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Institute of Physics
www.tu-chemnitz.de/physik/
The new physics building inaugurated in spring 2008 provides excellent conditions for experimental and theoretical research.
Figures on front pageLeft: Dielectric microcavity with embedded semiconductor quantum dotsRight: STM image of adsorbed tin-phthalocyanine molecules switched to show “TUC”Background: Quasiperiodic two-dimensional lattice - Penrose tiling
I n t r o d u c t I o n
The Institute of Physics which is part of the Faculty of Science of the Chemnitz University of Technology comprises currently 12 professorships. The Institute was relocated in 2008 to a new building. It contains state-of-the-art labo-ratories with cleanroom facilities that allow a new quality of research and is part of the Smart Systems Campus. The research fields are focused to the areas of Complex Materials (i.e., quasicrystals, thin films, nanocrystals, magnetic heterostructures), Molecular Systems (i.e., blockcopolymers, organic photoactive materials, molecular assemblies), and Modelling and Simulations (i.e., nonlinear dynamics, diffusion processes, thermodynamic cyles, transport in disordered solids) with close links between physics, chemistry, and engineering which strongly emphasizes the in-terdisciplinary research profile of our Institute. There is a viable mixture of fundamental and application oriented research embedded in national and international collaborations. In this regard, innovation has a strong tradition in Chemnitz and new cooperative projects such as Graduate Colleges and cooperations in Collaborative Research Cen-ters (Sonderforschungsbereiche) are further developed.
The Institute of Physics has been able to present a wide educational spectrum to its students including bachelor and master programs in Physics, Computational Science, and Sensoric and Cognitive Psychology. In addition, it offers special programms for kids (Schülerlabor) to fascinate them and excite interest in physics at an early stage.
This brochure provides a short overview of the research activities at our Institute. A description of the professorships and their expertise are presented which is intended to provide an impression of the research fields for scientists in-terested in the work of the Institute as well as for interested students.
Prof. Dr. Manfred Albrecht · Director of the Institute
Dean of the Faculty of Natural ScienceProf. Dr. Karl Heinz HoffmannInstitute of Physics · Room P151Phone: +49 371 531 21000Fax: +49 371 531 [email protected]
Director of the Institute of PhysicsProf. Dr. Manfred AlbrechtInstitute of Physics · Room P150Phone: +49 371 531 21500Fax: +49 371 531 [email protected]
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P r o f e s s o r s H I P s
ExPErImENtal PhySIcS PageSurface and Interface Physics 4
Solid Surface Analysis 6
Physics of Thin Films 8
Dynamics of Nanoscopic and Mesoscopic Structures 10
Solid State Physics 12
Semiconductor Physics 14
Chemical Physics 16
Optical Spectroscopy and Molecular Physics 18
thEOrEtIcal PhySIcSSimulation of New Materials 20
Complex Systems and Nonlinear Dynamics 22
Theory of Disordered Systems 24
Theoretical and Computational Physics 26
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c o n t a c tReichenhainer Strasse 70 · Institute of Physics · P177Phone: +49 371 531 36831Fax: +49 371 531 [email protected]/physik/OFGF/
s u r f a c e a n d I n t e r f a c e P H y s I c sProf. Dr. Manfred Albrecht
r e s e a r c h f i e l d sMagnetic nanostructures - coupling phenomena and scaling -Magnetic alloy films and heterostructures -Amorphous magnetic phases and spin glasses -Thermoelectric materials -
