Soft X-ray Beamline Research Articles

Combining rotation and translation in a variable line space high-resolution soft-X-ray monochromator: Design requirements and performance evaluation of a novel grating mount

We describe a new fixed-slit single-element spherical-grating monochromator which has been designed, built and tested for the new high-resolution soft X-ray beamline at the University of Wisconsin Synchrotron Radiation Center. A novel grating mount utilizes a combined rotation and translation of a variable line space grating to minimize major aberration terms. The resolving power of the aberration-corrected monochromator is then primarily determined by the finite figure error and the mechanical performance of the grating mechanism. Assuming a 0.2 arc sec figure error, a resolving power ranging from E ΔE = 10 4 to 4.6 × 10 3 over the energy range of 500 to 1150 eV requires grating rotation and translation to be synchronized with a precision and accuracy of the order of 0.1 arc sec and 10 μm respectively. Extensive testing has verified precision and allowed appropriate calibrations to be developed to obtain the required accuracy. Calibrations minimize the impact of specific component behavior such as the compression of linear crossed roller bearings, the characteristic signature of a lead screw and the elastic response of the support structure.

Performance of the modified SX-700 plane grating monochromator at the Finnish beamline in MAX-lab

A soft x-ray beamline designed principally for gas phase measurements has been constructed and tested at the 550-MeV MAX I electron storage ring in Lund, Sweden. The beamline uses synchrotron radiation from a short 35-period undulator with a magnetic period of 24 mm. The photon energy range of the undulator is about 60–600 eV covering, e.g., the important C, N and O 1s ionization regions. The beamline is based on a modified SX-700 plane grating monochromator with a plane elliptical focusing mirror. The beamline has been tested by measuring total ion and electron yield spectra from the rare gases Kr and Ar in the resonance excitation regions just below the Kr M4,5 and Ar L2,3 ionization thresholds. These results show that the monochromator has very high resolution, E/ΔE≊4800 at 244 eV and ≊7600 at 91 eV, comparable with the best spherical and plane grating monochromators. The beamline is equipped with an effective differential pumping system for the gas phase experiments combined with a refocusing mirror in order to provide a small spot size (φ<1 mm) at the sample region.

Nondestructive Depth Profile Analysis by Changing Escape Depth of Photoelectrons

Nondestructive depth profile analysis by changing the photoelectron escape depth was investigated at a soft X-ray beamline of the Photon Factory (KEK-PF). The escape depth was controlled by changing the energy of incident soft X-rays. The depth profile was determined from the observed photoelectron intensities based on the fact that the photoelectron intensity can be described by the Laplace transform of the depth profile. The oxidized silicon thin film on a silicon substrate was analyzed with this method, and depth profiles of SiO2 and Si were obtained. The depth resolution was 0.4 nm according to the 10-90% width of the transition region between the SiO2 and the Si. Improvement of depth resolution is discussed in terms of several simulations performed using a simple depth structure.

Lateral resolution of microscopic X-ray photoelectron spectroscopy in detecting striped patterns

A Wolter-type X-ray mirror is installed at a soft X-ray beamline to form focused 150 eV X-rays for μ-XPS analysis. The focused beam scans across gold striped patterns (10–50 μm wide) delineated on a Si wafer, as the Si(2p) photoelectrons from the substrate are monitored to detect the patterns. Each pattern is clearly observed, although the observed pattern width is 10–40% larger than the actual width. The experimental results are evaluated using photoelectron count rate calculations that take the intensity profile of the focused beam into account. The calculations are also carried out for a 1-μm focused beam achieved in a previous study, which is assumed to scan across 1 to 5 μm-wide striped patterns. The modulation transfer function indicates that a lateral resolution below 1 μm is achievable in the one-dimensional imaging of striped patterns.

