The use of lithium fluoride ͑LiF͒ crystals and films as imaging detectors for EUV and soft-x-ray radiation is discussed. The EUV or soft-x-ray radiation can generate stable color centers, emitting in the visible spectral range an intense fluorescence from the exposed areas. The high dynamic response of the material to the received dose and the atomic scale of the color centers make this detector extremely interesting for imaging at a spatial resolution which can be much smaller than the light wavelength. Experimental results of contact microscopy imaging of test meshes demonstrate a resolution of the order of 400 nm. This high spatial resolution has been obtained in a wide field of view, up to several mm 2 . Images obtained on different biological samples, as well as an investigation of a soft x-ray laser beam are presented. The behavior of the generated color centers density as a function of the deposited x-ray dose and the advantages of this new diagnostic technique for both coherent and noncoherent EUV sources, compared with CCDs detectors, photographic films, and photoresists are discussed.

The photopyroelectric effect has been used to measure simultaneously specific heat (c), thermal conductivity (k) and thermal diffusivity (α) at low temperatures. A calibration procedure which allows the use of a pyroelectric transducer at low temperatures is described. Simultaneous measurements of c, k, and α over a high Tc superconducting phase transition are reported. © 1990 Springer-Verlag

͑BaCuO 2 ͒ 2 /͑CaCuO 2 ͒ n superconducting superlattices have been grown by pulsed laser deposition for n ranging from 1 to 6. The critical temperature was found to depend strongly on the growth conditions. A maximum T c value of about 80 K ͑zero resistance temperature͒ was found for superlattices grown at high oxygen pressure ( P O 2 Ӎ0.8 mbar) and relatively high temperature (T g Ӎ600°C). The dependence of T c on the number n of CaCuO 2 layers ͑for superlattices grown exactly in the same conditions͒ was investigated. T c versus n showed the expected behavior with a maximum T c value of 80 K for nϭ2 -3. However, such value is somewhat lower than that expected for a cuprate structure containing 3-4 CuO 2 planes and having an optimum carrier concentration. Two possible explanations for this effect can be envisaged. The first one deals with the chemistry of the ''charge reservoir'' block, the second one with the special role of interelectron interaction in these highly disordered artificial structures. Finally, it is shown that, taking into account the degree of disorder, a shift of T c of about 20 K relative to the bulk value T c 0 , consistent with the microscopic parameters of these materials, can be foreseen. ͓S0163-1829͑98͒51334-3͔Phys. ͑to be published͒. 18 M. Randeria ͑unpublished͒. RAPID COMMUNICATIONS R8928PRB 58 G. BALESTRINO et al.

Spectra in the 7.10 to 8.60 A range from highly charged copper ions are observed from three different laser-produced plasmas (LPPs). The LPPs are formed by a 15-ns Nd:glass laser pulse (type I: E(pulse)=1-8 J, lambda=1.064 microm), a 1-ps Nd:glass laser pulse (type II: E(pulse)=1 J, lambda=1.055 microm), and a 60-fs Ti:sapphire laser pulse (type III: E(pulse)=800 mJ, lambda=790 nm). The spectra of high-n (n

High quality epitaxial films of the 'infinite layer' (IL) compound Sr, Ca, -, CuO, (x=O-l) have been grown by pulsed laser deposition on NdGaO, (1 10) substrates, thus including the last member of this series CaCuO,, for the first time, to our knowledge. The quality of films varied with the composition: higher quality films were obtained for x = 0 and 0.1. The experimental results have been explained by taking into account the lattice match between film and substrate: a better match results in a better film quality. A very good match is obtained on NdGaO, substrates for IL films with small or zero Sr content. Attempts to grow IL films were also carried out on SrTiO, and LaAIO, substrates. On SrTiO, substrates it was not possible to grow IL films in the absence of Sr, while on LaAIO, substrates no IL films could be grown at all.In the case of SrTiO,, the lattice match is good only for Sr-rich films, while in the case of LaA103, no good match can be obtained for any composition. Such substrate effects are not unexpected due to the importance of the substrate for the pseudomorphic stabilization of the otherwise unstable IL structure.