共查询到20条相似文献,搜索用时 62 毫秒
1.
Markus Gühr 《Synchrotron Radiation News》2016,29(5):8-12
The molecular ability to selectively and efficiently convert sunlight into other forms of energy like heat, bond change, or charge separation is truly remarkable. The decisive steps in these transformations often happen on a femtosecond timescale and require transitions among different electronic states that violate the Born-Oppenheimer approximation (BOA) [1]. Non-BOA transitions pose challenges to both theory and experiment. From a theoretical point of view, excited state dynamics and nonadiabatic transitions both are difficult problems [2, 3] (see Figure 1(a)). However, the theory on non-BOA dynamics has advanced significantly over the last two decades. Full dynamical simulations for molecules of the size of nucleobases have been possible for a couple of years [4, 5] and allow predictions of experimental observables like photoelectron energy [6] or ion yield [7–9]. The availability of these calculations for isolated molecules has spurred new experimental efforts to develop methods that are sufficiently different from all optical techniques. For determination of transient molecular structure, femtosecond X-ray diffraction [10, 11] and electron diffraction [12] have been implemented on optically excited molecules. 相似文献
2.
C.-L. Dong J.-W. Chiou H.-M. Tsai H.-W. Fu H.-J. Lin C.T. Chen 《Synchrotron Radiation News》2017,30(2):24-29
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, 2]. 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, 4]. 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, 6]. 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, 8]. 相似文献
3.
Although nineteen years have passed since the discovery of high temperature cuprate superconductivity 1, 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, 3. 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 ?
Published online:
19 February 2007Table 相似文献
4.
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 [1–3], which is now routinely used to rapidly determine ab initio low-resolution (>1 nm) protein structures [4]. 相似文献
5.
Ray Conley Nathalie Bouet Yong S. Chu Xiaojing Huang Hyon Chol Kang Albert T. Macrander 《Synchrotron Radiation News》2016,29(4):16-20
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], refractive [2], and diffractive [3, 4] 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]. 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. 相似文献
6.
Henry N. Chapman 《Synchrotron Radiation News》2015,28(6):20-24
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]. 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], confirming predictions [3] 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, 5]. 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. 相似文献
7.
The fourth international user workshop focusing on high-power lasers at the Linac Coherent Light Source (LCLS) was held in Menlo Park, CA, USA, on October 3–4, 2016 [1–3]. The workshop was co-organized by Los Alamos National Laboratory and SLAC National Accelerator Laboratory (SLAC), and garnered the attendance of more than 110 scientists. Participants discussed the warm dense matter and high-pressure science that is being conducted using high-power lasers at the LCLS Matter in Extreme Conditions (MEC) endstation. During the past year, there have been seven journal articles published from research at the MEC instrument [4–10]. The specific topics discussed at this workshop were experimental highlights from the past year, current status and future commissioning of MEC capabilities, and future facility upgrades that will enable the expanded science reach of the facility. 相似文献
8.
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 [1–4]. 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 [5–7] or tertiary structural changes associated with allosteric transitions [8, 9]. On the other hand, time-resolved X-ray scattering in the so-called wide-angle X-ray scattering (WAXS) region [10] has been used to track conformational changes corresponding to large-amplitude protein motions such as the quaternary R-T transition of human hemoglobin [11–13], the relative motion of bacteriorhodopsin α-helices following retinal isomerization [14], or the open-to-close transition in bacterial phytochromes [15]. 相似文献
9.
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], 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] and SAXS [3, 4]. 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? 相似文献
10.
The discovery of the nonlinear optical response [1] has triggered the development of new theoretical and experimental approaches. These are based on the perspective that light-matter interactions are not necessarily cast in the picture of “one photon at a time,” typical of linear processes, but more photons can “work together” in order to coherently stimulate and probe (via nonlinear interactions) different kinds of dynamics in a sample. Nowadays, such a “multi-wave” concept is extensively used in a large array of methods, also termed wave-mixing, that have found numerous applications in almost all fields of physics, chemistry, and biology [2, 3]. Such methods are often based on third-order processes, referred to as four-wave-mixing (FWM), in which a threefold light-matter interaction results in the generation of a (fourth) signal photon, whose photon parameters (frequency, wave vector, polarization, etc.) may differ from those of the input fields. The possibility to control the latter parameters turns into the capability to selectively probe different FWM processes, which can contain distinct and complementary information. In addition to this high degree of selectivity, FWM is often featured in ultrafast time resolution and can be used to study dynamics hardly accessible by linear methods [3], such as spin waves and relaxations [4, 5] or Raman transitions between unoccupied electronic states [6, 7]. 相似文献
11.
Uwe Mueller Marjolein Thunnissen Jie Nan Mikel Eguiraun Fredrick Bolmsten Antonio Milàn-Otero 《Synchrotron Radiation News》2017,30(1):22-27
The outstanding success of structural biology within the last two decades is closely related to the development and evolution of macromolecular crystallography (MX) beamlines. Indeed, many of today's synchrotron-based MX experimental sessions aim for fast but rigorous evaluations and data collections from very large numbers of samples [1–7]. To facilitate this, sample changing on most MX beamlines is now carried out by robots and the centering of a crystal in the X-ray beam to micrometer precision is now automatically performed using either optical or diffraction-based techniques [8]. Once a crystal is centered, users have a wide array of options at their disposal to prepare any given experiment. This includes: X-ray fluorescence (XRF) [9] analysis to confirm the presence of anomalous scatterers in crystals; X-ray absorption near-edge scans (XANES) to determine the best X-ray wavelengths for MAD/SAD data collection [10]; and the probing of the diffraction properties of crystals to determine the best crystal, or area of a crystal [11], for data collection. All of these operations are now also automated, as is the collection of the final diffraction data set either from single or multiple crystals and the subsequent data analysis and reduction. 相似文献
12.
