Roger W.C. Hansen

Ultraviolet/ozone cleaning of carbon-contaminated optics

It is shown that ozone generated by UV light can be used to clean carbon-contaminated synchrotronradiation optics.

Uv-ozone ashing of cells and tissues for spatially resolved trace element analysis

UV/ozone ashing of thin tissue sections and cell cultures is a simple technique to enhance relative elemental concentrations, while maintaining their spatial location at the sub-micron level. This approach may enhance the capability of spatially resolved analysis techniques to detect the distribution of trace elements in biological matrices. We present results from light microscopy and x-ray spectromicroscopy studies of tissues and cells demonstrating that the micro-structure is very well conserved. We show the signal enhancement resulting from the removal of carbon, which allows otherwise undetectable gadolinium to be mapped in cancer tissue for a novel neutron capture therapy.

Cleaning of optical surfaces with photogenerated reactants

Abstract Cleaning of synchrotron radiation optics with photogenerated reactants has several advantages over discharge cleaning methods. In discharge cleaning, reactive species from the discharge must react with contamination on the surface while the surface is shielded from the harsher elements of the discharge which can contaminate or degrade the surface. In contrast, if reactive species can be generated near the surface by photons, the problem of shielding can be eliminated and in some cases higher cleaning rates can be obtained. Different cleaning methods were evaluated by measuring the rates of removal of polymethylmethacrylate films with a thickness monitor. A number of different light sources and geometries were tested. The highest cleaning rates were observed with atmospheric-pressure UV/ozone cleaning. This method has been extensively investigated for cleaning of hydrocarbon contamination from semiconductor surfaces. Our studies indicate that it is also effective in removing the graphite-like contamination from synchrotron radiation optics. Compared to lower pressure methods it is simple, low cost, faster, and more selective. It does require venting of vacuum chambers; however, in many cases optics can be cleaned without demounting, saving considerable time and effort. This method has been used successfully to clean gratings and mirrors in several beamlines.

A plane grating monochromator for the new undulator at Aladdin: 8–240 eV

Abstract A comparative study on the expected performance of two monochromator designs for the new undulator beamline at the Aladdin storage ring is reported. The undulator, a 3.5 m device, will cover the energy range 8–240 eV in the first and third harmonic. The flux and resolution of a stigmatic plane grating monochromator (PGM) equipped with an entrance slit and of a spherical grating monochromator (SGM) with a movable exit slit were calculated analytically and by means of ray-tracings. The PGM design, tuned to a resolving power of 10 4 , can deliver more than 10 12 photons/s at the sample position in the photon energy range 20–170 eV. The illuminated spot size at the sample position will be less than 500 μm (horizontal) by 50 μm (vertical). This performance is not achieved with the SGM design.

Feasibility tests of transmission x-ray photoelectron emission microscopy of wet samples

We performed feasibility tests of photoelectron emission spectromicroscopy of wet samples in the water window (285-532 eV) soft x-ray spectral region. Water was successfully confined in an ultrahigh vacuum compatible compartment with x-ray transparent sides. This water cell was placed in the MEPHISTO spectromicroscope in a transmission geometry, and complete x-ray absorption spectra of the water window region were acquired. We also show micrographs of test samples, mounted outside of the compartment, and imaged through the water. This technique can be used to study liquid chemistry and, at least to the micron level, the microstructure of wet samples. Possibilities include cells in water or buffer, proteins in solution, oils of tribological interest, liquid crystals, and other samples not presently accessible to the powerful x-ray photoelectron emission spectromicroscopy technique

Photoemission Spectromicroscopy with Maximum at Wisconsin

We describe the development of the scanning photoemission spectromicroscope MAXIMUM at the Wisoncsin Synchrotron Radiation Center, which uses radiation from a 30-period undulator. The article includes a discussion of the first tests after the initial commissioning.

Alignment techniques for calibration and installation of a 6-m Toroidal Grating Monochromator

Abstract The University of Wisconsin Synchrotron Radiation Center Optics Group has recently completed the installation of three 6-m Toroidal Grating Monochromator (TGM) beamlines on the Aladdin ring. Two of these beamlines image bending-magnet radiation and the third images radiation from the 30-period undulator on loan to the Synchrotron Radiation Center from the Stanford Synchrotron Radiation Laboratory and Lawrence Berkeley Laboratory. Each beamline required an accurate alignment strategy. This is due to the long source-to-final-image distance and the five independent critical elements: entrance mirror, entrance slit, grating chamber, exit slit, and exit mirror. The TGM grating chamber houses up to six gratings on a revolving carousel which is scanned with a sine-drive. We will describe grating stability checks and adjustments to linearize the grating scan calibration. We will also outline the basic alignment procedures from the source point, through the grating chamber, to the final focus. The procedure we have used provided sufficiently accurate alignment to realize the high throughput and resolution capabilities of the 6-m TGMs. The methods also allow later checks on critical degrees of freedom of the optical components.

UV/ozone cleaning of a replica grating

Abstract UV/ozone cleaning was evaluated for cleaning a carbon-contaminated replica grating. Replica optics represent a challenging test of any cleaning process because of the potential for damage to the epoxy layer which can severely degrade the surface figure and finish. A badly contaminated replica grating was divided into three sections for this study. One section was cleaned using a mercury lamp, another section was cleaned using a deuterium lamp, and the third section was left as a control. The results were evaluated using a Ronchi test to determine figure error, a Fotonic sensor to estimate reflectivity, and a microscopic evaluation using a Nomarski objective to look for surface damage. Surface roughness measurements were also performed with a Micromap surface profiler. The results indicated that the surface figure and finish were not significantly degraded, and the surface figure was actually improved compared to the contaminated condition. The visible light reflectivity was fully restored in the areas that were cleaned.

New Synchrotron Radiation Center beamlines at Aladdin

In the past year, the Synchrotron Radiation Center (SRC) staff has installed five new beamlines at SRC. Three of these beamlines are ‘‘public’’ beamlines operated by SRC for experiments selected from peer‐reviewed proposals. Fifty to seventy‐five percent of the experimental time on the other two beamlines is managed by the SRC as a consequence of the SRC being a partner in participating research teams (PRTs). These new beamlines bring the number of VUV and soft x‐ray research beamlines installed on Aladdin to 17 as of August 1988. Including two storage ring optical diagnostic ports, there will be 20 ports in use on Aladdin by the end of 1988.

A system for magnetic circular dichroism measurements with a 10 m toroidal grating monochromator

Abstract A system of remotely-controlled apertures have been installed in the Synchrotron Radiation Center 10-m toroidal grating monochromator (TGM) for production of circularly-polarized light. In addition to allowing normal operation of the beamline, the apertures can be adjusted to block any fraction of the incoming beam without excessive heating and outgassing. This selective blocking of the light produces an appreciable elliptical polarization of the incoming light. Over the energy range of the 10 m TGM high energy grating, from 200 to 800 eV, the beamline optics do not significantly affect the polarization. The 10-m instrumental energy range overlaps the binding energies of the L-shell core levels of the important transition-metal materials. Calculations have been performed to estimate the performance of the aperture system as a function of energy. The results indicate that for an aperture position transmitting 20% of the synchrotron flux, the degree of polarization should be about 85% and should be reasonably constant over the photon energy range. With the light masked, magnetic circular dichroism was observed by measuring total yield with different orientations of sample magnetization and photon spin. Thin films of magnetic materials on magnetic and non-magnetic substrates have been studied.