M e t h o d sMolecular beam epitaxy (MBE) and sputter deposition -In-situ growth and surface characterization (RHEED, LEED, AES, UHV-STM) -Magnetic characterization (SQUID, MOKE, MFM) -Structural characterization (XRD, TEM, SEM) -
e q u i p m e n tDeposition tools (MBE-Systems, DC sputter deposition) and processing equip- -ment (Plasma Processor (TePla) and RTA setup)VSM-SQUID magnetometer (QUANTUM DESIGN) -MOKE magnetometer (in-plane, out-of plane) -5-Tesla Cryostat (OXFORD INSTRUMENTS) for temperature-dependent transport -measurements Scanning Magneto-Resisitive Microscope -High-resolution Magnetic Force Microscope -
s c i e n t i f i c c o o p e r a t i o nHitachi Global Storage Technologies, San Jose (USA) -Oerlikon-Balzers AG, Balzers (Liechtenstein) -University of California, Santa Cruz (USA) -St. Pölten University of Applied Sciences, St. Pölten (Austria) -H. Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, -Kraków (Poland) Helmholtz-Zentrum Dresden-Rossendorf, Institut für Ionenstrahlphysik und -Materialforschung (Germany) SIMaP CNRS, Grenoble (France) -
The MBE lab
Group picture
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rESEarchM a g n e t i c d a t a s t o r a g eMass data storage on magnetic hard drives in portable products is a fast growing market with an estimated turn-over of several billion EUR per year. However, continued growth of storage density is limited as a result of the ther-mal instability of recorded data. To overcome this so called “superparamagnetic effect”, the use of discrete media, in which information is stored in single nanostructures, will become mandatory. Therefore, it is likely that magnetic recording media will be the first technology which requires the introduction of nanostructuring by self-assembly pro-cesses.In this regard, it is expected that self-assembly of nano-particles can be governed and expanded to wafer size scale by pre-patterning the substrate. New material function-ality can be introduced by magnetic material deposition
onto particle arrays, as illustrated in Fig. 1A. The magnetic Co/Pd nanostructures formed on top of the particles are in a magnetic single-domain state, as indicated by the dark and bright contrast in magnetic force microscope (MFM) imaging of the particle caps (see Fig. 1A). This nanoscale system is quite distinct from the classical geometries: The Co/Pd multilayer film is extended over a wide region of the sphere and thus shows substantial curvature even for 50-nm-size particles as presented in the dark field trans-mission electron microscope (TEM) image of Fig. 1B.Moreover, further concepts for recording media such as exchange coupled composite bit patterned media are currently investigated in a European FP7-project called “TERAMAGSTOR” (TERAbit MAGnetic STORage technolo-gies).
Fig. 1: (A) MFM image of a magnetic cap array fabricated by Co/Pd multilayer deposition onto a 320 nm poly-styren particle array. (B) TEM image of Co/Pd covered 50-nm-size particles (in co-operation with Hitachi GST).
n a n o s t r u c t u r i n g o f t h i n m a g n e t i c f i l m sThese investigations include thin films (i.e. FePt, Co/Pd, CoCrPt) with strong perpendicular magnetic anisotropy that are grown on suitable substrates by molecular beam epitaxy or sputter deposition. These films can be structured
by focused ion beam (FIB) as shown in Fig. 2A or laser in-terference lithography (Fig. 2B), where line and dot struc-tures can be formed by 2-beam and 3-beam interference patterning, respectively.
Fig. 2: (A) AFM image of a single row of 80-nm FIB patterned CoCrPt islands. (B) Morphology of a Co/Pd multilayer film after exposure to a 3-beam laser interference pattern.
