annealing in the liquid crystalline mesophase. Although the X-ray scattering from PBTTT is nearly identical on both surfaces, atomic force microscopy showed that the domain size of the crystalline regions depends on the substrate surface. These results suggest that electrical transport in PBTTT films is strongly affected by the domain size of the crystalline regions and the disordered regions between them. [ABSTRACT FROM AUTHOR]

Abstract: We report on synthesis–structure–activity–stability relationships of Pt3Co nanoparticle electrocatalysts for the oxygen reduction reaction (ORR). We have synthesized Pt3Co alloy electrocatalysts using liquid impregnation techniques followed by reductive annealing at high and low temperatures. We have performed detailed structural X-ray diffraction (XRD)-based structural characterization (symmetry, lattice parameters and composition) of individual Pt–Co alloy phases before and, importantly, after electrochemical rotating disk electrode (RDE) measurements. This enables us to directly evaluate the corrosion stability of various Pt–Co alloy phases under typical fuel cell cathode conditions. Pt3Co prepared at low annealing temperatures (600°C) resulted in multiple phases including (i) a disordered face-centered cubic (fcc) Pt95Co5 phase and (ii) an ordered face-centered tetragonal (L10) Pt50Co50 phase; high temperature annealing (950C) resulted in a single ordered primitive cubic (L12) Pt3Co phase. The ordered alloy phases in both catalysts were not stable under electrochemical treatment: The ordered face-centered tetragonal (fct) phase showed corrosion and dissolution, while the ordered primitive cubic (L12) Pt3Co phase transformed into a disordered structure. The ordered primitive cubic structure exhibited higher resistance to sintering. Low annealing temperatures resulted in higher Pt surface-area specific activities for ORR. Kinetic Tafel analysis confirmed a general shift in the formation potential of oxygenated surface species, such as Pt–OH, for both alloy catalysts. Reduced OH coverage alone proved insufficient to account for the observed activity trends of the two alloy catalysts. [Copyright &y& Elsevier]

Abstract: A Ta2O5–Pt nanostructure electrode was fabricated by means of cosputtering deposition method. Worm-like Pt nanoparticles were produced in Ta2O5 matrix as observed by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The electrochemical and electrochromic properties of nanoworm-shaped Ta2O5–Pt electrode are compared with those of Ta2O5 thin-film electrode without Pt nanoparticles. [Copyright &y& Elsevier]

We report polarized neutron reflectivity (PNR) studies of antiferromagnetically coupled (AFC) magnetic recording media with the aim of understanding how the two ferromagnetic layers switch magnetization direction. The PNR measurements were conducted at applied magnetic fields from near saturation to near the coercive field of the upper layer. From the PNR spectra, we obtain the magnetization profile of the AFC media. The results verify that the lower layer is aligned antiparallel to the magnetically hard upper layer in low fields. However, the magnetization of the upper layer shows an unexpected decrease as the lower layer reverses direction, which indicates that the interaction between the upper and lower layers is more complex than previously thought. [ABSTRACT FROM AUTHOR]

We describe small-angle neutron scattering measurements of the magnetic cluster size distributions for several longitudinal magnetic recording media. We find that the average magnetic cluster size is slightly larger than the average physical grain size, that there is a broad distribution of cluster sizes, and that the cluster size is inversely correlated to the media signal-to-noise ratio. These results show that intergranular magnetic coupling in these media is small and they provide empirical data for the cluster-size distribution that can be incorporated into models of magnetic recording. [ABSTRACT FROM AUTHOR]

We describe x-ray diffraction and magnetic measurements of annealed MnPt and NiMn spin valves as a function of MnPt (NiMn) film thickness. Thin films (... 5-10 nm) are not chemically ordered and hence not antiferromagnetic, which explains the lack of exchange coupling in these films. With increasing thickness, the L1[sub 0] chemical order develops (through coexistence between fcc and L1[sub 0] phases) and there is a strong correlation between chemical order and exchange coupling. The lack of chemical order in the thin films is likely due to a lack of nucleation sites for the L1[sub 0] phase. [ABSTRACT FROM AUTHOR]

Presents a study on the thickness and lubricant-air roughness of a perfluoropolyether lubricant on silicon wafers and carbon overcoats. Density of magnetic bits on disk drives; Theory for capillary waves; Results and conclusions.

