Note: poster presented at the International Conference on
Fifth International Conference on X-ray and Neutron Surface Scattering,
Oxford, July 1997.
A.A. Darhuber, J. Zhu, V. Holý, J. Stangl,
P. Mikulík, K. Brunner, G. Abstreiter, and G. Bauer,
Highly regular self-organization of step bunches during growth of SiGe on Si(113),
Appl. Phys. Lett. 73, 1535–1537 (1998).
P. Mikulík and T. Baumbach,
X-ray reflection by rough multilayer gratings.
Dynamical and kinematical scattering.
Phys. Rev. B 59, 7632–7643 (1999).
Abstract
X-ray reflectivity by rough multilayer gratings is treated in the framework of the
kinematical and dynamical theories. The kinematical scattering integral is
calculated without the restrictions of the Fraunhofer approximation. The
dynamical theory is presented by the matrix modal eigenvalue approach. In both
theories we generalize the Fresnel reflection and transmission coefficients for
the case of grating diffraction. We obtained one unique formalism which permits
us to compare directly the results of both theories. Furthermore, interface and
side wall roughnesses are taken into account. The dynamical approach allowed to
explain the experimental results obtained from a partially etched GaAs/InP
periodic multilayer grating.
M. Jergel, P. Mikulík, E. Majková, Š. Luby, R. Senderák, E. Pinčík, M. Brunel,
P. Hudek, I. Kostič, and A. Konečníková,
Structural characterization of a lamellar W/Si multilayer grating,
J. Appl. Phys. 85, 1225–1227 (1999).
Abstract
A lamellar multilayer grating of the nominal normal and lateral periods
8 nm and 800 nm, respectively, was obtained by etching a planar
amorphous W/Si multilayer up to the substrate. The specular reflectivity,
grating truncation rods of non-zero orders, and a reciprocal space map of the
scattered intensity close to the total external reflection were measured using
the CuKa radiation. For the first time, we demonstrate an extraction of real
structural parameters of a fully etched periodic multilayer grating from fitting
the measured truncation rods based on the matrix modal eigenvalue approach to
the dynamical theory of reflectivity by gratings.
M. Jergel, P. Mikulík, E. Majková, Š. Luby, R. Senderák, E. Pinčík, M. Brunel,
P. Hudek, I. Kostič, and A. Konečníková,
Structural characterization of lamellar multilayer gratings
by X-ray reflectivity and scanning electron microscopy,
J. Phys. D 32, A220–A223 (1999).
Abstract
Structural characterisation of a fully etched amorphous W/Si multilayer grating
with lateral periodicity 800 nm is performed by X-ray reflectivity.
Grating truncation rod profiles have been calculated using a matrix modal
eigenvalue approach of the dynamical theory of reflectivity by gratings which
generalizes the Fresnel transmission and reflection coefficients for lateral
diffraction. The interface roughness in rough gratings has been taken into
account by a coherent amplitude approach which damps the generalized Fresnel
coefficients. Scanning electron microscopy pictures complete the study.
Y. Zhuang, V. Holý, J. Stangl, A.A. Darhuber, P. Mikulík, S. Zerlauth,
F. Schäffler, G. Bauer, N. Darowski, and D. Lübbert,
Strain relaxation in periodic arrays of Si/SiGe quantum wires
determined by coplanar high resolution x-ray diffraction and grazing
incidence diffraction,
J. Phys. D 32, A224–A229 (1999).
Abstract
Elastic relaxation in dry-etched periodic wires fabricated from molecular beam
epitaxy grown Si/SiGe multilayers was studied by coplanar and grazing incidence
(GID) high-resolution x-ray diffraction. The inhomogeneous strain distribution
in the wires was calculated by the finite element method, which provided the
input data for simulations of the scattered intensities using kinematical
diffraction theory used for comparison with measured reciprocal space maps. A
fabrication-induced layer covering the wire surfaces, modifies the strain
distribution. Using GID, the geometrical shape of the wires and their in-plane
strain can be determined independently of each other.
J. Stangl, V. Holý, A.A. Darhuber, P. Mikulík, G. Bauer, J. Zhu, K. Brunner, G. Abstreiter,
High-resolution x-ray diffraction on self-organized step bunches of
Si1-xGex grown on (113)-oriented Si,
J. Phys. D 32, A71–A74 (1999).
Abstract
We present investigations of a highly regular terraced surface and interface
structure of Si/SiGe multilayers on Si(113) by x-ray diffraction, x-ray
reflectivity and atomic force microscopy. A regular array of step bunches with
lateral periods of several hundred nanometres is formed during the growth of the
Si/Si1-xGex multilayers. X-ray diffraction patterns are
simulated using the elastic Green function approach for the evaluation of the
strain fields associated with the step edges, taking into account the relaxation
towards the free surface. In addition to the terrace structure, a surface
waviness on the micrometer length scale is present, leading to a modulation of
the terrace widths.
T. Baumbach and P. Mikulík,
X-ray reflectivity by rough multilayers
(review article, pages 155–161 and 232–280).
Proceedings of the Ecole Française de Reflectivité
(Luminy, France, 1997): X-Ray and Neutron Reflectivity: Principles
and Applications, edited by J. Daillant and A. Gibaud,
Berlin: Springer, Lecture Notes in Physics: 58 (1999).
Online here:
chapter 4.
and
chapter 8.
Excerpt from the table of contents:
4.A Appendix contributed by T. Baumbach and P. Mikulík.
Incoherent approach for scattering by randomly disturbed
multilayers ................................................. 3
4.A.1 Formal theory ......................................... 3
4.A.2 Formal kinematical treatment by first order Born ap-
proximation ............................................ 5
4.A.3 Formal treatment by a distorted wave Born approximation 6
imation ...........................................
8 X-ray reflectivity by rough multilayers
by Tilo Baumbach and Petr Mikulík 11
8.1 Introduction ................................................. 12
8.2 Description of rough multilayers ............................. 13
8.2.1 Ideal planar multilayers ............................... 14
8.2.2 Multilayers with rough interfaces ...................... 15
8.2.3 Correlation properties of different interfaces ......... 15
8.3 Setup of X-ray reflectivity experiments ...................... 17
8.3.1 Experimental setup ..................................... 17
8.3.2 Experimental scans ..................................... 19
8.4 Specular X-ray reflection .................................... 21
8.4.1 Roughness with a Gaussian interface distribution
function .............................................. 21
8.4.2 Stepped surfaces ....................................... 28
8.4.3 Reflection by "virtual interfaces" between porous layers 30
8.5 Non-specular X-ray reflection ................................ 31
8.5.1 Interfaces with a Gaussian roughness profile ........... 31
8.5.2 The main scattering features of non-specular reflection
by rough multilayers ................................... 35
8.5.3 Stepped surface and interfaces ......................... 40
8.5.4 Non-coplanar NSXR ...................................... 43
8.6 Interface roughness in surface sensitive diffraction methods . 44
8.7 X-ray reflection from multilayer gratings .................... 47
8.7.1 Theoretical treatments ................................. 48
8.7.2 Discussion ............................................. 53
8.7.3 Reflectivity from rough multilayer gratings ............ 54
8.A Appendix. Reciprocal space constructions for reflectivity .... 57
8.A.1 Reflection from planar surface and interfaces .......... 57
8.A.2 Periodic multilayer .................................... 59
8.A.3 Reciprocal space representation of DWBA ................ 60
Bibliography ..................................................... 62
Y. Zhuang, J. Stangl, A.A. Darhuber, G. Bauer, P. Mikulík, V. Holý, N. Darowski,
and U. Pietsch,
X-ray diffraction from quantum wires and quantum dots,
Journal of Materials Science: Materials in Electronics 10, 215–221
(1999).
Abstract
From the distribution of the scattered intensity in reciprocal space,
information on the shape as well as on the strain distribution in
nanostructured samples can be obtained. This is exemplified by applying this
method to laterally patterned periodic Si/SiGe superlattices as well as to
periodic SiGe dot arrays embedded in Si.
O. Litzman and P. Mikulík,
The crystal truncation rod scattering of neutrons and the multiwave
dynamical theory of diffraction,
J.Phys.: Condens. Matter 11, 5767 (1999).
Abstract
The influence of the Bragg diffractions on the coplanar and non-coplanar
crystal truncation rod scattering is studied using the Ewald multiwave
dynamical theory of diffraction. The resulting formulae are compared with the
approximate ones of the kinematical theory and geometrical optics
approximations.
J. Stangl, V. Holý, P. Mikulík, G. Bauer, I. Kegel, T.H. Metzger, O.G. Schmidt,
C. Lange, and K. Eberl,
Self-assembled carbon-induced germanium quantum dots studied by
grazing-incidence small-angle x-ray scattering,
Applied Physics Letters 74, 3785–3787 (1999).
Abstract
We present a structural investigation of buried C-induced Ge quantum dot
multilayers grown on (001) Si by molecular-beam epitaxy. Using grazing-incidence
small-angle x-ray scattering, we determine the shape, the mean radius, height,
and dot distance. The dot distribution is isotropic within the (001) interfaces,
and no correlation of the dot positions along growth direction was found.
