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Ellipsometric characterisation of anisotropic thin organic films [Elektronische Ressource] / vorgelegt von Dana-Maria Rosu

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75 pages
Ellipsometric characterisation of anisotropic thin organic films vorgelegt von MSc Phys. Dana - Maria Rosu aus Hunedoara, Rumänien von der Fakultät II - Mathematik und Naturwissenschaften der Technischen Universität Berlin zur Erlangung des akademischen Grades Doktor der Naturwissenschaften - Dr. rer. nat. – genehmigte Dissertation Promotionsausschuss: Vorsitzender: Prof. Dr. Birgit Kanngießer Berichter: Prof. Dr. Norbert Esser rof. Dr. Christian Thomsen Berichter: Prof. Dr. Georgeta Salvan Tag der wissenschaftlichen Aussprache: 17.06.2010 Berlin 2010 D 83 Parts of this work have been already published in: Journals: Dana M. Rosu, Jason C. Jones, Julia W. P. Hsu, Karen L. Kavanagh, Dimiter Tsankov, Ulrich Schade, Norbert Esser, Karsten Hinrichs, Langmuir 25 (2009) 919: Molecular orientation in octanedithiol and hexadecanethiol monolayers on GaAs and Au measured by infrared spectroscopic ellipsometry. Reports: K. Hinrichs, M. Gensch, G. Dittmar, S. D. Silaghi, D.-M. Rosu, U. Schade, D.R.T. Zahn, S. Kröning, R. Volkmer and N. Esser, BESSY ANNUAL REPORTS, 285 (2006): IR - Synchrotron Mapping Ellipsometry for Characterisation of Biomolecular Films.
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Berichter: Prof. Dr. Christian Thomsen
Tag der wissenschaftlichen Aussprache: 17.06.2010
Berichter: Prof. Dr. Georgeta Salvan
Promotionsausschuss:
Berichter: Prof. Dr. Norbert Esser
Vorsitzender: Prof. Dr. Birgit Kanngießer
Berlin 2010
D 83
Dana - Maria Rosu
Ellipsometric characterisation of anisotropic thin organic films
MSc Phys.
vorgelegt von
zur Erlangung des akademischen Grades
der Technischen Universität Berlin
von der Fakultät II - Mathematik und Naturwissenschaften
Doktor der Naturwissenschaften
aus Hunedoara, Rumänien
genehmigte Dissertation
- Dr. rer. nat. 
K. Hinrichs, M. Gensch, G. Dittmar, S. D. Silaghi, D.-M. Rosu, U. Schade, D.R.T.
Zahn, S. Kröning, R. Volkmer and N. Esser, BESSY ANNUAL REPORTS, 285 (2006):
IR - Synchrotron Mapping Ellipsometry for Characterisation of Biomolecular Films.
Parts of this work have been already published in:
2
Ulrich Schade, Norbert Esser, Karsten Hinrichs, Langmuir 25 (2009) 919: Molecular
Dana M. Rosu, Jason C. Jones, Julia W. P. Hsu, Karen L. Kavanagh, Dimiter Tsankov,
Journals:
orientation in octanedithiol and hexadecanethiol monolayers on GaAs and Au measured
Reports:
by infrared spectroscopic ellipsometry.
1.
Table of contents
Introduction 5
Einleitung 7
Theoretical background 10
1.1 Polarized light10
1.2 Ellipsometric quantities.12
1.3 Mathematical description of polarized light..15
1.4 Electronic spectra. Franck-Condon principle20
2. Experimental techniques 23
3
4
5
2.1Spectroscopic ellipsometry (SE)...23
2.2Synchrotron mapping ellipsometry...24
Optical modelling 27
3.1 Cauchy model27
3.2 Gaussian oscillator model..28
3.3 Lorentz model29
Self assembled monolayers of alkanethiol 31
4.1Sample preparation32
4.2IRSE characterisation of alkanethiol thin films.33
4.3IR synchrotron mapping ellipsometry...42
Cytosine 44
5.1Sample preparation45
3
5.2AFM characterisation of cytosine films46
5.3Visible spectroscopic ellipsometry47
5.4Infrared spectroscopic ellipsometry.51
5.5Synchrotron mapping ellipsometry..60
 6. Concluding remarks 63
 References 65
 List of figures 70
 List of tables 73
 Acknowledgements 74
4
Introduction
The aim of the present work was to investigate the structural properties of
organic molecules on different substrates using different optical spectroscopic
techniques. The two studied systems were: self assembled monolayers of alkanethiols
on GaAs and Au and cytosine thin films on H-passivated Si(111) surface. As it will be
introduced in chapters 4 and 5, the studied organic molecules are very attractive due to
their application in various fields, ranging from biosensors to optoelectronic devices.
