Winter school/Compact course “Characterization of micro- and nano-materials”

Modul 13-4-43

Cottbus, February 18th – 22nd, 2013

Panta Rhei, Konrad Wachsmann Allee, 17

BOOK OF ABSTRACTS

Faculty 1: Mathematics, Natural

Sciences and Computer Science

Institute of Physics and Chemistry

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BTU IN NUMBERS 6,752 students, including 1048 international students from 89 countries 119 Professors · 594 Research Assistants, including 313 Externally funded staff University Budget 2011 (including reinforcement of staff funds): 51,8 million ! External Funding 2011: 34,0 million ! FACULTIES

Faculty 1 – Mathematics, Natural Sciences and Computer Science Faculty 2 – Architecture, Civil Engineering and Urban Planning Faculty 3 – Mechanical, Electrical and Industrial Engineering Faculty 4 – Environmental Sciences and Process Engineering

CORE RESEARCH FIELDS

Environment Building Energy Material Information and

Communications Technology

CENTRAL SCIENTIFC FACILITIES Centre of Energy Technology Brandenburg (CEBra) · Research Centre Landscape Development and Mining Landscapes (FZLB) · Centre for Human Ecology (HöZ) · Centre for Law and Administration (ZfRV) · Centre for Flow and Transport Modelling and Measurement (CFTM") THE CAMPUS Total campus area: approx. 300,000 m" · Built-up areas: approx. 82,000 m"

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OTHER SCIENTIFIC FACILITIES Joint Laboratory of IHP and BTU (JointLab) · Center for research and material testing (FMPA) · Panta Rhei gGmbH · Center for lightweight construction materials · Center for Energy-Technology Bran-denburg (CEBra) OTHER FACILITIES Information, Communication and Media Centre (IKMZ) · University Library / University Computing Centre / Multimedia-Centre / Operations Data processing · Centre for Continuing Education (ZfW) · Language Centre (ZES) · University Sports Centre (ZEH) · Central Workshop ADADEMIC PROGRAMMES Applied Mathematics · Architecture · Architektur.Studium.Generale. · Building and Conservation · Civil Engineering · Business Administration · Civil Engineering · eBusiness · Electrical Engineering · Fuel from Biomass and Waste · Environmental and Resource Management (in English) · Euro Hydro-Informatics and Water Management (in English) · Forensic Sciences and Engineering (in English and Ger-man) · Computer Science · Information and Media Technology · Culture and Technology · Land Use and Water Management · Mechanical Engineering · Mathematics · Renewable Raw Materials and Regenerative Energy · Physics · Power Engineering (in English) · Urban and Regional Planning · Struc-tural Engineering · Technology and Innovation Management (joint study programme with the Brandenburg University of Applied Sciences) · Technologies of Biogenous Raw Materials · Environmental Engineering · processing technologies of materials (in Russian and German) · Process Engineering · Environmental En-gineering Process Technology · Industrial Engineering · Economathematics · Business Law for Tech-nological Enterprises · World Heritage Studies (in English) LIVING SCIENCE

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Time Monday,

18.02.2013

Tuesday,

19.02.2013

Wednesday,

20.02.2013

Thursday,

21.02.2013

Friday,

22.02.2013

9:15-10:45

U.I. Kramm Mössbauer

Spectroscopy for

the investigation of

Fe-N-C catalysts

I. Herrmann-

Geppert Solar Fuel

Production: From

catalysts to

electrodes

H. Schenk Analysis of

parametrical excited

Microscanners

D. Schmeißer Hematite – a

prototype for TCO

electronic structure

M. Ratzke Scanning Probe

Microscopy

11:00-12:30

M. Arenz IL-TEM and DEMS

for the investigation

of Pt/C catalysts

J. Rossmeisl Theory of ORR and

OER

Z. Galazka Bulk single crystals

of transparent

semiconducting /

conducting oxides

K. Irmscher Optical and

electrical properties

of transparent

semiconducting

oxides

M. Muth Thin layer detection

with ellipsometry

Lunch 12:30-13:30

13:30-15:00

M. Richter Co-oxide catalysts

studied by resPES

M. Bär

HAXPES, RIXS &

Co:

