High Intensity Synchrotron Radiation Research Articles

A versatile electrochemical cell for in-situ GI-XRD measurements on lab-scale XRD devices

In-situ X-ray diffraction (XRD) cells for electrochemical experiments suffer from strong attenuation of primary and diffracted beams within the electrolyte solution. To reduce the intensity loss of the X-rays, the use of a thin layer of electrolyte solution is an essential element of the conventional cell design. On the other hand, the thin layer electrolyte geometry is a considerable limitation for electrochemical measurements. To overcome these drawbacks a versatile electrochemical cell for in-situ GI-XRD measurements was constructed and used for the electrodeposition of Cu2O thin films on a copper substrate.In this design, a thin copper metal film working electrode is applied on a polyimide foil and then backside-illuminated in GI-XRD geometry. In this way, the XRD pattern is measured from the electrolyte/electrode interface of the working electrode. The X-rays only have to penetrate the polymer foil and the sputtered metal layer, resulting in high-intensity signals.In this work, we demonstrate the abilities of the in-situ cell with quantitative measurements of cathodic deposition of Cu2O thin layers. The results show a good agreement between the diffracted X-ray peak intensities and the calculated and measured thicknesses of the oxide layers. The cell design allows the structural characterization of electrode surfaces during electrochemical measurements without the disadvantages of thin layer cells and therefore does not require high intensity synchrotron radiation to perform X-ray diffraction during electrochemical investigations.

Electronic structure and composition of tin oxide thin epitaxial and magnetron layers according to synchrotron XANES studies

The materials of the tin-oxygen system and thin-film structures based on them are modern and actual for the creation of a wide range of electronic devices, for example, resistive gas sensors of high sensitivity and short response time with low energy consumption and high manufacturability. An important direction in the study of such materials and structures is the control of properties with variations in technological formation regimes. Information on the composition, local atomic and electronic structure of thin layers of the tin-oxygen system with varying approaches to their production is in demand. The work is devoted to the study of the electronic structure of thin layers of tin oxides obtained by modern methods of molecular beam epitaxy and magnetron sputtering. A study of the local partial density of electronic states in the conduction band by X-ray absorption near edge structure spectroscopy of tin and oxygen has been carried out. The data were obtained using high-intensity synchrotron radiation, which allows varying the monochromatized radiation quantum energy without loss in intensity, that is necessary to obtain high-resolution X-ray spectral data. It is shown that the composition, local atomic surrounding, electronic spectrum and their features depend on the technology of formation and storage conditions of the studied structures. Synchrotron X-ray spectroscopy data show the presence of intermediate oxides of the tin-oxygen system in the studied materials after prolonged storage in laboratory conditions. The data obtained indicate the possibility of controlled variation in the composition, local atomic surrounding and electronic spectrum of thin-film structures of tin oxides of small thickness. The results of the work can be used in the formation and subsequent modification of thin and ultrathin layers of tin oxides by magnetron sputtering and molecular beam epitaxy, as well as in their further application as active layers of microelectronics devices

Technical note: In situ measurements and modelling of the oxidation kinetics in films of a cooking aerosol proxy using a quartz crystal microbalance with dissipation monitoring (QCM-D)

Abstract. Aerosols and films are found in indoor and outdoor environments. How they interact with pollutants, such as ozone, has a direct impact on our environment via cloud droplet formation and the chemical persistence of toxic aerosol constituents. The chemical reactivity of aerosol emissions is typically measured spectroscopically or by techniques such as mass spectrometry, directly monitoring the amount of material during a chemical reaction. We present a study which indirectly measures oxidation kinetics in a common cooking aerosol proxy using a low-cost quartz crystal microbalance with dissipation monitoring (QCM-D). We validated this approach by comparison with kinetics measured both spectroscopically and with high-intensity synchrotron radiation. Using microscopy, we found that the film morphology changed and film rigidity increased during oxidation. There was evidence of surface crust formation on oxidised particles, though this was not consistent for all experiments. Crucially, our kinetic modelling of these experimental data confirmed that the oleic acid decay rate is in line with previous literature determinations, which demonstrates that performing such experiments on a QCM-D does not alter the underlying mechanism. There is clear potential to take this robust and low-cost but sensitive method to the field for in situ monitoring of reactions outdoors and indoors.