Presents information on a study which determines the validity of thickness measurements by electron spectroscopy for chemical analysis (ESCA) and ellipsometry. Techniques used to determine the thickness of perfluoroplyether (PFPE) on lubricant surfaces; Benefits from the technique; Details on the ellipsometry measurement.

Presents the results of the study on near-surface alignment of polymer molecules caused by the rubbing of a polyimide film. Use of grazing-incidence X-ray scattering (GIXS); Derivation of the polyimide used in the experiment; Observation of X-ray scattering.

Presents measurements of the water density profile perpendicular to a silver (111) surface using X-ray scattering. Comparison of the density of the first layer with bulk water; Disruption of the hydrogen-bonding network in the first layer.

Glasses prepared by physical vapor deposition (PVD) are anisotropic, and the average molecular orientation can be varied signifi- cantly by controlling the deposition conditions. While previous work has characterized the average structure of thick PVD glasses, most experiments are not sensitive to the structure near an underlying substrate or interface. Given the profound influence of the substrate on the growth of crystalline or liquid crystalline materials, an underlying substrate might be expected to substantially alter the structure of a PVD glass, and this near-interface structure is important for the function of organic electronic devices prepared by PVD, such as organic light-emitting diodes. To study molecular packing near buried organic--organic interfaces, we prepare superlattice structures (stacks of 5- or 10-nm layers) of organic semiconductors, Alq3 (Tris-(8-hydroxyquinoline)aluminum) and DSA-Ph (1,4-di-[4-(N,N-diphenyl)amino]styrylbenzene), using PVD. Superlattice structures significantly increase the fraction of the films near buried interfaces, thereby allowing for quantitative characterization of interfacial packing. Remarkably, both X-ray scattering and spectroscopic ellipsometry indicate that the substrate exerts a negligible influence on PVD glass structure. Thus, the surface equilibration mechanism previously advanced for thick films can successfully describe PVD glass structure even within the first monolayer of deposition on an organic substrate. [ABSTRACT FROM AUTHOR]

The process dependence of the mixed ionic-electronic conductivity of sintered octadecylamine-encapsulated silver sulfide nanoparticle thin films has been studied and correlated with the film structure. Although grain growth begins around 120 °C, there is no significant electrical conductivity until 350 °C and mixed conductivity until 400 °C, when the nanoparticle encapsulant evaporates. Higher temperatures decompose the silver sulfide. In lateral structures, no filaments form until sintering at 400 °C. The process dependence of mixed ionic electronic conducting properties may provide a method for engineering materials for use in electrochemical metallization resistive random access memories. [ABSTRACT FROM AUTHOR]

Delamination of the electron-transporting polymer N2200 from indium tin oxide (ITO) in aqueous electrolytes is mitigated by modifying ITO with an azide-functionalized phosphonic acid (PA) which, upon UV irradiation, reacts with the polymer. The optical, electrochemical, and spectroelectrochemical properties of N2200 thin films are retained in aqueous and non-aqueous media. [ABSTRACT FROM AUTHOR]

Hard carbon (HC) is the most promising anode for the commercialization of sodium‐ion batteries (NIBs); however, a general mechanism for sodium storage in HC remains unclear, obstructing the development of highly efficient anodes for NIBs. To elucidate the mechanism of sodium storage in the pores, operando synchrotron small‐angle X‐ray scattering, wide‐angle X‐ray scattering, X‐ray absorption near edge structure, Raman spectroscopy, and galvanostatic measurements are combined. The multimodal approach provides mechanistic insights into the sodium pore‐filling process for different HC microstructures including the pore sizes that are preferentially filled, the extent to which different pore sizes are filled, and how the defect concentration influences pore filling. It is observed that sodium in the larger pores has an increased pseudo‐metallic sodium character consistent with larger sodium clusters. Furthermore, it is shown that the HCs prepared at higher pyrolysis temperatures have a larger capacity from sodium stored in the pores and that sodium intercalation between graphene layers occurs simultaneously with the pore filling in the plateau region. Opportunities are outlined to improve the performance of HC anodes by fully utilizing the pores for sodium storage, helping to pave the way for the commercialization of sodium ion batteries. [ABSTRACT FROM AUTHOR]

Review: 81 refs. [ABSTRACT FROM AUTHOR]

