D. Menke

Time-of-flight photoelectron emission microscopy TOF-PEEM: first results

The time structure of the synchrotron radiation at BESSY (Berlin) is used to operate a photoemission electron microscope in a time-of-flight (TOF) mode. The electrons which are emitted from the sample surface with different energies are dispersed in a drift tube subsequent to the imaging optics. The screen of the microscope was replaced by a fast scintillator (tau = 1.4 ns) and the light is detected by an ultra fast gated intensified CCD camera (800 ps gate 1 MHz repetition rate). The resolving power in the energy domain is demonstrated and possible implications on the spatial resolution (chromatic correction) are discussed. Additionally, an improved contrast at very low emission energies is shown. The capability of the setup as an efficient microspectroscopic tool is illustrated

Efficiency of a multilayer-coated, ion-etched laminar holographic grating in the 14.5–16.0-nm wavelength region

The efficiency of an ion-etched laminar holographic grating was measured at near-normal incidence in the 14.5-16.0-nm wavelength range. The grating had an electron-beam-evaporated Mo/Si multilayer coating matched to the grating groove depth. The efficiency peaked at 16.3% in the first inside order at 15.12 nm and 15.0% in the first outside order at 14.94 nm. These are believed to be the highest efficiencies obtained to date from a multilayer-coated laminar grating at near-normal incidence in the EUV (lambda<30.0nm) . Zero and even orders were almost completely suppressed. The grating groove efficiency in the first order approached the theoretical limit of 40.5%.

Carbon buffer layers for smoothing superpolished glass surfaces as substrates for molybdenum/silicon multilayer soft-x-ray mirrors

Zerodur and BK7 glass substrates (developed by Fa. Glaswerke Schott, D-55014 Mainz, Germany) from Carl Zeiss Oberkochen polished to a standard surface roughness of varsigma = 0.8 nm rms were coated with a C layer by electron-beam evaporation in the UHV. The roughness of the C-layer surfaces is reduced to 0.6 nm rms. A normal-incidence reflectance of 50% at a wavelength of 13 nm was measured for a Mo/Si multilayer soft-x-ray mirror with 30 double layers (N = 30) deposited onto the BK7/C substrate, whereas a similar Mo/Si multilayer (N = 30) evaporated directly onto the bare BK7 surface turned out to show a reflectance of only 42%.

Mo/Si multilayer coated laminar phase and ruled blaze gratings for the soft X-ray region

Abstract MoSi multilayer coated laminar and blaze gratings with about 1200 L/mm have been manufactured for near normal incidence operation at soft x-ray wavelengths above the Si L-edge λ ≥ 12.4 nm. Higher diffraction efficiencies (up to 11% at λ = 13.6 nm), as opposed to simple amplitude gratings, are achieved for a soft x-ray laminar phase grating coated with 24 Mo/Si bilayers. Two mechanically ruled blaze gratings have been coated with Mo/Si multilayers. The maximum 1st order efficiency of 32% at λ = 13.8 nm has been achieved for one of them due to a refined groove forming technique and an optimum matching of the blaze angle (0.8°) and the bilayer thickness (10.5 nm).

X-ray scattering study of interface roughness correlation in Mo/Si and Ti/C multilayers for X-UV optics

The X-ray reflectivity and interface diffuse scattering at grazing incidence were measured on two couples of multilayers, namely on Mo/Si multilayers (50 periods) prepared by e-beam evaporation and sputtering techniques and on e-beam evaporated Ti/C multilayers (87 periods) prepared with and without Ar+ ion-beam polishing after each layer deposition. The results were evaluated using Fresnels optical algorithm and a semikinematical modification of the distorted-wave Born approximation to extract and compare the basic interface parameters within each couple. For both Mo/Si multilayers, a frequency-dependent vertical correlation function of the interface roughness corresponding to a model of kinetic roughening was applicable, the vertical correlation length (at a given frequency) being more than an order of magnitude shorter for the sputtered sample. This effect may be explained by high lateral mobility of sputtered adatoms when the Ar plasma pressure is below the thermalization threshold. The main effect of polishing the Ti/C multilayer is a decrease of both the lateral and vertical correlation lengths by about an order of magnitude which may be ascribed to an interfacial reaction at the underlying interface induced by penetrating Ar+ ions. Different lateral and vertical correlations of the interface profiles evidenced within each couple of multilayers affect the distribution of the interface diffuse scattering intensity in the reciprocal space which has some implications for X-UV optics applications

Photoemission microscopy with microspot-XPS by use of undulator radiation and a high-throughput multilayer monochromator at BESSY

Abstract We present a new experiment for photoelectron microspectroscopy by use of undulator radiation, which has been set up at the beamline U2 at the Berlin electron storage ring BESSY 1. This approach employs a non-imaging simulated hemispherical electron energy analyser attached to an imaging photoemission electron microscope (FOCUS IS-PEEM) with integrated microarea selector. The photoemission microscope exhibits a lateral resolution of 25 nm (with 4.9 eV UV-excitation), while the resolution with incident synchrotron radiation in the soft X-ray range is about 100–120 nm (mainly due to chromatic aberrations). Photoemission microscopy as well as photoelectron microspectroscopy of selected areas on the sample surface were performed by using the third harmonic of the direct undulator beam which was monochromatized and refocused by a two-element multilayer optic in the 70–95 eV energy range. The multilayer monochromator operating at near-normal incidence consists of a concave spherical multilayer mirror ( r =650 mm) and a plane multilayer grating (blazed grating 1221 L/mm, blaze angle 0.8 deg). Both elements were coated with a Mo/Si multilayer of equal d -spacing (20 doublelayers, d =10.5 nm) to enhance the reflectivity for EUV radiation at near-normal incidence angles. The characterization of the individual optical components by EUV reflectometry shows a peak reflectance of about 47% at a photon energy of 95 eV in the case of the focusing multilayer mirror while the first order diffraction efficiency of the multilayer blaze grating was measured to be up to 32%. The evaluation of the photoelectron spectra measured with this set-up displays that the spectral resolution of the incident radiation is better than 0.7 eV, while it is about 2–4 eV in the case of a two-multilayer-mirror configuration. Analysis of the surface topography and the chemical composition of inhomogeneities of thin evaporated layers on a mesoscopic scale are the main applications of this experiment.

