The electron spectro-microscopy beamline at National Synchrotron Light Source II: a wide photon energy range, micro-focusing beamline for photoelectron spectro-microscopies

A comprehensive optical design for a high-resolution, high-flux, wide-energy range, micro-focused beamline working in the vacuum ultraviolet and soft x-ray photon energy range is proposed. The beamline is to provide monochromatic radiation to three photoelectron microscopes: a full-field x-ray photoelectron emission microscope and two scanning instruments, one dedicated to angle resolved photoemission spectroscopy (μ-ARPES) and one for ambient pressure x-ray photoelectron spectroscopy and scanning photoelectron microscopy (AP-XPS/SPEM). Microfocusing is achieved with state of the art elliptical cylinders, obtaining a spot size of 1 μm for ARPES and 0.5 μm for AP-XPS/SPEM. A detailed ray tracing analysis quantitatively evaluates the overall beamline performances.

Calculations of synchrotron radiation emission in the transverse coherent limit

We present approximations for the synchrotron radiation emission for low emittance light sources, which provide a connection between user needs and the electron beam parameters. The results and calculations are a consequence of the phase coherence in the emission from the electrons. We derive the remarkable result that if the electron beam is energetic enough, the emitted flux is independent of the photon energy, electron beam energy, or bending radius in the transverse coherent limit. Similarly the brightness is identical for all machines at a given current.

Direct evidence for dynamic broadening of the energy spectra associated with the later steps of an Auger cascade

Auger cascade decay processes are of critical importance in x-ray-induced biological damage, chemical reactions, and desorption. Here, we report the first measurements of the isolated energy spectra of electrons emitted during the later steps of an Auger cascade process in a solid (MnO). The large widths and energy gains observed in cascade-induced Mn MVV Auger spectra (as compared to the spectra resulting from direct photoexcitation of the M core hole) provide strong evidence that valence holes created in previous cascade steps participate dynamically in later cascade steps.

Comparison of calculated brightness and flux of radiation from a long-period wiggler and a short-period undulator

In this article the calculation of brightness and flux for two insertion devices of the 2.8 GeV X-ray storage ring at the NSLS is discussed. The radiation properties from the X25 linearly polarized wiggler and the new X25 short-period undulator are compared at a fixed photon energy (11.3 keV) corresponding to emission from the fifth harmonic of the short-period undulator. For this computation, three commonly available synchrotron radiation programs are used. The capabilities of each of these codes are briefly discussed, and their range of applicability are commented on. It is concluded that special care is needed when modeling the radiation of the classes of insertion devices considered here.

A soft x-ray beamline capable of canceling the performance impairment due to power absorbed on its optical elements

We present an entrance slitless beamline design capable of maintaining its very high performance in terms of energy resolution (>10(4)) and spot size (4x4 microm2) at the sample position despite being exposed to more than 2.15 kW of undulator radiation and a maximum power density on the optics of more than 0.9 W/mm2. Ray tracing simulations of this beamline under the worst-case thermal deformations of the optical element surfaces verify that appropriate focusing corrections are able to cancel the deleterious effects of these deformations. One of the necessary conditions for this cancellation is to illuminate the optical elements with a larger solid angle than the undulator's central cone, which contains the usable photons but is considerably smaller than the angular power distribution.

Giant Coster-Kronig transitions and intrinsic line shapes of the anomalous Pd M45VV Auger spectrum of Pd/Ag(100) dilute surface alloys

The Pd M4VV and M5VV Auger spectra of the 0.1 ML Pd/Ag(100) dilute surface alloy have been measured using Auger-photoelectron coincidence spectroscopy. The M4VV spectrum indicates that Pd 3d(3/2) core holes have a Coster-Kronig decay rate that is approximately 10 times that of Pd metal. Our calculations show that this giant enhancement arises from the local electronic structure of excited Pd atoms at the surface. Anomalous features in the Auger line shape are similar to those seen in dilute bulk PdAg alloys, and these features in the M5VV and M4VV lines are in good agreement with theoretical predictions.

Evidence for quantum critical behavior in the optimally doped cuprate Bi(2)Sr(2)CaCu(2)O(8+delta)

The photoemission line shapes of the optimally doped cuprate Bi(2)Sr(2)CaCu(2)O(8+delta) were studied in the direction of a node in the superconducting order parameter by means of very high resolution photoemission spectroscopy. The peak width or inverse lifetime of the excitation displays a linear temperature dependence, independent of binding energy, for small energies, and a linear energy dependence, independent of temperature, for large binding energies. This behavior is unaffected by the superconducting transition, which is an indication that the nodal states play no role in the superconductivity. Temperature-dependent scaling suggests that the system displays quantum critical behavior.