Evaluation of high intensity synchrotron radiation x-ray imaging using Si crystals with lapped surface at 33.3 keV.

In x-ray imaging methods, such as synchrotron radiation microangiography, the x-ray intensity has become more important in recent years for real-time dynamic observations to evaluate temporal changes in samples. Many synchrotron radiation facilities use x-rays monochromated by diffraction from perfect Si crystals to improve the spatial resolution of x-ray images and obtain detailed information about a sample. In this paper, monochromatic synchrotron x-ray images were acquired using Si crystals lapped with abrasives to enhance the x-ray intensity using white synchrotron radiation x-rays for observing dynamic changes in samples. The x-ray intensity, spatial resolution, and contrast noise ratio (CNR) in the acquired x-ray images were quantitatively evaluated using a state-of-the-art high-spatial-resolution detector. The x-ray intensity was substantially increased by a factor of ∼8 when a lapped Si crystal was used. When the lapped Si crystal was used, the spatial resolution of x-ray images in the diffraction-plane direction was ∼70% lower than when an etched Si crystal was used at a spatial resolution of 10 lp/mm. By contrast, the CNR in x-ray images, which is important for observing the interior of a sample, increased threefold when a contrast agent containing iodine at a concentration of 38 wt. % was used. It was confirmed that the combination of white synchrotron radiation x-rays and a lapped crystal produces an intense monochromatic x-ray, providing an important evaluation for the use of optics for each research purpose.

Three-dimensional angle-resolved photoemission study of bulk SiGe single crystals

The composition- and structure-dependent electronic band structure of SiGe alloys facilitates a rich variety of its application in various fields. In this study, we performed high-resolution core-level and angle-resolved photoemission spectroscopy (ARPES) of unstrained SiGe single crystals with the (001) surface. Thermally cleaned surfaces of the single crystals of SiGe alloys exhibited double domain (2 × 1) reconstruction, wherein the asymmetric dimer was composed of Ge atoms, and Si atoms were located below the subsurface region. The compositional dependence of three valence bands and their constant energy contours were clearly resolved by three-dimensional ARPES measurements using the high-intensity synchrotron radiation. The valence bands of unstrained SiGe alloys could be well described by the composition-based interpolation of the band parameters of pristine Si and Ge crystals.

Frozen storage of proteins: Use of mannitol to generate a homogenous freeze-concentrate

Therapeutic proteins may be subjected to several freeze–thaw cycles throughout manufacturing and storage. The protein solution composition and the freezing conditions may lead to incomplete ice crystallization in the frozen state. This can also result in freeze-concentrate heterogeneity characterized by multiple glass transition temperatures and protein destabilization. The overall objective was to investigate the potential advantages of including a crystallizing excipient (mannitol) along with a sugar (sucrose or trehalose) for frozen storage. This study showed that the addition of mannitol, a readily crystallizing excipient, facilitated ice crystallization. Inclusion of an isothermal hold during cooling (annealing) maximized the mannitol crystallization and resulted in a homogenous freeze-concentrate of a constant composition characterized by a single glass transition temperature. The role of freezing rate and annealing on both mannitol and ice crystallization were discerned using high intensity synchrotron radiation. The addition of sucrose or trehalose, at an appropriate concentration, stabilized the protein. The mannitol to sugar ratio (3:1 or 1:1, 5 % w/v) was optimized to selectively cause maximal crystallization of mannitol while retaining the sugar amorphous. Human serum albumin (1 mg/mL) in these optimized and annealed compositions did not show any meaningful aggregation, even after multiple freeze–thaw cycles. Thus, in addition to a sugar as a stabilizer, the use of a crystallizing excipient coupled with an annealing step can provide an avenue for frozen storage of proteins.

Advanced X-ray imaging at beamline 07 of the SAGA Light Source.