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c o n t a c tReichenhainer Strasse 70 · Institute of Physics · P178Phone: +49 371 531 33203Fax: +49 371 531 [email protected]/physik/AFKO/
s o l I d s u r f a c e a n a ly s I sProf. Dr. Michael Hietschold
r e s e a r c h f i e l d sSelf-Assembling, Organic Molecules, Clusters and Thin Films -Scanning Probe and Electron Microscopies -Surfaces, Interfaces and Nanostructures -
M e t h o d sScanning Probe Microscopies and Spectroscopies (STM, STS, AFM, c-AFM, EFM) -Electron Microscopies (TEM, SEM, EELS, EDX, EBSD, CL) -Sample Preparation (Self-Assembled Monolayers, Cross-Sections) -
e q u i p m e n tTransmission Electron Microscope CM20 FEG (FEI) with Gatan Imaging Filter -Scanning Electron Microscope NovaNanoSEM (FEI) with EDX, EBSD, and CL -Scanning Electron Microscope SEM 515 Philips -UHV Surface Lab (Omicron with in-Situ Peparation, LEED and VT-STM) -Digital Optical Microscope Keyence VHX-500 -Ion Milling Systems RES100 -Ambient STMs (Burleigh Instructional, TU Munich) -AFM (Agilent 5500 AFM) -
s c i e n t i f i c c o o p e r a t i o nGermany (LMU Munich, CAU Kiel, Univ. Kaiserslautern, IFW Dresden) -USA (Washington State University, Portland State University) -UK (University Glasgow, Daresbury Laboratory) -Vietnam (TU Hanoi, NU Ho-Chi-Minh-City, Vinh University) -France (CEMES CNRS Toulouse) -Thailand (MTEC Pathumthani, King Mongkut IT Ladkrabang) -
P a r t i c i p a t i o n i n c o o p e r a t i v e r e s e a r c hDFG GRK 1215 “Materials and Concepts for Advanced Interconnects and Nano- -systems”DFG FOR 1154 “Towards Molecular Spintronics” -DFG FOR 1713 “Sensorische Mikro- und Nanosysteme” -
Group photo
STM crew
Imaging with the SEM
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rESEarchVe r y h i g h l y r e s o l v e d s t M t o p v i e w i m a g e o f a s i n g l e t i n - p h t h a l o c y a n i n e m o l e c u l eA single Sn-phthalocyanine molecule adsorbed on an Ag(111) substrate has been imaged by STM with very high spatial resolution in UHV. The clearly visible sub-molecular features are highly coinciding with the pi-electron clouds delocalized over the molecular backbone which define the
contour of the highest occupied molecular orbital (HOMO). For comparison the same orbital calculated for a free mol-ecule using density functional theory (DFT) is given.
STM image by M.Toader
(Left) High resolution STM image and (right) HOMO caclulated by DFT of a single SnPc molecule
n o v e l a d s o r p t i o n s t r u c t u r e o f t r i m e s i c a c i d ( t M a )Self-assembling of organic molecules on liquid-solid inter-faces is a challenging subject since the assembled pattern can be influenced by several control parameters. These findings are largely based on foregoing results obtained in our group. The STM image shows the newly discovered zig-zag structure of trimesic acid on a crystalline graphit
surface deposited out of a phenyloctane solution after a special sonication proceedure. This research is funded in part by the German Academic Exchange Service (DAAD). N.T.N.Ha et al. J.Phys.Chem. C 114, 3531 (2010)
Zig-zag structure of TMA on graphite (0001)
s t r u c t u r e o f n a n o p o r o u s l o w - k d i e l e c t r i c sLow-k dielectrics are of great importance in modern mi-croelectronics. They can be realized by special nanoporous systems as SiCOH. The SEM image shows a cross-section through a trench structure opening a SiCOH layer as side-wall (left side) and the radial distribution function RDF (right side) to characterize the short-range order in this material. The RDF has been obtained from electron dif-
fraction in the TEM. This project is part of the DFG funded International Research and Training Group “Materials and Concepts for Advanced Interconnects and Nanosystems” in cooperation with the Fraunhofer Institute for Electronic Nanosystems.
