Looking Deeper: Angle-Resolved Photoemission with Soft and Hard X-rays

Traditional angle-resolved photoemission (ARPES) with excitation in the ca. 20 to 150 eV range has clearly evolved to be the technique of choice for studying the electronic structure of surfaces and complex new strongly correlated and magnetic materials. However, it is clear that ARPES with excitation only up to 150 eV or so remains a very surface-sensitive probe, thus necessitating careful in-situ sample treatment, cleaving, or even synthesis to avoid the measurement of surface-associated artifacts. A key measure of this surface sensitivity is the electron inelastic mean free path (IMFP orΛ_e), which measures the mean depth of electron emission without inelastic scattering, and both experimental [1 Offi, F., Iacobucci, S., Vilmercati, P., Rizzo, A., Goldoni, A., Sacchi, M. and Panaccione, G. 2008. Physical Review B, 77: 201101R[Crossref] , [Google Scholar], 2 Offi, F., Iacobucci, S., Petaccia, L., Gorovikov, S., Vilmercati, P., Rizzo, A., Ruocco, A., Goldoni, A., Stefani, G. and Panaccione, G. 2010. Journal of Physics: Condensed Matter, 22: 305002[Crossref] , [Google Scholar]] and theoretical [3 Tanuma, S., Powell, C. J. and Penn, D. R. 2011. Surface and Interface Analysis, 43: 689[Crossref], [Web of Science ®] , [Google Scholar]] IMFP studies showing that the only reliable way to increase bulk or buried layer/interface sensitivity for all material types is to go to higher photon energies in the soft X-ray (ca. 0.5–2 keV) or hard X-ray (ca. 2–10 keV) regime.     

Boundary conditions for phase transitions and interfacial reactions

Abstract

Si et al. [1 Si, X., Oh, E.S. and Slattery, J.C. 2010. Phil. Mag., 90: 655[Taylor & Francis Online] , [Google Scholar]] pointed out that it was inappropriate to use continuity of displacement at interfaces during phase transitions or in the case of reactions at interfaces as in the case of oxidation, since appropriate reference configurations cannot be identified. They instead derived a new compatibility constraint, when atleast one of the adjoining phases is crystalline. The test of these ideas offered by Slattery et al. [2 Slattery, J.C., Si, X., Fu, K.B. and Oh, E.S. 2010. Phil. Mag., 90: 665[Taylor & Francis Online] , [Google Scholar]] was successful, but it likely was too simple, since the deformations were so small. A more stringent and successful test has recently been offered by [3 Slattery, J.C., Fu, K-B and Philos, E-SOh. 2012. Mag., 92: 1788 [Google Scholar]]. Here, we analyze oxidation on the surface of a cylinder both using an extension of the compatibility constraint and using continuity of displacement, comparing the results with the experimental observations of Imbrie and Lagoudas [4 Imbrie, P.K. and Lagoudas, D.C. 2001. Oxid. Met., 55: 359[Crossref], [Web of Science ®] , [Google Scholar]].     

Low-temperature high-resolution absorption spectrum of 14NH3 in the ν1+ν3 band region (1.51 μm)

