Introduction to distributed systems

The first four decades of computer technology are each characterized by a different approach to the way computers were used. In the 1950s, programmers would reserve time on the computer and have the computer all to themselves while they were using it. In the 1960s, batch processing carne about. People would submit their jobs which were queued for processing. They would be run one at a time and the owners would pick up their output later. Time-shanng became the way people used computers in the 1970s so that users could share a computer under the illusion that they had it to themselves. The 1980s are the decade of personal computing: people have their own dedicated machine on their desks

Inelastic X-Ray Scattering Measurements at BM29

An inelastic x-ray scattering spectrometer has been implemented on the bending magnet beamline BM29 at the ESRF. It comprises a spherically bent perfect crystal as a Bragg analyser in near back reflection and a linear position sensitive detector (PSD) in Rowland's geometry. The setup exploits the wide horizontal radiation fan from a dipole magnet to create an extended source so that several eV of scattered radiation are simultaneously imaged onto the PSD with a static analyser crystal. This is in contrast to existing configurations using undulator or wiggler sources where one component of the emission spectrum is imaged and the analyser has to be scanned in angle. Results are shown at the holmium Lm edge where the resolution is better than ~0.3 eV throughout the whole spectrum

Surface morphology of Kr+-polished amorphous Si layers

The surface morphology of low-energy Kr+-polished amorphous Si layers is studied by topographical methods as a function of initial substrate roughness. An analysis in terms of power spectral densities reveals that for spatial frequencies 2×10−2–2×10−3 nm−1, the layers that are deposited and subsequently ion polished reduce the initial substrate roughness to a rms value of 0.1 nm at the surface. In this system, the observed dominant term in linear surface relaxation, proportional to the spatial frequency, is likely to be caused by the combined processes of (a) ion-induced viscous flow and (b) annihilation of (subsurface) free volume during the ion-polishing treatment. Correspondingly, a modification of the generally assumed boundary conditions, which imply strict surface confinement of the ion-induced viscous flow mechanism, is proposed. Data on surface morphology are in agreement with the optical response in extreme ultraviolet from a full Mo/Si multilayered system deposited onto the modified substrate

Bufferlayer and Caplayer Engineering of Mo/Si EUVL Multilayer Mirrors

Kleineberg U, Westerwalbesloh T, Wehmeyer O, et al. Bufferlayer and Caplayer Engineering of Mo/Si EUVL Multilayer Mirrors. SPIE Proc. 4506. 2001:113-113

Monolithic Crystal Bender for Dynamical Sagittal Focusing with Compensation for Anticlastic Curvature and Twist Distortions

Two types of diamond shaped monolithic crystal benders have been developed for dynamical sagittal focusing on the general purpose EXAFS beamline BM29 at the ESRF. The commissioning tests proved to be fairly encouraging and confirmed that the most convenient option was to provide an active correction for the residual twist deformations combined with a static control of the anticlastic curvature

Stress reduction in multilayers used for X ray and neutron optics

Multilayer systems have important applications in many areas of X ray and neutron optics. For some applications the positions of the optical surfaces have to be controlled with accuracies in the sub nanometre range. For neutron supermirrors with over a thousand layers, stresses above 1000MPa can occur. In addition to bending the substrate such stresses can lead to the films peeling from the substrate, or even to the destruction of the substrate surface, and so must be avoided. After an introduction to stress, this chapter describes how stresses can be reduced to acceptable values and discusses two examples FeCo Si polarizing neutron supermirrors and Mo Si multilayer mirrors for extreme ultraviolet lithograph

Ultra High Harmonie Rejection using Multilayers

A novel instrument recently installed on BM29 at the ESRF has been shown to yield harmonic suppression of the order of 10-6 . It comprises two mirrors coated with W/Si multilayers which operate in Bragg diffraction mode like a second monochromator with a poor energy resolution. The device is a tunable filter with an energy band width of ~ 3 % and a total throughput of about 30 %. The harmonic suppression from the multilayers is shown to be three orders of magnitude more effective than that achieved via detuning of the monochromator crystals. The system provides an efficient way to eliminate the second harmonic transmitted from Si[220] monochromators

Short period La/B and LaN/B multilayer mirrors for ~6.8 nm wavelength

In the first part of this article we experimentally show that contrast between the very thin layers of La and B enables close to theoretical reflectance. The reflectivity at 6.8 nm wavelength was measured from La/B multilayer mirrors with period thicknesses ranging from 3.5 to 7.2 nm at the appropriate angle for constructive interference. The difference between the measured reflectance and the reflectance calculated for a perfect multilayer structure decreases with increasing multilayer period. The reflectance of the multilayer with the largest period approaches the theoretical value, showing that the optical contrast between the very thin layers of these structures allows to experimentally access close to theoretical reflectance. In the second part of the article we discuss the structure of La/B and LaN/B multilayers. This set of multilayers is probed by hard X-rays (λ = 0.154 nm) and EUV radiation (λ = 6.8 nm). The structure is reconstructed based on a simultaneous fit of the grazing incidence hard X-ray reflectivity and the EUV reflectivity curves. The reflectivity analysis of the La/B and LaN/B multilayer mirrors shows that the lower reflectance of La/B mirrors compared to LaN/B mirrors can be explained by the presence of 5% of La atoms in the B layer and 63% of B in La layer. After multi-parametrical optimization of the LaN/B system, including the nitridation of La, the highest near normal incidence reflectivity of 57.3% at 6.6 nm wavelength has been measured from a multilayer mirror, containing 175 bi-layers. This is the highest value reported so far