Erik D. Johnson

X‐ray spectromicroscopy with a zone plate generated microprobe

The scanning photoelectron microscope at the National Synchrotron Light Source (NSLS) has recently recorded micrographs with a resolution below half a micron. To demonstrate elemental and chemical sensitivity at the submicron level, an artificial structure consisting of Al and SiO2 lines on a boron‐doped silicon substrate was examined. Al 2p and Si 2p primary photoelectrons as well as O KVV Auger electrons were used for image formation. Contrast reversal between the the Si and SiO2 areas was observed in images formed from Si 2p and oxide‐shifted Si 2p photoelectrons. The soft x‐ray undulator at the NSLS provides coherent illumination of a zone plate to produce the microprobe. The sample is mechanically scanned through the beam allowing the formation of images from photoelectrons detected by a single‐pass cylindrical mirror analyzer, or a more complete spectroscopic examination of a selected area of the sample.

In situ reactive glow discharge cleaning of x‐ray optical surfaces

We report the first implementation of an in situ glow discharge cleaning procedure for the removal of carbon contamination from x‐ray optical surfaces. In situ cleaning obviates the need for the time‐consuming and costly process of element removal, cleaning or repolishing, remounting, and realignment usually necessary to restore x‐ray optics to their original condition. The apparatus required is quite simple and can easily be fitted to most existing UHV (ultrahigh vacuum) mirror boxes or monochromators. Results with several monochromators at the Brookhaven National Labs National Synchrotron Light Source (NSLS) show that better than original performance can be obtained at the carbon K edge, since the elements are not exposed to atmosphere after in situ cleaning and do not accumulate the adventitious carbon layer associated with more traditional methods. Possible improvements and extensions of the technique are also described.

Scanning photoelectron microscope with a zone plate generated microprobe

Abstract We describe instrumentation of a scanning photoelectron microscope (SPEM), which we are presently developing and commissioning at the X1A beamline of the National Synchrotron Light Source (NSLS). This instrument is designed to use the soft-X-ray undulator (SXU) at the NSLS as a high-brightness source to illuminate a Fresnel zone plate, thus forming a finely focused probe, ≤ 0.2 μ m in size, upon the specimen surface. A grating monochromator selects the photon energy in the 400–800 eV range with an energy resolution better than 1 eV. The expected flux in the focus is in the range 5 × 10 7 –10 9 photons s −1 . A single pass cylindrical mirror analyzer (CMA) is used to record photoemission spectra, or to form an image within a fixed electron energy bandwidth as the specimen is mechanically scanned. As a first test, a 1000-mesh Au grid was successfully imaged with Au 4f primary photoelectrons, achieving a resolution of about 1 μm.

Performance Measurements of CMOS Position Sensitive Solid-State Photomultipliers

We have designed position sensitive solid-state photomultipliers (PS-SSPM) using a complementary metal-oxide-semiconductor (CMOS) process. Four variations of the PS-SSPM design were fabricated, however, one of the variations did not function properly. The remaining three functional variations were characterized for their energy and coincidence timing resolution, spatial resolution, and scintillator array imaging. Each PS-SSPM is 1.5 × 1.5 mm2, however, each device has different micro-pixel geometries and different micro-pixel electrical readout for event position sensing. When coupled to 1 × 1 × 20 mm3 LYSO, the energy resolution at 511 keV was measured as a function of bias. The same LYSO scintillator was used to measure the coincidence timing resolution. Results between the PS-SSPMs varied from 2.0 ns to 0.9 ns (FWHM) at 511 keV. Spatial resolution studies were conducted using a focused (15 μm beam spot diameter) pulsed 635 nm diode laser. For each PS-SSPM, the X and Y spatial resolution was measured between 70 and 75 μm (FWHM). Lastly, scintillator array images were generated using a CsI:Tl and LYSO array having 300 × 300 μm2 and 500 × 500 μm2 pixels respectively.