M. Jergel, P. Mikulík, E. Majková, E. Pinčík, Š. Luby, M. Brunel, P. Hudek,
I. Kostič,
Multilayer gratings for X-UV optics,
acta physica slovaca 50, 427–438 (2000).
Abstract
Multilayer gratings are thin film structures possessing periodicities both in
the normal and lateral directions. They combine the properties of surface
gratings and planar multilayers thus providing a high throughput and high
spectral resolution on higher diffraction orders. The unique diffraction
properties are utilized in the X-ray and ultraviolet optics where no lenses or
mirrors comparable with those for visible light are available. Multilayer
gratings act as constant resolution dispersion elements in a broad spectral
range. A fan of grating diffractions in real space is represented by a set of
points on equidistant truncation rods in the reciprocal space. The kinematical
theory of X-ray scattering explains well the positions of the grating truncation
rods while the dynamical theory is inevitable to calculate the intensities along
the truncation rods (grating efficiency). The properties of multilayer gratings
are exemplified on two differently prepared lamellar gratings with the nominal
normal and lateral periods of 8 nm and 800 nm, respectively. The fabrication
steps are described in detail. The specular and non-specular X-ray
reflectivities at wavelength 0.15418 nm were measured on one of the samples.
The dynamical theory of X-ray scattering with a matrix modal eigenvalue
approach was applied to extract the real structural parameters such as the
surface and interface roughnesses, individual layer thicknesses, and the lamella
width to the grating period ratio. The X-ray reflectometry is completed by
microscopy observations which provide complementary and direct information on
the local surface profile.
G. Springholz, J. Stangl, M. Pinczolits, V. Holý, P. Mikulík, P. Mayer,
K. Wiesauer, G. Bauer, D. Smilgies, H.H. Kang, and L. Salamanca-Riba,
Nearly perfect 3D ordering in IV-VI quantum dot superlattices with
ABCABC... vertical stacking sequence,
Physica E 7, 870–875 (2000).
Abstract
Self-organization of PbSe islands in epitaxial PbSe/Pb1-xEuxTe superlattices is shown to result in
a spontaneous three-dimensional ordering of the PbSe dots in a trigonal lattice with a fee-like
ABCABC vertical stacking sequence. From X-ray diffraction reciprocal space maps, the
interlayer correlation direction of the PbSe dots is found to be inclined by 40 degrees with
respect to the [111] surface normal. Peak profile measurements in the reciprocal space maps
yield a coherence length of the ordered regions of 300 +/- 100 nm in the lateral, and of 530 +/-
50 nm in the vertical direction. This corresponds to ordered regions that contain as many as 250
PbSe dots.
P. Mikulík, M. Jergel, T. Baumbach, E. Majková, E. Pinčík, Š. Luby,
L. Ortega, R. Tucoulou, P. Hudek, and I. Kostič,
Coplanar and non-coplanar x-ray reflectivity characterization of
lateral W/Si multilayer gratings,
J. Phys. D: Appl. Phys. 34, A188–A192 (2001).
Abstract
Structural characterization of a fully etched amorphous W/Si multilayer grating
with a lateral periodicity of 800 nm is performed by x-ray reflectivity in the
coplanar and non-coplanar modes using a scintillation detector and a
two-dimensional gas-filled detector, respectively. Three-dimensional reciprocal
space constructions were used to explain the scattering features recorded in
both geometries. Coplanar coherent grating truncation rods were fitted by a
dynamical theory for rough gratings. Comparison of the reflectivity from the
reference planar multilayer completes the study.
A. Ulyanenkov, K. Inaba, P. Mikulík, N. Darowski, K. Omote, U. Pietsch,
J. Grenzer, and A. Forchel,
X-ray diffraction and reflectivity analysis of GaAs/InGaAs
free-standing trapezoidal quantum wires,
J. Phys. D: Appl. Phys. 34, A179–A182 (2001).
Abstract
Combined x-ray diffraction and reflectivity experiments have been performed on
free-standing trapezoidal GaAs/InGaAs quantum wires using a conventional x-ray
tube. Interpreting the intensity distribution around (004) by curve simulation
of the extracted coherent grating truncation rods on the basis of a
semikinematical diffraction theory (DWBA) the shape and geometric parameters as
well as the strain within the wires could be determined taking the results of a
finite element calculation of the atomic displacements into account. The map of
the coplanar x-ray reflectivity around (000), as well as the intensity profiles
of the coherent grating truncation rods, located equidistantly around the
specularly reflected beam, have been recorded in order to estimate the
roughness properties of the sample interfaces as well as the wire shape and
layer set-up without the influence of strain. All small-angle as well as
wide-angle scattering experimental results went in to the mutually consistent
estimate of the sample properties. The experiments performed for a conventional
x-ray tube supply a parameter set comparable in completeness and precision to
that obtained from similar samples by interpreting synchrotron experiments.
M. Jergel, C. Falcony, P. Mikulík, L. Ortega, E. Majková, E. Pinčík, Š. Luby,
I. Kostič, and P. Hudek,
Coplanar and non-coplanar x-ray reflectivity characterization
of lateral W/Si multilayer gratings,
Sup. y Vac. 13, 10 (2001).
Abstract
Multilayer gratings a re artificially patterned multilyer thin films with the
periodicities both in the lateral and normal directions which renders them
attracting for microelectronic and optical applications. A proper structural
characterization is of primary importance. To test the capability of the X-ray
reflectometry technique to fulfil this task, a tungsten/silicon multilayer
grating prepared by electron beam evaporation and electron beam lithography was
studied both in the coplanar and non-coplanar geometries., the nominal lateral
and normal periods being 800 nm and 8 nm, respectively. The coplanar
measurements were evaluated within the dynamical theory of X-ray scattering on
rough gratings and provided the structural parameters of a real structure with
a reasonable precision which are close to the nominal ones. The results
revealed also some imperfections of the deposition and masking procedures which
are discussed. The non-coplanar measurements were evaluated qualitatively using
three-dimensional constructions in the reciprocal space. The advantage of the
technique used is its non-destructive character and a simultaneous access both
to the surface shape of the grating as well as to its internal structure.
V.M. Kaganer, B. Jenichen, G. Paris, K.H. Ploog, O. Konovalov, P. Mikulík,
and S. Arai,
Strain in buried quantum wires: Analytical calculations and x-ray
diffraction study,
Phys. Rev. B 66, 035310-1–035310-7 (2002).
Abstract
The displacement field in and around periodically arranged quantum wires
embedded in a crystalline matrix is calculated analytically for an arbitrary
finite thickness of the cover layer. A good agreement is obtained between
measured x-ray-diffraction peaks of a wire structure and kinematical
calculations with the displacement field derived in the paper. The strain and
quantum size effects on the photoluminescence line shift are found to be
comparable, due to small width (35 nm) of the wires.
P. Mikulík, T. Baumbach, D. Korytár, P. Pernot, D. Lübbert, L. Helfen,
Ch. Landesberger,
Advanced X-ray diffraction imaging techniques for semiconductor wafer
characterisation,
Materials Structure 9, 87–88 (2002).
Abstract
Wafer quality inspection and defect analysis are crucial for improvements of
the wafer fabrication technology as well as for the correlation of device
properties with the processes of wafer treating. This work demonstrates trends
of high-resolution X-ray diffraction imaging techniques with synchrotron
radiation sources and their capability for detailed quality inspection of
wafers concerning their structural perfection. We apply these methods to
visualise and to characterise the defects and deformations induced by growing,
cutting, grinding, etching and gluing in the production of semiconductor wafers
(in particular Si and GaAs wafers) and in ultra-thin wafers. We present
synchrotron topography and synchrotron area diffractometry methods to analyse
qualitatively and quantitatively: dislocations and lineages, micro-defects and
micro-cracks, wafer tilts and warpages, tensors of local lattice rotations.
P. Mikulík, D. Lübbert, D. Korytár, P. Pernot, and T. Baumbach,
Synchrotron area diffractometry as a tool for spatial high-resolution
three-dimensional lattice misorientation mapping,
J. Phys. D: Appl. Phys. 36, A74–A78 (2003).
Abstract
We have developed a high-resolution diffraction imaging method for
determination of the complete three-dimensional rotational local lattice
misorientation of crystalline samples. The method, called synchrotron area
diffractometry, is based on recording double-crystal diffraction rocking scans
in three mutually non-coplanar scattering planes with a two-dimensional area
detector. The subsequent multiple-peak analysis of the rocking curve image
series for all pixels and their backprojection to the wafer surface provides
local misorientation angles (Euler angles) with spatial resolution up to
micrometre range over the wafer surface. We applied this technique to determine
the distribution of tilt and twist angles of the lattice misorientation of a
macroscopic defect localized in a 6 inch semi-insulating GaAs(001) wafer.
