316 research outputs found
Grazing Incidence Small Angle X-Ray Scattering (GISAXS) on Small Targets Using Large Beams
GISAXS is often used as a versatile tool for the contactless and
destruction-free investigation of nanostructured surfaces. However, due to the
shallow incidence angles, the footprint of the X-ray beam is significantly
elongated, limiting GISAXS to samples with typical target lengths of several
millimetres. For many potential applications, the production of large target
areas is impractical, and the targets are surrounded by structured areas.
Because the beam footprint is larger than the targets, the surrounding
structures contribute parasitic scattering, burying the target signal. In this
paper, GISAXS measurements of isolated as well as surrounded grating targets in
Si substrates with line lengths from down to
are presented. For the isolated grating targets, the changes in the scattering
patterns due to the reduced target length are explained. For the surrounded
grating targets, the scattering signal of a target grating structure is separated from the
scattering signal of nanostructured
surroundings by producing the target with a different orientation with respect
to the predominant direction of the surrounding structures. The described
technique allows to apply GISAXS, e.g. for characterization of metrology fields
in the semiconductor industry, where up to now it has been considered
impossible to use this method due to the large beam footprint
Correlated Diffuse X-ray Scattering from Periodically Nano-Structured Surfaces
Laterally periodic nanostructures were investigated with grazing incidence
small angle X-ray scattering. To support an improved reconstruction of
nanostructured surface geometries, we investigated the origin of the
contributions to the diffuse scattering pattern which is correlated to the
surface roughness. Resonant diffuse scattering leads to a palm-like structure
of intensity sheets. Dynamic scattering generates the so-called Yoneda band
caused by a resonant scatter enhancement at the critical angle of total
reflection and higher-order Yoneda bands originating from a subsequent
diffraction of the Yoneda enhanced scattering at the grating. Our explanations
are supported by modelling using a solver for the time-harmonic Maxwell's
equations based on the finite-element method
Stripes and cycloids
Diese Arbeit beschäftigt sich mit resonanter Streuung im weichen
Röntgenenergiebereich (RSXS) zur Untersuchung komplexer Ordnungsphänomene in
oxidischen Materialien. Die Methode adressiert die Elektronen, die für die
interessanten physikalischen Eigenschaften dieser Systeme maßgeblich
verantwortlich sind. Die 3d- und 4f-Elektronen spielen dabei eine
entscheidende Rolle und ihre Strukturen können mit RSXS sehr empfindlich
elementspezifisch untersucht werden. In dieser Arbeit wurden zwei verschiedene
Systeme untersucht, deren physikalische Eigenschaften eine Vielzahl
technologischer Einsatzmöglichkeiten versprechen. Eines dieser Systeme sind
die Seltenerdmanganate der Form REMnO3, wobei RE für die Seltenerden steht. In
diesen multiferroischen Materialien kann sich bei tiefen Temperaturen eine
ferroelektrische Polarisation bilden, die mit einer zykloidalen Modulation der
Mn-3d-Momente verbunden ist. Die hier durchgeführte Studie an DyMnO3 zeigt,
dass die Dy-4f-Momente ebenfalls einer zykloidalen Ordnung folgen. Dies bietet
eine Erklärung für die bisher beobachteten Anomalien in der ferroelektrischen
Polarisation als Funktion der Temperatur. In GdMnO3 ist die Situation anders.
Starke zirkular dichroische Effekte in RSXS konnten erstmals die bisherigen
Vermutungen bestätigen, dass auch in GdMnO3 eine Zykloide der Mn-3d-Momente
existiert, die als alleinige Ursache der ferroelektrischen Polarisation
angenommen werden muss. In den REMnO3 konnten Manipulationsexperimente
ferroischer Domänen durch den Synchrotronstrahl durchgeführt werden, sie sind
ein anschauliches Beispiel für das enorme Potential multiferroischer Systeme.
