X‐ray sources for studies of ultrafast processes

Radio signals from Jupiter were first detected in 1955 in the radio range at a frequency of 22.2 MHz. The emissions were sporadic in character, and were confined to frequencies below 40 MHz. These decametric (DAM) emissions have been interpreted as coherent cyclotron radiation from electrons in the tens of keV range. The innermost jovian moon Io, which orbits Jupiter in only 1.8 days, appears to modulate the emission: both the intensity and the probability of the occurrence of bursts increase when Io is at certain locations in its orbit with respect to Jupiter and the observer. The emissions originate in Jupiter's aurora, being produced by electrons that travel along magnetic field lines. Particles that enter the atmosphere may locally excite atoms and molecules, which upon de-excitation are visible as aurora at UV and infrared wavelengths (sometimes also at X-ray wavelengths). A fraction of the electrons is reflected back along the field lines, and produces DAM emissions.     

Techniques for inelastic X‐ray scattering with μeV‐resolution

A new spectroscopic technique is introduced that allows tuning of a eVwide beam of synchrotron radiation over a range of a few meV. It relies on nuclear resonant scattering that is subject to the Doppler effect in high speed rotary motion. Two mechanisms are discussed how to extract the resonantly scattered radiation out of the broad band of synchrotron radiation: (a) grazing incidence reflection from a rotating disk in combination with a polarization filtering technique and (b) deflection of resonantly scattered radition via the recently discovered Nuclear Lighthouse Effect. Implications for inelastic Xray scattering and elastic nuclear resonant scattering are discussed.     

Ultrafast time‐resolved X‐ray absorption spectroscopy of chemical systems

The semiconductor industry continues in its relentless march to miniaturization [1 See, for instance http://www.itrs.net/Links/2007ITRS/2007_Chapters/2007_Lithography.pdf  [Google Scholar]]. Every four years or so, the dimensions of the features on an integrated circuit are halved, yielding an increase in density and functionality of the electronic “chip.” The economic advantages of more devices per unit area outweigh increases in fabrication costs and performance limitations, pushing the industry to seek ever-smaller patterns. At the time of writing (April 2008) advanced devices are patterned with the smallest features hovering around 45 nm, and the next generation of ～32 nm devices is on the horizon. What is perhaps most remarkable is that this level of nanopatterning is achieved with optical imaging tools and processes that use an actinic wavelength of 193 nm, the ArF laser emission line. As taught in any elementary physics textbook, the wavelength of light ultimately limits the achievable optical resolution [2 Hecht, E. and Zajac, A. 2002. Optics. Addison Wesley, : 471–474.  [Google Scholar]]. So how can we pattern 32 nm features using 193 nm radiation?     

Equation of state SAFT-CP for vapour–liquid equilibria and mutual solubility of carbon dioxide and water

ABSTRACT

The statistical associating fluid theory (SAFT) was proposed first in 1990, and has been extended to various forms for the calculation of thermodynamic properties of complex systems, such as oil reservoir fluids, polar systems, polymers, electrolytes, near-critical systems, interfacial phenomena, solids and even biomaterials. SAFT-CP (critical point) has been established for nonpolar fluids in 2001 with excellent expression of thermodynamic properties across critical points. It was extended later for polar and associating fluids with the addition of just a dipole–dipole interaction, which leads simple calculation procedure without an association term. In this article SAFT-CP is applied to carbon dioxide, water and their mixture. Vapour–liquid equilibria for pure components CO₂ and H₂O, CO₂ solubility in water and H₂O solubility in dense CO₂ are analysed. Expression of pure CO₂ properties is improved with the dipole–dipole interaction term used, while expression of pure water is a little bit improved with the non-spherical degree parameter less than 1.0. For the high asymmetry in polarity and association between CO₂ and H₂O molecules, the Stryjek–Vera combining rule is used with different temperature-dependent parameters. With the quadratic temperature-dependent parameters, the mutual solubilities in the system are calculated with good agreement with experimental ones over the wide range of temperature as 298–474 K and of pressure as 0.1–70 MPa.     

National school on Neutron and X‐ray scattering alumni presentations

The 4th joint Stanford–Berkeley summer school on synchrotron radiation and its applications in physical science was held June 12–17, 2005, at the Stanford Linear Accelerator Center (SLAC). The Stanford–Berkeley summer school is jointly organized by Stanford University, University of California Berkeley, Lawrence Berkeley National Laboratory (LBNL), and the Stanford Synchrotron Radiation Laboratory (SSRL). Since 2001, Anders Nilsson (Stanford/SSRL) and Dave Attwood (UC Berkeley) have been the organizers of this annual weeklong summer school, which alternates each year between Stanford and Berkeley. The summer school provides lecture programs on synchrotron radiation and its broad range of scientific applications in the physical science as well as visits to the Stanford Synchrotron Radiation Laboratory and the Advanced Light Source (ALS), where the students also have the opportunity to experience a beam line.     