X-ray spectroscopy

for solar energy

materials research

Ch. Janowitz

Angle-Resolved

Photoemission

A. Klein Energy band

alignment of

semiconducting

metal oxides

J. Reif Optical

Spectroscopy (1/2)

15:15-16:45

H. Dau Co-catalysts studied

with EXAFS

Ch. Pettenkofer

From band structure

to band alignment

S. Niese X-ray Microscopy

and tomography

R. van de Krol Vanadate absorbers

for solar fuels

J. Reif

Optical

Spectroscopy (2/2)

17:00-19:00 Students Students H. Torlee Master thesis

D. Gerlach Dissertation

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In   recent   years   the   Brandenburg   University   of   Technology   in   Co;bus   has   been   promo>ng   the  growth   of   a   network   of   competence   in   the   Co;bus-­‐Berlin-­‐Dresden   region   focused   on   the  development  of  powerful  characteriza>on  techniques  for  micro-­‐  and  nano-­‐systems.  The  scope  of  the  compact   course   is   to  give  a  wide   insight   into   the  possible   characteriza>on   tools  available   in  this   area   focusing   on   material   proper>es   important   for   the   Si-­‐based   technology   and   energy  storage.  As   the   func>onality  of   this  kind  of  materials   is   related   to   their  use   in  micro-­‐  and  nano-­‐sized   structures,   the   limited  dimension  of   such   structures   requires   the  use  of   techniques  with  a  high  degree  of  accuracy  and  accurate  theore>cal  descrip>on.  The  use  of  special  characteriza>on  tools   for   these   materials   is   a   necessary   step   in   the   development   of   newest   materials   with  enhanced   func>onality.   This   year   we   started   to   open   our   view   towards   wider   na>onal   and  interna>onal  competences,  and  offer  a  winter  school  with  a  high  scien>fic  impact  for  Master-­‐  and  PhD-­‐students  in  physics,  chemistry  or  materials  science.  

Massimo  Tallarida  

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Program: M. Tallarida, U. I. Kramm, J. Reif, D. Schmeisser On-site organization: A. Kallweit, J. Paloumpa, U.I. Kramm, G. Beuckert, M. Tallarida Webmeister: K. Henkel We thank the Panta Rhei gGmbH for the technical support.

Monday, February 18th, 2013

MÖßBAUER SPECTROSCOPY FOR THE INVESTIGATION OF FE-N-C CATALYSTS

Ulrike. I. Kramm Brandenburgische Technische Universität, Angewandte Physik,

Konrad-Wachsmann-Allee 17, 03046 Cottbus; kramm@tu-cottbus.de

Today, Fe-N-C catalysts are the most promising materials for a replacement of platinum-based oxygen reduction catalysts in polymer electrolyte membrane fuel cell (PEM FC). This lecture will summarize the most important steps in the development of this type of catalyst from materials science perspective. Furthermore, a short introduction to Mößbauer spectroscopy as a powerful tool for the characterization of these catalysts will be given. Differences and similarities caused by variations in the preparation process will be discussed and correlated to the catalytic activity for oxygen reduction. On the basis of the given results predictions for a further improvement of the catalysts can be made.

ELECTROCHEMICAL ENERGY CONVERSION IN LOW TEMPERATURE FUEL CELLS Matthias Arenz

University of Copenhagen, Department of Chemistry, Copenhagen, Denmark; m.arenz@chem.ku.dk

Fuel cells are potential candidates for future energy conversion systems, in particular polymer electrolyte membrane fuel cells (PEMFC) for mobile or stationary applications. PEMFCs convert chemical into electric energy in a clean and efficient fashion and can deliver high power densities. The main reactions in a PEMFC operated with hydrogen are the hydrogen oxidation and oxygen reduction reaction. The efficiency of a PEMFC depends on the activity of the employed catalysts for these reactions and therefore the improvement of catalyst activity, but also of the stability are the main challenges for commercialization of the technology. There are two different types of catalysts available for the most critical reaction, the oxygen reduction reaction: Non-precious metal type catalysts and precious metal based catalysts. In this presentation, we concentrate on the latter, i.e. catalysts that are based on Pt (or Pt-alloy) nanoparticles supported on a high surface area carbon. In the presentation, an overview of the general aspects of activity determinations, accelerated degradation tests, and a new tool for studying fuel cell catalyst degradation mechanisms, IL-TEM, developed in our laboratory will be introduced and discussed based on specific examples.