The design and performance of a soft X-ray double crystal monochromator beamline at Aladdin

We report the design, construction, and performance of a soft X-ray beamline with accessible photon energy 0.8–4.0 keV at the Synchrotron Radiation Center, University of Wisconsin-Madison. The beamline features an ultrahigh vacuum (UHV) compatible high precision double crystal monochromator (DCM) which was designed and built by the Physical Science Laboratory (PSL), University of Wisconsin-Madison. It employs a Boomerang mechanism both to keep the crystals parallel and to maintain a fixed exit beam height during spectral scans (Bragg angle 12°–72°). The monochromator X-rays are focused by a bent cylindrical mirror (Ni-coated fused silica, located 7.5 m from the source) into the experimental chamber (located 5.5 m from the mirror) down to a spot less than 1 mm (h)×3 mm (v). During the initial runs, the DCM used a pair of InSb(111) crystals and covered photon energy 1.75–3.7 keV. At the silicon K-edge (1840 eV), the beamline delivered about 4×10 10 photons/s (while stored electron beam was at 100 mA at 1 GeV), among the most intense and stable sources (over 6 months continuous operation) currently available at this energy. The energy resolution is about or better than 0.9 eV at the Si K-edge. High beam stability makes it possible to obtain routinely, for the first time, good EXAFS spectra as far as 1000 eV above the silicon K-edge. A detailed analysis of the effects due to misalignment of all DCM components is given in the appendix.

A high counting rate parallel-plate gas proportional counter for fluorescence extended x-ray-absorption fine structure studies

Gas proportional counters (GPCs) are well suited for fluorescence extended x-ray-absorption fine structure (EXAFS) experiments in the soft x-ray (<4 keV) region. They have a near unity detection efficiency and offer good energy resolution. Of the different types of GPC, the parallel-plate device is an attractive option for use with synchrotron radiation beam lines where its intrinsically high count rate permits optimum use of the high photon flux available. The development of a parallel-plate gas proportional counter for use on soft x-ray beam lines at the Daresbury synchrotron source is described. This device is demonstrated to have a counting rate in excess of 1 MHz, and data are presented on its performance including its energy resolution, long-term gain stability, and sample EXAFS spectra.

Soft x-ray beamline BL7A at the UVSOR

A vacuum-compatible double-crystal monochromator with constant exit-beam height has been installed and operated for several years at beamline BL7A at the UVSOR facility at the Institute for Molecular Science, Okazaki, Japan, The beamline is used both for the photons from a normal bending-magnet section and those from a 4 T superconducting three-pole horizontal wiggler. Various pairs of monochromator crystals are being used with sufficient intensity and signal to noise ratio of the output signal. Basic structure of the beamline, the mechanism of the monochromator, and some typical spectra of materials with absorption edges between 850 eV and 4 keV are reported.

Elliptical-polarization analyses of synchrotron radiation in the 5–80-eV region with a reflection polarimeter

The Stokes parameters, which completely represent the polarization state of light, have been measured in the 5–80-eV energy region for synchrotron-radiation beams on the VUV to soft X-ray beamlines at the Photon Factory. Various states of polarization were produced for the emerging beam by deflecting the incoming beam vertically with respect to the entrance slit of the monochromator with a premirror of the beamline. The resultant beam was polarization-analyzed using a polarimeter comprising two triple-reflection polarizers. Increasing the beam-deflection angle was found to result in a change in the polarization state from predominantly horizontal linear polarization to elliptical polarization. This procedure could be used both to produce and to verify circular polarization with | P c| ≳ 80% in the energy range 60–80 eV, which could be immediately applied to MCD experiments. Unpolarized light could clearly be distinguished from circularly polarized light. The unpolarized component was found to become larger with increasing energy on a soft X-ray beamline; this was shown to be mainly due to scattering by beamline optical elements.

The Adone wiggler x-ray lithography beamline

A soft x-ray beamline, utilizing the radiation produced by the six-pole wiggler of the Adone storage ring, has been realized. The beamline allows the exposure of large area resists by means of a double-mirror scanning system or mechanically moving the wafer. The mechanical, geometrical, and spectral characteristics of the beamline will be described.

Soft x-ray beamline and a double-crystal monochromator of UVSOR (abstract)

