NANOPTICUM
Meet Accurion at Conferences & Exhibitions
Traceable characterisation of thin-film materials for energy applications,
Workshop on advanced optical measurements
January, 27th, 2016, in Berlin-Adlershof, Germany
www.ptb.de/emrp/2597.h
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www.bitcongress.com/wc
sm2016
Nanopticum 01/2016
Oral Presentation: New Trends in Spectroscopic Imaging Ellipsometry.
SEBASTIAN FUNKE
BIT’s 2nd Annual World Congress of Smart Materials-2016
Develop New Path of Smartness
March 4-6, 2016, in Singapore
Oral Presentation: Characterization of 2D Materials with Spectroscopic
Imaging Ellipsometry – an overview. PETER H. THIESEN
http://www.controlmesse.de
30th Control – International trade fair
for quality assurance
April, 26-29, 2016, in Stuttgart, Germany
7th International Conference on Spectroscopic Ellipsometry (ICSE-7)
June 06-10, 2016, in Berlin, Germany
www.icse-7.de
Abstract submission is still open until the 15th of January.
… or visit our youtube channel
Highlight: Nanofilm_Ultrabam
NANOPTICUM
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Contents
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Fascination Water Surface: Brewster angle Microscopy.
3
Ellipsometry on microscopic structures: Characterization
of SiO2 nanoparticle layers on a glass substrate by
spectroscopic imaging ellipsometry.
4
Spotlight on Literature: Ion adsorption and -induced
wetting transition in oil-water-mineral systems.
5
New Application - Characterization of Substrates for
Green Laser Annealing
6
New „single shot“ thickness control of ultrathin films:
Referenced Spectral Ellipsometry
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Fascination Water Surface
Brewster Angle Microscopy
Nanofilms at the air water interface are fascinating and of highest
scientific interest, because of the biological relevance. Interest is also
high because of the unique options from using Langmuir Blodgett
techniques. This allows control of the film morphology as well as the fact
that the air/water interface is a unique surface model for evaluation of
theoretical works. In general, scanning techniques do not work at the
air/water interface and that fact can have a huge influence on the
properties of the observed film. Brewster angle microscopy is the
preferential method for the mesoscopic characterization of monolayers
at the air interface without a transfer to a solid substrate. Recently, a
very interesting review was published by Vollhardt (2014).
Conferences & Exhibitions
Image of the month: Ellipsometric contrast micrographs at wavelength in the range between 250 nm
and 1700 nm, recorded with a Spectroscopic Imaging Ellipsometer (SIE):
Recorded with an
The “trick” is based on the fact that at the Brewster angle of incidence a
parallel polarized laser beam has zero reflectance and the image is black.
But even after tiny impacts to the refractive index like a domain of a
condensed monolayer, the Brewster law is not full filled anymore. The
surface is reflecting light and by using a high intensity light source like a
laser, nanofilms can be imaged directly on the water surface. From the
point of view of biological or medical relevance, the properties of Lipids
at the air /water interface as a membrane model are still the main focus.
A common example is the behavior of lung surfactants. Current
applications are frequently focused on the interaction of the lipid
monolayer with bioactive molecules and proteins from the subphase or
the degradation by enzymes. BAM can help to learn more about the
interaction between lipid monolayers and nanoparticles. This
information is required in nanomedicine to develop drugs and to
investigate the toxicity of nanoparticles in the environement. From the
point of view of nano engineering, this information is also required for
characterizing the interfacial assembly of nanoparticles, conjugated
polymers and metal complexes for OLEDs and photovoltaic applications.
Concerning the instrumentation, it is important to have a Brewster angle
microscope with a high quality polarizer and an exact goniometer to
obtain the best contrast (A) and a large variation in the greyscale (E). To
visualize the segments of different domains (A,D) or to invert the
contrast (B,C), it is essential that the Brewster angle microscope has a
motorized polarizer and analyzer. From the point of view of image
quality, the most important innovation of the last decade in the field of
Brewster angle microscopy was the development of the ultraobjective
that is used in the nanofilm_ultrabam. The specifically developed
imaging optics provides fully focused images at 20-35 frames per second
with a high lateral resolution. This enables the visualization of filigree
elements like thin lines (D) without being disturbed by the movement of
the film. But still a vibration free environment improves the results. The
use of active vibration isolation systems is state of the art in Brewster
Angle Microscopy.
