RESUMEN
The influence of the number of bilayers on the optical performances of actual X-UV multilayer interferential mirrors (MIMs) has been studied in order to emphasize the experimental restrictions in the designing of "thick" mirrors used for the development of etched multilayer gratings. Several sets of samples (W/C, Mo/Si) with increasing number of bilayers have been manufactured in the very same conditions by means of a sputtering technique. X-ray diffraction characterization at Cu-Kα radiation (λ = 1.54018 Å) exhibits technical constraints in the achievement of multilayer structures with large number of bilayers. We obtain a gradual loss of reflectivity for deposition times greater than 1h 30 min to 2h without significant drift of the MIM's geometrical parameters (period and division parameter). In the same time, absolute reflectivity measurements at Cu-Lα radiation (λ = 1.333 nm) emphasize satisfying optical and spectroscopic performances of W/C thick samples ( 150 bilayers).
RESUMEN
XUV and x-ray scattering by a LiF crystal is measured. The angular distribution of the scattered radiation (ADSR) reveals characteristic features, side peaks or asymmetry. The surface of the sample is statistically characterized by a microdensitometer analysis of electron micrographs resolving the short spatial wavelengths of the surface roughness. This analysis shows that the surface has a large microroughness with an autocovariance function which is Gaussian in its initial portion. The first-order perturbation vector theory of the roughness-induced scattering leads to an interpretation of the ADSR features in terms of the modulation of the surface power spectral density function associated with the microroughness by an optical factor. The possibility of obtaining short scale roughness characterization from XUV or x-ray measurements is discussed.
RESUMEN
Recent sputtering techniques have been used to produce layered synthetic microstructures (LSMs) as dispersing devices for varied applications in x-ray optics and spectroscopy. These analyzers, specially suited for synchrotron radiation, have been mounted in a two-parallel crystal monochromator. In this paper we show the first experimental results obtained with beryl crystals and multilayers for analyzing x-ray spectral distributions transmitted through screens or reflected on mirrors of copper near the L(2) and L(3) absorption edges. The significance of these findings is discussed in terms of comparison with natural and synthetic crystals and of designing a useful dispersing device for x-ray spectroscopy.
RESUMEN
A study was made of the behavior of the photoelectric efficiency of very thin films of calcium-thicknesses between 1 nm and 20 nm-when an electric field was applied to them, of intensity between 2 x 10(3) V and 10(6) V.m(-1), perpendicular to the plane of their substrate. The corresponding work functions and their variations in accordance with the field were determined using Fowler's graphic method. It was seen that when the field increased, the work function relating to the normal photoelectric threshold decreased. This variation depends on the thickness of the thin film; it is greatest for a thickness d(0) of about 5.5 nm. There is a second photoelectric threshold for a thickness less than d(0) even when the field applied perpendicularly to the substrate is zero. The work function Phi(s) relating to it does not vary when the field is increased. When the thickness is greater than d(o), the second threshold no longer exists for a zero applied field; it appears again when the field is higher than a certain value, which is a function of film thickness.
RESUMEN
Thin films of calcium were evaporated under ultrahigh vacuum conditions (pressures less than 5 x 10(-10) Torr) onto quartz substrates to a thickness of 20 nm. The photoelectric yield and hence the work function of the layers were determined as a function of thickness. For film thicknesses greater than 10 nm, the work function was constant with a value of 2.87 +/- 0.06 eV. The work function suows minima at film thicknesses of about 2.5 nm and 5.5 nm. Results from films thicker from 5.5 are a good fit to the Fowler function; for thinner films, the results suggest the existence of a second photoelectric threshold with a corresponding work function ø(s). A theory based on the energy states of the surface electrons is proposed to explain both this second threshold and the ir absorption of thin calcium films.