Y. Li S. Abeghyan K. Berndgen M. Baha-Shanjani G. Deron U. Englisch 《Synchrotron Radiation News》2015,28(3):23-28
The European X-ray free electron laser (EXFEL) facility is currently under construction [1]. Using the principle of self-amplified spontaneous emission (SASE) [2, 3], intense FEL radiation is generated in three gap-tuneable undulator systems called SASE1, SASE2, and SASE3. The electron beam energy of the EXFEL is variable between 8.5 and 17.5 GeV. SASE1 and SASE2 are hard X-ray FELs using planar undulators with a period length of 40 mm, called U40s. By a suitable choice of the beam energy and undulator gap, the wavelength can be tuned from 0.05 to 0.4 nm. SASE3 is a soft X-ray FEL using planar undulators with a period length of 68 mm, called U68s. Under the same conditions, the wavelength can be tuned from 0.4 to 5.2 nm. 相似文献
13.
Hirokatsu Yumoto Takahisa Koyama Satoshi Matsuyama Yoshiki Kohmura Kazuto Yamauchi Tetsuya Ishikawa 《Synchrotron Radiation News》2016,29(4):27-31
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]. 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 [2–8] in synchrotron radiation facilities and X-ray free electron laser facilities [9, 10]. 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. 相似文献
14.
Farrel Lytle 《Synchrotron Radiation News》2015,28(4):30-33
The study of X-ray absorption spectroscopy (XAS) began at an exciting time in science. In the early years of the twentieth century, wave mechanics, X-ray diffraction, X-ray scattering from non-crystalline materials, electron diffraction, and XAS were all being developed simultaneously. Many XAS concepts and experimental techniques advanced in parallel with these other subjects; however, the difficulty of obtaining good XAS data from conventional X-ray tubes limited the field to a potentially interesting minor subject [1, 2]. 相似文献
15.
Ambient-pressure X-ray photoelectron spectroscopy (APXPS) has contributed greatly to a wide range of research fields, including environmental science [1], catalysis [2], and electrochemistry [3], 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, 5] and solid/liquid interfaces through an X-ray-transparent window [6–8]. 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]. This innovation allows us to probe interfacial chemistries of electrochemically controlled solid/liquid interfaces undergoing charge transfer reactions [9]. These advancements have transitioned APXPS from a traditional surface science tool to an essential interface science technique. 相似文献
16.
Eugenio Ferrari 《Synchrotron Radiation News》2016,29(3):4-9
The advent of FEL sources delivering two synchronized pulses of different wavelengths has made available a whole range of novel pump-probe experiments [1], allowing the exploration of the dynamics of matter driven to extreme non-equilibrium states by an intense ultrashort X-ray pulse and then probing the sample response at variable time delay with a second pulse [2]. 相似文献
17.
18.
Kensuke Tono 《Synchrotron Radiation News》2017,30(1):12-15
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, 2]. 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 [3–6], nonlinear X-ray optics [7, 8], ultrafast physics and chemistry [9–11], and high-energy-density science [12]. 相似文献
19.
Kiyoshi Ueda 《Synchrotron Radiation News》2016,29(5):3-7
In recent years, short wavelength free electron lasers (FELs) have opened up access to ultrafast electronic and structural dynamics in matter. Currently, four FEL facilities are in operation in the world. FLASH [1] in Germany and FERMI [2] in Italy cover the range from extreme ultraviolet (EUV) to soft X-rays, while LCLS [3] in the U.S. and SACLA [4] in Japan provide pulses in the hard X-ray regime. In addition, an upgrade version of SCSS [5], nicknamed SCSS+, has also just started user operation as a beamline of SACLA [6]. These FELs deliver coherent pulses combining unprecedented power densities up to ~1020 W/cm2 and extremely short pulse durations down to a few femtoseconds. The intense coherent FEL pulse focused down to ~1 μm2 makes single-shot diffractive imaging of nano-crystals or even non-crystallized bio-samples as well as other small objects a reality. Time-resolved spectroscopic and structural studies on the timescale of femtoseconds, having FEL pulses as a probe, allow us to probe electrons and atoms in action. Additionally, since FEL pulses are in a new regime of intensity, they are opening up new research fields that exploit the interaction between intense short wavelength pulses and matter, leading to matter at extremely high energy. Relevant theories dealing with such extreme conditions are also rapidly growing. 相似文献
20.
Modern synchrotron-based X-ray fluorescence microscopy (XFM) has become a critical tool for many a research program, addressing extremely broad and highly relevant scientific questions. Their ability to map trace elemental content and probe local chemical state has been applied to numerous scientific areas in the life sciences [1–3], the environmental and earth sciences [4, 5], the materials sciences, as well as in cultural heritage studies. The newest generation of instruments utilizes high-brightness X-ray sources and incorporate state-of-the-art focusing optics and detector systems. Advances in X-ray sources and nanofocusing optics, for example, have allowed these instruments to achieve spatial resolutions of 20–30 nm using diffractive optics such as Fresnel zone plates and 200 nm using reflective optics such as Kirkpatrick-Baez mirrors. New beamlines, now in the design stage, aim to achieve similar (and better) resolutions within the next five years. 相似文献