The SAGA Light Source provides X-ray imaging resources based on high-intensity synchrotron radiation (SR) emitted from the superconducting wiggler at beamline 07 (BL07). By combining quasi-monochromatic SR obtained by the newly installed water-cooled metal filter and monochromatic SR selected by a Ge double-crystal monochromator (DCM) with high-resolution lens-coupled X-ray imagers, fast and low-dose micro-computed tomography (CT), fast phase-contrast CT using grating-based X-ray interferometry, and 2D micro-X-ray absorption fine structure analysis can be performed. In addition, by combining monochromatic SR obtained by a Si DCM with large-area fiber-coupled X-ray imagers, high-sensitivity phase-contrast CT using crystal-based X-ray interferometry can be performed. Low-temperature CT can be performed using the newly installed cryogenic system, and time-resolved analysis of the crystallinity of semiconductor devices in operation can be performed using a time-resolved topography system. The details of each instrument and imaging method, together with exemplary measurements, are presented.

電子線三次元結晶構造解析/3D ED/マイクロED

The scattering powers of electron and X-ray differ by 4 - 5 orders of magnitude. Thanks to this property, the electron beam yields high-resolution diffraction spots from undersized crystals of various samples, which are hard to grow to a suitable size for X-ray diffraction even with a high-intensity synchrotron radiation beam. Thus, the technique known as electron 3D crystallography/3D ED/MicroED is recognized as being important especially in synthetic chemistry, material sciences and related areas, while single particle analysis can be used for larger-sized proteins. Here I review this technology including our recent developments and results.

Design and Performance of a Full Functional Electrochemical Cell for Lab Scale in-Situ GI-XRD Instruments

In-situ XRD may support electrochemical measurements by delivering analytical information about electrochemical processes. Since structural changes at the electrode/electrolyte interface are of specific interest, measurements are done usually in small angle reflection mode geometry. The surface sensitive grazing incidence – XRD (GI-XRD) in-situ technique allows the detection of short-lived electrode reaction products or products sensitive to ambient atmosphere exposure. This method finds applications for quite a number of investigations of electrochemical processes including corrosion, film growth and deposition, reconstruction of superficial regions, ion insertion battery materials, etc. The common cell designs for lab scale XRD equipment use thin electrolyte layers to avoid unacceptable beam intensity loss through water. The use of synchrotron radiation would reduce this shortcoming to some extent but is much less accessible.In 1986, Fleischmann et al. presented an in-situ XRD thin layer cell in reflection as well as in transmission mode, where a X-ray transparent Mylar foil was used as window material [1]. However, this geometry restricts the positioning of counter and reference electrodes and therefore has unfavorable current density distribution, has very small electrolyte volume, is vulnerable to side reactions with gas evolution and does not allow high flow rates for the solution. Thus, the general applicability is limited.In our proposed in-situ cell design for GI-XRD, the electrochemical cell is fully functional, avoiding all of the above mentioned drawbacks [2]. The solution of this issue is the "backside-illumination" (or "inverse" illumination) of a thin film working electrode applied on a thin polymer foil as a support by the X-ray beam at a small incident angle. On the opposite side a conventional electrochemical cell with reference electrode and counter electrode and sufficient solution volume can be used. The big advantage of this design is that the X-ray only has to penetrate the foil and the thin layer of electrode material resulting in high signals from the region of interest. It is used with a conventional laboratory X-ray source and does not need high intensity synchrotron radiation. With this cell design, problems with bulk solution resistance, inhomogeneous current-density distribution, insufficient bath agitation or gas evolution as side reaction are eliminated.In this contribution, details of the cell design, analysis of current density distribution within the thin current collector and the electrochemical cell, results of calibration measurements and measurements on copper as an example for a galvanic deposition/dissolution process are presented.[1] M. Fleischmann, A. Oliver, and J. Robinson, ‘In Situ X-ray diffraction studies of electrode solution interfaces’, Electrochimica Acta, vol. 31, no. 8, pp. 899–906, (1986)[2] S. Reither, W. Artner, A. Eder, S. Larisegger, M. Nelhiebel, C. Eisenmenger-Sittner, G. Fafilek, ‘On the In-Situ Grazing Incidence X-Ray Diffraction of Electrochemically Formed Thin Films’, ECS Transactions, 80 (10) 1231-1238, (2017) 10.1149/08010.1231ecst Figure 1