Equation of state of fluid helium at high temperatures and densities

Helium, hydrogen, and their isotopes are the simplest monoatomic and diatomic molecules. It is relatively easy to describe their properties using the basic principles of quantum mechanics. In condensed matter physics, hydrogen and helium serve as the models for the condensed matter properties at extreme conditions so that both experi- mental and theoretical physicists pay much attention to the study of their properties[1], especially the insulator-metal transition of hydrogen[2]. The aim to st…     

Study of strain and compostion of the self—organized GE dots by grazing incident X—ray diffraction

Grazing incident X-ray diffraction at different grazing angles for self-organized Ge dots grown on Si(001) are carried out and lattice constant expansions of 1.2?parallel to the surface as compared with the Si lattice are found within the Ge dots.A 3.1?lattice expansion of the Ge dots along the growth direction is also fund by ordinary X-ray(004) diffraction.According to the Poisson equation and the Vegard law,our results infer that the Ge dot should be a partially strain relaxed SiGe alloy with Ge content of abuot 55?2001 Elsevier Science B.V.All rights reserved.     

Analyses and computations of asymmetric Z-scan for large phase shift from diffraction theory

Based on Presnel-Kirchhoff diffraction theory, we set up a diffraction model of nonlinear optical media to Gaussian beam, which can interpret the Z-scan phenomenon from a new way. This theory is not only well consistent with the conventional Z-scan theory in the case of small nonlinear phase shift, but also can fit for the lager nonlinear phase shift. Numeric computations indicate the shape of the .Z-scan curve is greatly affected by the value of the nonlinear phase shift. The symmetric dispersion-like Z-scan curve is only valid for small nonlinear phase shift (|Δφ0| < π), but with increasing the nonlinear phase shift, the valley of the transmittance is severely suppressed and the peak is greatly enhanced. Further calculations show some new interesting results.     

X‐ray microscopy at the advanced photon source

In modern third generation synchrotron sources, undulators have become the principal source of X-rays and today a brilliance close to 10²¹ photons/sec?mm²?mrad?0.1%BW is routinely attained for photon energies of 10 keV. However, generating brilliant beams of photons with energies of 50 keV and above leads to conflicting choices for the undulator parameters as the following analysis shows.     

Revised molecular constants and term values for the XΠ state of CH

An improved set of molecular constants and term values are given for the X²Π (v = 0-5) state of the CH radical. They are derived from a fit of previously published data and additional lines taken from infrared solar spectra recorded on orbit and from new laboratory IR emission data.     

Observation and identification of X－ray（0．3－30Bnm) multiple－order diffraction spectra

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Structural Characterization of RF‐Sputtered a‐C:N Thin Films by Raman,IR, and X‐ray Reflectometry Spectroscopies

Abstract

Amorphous carbon nitride thin films (a‐C:N) were deposited from a carbon target, at room temperature onto silicon substrates, by reactive RF sputtering in a gas mixture of argon and nitrogen. The structural properties of these films have been studied by Raman, infrared (IR), and X‐ray reflectometry spectroscopies. Both the IR and Raman spectra of the a‐C:N films reveal the presence of C–C, C?C, C?N, and C≡N bonding types. The Raman spectra analysis shows, an increase of the C≡N triple bonds content when the concentration of nitrogen C(N₂) in the gas mixture is increased. The Raman intensities ratio between the disorder (D) and graphitic (G) bands increases with C(N₂) suggesting an increased disorder with the incorporation of nitrogen in the carbon matrix. The effect of C(N₂) on the density of a‐C:N films was also investigated by X‐ray reflectometry measurement. The increase of the nitrogen concentration C(N₂) was found to have a significant effect on the density of the films: as C(N₂) increases from 0 to 100%, the density of the a‐C:N films decreases slightly from 1.81 to 1.62 g/cm³. The low values of density of the a‐C:N films were related (i) to the absence of C–N single bonds, (ii) to the increase of disorder introduced by the incorporation of nitrogen in the carbon matrix, and (iii) to the presence of the bands around 2350 cm^?1 and 3400 cm^?1 associated with the C–O bond stretching modes and the O–H vibration, respectively, suggesting a high atmospheric contamination by oxygen and water. The presence of these bands suggests the porous character of the studied samples.     

Equation of state and liquid–vapour equilibrium in a triangle-well fluid

The second-order thermodynamic perturbation theory formulation of Barker and Henderson is used to derive the equation of state of the triangle-well fluid. This is combined with the rational function approximation to the radial distribution function of the hard-sphere fluid. Results are obtained for the critical parameters and the liquid–vapour coexistence curve for various values of the range of the potential. A comparison with available simulation data is presented.