Ion-beam figuring (IBF) capable of providing sub-nanometer shape accuracy, is often used for fabrication of ultra-precise x-ray optics. However, in the case of gratings, the optical surface may degrade during the following ruling procedure or etching processes. This leads to the necessity for a post-ruling surface correction to recover the ultra-precise shape of the optics, while the IBF substrate finish prior the ruling could be omitted. If so, the gratings can be made using relatively inexpensive substrates produced with conventional mechanical or chemical-mechanical polishing with medium optical surface quality and then processed with a post-ruling IBF to bring the shape to the sub-nanometer accuracy. The key question is whether the grating grooves survive the IBF treatment. In this work we investigate the possibility of post-production IBF correction for lamellar x-ray gratings. A 200 lines/mm lamellar grating made using a lambda/20 Si substrate was processed with IBF to achieve a sub-nanometer flat optical surface of the final grating. We report on impact of the IBF process on groove profile, surface roughness, and diffraction efficiency of the grating.
We developed a new process for low blaze angle (LBA) diffraction gratings for x-ray applications. The process provides a perfect shape of the saw-tooth grooves and preserves high precision of the optical surface of the grating substrate. An LBA grating is made by double-replication of a master blazed grating by nanoimprinting followed by a transfer of the polymer replica into a Si grating substrate by a plasma etch. The plasma etch process optimized for a certain etch rate ratio for the polymer and Si provides a reduction of the groove depth and the blaze angle down to 0.2 degrees. The reduction results in an improvement of surface roughness compared to the master grating and mitigate process non-uniformity owing to the scaling down effect. We investigate the quality and performance of the fabricated LBA gratings and evaluate process accuracy and reproducibility. This work was supported by the US Department of Energy under contract number DE-AC02-05CH11231.
We suggest a new method of making ultra-low blaze angle gratings for synchrotron application. The method is based on reduction of the blaze angle of a master grating by replication followed by a plasma etch. A master blazed grating with a relatively large blaze angle is fabricated by anisotropic wet etching of a Si single crystal substrate. The surface of the master grating is replicated by a polymer material on top of a quartz substrate by nanoimprinting and then transferred into quartz by a plasma etch. Then a 2 nd nanoimprint step is applied to transfer the saw-tooth surface into a resist layer on top of a Si grating substrate. The plasma etch through the patterned resist layer provides transfer of the grooves into the Si substrate and results in reduction of the blaze angle due to the difference in etch rates of the resist and Si. We investigated the impact of the replication process on the groove shape, facet surface roughness, and diffraction efficiency of the fabricated 200 lines/mm low blaze angle grating.
Low groove density gratings with blaze angles as low as 0.1‡ are required for plane grating monochromators for x-ray synchrotron and Free Electron Laser applications. To achieve so small a blaze angles we developed a process of reduction of the blaze angle of a coarse Si grating fabricated by anisotropic wet etching. The coarse grating with a blaze angle of 4° is planarized by a polymer layer and then plasma etching is applied to remove the polymer and underlying silicon material. The appropriate ratio of etch rates of Si and the polymer material provides reduction of the groove depth and the blaze angle. We developed a set of reduction recipes which provide blaze angle reduction down to 0.04° with high accuracy and which preserves the perfect triangular shape of the grooves. The ultra-low blaze angle grating coated with a Mo/Si multilayer exhibits a record diffraction efficiency of 58% due to the perfect match of the groove depth with the multilayer d-spacing. This opens up wide possibilities for making highly accurate and efficient diffraction gratings for tender x-ray, free electron laser, and EUV lithography applications. The low blaze angle gratings have a perfect triangular groove profile and highly smooth surfaces of the blazed facets which ensures high diffraction efficiency of the x-ray gratings.
Planarization is important in many areas of nanostructure fabrication. Here we describe a new process for planarization saw-tooth surface of blazed gratings used for the monochromatization of light, but the applications should be much wider. Such gratings consist of relatively wide and very shallow triangular grooves with slanted facets which are machined with nanometer accuracy. The process of making such gratings includes planarization of a relatively coarse saw-tooth surface with micron deep grooves following by a plasma etch which provides reduction of the facet angle and hence groove depth by a factor of 10 - 100. To achieve high quality of the final grating the planarization step should provide a flat surface over the grating facets with sub-nanometer level planarity. We investigated planarization of coarse saw-tooth surfaces with a groove width of 10 μm and a facet angle of 4° by a polymer coating spun on the grating. The optimized planarization procedure provides 100% planarization even on these highly structured surfaces.