Protein-crystal detection with a compact multimodal multiphoton microscope

There is an increasing demand for rapid, effective methods to identify and detect protein micro- and nano-crystal suspensions for serial diffraction data collection at X-ray free-electron lasers or high-intensity micro-focus synchrotron radiation sources. Here, we demonstrate a compact multimodal, multiphoton microscope, driven by a fiber-based ultrafast laser, enabling excitation wavelengths at 775 nm and 1300 nm for nonlinear optical imaging, which simultaneously records second-harmonic generation, third-harmonic generation and three-photon excited ultraviolet fluorescence to identify and detect protein crystals with high sensitivity. The instrument serves as a valuable and important tool supporting sample scoring and sample optimization in biomolecular crystallography, which we hope will increase the capabilities and productivity of serial diffraction data collection in the future.

Surface X-Ray Diffraction Studies of Single Crystal Electrochemistry

The atomic structure on the metal side of the electrochemical interface depends on the applied electric potential and the nature of the adsorbing species in the electrolyte solution. In this poster we will present some recent results probing surface stress and surface relaxation effects in single crystal metal electrodes that are driven by potential changes. The principal method for probing changes in the atomic structure at the interface is surface x-ray diffraction employing the use of high intensity synchrotron radiation [1]. Measurements on Pt(hkl), Au(hkl) and Ag(hkl) electrodes enable a comprehensive study of the phenomena of surface reconstruction and surface relaxation. The measurements also give insight into the potential-dependent layering in the liquid side of the interface. Both the potential and the structure in the electrolyte layers at the interface alter the metal electronic structure so that the surface in the electrochemical environment is strongly modified from the ultra-high vacuum (UHV) counterpart. A methodology for linking experimental and theoretical approaches for a fundamental understanding of electrochemical reactions will be presented.[1] Y. Gründer and C. A. Lucas, NanoEnergy, 29, 378-393 (2016).

Soft X-ray diffraction patterns measured by a LiF detector with sub-micrometre resolution and an ultimate dynamic range.

The unique diagnostic possibilities of X-ray diffraction, small X-ray scattering and phase-contrast imaging techniques applied with high-intensity coherent X-ray synchrotron and X-ray free-electron laser radiation can only be fully realized if a sufficient dynamic range and/or spatial resolution of the detector is available. In this work, it is demonstrated that the use of lithium fluoride (LiF) as a photoluminescence (PL) imaging detector allows measuring of an X-ray diffraction image with a dynamic range of ∼107 within the sub-micrometre spatial resolution. At the PETRA III facility, the diffraction pattern created behind a circular aperture with a diameter of 5 µm irradiated by a beam with a photon energy of 500 eV was recorded on a LiF crystal. In the diffraction pattern, the accumulated dose was varied from 1.7 × 105 J cm-3 in the central maximum to 2 × 10-2 J cm-3 in the 16th maximum of diffraction fringes. The period of the last fringe was measured with 0.8 µm width. The PL response of the LiF crystal being used as a detector on the irradiation dose of 500 eV photons was evaluated. For the particular model of laser-scanning confocal microscope Carl Zeiss LSM700, used for the readout of the PL signal, the calibration dependencies on the intensity of photopumping (excitation) radiation (λ = 488 nm) and the gain have been obtained.

Competition between Itineracy and Localization of Electrons Doped into the Near-Surface Region of Anatase TiO2

The competition between itineracy and localization of electrons doped into the near-surface region of anatase TiO2 (a-TiO2) is examined by photoemission spectroscopy. Since a-TiO2 samples used in this study are naturally grown single crystals, some electrons derived from oxygen vacancies are inherently present within the bulk and result in both a metallic state just below the Fermi level (EF) and a localized state tightly trapped by the oxygen vacancies (deep-trap state) within the energy gap. Additional electrons were doped to the surface by in situ deposition of potassium and by irradiation with high-intensity synchrotron radiation (SR). The potassium deposition does not cause a direct disturbance in the conduction pathway of the doped electrons, whereas the SR radiation produces oxygen vacancies in the pathway. Most of the doped electrons produced by depositing potassium contribute to a metallic state just below EF and behave as the carriers responsible for the surface conductivity. The remaining fract...

