Single layers of MgF<sub>2</sub> and LaF<sub>3</sub> were deposited upon superpolished fused-silica and CaF<sub>2</sub> substrates by ion-beam sputtering (IBS) as well as by boat and electron beam (e-beam) evaporation and were characterized by a variety of complementary analytical techniques. Besides undergoing photometric and ellipsometric inspection, the samples were investigated at 193 and 633 nm by an optical scatter measurement facility. The structural properties were assessed with atomic-force microscopy, x-ray diffraction, TEM techniques that involved conventional thinning methods for the layers. For measurement of mechanical stress in the coatings, special silicon substrates were coated and analyzed. The dispersion behavior of both deposition materials, which was determined on the basis of various independent photometric measurements and data reduction techniques, is in good agreement with that published in the literature and with the bulk properties of the materials. The refractive indices of the MgF<sub>2</sub> coatings ranged from 1.415 to 1.440 for the wavelength of the ArF excimer laser (193 nm) and from 1.435 to 1.465 for the wavelength of the F<sub>2</sub> excimer laser (157 nm). For single layers of LaF<sub>3</sub> the refractive indices extended from 1.67 to 1.70 at 193 nm to ~1.80 at 157 nm. The IBS process achieves the best homogeneity and the lowest surface roughness values (close to 1 nm<sub>rms</sub>) of the processes compared in the joint experiment. In contrast to MgF<sub>2</sub> boat and e-beam evaporated coatings, which exhibit tensile mechanical stress ranging from 300 to 400 MPa, IBS coatings exhibit high compressive stress of as much as 910 MPa. A similar tendency was found for coating stress in LaF<sub>3</sub> single layers. Experimental results are discussed with respect to the microstructural and compositional properties as well as to the surface topography of the coatings.
© 2002 Optical Society of America
Detlev Ristau, Stefan Günster, Salvador Bosch, Angela Duparré, Enrico Masetti, Josep Ferré-Borrull, George Kiriakidis, Francesca Peiró, Etienne Quesnel, and Alexander Tikhonravov, "Ultraviolet Optical and Microstructural Properties of MgF2 and LaF3 Coatings Deposited by Ion-Beam Sputtering and Boat and Electron-Beam Evaporation," Appl. Opt. 41, 3196-3204 (2002)