High diffraction efficiency of a grating can be achieved by use of inclined facets. This type of grating, normally referred to as a blazed grating, has facets that are arranged so that there is an equal angle on the incident and diffracted sides, and thus can be thought of as reflecting light into a particular order. Conventionally blazed gratings are made by diamond mechanical ruling, or more recently by anisotropic etching of silicon. However it is difficult with these processes to achieve a very low blaze angle as well as to precisely control it. This has become particularly important for applications involving Free Electron Lasers, where a very grazing incidence angle has to be used to avoid damage, and for extension of the working range up to high energies on synchrotrons. In each case, the very small angular size of the source results in a low line density, which in turn results in a low blaze angle. In high groove density multilayer blazed gratings, high precision for the blaze angle is required to match the groove depth to the multilayer d-spacing. We have developed a process which gives the possibility for alteration of the groove profile of a fabricated grating and tune the blaze angle with high precision. The method is based on planarization of the grating grooves by deposition of a SiO2 sacrificial layer followed by smoothing the surface with Ar plasma etch. Finally, a reactive plasma etching is used to etch off the sacrificial layer together with the surface layer of the Si grating. The optimized plasma etching provides a certain ratio of etch rates of the sacrificial layer and Si and results in reduction of the blaze angle down to a desired value.
Stochastic effects in extreme ultraviolet lithography are contributed by the EUV optical speckle and diffusion chemistry of the photoresist. These cause line edge roughness (LER) in the etched features, shrinking the process window at the sub-20nm lithography node. We explore possibilities of utilizing the speckle for optical metrology and resist characterization by measuring the latent image of the EUV light on photoresist. The latent image on a standard photoresist measured using atomic force microscopy is shown to linearly depend on the aerial image intensity within a specific dose range, hence serving as an in-situ imaging modality to measure the EUV aerial image without a camera. Potential applications include EUV wavefront measurement, resist characterization, and LER engineering.
We developed a process for fabrication of ultra-precise blazed diffraction gratings for high resolution x-ray spectroscopy. The process based on nanofabrication techniques provides high fidelity for groove placement, high groove density, and perfect saw-tooth profile of grating grooves. A grating pattern is recorded on a quartz plate by use of e-beam lithography with a nanometer scale accuracy over the grating size. The pattern is transferred to a grating substrate by large area nanoimprint and then a hard Cr mask is formed via a lift-off process. Fidelity of the transfer step in terms of groove placement accuracy was investigated by differential wavefront interferometry. Anisotropic wet etch was applied to the patterned Si single crystal substrate to shape triangular grooves. Fabrication of a blazed grating of area 120 mm × 30 mm with groove density of 2000 lines/mm was demonstrated.
A blazed diffraction grating for the EUV lithography Beamline 12.0.1 of the Advanced Light Source has been
fabricated using optical direct write lithography and anisotropic wet etching technology. A variable line spacing
pattern was recorded on a photoresist layer and transferred to a hard mask layer of the grating substrate by a plasma
etch. Then anisotropic wet etching was applied to shape triangular grating grooves with precise control of the ultralow
blaze angle. Variation of the groove density along the grating length was measured with a Long Trace Profiler
(LTP). Fourier analysis of the LTP data confirmed high groove placement accuracy of the grating. The grating
coated with a Ru coating demonstrated diffraction efficiency of 69.6% in the negative first diffraction order which is
close to theoretical efficiency at the wavelength of 13.5 nm. This work demonstrates an alternative approach to
fabrication of highly efficient and precise x-ray diffraction gratings with ultra-low blaze angles.
A Variable Line Spacing (VLS) diffraction grating has been fabricated using an optical direct write technique. This
grating is now in use at the Advanced Light Source, in beamline 12.0.1, delivering light for EUV lithography. Direct
Write Lithography (DWL) with focused light at λ = 442 nm was used for the first time to record a VLS grating pattern
on a substrate coated with a photoresist. The pattern was transferred to the Si substrate surface using reactive plasma
etch. Precision of groove placement was verified by wavefront measurements of a witness grating recorded
simultaneously with the VLS pattern. Atomic force microscope measurements confirmed near ideal groove shape and
high smoothness of the grating grooves. The grating coated with a Ru coating demonstrated diffraction efficiency of
39.5% in the negative first diffraction order which corresponds to theoretical efficiency at the wavelength of 13.5 nm.
This work validates the DWL approach as a promising technique for advanced grating fabrication.