D. Korytár, P. Mikulík, C. Ferrari, J. Hrdý, T. Baumbach, A. Freund, and
A. Kuběna,
Two-dimensional x-ray magnification based on a monolithic beam conditioner,
J. Phys. D: Appl. Phys. 36, A65–A68 (2003).
Abstract
In x-ray imaging and beam conditioning it is useful to magnify or demagnify the
x-ray beam, or an image, approaching (sub)micrometre resolution or the
(sub)micrometre illuminated region. Using an asymmetric diffractor it is
possible to expand or compress the x-ray beam in one direction. Combining two
such diffractors with mutually perpendicular planes of diffraction even
two-dimensional beam expansion or compression can be obtained and, for suitable
wavelengths, it is even possible to design and cut a single crystal in such a
way that it works as a monolithic device expanding or compressing the x-ray
beam in two directions. In this paper, a new magnifying monolithic optical
device for a two-dimensional magnification of 25 at 10 keV, based on two
noncoplanar asymmetrically inclined {311} diffractors, was designed and made
from a single silicon crystal. A ray-tracing image has been simulated to check
the functionality of the device. The experimental testing of this device was
performed at Optics beamline BM5 at ESRF Grenoble. An undistorted image
magnification of about 15 was achieved at a photon beam energy of 9.6 keV. When
the photon energy was increased, a higher magnification and increased
distortion were observed (horizontal magnification of 39, vertical
magnification of 20) at an energy of 10.045 keV. The advantages and
disadvantages of the device, as well as further steps to improve it are briefly
discussed.
C. Ferrari, N. Verdi, D. Lübbert, D. Korytár, P. Mikulík, T. Baumbach,
L. Helfen, and P. Pernot,
Determination of lattice plane curvature and dislocation Burgers vector density
in crystals by rocking curve imaging technique,
Proceedings SPIE Volume 5195: Crystals, Multilayers, and Other Synchrotron Optics,
edited by T. Ishikawa, A.T. Macrander, and J.L. Wood,
84–93 (2003).
Abstract
In the present work the lattice plane curvature of a nearly dislocation free
S:doped InP and a semi-insulating GaAs wafer crystals has been investigated
using the method of X-ray rocking curve imaging based on the FReLoN CCD area
detector with a pixel resolution from 10 to 40 μm at the ID19 ESRF
beamline. The geometry of the experiment is based on a vertical Si (111)
monochromator and a horizontal sample scattering planes in the Bragg geometry
(σ-π geometry). To determine the local lattice inclination, the effect
of such dispersive setup on the measured local diffraction peak position has
been accurately determined and the equations to determine the lattice plane
curvature of the crystals under the condition of isotropic distribution of
dislocation Burgers vectors are obtained. The analysis of the data showed that
the shift of the Bragg condition is almost completely due to the lattice tilt
rather than to the lattice parameter variation. Lattice displacements from the
ideal lattice as large as 200 μm are found at the edges of the InP
crystal. Non random distributions of dislocation Burgers vectors are observed
in both samples.
B. Köhler, J. Schreiber, B. Bendjus, M. Herms, V. Melov, L. Helfen, P. Mikulík,
and T. Baumbach,
Micro- and nano-NDE in the laboratory for acoustic diagnosis and quality assurance,
Proceedings SPIE Volume 5392: Testing, Reliability, and Application of Micro- and
Nano-Material Systems II, edited by N. Meyendorf, G.Y. Baaklini, and B. Michel,
63–77 (2004).
Abstract
NDE activities at the Laboratory for Acoustic Diagnosis and Quality Assurance
(EADQ) Dresden are outlined. The applied methods comprise acoustic, thermal,
optical and X-ray ones. Additionally, scanning probe methods (SPM) and scanning
electron microscopy (SEM) are used. Combinations of different methods are
especially effective. This is demonstrated for the coupling of an acoustic
approach with SEM. For NDE on a micro- and nano-meter scale, preparation of
appropriate test flaws and the verification of the NDE results turn out to be a
challenge. To meet this challenge, we propose an approach based on focused ion
beam technique.
T. Baumbach, L. Helfen, P. Mikulík, and F. Dehn
and T. Baumbach,
Synchrotron-radiation X-ray tomography: a method for 3D imaging of cement
microstructure and its evolution during hydration
,
Proceedings of XIV. International Symposium SANACE 2004, 71–80 (2004).
Abstract
New possibilities opened up by synchrotron radiation present x-ray tomography
as an experimental imaging method to study the microstructural evolution during
cement hydration. The present work demonstrates the potential of
synchrotron-radiation microtomography for the investigation of cement structure
after solidification. Quantitative determination of the spatial absorption-
coefficient distribution due to the use of monochromatic radiation and the
achieved high spatial resolution allows us to characterise the hydration
process of cement volume on a micrometre scale in three dimensions. In
particular, effects as the formation of microcracks and pores related to
autogeneous shrinkage involved with the hydration process could be observed for
the first time with down to one micrometre resolution.
D. Lübbert, C. Ferrari, P. Mikulík, P. Pernot, L. Helfen, N. Verdi, D. Korytár,
and T. Baumbach,
Distribution and Burgers vectors of dislocations in semiconductor wafers investigated
by rocking-curve imaging,
Journal of Applied Crystallography 38, 91–96 (2005).
Abstract
The method called rocking-curve imaging (RCI) has recently been developed to
visualize lattice imperfections in large crystals such as semiconductor wafers
with high spatial resolution. The method is based on a combination of X-ray
rocking-curve analysis and digital X-ray diffraction topography. In this
article, an extension of the method is proposed by which dislocation densities
in largescale samples (semiconductor wafer crystals) can be quantified and
their variation across the sample surface determined in an instrumentally
simple way. Results from a nearly dislocation-free S-doped InP crystal and a
semi-insulating GaAs are presented; both display a clearly non-random
distribution of dislocations.
D. Lübbert, T. Baumbach, P. Mikulík, P. Pernot, L. Helfen, R. Köhler,
T.M. Katona, S. Keller, and S.P. DenBaars,
Local wing tilt analysis of laterally overgrown GaN by x-ray rocking curve
imaging,
Journal of Physics D 38, A50–A54 (2005).
Abstract
We report on recent advances in spatially resolved x-ray diffraction, extending
the technique known as rocking curve imaging down to 1–2 um
spatial resolution. Application to a set of gallium nitride samples grown by
epitaxial lateral overgrowth (ELO) shows the potential of the technique.
Quantitative information on crystallographic misorientations and lattice quality
can be obtained by direct imaging with high lateral resolution. Results from two
samples of ELO-GaN grown on different substrates are compared. Tilt in individual
lateral periods of the ELO structure can be quantified. Local tilt fluctuations
are distinguished from macroscopic variations (curvature). The local lattice
quality can be investigated via the peak width of diffraction profiles recorded
in individual camera pixels. The peak broadening previously observed in laboratory
x-ray diffraction measurements is found to have (at least) two different reasons.
In both cases, peak broadening does not indicate a degradation in local crystalline
quality.
D. Korytár, T. Baumbach, C. Ferrari, L. Helfen, N. Verdi, P. Mikulík,
A. Kuběna, and P. Vagovič,
Monolithic two-dimensional beam compressor for hard x-ray beams,
Journal of Physics D 38, A208–A212 (2005).
Abstract
Using asymmetric diffraction in grazing incidence or in grazing emergence it is
possible to expand or compress an x-ray beam in one dimension. Combining two
asymmetric diffractions with non-coplanar planes of diffraction it is possible
to obtain two-dimensional beam expansion or compression. This paper reports on
a monolithic two-dimensional x-ray beam compressor consisting of two
non-coplanar asymmetrically inclined {311} diffractors prepared in one silicon
crystal block and tested at Optics beamline BM05 at ESRF, Grenoble. The design
of the x-ray beam compressor, the results of beam tracing image simulation, the
experimental arrangement used for testing and the properties of the x-ray
microbeams formed are presented. For the beam energy of 9.5 keV 10- and
13-times beam compression in two directions was observed. Using a metal grid in
the incident beam more than 400 microbeams smaller than 10 um and separated by
less than 5 um were obtained in the outgoing beam. A gain of up to 100 times
in intensity per unit area was obtained in comparison with the x-ray beam
magnifier geometry, demonstrating a real two-dimensional beam compression.
L. Helfen, T. Baumbach, P. Mikulík, D. Kiel, P. Pernot, P. Cloetens,
and J. Baruchel,
High-resolution three-dimensional imaging of flat objects by synchrotron-radiation
computed laminography,
Applied Physics Letters 86, 071915 (2005).
Abstract
Computed laminography with synchrotron radiation is developed and carried out
for three-dimensional imaging of flat, laterally extended objects with high
spatial resolution. Particular experimental conditions of a stationary
synchrotron source have been taken into account by a scanning geometry
different from that employed with movable conventional laboratory x-ray
sources. Depending on the mechanical precision of the sample manipulation
system, high spatial resolution down to the scale of 1 um can be attained
nondestructively, even for objects of large lateral size. Furthermore, high
beam intensity and the parallel-beam geometry enables easy use of monochromatic
radiation for optimizing contrast and reducing imaging artifacts. Simulations
and experiments on a test object demonstrate the feasibility of the method.
Application to the inspection of solder joints in a flip-chip bonded device
shows the potential for quality assurance of microsystem devices.