Compact high flux photon beam position monitor

We have developed a new compact water‐cooled beam position monitor for use at the NSLS X‐13 Insertion Device Development beamline, currently fitted with a high‐power, high‐brightness soft‐x‐ray undulator. We describe the novel geometry of the monitor and present the results of tests which explore its sensitivity, stability, and linearity. These results were obtained on the NSLS Beamline Research and Development white light beamline, U14B, on the VUV ring and suggest that beam position monitors of this type might be adapted to other facilities with similar spectral characteristics.

In situ reactive cleaning of X-ray optics by glow discharge

Abstract We have developed a method of in situ reactive glow discharge cleaning of X-ray optical surfaces which is capable of complete removal of carbon contamination [E.D. Johnson et al., Rev. Sci. Instr. 58 (1987) 1042]. Our work is the first to successfully clean an entire optical system in situ and characterize its performance at short wavelengths (as low as 10 A). The apparatus required is quite simple and can easily be fitted to most existing UHV (ultrahigh vacuum) mirror boxes or monochromators. The advantages of this technique over previously available methods include dramatic improvements in instrument performance and reductions in down time since the whole process typically takes a few days. This paper will briefly describe our results and detail the experimental considerations for application of the technique on different monochromator geometries. Possible improvements and extensions of the technique are also discussed.

Development of a second generation scanning photoemission microscope with a zone plate generated microprobe at the National Synchrotron Light Source

We have been developing an instrument that combines the techniques of x‐ray photoelectron spectroscopy and zone plate microfocusing to perform spectromicroscopy. The X1A undulator provides a bright photon source in the soft x‐ray range with a high degree of spatial coherence (a requirement for zone plate focusing). A spherical grating monochromator selects the desired photon energy in the 280–800 eV range. A Fresnel zone plate focuses the beam to a small spot. Photoelectron spectra can be acquired from the small irradiated area with an electron energy analyzer. With the beam focused on the surface and the sample mechanically scanned, element‐specific or chemical‐state‐specific images of the surface can be obtained.

Images of a microelectronic device with the X1‐SPEM, a first generation scanning photoemission microscope at the National Synchrotron Light Source

We have recently completed the first generation scanning photoemission microscope at beamline X1A at the National Synchrotron Light Source (NSLS), the X1‐SPEM. The instrument is designed to use the soft x‐ray undulator at the NSLS as a high brightness source to illuminate a Fresnel zone plate, thus forming a finely focused probe, ≤0.4 μm in size, on the specimen surface. A grating monochromator selects the photon energy in the 400–800 eV range with an energy resolution of 0.8–2 eV. The flux in the zone plate focus is in the 108–109 photons/s range. A single pass cylindrical mirror analyzer (CMA) is used to record photoemission spectra, or to form an image within a fixed electron energy bandwidth as the specimen is mechanically scanned. The best one‐dimensional resolution achieved so far is 0.1 μm, as judged by the 25%–75% intensity rise across an edge. This is close to the diffraction limit of the zone plate used. Due to astigmatism introduced by the beamline optics, the two‐dimensional resolution in the ...

Storage ring development at the National Synchrotron Light Source

Beam monitoring systems and other electronic systems at the NSLS storage rings are described in detail. Both the VUV and X‐ray rings are discussed and applications, such as lithography, are proposed. (AIP)

Recent advances in soft x-ray scattering instrumentation at the National Synchrotron Light Source

For the study of condensed‐matter systems x‐ray scattering experiments are often the best choice as they have several desirable features including complete conservation of momentum in the incident and detected particles, well characterized initial and final electronic states, and insensitivity of photon transport to external electric and magnetic fields (as compared to photoelectrons, for example). To extend these techniques to soft x‐ray region (ℏν<1 keV) the lack of suitable detectors, and the difficulties associated with performing scattering experiments in vacuum must be overcome. In this article we provide details of our instrumental development program, and show some representative examples of experiments we have performed to date.