Igor A. Artioukov

Nanoimaging with a compact extreme-ultraviolet laser

Images with a spatial resolution of 120-150 nm were obtained with 46.9 nm light from a compact capillary-discharge laser by use of the combination of a Sc-Si multilayer-coated Schwarzschild condenser and a free-standing imaging zone plate. The results are relevant to the development of compact extreme-ultraviolet laser-based imaging tools for nanoscience and nanotechnology.

Focusing of a tabletop soft-x-ray laser beam and laser ablation

We focused the beam of a high-repetition-rate capillary-discharge tabletop laser operating at a wavelength of 46.9 nm, using a spherical Si/Sc multilayer mirror. The energy densities significantly exceeded the thresholds for the ablation of metals. Single-shot laser ablation patterns were used in combination with ray-tracing computations to characterize the focused beam. The radiation intensity within the 2-mum -diameter central region of the focal spot was estimated to be approximately 10(11)W/cm(2), with a corresponding energy density of ~100 J/cm(2).

Reflection mode imaging with nanoscale resolution using a compact extreme ultraviolet laser

We report the demonstration of reflection mode imaging of 100 nm-scale features using 46.9 nm light from a compact capillary-discharge laser. Our imaging system employs a Sc/Si multilayer coated Schwarzschild condenser and a freestanding zone plate objective. The reported results advance the development of practical and readily available surface and nanostructure imaging tools based on the use of compact sources of extreme ultraviolet light.

Schwarzschild soft-x-ray microscope for imaging of nonradiating objects

A soft-x-ray optical system based on multilayer mirrors was designed and fabricated for the production of magnified images of micro-objects with a spatial resolution of ~0.2 μm at a wavelength λ ≈ 20 nm. The system consists of a laser-produced plasma source, a condenser mirror, a 20× Schwarzschild objective, a filter set, and a detector. The quality of the x-ray optics and the precision of the system adjustment enabled us to achieve, for the first time to our knowledge, ~0.2-μm resolution using the full aperture (numerical aperture 0.2) of the objective and a single shot of a frequency-doubled Nd laser (pulse energy ~0.5 J, pulse duration ~1.5 ns).

Determination of XUV optical constants by reflectometry using a high-repetition rate 46.9-nm laser

We report the measurement of the optical constants of Si, GaP, InP, GaAs, GaAsP, and Ir at a wavelength of 46.9 nm (26.5 eV). The optical constants were obtained from the measurement of the variation of the reflectivity as a function of angle utilizing, as an illumination source, a discharge pumped 46.9-nm table-top laser operated at a repetition rate of 1 Hz. These measurements constitute the first application of an ultrashort wavelength laser to materials research.

Damage to extreme-ultraviolet Sc/Si multilayer mirrors exposed to intense 46.9-nm laser pulses

The damage threshold and damage mechanism of extreme-ultraviolet Sc/Si multilayer mirror coatings are investigated with focused nanosecond pulses at 46.9-nm radiation from a compact capillary-discharge laser. Damage threshold fluences of approximately 0.08 J/cm2 are measured for coatings deposited on both borosilicate glass and Si substrates. The use of scanning and transmission electron microscopy and small-angle x-ray diffraction techniques reveals the thermal nature of the damage mechanism. The results are relevant to the use of newly developed high-flux extreme-ultraviolet sources in applications.

Sequential single-shot imaging of nanoscale dynamic interactions with a table-top soft x-ray laser

We demonstrate the first real-space recording of nanoscale dynamic interactions using single-shot soft x-ray (SXR) full-field laser microscopy. A sequence of real-space flash images acquired with a table-top SXR laser was used to capture the motion of a rapidly oscillating magnetic nanoprobe. Changes of 30 nm in the oscillation amplitude were detected when the nanoprobe was made to interact with stray fields from a magnetic sample. The table-top visualization of nanoscale dynamics in real space can significantly contribute to the understanding of nanoscale processes and can accelerate the development of new nanodevices.

Structure, thermal stability, and reflectivity of Sc/Si and Sc/W/Si/W multilayer x-ray mirrors

Processes going on at elevated temperatures between Sc and Si layers in Sc/Si coatings are studied by X-ray scattering and cross-sectional transmission electron microscopy. It is shown that the W layers of 0.5-0.8 nm placed at Sc-Si interfaces form effective barriers preventing the penetration of Si into Sc. The effects of Si-Sc diffusion and W-barriers on the reflectivity of coatings are calculated in good agreement with experimental results. Presented measurements show that the Sc/W/Si/W multilayers with the period of 20.5 nm fabricated by dc-magnetron sputtering possess thermal stability up to 250 C and the normal incidence reflectivity of 24% at wavelengths about 40 nm.

Extreme UV optical constants of rare-earth metals free from effects of air contamination

The determination of EUV optical constants in rare-earth metals is much hampered by the high reactivity and easy air contamination of these materials. The most difficult regions are a long wavelengths part of the EUV interval and the vicinity of absorption edges. In this study the optical constants of La and Tb are determined in a wide energy interval 14-400 eV. The study is performed by our recent method, which is suitable for reactive materials and for intervals around the absorption edges of elements. The samples are identically protected films with thickness ~ 10 nm or ~ 100 nm, which are deposited on silicon photodiodes. Mathematical treatment separates the contributions of a capping layer and a rare-earth metal and provides data which are free from the effects of air contamination. The precision and behavior of optical constants, as well as the parameters of the O2,3 and N4,5 edges in La and Tb are analyzed.

Effects of a near-surface transition layer on x-ray reflection and scattering.

The influence of smooth (not step-like) variation of the dielectric function near a surface on the reflectivity and scattering of x rays is investigated theoretically with the model function ε(z) = 1 - 0.5(1 - ε+)(l + tanh(z/(2L))) taken as an example. It is shown that the presence of the transition layer can essentially change the shape of the differential scattering intensity diagram, especially when the incidence angle of the x-ray beam is greater than the critical angle of the total external reflection (TER). The results of measurements of the x-ray reflection coefficient and the differential scattered intensity are discussed. The model of the near-surface transition layer is shown to describe quantitatively the specific features of experimental curves for the incident beam beyond the TER region, whereas these experimental data cannot be explained in the framework of a step-like model of the dielectric function, taking into account the scattering from surface roughness.