To understand the origins of failure and limited cycle life in lithium-ion batteries (LIBs), it is imperative to quantitatively link capacity-fading mechanisms to electrochemical and chemical processes. This is extremely challenging in real systems where capacity is lost during each cycle to both active material loss and solid electrolyte interphase (SEI) evolution, two indistinguishable contributions in traditional electrochemical measurements. Here, we have used a model system in combination with (1) precision measurements of the overall Coulombic efficiency via electrochemical experiments and (2) x-ray reflectivity measurements of the active material losses. The model system consisted of a 515 Å thick amorphous silicon (a-Si) thin film on silicon carbide in half-cell geometry using a carbonate electrolyte with LiPF6 salt. This approach allowed us to quantify the capacity lost during each cycle due to SEI evolution. Combined with electrochemical analysis, we identify SEI growth as the major contribution to capacity fading. Specifically, the continued SEI growth results in increasing overpotentials due to increased SEI resistance, and this leads to lower extent of lithiation when the cutoff voltage is reached during lithiation. Our results suggest that SEI grows more with increased time spent at low voltages where electrolyte decomposition is favored. Finally, we extracted a proportionality constant for SEI growth following a parabolic growth law. Our methodology allows for the quantitative determination of lithium-ion loss mechanisms in LIBs by separately tracking lithium ions within the active materials and the SEI and offers a powerful method of quantitatively understanding LIB loss mechanisms. [ABSTRACT FROM AUTHOR]

The frequency of reports utilizing synchrotron‐based grazing incident wide angle X‐ray scattering (GIWAXS) to study metal halide perovskite thin films has exploded recently, as this technique has proven invaluable for understanding several structure‐property relationships that fundamentally limit optoelectronic performance. The GIWAXS geometry and temporal resolution are also inherently compatible with in situ and operando setups (including ISOS protocols), and a relatively large halide perovskite research community has deployed GIWAXS to unravel important kinetic and dynamic features in these materials. Considering its rising popularity, the aim here is to accelerate the required learning curve for new experimentalists by clearly detailing the underlying analytical concepts which can be leveraged to maximize GIWAXS studies of polycrystalline thin films and devices. Motivated by the vast range of measurement conditions offered, together with the wide variety of compositions and structural motifs available (i.e., from single‐crystal and polycrystalline systems, to quantum dots and layered superlatices), a comprehensive framework for conducting effective GIWAXS experiments is outlined for different purposes. It is anticipated that providing a clear perspective for this topic will help elevate the quality of future GIWAXS studies—which have become routine—and provide the impetus required to develop novel GIWAXS approaches to resolve unsettled scientific questions. [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]

Performance of nonfullerene‐based organic solar cells is largely dependent on the donor:acceptor blend morphology, which is initially tuned by composition. However, morphological design rules are difficult to identify due to the complex relationship between composition‐dependent phase behavior and performance properties. In this study, the authors are able to establish a direct link between PM6:Y6 film morphology and device properties by combining grazing‐incidence wide‐angle X‐ray scattering with highly sensitive Fourier transform photocurrent spectroscopy. By analyzing properties across the full composition range, interfacial microstructure and the corresponding charge transfer (CT) states are identified and direct structure–property relationships are established. The results indicate that open‐circuit voltage is controlled by the CT state at amorphous‐PM6:crystalline‐Y6 interfaces. Crystalline Y6 is found to increase both transport and non‐radiative recombination, suggesting that morphological tradeoffs may be necessary for overall device optimization. [ABSTRACT FROM AUTHOR]

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 ( 110 / 1 1 ¯ 0 ) lattice spacing decreases slightly upon drying, while the (200) lattice parameters are unchanged. Additionally, the ( 110 / 1 1 ¯ 0 ) 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. [ABSTRACT FROM AUTHOR]