Characterisation of the molecular orientation and molecular packing in systems
as biological sensors, electronic and optical organic devices, novel solid lubricants,
corrosion inhibitors, as well as hydrophobic and hydrophilic coatings has gained
considerable attention [Ulm91, Tre94, Fra98]. Various surface sensitive methods have
been applied over time in order to study the packing and orientation of organic
molecules on different substrates. Standard investigation techniques for quantifying
molecular orientation and packing in organic thin films include reflection infrared
absorption spectroscopy (RAIRS) [Tol03], UV- visible and infrared spectroscopic
ellipsometry [Lec98], X-ray photoelectron spectroscopy (XPS) [Yan99], scanning
tunnelling microscopy (STM) [Sch00], near-edge X-ray absorption fine structure
(NEXAFS) [Stö92, Gie99], polarized ultraviolet (UV) spectroscopy [Kai99], angle-
resolved photoelectron spectroscopy (ARUPS) [Oku99], near-infrared (NIR) Fourier
transform surface-enhanced Raman spectroscopy [Wu99], and grazing-incidence X-ray
diffraction (GIXD) [Pra86].
The main investigation technique used to obtain the results presented in this
work was infrared spectroscopic ellipsometry. Ellipsometric technique in the visible
(VIS) as well as in the infrared (IR) spectral range is a typical method for thickness
determination and structural investigation of thin films. The ellipsometric experiment is
non-invasive, contact-free, and does not depend on special requirements such as (ultra-
high) vacuum. Depending on the photon energy, electronic or vibrational properties are
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investigated. Since many organic compounds do not exhibit characteristic electronic
transitions in the VIS spectral range, a detailed structural characterisation is often not
possible from VIS ellipsometric spectra. On the other hand IR ellipsometry is
extensively used for this purpose because characteristic IR bands associated with
vibrations of specific molecular groups are noticed. The band amplitudes and shapes in
the IR ellipsometric spectra are directly related with the directions of transition dipole
moments of specific molecular vibrations, thus enabling determination of the molecular
orientation [Hin02, Par92, Deb84, Ros09].
The current work is structured in 6 chapters as follows:
Chapter 1 introduces the notion of polarized light, presents the description of the
spectroscopic ellipsometry technique and the mathematical formalism that describes the
propagation of the light in stratified media.
In chapter 2 the experimental set-ups used in order to obtain the desired
information about the studied samples are in detail presented.
Self assembled monolayers of octanedithiol and hexadecanemonothiol on GaAs and Au are the topic of the 4thchapter. The orientation of the molecules on the substrate
was determined from simulations on spectroscopic measurements in the mid infrared
range. The inhomogeneity of the organic layer was proved by infrared mapping
ellipsometry.
Chapter 5 is dedicated to the investigation of cytosine thin films with different
thicknesses deposited on Si(111) substrates. Various investigation techniques were used
in order to determine the optical and structural properties of the organic layers. The
thickness of each layer was determined using visible ellipsometry while the molecular
orientation was deduced from the ellipsometric measurements in the infrared spectral
range.
The conclusions of this work are summarized in the last chapter.
6
Einleitung
Das Ziel der vorliegenden Studie war es, die strukturellen Eigenschaften von
organischen Molekülen auf verschiedenen Substraten mit verschiedenen optischen
spektroskopischen Methoden zu untersuchen. Die folgenden zwei Systeme wurden
untersucht: Selbstorganisierende Monoschichten aus Alkanthiolen auf GaAs und Au,
sowie dünne Cytosinschichten auf H-Si(111) Oberflächen. Wie in Kapitel 4 und 5
eingeführt wird, sind die untersuchten organischen Moleküle aufgrund ihrer
Anwendung in verschiedensten Bereichen, von Biosensoren bis hin zu
optoelektronischen Bauelementen sehr attraktiv.
Die Charakterisierung der molekularen Orientierung und Packung der Moleküle
in biologischen Systemen wie Sensoren, elektronischen und optischen organischen
Bauelementen, neuartigen Festschmierstoffen, Korrosionsinhibitoren, ebenso wie
hydrophobe und hydrophile Beschichtungen hat beträchtliche Aufmerksamkeit
gewonnen [Ulm91, Tre94, Fra98]. Verschiedene oberflächenempfindliche Methoden
wurden im Laufe der Zeit angewendet, um die Packung und die Orientierung von
organischen Molekülen auf verschiedenen Substraten zu untersuchen. Zu den
Standarduntersuchungsmethoden zur Quantifizierung molekularer Orientierung und
Packung in den organischen dünnen Schichten gehören Reflexions-
Infrarotabsorptionsspektroskopie (RAIRS) [Tol03], Ellipsometrie im UV-sichtbaren
Spektralbereich und spektroskopische Infrarotellipsometrie [Lec98], Röntgen-
Photoelektronenspektroskopie (XPS) [Yan99], Rastertunnelmikroskopie (STM)
[Sch00], Röntgen Nahkanten Absorptionsspektroskopie (NEXAFS) [Stö92, Gie99],
polarisierte UV-Spektroskopie [Kai99], Winkel-Photoelektronen-Spektroskopie
(ARUPS) [Oku99], oberflächenverstärkte Nah-Infrarot (NIR) Fourier Transform
Ramanspektroskopie [Wu99] und Röntgendiffraktometrie unter streifendem Einfall
(GIXD) [Pra86] .
Die Hauptuntersuchungstechnik, die verwendet wurde um die Ergebnisse dieser
Arbeit zu erzielen war die spektroskopische Infrarotellipsometrie. Ellipsometrie im
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