X-ray Undulator Beamline Research Articles

HESEB: The Helmholtz state-of-the-art Soft-X-Ray Undulator beamline at SESAME

SESAME and a consortium of five Helmholtz Centers are designing and installing a state-of-the-art soft X-Ray undulator beamline at the SESAME light source in Amman, Jordan. Funding is provided by the Helmholtz Association over a four year project cycle that started in January 2019. This is an interim report covering the first 36 months of the project where the construction and installation has been almost completed and commissioning and characterization of the beamline is about to start. Additionally, seminars, workshops, and a training program are part of the project aimed at establishing a broad user community.

Design and simulation of a mirror-mitigated thermal load on Korea-4GSR hard X-ray undulator beamline optics

Design and simulation of a mirror-mitigated thermal load on Korea-4GSR hard X-ray undulator beamline optics

Beamline commissioning for microscopic measurements with ultraviolet and soft X-ray beam at the upgraded beamline BL-13B of the Photon Factory.

Beamline 13 of the Photon Factory has been in operation since 2010 as a vacuum ultraviolet and soft X-ray undulator beamline for X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and angle-resolved photoelectron spectroscopy (ARPES) experiments. The beamline and the end-station at branch B have been recently upgraded, enabling microscopic XPS, XAS, and ARPES measurements to be performed. In 2015, a planar undulator insertion device was replaced with an APPLE-II (advanced planar polarized light emitter II) undulator. This replacement allows use of linear, circular, and elliptical polarized light between 48 and 2000 eV with photon intensities of 109-1013 photons s-1. For microscopic measurements, a toroidal post-mirror was renewed to have more focused beam with profile sizes of 78 µm (horizontal) × 15 µm (vertical) and 84 µm × 11 µm at photon energies of 100 and 400 eV, respectively. A high-precision sample manipulator composed of an XYZ translator, a rotary feedthrough, and a newly developed goniometer, which is essential for microscopic measurements, has been used to control a sample specimen in six degrees of freedom, i.e. translation in the X, Y, and Z directions and rotation in the polar, azimuthal, and tilt directions. To demonstrate the performance of the focused beams, one- and two-dimensional XPS and XAS scan measurements of a copper grid have been performed. It was indicated from analysis of XPS and XAS intensity maps that the actual spatial resolution can be determined by the beam size.

Comparative study of hard X-ray undulator beamline performance in the Korean 4GSR and the PLS-II

A new light source based on the electron storage ring, dubbed the “diffraction-limited storage ring” (DLSR) to keep the full intrinsic wave nature of X-rays had been proposed since the early stage of storage ring history and has finally been developed successfully, and an upgrade and a new construction programs have now chosen in the worldwide synchrotron facilities. The construction of the so-called “4th generation storage ring” (4GSR), which is a newly-coined term aiming in the same direction, was decided in Korea. The Korean 4GSR is expected to be 10–100 times brighter than the Pohang Light Source-II (PLS-II). Hard X-ray undulator beamlines will benefit from the 4GSR due to its low emittance approaching the diffraction limit. In the PLS-II, more than 10 hard X-ray undulator beamlines are currently in operation. We present a comparative study of the representative hard X-ray undulator beamlines by using the cutting-edge diffraction-spectroscopy techniques in the PLS-II and the 4GSR for better understanding the upcoming light source in Korea. The figures-of-merit of the two specific experimental techniques, resonant inelastic X-ray scattering (RIXS) and resonant X-ray emission spectroscopy (RXES), are discussed for comparison of the two light sources. Both RIXS and RXES are sometimes referred to as a “renaissance” in X-ray science and are, therefore, strongly expected to be adopted in the 4GSR beamlines.

Development of a high-precision XYZ translator and estimation of beam profile of the vacuum ultraviolet and soft X-ray undulator beamline BL-13B at the Photon Factory.

A high-precision XYZ translator was developed for the microanalysis of electronic structures and chemical compositions on material surfaces by electron spectroscopy techniques, such as photoelectron spectroscopy and absorption spectroscopy, utilizing the vacuum ultraviolet and soft X-ray synchrotron radiation at an undulator beamline BL-13B at the Photon Factory. Using the high-precision translator, the profile and size of the undulator beam were estimated. They were found to strongly depend on the photon energy but were less affected by the polarization direction. To demonstrate the microscopic measurement capability of an experimental apparatus incorporating a high-precision XYZ translator, the homogeneities of an SnO film and a naturally grown anatase TiO2 single crystal were investigated using X-ray absorption and photoemission spectroscopies. The upgraded system can be used for elemental analyses and electronic structure studies at a spatial resolution in the order of the beam size.