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Co-OXIDE CATALYST STUDIED BY ResPES Matthias Richter

Brandenburgische Technische Universität, Angewandte Physik, Konrad-Wachsmann-Allee 17, 03046 Cottbus;

matthias.h.richter@gmail.com The electronic structure of cobalt-based catalysts used for photocatalytic water splitting in solar cells is analysed using synchrotron radiation photoelectron spectroscopy. The catalyst films are prepared by electrochemical deposition. We employ X-ray photoelectron spectroscopy to analyse the Co2p and O1s core levels, absorption edges and valence bands. We discuss our resonant data in terms of the partial density of states of valence and conduction bands. We find a difference in the Co oxidation state as a function of film thickness (deposited charge). Further, at resonant PES (ResPES) at the Co2p edge we find the Co2p partial DOS to exhibit no sharp features next to the VBM for the initial thin catalyst layers, instead there is a broad emission at around 6eV below EFermi. The former are found in LiCoO2 and other Co-oxide systems with a Co3+ ground state. We attribute such sharp features to the low spin (LS) configuration of Co3+ and deduce that in the Co catalysts there is no evidence for the corresponding LS contributions. Our data prove the Co2+ ground state and demonstrate that it is exclusively in the Co3d7 high spin state in the pristine catalyst films.

CO-CATALYSTS STUDIED WITH EXAFS Holger Dau

Freie Universität Berlin, Arnimallee 14, 14195 Berlin; holger.dau@fu-berlin.de

Efficient water oxidation requires use of a 'dark catalyst', which in the context of photocatalysis may be called a co-catalyst. The use of amorphous oxide-materials based on the earth-abundant elements Co, Ni or Mn is of high interest. These oxides exhibit non-classical properties and may be best described as hydrated oxides with molecular properties. Fluorescence-detected X-ray absorption spectroscopy (XAS, XANES, EXAFS) at the K-edge of the element of interest appears to be the method of choice for structural investigation of the catalyst under under quasi-in-situ conditions (freeze-quench approach) or in full-fledged 'in-operando' experiments.

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Tuesday, February 19th, 2013

SOLAR FUEL PRODUCTION: FROM CATALYSTS TO ELECTRODES Iris Herrmann-Geppert

Helmholtz-Zentrum Geesthacht, Institute for Materials Research, Max-Planck-Str 1, 21502 Geesthacht;

Helmut-Schmidt-University, Institute of Materials Technology, Holstenhofweg 85, 22043 Hamburg;

iris.herrmann-geppert@hzg.de iris.herrmann-geppert@hsu-hh.de Analogous to photosynthesis, artificial solar fuel production can be regarded as an option to store energy in large quantities. However, the efficiency of such a device is limited by the kinetically hindered water oxidation reaction. To reduce present overvoltages at the electrode/electrolyte interface the photoactive electrode surface should be in addition catalytically active. This is necessary due to a four electron transfer mechanism at the water oxidizing photoanode where the activity is the rate limiting step in the process. In this lecture an introduction to solar fuel production and an overview about the recent progress are given. Thereby the photoeletrococatalyst hematite (!-Fe2O3) is presented as a potential material for the photo-assisted water oxidation reaction (OER). Surface-relevant aspects are investigated and correlated with the catalytic activity of layers which has been produced by a gel technique. Heat- and plasma- treatments of the pristine !-Fe2O3 layers are applied which adjust the energetic properties of the bulk and the catalytic behaviour of the electrochemical interface with respect to an efficient photoinduced oxygen evolution reaction. Finally, in the lecture a new technical way of fabrication of photoelectrodes for a prototype cell is presented. It is demonstrated that active photocatalytic electrodes can be produced from photoelectrocatalyst powders (e.g. !-Fe2O3, TiO2) by the promising technique “cold gas spraying”. In this process the photoelectrocatalyst particles are accelerated by a laval nozzle to high velocity and are impacted on the substrate. First results obtained on these electrodes are presented.