L. Helfen, F. Dehn, L. Helfen, P. Mikulík, and T. Baumbach
Three-dimensional imaging of cement microstructure evolution during hydration
,
Advances in Cement Research 17, 103–111 (2005).
Abstract
Synchrotron radiation is used for X-ray computed tomography to characterise the
hydration process of Portland cement. Quantitative determination of the
three-dimensional absorption coefficient distribution due to the use of
monochromatic radiation and the achieved high spatial resolution allows the
study of the spatial microstructure of cement volume during hydration. The
present study has demonstrated the potential of the method for real-time
imaging of the evolution of cement structure after solidification. The method
yields three-dimensional (3-D) images of the sample volume in a non-destructive
manner. Thus, by reiterated imaging of the same sample region at different
times, processes in the sample volume can be tracked. During cement hydration,
effects such as the formation and further evolution of microcracks and pores –
mainly related to autogeneous shrinkage – could be observed for the first time
in the cement volume with up to 1 μm resolution. Image analysis of the acquired
3-D data sets allows the determination of the temporal evolution of
microporosity and of the fraction of contiguous pore volume for different water
: cement ratios of the initial cement paste.
O. Caha, P. Mikulík, J. Novák, V. Holý, S.C. Moss, A. Norman, A. Mascarenhas,
J.L. Reno, and B. Krause,
Spontaneous lateral modulation in short-period superlattices investigated
by grazing-incidence x-ray diffraction,
Physical Review B 72, 035313 (2005).
Abstract
The process of spontaneous lateral composition modulation in short-period InAs
AlAs superlattices has been investigated by grazing-incidence x-ray
diffraction. We have developed a theoretical description of x-ray scattering
from laterally modulated structures that makes it possible to determine the
lateral composition modulation directly without assuming any structure model.
From experimental intensity distributions in reciprocal space we have
determined the amplitudes of the modulation and its degree of periodicity and
their dependence on the number of superlattice periods. From the data it
follows that the modulation process cannot be explained by bunching of
monolayer steps and most likely, it is caused by stress-driven morphological
instabilities of the growing surface.
J. Hrdý, A. Kuběna, and P. Mikulík,
Aberrations of diffractive–refractive optics: Bragg-case sagittal focusing
of multiple parabolic elements,
Journal of Physics D 38, 4325–4328 (2005).
Abstract
The diffractive–refractive optical device consisting of four crystals in
(+,–,–,+) setting with longitudinal parabolic grooves has a
geometrical aberration which influences the achievable focus size. This
aberration is discussed analytically by using a new, more precise formula for
the calculation of focusing distance, which respects the finite distance
between optical elements. The calculation of the intensity distribution
surrounding the focus is illustrated by a ray-tracing method based on the
dynamical theory of diffraction. It demonstrates an achievable focus size.
Finally we discuss that this aberration may be suppressed by the slight
narrowing of the groove profile. In particular, the parameter a in the equation
of parabola has to slightly grow with x. A practical application may
require an ultra-precise fabrication of the grooves.
D. Lübbert, P. Mikulík, P. Pernot, L. Helfen, M.D. Craven, S. Keller,
S. DenBaars, and T. Baumbach,
X-ray microdiffraction imaging investigations of wing tilt in epitaxially
overgrown GaN,
physica status solidi (a) 203, 1733–1738 (2006).
Abstract
The crystalline quality in epitaxially laterally overgrown (ELO) GaN and the
amount of wing tilt is characterized on a local basis, with high spatial and
angular resolution. A method of full-field X-ray microdiffraction imaging,
termed rocking curve imaging, is used to record simultaneously a large set of
local X-ray diffraction profiles originating from sample surface areas of
micrometer size. x-omega maps of diffracted intensity allow to quantify the
amount of wing tilt in individual lateral ELO periods as well as to monitor the
fluctuations of tilt between adjacent periods. Automated shape analysis of the
full set of local rocking curves provides a means to quantitatively
characterize the local crystalline perfection of GaN. The ELO window and wing
regions can be clearly separated; comparison indicates an average improvement
of crystal quality by a factor 3–4 due to the lateral overgrowth process.
L. Helfen, A. Myagotin, P. Pernot, M. DiMichiel, P. Mikulík, A. Berthold,
and T. Baumbach,
Investigation of hybrid pixel detector arrays by synchrotron-radiation imaging,
Nuclear instruments & methods in physics research A 563, 163–166 (2006).
Abstract
Synchrotron-radiation imaging was applied to the non-destructive testing of
detector devices during their development cycle. Transmission imaging known as
computed laminography was used to examine the microstructure of the
interconnections in order to investigate the perfection of technological steps
necessary for hybrid detector production. A characterisation of the solder bump
microstructure can reveal production flaws such as missing or misaligned bumps,
voids in bumps or bridges and thus give valuable information about the bonding
process.
P. Mikulík, D. Lübbert, P. Pernot, L. Helfen, and T. Baumbach,
Crystallite misorientation analysis in semiconductor wafers and ELO samples by rocking curve imaging,
Applied Surface Science 253, 188–193 (2006).
Online fulltext.
Abstract
Rocking curve imaging is based on measuring a series of Bragg-reflection
digital topographs by monochromatic parallel-beam synchrotron radiation in
order to quantify local crystal lattice rotations within a large surface area
with high angular and high spatial resolution. In this paper we apply the
method to map local lattice tilts in two distinct semiconductor sample types
with lattice misorientations up to 0.5° and with spatial resolution from 30 um
down to 1 um. We analyse the measured surface-tilt data volumes for samples
with almost smoothly varying specific misoriented defect formation in GaAs
wafers and for an inherent subsurface grain structure of epitaxial lateral
overgrowth wings in GaN. Back-projected tilt maps and histograms provide both
local and global characteristics of the microcrystallinity.
L. Helfen, A. Myagotin, A. Rack, P. Pernot, P. Mikulík, M. Di Michiel, T. Baumbach,
Synchrotron-radiation computed laminography for high-resolution three-dimensional
imaging of flat devices,
physica status solidi (a) 204, 2760–2765 (2007).
Online here.
Abstract
Synchrotron-radiation computed laminography (SRCL) is developed as a method for
high-resolution three-dimensional (3D) imaging of regions of interest (ROIs) in
all kinds of laterally extended devices. One of the application targets is the
3D X-ray inspection of microsystems. In comparison to computed tomography (CT),
the method is based on the inclination of the tomographic axis with respect to
the incident X-ray beam by a defined angle. With the microsystem aligned
roughly perpendicular to the rotation axis, the integral X-ray transmission on
the two-dimensional (2D) detector does not change exceedingly during the scan.
In consequence, the integrity of laterally extended devices can be preserved,
what distinguishes SRCL from CT where ROIs have to be destructively extracted
(e.g. by cutting out a sample) before being imaged. The potential of the method
for three-dimensional imaging of microsystem devices will be demonstrated by
examples of flip-chip bonded and wire-bonded devices.
J. Kuběna, A. Kuběna, O. Caha, and P. Mikulík,
Development of oxide precipitates in silicon: calculation of the distribution
function of the classical theory of nucleation by a nodal-points approximation
,
J. Phys.: Condens. Matter 19, 496202–496212 (2007).
Online here.
Abstract
The classical theory of nucleation in solids is mathematically expressed by a
system of differential equations for temporal development of cluster
distribution (sizes and their concentration). Cluster sizes reach hundreds of
nanometers during long annealing times, requiring us to deal with up to
107–108 differential equations. The full numerical
simulation grows linearly with the number of equations, making the numerical
solution extremely time-consuming. In this paper we develop a nodal-points
approximation method with a logarithmic efficiency, which allows us to
calculate the cluster distribution very quickly. The method is based on
modified Becker–Döring equations solved precisely only within a given set of
nodal points and approximated in between them. Availability of the method is
shown by monitoring the kinetics of oxygen precipitation in Czochralski silicon
for the case of a three-stage annealing for 8 h at 600 °C+4 h at 800 °C+8 h at
1000 °C, where the number of monomers in the clusters reaches more than
2×107. Examples are discussed, mainly about the development of a
concentration gap and concentration wavelet of the cluster distribution and
about interstitial oxygen concentration.
P. Vagovič, D. Korytár, P. Mikulík, and C. Ferrari,
On the design of a monolithic 4-bounce high resolution X-ray monochromator
,
Nuclear Instruments and Methods in Physics Research Section B,
265, 599–604 (2007).
Online here.
Abstract
A monolithic monochromator (+n, −n, −m, +m) made of a single block of Ge
crystal designed for CoKα1 radiation was developed and tested numerically and
experimentally by means of X-ray diffraction. The advantage of monolithic
devices is their mechanical stability and the alignment of such optics is much
easier than with polylithic optics, but the development of these devices is
rather demanding. The presented monochromator belongs to a group of coplanar
in-line devices, which means that the input beam is parallel with the output
beam. For the estimation of the spectral and angular properties of a diffracted
beam of this monochromator (such as bandpass width, output divergence and input
acceptance) we used a numerical approach which we call spectral-angular
function. It takes into account both the vertical and the horizontal divergence
of the input radiation and uses two-beam X-ray dynamical theory of diffraction.