Present status of photoemission electron microscope newly installed in SPring-8 for time-resolved nanospectroscopy

A photoemission electron microscope (PEEM) system has been newly installed at the soft X-ray undulator beamline (BL17SU) of SPring-8 to realize time-resolved nanospectroscopy for the local transient electronic structures of advanced materials. This PEEM is a versatile machine composed of an electrostatic lens system and is intended for use in specific experiments such as time-resolved measurements. Pump–probe measurements in tandem with a femtosecond pulsed-laser system and an X-ray chopper are now readily available.

Development and application of in situ/operando soft X-ray transmission cells to aqueous solutions and catalytic and electrochemical reactions

In this review, we have demonstrated several applications of newly-developed in situ/operando liquid flow cells for the transmission XAS (X-ray absorption spectroscopy) measurement in the soft X-ray undulator beamline BL3U dedicated to the chemical application of UVSOR-III Synchrotron. The liquid layer is sandwiched between two thin membranes and its thickness is easily controllable to optimize the absorbance. Liquid samples are exchangeable in situ. Molecular spectra in liquid and gas phases are simultaneously measureable and it makes the energy calibration rather easy. By using a standard version of the liquid cells, we have investigated local structures of several aqueous solutions of alkali halides, methanol, pyridine, and acetonitrile. To observe catalytic and electrochemical reactions under realistic conditions, we have developed in situ/operando versions of the liquid cells. We have investigated local structures of the catalytic hydration reaction of cyanopyrazine under the temperature control and the electrochemical reaction of aqueous iron sulfate solutions using the built-in electrodes under the same scan rate as in cyclic voltammetry. We have discussed future perspectives of our in situ/operando liquid flow cells applied to XAS in the soft X-ray region.

Measurement of coherence length and incoherent source size of hard x-ray undulator beamline at Pohang Light Source-II.

We measured the spatial coherence length and incoherent source size of a hard x-ray undulator beamline at Pohang Light Source-II, the stored electron energy of which has been increased from 2.5 GeV to 3 GeV. The coherence length was determined by single-slit measurement of the visibility of the Fresnel diffraction pattern. The correlated incoherent source size was cross-checked for three different optics: the single slit, beryllium parabolic compound refractive lenses, and the Fresnel zone plate. We concluded that the undulator beamline has an effective incoherent source size (FWHM) of 540 μm (horizontal) × 50 μm (vertical).

Development of a single-shot CCD-based data acquisition system for time-resolved X-ray photoelectron spectroscopy at an X-ray free-electron laser facility

In order to utilize high-brilliance photon sources, such as X-ray free-electron lasers (XFELs), for advanced time-resolved photoelectron spectroscopy (TR-PES), a single-shot CCD-based data acquisition system combined with a high-resolution hemispherical electron energy analyzer has been developed. The system's design enables it to be controlled by an external trigger signal for single-shot pump-probe-type TR-PES. The basic performance of the system is demonstrated with an offline test, followed by online core-level photoelectron and Auger electron spectroscopy in 'single-shot image', 'shot-to-shot image (image-to-image storage or block storage)' and `shot-to-shot sweep' modes at soft X-ray undulator beamline BL17SU of SPring-8. In the offline test the typical repetition rate for image-to-image storage mode has been confirmed to be about 15 Hz using a conventional pulse-generator. The function for correcting the shot-to-shot intensity fluctuations of the exciting photon beam, an important requirement for the TR-PES experiments at FEL sources, has been successfully tested at BL17SU by measuring Au 4f photoelectrons with intentionally controlled photon flux. The system has also been applied to hard X-ray PES (HAXPES) in `ordinary sweep' mode as well as shot-to-shot image mode at the 27 m-long undulator beamline BL19LXU of SPring-8 and also at the SACLA XFEL facility. The XFEL-induced Ti 1s core-level spectrum of La-doped SrTiO3 is reported as a function of incident power density. The Ti 1s core-level spectrum obtained at low power density is consistent with the spectrum obtained using the synchrotron source. At high power densities the Ti 1s core-level spectra show space-charge effects which are analysed using a known mean-field model for ultrafast electron packet propagation. The results successfully confirm the capability of the present data acquisition system for carrying out the core-level HAXPES studies of condensed matter induced by the XFEL.

