Volker Saile

Photoemission study of pristine and photodegraded poly(methyl methacrylate)

Degradation of poly(methyl methacrylate) (PMMA) thin films by vacuum ultraviolet (VUV) monochromatic synchrotron radiation was investigated by ultraviolet photoelectron spectroscopy. The photodegradation reaction was analyzed, for the first time, by different spectrometry techniques and ab initio molecular orbital calculations. It is concluded that the main degradation mechanism in PMMA by VUV photons is ascribed to the disappearance of ester groups and formation of double bonds in the polymer chain. The final product of the degradation seems to possess a relatively rich conjugation of unsaturated bonds. The rate constant of the degradation by VUV photons is evaluated to be 2.4×10−17 photons−1 cm2.

Design of soft x-ray plane-grating monochromator for CAMD

A plane‐grating monochromator (PGM), the CAMD‐PGM, designed for bending magnet radiation is described. In contrast with many other similar PGMs, the CAMD‐PGM is equipped with an entrance slit. The wavelength range of 6–1500 A is covered with two gratings (1220 and 360 gr/mm). The expected performance is a resolving power, λ/Δλ, of ∼2000 with the photon flux of ∼ 1010 photons/s at the photon wavelength of 10.0 A. The beam spot size at the sample position is approximately 1×1 mm2. The monochromator is being constructed and will be installed in the summer of 1992.

Angle-resolved UV photoelectron spectra (UPS) of thin films of perylene-3,4,9,10-tetracarboxylic dianhydride on MoS2

Angle-resolved UV photoelectron spectra (ARUPS) were measured for thin films of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) deposited on cleaved MoS(2) surfaces. The take-off angle (theta) dependence of the photoelectron intensity of the highest pi band showed a sharp maximum at theta = 32-34 degrees. A spectral feature of the binding energy at approximately 8.9 eV, which is believed to originate from a pi state, showed a remarkably different theta dependence from that of the pi band. A quantitative analysis of the observed theta dependencies clearly indicates that (a) the feature at approximately 8.9 eV originates from the oxygen 2p non-bonding states and (b) the molecules lie flat on the substrate surface.

Planar sets of cross x-ray refractive lenses from SU-8 polymer

Sets of planar SU-8 cross lenses focusing in two directions have been fabricated by tilted deep X-ray lithography using an X-ray mask with tilted absorber structures. The profile of the absorber structures on the mask take into account the lithographic peculiarities of SU-8 resist to reproduce the designed profile of the lens elements exactly. The cross lenses are placed on one substrate and have identical focal distances, which allow to scan the spectral range from 5 keV to 30 keV by stepping the lens substrate from one lens to the next. Another set of cross lenses was developed with different quasi-parabolic profiles to obtain a large focus depth (up to several centimeters) with uniform intensity distribution in the micron focal spot. This together with the stepping possibilities between lenses satisfies the requirement of static spectroscopy experiments. For the truncated parabolic profile, these cross lenses consist of separate segments arranged in a new mosaic form. In comparison with the known “fern”-like kinoform profile, the lenses have been developed with smaller gain loss. The testing of the new sets have been performed at the undulator ID-18F and ID-22 beamlines (ESRF, Grenoble, France) and the experimental results are compared to simulations.

RADIATION DAMAGE OF POLY(METHYLMETHACRYLATE) THIN FILMS ANALYZED BY UPS

Abstract Radiation damage of poly(methylmethacrylate) (PMMA) caused by vacuum ultraviolet monochromatic synchrotron radiation was studied by ultraviolet photoelectron spectroscopy. An independent atomic center approximation combined with molecular orbital calculation was employed to study the radiation damage of PMMA quantitatively for the first time. The results of the analysis indicate that main photodegradation is ascribed to abstraction of ester groups and formation of double bonds in the polymer chain.

Surface temperature and distortion of optical elements exposed to high power synchrotron radiation beams (invited)

Mirrors made of various materials have been investigated under surface power densities of approximately 1–2 W/mm2 emitted by a powerful hybrid wiggler installed in the 5.3‐GeV DORIS storage ring. Thermal inhomogeneities and deformations at surfaces with a height resolution of 50 nm have been determined quantitatively. The only material withstanding these power levels without a significant deformation is SiC. Conventional cooling geometries are found to be useless for a reduction of the surface distortion.

Electronic structure and molecular orientation of well-ordered polyethylene oligomer (n-C44H90) on Cu(100) and Au(111) surfaces studied by UV photoemission and low energy electron diffraction

Abstract The electronic structure and molecular orientation of tetratetracontane (n-C44H90) films on Cu(100) and Au(111) surfaces were investigated by angle-resolved UV photoemission spectroscopy (ARUPS) and low energy electron diffraction (LEED). The observed ARUPS spectra showed the drastic take-off angle dependence due to intramolecular band dispersion. A 2×1-like LEED pattern was observed for both substrates. From these results and theoretical simulation of ARUPS spectra based on independent-atomic center (IAC) approximation, we found that the C–C–C plane of the adsorbed TTC molecule is parallel to the substrate surface and its molecular axis is along a [110] direction for both substrates. We also measured the work function change by adsorption of TTC. The observed values were c.a. −0.3eV and −0.7eV for Cu(100) and Au(111) systems, respectively. Such decrease of the work function indicates the existence of a dipole layer at the interfaces in contrast to the traditional picture of energy level alignment at organic/metal interface assuming a common vacuum level at the interface. The dipole formation in such physisorbed systems can be explained by the polarization of the TTC molecule due to an image force.

Pendant group orientation of poly(2-vinylnaphthalene) thin film surface studied by near-edge x-ray absorption fine structure spectroscopy (NEXAFS) and angle-resolved ultraviolet photoelectron spectroscopy (ARUPS)

Angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy were applied to the investigation of the tilt angles of the naphthalene pendant groups at the surface of a poly(2-vinylnaphthalene) thin film. In contrast to NEXAFS, which provides only an average determination of the tilt angle, ARUPS combined with a sophisticated analysis of photoelectron angular dependence offers more detailed information. It was concluded that the naphthalene pendant groups are tilted randomly at the polymer surface, and that the tilt angle distribution is well described as a three-dimensional isotropic random orientation.

PMMA as an X-ray resist for micro-machining application: latent image formation and thickness losses

Abstract This paper reports preliminary results of direct observation of a latent image formed in thick PMMA resist after X-ray exposure.

A new synchrotron light source at Louisiana State University's Center for Advanced Microstructures and Devices

Abstract A 1.2-GeV synchrotron light source is being constructed at the Center for Advanced Microstructures and Devices (CAMD) at Louisiana State University. The expressed purpose of the center, which has been funded by a grant from the US Department of Energy, is to develop X-ray lithography techniques for manufacturing microcircuits, although basic science programs are also being established. The storage ring will be optimized for the soft-X-ray region and will be the first commercially manufactured electron storage ring in the United States. The magnetic lattice is based on a design developed by Chasman and Green and will allow up to three insertion devices to be installed for higher-energy and higher-intensity radiation. In addition to the lithography effort, experimental programs are being established in physics, chemistry, and related areas.