Experimentally, the monochromator was tested by means of X-ray diffraction
(synchrotron radiation testing) and the results from this characterization are
presented. The influence of the vertical divergence on the spectral
distribution of the diffracted beam is discussed and compared with previously
published analytical results.
V. Holý, T. Baumbach, D. Lübbert, L. Helfen, M. Ellyan, P. Mikulík, S. Keller, S. P. DenBaars, and J. Speck,
Diffuse x-ray scattering from statistically inhomogeneous distributions
of threading dislocations beyond the ergodic hypothesis,
Physical Review B
77, 094102–94110 (2008).
Online here.
Abstract
Diffuse x-ray scattering from threading dislocations in epitaxial structures is
simulated numerically by a Monte Carlo method. The method allows one to
simulate diffraction curves for dislocation types, where macroscopic approaches
fail. That includes dislocation types for which analytical ensemble averaging
is not feasible as well as microdiffraction curves from small sample volumes.
In the latter case, the degree of statistic fluctuation of characteristic
features is determined. The Monte Carlo method makes it possible to correlate
quantitatively the widths of the microdiffraction curves to the densities of
various dislocation types. The potential of the method has been demonstrated by
a quantitative estimation of the density distribution of edge and screw
threading dislocations in laterally overgrown epitaxial GaN structures, which
is investigated by a full-field microdiffraction imaging technique. Measuring
the asymptotic behavior of the microdiffraction curves allows one to conclude
on the prevailing type of threading dislocations.
D. Korytár, C. Ferrari, P. Mikulík, F. Germini, P. Vagovič, and T. Baumbach,
High Resolution 1D and 2D Crystal Optics Based on Asymmetric Diffractors,
chapter 29, book
Modern Developments in X-Ray and Neutron Optics, edited by
A. Erko, M. Idir, T. Krist, and A.G. Michette,
Springer (Springer Series in Optical Sciences), Berlin 2008.
Abstract
The development of high resolution X-ray measurements and imaging in real and
reciprocal space is related to the improvement of the optical elements
available for use. Crystal diffractive optics still give the highest resolution
in reciprocal space and in energy, and progress has also been made in improving
resolution in real space. In this chapter a short introduction to the dynamical
theory behind crystal diffractors and their coupling is given and modern one-
and two-dimensional elements based on symmetric, asymmetric and inclined
diffractions are introduced. The design, the modeling of the output parameters
and the experimental results are presented for a special 2-bounce V-shaped
monochromator, for a monolithic 4-bounce monochromator and for a monolithic 2D
beam de/magnifier.
V. Áč, P. Perichta, D. Korytár, and P. Mikulík,
Thermal effects under synchrotron radiation power absorption,
chapter 30, book
Modern Developments in X-Ray and Neutron Optics, edited by
A. Erko, M. Idir, T. Krist, and A.G. Michette,
Springer (Springer Series in Optical Sciences), Berlin 2008.
Abstract
Analyses of the effects of silicon crystal beam heating under static and
dynamic synchrotron radiation power loads are presented. This research is
related to monochromator design and crystal optics in general. The aim of work
is to analyse the conditions for insertion of the crystal X-ray optics into the
high flux primary beam of the synchrotron. Suggestions for the optimization of
the target geometry and cooling system arrangement are given.
D. Lübbert, T. Baumbach, V. Holý, P. Mikulík, L. Helfen, P. Pernot,
M. Ellyan, S. Keller, S. P. DenBaars, and J. Speck,
Microdiffraction imaging of dislocation densities in microstructured samples,
Europhysics Letters
82, 56002–56006 (2008).
Online here.
Abstract
A full field X-ray microdiffraction technique is developed providing
simultaneously both micrometer-resolved information of crystalline perfection
as well as statistical information about the macroscopically illuminated
sample. The method allows a detailed characterization of patterned substrates
grown by epitaxial lateral overgrowth. Local wing tilts and their fluctuation
over the sample area as well as the local and average number of grains in the
wings are determined, and the reduction of threading dislocation densities in
the grains of the ELO wings can be quantitatively estimated.
J. Humlíček and P. Mikulík,
ÚFKL PřF MU: polovodiče, nanostruktury, čisté prostory,
Československý časopis pro fyziku
58, 85 (2008).
See here.
Abstract
V tomto článku informujeme stručně o výzkumu v oblasti polovodičových materiálů
a struktur na ÚFKL, podrobněji pak o nově otevřené laboratoři polovodičů –
čistých prostorách pro křemíkovou technologii.
P. Kulha, A. Boura, M. Husák, P. Mikulík, M. Kučera, and S. Valenda,
Design and Fabrication of High-Temperature SOI Strain-Gauges,
In proceedings of the
7th International Conference on Advanced Semiconductor Devices and Microsystems
ASDAM 2008,
175–178 (2008).
See here.
Abstract
The following paper introduces the coventor ware design environment for SOI
based piezoresistive sensor design. Fabrication process and characterization of
designed sensors is also presented. The software package Coventor Ware has been
used for design of mechanical and electrical characteristics of the structure.
The tools enable design, modelling and successive modification of designed MEMS
structures. The program enables: drawing of 2D layout and its editing,
simulation of production process, generation of 3D model from 2D masks,
generation of network by the method offinite elements, solution of mechanical,
piezoresistive, thermal and further simulations. Simple passive elements
(strain sensitive resistors - piezoresistors) were fabricated on SIMOX SOI
substrates with sputtered AlCuSi metallization. Basic parameter extraction and
their temperature dependence were performed.
P. Mikulík, Z. Pokorná, B. Růžička, and S. Kozubek,
Projekt Středoevropské synchrotronové laboratoře – CESLAB,
Československý časopis pro fyziku
58, 244 (2008).
Abstract
Středoevropská synchrotronová laboratoř (Central European Synchrotron
Laboratory, CESLAB) byla navržena pro realizaci ze Strukturálních fondů
Evropské unie. Jedná se o moderní synchrotron třetí generace s energií
elektronů 3 GeV a průměrem 270 m pro experimenty se zářením v oblasti
od infračervené po rentgenovou se spuštěním v roce 2015. V tomto článku se
zabýváme důležitostí experimentů se synchrotronovým zářením pro vědu, výzkum a
aplikace a dále popisujeme stručně principy fungování urychlovacího komplexu
synchrotronu. Poté se konkrétně věnujeme příslušným parametrům CESLAB a nakonec
se zmiňujeme o vědeckých aplikacích navržených experimentálních stanic.
I. Bauer, P. Mikulík, and T. Baumbach,
Correctness of a particular solution of inverse problem in rocking curve imaging,
Physica Status Solidi A
206, 1860–1864 (2009).
Abstract
Local lattice misorientations on crystalline substrates can be visualized by
rocking curve imaging. Local deviations from Bragg peak positions are extracted
from a series of digital topographs recorded by a CCD detector under different
azimuths. Bragg peaks from surface regions such as crystallites with a larger
local misorientation overlap on the detector, which requires a back-projection
method in order to reconstruct the misorientation components on the sample
surface from the measured angular position on the detector planes. From
mathematical point of view, the reconstruction problem is at inverse problem.
In this paper, we formulate the forward and back-projection problems and we
prove the correctness of a particular solution. The usability of the method is
demonstrated on a phantom data set.
T. Baumbach and P. Mikulík,
X-ray reflectivity by rough multilayers
(review article, pages 175–180 and 235–282).
X-Ray and Neutron Reflectivity: Principles
and Applications, edited by J. Daillant and A. Gibaud,
Berlin: Springer, Lecture Notes in Physics: 770 (2009).
Online at Springer
(chapter 6 and appendix to chapter 4); see also
table of contents.
D. Nečas, L. Zajíčková, D. Franta, P. Sťahel, P. Mikulík,
M. Meduňa, and M. Valtr,
Optical Characterization of Ultra-Thin Iron and Iron Oxide Films,
e-Journal of Surface Science and Nanotechnology
7 486–490 (2009).
Online here.
Abstract
Ultra-thin films of 57Fe deposited on silicon substrates and
SiOxCyHz support layers and subsequently
oxidized in laboratory atmosphere are studied by two optical methods: the
combination of UV/VIS/NIR spectroscopic ellipsometry and spectrophotometry,
used to find layer thicknesses and optical constants, and X-ray specular
reflectometry, used to obtain the electron density depth profile. The results
of both methods are compared and found to be in a relatively good agreement.
P. Oberta, P. Mikulík, M. Kittler, J. Hrdý, and L. Peverini,
Diffractive-refractive optics: low-aberration Bragg-case focusing by precise parabolic surfaces,
Journal of Synchrotron Radiation
17, 36 (2010).
Online here.
Abstract
Based on analytical formulae calculations and ray-tracing simulations a
low-aberration focal spot with a high demagnification ratio was predicted for a
diffractive–refractive crystal optics device with parabolic surfaces. Two
Si(111) crystals with two precise parabolic-shaped grooves have been prepared
and arranged in a dispersive position (+,−,−,+) with high asymmetry.