X-ray reflectivity has been used to measure the roughness of perfluoropolyether (PFPE) polymer films on silicon substrates and carbon overcoats. For PFPE on smooth silicon, we find that the rms roughness of the PFPE-air interface increases slowly from about 2 to 4 Å as PFPE thickness increases from 5 to 33 Å. This increase is consistent with capillary waves roughening the polymer film, but inconsistent with current theories for the dewetting of polymer films. For PFPE on the rougher surface of amorphous hydrogenated carbon, we find that the PFPE polymer smoothes the surface with the rms roughness decreasing from 9 to 4 Å. We also discuss the implications of these results on the limits of disk drive technology. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A class of tunable, mesostructured self-assembled hydrogels has been developed based on a library of π–π stacking ABA-type telechelic triblock copolymers prepared by organocatalytic ring-opening polymerization (ROP). Poly(ethylene glycol) (PEG) served as a macroinitiator for ROP of methylene tricarbonate-benzyl ester (MTC-OBn), a benzyl-ester functionalized cyclic carbonate monomer, resulting in polymers with well-defined length and narrow polydispersity. Self-assembled hydrogels were formed by dissolving poly(MTC-OBn)- b -PEG- b- poly(MTC-OBn) copolymers in water. Physical cross-links in the hydrogels formed through hydrophobic and π–π stacking intermolecular interactions between poly(MTC-OBn) segments. The mesoscale material properties were probed using small angle X-ray scattering (SAXS) and dynamic mechanical measurements. SAXS spectra show a scattering peak, corresponding to a molecular domain spacing of 20–25 nm, which we attribute to the formation of electron-dense poly(MTC-OBn) assemblies. Results from oscillatory shear experiments were analyzed in conjunction with SAXS data in order to develop an understanding of the influence that nanoscale structure has on the mechanical properties of self-assembled gels. Modeling of scattering peaks using the Bragg spacing model demonstrated that the hydrophilic PEG network chains connecting the scattering moieties behaved as a two-dimensional self-avoiding walk. We compared the observed microstructural features with the mechanical properties of self-assembled gels and determined that the molecular weight of the polycarbonate and PEG segments controls the gel structure on both the mesoscale and macroscale. A central contribution of this work is a synthetic strategy that utilizes ROP to control polymer structure, which in turn controls both the structure and mechanical properties of these biodegradable self-assembled hydrogels. [ABSTRACT FROM AUTHOR]

ZnO nanotubes were prepared by selectivedissolution of electrodepositednanorods. The effect of solution pH, rod morphology, and chlorideion concentration on the dissolution mechanism was studied. The selectiveetching was rationalized in terms of the surface energy of the differentZnO crystal faces and reactant diffusion. The nanorod diameter andchloride concentration are the most influential parameters on thedissolution mechanism because they control homogeneous dissolutionor selective etching of the (110) and (002) surfaces. Bulk solutionpH only has an effect on the rate of dissolution. By accurate controlof the dissolution process, the nanomorphology can be tailored, andthe formation of rods with a thin diameter (10–20 nm), cavity,or ultra-thin-walled tubes (2–5 nm) can beachieved. [ABSTRACT FROM AUTHOR]

Molecular aggregation and crystallization during film coating play a crucial role in the realization of high‐performing organic photovoltaics. Strong intermolecular interactions and high solid‐state crystallinity are beneficial for charge transport. However, fast crystallization during thin‐film drying often limits the formation of the finely phase‐separated morphology required for efficient charge generation. Herein, the authors show that twisted acceptor‐donor‐acceptor (A‐D‐A) type compounds, containing an indacenodithiophene (IDT) electron‐rich core and two naphthalenediimide (NDI) electron‐poor units, leads to formation of mostly amorphous phases in the as‐cast film, which can be readily converted into more crystalline domains by means of thermal annealing. This design strategy solves the aforementioned conundrum, leading to an optimal morphology in terms of reduced donor/acceptor domain‐separation sizes (ca. 13 nm) and increased packing order. Solar cells based on these acceptors with a PBDB‐T polymer donor show a power conversion efficiency over 10% and stable morphology, which results from the combined properties of desirable excited‐state dynamics, high charge mobility, and optimal aggregation/crystallization characteristics. These results demonstrate that the twisted A‐D‐A motif featuring thermally‐induced crystallization behavior is indeed a promising alternative design approach toward more morphologically robust materials for efficient organic photovoltaics. [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]

The driving forces and processes associated with the development of phase separation upon thermal annealing are investigated in solution-processed small molecule bulk heterojunction (BHJ) organic solar cells utilizing a diketopyrrolopyrrole-based donor molecule and a fullerene acceptor (PCBM). In-situ thermal annealing X-ray scattering is used to monitor the development of thin film crystallization and phase separation and reveals that the development of blend phase separation strongly correlates with the nucleation of donor crystallites. Additionally, these morphological changes lead to dramatic increases in blend electron mobility and solar cell figures of merit. These results indicate that donor crystallization is the driving force for blend phase separation. It is hypothesized that donor crystallization from an as-cast homogeneous donor:acceptor blend simultaneously produces donor-rich domains, consisting largely of donor crystallites, and acceptor-rich domains, formed from previously mixed regions of the film that have been enriched with acceptor during donor crystallization. Control of donor crystallization in solution-processed small molecule BHJ solar cells employing PCBM is thus emphasized as an important strategy for the engineering of the nanoscale phase separated, bicontinuous morphology necessary for the fabrication of efficient BHJ photovoltaic devices. [ABSTRACT FROM AUTHOR]