Jet-cooled spectra of ¹⁴NH₃ and ¹⁵NH₃ in natural abundance were recorded using cavity ring-down (CRDS, 6584–6670 cm^?1) and cavity enhanced absorption (CEAS, 6530–6700 cm^?1) spectroscopy. Line broadening effects in the CRDS spectrum allowed lines with J ^″-values between 0 and 3 to be identified. Intensity ratios in ¹⁴NH₃ between the jet-cooled CRDS and literature room-temperature data from Sung et al. (J. Quant. Spectrosc. Radiat. Transfer, 113 (2012 K. Sung , L.R. Brown , X. Huang , D.W. Schwenke , T.J. Lee , S.L. Coy , and K.K. Lehmann , J. Quant. Spectrosc. Radiat. Transfer 113 , 1066 (2012).[Crossref], [Web of Science ®] , [Google Scholar]), 1066) further assisted the line assignments. Ground state combination differences were extensively used to support the assignments, providing reliable values for J, K and inversion symmetry of the ground state vibrational levels. CEAS data helped in this respect for the lowest J lines, some of which are saturated in the CRDS spectrum. Further information on a/s doublets arose from the observed spectral structures. Thirty-two transitions of ¹⁴NH₃ were assigned in this way and a limited but significant number (19) of changes in the assignments results, compared to Sung et al. or to Cacciani et al. (J. Quant. Spectrosc. Radiat. Transfer, 113 (2012 P. Cacciani , P. Cermak , J. Cosleou , M. Khelkhal , P. Jeseck , and X. Michaut , J. Quant. Spectrosc. Radiat. Transfer 113 , 1084 (2012).[Crossref], [Web of Science ®] , [Google Scholar]), 1084). Sixteen known and 25 new low-J transitions were identified for ¹⁵NH₃ in the CRDS spectrum but the much scarcer literature information did not allow for any more refined assignment. The present line position measurements improve on literature values published for ¹⁵NH₃ and on some line positions for ¹⁴NH₃.     

Vibrational and computational analysis for molecular structure properties of N-(2-(trifluoromethyl)phenyl)acetamide: Density functional theory approach

Abstract

The conformational study using Potential Energy Surface analysis was performed and its minimum energy conformer has been obtained for N-(2-(Trifluoromethyl)phenyl)acetamide. Fourier Transform Infrared and Fourier Transform Raman investigation have been done experimentally and theoretically. Nuclear Magnetic Resonance analysis has been performed to obtain ¹H and ¹ Bassetto, M.; Ferla, S.; Pertusati, F. Polyfluorinated Groups in Medicinal Chemistry. Future Med. Chem. 2015, 7, 527–546.[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]C chemical shifts. Ultraviolet-Visible analysis has been performed to obtain maximum absorption wavelength. The molecular orbital diagram with different energies has been obtained and compared with the band gap of Ultraviolet-Visible data. Wave function analysis has been discussed to know the electronic properties. Thus, this present study reports the structural, electrical, chemical activities of the title compound.     

The pseudogap: friend or foe of high T c ?

Although nineteen years have passed since the discovery of high temperature cuprate superconductivity 1 Bednorz, JG and Müller, KA. 1986. Z. Phys. B, 64: 189[Crossref] , [Google Scholar], there is still no consensus on its physical origin. This is in large part because of a lack of understanding of the state of matter out of which the superconductivity arises. In optimally and underdoped materials, this state exhibits a pseudogap at temperatures large compared to the superconducting transition temperature 2 Warren, WW Jr., Walstedt, RE, Brennert, GF, Cava, RJ, Tycko, R, Bell, R and Dabbagh, G. 1989. Phys. Rev. Lett., 62: 1193[Crossref], [PubMed], [Web of Science ®] , [Google Scholar], 3 Alloul, H, Ohno, T and Mendels, P. 1989. Phys. Rev. Lett., 63: 1700[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]. Although discovered only three years after the pioneering work of Bednorz and Müller, the physical origin of this pseudogap behavior and whether it constitutes a distinct phase of matter is still shrouded in mystery. In the summer of 2004, a band of physicists gathered for five weeks at the Aspen Center for Physics to discuss the pseudogap. In this perspective, we would like to summarize some of the results presented there and discuss the importance of the pseudogap phase in the context of strongly correlated electron systems.

The pseudogap: friend or foe of high T _c ?

All authors

M. R. Norman, D. Pines &; C. Kallin

https://doi.org/10.1080/00018730500459906

Published online:

19 February 2007

Table     

A new integral equation method for direct electromagnetic scattering in homogeneous media and its numerical confirmation