Experimental testing of the device at beamline BM05 at the ESRF provided a
focal spot size of 38.25 µm at a focal distance of 1.4 m for 7.31 keV. This
is the first experiment with a parabolic-shaped groove; all previous
experiments were performed with circular grooves which introduced extreme
aberration broadening of the focal spot. The calculated and simulated focal
size was 10.8 µm at a distance of 1.1 m at 7.31 keV. It is assumed that the
difference between the measured and calculated/simulated focal spot size and
focal distance is due to insufficient surface quality and to alignment
imperfection.
D. Korytár, C. Ferrari, P. Mikulík, P. Vagovič, E. Dobročka, V. Áč, P. Konopka,
A. Erko, and N. Abrosimov,
Linearly graded GeSi beam-expanding/compressing X-ray monochromator,
Journal of Applied Crystallography
43 176–178 (2010).
Online here.
Abstract
In standard single-crystal V-channel germanium (220) X-ray
beam-expanding/compressing monochromators for Cu K[alpha]1 radiation, a total
beam expansion/compression of 5 and 10 corresponding to the asymmetry angles of
9 and 12° is achieved, respectively. Higher one-dimensional beam
expansion/compression is achievable using larger angles of asymmetry at the
expense of a decrease in the total intensity. To increase the intensity, a
linearly graded Ge-rich GexSi1-x single crystal was used to prepare a
monochromator with 15° asymmetry angles (total expansion/compression factor of
21) for Cu K[alpha]1 radiation. The X-ray diffraction measurements show more
than three times higher peak intensity at the output compared with that of a
pure Ge monochromator.
M. Hovorka, F. Mika, P. Mikulík, and L. Frank,
Profiling N-Type Dopants in Silicon,
Materials Transactions
51 237–242 (2010).
Online here.
Abstract
Variously doped n-type structures (dopant concentration between
1.5*1016 cm-3 and 1.5*1019 cm-3)
on a lightly doped p-type silicon substrate (doped to 1.9*1015
cm-3) have been examined by a photoemission electron microscope
equipped with a high-pass energy filter and by an ultra-high vacuum scanning
low energy electron microscope. High contrast have been observed between the
n-type areas and the p-type substrate and its monotone dependency on the doping
level of structures has been manifested. The relation between the energy
spectra of photoelectrons and the doping level has been studied, too. The
scanning electron microscope images obtained with the landing energy of the
primary beam in the low keV range exhibit contrasts similar to those appearing
in the full threshold photoemission micrographs.
V. Čech, S. Lichovníková, R. Trivedi, V. Peřina, J. Zemek, P. Mikulík, and O. Caha,
Plasma polymer films of tetravinylsilane modified by UV irradiation,
Surface and Coatings Technology
205 S177–S181 (2010).
Online here.
Abstract
As-deposited plasma polymer films of tetravinylsilane were modified by UV
irradiation at ambient conditions. Surface and bulk spectroscopic techniques
confirmed significant changes in chemical composition and structure that
resulted in increased mechanical constants (Young's modulus, hardness) and
density of the material due to the formation of a stronger polymer network with
higher cross-linking. A decrease of the refractive index and extinction
coefficient of the UV-irradiated material was caused by UV-induced chain
scission and subsequent oxidation of the plasma polymer network. The surface
morphology (RMS roughness) and wettability (surface free energy) of films can
be controlled by UV exposition time. The most intensive aging effect was
observed for the as-deposited film; in contrast, the 1000-min-UV-irradiated
film appeared stable over 134 days. UV treatment can be characterized as an
effective tool for additional tailoring of plasma polymer films according to
their applications.
P. Oberta, P. Mikulík, J. Hrdý, and M. Kittler,
Highly asymmetric Laue focusing monochromator,
SRI 2009: The 10th international conference on synchrotron radiation
instrumentation:
AIP Conference Proceedings
1234 724–727 (2010).
Reference here.
Abstract
By using two highly asymmetric Laue crystals in a dispersive arrangement with a
circular profile (Ø 8 mm) we have created a sagittaly focusing Laue system for
the first time. The crystallographic planes (111) of the two Si crystals formed
an angle of 7.95° with the entrance surface. The crystals dimensions were 40
mm×20 mm and the diffracting surface was a 0.5 mm thick neck between the two
circular profiles. The 15.35 keV diffracted beam formed an angle of 0.55° with
the exit surface. The calculated focusing distance of the Laue-Laue focusing
system was 14 m.
D. Korytár, C. Ferrari, P. Mikulík, P. Vagovič, E. Dobročka, V. Áč, P. Konopka, A. Erko,
N. Abrosimov, and Z. Zápražný,
1D X-ray Beam Compressing Monochromators,
20th International Congress on X-Ray Optics and Microanalysis:
AIP Conference Proceedings
1221 59–62 (2010).
Reference here.
Abstract
A total beam compression of 5 and 10 corresponding to the asymmetry angles of
9° and 12° is achieved with V-5 and V-10 monochromators, respectively, in
standard single crystal pure germanium (220) X-ray beam compressing (V-shaped)
monochromators for CuK1 radiation. A higher 1D compression of X-ray beam is
possible using larger angles of asymmetry, however it is achieved at the
expense of the total intensity, which is decreased due to the refraction
effect. To increase the monochromator intensity, several ways are considered
both theoretically and experimentally. Linearly graded germanium rich
GexSi(1−x) single crystal was used to prepare a V-21 single crystal
monochromator with 15° asymmetry angles (compression factor of 21). Its
temperature gradient version is discussed for CuK1 radiation. X-ray diffraction
measurements on the graded GeSi monochromator showed more than 3-times higher
intensity at the output compared with that of a pure Ge monochromator.
J. Hrdý, P. Mikulík, and P. Oberta,
Diffractive-refractive optics: (+,-,-,+) X-ray crystal monochromator
with harmonics separation,
Journal of Synchrotron Radiation
18 229–301 (2011).
Reference here.
Abstract
A new kind of two channel-cut crystals X-ray monochromator in dispersive
(+,-,-,+) position which spatially separates harmonics is proposed. The
diffracting surfaces are oriented so that the diffraction is inclined. Owing to
refraction the diffracted beam is sagittally deviated. The deviation depends on
wavelength and is much higher for the first harmonics than for higher
harmonics. This leads to spatial harmonics separation. The idea is supported by
ray-tracing simulation.
C. Ferrari, F. Germini, D. Korytár, P. Mikulík, and L. Peverini,
X-ray diffracted intensity for double-reflection channel-cut Ge
monochromators at extremely asymmetric diffraction conditions,
Journal of Applied Crystallography
44 353–358 (2011).
Reference here.
Abstract
The width and integrated intensity of the 220 X-ray double-diffraction profile
and the shift of the Bragg condition due to refraction have been measured in a
channel-cut Ge crystal in an angular range near the critical angle of total
external reflection. The Bragg angle and incidence condition were varied by
changing the X-ray energy. In agreement with the extended dynamical theory of
X-ray diffraction, the integrated intensity of the double diffraction remained
almost constant, even for the grazing-incidence condition very close to the
critical angle for total external reflection. A broadening of the diffraction
profile not predicted by the extended theory of X-ray diffraction was observed
when the Bragg condition was at angles of incidence lower than 0.6 degrees.
Plane wave topographs revealed a contrast that could be explained by a slight
residual crystal surface undulation of 0.3 degrees due to etching to remove the
cutting damage and the increasing effect of refraction at glancing angles close
to the critical angle. These findings confirm that highly asymmetric
channel-cut Ge crystals can also work as efficient monochromators or image
magnifiers at glancing angles close to the critical angle, the main limitation
being the crystal surface preparation.
P. Oberta, P. Mikulík, M. Kittler, and J. Hrdý,
X-ray collimation by crystals with precise parabolic holes based on
diffractive-refractive optics,
Journal of Synchrotron Radiation
18 522–526 (2011).
Reference here.
Abstract
Two crystals with precise parabolic holes were used to demonstrate sagittal
beam collimation by means of a diffractive-refractive double-crystal
monochromator. A new approach is introduced and beam collimation is
demonstrated. Two Si(333) crystals with an asymmetry angle of alpha = 15
degrees were prepared and arranged in a dispersive position (+,-,-,+). Based on
theoretical calculations, this double-crystal set-up should provide tunable
beam collimation within an energy range of 6.3-18.8 keV (Theta(B) = 71-18.4
degrees). An experiment study was performed on BM05 at ESRF. Using 8.97 keV
energy, the beam profile at various distances was measured. The experimental
results are in good agreement with theoretical predictions. Owing to
insufficient harmonic suppression, the collimated (333) beam was overlapped by
horizontally diverging (444) and (555) beams.
L. Helfen, A. Myagotin, P. Mikulík, P. Pernot, A. Voropaev,
M. Elyyan, M. Di Michiel, J. Baruchel, and T. Baumbach,
On the implementation of computed laminography using synchrotron radiation,
Review of Scientific Instruments
82 063702 (2011).
Reference here.