Fabrication of diffraction grating for x-rays is a very challenging problem due to the exacting requirements of surface quality, groove position, and groove profile. Traditional fabrication techniques have significant limitations and do not cover all the necessary requirements. For example, classical holographic recording is limited in the type of groove patterns that can be produced. This is particularly important in the design of wide aperture high resolution spectrometers, where aberration correction using complex groove patterns is necessary. We are pioneering the use of direct-write mask-less optical lithography to make grating patterns of arbitrary complexity. In this work we report on the first results from our direct-write mask-less approach, including quality assessment of the patterns using interferometric techniques.
By methods of cross-sectional transmission electron microscopy and small-angle x-ray scattering (λ=0.154 nm ) the influence of Ar gas pressure (1 to 4 mTorr) on the growth of amorphous interfaces in Mo/Si multilayers (MLs) deposited by DC magnetron sputtering is studied. The significant reduction in the ML period, which is evident as a volumetric contraction, is observed in MLs deposited at Ar pressure where the mean-free path for the sputtered atoms is comparable with the magnetron-substrate distance. Some reduction in the thickness of the amorphous interlayers with Ar pressure increase is found, where the composition of the interlayers is enriched with molybdenum. The interface modification resulted in an increase in EUV reflectance of the Mo/Si MLs.
Impact of Ar gas pressure (1-4 mTorr) on the growth of amorphous interlayers in Mo/Si multilayers deposited by
magnetron sputtering was investigated by small-angle x-ray scattering (λ=0.154 nm) and methods of cross-sectional
transmission electron microscopy. Some reduction of thickness of the amorphous inter-layers with Ar pressure increase
was found, while composition of the layers was enriched with molybdenum. The interface modification resulted in raise
of EUV reflectance of the Mo/Si multilayers.
Diffraction gratings with high efficiency and high groove density are required for EUV and soft x-ray spectroscopy
techniques (such as Resonant Inelastic X-ray Scattering, RIXS) designed for state-of-the-art spectral resolution and
throughput. A multilayer coated blazed grating (MBG) fabricated by deposition of a multilayer on a saw-tooth substrate
could address these challenges. In order to obtain high diffraction efficiency one should provide perfect triangular
grooves on a substrate and perfect replication of the groove profile during the multilayer deposition. However,
multilayers trend to smooth out the corrugated surface of the substrates, resulting in the main limiting factor for
efficiency of ultra-dense MBGs. Understanding of the growth of multilayers on saw-tooth substrates is a key for further
grating improvement. In this work we investigate growth behavior of Al/Zr multilayers on saw-tooth substrates with a
groove density of 10,000 lines/mm. We apply existing growth models to describe an evolution of Power Spectral
Density functions of a grating surface during the multilayer deposition, and identify a main smoothing mechanism. We
found that growth of flat multilayers is well modeled with surface diffusion caused by surface curvature as a main
relaxation mechanism, while growth of the multilayer on saw-tooth substrates obeys different kinetics. Limitations of the
linear approach and possible model improvements by accounting for an additional component of the surface diffusion
flux, caused by a gradient of adatom concentration on a corrugated surface are discussed.
KEYWORDS: Modulation transfer functions, Calibration, Transmission electron microscopy, Scanning electron microscopy, Electron microscopes, Binary data, Interferometers, Profilometers, Spatial frequencies, Microscopes
A modulation transfer function (MTF) calibration method based on binary pseudorandom (BPR) gratings and arrays has been proven to be an effective MTF calibration method for interferometric microscopes and a scatterometer. Here we report on a further expansion of the application range of the method. We describe the MTF calibration of a 6 in. phase shifting Fizeau interferometer. Beyond providing a direct measurement of the interferometer's MTF, tests with a BPR array surface have revealed an asymmetry in the instrument's data processing algorithm that fundamentally limits its bandwidth. Moreover, the tests have illustrated the effects of the instrument's detrending and filtering procedures on power spectral density measurements. The details of the development of a BPR test sample suitable for calibration of scanning and transmission electron microscopes are also presented. Such a test sample is realized as a multilayer structure with the layer thicknesses of two materials corresponding to the BPR sequence. The investigations confirm the universal character of the method that makes it applicable to a large variety of metrology instrumentation with spatial wavelength bandwidths from a few nanometers to hundreds of millimeters.