P.K.Singh et al. Proc. ICSICT, Shanghai 2010
SEM cross-section (left) and radial distribution function (right) of a SiCOH layer
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c o n t a c tReichenhainer Straße 70 · Institute of Physics · P053Phone: +49 371 531 33140Fax: +49 371 531 8 [email protected]/physik/PHDS/
P H y s I c s o f t H I n f I l M sProf. Dr. Peter Häussler
r e s e a r c h f i e l d sFundamental research on structure formation at very early stages -Resonance stabilization on different scales, between different subsystems -General dynamics of phase formation -Amorphous systems (metals, semiconductors, Zintl systems,TM-Al alloys) -New materials (quasicrystals, Heusler/Half-Heusler alloys, magnetic systems) -Electronic and thermal transport anomalies at various temperatures -
M e t h o d sIn-situ preparation of multicomponent thin films by sequential flash evaporation, -at low temperature (4 K) and HV or UHV, with high compositional accuracyIn-situ measuring techniques: electron diffraction, resistivity, thermopower, -Hall effect, thermal conductivityEx-situ measuring techniques: electron diffraction, Hall effect, EELS, resistivity, -profilometry
e q u i p m e n t6 high vacuum cryostats for in-situ measurements between 1 K and 350 K -
Electron scattering and resistivity -Thermopower and resistivity -Hall coefficient and resistivity at 7 Tesla -Magnetoresistance at 7 Tesla -Thermal conductance and resistivity -Resistivity (for screening measurements of 6 different alloys) -
UHV cryostat for electron scattering and resistivity between 1 K and 750 K -Cryostat for ex-situ Hall effect measurements at 7 Tesla -UHV chamber for resistivity measurements between 300 K and 1000 K -Glove-box for the handling of highly reactive samples -Surface profilometer (white-light technique) -
s c i e n t i f i c c o o p e r a t i o nState Key Lab for Materials Modification by Laser,Ion and Electron Beams, -Dalian University of Technology, China
Sample holder for in situ resistivity measurements
Sequential flash evaporater for the preparation of ten different alloys
Cryostat for measuring the thermal conductivity
2D electron density around four atoms resonable for spherical periodic structural order of disordered systems
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rESEarchs t r u c t u r e f o r m a t i o n a t e a r l y s t a g e sCrystal formation is by no means well understood. Bottom-up as well as top-down techniques are often applied. On the other hand, any crystalline system has a disordered state (liquid, amorphous) as its precursor, in which medi-um-range order arises for the first time. Its understanding may once give us a flavour how crystals themselves get formed. Analysing many different disordered systems, as the driving effect we found resonance effects between global subsystems, as there are all the electrons as one and the forming static structure as another one. The resonances can be based on an exchange of momentum as well as angular momentum. By their internal degrees of freedom (via an adjustment of the electron-density and/or particle-density oscillations) the subsystems are able to adjust each other in a way that gaps or pseudogaps are formed at the Fermi energy EF, decreasing effectively the total energy of the system (Peierls-, Hume-Rothery-like). Subsequently, spherical periodic structural order (SPO) arises in the mean around any atom (Fig. 1), causing band-structure effects.
Different scenarios have been observed: the static structure may adjust to the electronic system, as well as, vice versa, the electronic system to the static structure. Charge trans-fer as well as hybridization effects have been observed to enhance the global resonance. Since there is a gap or pseudogap involved, the evolution of the static structure is accompanied by the evolution of electronic transport prop-erties too (Fig. 3). Therefore, any electronic transport mea-surement delivers valuable additional information, helping to understand the resonance stabilization and hence struc-ture formation. The model has successfully been applied to amorphous non-magnetic as well as magnetic metals, semiconductors, to amorphous quasicrystals and Zintl sys-tems (the latter showing ionic bonding features), as well as to all the alloys between Aluminum and any 3d-transition element with d-electrons at EF, to Heusler- as well as Half-Heusler alloys, to pure elements, binary as well as ternary alloys (Fig. 2). Presently it gets extended to alloys contain-ing rare earth elements with f-electrons at EF.
d y n a m i c l o w -t a n o m a l i e s i n d i s o r d e r e d s y s t e m sThe spatially limited SPO-regions cause, due to their lim-ited total mass, anomalies in the dynamic excitations at low energies at wave numbers related to the Fermi wave-length and the resonance-triggered atomic positions. All the electrons, the static structure, as well as the dynamic excitations are resonantly coupled to each other. The dy-namic dispersion shows so called phonon rotons a shift of
low-lying dynamic states to higher energies. Phonon-roton states can get occupied thermally as well as by a scattering of other particles. Accordingly, low-temperature anomalies may exist in the electronic and thermal transport. This may also be true for those systems showing extreme resonanc-es, for amorphous semiconductors and insulators.