Abstract
Hard x rays from a synchrotron source are used in this implementation of
computed laminography for three-dimensional (3D) imaging of flat, laterally
extended objects. Due to outstanding properties of synchrotron light, high
spatial resolution down to the micrometer scale can be attained, even for
specimens having lateral dimensions of several decimeters. Operating either
with a monochromatic or with a white synchrotron beam, the method can be
optimized to attain high sensitivity or considerable inspection throughput in
synchrotron user and small-batch industrial experiments. The article describes
the details of experimental setups, alignment procedures, and the underlying
reconstruction principles. Imaging of interconnections in flip-chip and
wire-bonded devices illustrates the peculiarities of the method compared to its
alternatives and demonstrates the wide application potential for the 3D
inspection and quality assessment in microsystem technology.
P. Vagovič, D. Korytár, P. Mikulík, A. Cecilia, C. Ferrari, Y. Yang,
D. Hanschke, E. Hamann, D. Pelliccia, T.A. Lafford, M. Fiederle, and T. Baumbach,
In-line Bragg magnifier based on V-shaped germanium crystals,
Journal of Synchrotron Radiation
18 753–760 (2011).
Reference here.
Abstract
In this work an X-ray imaging system based on a recently developed in-line
two-dimensional Bragg magnifier composed of two monolithic V-shaped crystals
made of dislocation-free germanium is presented. The channel-cut crystals were
used in one-dimensional and in two-dimensional (crossed) configurations in
imaging applications and allowed measurement of phase-contrast radiograms both
in the edge-enhanced and in the holographic regimes. The measurement of the
phase gradient in two orthogonal directions is demonstrated. The effective
pixel size attained was 0.17 um in the one-dimensional configuration and 0.5
um in the two-dimensional setting, offering a twofold improvement in spatial
resolution over devices based on silicon. These results show the potential for
applying Bragg magnifiers to imaging soft matter at high resolution with
reduced dose owing to the higher efficiency of Ge compared with Si.
P. Oberta, J. Hrdý, and P. Mikulík,
A proof-of-principle experiment of a novel harmonics separation optics
for synchrotron facilities,
Journal of Synchrotron Radiation
19 1012–1014 (2012).
Reference here.
Abstract
A proof-of-principle experiment of a novel harmonics separation optics for
synchrotron facilities is presented. The harmonic separator is a Si crystal cut
in an inclined geometry in which the impinging beam undergoes a
diffractive-refractive effect owing to the dispersive nature of X-ray
refraction. A polychromatic beam containing higher-order energies is spatially
separated behind the separator into individual monochromatic diffraction spots.
A synchrotron experiment at a bending-magnet beamline with 7 keV fundamental
energy is presented. The spot of the third-order harmonic of 21 keV is deviated
from the fundamental by 0.35 mm at a distance 1 m behind the device.
Z. Zápražný, D. Korytár, P. Mikulík, and V. Áč,
Processing of projections containing phase contrast in laboratory micro-computerized tomography imaging,
Journal of Applied Crystallography
46 933–938 (2013).
Reference here.
Abstract
Free-space-propagation-based imaging belongs to several techniques for
achieving phase contrast in the hard X-ray range. The basic precondition is to
use an X-ray beam with a high degree of coherence. Although the best sources of
coherent X-rays are synchrotrons, spatially coherent X-rays emitted from a
sufficiently small spot of laboratory microfocus or sub-microfocus sources
allow the transfer of some of the modern imaging techniques from synchrotrons
to laboratories. Spatially coherent X-rays traverse a sample leading to a phase
shift. Beam deflection induced by the local change of refractive index may be
expressed as a dark-bright contrast on the edges of the object in an X-ray
projection. This phenomenon of edge enhancement leads to an increase in spatial
resolution of X-ray projections but may also lead to unpleasant artefacts in
computerized tomography unless phase and absorption contributions are
separated. The possibilities of processing X-ray images of lightweight objects
containing phase contrast using phase-retrieval methods in laboratory
conditions are tested and the results obtained are presented. For this purpose,
simulated and recorded X-ray projections taken from a laboratory imaging system
with a microfocus X-ray source and a high-resolution CCD camera were processed
and a qualitative comparison of results was made.
D. Korytár, P. Vagovič, K. Végsö, P. Šiffalovič, E. Dobročka, W. Jark,
V. Áč, Z. Zápražný, C. Ferrari, A. Cecilia, E. Hamann, P. Mikulík,
T. Baumbach, M. Fiederle, and M. Jergel,
Potential use of V‐channel Ge(220) monochromators in X‐ray metrology and imaging,
Journal of Applied Crystallography
46 945–952 (2013).
Reference here.
Abstract
While channel-cut crystals, in which the diffracting surfaces in an asymmetric
cut are kept parallel, can provide beam collimation and spectral beam shaping,
they can in addition provide beam compression or expansion if the cut is
V-shaped. The compression/expansion ratio depends in this case on the total
asymmetry factor. If the Ge(220) diffraction planes and a total asymmetry
factor in excess of 10 are used, the rocking curves of two diffractors will
have a sufficient overlap only if the second diffractor is tuned slightly with
respect to the first one. This study compares and analyses several ways of
overcoming this mismatch, which is due to refraction, when the CuK1 beam is
compressed 21-fold in a V21 monochromator. A more than sixfold intensity
increase was obtained if the matching was improved either by a compositional
variation or by a thermal deformation. This provided an intensity gain compared
with the use of a simple slit in a symmetrical channel-cut monochromator. The
first attempt to overcome the mismatch by introducing different types of X-ray
prisms for the required beam deflection is described as well. The performance
of the V-shaped monochromators is demonstrated in two applications. A narrow
collimated monochromatic beam obtained in the beam compressing mode was used
for high-resolution grazing-incidence small-angle X-ray scattering measurements
of a silicon sample with corrupted surface. In addition, a two-dimensional
Bragg magnifier, based on two crossed V15 channel monochromators in beam
expansion mode and tuned by means of unequal asymmetries, was successfully
applied to high-resolution imaging of test structures in combination with a
Medipix detector.
D. Korytár, P. Vagovič, C. Ferrari, P. Šiffalovič, M. Jergel, E. Dobročka,
Z. Zápražný, V. Áč, and P. Mikulík,
Process-induced inhomogeneities in higher asymmetry angle X-ray monochromators,
Proceedings SPIE Volume 8848: Advances in X-Ray/EUV Optics and Components VIII,
edited by A. Khounsary, S. Goto, and C. Morawe,
88480U-1–88480U-8 (2013).
Reference here.
Abstract
Beam inhomogeneities of asymmetric Ge(220)-based V-shaped and single bounce
monochromators have been studied both in metrological and imaging applications
for photon energies around 8 keV. Presence of growth striations in graded GeSi,
grains in single Cu crystal, and strains in thermally tuned V-channel
monochromators observed in X-ray topographs excludes these materials from
imaging applications. As for stochastic surface processing, chemomechanical
polishing (CMP) produces better surface homogeneity than chemical polish.
However, CMP is more difficult to be applied in V-channels, where chemical
polishing is prefered. For comparison, measurements on surfaces processed by a
deterministic mechanical method of single point diamond turning (SPDT) have
shown SPDT to be a perspective technology. Again, to prepare deep grooves with
this technique is also a challenge, mainly for tool makers. Some process
induced features are observed as wavefield distortions in interference fringes.
Z. Zápražný, D. Korytár, P. Šiffalovič, M. Jergel, M. Demydenko,
P. Mikulík, E. Dobročka, C. Ferrari, P. Vagovič, and M. Mikloška,
Simulations and surface quality testing of high asymmetry angle X-ray
crystal monochromators for advanced X-ay imaging applications,
Proceedings SPIE Volume 9207: Advances in X-Ray/EUV Optics and Components IX,
edited by C. Morawe, A. Khounsary, and S. Goto,
035101-1–035101-12 (2014).
Reference here.
Abstract
Advanced X-ray imaging techniques of weakly absorbing structures require an
increase of the sensitivity to small refractive angles considering that they
are based more on coherent X-ray phase contrast than on X-ray absorption one.
Simulations of diffraction properties of germanium (Ge) X-ray crystal
monochromators and of analyzer based imaging (ABI) method were performed for
various asymmetry factors and several lattice plane orientations using an X-ray
energy range from 8 keV to 20 keV. Using an appropriate phase/amplitude
retrieval method one can recover the phase information from the ABI image,
which is directly proportional to the projected electron density. We are using
germanium based optics for X-ray imaging or image magnification. The use of Ge
crystals offers several advantages over silicon crystals. The integrated
reflectivity of Ge crystals is two to three times larger than that of Si
crystals. The spatial resolution of Ge magnifiers is typically two times better
than the spatial resolution of Si magnifiers. We used high asymmetry
diffractions to increase effectively the propagation distance and decrease the
effective pixel size of the detector, to achieve a sufficient magnification of
the sample and to improve coherence and increase output intensity. The most
important parameter of a highly asymmetric monochromators as image magnifiers
is the crystal surface quality. We have applied several crystal surface
finishing methods including conventional mechanical lapping, chemical
polishing, chemo-mechanical polishing and advanced nano-machining using single
point diamond turning (SPDT), and we have evaluated these methods by means of
AFM, diffractometry, reciprocal space mapping and others.