KEYWORDS: Modulation transfer functions, Transmission electron microscopy, Scanning electron microscopy, Calibration, Binary data, Interferometers, Electron microscopes, Silicon, Spatial frequencies, Interferometry
A modulation transfer function (MTF) calibration method based on binary pseudo-random (BPR) gratings and arrays
[Proc. SPIE 7077-7 (2007), Opt. Eng. 47(7), 073602-1-5 (2008)] has been proven to be an effective MTF calibration
method for a number of interferometric microscopes and a scatterometer [Nucl. Instr. and Meth. A 616, 172-82 (2010].
Here we report on a significant expansion of the application range of the method. We describe the MTF calibration of a
6 inch phase shifting Fizeau interferometer. Beyond providing a direct measurement of the interferometer's MTF, tests
with a BPR array surface have revealed an asymmetry in the instrument's data processing algorithm that fundamentally
limits its bandwidth. Moreover, the tests have illustrated the effects of the instrument's detrending and filtering
procedures on power spectral density measurements. The details of the development of a BPR test sample suitable for
calibration of scanning and transmission electron microscopes are also presented. Such a test sample is realized as a
multilayer structure with the layer thicknesses of two materials corresponding to BPR sequence. The investigations
confirm the universal character of the method that makes it applicable to a large variety of metrology instrumentation
with spatial wavelength bandwidths from a few nanometers to hundreds of millimeters.
Multilayer coated blazed gratings with high groove density are the best candidates for use in high resolution EUV and
soft x-ray spectroscopy. Theoretical analysis shows that such a grating can be potentially optimized for high dispersion
and spectral resolution in a desired high diffraction order without significant loss of diffraction efficiency. In order to
realize this potential, the grating fabrication process should provide a perfect triangular groove profile and an extremely
smooth surface of the blazed facets. Here we report on recent progress achieved at the Advanced Light Source (ALS) in
fabrication of high quality multilayer coated blazed gratings. The blazed gratings were fabricated using scanning beam
interference lithography followed by wet anisotropic etching of silicon. A 200 nm period grating coated with a Mo/Si
multilayer composed with 30 bi-layers demonstrated an absolute efficiency of 37.6% in the 3rd diffraction order at 13.6
nm wavelength. The groove profile of the grating was thoroughly characterized with atomic force microscopy before and
after the multilayer deposition. The obtained metrology data were used for simulation of the grating efficiency with the
vector electromagnetic PCGrate-6.1 code. The simulations showed that smoothing of the grating profile during the
multilayer deposition is the main reason for efficiency losses compared to the theoretical maximum. Investigation of the
grating with cross-sectional transmission electron microscopy revealed a complex evolution of the groove profile in the
course of the multilayer deposition. Impact of the shadowing and smoothing processes on growth of the multilayer on the
surface of the sawtooth substrate is discussed.
The major problem of measurement of a power spectral density (PSD) distribution of surface heights with surface profilometers arises due to the unknown modulation transfer function (MTF) of the instruments, which tends to distort the PSD at higher spatial frequencies. The special mathematical properties of binary pseudo-random patterns make them an ideal basis for developing MTF calibration test surfaces. Two-dimensional binary pseudo-random arrays have been fabricated and used for the MTF calibration of the MicroMapTM-570 interferometric microscope with all available objectives. An investigation into the effects of fabrication imperfections on the quality of the MTF calibration and a procedure for accounting for such imperfections are presented.
We report on recent progress in developing diffraction gratings which can potentially provide extremely high spectral
resolution of 105-106 in the EUV and soft x-ray photon energy ranges. Such a grating was fabricated by deposition of a
multilayer on a substrate which consists of a 6-degree blazed grating with a high groove density. The fabrication of the
substrate gratings was based on scanning interference lithography and anisotropic wet etch of silicon single crystals. The
optimized fabrication process provided precise control of the grating periodicity, and the grating groove profile, together
with very short anti-blazed facets, and near atomically smooth surface blazed facets. The blazed grating coated with 20
Mo/Si bilayers demonstrated a diffraction efficiency in the third order as high as 33% at an incidence angle of 11° and
wavelength of 14.18 nm. This work was supported by the US Department of Energy under contract number DE-AC02-05CH11231.
The major problem of measurement of a power spectral density (PSD) distribution of the surface heights with surface
profilometers arises due to the unknown Modulation Transfer Function (MTF) of the instruments. The MTF tends to
distort the PSD at higher spatial frequencies. It has been suggested [Proc. SPIE 7077-7, (2007), Opt. Eng. 47 (7),
073602-1-5 (2008)] that the instrumental MTF of a surface profiler can be precisely measured using standard test
surfaces based on binary pseudo-random (BPR) patterns. In the cited work, a one dimensional (1D) realization of the
suggested method based on use of BPR gratings has been demonstrated. Here, we present recent achievements made in
fabricating and using two-dimensional (2D) BPR arrays that allow for a direct 2D calibration of the instrumental MTF.