In this paper, we derive a new integral equation method for direct electromagnetic scattering in homogeneous media and present a numerical confirmation of the new method via a computer simulation. The new integral equation method is based on a paper written by DeSanto [1 DeSanto, J. A. 1993. A New formulation of electromagnetic scattering from rough dielectric interfaces. Journal of Electromagnetic Waves and Applications, 7: 1293–1306. [CSA][Taylor & Francis Online], [Web of Science ®] , [Google Scholar]], originally for scattering from an infinite rough surface separating homogeneous dielectric half-spaces. Here, it is applied to a bounded scatterer, which can be an ohmic conductor or a dielectric, with some simplification of the continuity conditions for the fields. The new integral equation method is developed by choosing the electric field and its normal derivative as boundary unknowns, which are not the usual boundary unknowns. The new integral equation method may provide significant computational advantages over the standard Stratton–Chu method [2 Stratton, J. A. and Chu, L. J. 1939. Diffraction theory of electromagnetic waves. Physical Review, 56: 99–107. [CSA][CROSSREF][Crossref] , [Google Scholar]] because it leads to a 50% sparse, rather than 100% dense, impedance (collocation) matrix. Our theoretical development of the new integral equation method is exact.     

Photon-In/Photon-Out Soft X-ray Spectroscopy at the TPS 45A Beamline

Owing to the current energy crisis and extreme changes in the global climate, there is great interest in finding renewable energy resources. Vast progress has been made in the development of new materials related to renewable energy, and their physical/chemical properties can be tailored by nanostructuring and other advanced synthetic approaches. In many important energy systems, such as solar hydrogen systems, the atomic/electronic structures of materials and fundamental interfacial phenomena of systems critically determine the energy conversion efficiency of materials [1 S. Shen et al., Energy Environ. Sci. 9, 2744 (2016).[Crossref], [Web of Science ®] , [Google Scholar], 2 J. Chen et al., J. Mater. Chem. A 2, 4605 (2014).[Crossref], [Web of Science ®] , [Google Scholar]]. Without knowledge of the fundamental electronic structures of the materials during conversion reactions, better engineering of the material for practical use is difficult. Understanding and controlling the interfaces in energy generation/conversion/storage materials requires in-situ/operando approaches [3 V. Iablokov et al., Nano Lett. 12, 2091 (2012).[Crossref], [Web of Science ®] , [Google Scholar], 4 F. Zheng et al., Nano Lett. 11, 847 (2011).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. The Taiwan Photon Source (TPS) Soft X-ray Spectroscopic beamline provides the capabilities for X-ray absorption (XAS) and X-ray emission (XES) spectroscopies, which can be utilized to investigate unoccupied (conduction-band) and occupied (valence-band) electronic states, respectively. Moreover, resonant inelastic X-ray scattering (RIXS) can be used to study intra-band (including d-d or f-f excitations) and inter-band (charge transfer) transitions [5 S. M. Butorin et al., Phys. Rev. Lett. 77, 574 (1996).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar], 6 P. Kuiper et al., Phys. Rev. Lett. 80, 5204 (1988).[Crossref], [Web of Science ®] , [Google Scholar]]. The former provides details about electronic energy splitting in various crystal fields and the latter involves electron transfer between a metal and a ligand, which determines chemical activity [7 H. Liu, Nano Lett. 7, 1919 (2007).[Crossref], [Web of Science ®] , [Google Scholar], 8 V. Bisogni et al., Phys. Rev. Lett. 114, 096402 (2015).[Crossref], [Web of Science ®] , [Google Scholar]].     

Future light sources based upon photo-injected energy recovery linacs

X-ray scattering techniques have long ranked among the most important methods for studying amorphous materials and other highly disordered targets. Well-established X-ray scattering methods often consist of recording time-averaged scattered intensity maps which, under the Born approximation, straightforwardly reveal information about ensemble-averaged, two-point, electron density correlations within the target. In the case of isotropic targets that consist of disordered ensembles of randomly oriented particles, scattering data are typically reduced to a histogram of electron pair distances (the “pair distribution function,” or PDF). While the information contained in the one-dimensional PDF is limited, a rich set of structural properties can often be determined straightforwardly (e.g., radius of gyration, surface area, short-range correlation length scales, fractal dimension). One of the well-known pinnacles of the methodology is the application of small-angle X-ray scattering (SAXS) to solutions of identical biological macromolecules [1 Elser, V. 2011. New J. Phys., 13: 123014[Crossref] , [Google Scholar]–3 Putnam, C. D., Hammel, M., Hura, G. L. and Tainer, J. A. 2007. Quarterly Reviews of Biophysics, 40: 191–285. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], which is now routinely used to rapidly determine ab initio low-resolution (>1 nm) protein structures [4 Hura, G. L. 2009. Nature Methods, 6: 606–614. [Crossref], [PubMed] , [Google Scholar]].     