The UVSOR is a 750-MeV dedicated electron storage ring in the Institute for Molecular Science at Okazaki, Japan. The ring was constructed mainly for the use of VUV photons. However, the intensity of the soft x-ray region around 10 Å region is not negligible. The ring is also equipped with a 4 T superconducting three-pole horizontal wiggler. We have constructed a beamline equipped with a monochromator in order to utilize the soft and normal x-ray photons from the ring. In order to separate the vacuum of the ring from that of the monochromator, a light tight Be foil of 10 μm in thickness is placed in the upstream of the monochromator in the beamline. The monochromator constructed is a high vacuum compatible with double crystal which provides constant offset of the output beam. The constant offset during the rotation of crystal plane was realized by a simple linkage of linear motions of the two crystals with two linear guides placed on both input and output beam levels. The mechanical movement was found to be very smooth through a full rotation of 60° (between 15° and 75° of Bragg angle). Monochromator crystals such as beryl (101̄0), quartz (101̄0), InSb(111), Ge(111), and Ge(220) whose 2d value is 15.965, 8.512, 7.481, 6.532, and 4.00 Å, respectively, are being used with a reasonable intensity and signal-to-noise ratio of output signal. The range of photon energy which can be used with this line is from 850 eV to 4 keV in the bending magnet section, and from 850 eV to 6 keV with a wiggler. Because of the comparatively low energy of 750 MeV of the electron, the heat load is not a severe problem, and no radiation damage was observed for the first beryl crystal during an exposure to the beam for several months. We have measured the Na K-edge XANES spectrum of a thin film of NaCl which was evaporated in situ on a collodion film in the sample chamber at room temperature by using beryl as monochromator crystal. From the doublet separation of the spectrum, we can estimate the resolution better than 1 eV, which is sufficient for this energy range. With Ge(220) as monochromator crystal, K edge of potassium has been measured with a reasonable signal-to-noise ratio. Therefore, the practical limit of the energy attainable in this beamline of bending magnet section is about 4 keV.

Performance of the Dragon soft x-ray beamline (invited)

We report on the performance of a newly constructed synchrotron radiation soft x-ray beamline. This beamline, dubbed Dragon, is a spherical version of the cylindrical element monochromator design proposed previously. By measuring the K-edge absorption spectra of condensed nitrogen, it is determined that this monochromator has achieved resolving power 104 at 400-eV photon energy, using its full 15 by 1 mrad angular acceptance. The ideas and advantages contained in the CEM design have also been experimentally confirmed.

Soft x-ray beamline (10–1000 eV) with a plane grating monochromator for surface studies

The optical design and mechanical solution for a soft x-ray beamline BL-7A in PF-KEK for the energy range 10–1000 eV with a PGM are described. The optical characteristics of the beamline are tested with gas phase absorption and photoelectron spectroscopy.

Higher-harmonics suppressor for soft x rays

We have developed an apparatus for suppressing higher harmonics contained in the soft x-ray output beam of grazing-incidence grating monochromators. It consists of eight pairs of total-reflection mirrors. Each pair serves as a low-pass filter with the cutoff energy different from one another. The eight pairs are designed to cover an energy range of 80–1600 eV with an efficiency of harmonic suppression better than 97%, while transmitting more than 50% of the fundamental photons. We have tested its preliminary performance on the soft x-ray beamline BL-8A at the Photon Factory. We present the observed transmission efficiencies and the effects of the harmonic suppressor on measurements of reflectivity and fluorescence spectra.

Beamline for the characterization of radiation transfer standards ranging from 200 to 2000 eV

A novel soft x-ray beamline equipped with a specially designed Rowland circle monochromator has been installed at the laboratory of the Physikalisch-Technische Bundesanstalt (PTB) at the Berliner Elektronenspeicherring-Gesellschaft für Synchrotronstrahlung mbH (BESSY) for spectral radiant power determination of radiation sources and for spectral responsivity calibration of detectors in the photon energy range from 200 to 2000 eV. The mechanical and optical performances are presented, together with data on output flux and resolution of the monochromator.

Design and fabrication of condenser zone plates for a soft x-ray microscopy beamline in Hefei

A synchrotron radiation soft x-ray beamline for scanning microscopy mainly, is being constructed in Hefei. It contains a linear monochromator consisting of a diaphragm of 7 μm diameter and one of three condenser zone plates (CZP). The three CZPs are for three overlapping wavelength ranges 1.97–2.78 nm (CZP23), 2.74–3.87 nm (CZP32), and 3.84–5.44 nm (CZP45), respectively. The processing steps for the condenser zone plate fabrication are summarized, especially the holographic exposure with a special optical system as a key step. Parameters of a prototype of CZP45 fabricated in Hefei are the following: D=2.9 mm, n=826, R1=0.05 mm, and ΔRn≊0.9 μm.

