Alexander V. Vinogradov

Single-shot extreme ultraviolet laser imaging of nanostructures with wavelength resolution

We have demonstrated near-wavelength resolution microscopy in the extreme ultraviolet. Images of 50 nm diameter nanotubes were obtained with a single ~1 ns duration pulse from a desktop-size 46.9 nm laser. We measured the modulation transfer function of the microscope for three different numerical aperture zone plate objectives, demonstrating that 54 nm half-period structures can be resolved. The combination of near-wavelength spatial resolution and high temporal resolution opens myriad opportunities in imaging, such as the ability to directly investigate dynamics of nanoscale structures.

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).

Thermal stability of soft x-ray Mo–Si and MoSi 2 -Si multilayer mirrors

The thermal stability of Mo-Si multilayers prepared by magnetron sputtering is studied. It is found that degradation of x-ray reflectivity of Mo-Si multilayers under heat loading is connected with the roughening of Mo-Si interfaces and the formation of compounds Mo(x)Si(y),. To avoid these degradation mechanisms we fabricated and tested MoSi(2)-Si multilayers under heat loading. The MoSi(2)-Si multilayer appeared to be much more stable both in period and x-ray reflectivity because of thermodynamic equilibrium of the components MoSi(2) and Si at the interface. The working temperature of MoSi(2)-Si multilayers reaches 1000 K.

Efficient method for the determination of extreme-ultraviolet optical constants in reactive materials: application to scandium and titanium

The chemical reaction of a sample with atmospheric gases causes a significant error in the determinantion of the complex refractive index n = 1 - delta + ibeta in the extreme-ultraviolet region. The protection of samples removes this effect but hampers the interpretation of measurements. To overcome this difficulty, we derive the exact dependences on film thickness of the reflectivity and transmissivity of a protected film. These dependences greatly simplify the determination of delta and beta when the spectra of several films with different thickness and identical protection are measured. They also allow the verification of the delta(omega) obtained from the Kramers-Kronig relation and even make the Kramers-Kronig method unnecessary in many cases. As a practical application, the optical constants of Sc and Ti are determined at h omega = 18-70 eV and 18-99 eV, respectively. The essential feature of our experimental technique is deposition of a film sample directly on a silicon photodiode that allows easy operation with both thin (approximately 10-nm) and thick (approximately 100-nm) films. The comparison of calculated reflectivities of Si-Sc multilayers with the measured values shows the high accuracy of the determined delta(omega) and beta(omega).

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.

Synthesis and measurement of normal incidence X-ray multilayer mirrors optimized for a photon energy of 390 eV

Abstract The problems inherent in the fabrication of short period multilayer mirrors are discussed and results of the synthesis of multilayer structures with nanometer period are presented. The shortest period observed is 13 A for WSi and WB 4 C sputtered multilayers. Measurements of near normal incidence reflectivity at λ = 31–32A are presented for WSc multilayers with a period approximately 16 A. The measured reflectivity reaches a maximum of 3.3% and is in good agreement with theoretical modeling after the inclusion of interfacial roughness.

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.