Serial Femtosecond Crystallography

X-ray free-electron lasers produce brief flashes of X-rays that are of about a billion times higher peak brightness than achievable from storage ring sources. Such a tremendous jump in X-ray source capabilities, which came in 2009 when the Linac Coherent Light Source began operations, was unprecedented in the history of X-ray science. Protein structure determination through the method of macromolecular crystallography has consistently benefited from the many increases in source performance from rotating anodes to all generations of synchrotron facilities. But when confronted with the prospects of such bright beams for structural biology, enthusiastic proposals were tempered by trepidation of the effects of such beams on samples and challenges to record data [1 M. Wilmanns, J. Synchr. Rad. 7, 41 (2000).[Crossref], [PubMed] , [Google Scholar]]. A decade after these discussions (and others in the USA) on the applications of X-ray FELs for biology, the first experiments took place at LCLS, giving results that fulfilled many of the dreams of the early visionaries. In particular, the concept that diffraction representing the pristine object could be recorded before the X-ray pulse completely vaporizes the object was validated [2 H.N. Chapman, Nature 470, 73 (2011).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], confirming predictions [3 R. Neutze, Nature 406, 753 (2000).[Crossref], [Web of Science ®] , [Google Scholar]] that established dose limits could be vastly exceeded using femtosecond-duration pulses. The first experiments illuminated a path to achieve room-temperature structures free of radiation damage, from samples too small to provide useful data at synchrotron facilities, as well as providing the means to carry out time-resolved crystallography at femtoseconds to milliseconds. In the five years since, progress has been substantial and rapid, invigorating the field of macromolecular crystallography [4 J.C.H. Spence and H.N. Chapman, Phi. Trans. Roy. Soc. B 369, 20130309 (2014).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar], 5 I. Schlichting, IUCrJ 2, 246 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. This phase of development is far from over, but with both the LCLS and the SPring-8 Ångström Compact Free-electron Laser (SACLA) providing facilities for measurements, the benefits of X-ray FELs are already being translated into new biological insights.     

Femtosecond Structural Dynamics of Proteins

Proteins are the workhorses of living cells, providing essential functions such as structural support, signal transduction, enzymatic catalysis, transport and storage of small ligands. Atomic-resolution structures obtained with conventional X-ray crystallography show proteins essentially as static. In reality, however, proteins move and their motion is crucial for functioning. Although the structure and dynamics of proteins are intimately related, they are not equally well understood. A very large number of protein structures have been determined, but only a few studies have been able to monitor experimentally the dynamics of proteins in real time. In the last two decades, the availability of short (~100 ps) and intense (~10⁹–10¹⁰ photons) X-ray pulses produced by third-generation synchrotrons have allowed the implementation of structural methods like time-resolved X-ray crystallography and time-resolved X-ray solution scattering that have allowed us to monitor protein motion in the nanosecond-to-millisecond timescale [1 K. Moffat, Chem. Rev. 101, 1569–1582 (2001).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–4 J. G. Kim, Acc. Chem. Res. 48, 2200–2208 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. Time-resolved X-ray crystallography has been used to monitor processes such as the migration of a ligand from the protein active site to the surrounding solvent [5 V. Srajer, Science 274, 1726–1729 (1996).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–7 D. Bourgeois, Proc. Natl. Acad. Sci. U. S. A. 100, 8704–8709 (2003).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] or tertiary structural changes associated with allosteric transitions [8 J. E. Knapp, Proc. Natl. Acad. Sci. 103, 7649–7654 (2006).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar], 9 J. G. Kim, Struct. Dyn. 3, 023610 (2016). [Google Scholar]]. On the other hand, time-resolved X-ray scattering in the so-called wide-angle X-ray scattering (WAXS) region [10 M. Cammarata, Nat. Methods 5, 881–886 (2008).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] has been used to track conformational changes corresponding to large-amplitude protein motions such as the quaternary R-T transition of human hemoglobin [11 M. Cammarata, J. Mol. Biol. 400, 951–962 (2010).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–13 A. Spilotros, Soft Matter 8, 6434–6437 (2012).[Crossref], [Web of Science ®] , [Google Scholar]], the relative motion of bacteriorhodopsin α-helices following retinal isomerization [14 M. Andersson, Structure 17, 1265–1275 (2009).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], or the open-to-close transition in bacterial phytochromes [15 H. Takala, Nature 509, 245–8 (2014).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]].     

