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In the first part of this article we experimentally show that contrast between the very thin layers of La and B enables close to theoretical reflectance. The reflectivity at 6.8 nm wavelength was measured from La/B multilayer mirrors with period thicknesses ranging from 3.5 to 7.2 nm at the appropriate angle for constructive interference. The difference between the measured reflectance and the reflectance calculated for a perfect multilayer structure decreases with increasing multilayer period. The reflectance of the multilayer with the largest period approaches the theoretical value, showing that the optical contrast between the very thin layers of these structures allows to experimentally access close to theoretical reflectance. In the second part of the article we discuss the structure of La/B and LaN/B multilayers. This set of multilayers is probed by hard X-rays (lambda = 0.154 nm) and EUV radiation (lambda = 6.8 nm). The structure is reconstructed based on a simultaneous fit of the grazing incidence hard X-ray reflectivity and the EUV reflectivity curves. The reflectivity analysis of the La/B and LaN/B multilayer mirrors shows that the lower reflectance of La/B mirrors compared to LaN/B mirrors can be explained by the presence of 5% of La atoms in the B layer and 63% of B in La layer. After multi-parametrical optimization of the LaN/B system, including the nitridation of La, the highest near normal incidence reflectivity of 57.3% at 6.6 nm wavelength has been measured from a multilayer mirror, containing 175 bi-layers. This is the highest value reported so far. (C) 2013 Optical Society of America

Lithography based on the wavelength of 6.x nm is considered to be a potential extension of the current 13.5 nm EUV lithography. Light sources might be based on Tb or Gd. The published spectra of plasmas created from these materials show highest intensities at 6.5 and 6.8 nm respectively. Multilayer mirrors (MLMs) based on La and B show the highest optical contrast for the 6.6-7 nm wavelength range and a maximum reflectance at 6.64 nm, where the B absorption is minimal. It is not possible to design high reflective B-based mirrors for 6.5 nm because this would be below the B-K absorption edge. In theory the reflectivity of La/B MLMs at 6.8 nm is only a few percent lower than at the optimal wavelength of 6.64 nm, but measurements of real multilayer mirrors show a significantly larger reduction of reflectivity at 6.8 nm. The origin of this larger drop is the reduced optical contrast of the deposited La/B mirror with respect to theoretical case. In the presentation we will discuss how the multilayer structure influences its reflectivity profile and the ways to optimize La/B mirrors for 6.8 nm.

in thesis

The growth of low-temperature In/sub 1-x/Mn/sub x/As quantum dots (QD) on low-temperature GaAs(001) was investigated. Three different growth conditions with variable As/sub 2/ flux, Mn:In flux ratio and QD layer thickness were studied by atomic force microscopy and transmission electron microscopy. All three conditions generated In/sub 1-x/Mn/sub x/As QD with a cubic crystal structure. It is shown that an excess of As/sub 2/ combined with a flux ratio of Mn:In=0.10 and a limited deposited thickness of 5.4ML In/sub 0.59/Mn/sub 0.41/As are the best conditions to obtain symmetric QD coherent to the substrate. Photoluminescence analysis performed on the latter samples showed a narrow band near 1100nm, indicating 3D-confinement of the dots. The magnetic properties of a multilayer of 5.4ML In/sub 0.59/Mn/sub 0.41/As QD were analyzed by magneto-optical Kerr effect at 1.6K. No magnetization could be detected, whereas measurements performed on a multilayer of 2.4ML In/sub 0.59/Mn/sub 0.41/As quantum wells indicated ferromagnetism. The absence of ferromagnetism for the QD is assigned to the superparamagnetism of the islands and the low Mn:In ratio used for the growth. It is suggested that these growth conditions are generating QD with a lower chance for interdot exchange interaction within a layer. [All rights reserved Elsevier]

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