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

Dennis.Aulich

Description

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.

Sujets

• Physik

Informations

• Publié par: technische_universitat_berlin
• Publié le: 01 janvier 2010
• Nombre de lectures: 26
• Langue: English
• Poids de l'ouvrage: 5 Mo

Extrait

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Berichter: Prof. Dr. Christian Thomsen

Tag der wissenschaftlichen Aussprache: 17.06.2010

Berichter: Prof. Dr. Georgeta Salvan

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Promotionsausschuss:

Berichter: Prof. Dr. Norbert Esser

Vorsitzender: Prof. Dr. Birgit Kanngießer

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Berlin 2010

D 83

Dana - Maria Rosu

Ellipsometric characterisation of anisotropic thin organic films

MSc Phys.

vorgelegt von

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zur Erlangung des akademischen Grades

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der Technischen Universität Berlin

   von der Fakultät II - Mathematik und Naturwissenschaften

Doktor der Naturwissenschaften

aus Hunedoara, Rumänien 

genehmigte Dissertation

- Dr. rer. nat. 

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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):

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IR - Synchrotron Mapping Ellipsometry for Characterisation of Biomolecular Films.

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Parts of this work have been already published in:

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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,

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Journals:

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orientation in octanedithiol and hexadecanethiol monolayers on GaAs and Au measured

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Reports:

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by infrared spectroscopic ellipsometry.

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1.

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Table of contents

Introduction 5

Einleitung 7

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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

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2. Experimental techniques 23

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2.1Spectroscopic ellipsometry (SE)...23

2.2Synchrotron mapping ellipsometry...24

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Optical modelling 27

3.1 Cauchy model27

3.2 Gaussian oscillator model..28

3.3 Lorentz model29

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Self assembled monolayers of alkanethiol 31

4.1Sample preparation32

4.2IRSE characterisation of alkanethiol thin films.33

4.3IR synchrotron mapping ellipsometry...42

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Cytosine 44

5.1Sample preparation45

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5.2AFM characterisation of cytosine films46

5.3Visible spectroscopic ellipsometry47

5.4Infrared spectroscopic ellipsometry.51

5.5Synchrotron mapping ellipsometry..60

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 6. Concluding remarks 63

 References 65

 List of figures 70

 List of tables 73

 Acknowledgements 74

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Introduction

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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 4 th chapter. 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.

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The conclusions of this work are summarized in the last chapter.

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Einleitung

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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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