THEORY OF OXYGEN REDUCTION REACTIONS (ORR) AND OXYGEN EVOLUTION REACTIONS (OER)

Jan Rossmeisl Technical University of Denmark, Lyngby, Denmark;

jross@fysik.dtu.dk

For energy conversion the oxygen reduction and oxygen evolution reactions are of extreme interest. For both reactions a huge over potential is needed to obtain a reasonable current, and in both cases this is mainly due to sluggish catalysis. I study the reasons for the over potential on the basis of density functional simulations and determine activity descriptors, which are easy to calculate and therefore suited for computational screening for more active catalyst materials. I will show examples on rational design of electrocatalyst materials. Furthermore, I

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will discuss the challenges related with atomic scale modelling of the electrochemical interface.

HAXPES, RIXS & Co: X-RAY SPECTROSCOPIES FOR SOLAR ENERGY MATERIALS RESEARCH

Marcus Bär Solar Energy Research, Helmholtz-Zentrum Berlin für Materialien und Energie

GmbH, Lise-Meitner-Campus, Hahn-Meitner-Platz 1, 14109 Berlin; Brandenburgische Technische Universität Cottbus, Konrad-Wachsmann-Allee 1,

03046 Cottbus; Department of Chemistry, University of Nevada, Las Vegas, 4505 Maryland

Parkway, Box 454003, Las Vegas, NV 89154-4003; marcus.baer@helmholtz-berlin.de

The purpose of this talk is to demonstrate how a tool chest of x-ray spectroscopies (in particular using high-brilliance synchrotron radiation) is uniquely suited to unravel the electronic and chemical properties of solar energy materials. We will show how soft (PES) and hard (HAXPES) x-ray photoelectron spectroscopy, inverse photoemission (IPES), x-ray emission spectroscopy (XES), and x-ray absorption spectroscopy (XAS) can be suitably combined to derive band gaps as a function of depth, energy level alignments at surfaces and interfaces, local chemical bonding, and insights into chemical stability in ambient environments. Furthermore, resonant inelastic soft x-ray scattering (RIXS) is an additional unique tool. It is able to probe the band structure of materials, is bulk sensitive and allows investigations of insulating, polycrystalline, and disordered samples. As example materials, Cu(In,Ga)(S,Se)2, Si and CdS films will be discussed.

FROM BAND STRUCTURE TO BAND ALIGNMENT Christian Pettenkofer

Institut für Silizium-Photovoltaik, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Kekuléstraße 5 12489 Berlin;

A short introduction into band alignment at semiconductor hetero-structures will be given and recent results on the junction formation at chalcopyrites will explained. Implications of models dealing with abrupt interfaces and the problems arising at reacted interfaces will be discussed.

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Wednesday, February 20th, 2013

ANALYSIS OF PARAMETRICAL EXCITED MICROSCANNERS Harald Schenk

Fraunhofer Institute for Photonic Microsystems Maria-Reiche-Str.2, 01109 Dresden;

harald.schenk@ipms.fraunhofer.de Micro scanning mirrors are deployed e.g. for laser beam projectors or 3D cameras. A widespread driving method for micro scanning mirrors is based on in-plane comb electrodes. Results of experimental investigations show that their properties cannot be explained in the model of an harmonic oscillator. However, the scanning mirrors’ behavior can be described in the model of a socalled parametric oscillator. Basic properties of parametric oscillators, like the well-known child swing, are explained and mathematically described. The experimental observed detailed properties are described using approximations to the differential equation of motion in the framework of linear as well as non-linear dynamics.