Ein anderes komplexes Ordnungsphänomen, welches hier untersucht wurde, sind
die Ladungs- und Spinstreifenordnungen einiger Hoch-TC (HTC)-Supraleiter. In
den Kupraten La1.8-xEu0.2SrxCuO4 (LESCO) und La2-xBaxCuO4 (LBCO) lässt sich
bei einer Ladungsträgerdotierung von x = 1/8 ein Absinken der
Sprungtemperaturen der Supraleitung beobachten, das mit der Bildung einer
Streifenordnung koinzidiert. Die hohe Sensitivität resonanter Röntgenstreuung
auf kleinste Ladungsmodulationen zeigt sich bei den Untersuchungen an LESCO
Kupraten. Hier konnten erstmalig Überstrukturreflexe der
Ladungsstreifenordnung bis zu einer Temperatur von 80 K nachgewiesen und im
Zusammenhang mit einem strukturellen Phasenübergang untersucht werden. Die
durch diese Untersuchungen möglich gewordene Erweiterung der Phasendiagramme
von LBCO und LESCO verdeutlicht, dass LESCO eines der ersten HTC-Kuprate ist,
in dem die Ladungsstreifenordnung nicht durch die strukturelle Phase begrenzt
wird. Dieses Ergebnis hat bereits zu zahlreichen Diskussionen innerhalb der
HTC-Wissenschaftsgemeinschaft geführt, insbesondere über den Zusammenhang mit
der Spinordnung. Für die Experimente wurde im Rahmen der Arbeit ein neues UHV-
Diffraktometer entwickelt und aufgebaut, welches sich besonders durch seine
Flexibilität und Stabilität für den Einsatz an einer
Synchrotronstrahlungsquelle wie BESSYII in Berlin auszeichnet.The present work describes resonant soft X-Ray scattering (RSXS) as a probe to
investigate complex ordering phenomena in oxide materials. RSXS allows to
probe in an elementspecific way the 3d- and 4f-valence electrons that are
responsible for the interesting physical characteristics of these materials.
Two different material systems with promising possible technological
application were studied. One of these systems is the rare-earth manganites
(REMnO3). These multiferroic materials exhibit ferroelectric polarisation at
low temperatures induced by cycloidal magnetic order of the Mn-3d-moments. It
is clear from the present results on DyMnO3 that the 4f ordering itself is of
cycloidal character, which offers an explanation for the anomalies in the
ferroelectric polarisation as a function of temperature in this material. In
GdMnO3 the situation is different. Strong circular dichroic effects in RSXS
confirm for the first time that ferroelectricity in GdMnO3 follows also from a
cycloidal modulation of the Mn-3d-moments, as previously anticipated. In
REMnO3, ferroic domains could be manipulated by the synchrotron x-ray beam,
which is an illustrative example for the potential of multiferroic systems.
Another complex ordering phenomenon studied in this work is charge stripe
formation in High-TC (HTC)-superconductors. The critical temperature of the
superconducting state decreases substantially in the cuprates
La1.8-xEu0.2SrxCuO4 (LESCO) and La2-xBaxCuO4 (LBCO) at a doping concentration
of x = 1/8. This coincides with the formation of the stripe phase. The very
high sensitivity of resonant soft X-Ray diffraction to small charge
modulations offered for the first time the possibility to determine the
transition temperature of the charge order in LESCO (up to 80 K), particularly
in relation to the structural phase transition. With these results it was
possible to extend the phase diagrams of both cuprates, demonstrating that
LESCO is the first HTC-cuprate were the charge order is not limited by the
structural phase transition. This result already triggered substantial
discussion in the HTC scientific community, especially in connection with
reported spin ordering temperatures. For the present experiments, a new UHV
diffractometer was developed and built, offering the flexibility and stability
required for an instrument at a synchrotron radiation source, such as BESSY II
in Berlin
Reconstructing Detailed Line Profiles of Lamellar Gratings from GISAXS Patterns with a Maxwell Solver
Laterally periodic nanostructures were investigated with grazing incidence
small angle X-ray scattering (GISAXS) by using the diffraction patterns to
reconstruct the surface shape. To model visible light scattering, rigorous
calculations of the near and far field by numerically solving Maxwell's
equations with a finite-element method are well established. The application of
this technique to X-rays is still challenging, due to the discrepancy between
incident wavelength and finite-element size. This drawback vanishes for GISAXS
due to the small angles of incidence, the conical scattering geometry and the
periodicity of the surface structures, which allows a rigorous computation of
the diffraction efficiencies with sufficient numerical precision. To develop
dimensional metrology tools based on GISAXS, lamellar gratings with line widths
down to 55 nm were produced by state-of-the-art e-beam lithography and then
etched into silicon. The high surface sensitivity of GISAXS in conjunction with
a Maxwell solver allows a detailed reconstruction of the grating line shape
also for thick, non-homogeneous substrates. The reconstructed geometrical line
shape models are statistically validated by applying a Markov chain Monte Carlo
(MCMC) sampling technique which reveals that GISAXS is able to reconstruct
critical parameters like the widths of the lines with sub-nm uncertainty
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