E. Barrier, F.M.B. Fernandes, M. Bujan, M.C. Feiters, A. Froideval, J. Ghijsen, T. Hase, M.A. Hough,
M. Jergel, I. Jimenez, T. Kajander, A. Kikas, M. Kokkinidis, L. Kover, H.B. Larsen, D.M. Lawson,
K. Lawniczak-Jablonska, C. Mariani, P. Mikulik, J. Monnier, S. Morera, C. McGuinness, P. Müller-Buschbaum,
M.M. Nielson, U. Pietsch, M. Tromp, M. Simon, J. Stangl, and G. Zanotti,
The benefit of the European User Community from transnational access to national radiation facilities,
Journal of Synchrotron Radiation 21 638–639 (2014).
Reference here.
Abstract
Transnational access (TNA) to national radiation sources is presently provided
via programmes of the European Commission by BIOSTRUCT-X and CALIPSO with a
major benefit for scientists from European countries. Entirely based on
scientific merit, TNA allows all European scientists to realise synchrotron
radiation experiments for addressing the Societal Challenges promoted in
HORIZON2020. In addition, by TNA all European users directly take part in the
development of the research infrastructure of facilities. The mutual
interconnection of users and facilities is a strong prerequisite for future
development of the research infrastructure of photon science. Taking into
account the present programme structure of HORIZON2020, the European
Synchrotron User Organization (ESUO) sees considerable dangers for the
continuation of this successful collaboration in the future.
Z. Zápražný, D. Korytár, M. Jergel, P. Šiffalovič, E. Dobročka, P. Vagovič, C. Ferrari, P. Mikulík, M. Demydenko,
and M. Mikloška,
Calculations and surface quality measurements of high-asymmetry angle x-ray crystal monochromators
for advanced x-ray imaging and metrological applications,
Optical Engineering 54 035101 (2015).
Reference here.
Abstract
We present the numerical optimization and the technological development
progress of x-ray optics based on asymmetric germanium crystals. We show the
results of several basic calculations of diffraction properties of germanium
x-ray crystal monochromators and of an analyzer-based imaging method for
various asymmetry factors using an x-ray energy range from 8 to 20 keV. The
important parameter of highly asymmetric monochromators as image magnifiers or
compressors is the crystal surface quality. We have applied several crystal
surface finishing methods, including advanced nanomachining using single-point
diamond turning (SPDT), conventional mechanical lapping, chemical polishing,
and chemomechanical polishing, and we have evaluated these methods by means of
atomic force microscopy, diffractometry, reciprocal space mapping, and others.
Our goal is to exclude the chemical etching methods as the final processing
technique because it causes surface undulations. The aim is to implement very
precise deterministic methods with a control of surface roughness down to
0.1 nm. The smallest roughness (∼0.3 nm), best planarity, and absence of the
subsurface damage were observed for the sample which was machined using an SPDT
with a feed rate of 1 mm/min and was consequently polished using a fine
polishing 15-min process with a solution containing SiO2 nanoparticles
(20 nm).
Z.J. Li, A.N. Danilewsky, L. Helfen, P. Mikulík, D. Haenschke, J. Wittge,
D. Allen, P. McNally, and T. Baumbach,
Local strain and defects in silicon wafers due to nanoindentation revealed by full-field X-ray microdiffraction imaging,
Journal of Synchrotron Radiation 22 1083–1090 (2015).
Reference here.
Abstract
Quantitative characterization of local strain in silicon wafers is critical in
view of issues such as wafer handling during manufacturing and strain
engineering. In this work, full-field X-ray microdiffraction imaging using
synchrotron radiation is employed to investigate the long-range distribution of
strain fields in silicon wafers induced by indents under different conditions
in order to simulate wafer fabrication damage. The technique provides a
detailed quantitative mapping of strain and defect characterization at the
micrometer spatial resolution and holds some advantages over conventional
methods.
K. Végsö, M. Jergel, P. Šiffalovič, E. Majková, D. Korytár, Z. Zápražný,
P. Mikulík, and P. Vagovič,
Towards high-flux X-ray beam compressing channel-cut monochromators,
Journal of Applied Crystallography 49 1885–1892 (2016).
Reference here.
Abstract
The issue of a high-flux X-ray beam compressing channel-cut monochromator for
applications in X-ray metrology is addressed. A Ge(111) compressor with
compression ratio 20.3 was designed on the principle of a combination of
symmetric and highly asymmetric diffractions. A pilot application of the
single-point diamond technology (SPDT) to finish active surfaces of X-ray
optics was tested, providing 50% flux enhancement as compared to a Ge(220)
counterpart prepared by traditional surface treatment. This is much more than
the theoretical 22% forecast and shows the potential of SPDT for preparation of
high-flux X-ray compressors with a high compression ratio, where highly
asymmetric diffraction with a very low exit angle is inevitable. The
implications for efficient collection of X-rays from microfocus X-ray sources
are discussed. A comparison of Ge compressors with Ge parallel channel-cut
monochromators combined with a 50 µm slit shows the several times higher flux
of the former, making them applicable in X-ray diffraction experiments at
medium resolution. Furthermore, the Ge(111) compressor was tested as a
collimator in high-resolution grazing-incidence small-angle X-ray scattering
(GISAXS) measurements of surface gratings, providing experimental resolution
close to 400 nm. This is ~100 nm smaller than that achieved with the Ge(220)
compressor but still approximately twice that of commercial SAXS/GISAXS
laboratory setups.
D. Fialová, E. Drozdová, R. Skoupý, P. Mikulík, and B. Klíma.
Scanning electron microscopy of dental calculus from Great Moravian necropolis Znojmo-Hradiště,
Anthropologie 55 343–351 (2017).
Reference here.
Abstract
Thirteen samples of ancient human dental calculus were analyzed by scanning
electron microscopy (SEM). Samples came from ten adults from the necropolis
Znojmo-Hradiště which is dated to the Great Moravian period (the end of the 9th
and beginning of the 10th century AD). SEM allowed observation and measurement
of the excavated calculus objects with submicrometer resolution. Therefore it
was possible to estimate plant/vegetable fibers and all bacterial morphological
types like rods, cocci, spirals and filamentous forms. This confirms high oral
bacterial diversity of medieval agriculturalists which is in agreement with
recent molecular studies, but without destruction of samples and with lower
costs. Presence of plant/vegetable fibers in dental calculus validated the
vegetable part of the diet of early medieval Slavs found directly in excavated
human skeletons.
V. Prajzler, M. Neruda, P. Nekvindová, and P. Mikulík.
Properties of Multimode Optical Epoxy Polymer Waveguides Deposited on Silicon and TOPAS Substrate,
Radioengineering 26 10–15 (2017).
Reference here.
Abstract
The paper reports on the fabrication and characterization of multimode polymer
optical waveguides. Epoxy polymer EpoCore was used as the waveguide core
material and EpoClad was used as a cladding and cover protection layer. The
design of the waveguides was schemed for geometric dimensions of 50 mu m core
and for 850 nm and 1310 nm wavelengths. Proposed shapes of the waveguides were
fabricated by standard photolithography process. Optical losses of the planar
waveguides were measured by the fibre probe technique at 632.8 nm and 964 nm.
Propagation optical loss measurements for rectangular waveguides were done by
using the cut-back method and the best samples had optical losses lower than
0.53 dB/cm at 650 nm, 850 nm and 1310 nm.
T. Faragó, P. Mikulík, A. Ershov, M. Vogelgesang, D. Hanschke, and T. Baumbach.
Towards high-flux X-ray beam compressing channel-cut monochromators,
Journal of Synchrotron Radiation 24 1283–1295 (2017).
Reference here.
Abstract
An open-source framework for conducting a broad range of virtual X-ray imaging
experiments, syris, is presented. The simulated wavefield created by a source
propagates through an arbitrary number of objects until it reaches a detector.
The objects in the light path and the source are time-dependent, which enables
simulations of dynamic experiments, e.g. four-dimensional time-resolved
tomography and laminography. The high-level interface of syris is written in
Python and its modularity makes the framework very flexible. The
computationally demanding parts behind this interface are implemented in
OpenCL, which enables fast calculations on modern graphics processing units.
The combination of flexibility and speed opens new possibilities for studying
novel imaging methods and systematic search of optimal combinations of
measurement conditions and data processing parameters. This can help to
increase the success rates and efficiency of valuable synchrotron beam time. To
demonstrate the capabilities of the framework, various experiments have been
simulated and compared with real data. To show the use case of measurement and
data processing parameter optimization based on simulation, a virtual
counterpart of a high-speed radiography experiment was created and the
simulated data were used to select a suitable motion estimation algorithm; one
of its parameters was optimized in order to achieve the best motion estimation
accuracy when applied on the real data. syris was also used to simulate
tomographic data sets under various imaging conditions which impact the
tomographic reconstruction accuracy, and it is shown how the accuracy may guide
the selection of imaging conditions for particular use cases.
Last update: 8. 2. 2018