Solution deposition using high-boiling- point additives such as octanedithiol (ODT) provides a simple and widely used fabrication option for improving the power conversion efficiencies of solar cells composed of narrow-band-gap conjugated polymer donor/fullerene acceptor blends. Previous examination of the resulting device active layers has shown that the use of additives influences the degree of phase segregation within the bulk heterojunction (BHJ) blend and also improves ordering within the polymeric domains. In this work, in situ grazing- incidence wide-angle X-ray scattering as a function of time was used to explore the dynamics of the BHJ evolution. These studies showed that a small percentage of ODT in chlorobenzene (CB) induced the nucleation of polymeric crystallites within 2 mm of deposition, increased the orientational order of specific polymorphs, and promoted further crystallite nucleation over a period longer than 40 mm after casting. Similar structural changes did not occur when the same BHJ blend was cast from pure CB. [ABSTRACT FROM AUTHOR]

One of the greatest challenges facing humanity in the 21st century is providing the world's population with the energy it needs without significantly raising the concentration of greenhouse gases in the atmosphere [1]. Many studies predict that a significant fraction of our power will have to come from solar cells taking advantage of the sun bathing our planet with an average power of 120,000 TW. Solution processable organic photovoltaics (OPVs) show great promise for providing a cost-effective route for creating lightweight and flexible solar energy conversion devices [2-42, 4]. Polymer-fullerene bulk heterojunctions (BHJ) have been intensely studied over the past decade for use as the active layer in such devices (Figure 1); one of the most popular blends consists of poly(3-hexylthiophene) (P3HT), as the electron donor phase, and phenyl-C61-butyric acid methyl ester (PCBM), as the electron acceptor phase. In OPV devices, optical photons are absorbed in the polymer and create excitons (bound electron-hole pairs). These diffuse to donor/acceptor interfaces, where they dissociate to create free electrons and holes that are then transported through the acceptor PCBM and donor P3HT, respectively, to the electrodes. Thus, current is generated. The optimization of BHJ blend morphologies on multiple length scales is critical in order to achieve high performance in these devices [5]. In an organic solar cell device, incident light is absorbed by the electron donor phase creating an exciton. The exciton must then diffuse to the donor-acceptor interface where charge separation can occur. The molecular packing and crystallite size of both the acceptor and donor within their respective domains must be optimized for exciton transport (diffusion) and maximum charge carrier mobilities for efficient transfer of electrons and holes to their respective electrodes. In addition, the nano-scale phase separation of the donor and acceptor materials must have domain sizes less than the exciton diffusion length in the polymer in order for efficient conversion of absorbed photons into electrical current. [ABSTRACT FROM AUTHOR]

Thin films of polymer semiconductors are being intensively investigated for large-area electronics applications such as light-emitting diodes, photovoltaic cells and thin-film transistors. Understanding the relationship between film morphology and charge transport is key to improving the performance of thin-film transistors. Here we use X-ray diffraction rocking curves to provide direct evidence for highly oriented crystals at the critical buried interface between the polymer and the dielectric where the current flows in thin-film transistors. Treating the substrate surface with self-assembled monolayers significantly varies the concentration of these crystals. We show that the polymer morphology at the buried interface can be different from that in the bulk of the thin films, and provide insight into the processes that limit charge transport in polythiophene films. These results are used to build a more complete model of the relationship between chain packing in polymer thin-films and charge transport. [ABSTRACT FROM AUTHOR]

Abstract: PtRu–WO3 alloy thin-film nanostructures for use as direct methanol fuel cells have been fabricated by co-sputtering for 20 and 40 at.% Ru. The structural and electrochemical properties of these nanostructures were characterized using transmission electron microscopy, X-ray diffraction, and electrochemical measurements. The nanostructures consist of PtRu alloy nanoparticles (4nm in size) dispersed in the WO3 matrix. For 20 at.% Ru, the alloy nanoparticles are face-centered cubic (fcc), but for 40 at.% Ru, the nanoparticles separate into Pt-rich fcc and Ru-rich hexagonal-close packed (hcp) phases. [Copyright &y& Elsevier]