The 2D BPRAs were used as standard test surfaces for 2D MTF calibration of the MicromapTM-570 interferometric
microscope with all available objectives. The effects of fabrication imperfections on the efficiency of calibration are also
discussed.
State of the art soft x-ray spectroscopy techniques like Resonant Inelastic X-ray Scattering (RIXS) require diffraction gratings which can provide extremely high spectral resolution of 105-106. This problem may be addressed with a sliced multilayer grating with an ultra-high groove density (up to 50,000 mm-1) proposed in the recent publication [Voronov, D. L., et al., Proc. SPIE 6705, 67050E (2007)]. It has been suggested to fabricate such a grating by deposition of a soft x-ray multilayer on a substrate which is a blazed saw-tooth grating (echellette) with low groove density. Subsequent polishing applied to the coated grating removes part of the coating and forms an oblique-cut multiline structure that is a sliced multilayer grating. The resulting grating has a short-scale periodicity of lines (bilayers), which is defined by the multilayer period and the oblique-cut angle. We fabricated and tested a Sc/Si multilayer sliced grating suitable for EUV applications, which is a first prototype based on the suggested technique. In order to fabricate an echellette substrate, we used anisotropic KOH etching of a Si wafer. The etching regime was optimized to obtain smooth and flat echellette facets. A Sc/Si multilayer was deposited by dc-magnetron sputtering, and after that it was mechanically polished using a number of diamond pastes. The resulting sliced grating prototype with ~270 nm line period has demonstrated a dispersive ability in the 41-49 nm photon wavelength range with a diffraction efficiency of ~7% for the optimized 38th order assigned to the echellette grating of 10 μm period.
The paper deals with the recent progress in fabrication of the graded multilayer mirrors to be used in a 21X Schwarzschild objective operating at the wavelengths about 4.5 nm ("carbon window" region). The graded Co/C reflective multilayer coatings were fabricated using DC-magnetron sputtering. Mask-assisted deposition was used to
create the required radial variation of the multilayer period. Accuracy of the multilayer's parameter measurements and quality of
nm-scale layer deposition were improved significantly with application of a number of new methods and approaches. The soft X-ray measurements were conducted at the ALS 6.3.2 beamline to quantify the graded periods on concave and convex mirrors of the Schwarzschild objective. They demonstrated that the reflectivity curves were adjusted with the accuracy of about 0.008 nm (0.3%) over the entire mirror surfaces. The total throughput of the objective with
full working aperture (NA ~ 0.2) is estimated to be as high as 0.25%.
Multilayer mirrors for the extreme ultraviolet (EUV) are key elements for numerous applications of coherent EUV
sources such as new tabletop lasers and free-electron lasers. However the field of applications is limited by the radiation
and thermal stability of the multilayers. Taking into account the growing power of EUV sources the stability of the optics
becomes crucial. To overcome this problem it is necessary to study the degradation of multilayers and try to increase
their temporal and thermal stability. In this paper we report the results of detailed study of structural changes in Sc/Si
multilayers when exposed to intense EUV laser pulses. Various types of surface damage such as melting, boiling, shock
wave creation and ablation were observed as irradiation fluencies increase. Cross-sectional TEM study revealed that the
layer structure was completely destroyed in the upper part of multilayer, but still survived below. The layers adjacent to
the substrate remained intact even through the multilayer surface melted down, though the structure of the layers beneath
the molten zone was noticeably changed. The layer structure in this thermally affected zone is similar to that of
isothermally annealed samples. All stages of scandium silicide formation such as interdiffusion, solid-state
amorphization, silicide crystallization etc., are present in the thermally affected zone. It indicates a thermal nature of the
damage mechanism. The tungsten diffusion barriers were applied to the scandium/silicon interfaces. It was shown that
the barriers inhibited interdiffusion and increased the thermal stability of Sc/Si mirrors.