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c o n t a c t Reichenhainer Strasse 70 · Institute of Physics · P 160 Phone: +49 371 531 21670 Fax: +49 371 531 21679 [email protected] www.tu-chemnitz.de/physik/DNMS/
d y n a M I c s o f n a n o s c o P I c a n d M e s o s c o P I c s t r u c t u r e s Prof. Dr. Rudolf Bratschitsch
r e s e a r c h f i e l d s Ultrafast quantum optics of solid state nanosystems -Ultrafast spintronics -Ultrafast magneto-plasmonics -Terahertz physics and technology -
M e t h o d s Time-resolved pump-probe spectroscopy of single nanosystems -Time-resolved Faraday rotation spectroscopy -Microphotoluminescence with single-photon counting -Nanostructuring -
e q u i p m e n t Femtosecond fiber laser system -Ti:sapphire laser system with femtosecond and picosecond option -Continuous-flow cryostat -
s c i e n t i f i c c o o p e r a t i o n
Universität Konstanz (Germany) -Universität Stuttgart (Germany) -Universität Münster (Germany) -Universität Kaiserslautern (Germany) -Universität Würzburg (Germany) -Institut für Angewandte Festkörperphysik in Freiburg (Germany) -University of Washington, Seattle (USA) -Universität Graz (Austria) -
Photonic crystal fabricated with a focused ion beam
Bright blue emission from a metal nanoantenna
Dielectric microcavity with embedded semiconductor quantum dots
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rESEarchu l t r a f a s t q u a n t u m o p t i c s w i t h s o l i d s t a t e n a n o s y s t e m sSemiconductor quantum dots are one of the most promis-ing candidates for implementing robust qubits in quantum information processing. The possibility to optically initial-ize, manipulate and read out the charge and spin state on ultrafast timescales makes them very attractive. We use femtosecond pump-probe experiments to study the ultra-fast dynamics in single semiconductor quantum dots. To reach the limit of only a single photon manipulating a single electron in a quantum dot the coupling of light with a wavelength of a few hundred nanometers into the object
of nanometer dimensions has to be optimized. We mainly study two nanophotonic elements to reach this goal: di-electric microcavities and metallic nanoantennas. Alternatively, we investigate color centers in diamond. Since their first optical characterization on a single emitter level, they have been used as robust single-photon sources. We optically study these nanoscopic light emitters, which operate at room-temperature. Photonic nanostructures are designed and fabricated to increase light coupling.
Dielectric pillar resonatoru l t r a f a s t ( m a g n e t o - ) p l a s m o n i c sMetal nanoantennas are one million times smaller than the well-known radio antennas. They are fabricated via electron-beam lithography, focused ion beam milling or via colloidal masks. We investigate both linear and nonlin-ear properties of these metallic devices via excitation with few-cycle laser pulses.A further area of research is surface plasmon interferom-
etry. A microinterferometer consists of slits and grooves, which are milled into a thin metal film. Ultrafast changes in the plasmonic wave vector may be induced via femtosec-ond laser pulses. We also look into magneto-plasmonics, where metal/ferromagnet/metal hybrid structures are in-vestigated. These experimental methods are also interest-ing for sensing applications.
Bowtie nanoantennau l t r a f a s t s p i n t r o n i c sSpintronics (short for spin-based electronics) deals with the development of new microelectronic devices, which are based on spin rather than the charge of particles as a carrier for information. Possible advantages of spintronic devices compared to conventional ones would be an in-creased data processing speed, less power consumption, higher integration densities, and new functionalities.Semiconductors are suitable spintronic materials be-cause of their widespread industrial use and the resulting
know-how in fabrication techniques. Therefore, magnetic semiconductors seem to be the best choice to reach one important goal in spintronics, which is the design of a single device, which incorporates both logic and memory elements (“single chip computer”). We investigate magnetic semiconductors with a wide bandgap, i.e. “transparent magnets”. Using time-resolved Faraday rotation spectroscopy, ultrafast carrier- and spin-based processes in these new materials are studied.