Performance of PF BL-13A, a vacuum ultraviolet and soft X-ray undulator beamline for studying organic thin films adsorbed on surfaces

We report on the present status of a vacuum ultraviolet and soft X-ray undulator beamline, BL-13A, located at the Photon Factory. BL-13A is mainly dedicated to the study of organic thin films adsorbed on well-defined surfaces, using angle-resolved photoelectron spectroscopy (ARPES), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS). The photon-energy resolution (E/ΔE) is estimated to be about 10000 at a photon energy of 64 eV with an exit-slit width of 30 μm. The photon intensity is estimated to be 2.9 × 1012 to 5.6 × 108 photons/s for photon energies of 30-1600 eV with an exit-slit width of 100 μm at the ring current of 450 mA. An ultrahigh vacuum (UHV) chamber equipped with an electron-energy analyzer (Gamma Data/Scienta, SES 200) is used as the main end station for ARPES, XPS, and XAS measurements. A sample can be transferred from a UHV chamber for sample preparation or from a UHV chamber for the evaporation of organic materials. The sample-holder acceptors are equipped with a heating and cooling system. The overall electron-energy resolution is estimated to be about 12 meV at a photon energy of 30 eV.

In situremoval of carbon contamination from optics in a vacuum ultraviolet and soft X-ray undulator beamline using oxygen activated by zeroth-order synchrotron radiation

Carbon contamination of optics is a serious issue in all soft X-ray beamlines because it decreases the quality of experimental data, such as near-edge X-ray absorption fine structure, resonant photoemission and resonant soft X-ray emission spectra in the carbon K-edge region. Here an in situ method involving the use of oxygen activated by zeroth-order synchrotron radiation was used to clean the optics in a vacuum ultraviolet and soft X-ray undulator beamline, BL-13A at the Photon Factory in Tsukuba, Japan. The carbon contamination of the optics was removed by exposing them to oxygen at a pressure of 10(-1)-10(-4) Pa for 17-20 h and simultaneously irradiating them with zeroth-order synchrotron radiation. After the cleaning, the decrease in the photon intensity in the carbon K-edge region reduced to 2-5%. The base pressure of the beamline recovered to 10(-7)-10(-8) Pa in one day without baking. The beamline can be used without additional commissioning.

Present Status of a New Vacuum Ultraviolet and Soft X-Ray Undulator Beamline BL-13A for the Study of Organic Thin Films Adsorbed on Surfaces

The present status of a new vacuum ultraviolet/soft X-ray (VUV/SX) beamline (BL-13A) used for the study of organic thin films adsorbed on surfaces is described. The base pressure of BL-13A is maintained below 1×10−8 Pa in order to prevent contamination of the optics by residual gases. The measured performance is as follows: photon-energy region, 30-1,200 eV; photon flux, 109-1011 photons s−1; photon-energy resolution (E/ΔE), 10,000 at a photon energy of 401 eV; spot size (horizontal\ imes;vertical) at the second focus, ≈630×120 μm; photon-energy drift, ≤±0.02 eV at a photon energy of 244.39 eV; reduction of photon flux in the C K-edge region, ∼50%.

Design of the first undulator beamline for the Siam Photon Laboratory

The first VUV/soft X-ray undulator beamline (BL3) is being constructed at the Siam Photon Laboratory. This beamline employs a varied line-spacing plane grating monochromator which operates in two constant-included-angle configurations to cover two photon energy ranges of 40–160 eV and 220–1040 eV. The two branchlines, designed for photoemission electron microscopy and photoemission measurements, will be operated in a time-sharing mode.

Electron-ion-coincidence spectra of K-shell excited Ne, Ar, and Kr clusters

Electron-ion-coincidence spectra were recorded for K-shell excited krypton, argon, and neon clusters covering the size range from 1 atom to about 3000 atoms by utilizing hard x-ray undulator beamlines. Multiply charged ions Rz+(z>or=2) and singly charged ions Rn+(n>or=1) are observed as cluster fragments, and their relative abundance exhibits a characteristic dependence on the average cluster size N. It is expected from these results that the charges generated on the cluster surface are strongly localized while those in the cluster core are more delocalized. The estimated charge separation distance increases with N, and it is longer for lighter elements.

A high-resolution angle-resolved photoemission spectrometer combined with laser molecular-beam epitaxy at SPring-8 BL17SU

We have constructed a high-resolution synchrotron-radiation photoemission spectrometer combined with a laser molecular-beam epitaxy (laser MBE) thin film growth system in order to investigate the electronic structure of oxide and nitride thin films. The system was installed at the newly built soft X-ray undulator beamline BL17SU of SPring-8. Total energy resolution of 102 meV was achieved at photon energy of 870 eV. The photoemission apparatus is connected to a laser MBE chamber through a preparation chamber. Single crystal thin-film samples fabricated by laser MBE can be transferred quickly into the photoemission chamber without breaking ultrahigh vacuum. Various new studies are possible using this system and third-generation soft X-ray synchrotron light source, such as direct observation of the bulk electronic band structure of single-crystal films with no cleavable plane, the interface electronic structure of oxide or nitride heterostructures, etc.