A)
B)
C)
D)
E)
F)
Recorded with
NANOPTICUM
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Ellipsometry on microscopic structures:
Spotlight on Literature
Characterization of SiO2 nanoparticle stripes on a glass substrate by
spectroscopic imaging ellipsometry
Figure 1. Ellipsometric contrast
micrograph, 5x magnification
a)
b)
Ion adsorption and -induced wetting transition in oil-water-mineral systems
The morphology of printed patterns of nanoparticles
is of increasing interest for photonic applications.
The height profile, the optical properties, the surface
roughness and the volume fraction of void are
critical parameters.
The relative wettability of oil and ion containing water on
solid surfaces is of interest for a number of technical
applications like enhanced oil recovery processes. It is
generally governed by a complex competition of molecular
interaction forces acting in such three-phase systems.
In this work aggregations of SiO2 nanoparticles in line
shaped patterns on a glass substrate (Fig. 4) were
characterized with our imaging spectroscopic
ellipsometer nanofilm_ep4 equipped with a beam
cutter and an AFM. The ellipsometric measure-
Lei Wang et al. (2015) used imaging Internal Reflection
Ellipsometry in combination with a microfluidic device to
study the adsorption of inorganic salt ions to silica-water
interfaces. The data were analyzed with an optical model
based on a layer stack, where the electric double layer is
modeled as a separate layer. Due to the high resolution of the
technique, they were able to quantify the adsorption of Na+
and Ca2+ ions from aqueous solutions of their chloride salts as
a function of their bulk concentrations at pH 3 and 10.
ments were performed with different magnifications. A lower magnification image includes
the complete shadow of the beamcutter. The
middle portion of the image is very clear and
sharp. Outside this region the image is disturbed
by backside reflected light (Fig. 1). Ellipsometric
contrast micrographs recorded at different
wavelength can be used to distinguish between
gradient-type profiles, were the number of
interference fringes varies with wavelengths
(Fig. 2,3a) and step like profiles with a fixed
regions of gray-scale values (Fig 2,3b).
Figure 2. Ellipsometric contrast
micrograph of the two samples
a)
b)
Figure 3. Croped Ellipsometric contrast
micrograph at different wavelengths for
gradient (a) and step like (b) profile
The ellipsometric measurements were
transferred into thickness maps by
using an optical model including a
roughness layer, a dense packed layer
and the glass substrate (Figure 5). The
step like sample was characterized
with spectra measured at tiny regions
of interest for each step. The profile
of the gradient like sample was
recorded with an array of regions of
interest and by micro mapping,
respectively. All results are in
agreement with AFM measurements.
Acknowledgment:
We thank Prof. Y. Mori, Doshisha
University, Japan for preparing the
samples.
Figure 4. Illustration of the sample
designe.
Figure 5. Illustration of the optical
model.
Figure 6. Wavelength-spectra of
Delta and Psi and results for the
first step of a step like sample.
a)
Additionally Mugele et al. (2015) demonstrated experimentally how the adsorption of divalent Ca2+ cations to solidliquid interfaces induces a macroscopic wetting transition
from finite contact angles (≈10°) with to near-zero contact
angles without divalent cations. They developed a
quantitative model based on DLVO theory to demonstrate
that this transition, which is observed on model clay surfaces,
and mica, but not on silica surfaces nor for monovalent K+ and
Na+ cations is driven by charge reversal of the solid-liquid
interface.
Small amounts of a polar hydrocarbon, stearic acid, added to
the ambient decane synergistically enhance the effect and
lead to water contact angles up to 70° in the presence of Ca2+.
The results imply that it is the removal of divalent cations that
makes reservoir rocks more hydrophilic, suggesting a
generalizable strategy to control wettability and an
explanation for the success of so-called low salinity water
flooding, a recent enhanced oil recovery technology.
b)
References
Wang L, Zhao C, Duits MGH, Mugele F, Siretanu I (2015)
Sensors and Actuators B: Chem. Vol. 210: 649–655
Figure 7. Thickness profile of the
gradient profile measured with
the regions of Interest array (a)
and with the micro mapping
option (b).
Poster, honored with the poster prize at the
WSE2015 ( Lei Wang et al.)
Mugele F, Bera B, Cavalli A, Siretanu I, Maestro A, Duits M,
Cohen-Stuart M, van den Ende D, Stocker I, Collins I
(2015) Sci. Rep. 5: 10519: 1-8
Time dependency of the ellipsometric angles Δ and
Ψ shifts upon consecutive flushing water and 0.5 M
CaCl2 (aq) at pH 3 and pH 10..