BULK SINGLE CRYSTALS OF TRANSPARENT SEMICONDUCTING / CONDUCTING OXIDES (TSOS / TCOS)

Zbigniew Galazka Leibniz Institute for Crystal Growth, Max-Born-Str. 2, 12489 Berlin;

zbigniew.galazka@ikz-berlin.de Transparent semiconducting and conducting oxides (TSOs/TCOs) have attracted, due to their unique properties, much attention in both research and industrial fields. Indeed, the combination of semiconducting or conducting properties and transparency from UV to IR paves the way to a number of applications in electronics, optoelectronics and photovoltaics. However, this field of research and technology is still emerging and requires a deeper insight into properties and behavior of the TSOs/TCOs. A better understanding is crucial for device designing and further development of bulk single crystals. Most of TSOs/TCOs applications are based on thin films and availability of bulk single crystals (and therefore substrates) would extend knowledge on properties and behavior of this new class of semiconductors and would also increase the range of their applications, especially at the industrial scale. The presentation will discuss basic electrical / optical properties and applications of the TSOs along with an overview of growth techniques utilized for obtaining bulk single crystals, as well as thermodynamics, which is important to understand behavior of such materials at high temperatures. The talk will also focus on bulk !-Ga2O3, ZnO, In2O3 and SnO2 single crystals in terms of their appearance, quality, stability, electrical / optical properties and sensitivity to post-growth heat treatments.

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ANGLE-RESOLVED PHOTOEMISSION Christoph Janowitz

Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin; janowitz@physik.hu-berlin.de

Photoemission spectroscopy (PES) has developed from the photoelectric effect by Hertz and Hallwachs to a state-of-the-art experimental tool for the determination of the electronic structure of solids and their surfaces. I present several examples for the application of ARPES (angular resolved photoemission spectroscopy) for the determination of the valence band structure, the investigation of many-body effects and in particular high resolution ARPES on the meV-scale. Furthermore, a brief overview about the wide spectrum of experimental methods based on ARPES is given, especially at very low and very high photon energies increasing the bulk sensitivity. The electronic structure and especially gap states of the transparent conducting oxides Ga2O3 and In2O3 and the formation of Au-Schottky contacts on Ga2O3 will be treated.

X-RAY MICROSCOPY AND TOMOGRAPHY Sven Niese

Fraunhofer Institute for Non-Destructive Testing, Maria-Reiche-Strasse 2, 01109 Dresden;

Sven.Niese@izfp-d.fraunhofer.de Topic of the talk is X-ray microscopy and computed tomography at laboratory systems as well as at synchrotron facilities, offering resolutions down to 50 nm and 10 nm, respectively. After an introduction to the method, some studies from materials science, engineering and life science will be presented.

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Thursday, February 21st, 2013

HEMATITE – A PROTOTYPE FOR TCO ELECTRONIC STRUCTURE Dieter Schmeißer

Brandenburgische Technische Universität, Angewandte Physik, Konrad-Wachsmann-Allee 17, 03046 Cottbus;

dsch@tu-cottbus.de We use resonant photoemission spectroscopy to study the valence and conduction band (VB / CB) partial density of states in Fe2O3, Ga2O3, and In2O3. For these oxides we distinguish between covalent contributions of O2p and Ga4s4p (In5s5p, Fe3d4s) states. In addition there are localized states, which are attributed to polaronic, oxygen based intrinsic defects and are not related to oxygen vacancies. They form a continuous band which appears throughout the electronic band gap and which is identified by a Fano type anti-resonant behavior of the valence electrons when passing the O1s resonance. In addition we identify O2p-In5s5p as well as O2p-Ga4s4p charge transfer (CT) states. These CT states are identified by a characteristic multiple Auger decay which we find at the O1s edge. They are localized within the electronic gap, appear as a band around the Fermi energy and are attributed to cause the n-type electronic behavior. Also, the CT band defines an optical gap, which is smaller than the covalent band gap. The CT-bands are found in all, the Fe2O3, the Ga2O3 and the In2O3 system. They appear well separated in energy from the empty CB states. We derive a band scheme and define both, the optical and the electronic band gap. Our findings are in excellent agreement with data from optical and cathode-luminescence studies. We propose a model in which the transport properties of these prototype oxide materials are based on the interplay of the polaronic and the CT states.