Synchrotron studies of top-down grown silicon nanowires

Abstract Morphology of the top-down grown silicon nanowires obtained by metal-assisted wet-chemical approach on silicon substrates with different resistance were studied by scanning electron microscopy. Obtained arrays of compact grown Si nanowires were a subject for the high resolution electronic structures studies by X-ray absorption near edge structure technique performed with the usage of high intensity synchrotron radiation of the SRC storage ring of the University of Wisconsin-Madison. The different oxidation rates were found by investigation of silicon atoms local surrounding specificity of the highly developed surface and near surface layer that is not exceeded 70 nm. Flexibility of the wires arrays surface morphology and its composition is demonstrated allowing smoothly form necessary surface oxidation rate and using Si nanowires as a useful matrixes for a wide range of further functionalization.

On the In-Situ Grazing Incidence X-ray Diffraction of Electrochemically Formed Thin Films

Existing designs of in-situ X-ray diffraction (XRD) cells for electrochemical experiments are usually cells in which the beam has to penetrate the electrolyte. In order to avoid strong attenuation of primary and diffracted beams, the electrolyte has to be a thin film which is a considerable restriction for electrochemical processes. In this contribution, a novel in-situ cell design is described which avoids the thin electrolyte configuration by backside-illumination of a thin metal film working electrode applied on a polyimide foil. This has the advantage that the X-rays only have to penetrate foil and sputtered electrode, resulting in high signals from the deposited material. Therefore, the cell does not need high intensity synchrotron radiation but works with a laboratory X-ray source. Problems with bulk solution resistance or inhomogeneous current-density distribution during deposition processes are also eliminated. The novel cell design was tested on the cathodic formation of Cu2O on copper.

Full-field fan-beam x-ray fluorescence computed tomography with a conventional x-ray tube and photon-counting detectors for fast nanoparticle bioimaging

X-ray fluorescence computed tomography (XFCT) was performed on a high-intensity synchrotron radiation source or a pencil beam with a long exposure time due to the low emission and detection efficiency of x-ray fluorescence photons. For the first time, the feasibility and experimental results of a full-field fan-beam XFCT with a photon-counting detector array are presented. This full-field fan-beam XFCT consists of a conventional low-intensity x-ray tube, an energy-sensitive photon-counting detector array, and a tungsten pinhole collimator. A phantom containing gadolinium solution (Kα, 42.74 keV) was scanned for 30 min using a polychromatic x-ray fan beam with a third-generation computed tomography (CT) geometry. After scattering and attenuation corrections, experimental results showed that XFCT had better accuracy and performance than spectral CT. Full-field XFCT is a promising modality for biomedical imaging of exogenous molecular probes containing nanoparticles of high atomic number.

Overview: Experimental studies of crystal nucleation: Metals and colloids.

Crystallization is one of the most important phase transformations of first order. In the case of metals and alloys, the liquid phase is the parent phase of materials production. The conditions of the crystallization process control the as-solidified material in its chemical and physical properties. Nucleation initiates the crystallization of a liquid. It selects the crystallographic phase, stable or meta-stable. Its detailed knowledge is therefore mandatory for the design of materials. We present techniques of containerless processing for nucleation studies of metals and alloys. Experimental results demonstrate the power of these methods not only for crystal nucleation of stable solids but in particular also for investigations of crystal nucleation of metastable solids at extreme undercooling. This concerns the physical nature of heterogeneous versus homogeneous nucleation and nucleation of phases nucleated under non-equilibrium conditions. The results are analyzed within classical nucleation theory that defines the activation energy of homogeneous nucleation in terms of the interfacial energy and the difference of Gibbs free energies of solid and liquid. The interfacial energy acts as barrier for the nucleation process. Its experimental determination is difficult in the case of metals. In the second part of this work we therefore explore the potential of colloidal suspensions as model systems for the crystallization process. The nucleation process of colloids is observed in situ by optical observation and ultra-small angle X-ray diffraction using high intensity synchrotron radiation. It allows an unambiguous discrimination of homogeneous and heterogeneous nucleation as well as the determination of the interfacial free energy of the solid-liquid interface. Our results are used to construct Turnbull plots of colloids, which are discussed in relation to Turnbull plots of metals and support the hypothesis that colloids are useful model systems to investigate crystal nucleation.

