A.K. Ray-Chaudhuri

High-Resolution X-Ray Microscopy Using an Undulator Source, Photoelectron Studies with Maximum

We present the first results of high‐spatial resolution x‐ray imaging studies with an upgraded version of the scanning photoemission multiple application x‐ray imaging undulator microscope. The microscope is a multilayer coated Schwarzschild objective that focuses undulator radiation onto the sample. The recent upgrade improved the spatial resolution by a factor six reaching a full width at half maximum value of 0.5 μm. Highly polished mirrors reduced the diffuse background by almost two orders of magnitude and drastically improved the contrast. The improved microscope was used to perform a series of tests on microgrids and reverse Fresnel zone plates. The microscope capability to detect chemical and topological contrast was verified by using patterned metal overlayers on Si and GaAs substrates. Further improvements to increase the flux and the spatial resolution are underway; this includes the installation of a new undulator beamline.

High resolution spectromicroscopy with MAXIMUM: Photoemission spectroscopy reaches the 1000 Å scale

Abstract We present new results from the soft X-ray scanning photoemission microscope: MAXIMUM. The microscope is installed at the U41 undulator at the Synchrotron Radiation Center at the University of Wisconsin. The instrument is based on a multilayer-coated Schwarzchild objective, operating at 95 eV, and it has demonstrated spatial resolution better than 0.1 μm and electron energy resolution of 300 meV. We review the design and the implementation of the microscope. We also present recent results as well as a summary of the research programs that are being conducted with MAXIMUM.

First results of microspectroscopy from a scanning photoemission microscope with a submicron probe size

Utilizing a Mo–Si multilayer coated Schwarzschild objective to focus 95 eV photons, we have recently demonstrated better than 0.1 μm resolution as a scanning x‐ray transmission microscope. Operating as a scanning photoemission microscope with submicron resolution, we have demonstrated its chemical mapping capabilities by studying a patterned Al/AlOx test structure. In addition, we have also studied the cleaved GaAs(110) surface and have identified lateral variations in the surface band bending on the scale of 100 meV. In both experiments, core level microspectroscopy was performed at selected points on the sample to elucidate the image contrast mechanisms.

Microscopic-Scale Lateral Inhomogeneities of the Photoemission Response of Cleaved Gaas

Photoelectron energy distribution spectra taken for the first time on micrometer‐sized areas of cleaved GaAs(110) reveal rigid shifts from location to location in the photoemission core level peak energies, indicating band‐bending changes on a microscopic scale.

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.

Scanning photoemission microscopy on MAXIMUM reaches 0.1 micron resolution

We present the first results from the upgraded version of the scanning photoemission spectromicroscope MAXIMUM, bared on synchrotron undulator fight and on a multilayer-coated Schwarzschild objective. The upgrade involved nearly all parts of the instrument, notably the beamline and the electron analysis system. Micro-images of Fresnel zone plates and of metal test patterns on semiconductor substrates reached a new record in lateral resolution, well beyond 0.1 micron. The first spectromicroscopy tests were also successfully performed on the new instrument, with analysis of f and d core levels in different systems.

The photoemission spectromicroscope multiple‐application x‐ray imaging undulator microscope (maximum)

We discuss the implementation of phase I of the spectromicroscopy program maximum (multiple‐application x‐ray imaging undulator microscope) at the Wisconsin Synchrotron Radiation Center. Successful feasibility tests included taking photoemission micrographs with lateral resolution of a few microns, line scans, knife‐edge tests, photon flux measurements, and characterization of the focusing performance.

The MAXIMUM Photoelectron Microscope at the University of Wisconsin’s Synchrotron Radiation Center

The Multiple Application X-Ray Imaging Undulator Microscope (or MAXIMUM) is a project being carried out jointly by the University of Wisconsin and the Lawrence Berkeley Laboratory. The principal mode of operation of the system is as a photoemission microscope. In this mode, the radiation from the 30-period undulator on the Aladdin 0.8 GeV storage ring is first passed through a monochromator and then focussed on a pinhole aperture. A 20X demagnified image of this pinhole is formed at the sample plane by a 2-clement microscope objective of the Schwarzschild design, whose surfaces are coated with multilayers to reflect soft x-rays (>77eV). While the diffraction limit of the microscope is around 300 A at a wavelength of 120 A, imperfections in the optics and intensity considerations limit the spatial resolution that can be obtained to about 1000 A. The sample to be studied is positioned at the focus of the microscope and the energy spectra of the emitted photoelectrons are analysed by a cylindrical mirror analyser. In this way it is possible to obtain detailed chemical maps of the specimen, with information on both its chemical components and their chemical status. In this paper we describe the design and operation of the the MAXIMUM beamline, and present some preliminary results obtained with solid state and biological samples.

Soft X-ray Foucault test: A path to diffraction-limited imaging

Abstract We present the development of a soft X-ray Foucault test capable of characterizing the imaging properties of a soft X-ray optical system at its operational wavelength and its operational configuration. This optical test enables direct visual inspection of imaging aberrations and provides real-time feedback for the alignment of high resolution soft X-ray optical systems. A first application of this optical test was carried out on a Mo-Si multilayer-coated Schwarzschild objective as part of the MAXIMUM project. Results from the alignment procedure are presented as well as the possibility for testing in the hard X-ray regime.

Photoelectron Microscopy in the Life Sciences - Imaging Neuron Networks

Photoemission techniques like electron spectroscopy for chemical analysis are the leading electronic probes in materials science—but their impact in the life sciences has been minimal. A critical problem is that the lateral resolution in ordinary photoemission does not exceed a few tenths of a millimeter. This space‐averaged probe is nearly useless for most of the fundamental problems in biophysics and biochemistry, which deal with microstructures in the submicron range or smaller. This limit is being overcome with photoemission microscopes, such as our scanning instrument maximum. The first scanning photoelectron micrographs of a cellular system with submicron resolution are presented. Minute details of neuron networks are imaged on maximum, thereby opening the way to novel applications of photoemission in the life sciences. The details include individual neurons, axons, dendrites, and synapses, and composite large‐area scanning micrographs were routinely produced with a lateral resolution of 0.5 μm.