NANOPTICUM
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New Applications
Characterization of Substrates for Green Laser Annealing
The OLED (organic light emitting diode) display consists of RGB
(red-green-blue) pixels which create the dynamic display image.
Each pixel is emitting light and its intensity is controlled by thin
film transistors. The thin film transistors (TFT) are built into a
silicon film of typically 50-65 nm thickness.
Figure 1. TFT schematics in a flat panel
display
Amorphous silicon films deposited on glass substrates to
prepare thin film transistors for the manufacture of flat panel
displays show variations of absorption performance in the green
wavelength range. Green laser beams are applied to heat the aSi film to the melting temperature and convert the film into high
electron mobility p-Si films. Most important is the a-Si
composition including crystalline fractions in the a-Si film. The
absorption of green laser light reaches 200.000 cm-1 for pure a-Si
material, however it is as low as 5.000-10.000 cm-1 for p-Si films.
The measurement of the complex index of refraction of the a-Si
film with the ACCURION EP4 ellipsometer gives important data
for the a-Si film composition. Measurements of a-Si samples
from a variety of display manufacturers have shown that the
extinction coefficient k varies from 0,54 to 0,62. The green laser
annealing process requires control of the low crystalline fraction
in the a-Si film.
New “single shot“ thickness control of
ultrathin films:
Referenced Spectral Ellipsometry
The thickness of thin layers is a critical control parameter in high tech fabrication. The demand of precise
and fast measurements for ultrathin nanofilm thickness is dramatically increasing. Also, emerging
technologies like 2D material based devices will boost this need. The State of the art in layer thickness
control includes sensors based on reflectometry and interferometry or confocal chromatic sensor as well
as classical spectroscopic ellipsometer. In in most cases these techniques are not able to precisely
measure the thickness of ultrathin nanofilms or they are not able to measure the thickness with a “single
shot”. One main question for innovations in the field of nanofilm related process control is:
How can we increase the sensitivity of a sensor for the layer thickness determination of nanofilms in a
“single shot” procedure?
A new approach, developed by Accurion, is Referenced Spectral Ellipsometry, where the sample is
compared to a specifically chosen reference. This technique enables the determination of the
ellipsometric difference between sample and reference. Furthermore none of the optical components
need to be moved or modulated during measurement. The full, high resolution spectrum can be
obtained in a single-shot measurement and the speed is only limited by the used spectrometer. The first
product based on this technology, the nanofilm_RSE, will be available in the second half of 2016. The
instrument enables 100 spectral measurements per second. In combination with a synchronized x-ystage a large-field film-thickness-map of the sample can be measured within a few minutes.
The key specifications of the nanofilm_RSE:
Table 1. Measured data on three
different samples: nc= n + i k, with
nc= complex index,
n = refractive index, k = extinction
coefficient,  = 4 k/ absorption
coefficient
.
Data was recorded with an EP4 imaging
spectroscopic ellipsometer equipped
with a 10x objective, a beam cutter, and
an automatic x,y stage. Data was
recorded between 360 and 800 nm at
an angle of incidence of 50°. To avoid
back side reflection, knife edge
illumination (beam cutter) was used.
Recorded with an:
Samples a and c showed good green laser annealing with the
VOLCANO LB750G line beam laser optics. The lower absorption
coefficient of sample c was compensated with the thickness.
Sample b was not useful for green laser annealing. This is caused
by the 31.8 µm film thickness and the lowest absorption
coefficient.
Using models from the ACCURION material data bank for a-Si
and p-Si led to the conclusion that all a-Si films include fractions
of crystalline silicon. This is the root cause for the difference in
absorption. The estimated fraction of crystalline silicon was
between 16…35%.
Acknowledgement
Substrates for measurement and report were provided by
INNOVAVENT GmbH, Goettingen (www.innovavent.com)
instrument type:
spectral range:
data rate:
spot size:
patterning:
referenced spectral ellipsometer (non imaging)
450-900 nm, 1.2 nm resolution
100 full spectra per second
~ 100 µm microspot
motorized X-Y-Stage, 200 mm range
film-thickness
-resolution:
-reproducibility:
typ. 0.1 nm
typ. ±0.5 %
Thickness,
Graphene
Thickness,
SiO2
Graphene|SiO2|Si sample: Graphene- and SiO2- film-thicknessmap. The entire sample of 1x1 cm is coated with a monolayer
of Graphene. The measurement reveals film-thicknessvariations in the SiO2-substrate. Defects also can clearly be
identified.
Technology demonstrator of a
Referenced Spectral Ellipsometer.