OPTICAL AND ELECTRICAL PROPERTIES OF TRANSPARENT

SEMICONDUCTING OXIDES (TSOS) Klaus Irmscher

Leibniz Institute for Crystal Growth, Max-Born-Str. 2, 12489 Berlin; klaus.irmscher@ikz-berlin.de

Part I: Rough literature survey of TSOs (ZnO, In2O3, SnO2, !-Ga2O3)

• Crystal structure • Electronic band structure • Heterostructures and band alignments • Doping and defects • Devices

Part II: Optical and electrical characterization of bulk TSO single crystals including some remarks on the basics of the used measurement methods

• Crystal growth of bulk TSO single crystals at IKZ (with reference to the talk by Z. Galazka)

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• Electrical characterization of !-Ga2O3 (Temperature dependent Hall effect and deep level transient spectroscopy)

• Schottky barriers on (100) !-Ga2O3 (Schottky-Mott rule versus metal-induced gap states)

• Optical characterization of In2O3 (Onset of optical absorption and temperature dependence of the energy gap)

ENERGY BAND ALIGNMENT OF SEMICONDUCTING METAL OXIDES

Andreas Klein Technische Universität Darmstadt, Institute of Materials Science, Surface

Science Division, Petersenstrasse 32 64287 Darmstadt; aklein@surface.tu-darmstadt.de

The experimental procedure for the determination of the energy band alignment at interfaces of metal oxides and its relation to electric material properties, including a large number of transparent conducting and dielectric oxides will be presented. Systematic dependencies are demonstrated, which provide a simple guideline for estimating the energy band alignment. Observations of the modification of band alignment by interfacial reduction/oxidation, ferroelectric polarization, and Fermi level pinning will be presented.

VANADATE ABSORBERS FOR SOLAR FUELS Roel van de Krol

Institute for Solar Fuels, Helmholtz-Zentrum Berlin für Materialien und Energie Hahn-Meitner-Platz 1, 14109 Berlin; roel.vandekrol@helmholtz-berlin.de

Direct splitting of water at the surface of a metal oxide semiconductor is an attractive route for the production of solar fuels. Most efforts have focussed on a selected number of binary oxides, such as WO3, Fe2O3, and Cu2O. While some exciting progress has been made in the past few years, several intrinsic material’s limitations hamper further progress. It is therefore essential to expand our materials database towards ternary and even more complex metal oxides. Here, one of the main challenges is to control the stoichiometry of the metal ions in order to avoid defects. Using InVO4 as an example, we will discuss which defects can be formed, how they affect the performance, and how impedance spectroscopy can be used to analyze this. In the second part of the lecture we will focus on another vanadate, BiVO4. Here, the key issues to address are electronic conductivity, water oxidation kinetics, and charge separation. We will outline how photo-electrochemical measurement techniques can be used to systematically analyse the performance-limiting factors in this material, and what can be done to solve these limitations.

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Friday, February 22nd, 2013

SCANNING PROBE MICROSCOPY Markus Ratzke

Brandenburgische Technische Universität, Konrad Wachsmann Allee 1, 03046 Cottbus;

markus.ratzke@googlemail.com

This talk will cover both principles and applications of Scanning Probe Microscopes. The focus is set on the explanation of the different working schemes of Atomic Force Microscopy, ranging from methods detecting surface inhomogeneities to methods able to map to distribution of electrical parameters. The theoretical description will be accompanied by some examples illustrating the versatility of these setups in research labs.

THIN LAYER DETECTION WITH ELLIPSOMETRY Marco Muth

Brandenburgische Technische Universität, Konrad Wachsmann Allee 1, 03046 Cottbus;

marco.muth@tu-cottbus.de Ellipsometry is an optical technique for the characterization/observation of events at an interface or film between two media. It is based on exploiting the polarization transformation that occurs as a beam of polarized (laser) light is reflected from the interface or film. Two factors make ellipsometry particularly attractive:

(1) its essentially non-perturbing character (proper wavelength and intensity), hence its suitability for in-situ measurements, and

(2) its remarkable sensitivity to minute interfacial effects, such as the formation of a sparsely distributed sub-monolayer of atoms or molecules.

The lecture gives an overview from the theoretical backround to current applications. (polarized light, reflection on and propagation through optical systems, ellipsometric setup, sample/film characterization) Prof. Reif BTU-Cottbus

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