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High precision large area PLD of x-ray optical multilayers


Russo, R.E.:
COLA '97. Proceedings of the Fourth International Conference on Laser Ablation
Amsterdam: North-Holland, 1998 (Applied surface science 127/129)
ISSN: 0169-4332
S.451-456 : Ill., Lit.
International Conference on Laser Ablation (COLA) <4, 1997, Monterey Bay/Calif.>
Fraunhofer IWS ()
PLD; nm-Präzisionsschicht; Röntgenoptik; Laserverfahren; Laserchemie; Optik; Multischicht; Nanomaterialien; Grenzfläche

To realize high quality X-ray optical multilayer stacks on large areas a double-beam PLD-source was integrated into a commercial MBE system. Optimization of ablation conditions and film growth regime, resp., for various kinds of homogeneous thin films and multilayer systems has been realized by a reproducible variation of pulse energy and repetition rate of each of the two Nd:YAG-lasers. In addition the lasers can be independently controlled by a predetermined pulse delay. Thus plasma parameters of two plumes generated from locally separated origins can be influenced by the pulse delay of the Nd:YAG-lasers, too. The influence of laser parameters and pulse delay on thin film growth is investigated by the deposition of Ni/C layer stacks. Optimum irradiation conditions are zero delay and moderate pulse energies. Multilayer interface roughnesses on the order of sigma R about 0.1 nm are deduced from high resolution electron microscopy (HREM) - micrographs. The interface roughness increases with higher pulse energy. For changing the pulse delay from tau= 0 ns to tau = 2.5 ms a destruction of the layer stack is observed. Laterally graded Ni/C multilayers showing X-ray optical activity were synthesized with these optimized deposition parameters in the period thickness range from 3 to 5 nm. Average values of thickness gradients typically delta t/delta x about 2 x 10(exp -8) for 4" substrate length in maximum and period thickness variations on the order of sigma t about 0.1 nm are confirmed by grazing incidence X-ray reflectometry and HREM.