Resonant Inelastic X-ray Scattering (RIXS) is the one of the most powerful methods for investigation of the electronic
structure of materials, specifically of excitations in correlated electron systems. However the potential of the RIXS
technique has not been fully exploited because conventional grating spectrometers have not been capable of achieving
the extreme resolving powers that RIXS can utilize. State of the art spectrometers in the soft x-ray energy range achieve
~0.25 eV resolution, compared to the energy scales of soft excitations and superconducting gap openings down to a
few meV. Development of diffraction gratings with super high resolving power is necessary to solve this problem. In
this paper we study the possibilities of fabrication of gratings of resolving power of up to 106 for the 0.5 - 1.5 KeV
energy range. This energy range corresponds to all or most of the useful dipole transitions for elements of interest in
most correlated electronic systems, i.e. oxygen K-edge of relevance to all oxides, the transition metal L2,3 edges, and the
M4,5 edges of the rare earths. Various approaches based on different kinds of diffraction gratings such as deep-etched
multilayer gratings, and multilayer coated echelettes are discussed. We also present simulations of diffraction efficiency
for such gratings, and investigate the necessary fabrication tolerances.
Two samples of the new type of X-ray spectral elements - sliced multilayer grating (SMG) for 4.4-5 nm interval have
been produced and tested. Spectra of A1 discharge plasma were obtained with one of the SMGs. A novel experimental
approach based on a flow proportional counter was introduced and used to measure diffraction efficiency of another
SMG. The properties of the SMG are discussed.
Two samples of the new type of X-ray spectral elements--sliced multilayer grating (SMG) for 4.4-5 nm interval based on Co/C multilayer coatings have been produced and tested. A novel experimental approach based on a flow proportional counter was introduced and used to measure diffraction efficiency of SMG gratings. Spectra of Al discharge plasma were obtained with one of the SMGs. The properties of the SMG gratings are discussed.
We demonstrate the use of a tabletop capillary-discharge Ne-like Ar laser emitting nanosecond duration pulses at a wavelength of 46.9 nm for investigation of radiation damage mechanism and damage threshold in Sc/Si extreme ultraviolet multilayer mirrors. To vary the emission load at the surface of the mirror under test the intense 0.13 mJ laser pulses were focused using a spherical Sc/Si multilayer mirror to obtain fluences ranging from ~ 0.01 to >10 J/cm2. Single spots and large area patterns (2x2 mm2) were irradiated depending on the type of surface analysis technique employed. Damage threshold fluences of ~ 0.08 J/cm2 were measured for Sc/Si coatings deposited on both borosilicate glass and Si substrates, compared to the 0.7 J/cm2 found necessary to damage a bare Si substrate. The use of scanning and transmission electron microscopy, and small-angle X-ray diffraction techniques revealed the thermal nature of the damage mechanism. These results are relevant to the use of the Sc/Si mirrors in combination with newly developed high power EUV sources, and provide a benchmark for their further improvement.
We report results of the development of capillary discharge driven metal-vapor plasma waveguides for the development of efficient laser-pumped soft x-ray lasers; and of the use of a previously developed capillary discharge Ne-like Ar 46.9 nm laser in study of the interaction of intense soft x-ray laser with materials. The guiding of a laser beam in a dense capillary discharge plasma channel containing a large density of Ag ions is reported. In term of applications we have conducted studies of materials modification and ablation with focalized 46.9 nm laser radiation at fluences between
0.1 and 100 J cm-2. The experiments demonstrated that the combined high repetition rate and high energy per pulse of the capillary discharge laser allows for the first time the processing of large surface areas with intense soft x-ray laser radiation. The damage threshold and damage mechanism of extreme ultraviolet Sc/Si multilayer mirror coatings was studied . Damage threshold fluences of ~ 0.08 J/cm2 were determined for coatings deposited on both borosilicate glass and Si substrates. Scanning and transmission electron microscopy, and small-angle X-ray diffraction techniques revealed the thermal nature of the damage mechanism. These results provide a benchmark for the use of Sc/Si multilayer mirrors in high fluence applications, and for the development of higher damage threshold mirrors. Soft x-ray laser ablation studies were also conducted for silicon and several plastic materials, including PMMA, Polyamide and PTFE.
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.
Victor Asadchikov, Valentin Beloglazov, Alexander Vinogradov, Dmitrii Voronov, V. Kondratenko, Yu. Kopylov, N. Lebedev, A. Ponomarenko, Alexei Popov, Andrei Postnov, Anatoli Fedorenko
Fresnel hard x-ray zone plate was manufactured by sputter- sliced technology to work on 2.29 A wavelength. Cu and Cr were used to create opaque and transparent zones. The experimental setup was prepared to investigate optical properties of obtained zone plate. The focusing effect was observed. The numerical methods and software were developed to simulate imaging properties of Fresnel zone plate. Experimental data was compared with calculations.
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