Multilayer Laue Lens: A Brief History and Current Status

X-rays are intrinsically capable of being used for the study of non-periodic objects with atomic resolution, with high penetration, in applied electromagnetic fields, and in fluids and gases. For direct imaging via nanofocused X-ray beams, reflective [1 K. Yamauchi, Journal of Physics: Condensed Matter 23(39), 394206 (2011).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], refractive [2 C.G. Schroer, Applied Physics Letters 87(12), 124103–3 (2005).[Crossref], [Web of Science ®] , [Google Scholar]], and diffractive [3 K. Burkhard, Journal of Physics: Condensed Matter 23(8), 083002 (2011).[Crossref], [Web of Science ®] , [Google Scholar], 4 J. Kirz, C. Jacobsen, and M. Howells, Quarterly Reviews of Biophysics 28(01), 33–130 (1995).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] optics are used in various approaches for high-resolution imaging. Diffractive X-ray optics are endowed with the highest numerical aperture, in principle allowing focusing of X-rays to sub-nanometer dimensions. Lithographically produced Fresnel zone plates (FZP) find broad deployment around the globe, in both nanofocusing and full-field imaging approaches, and have, for many years, been workhorse optics in both synchrotron-based and laboratory-based X-ray imaging systems [4 J. Kirz, C. Jacobsen, and M. Howells, Quarterly Reviews of Biophysics 28(01), 33–130 (1995).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. A FZP consists of a series of radially symmetric rings, which are known as Fresnel zones, which alternate between transparent and opaque. Radiation traversing into the FZP diffracts around the opaque zones, which are placed in an arrangement where light constructively interferes at the focal plane.     

LURE in the 1970s

In France, Yvette Cauchois, Director of the Laboratoire de Chimie Physique in Paris, was the first person who came up with the idea of using synchrotron radiation. The experiment was done in collaboration with Italian scientists at the Frascati synchrotron in 1963 [1 Y. Cauchois, C. Bonnelle and G. Missoni, C. R. Acad. Sci. Paris, 257, 409 (1963a) and 1242 (1963b). [Google Scholar]]. For a few years, interesting results were obtained by her group and that of Pierre Jaéglé (Orsay) [2 P. Jaeglé, P. Missoni and P. Dhez, Phys. Rev. Lett., 18, 887 (1967).[Crossref], [Web of Science ®] , [Google Scholar]]. After that, they contacted the laboratory for high-energy physics at Orsay (LAL), hoping to install a beamline on the ACO (electron-positron collider), but their request was turned down.     

Radiation Damage in Macromolecular Crystallography

Interest in radiation damage to macromolecules during structural experiments has a long history dating back to 1962, when the first room-temperature study of the phenomenon was carried out on crystals of myoglobin [1 C.C.F. Blake and D.C. Philips, Vienna: International Atomic Energy Agency, 183–191 (1962). [Google Scholar]], and this interest has not abated over the last few years, since there remains a need to understand both the parameters that affect radiation damage progression and also the artifacts produced by it. Although there is now a growing body of literature pertaining to this topic, clear and foolproof methods for experimenters to routinely minimize damage have yet to emerge. Additionally, radiation damage is also a concern and limiting problem in other methods used in structural biology, such as electron microscopy [2 A. Bartesaghi, Proceedings of the National Academy of Sciences of the United States of America 111, 11709–11714 (2014).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] and SAXS [3 S. Kuwamoto, S. Akiyama, and T. Fujisawa, J Synchrotron Radiat 11, 462–468 (2004).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar], 4 S.P. Meisburger, Biophys J 104, 227–236 (2013).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. However, the recently available free electron lasers (FELs) have presented the possibility and promise that samples will give “diffraction before destruction”; is this indeed the “cure” for the challenges of radiation damage?     