CHEMICAL MICROANALYSIS BY SELECTED-AREA ESCA USING AN ELECTRON ENERGY FILTER IN A PHOTOEMISSION MICROSCOPE

Abstract We present a new and simple device for microspectroscopy being independent of the mode of electron-excitation. Micro-X-ray photoelectron spectroscopy, electron-induced Auger-spectroscopy, as well as local energy-loss spectroscopy were used to investigate metal-adsorption on silicon. This new approach employs a non-imaging electron energy analyser attached to a new-generation photoemission electron microscope with integral microarea selector. Photoelectron microspectroscopy was performed using the direct beam of an undulator (U2 at BESSY) being monochromatised and focused by means of multilayer optics at hv = 95 eV. Similarly, local Auger-electron and EELS spectra have been taken using a simple electron gun for the excitation. The chemical compositions of inhomogenities in thin layers of indium on silicon and the local state of oxidation of a structured Pt Co multilayer have been determined.

Mo/Si multilayer-coated ruled blazed gratings for the soft-x-ray region

Two Mo/Si multilayer-coated blazed gratings have been fabricated for operation at soft-x-ray wavelengths above the Si L edge, λ ≥ 12.4 nm, at (near) normal incidence. The sawtooth profile of the grating structure was mechanically ruled into a 200-nm Au film that was deposited onto a plane glass substrate. To smooth the rough Au surface and to prevent interdiffusion of the Au film with the upper Mo/Si multilayer, a carbon film was evaporated onto the Au grating surface of one of the gratings before the deposition of the multilayer coating. We matched the multilayer grating, working on blaze in the third diffraction order, in which an absolute diffraction efficiency of 3.4% at a wavelength of 14 nm was measured, whereas only 1.1% was achieved for a similar grating (without a carbon interlayer). These efficiencies are higher than those obtained for other ruled blazed gratings reported in the literature. As a result of the multilayer and grating periodicity, the wavelength of diffraction can be tuned bya rotation of the grating, which is important for application in a soft-x-ray monochromator.

Multilayer reflection-type zone plates and blazed gratings for the normal incidence soft x-ray region

Here we report on the fabrication and analysis of two different types of laterally structured multilayers, which act as highly efficient x-ray optical elements for focusing or spectral dispersion of soft x-rays at (near) normal incidence. The microfocusing of soft x-rays at (near) normal incidence with plane reflection optics can be obtained by multilayer Bragg-Fresnel zone plates. A circular condensor zone plate structure (2.9 mm diameter, 417 zones, inner zone radius 50 micrometers , outer zone width 0.9 micrometers ) has been recorded by holographic lithography followed by ion beam etching into a Mo-Si multilayer mirror of 24 periods and a doublelayer thickness of 7.2 nm. The focusing properties analyzed by soft x-ray reflectometry at (lambda) equals 13.8 nm show a focal spot size smaller than 40 micrometers measured 160 mm behind the multilayer zone plate. Multilayer blazed gratings offer the opportunity for highly resolved spectral dispersion of soft x-rays due to the possible combination of high efficiency and high diffraction orders with almost the whole intensity diffracted in one diffraction order. The sawtooth profile of a blazed grating structure (1221 l/mm, blaze angle 1.5 degree(s)) has been ruled into a 200 nm thick Au-film which has been deposited onto a plane glass substrate. A Mo/Si multilayer of 15 periods and a doublelayer thickness of 7.2 nm has been deposited onto the grating substrate. In order to smooth the rough Au-surface and to prevent interdiffusion of the Au-film with the upper Mo-Si multilayer a carbon film has been evaporated onto the Au-grating surface before the deposition of the soft x-ray coating. This procedure results in a significant increase of diffraction efficiency. The multilayer grating has been matched working on blaze in the third diffraction order, where an absolute diffraction efficiency of 3.4% at (lambda) equals 14 nm has been measured, while only 1.1% has been achieved for a similar grating without a carbon interlayer.

Multilayer-coated soft x-ray diffraction gratings for synchrotron radiation applications

We report about the diffraction efficiencies of two new types of multilayer diffraction gratings, one of them being proposed for high spectral dispersion ability due to a high line density in the photon energy range around 90 eV, while the other is being proposed as a multilayer grating working in the water window spectral range around 470 eV at near normal incidence angles. For a 6600 L/mm sinusoidal interference grating coated with 18 Mo/Si doublelayers of d = 8.2 nm absolute diffraction efficiencies up to 11 % at a wavelength .\ = 13.2 nm were measured in each first diffraction order. A 2400 L/mm laminar grating was coated with 60 Ti/C bilayers of d = 2.2 nm for high efficiency in the water window spectral range near the Ti-L edge (.\ = 2.77 nm). For a similar Ti/C multilayer mirror refiectivities of 11 % were measured at a wavelength ) = 2.7 nm and an angle of incidence a = 59 deg. First order diffraction efficiencies of about 0.7 % were measured for the Ti/C multilayer grating.