Unexpected effects in non crystalline materials exposed to X-ray radiation

The interaction of high intensity synchrotron radiation X-rays in the energy range 5<E<30keV with matter can produce a large number of expected and less expected effects. Whether these be considered radiation damage or are simply ignored, perhaps depends on the context or the eye of the beholder. In many cases however, X-ray induced effects can easily be mistaken for experimental results, and non-crystalline materials and liquids are most affected. We give a brief overview of possible X-ray induced effects, including structural changes and nanoparticle formation in glass, reaction rates in catalysis, the formation of bubbles in aqueous environments due to the presence of salts, and discuss possible mechanisms. The results shown are relevant for time-resolved processes studied by X-ray methods in catalysis, glass devitrification and for liquid samples.

The investigations of changes in mineral–organic and carbon–phosphate ratios in the mixed saliva by synchrotron infrared spectroscopy

The objective of this study was to investigate the efficiency of the saturation of mixed saliva by mineral complexes and groups necessary for the remineralisation of tooth enamel using exogenous and endogenous methods of caries prevention.Using IR spectroscopy and high-intensity synchrotron radiation, changes in the composition of the human mixed saliva were identified when exogenous and endogenous methods of caries prevention are employed. Based on the calculations of mineral/organic and carbon/phosphate ratios, changes in the composition of the human mixed saliva depending on a certain type of prevention were identified.It is shown that the use of a toothpaste (exogenous prevention) alone based on a multi-mineral complex including calcium glycerophosphate provides only a short-term effect of saturating the oral cavity with mineral complexes and groups. Rinsing of the oral cavity with water following the preventive use of a toothpaste completely removes the effect of the saturation of the mixed saliva with mineral groups and complexes.The use of tablets of a multi-mineral complex with calcium glycerophosphate (endogenous prevention) in combination with exogenous prevention causes an average increase of ∼10% in the content of mineral groups and complexes in the mixed saliva and allows long-term saturation of the oral fluid by them. This method outperforms the exogenous one owing to a long-term effect of optimal concentrations of endogenous and biologically available derivatives of phosphates on the enamel surface.

Compression-induced crystallization of amorphous indomethacin in tablets: characterization of spatial heterogeneity by two-dimensional X-ray diffractometry.

Tablets of amorphous indomethacin were compressed at 10, 25, 50, or 100 MPa using either an unlubricated or a lubricated die and stored individually at 35 °C in sealed Mylar pouches. At selected time points, tablets were analyzed by two-dimensional X-ray diffractometry (2D-XRD), which enabled us to profile the extent of drug crystallization in tablets, in both the radial and axial directions. To evaluate the role of lubricant, magnesium stearate was used as "internal" and/or "external" lubricant. Indomethacin crystallization propensity increased as a function of compression pressure, with 100 MPa pressure causing crystallization immediately after compression (detected using synchrotron radiation). However, the drug crystallization was not uniform throughout the tablets. In unlubricated systems, pronounced crystallization at the radial surface could be attributed to die wall friction. The tablet core remained substantially amorphous, irrespective of the compression pressure. Lubrication of the die wall with magnesium stearate, as external lubricant, dramatically decreased drug crystallization at the radial surface. The spatial heterogeneity in drug crystallization, as a function of formulation composition and compression pressure, was systematically investigated. When formulating amorphous systems as tablets, the potential for compression induced crystallization warrants careful consideration. Very low levels of crystallization on the tablet surface, while profoundly affecting product performance (decrease in dissolution rate), may not be readily detected by conventional analytical techniques. Early detection of crystallization could be pivotal in the successful design of a dosage form where, in order to obtain the desired bioavailability, the drug may be in a high energy state. Specialized X-ray diffractometric techniques (2D; use of high intensity synchrotron radiation) enabled detection of very low levels of drug crystallization and revealed the heterogeneity in crystallization within the tablet.