Ambient-Pressure X-ray Photoelectron Spectroscopy to Characterize the Solid/Liquid Interface: Probing the Electrochemical Double Layer

Ambient-pressure X-ray photoelectron spectroscopy (APXPS) has contributed greatly to a wide range of research fields, including environmental science [1 H. Bluhm, Journal of Electron Spectroscopy and Related Phenomena 177, 71–84 (2010).[Crossref], [Web of Science ®] , [Google Scholar]], catalysis [2 D.E. Starr et al., Chemical Society Reviews 42, 5833–5857 (2013).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], and electrochemistry [3 E.J. Crumlin, H. Bluhm, and Z. Liu, Journal of Electron Spectroscopy and Related Phenomena 190, 84–92 (2013).[Crossref], [Web of Science ®] , [Google Scholar]], to name a few. The use of this technique at synchrotron facilities primarily focused on probing the solid/gas interface; however, it quickly advanced to the probing of liquid/vapor interfaces [4 D.E. Starr et al., Physical Chemistry Chemical Physics 10, 3093–3098 (2008).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar], 5 M.A. Brown et al., Physical Chemistry Chemical Physics 10, 4778–4784 (2008).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] and solid/liquid interfaces through an X-ray-transparent window [6 J. Kraus et al., Nanoscale 6, 14394–14403 (2014).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–8 T. Masuda et al., Appl Phys Lett 103 (2013).[Crossref], [Web of Science ®] , [Google Scholar]]. Most recently, combining APXPS with “Tender” X-rays (~2.5 keV to 8 keV) on beamline 9.3.1 at the Advanced Light Source in Lawrence Berkeley National Laboratory (which can generate photoelectrons with much longer inelastic mean free paths) has enabled us to probe the solid/liquid interface without needing a window [9 S. Axnanda et al., Scientific Reports 5 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. This innovation allows us to probe interfacial chemistries of electrochemically controlled solid/liquid interfaces undergoing charge transfer reactions [9 S. Axnanda et al., Scientific Reports 5 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. These advancements have transitioned APXPS from a traditional surface science tool to an essential interface science technique.     

Diverse Application Platform for Hard X-ray Diffraction in SACLA (DAPHNIS)

X-ray free electron lasers (XFELs) produce femtosecond X-ray pulses with nearly full spatial coherence and a peak power in the order of tens of GW [1 P. Emma et al., Nat. Photon. 4, 641–647 (2010).[Crossref], [Web of Science ®] , [Google Scholar], 2 T. Ishikawa et al., Nat. Photon. 6, 540–544 (2012).[Crossref], [Web of Science ®] , [Google Scholar]]. At present, two XFEL facilities, the Linac Coherent Light Source (LCLS) and SPring-8 Angstrom Compact free electron LAser (SACLA), offer research opportunities to scientists from various fields. The novel characteristics of XFELs necessitate new experimental styles, which are very different from those for conventional X-ray sources. Since many users were not familiar with these new styles in the early stage of scientific applications, user-friendly experimental systems were necessary to boost the XFEL applications into a state of practical use. XFELs are now producing unique results in, for example, structural biology [3 H. N. Chapman et al., Nature 470, 73–77 (2011).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–6 M. Suga et al., Nature 517, 99–103 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], nonlinear X-ray optics [7 K. Tamasaku et al., Nat. Photon. 8, 313–316 (2014).[Crossref], [Web of Science ®] , [Google Scholar], 8 H. Yoneda et al., Nature 524, 446–449 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], ultrafast physics and chemistry [9 W. Zhang et al., Nature 509, 345–348 (2014).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–11 K. H. Kim et al., Nature 518, 385–389 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], and high-energy-density science [12 S. M. Vinko et al., Nature 482, 59–62 (2012).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]].     