First observation of natural circular dichroism for biomolecules in soft x-ray region studied with a polarizing undulator

We measured natural circular dichroism (CD) for biomolecules in soft x-ray region for the first time. Natural linear dichroism (LD) for K(TiO)PO4 (KTP) crystal was also measured at the K-edge energy of oxygen. Measurements of CD and LD spectra were performed at the soft x-ray undulator beamline BL23SU of SPring-8 in Japan. In this beamline, an APPLE-2 type variable undulator was installed as a light source. This undulator was operated under the phase modulation mode in which left and right circularly polarized light (LCPL and RCPL) was switched with about 0.1 Hz.As a sample for CD measurement, we used sublimated film of L-, D- and DL-phenylalanine (Phe) and L- and D-serine (Ser) (thickness ∼300 nm) and measured CD (AL–AR) spectra in the nitrogen and the oxygen K-edge region, respectively. Here, AL and AR mean the abbreviation of absorption for LCPL and RCPL, respectively. For the Phe film, we observed a negative peak at about 407 eV for the L-Phe spectra. On the contrary, a positive peak for the D-Phe spectra and no spectral feature for the DL-Phe were observed. For the Ser film, we observed positive CD peaks at around 540 eV and 548 eV at the L-Ser spectra, on the contrary, negative peaks for the D-Ser. These results are the first CD spectra for biomolecules in the soft x-ray region.We also used KTP crystal cut parallel to the plane (1,2,0) or (1,−2,0) as a sample of LD measurement and measured (AL–AR) spectra in the oxygen K-edge region and observed some peaks at about 530 eV. Since sign of these peaks were dependent on sample rotation angle in a plane perpendicular to the incident light, we concluded that these peaks are derived from linear anisotropy of crystal. Because of a weak linear polarization component of incident light, we could measure such LD spectra.

The design and performance of beamline BL16XU at SPring-8

A new X-ray undulator beamline has been designed and constructed by an industrial consortium of 13 companies at SPring-8. The beamline, named BL16XU, is intended for the characterization of various materials developed for industrial purposes and, together with its sister bending-magnet beamline (BL16B2), has been open to user experiments since the autumn of 1999. The new beamline provides high-brilliance synchrotron radiation in the energy range from 4.5 to 40 keV from an X-ray undulator of the in-vacuo type. The beamline has an experimental hutch for the performance of several experiments: e.g. microscopic observation of materials and micro-fabricated devices by using X-ray beams that have spot sizes of 1 μm or less; X-ray diffraction experiments on thin films with nanometer-scale thickness by using an ω−2 θ diffractometer; fluorescence X-ray analysis of trace elements on Si wafer surfaces by using a total reflection fluorescence X-ray analysis system equipped with wavelength- and energy-dispersive detectors.

Microfocusing of 82 keV x rays with a sputtered-sliced Fresnel zone plate

An experiment to focus 82 keV x rays with a sputtered-sliced Fresnel zone plate (SS-FZP) optics was performed at an x-ray undulator beamline 20XU of SPring-8. The achieved beam size was 1.1 μm in vertical and 1.3 μm in horizontal directions. The measured flux density was 7×105 (photons/s/μm2).

High-energy photoemission spectroscopy of ferromagnetic Ga 1− xMn xN

Here we report investigation of valence band electronic states of ferromagnetic Ga 0.96Mn 0.04N by bulk-sensitive X-ray photoemission, which is realized at high flux X-ray undulator beamline BL29XU of SPring-8, at photon energy of 5.95 keV. We have observed that Mn doping introduces a new structure in the band gap region near the top of the valence band, and also a broader structure in deeper valence band region. Basing upon the first principle calculation, these structures are assigned as Ga 4s originated states, which are raised by hybridization between 3d orbitals of Mn with GaN host orbitals. The present result evidences the second nearest Ga bonds are affected by that Mn–N bond formation, suggesting the long-range interaction of Mn in this host material.

A novel crystal bender for x-ray synchrotron radiation monochromators

A new bending mechanism for an indirectly water cooled monochromator crystal has been developed. The main design goals were a lightweight construction, ease of manufacture, and control. The construction consists of a U-shaped first Si(111) crystal, which can be bent by compressed air to compensate the bowing induced by the heat load from the impinging white synchrotron radiation. The performance of the system was tested at the x-ray undulator beamline BW1 at HASYLAB (Hamburg, Germany). For heat loads between ∼100 and 400 W, rebending of the crystal significantly increases the intensity of the monochromatic beam while the rocking curve is narrowed accordingly, typical widths obtained at 8.9 keV photon energy amount to about 10 arc sec.