A dedicated soft x-ray beamline for x-ray absorption spectroscopy (abstract)

We will present the design, capabilities, and characteristics of the recently commissioned Beamline X-11B at the National Synchrotron Light Source. This line has been designed to optimally function in the ‘‘soft’’ x-ray regime (1–5 keV), but can easily be used up to the design limit of the storage ring. The beamline, which shares a common vacuum with the storage ring, is equipped with a double crystal fixed-exit UHV monochromator. The monochromator crystals are mounted on rotating carousels that can each carry four crystals, permitting crystal changes to cover different energy ranges without breaking vacuum. The incident radiation carousel is water cooled and the second carousel can be heated, allowing thermal equilibration of the crystals. The line can be equipped with a UHV backend or a ‘‘fast-turnaround’’ backend. The UHV backend can be used for surface EXAFS and other surface techniques (XPS, Auger) on line. The fast-turnaround backend has been designed to work under less stringent vacuum demands, permitting relatively rapid sample changes for systems that are not oxygen sensitive. We acknowledge the support of the US DOE, Division of Materials Sciences, under Contract No. DE-AS05-ER10742 for its role in the development and operation of Beamline X-11 at the NSLS. The NSLS is supported by the US DOE, Divisions of Materials Sciences and Chemical Sciences, under Contract No. DE-AC02-76CH00016.

Monochromator and beamline for soft x-ray studies in the photon energy range 500 eV–5 keV

The optical layout of a novel soft x-ray beamline at the Daresbury Synchrotron Radiation Source (SRS) is presented, together with the mechanical design of a precision-built soft x ray crystal monochromator. The mechanical and optical performance of the system are discussed, supported by data on the output flux and resolution of the monochromator. The flexibility of this optical arrangement for different kinds of experiments is examined.

Mirror And Grating Surface Figure Requirements For Grazing Incidence Synchrotron Radiation Beamlines: Power Loading Effects

At present, grazing incidence mirrors are used almost exclusively as the first optical element in VUV and soft x-ray synchrotron radiation beamlines. The performance of these mirrors is determined by thermal and mechanical stress-induced figure errors as well as by figure errors remaining from the grinding and polishing process. With the advent of VUV and soft x-ray undulators and wigglers has come a new set of thermal stress problems related to both the magnitude and the spatial distribution of power from these devices. In many cases the power load on the entrance slits and gratings in these beamlines is no longer negligible. The dependence of thermally induced front-end mirror figure errors on various storage ring and insertion device parameters (especially those at the National Synchrotron Light Source) and the effects of these figure errors on two classes of soft x-ray beamlines are presented.

The BEPC bending magnet beam port for diffraction, small angle scattering and photoemission research

A bending magnet synchrotron radiation beam port for diffraction, small angle scattering and photoemission research at the Synchrotron Radiation Laboratory, BEPC, has been designed. The port contains two beam lines: a focusing double crystal monochromator X-ray beam line and a spherical grating monochromator VUV and soft X-ray beam line. The optical system of the focusing X-ray beam line consists of a bent cylindrical mirror which focuses the synchrotron radiation with about 1:1 magnification and an improved right angle structure double crystal monochromator in the range of 3–12 keV. Since the design is such that it is compatible with UHV, the photon energy can be extended to the soft X-ray region by using a long d crystal instead of silicon. The optical system of the UHV and soft X-ray beam line consists of a monochromator with interchangeable gratings, a pair of stepping motors driving entrance and exit slits and a nickel-coated mirror. The photon energy of this beam line ranges from 10 eV to 1.1 keV.

Instrumentation for combined laser-synchrotron photoemission experiments

A combined laser-synchrotron photoemission experiment has been constructed on the Naval Research Laboratory soft X-ray beam line on the X-ray ring at the NSLS, Brookhaven National Laboratory. A pulsed copper vapor laser operating at 6 kHz is currently incorporated. The instrumentation is based on a time-to-digital converter and simultaneously records spectra for all times within a data window tens of microseconds in duration. A resolution of ∼ 2 ns is achieved when the ring is operated in single bunch mode and the laser and synchrotron are synchronized in time. When the laser is free running, resolution is determined by transit time spread in the cylindrical mirror analyzer, which has been measured directly. Examples of performance based on transient laser-induced photovoltages on silicon surfaces are given.