Data Analysis Environment for X-ray Free-Electron Laser Experiments at SACLA

X-ray free-electron lasers (XFELs) with full spatial coherence, extreme brilliance, and ultra-fast pulse duration [1 P. Emma et al., Nat. Photon. 4, 641–647 (2010).[Crossref], [Web of Science ®] , [Google Scholar], 2 T. Ishikawa et al., Nat. Photon. 6, 540–544 (2012).[Crossref], [Web of Science ®] , [Google Scholar]] allow the investigation of complex phenomena in physics, chemistry, and biology with angstrom and femtosecond resolutions. In particular, a concept of “diffraction before destruction” [3 R. Neutze et al., Nature 406, 752–757 (2000).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] has been demonstrated for serial femtosecond crystallography (SFX) [4 H. N. Chapman et al., Nature 470, 73–77 (2011).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar], 5 S. Boutet et al., Science 337, 362–364 (2012).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] and coherent diffractive imaging (CDI) [6 M. M. Seibert et al., Nature 470, 78–81 (2011).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. Using femto-second XFEL pulses, diffraction data are collected before radiation damage to samples has time to occur. Since samples are exchanged for each XFEL pulse, shot-to-shot data acquisition (DAQ) is mandatory to correlate the recorded data with the sample characteristics. The shot-to-shot DAQ must be synchronized with the repetition rate of the XFEL source, typically several tens to one hundred Hz for the machine based on normal-conducting accelerators. Shot-to-shot recording of XFEL pulse characteristics is also essential because they fluctuate due to the stochastic nature of a self-amplified spontaneous emission (SASE). We must carefully analyze a huge data set taking the fluctuation into account.     

Advancement of Hard X-ray Nano-focusing Ellipsoidal Mirror at SPring-8

Ellipsoidal mirror optics can produce a smaller, two-dimensional focus with diffraction-limited properties than is possible when using mirror optics in Kirkpatrick–Baez (K–B) geometry [1 P. Kirkpatrick and A.V. Baez, Journal of the Optical Society of America 38, 766–773 (1948).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. This is because ellipsoidal focusing mirrors can be designed such that they have a larger numerical aperture in the sagittal focusing direction as compared to that in the meridional focusing direction. Although ellipsoidal focusing mirrors have this crucial advantage over K–B optics, K–B optics are widely utilized as micro-/nano-focusing devices [2 H. Mimura, Nature Physics 6, 122–125 (2010).[Crossref], [Web of Science ®] , [Google Scholar]–8 H. Mimura, Nature Communications 5, 3539 (2014).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] in synchrotron radiation facilities and X-ray free electron laser facilities [9 P. Emma, Nature Photonics 4, 641–647 (2010).[Crossref], [Web of Science ®] , [Google Scholar], 10 T. Ishikawa, Nature Photonics 6, 540–544 (2012).[Crossref], [Web of Science ®] , [Google Scholar]]. Figure 1 shows a schematic of focusing mirror optics; Figure 1(a) shows the ellipsoidal mirror and Figure 1(b) the K–B mirror arrangement. In K–B geometry, two mirrors with a one-dimensionally curved surface, such as an elliptical cylinder, are orthogonally arranged in tandem to reflect and focus light independently in a direction perpendicular to each other under grazing-incidence conditions. Ellipsoidal focusing mirrors, which can generate a two-dimensional focusing beam by a single reflection, have a highly sloped surface with a two-dimensional aspherical shape, when compared to elliptical-cylinder mirrors that are used for line-focusing in K–B geometry. In addition, surface shapes of nano-focusing mirrors must be fabricated with nanometer-level accuracy. Therefore, fabrication of ellipsoidal nano-focusing mirrors is extremely difficult. There are no reports on ellipsoidal nano-focusing mirrors in the hard X-ray region with superior performances to provide diffraction-limited beams.