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Radiation stability of optical elements exposed to a high dose of laser radiation is an important issue in developing optical elements for x-ray free-electron laser light sources. In order to prevent optics from being damaged, the fundamental mechanisms governing the material response to ultrashort high peak power XFEL pulses must be identified and studied. In this paper we present a study on the interaction of fs laser pulses with Ru films in a wide range of incident photon energies from ~1 up to 104 eV. Since reflective thin metal films operate at grazing incidence conditions, absorption of the light occurs in the top part of the Ru mirrors (~1 – 10 nm). Hybrid multi-scale modeling of target evolution after irradiation is performed. The model takes into account photoabsorption and non-equilibrium electron cascading occurring on a fs timescale, thermal diffusion and electron-phonon energy exchange on a ps timescale and lattice dynamics up to ns timescale. Different photon energies result into qualitatively different absorbed energy profiles by the time of thermalization of the electronic system. The effects of such a difference on the hydrodynamical evolution and eventual damage of Ru are discussed. Details of processes such as melting, cavitation, ablation and recrystallization are revealed for selected photon energies. The results show good qualitative agreement with the experimental observations on Ru ablation.

Die Erfindung betrifft einen Spiegel, insbesondere für eine mikrolithographische Projektionsbelichtungsanlage. Gemäß einem Aspekt weist der Spiegel eine optische Wirkfläche (10a, 20a), ein Spiegelsubstrat (11, 21) und einen Reflexionsschichtstapel (12, 22) zur Reflexion von auf die optische Wirkfläche (10a, 20a) auftreffender elektromagnetischer Strahlung auf, wobei der Reflexionsschichtstapel (12, 22) eine alternierende Abfolge aus Absorber-Schichten (14, 24) aus einem ersten Material und Spacer-Schichten (15, 25) aus einem zweiten Material aufweist, und wobei das zweite Material eine Phosphor-Verbindung oder eine Schwefel-Verbindung ist.

Die vorliegende Erfindung betrifft einen Bragg-Reflektor (12) für ein optisches Element einer optischen Anordnung, insbesondere einer Projektionsbelichtungsanlage, mit einer Vielzahl von alternierend angeordneten Schichten (13, 14) mit unterschiedlichem Brechungsindex zur Reflexion von Licht, wobei die Schichten abwechselnd aus einer halbleitenden, binären Verbindung, insbesondere MoP, Ru2Si3 oder YN und Silizium gebildet sind. Außerdem betrifft die Erfindung ein kombiniertes Spiegel- und Filterelement für eine optische Anordnung, insbesondere eine Projektionsbelichtungsanlage, mit einem Substrat (10) und einem auf dem Substrat angeordneten Bragg-Reflektor (12), wie oben beschrieben.

Plasma based radiation sources optimized to emit 13.5 nm Extreme UV radiation also produce a significant amount of light at longer wavelengths. This so called out-of-band (OoB) radiation is detrimental for the imaging capabilities of an EUV lithographic imaging system, particularly the deep ultraviolet (DUV) and ultraviolet (UV) parts of the light (λ=100-400 nm). To suppress these wavelengths while maintaining the high efficiency of the mirror for EUV light, several methods have been developed, including phase-shift gratings (PsG) and anti-reflection layers (SPE layer). PsG’s use the diffraction properties of a quarter-wavelength high multilayer grating to filter out the DUV/UV light, while the SPE layer works as an anti-reflection coating. Both methods have achieved a suppression factor of 10 - 30 around the target wavelength. To achieve a full band suppression effect, a new scheme based on surface pyramid structures was developed. An average suppression ofmore than 10 times can be achieved with a relative EUV efficiency of 89% (compared to standard multilayer (ML)) in theory. Different methods were discussed and their results are presented.

A thermoelectric nanocomposite of Bi0.5Sb1.5Te3 with the C60 fullerene molecules has been synthesized and studied. The fullerene molecules provide the phonons blocking, reducing the lattice thermal conductivity. The reduction of the electrical conductivity is much less than the heat conductivity reduction at a low fullerene content. Therefore, the thermoelectric figure of merit increases up to 25% at 305 K. The thermoelectric properties of the synthesized materials have been analyzed theoretically in the frame of the Boltzmann equation approach. The calculations predict the optimal carrier concentration and C60 content for a maximal value of the thermoelectric figure of merit in a wide temperature range.