Crystal orientation mapping in the transmission electron microscope was used to quantify the twin boundary length fraction per unit area for five Ta38Si14N48/SiO2 encapsulated Cu films with thicknesses in the range of 26-111 nm. The length fraction was found to be higher for a given twin-excluded grain size for these films compared with previously investigated SiO2 and Ta/SiO2 encapsulated films. The quantification of the twin length fraction per unit area allowed the contribution of the twin boundaries to the size effect resistivity to be assessed. It is shown that the increased resistivity of the Ta38Si14N48 encapsulated Cu films compared with the SiO2 and Ta/SiO2 encapsulated films is not a result of increased surface scattering, but it is a result of the increase in the density of twin boundaries. With twin boundaries included in the determination of grain size as a mean-intercept length, the resistivity data are well described by 2-parameter Matthiessen's rule summation of the Fuchs-Sondheimer and Mayadas Shatzkes models, with p and R parameters that are within experimental error equal to those in prior reports and are p=0.48(+0.33/-0.31) and R=0.27±0.03. [ABSTRACT FROM AUTHOR]

We investigate high‐valent oxygen redox in the positive Na‐ion electrode P2‐Na0.67−x[Fe0.5Mn0.5]O2 (NMF) where Fe is partially substituted with Cu (P2‐Na0.67−x[Mn0.66Fe0.20Cu0.14]O2, NMFC) or Ni (P2‐Na0.67−x[Mn0.65Fe0.20Ni0.15]O2, NMFN). From combined analysis of resonant inelastic X‐ray scattering and X‐ray near‐edge structure with electrochemical voltage hysteresis and X‐ray pair distribution function profiles, we correlate structural disorder with high‐valent oxygen redox and its improvement by Ni or Cu substitution. Density of states calculations elaborate considerable anionic redox in NMF and NMFC without the widely accepted requirement of an A‐O‐A′ local configuration in the pristine materials (where A=Na and A′=Li, Mg, vacancy, etc.). We also show that the Jahn–Teller nature of Fe4+ and the stabilization mechanism of anionic redox could determine the extent of structural disorder in the materials. These findings shed light on the design principles in TM and anion redox for positive electrodes to improve the performance of Na‐ion batteries. [ABSTRACT FROM AUTHOR]

Thermal annealing is critical in governing the phase distribution, and ultimately the electrical properties, of ferroelectric hafnium oxide films. In particular, rapid thermal annealing (RTA) has been shown to favor the formation of ferroelectric crystal phases, but the dynamic behavior of the film over the course of the anneal is not well understood. Herein, synchrotron X‐ray diffraction is used to characterize the phase distribution of HfO2 films deposited by atomic layer deposition (ALD) in situ during RTA, revealing complex phase transformations occurring on the scale of seconds. All samples investigated here transform into a nonmonoclinic phase, which is required for ferroelectric films. However, this phase often converts into the more stable monoclinic phase as annealing proceeds. The kinetic barrier to the transformation to the monoclinic phase during heating is higher than 1 eV f.u.−1 The initial crystallization into the ferroelectric phase and relatively high barrier to transformation to the nonferroelectric phase suggests that careful control of the thermal annealing profile can greatly increase the ferroelectric fraction of the film. By using a fast ramp rate and a short annealing time above the ferroelectric crystallization temperature, the remanent polarization of a pure HfO2 film can be increased more than twofold. [ABSTRACT FROM AUTHOR]

We investigate high‐valent oxygen redox in the positive Na‐ion electrode P2‐Na0.67−x[Fe0.5Mn0.5]O2 (NMF) where Fe is partially substituted with Cu (P2‐Na0.67−x[Mn0.66Fe0.20Cu0.14]O2, NMFC) or Ni (P2‐Na0.67−x[Mn0.65Fe0.20Ni0.15]O2, NMFN). From combined analysis of resonant inelastic X‐ray scattering and X‐ray near‐edge structure with electrochemical voltage hysteresis and X‐ray pair distribution function profiles, we correlate structural disorder with high‐valent oxygen redox and its improvement by Ni or Cu substitution. Density of states calculations elaborate considerable anionic redox in NMF and NMFC without the widely accepted requirement of an A‐O‐A′ local configuration in the pristine materials (where A=Na and A′=Li, Mg, vacancy, etc.). We also show that the Jahn–Teller nature of Fe4+ and the stabilization mechanism of anionic redox could determine the extent of structural disorder in the materials. These findings shed light on the design principles in TM and anion redox for positive electrodes to improve the performance of Na‐ion batteries. [ABSTRACT FROM AUTHOR]