Wide-bandgap magnetic semiconductor
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c o n t a c t Reichenhainer Strasse 70 · Institute of Physics · P 137 Phone: +49 371 531 38046 Fax: +49 371 531 21719 [email protected] www.tu-chemnitz.de/physik/PHFK/
s o l I d s t at e P H y s I c s Prof. Dr. Frank Richter
r e s e a r c h f i e l d s plasma-assisted thin film deposition and surface engineering, -in-situ characterisation of pulsed plasmas, -modelling of thin film deposition processes, -mechanical characterisation and modelling of thin films and surfaces. -
M e t h o d s mechanical and geometrical characterisation (nanoindentation, AFM), -analytical and finite element modelling of mechanical contacts, -characterisation of thin film deposition processes by Langmuir probes, thermal -probe, optical emission, mass spectroscopy, and ion energy analysis.
e q u i p m e n t nanoindentation device UMIS 2000 (CSIRO), resolution of load/displacement, -universal nanomechanical tester (Asmec) using normal and lateral load, -advanced development surface profiler (Veeco), -plasma process monitor PPM 422 (Inficon) for positive/negative ions/neutrals, -optical UV/VIS spectrometer HR 460S (Jobin Yvon), with LN2 cooled camera, -thin film deposition facilities for both PVD and PECVD, up to industrial size. -
s c i e n t i f i c c o - o p e r a t i o n Universities of Manchester and Liverpool (Great Britain), Uppsala (Sweden), -Oak Ridge and Lawrence Berkely Natl. Labs. (USA),Fraunhofer-IST (Braunschweig), IWS, and FEP (both Dresden), -SFB Transregio PT-PIESA (Chemnitz, Dresden, Erlangen). -
I n d u s t r i a l c o - o p e r a t i o n INOVAP Vakuum- und Plasmatechnik Dresden, -von Ardenne Anlagentechnik Dresden, -FHR Anlagenbau Ottendorf-Okrilla. -
industrial size sputter deposition equipment
Nanomechanical Tester UMIS 2000
Group picture from October 2007
working at the plasma-assisted CVD apparatus
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rESEarchc o l l a b o r a t i v e r e s e a r c h c e n t r e / tr a n s r e g i o “ P t- P I e s a”(supported by DFG)This research is aimed at scientific fundamentals for an efficient production of active structural components. The contribution of the Solid State Physics group is the inves-
tigation and development of a thin film system which pro-vides electrical insulation but has at the same time desired mechanical properties.
c l u s t e r o f a d v a n c e d te c h n o l o g y e n e r g y - e f f i c i e n t P r o d u c t a n d P r o c e s s I n n o v a t i o n i n P r o d u c t i o n te c h n o l o g i e s “e n i P r o d ”(supported by EU)The cluster eniPROD aims at the realization of the vision of an almost emission-free production while simultaneously reducing the demand for energy as well as increasing the efficiency of resources. The contribution of our group con-
sists of the realisation of special coatings with low friction coefficient and low wear rate thus serving for low energy consumption.
s i l i c o n f i l m s f o r p h o t o v o l t a i c a p p l i c a t i o n s b y m a g n e t r o n s p u t t e r i n g : p r o c e s s a n d f i l m p r o p e r t i e s(supported by the Free State of Saxony)Solarfabrik 2020 aims at a drastic cost reduction for the production of silicon solar cells. Our contribution (together with Prof. Zahn´s group) is directed towards the investiga-
tion of the deposition process and the properties of grown Si films.
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c o n t a c t Reichenhainer Strasse 70 · Institute of Physics · P 166 Phone: +49 371 531 33015 Fax: +49 371 531 21739 [email protected] www.tu-chemnitz.de/physik/HLPH/
s e M I c o n d u c t o r P H y s I c s Prof. Dr. Dr. h. c. Dietrich R. T. ZahnDeputy Head: apl. Prof. Dr. Georgeta Salvan
r e s e a r c h f i e l d s Organic semiconductors -Organic/inorganic interfaces -Low dimensional semiconductor structures -Molecular Spintronics -Electronic and optoelectronic devices -
M e t h o d s (Magneto-)optical spectroscopies (Raman, IR, spectroscopic ellipsometry, -reflectance anisotropy magneto-optical Kerr effect spectroscopy)Electron spectroscopies (photoemission, NEXAFS, inverse photoemission) -Electrical characterisation methods (IV, CV, DLTS, QTS admittance) -
e q u i p m e n t Dilor XY 800 triple monochromator with Ar - +, Kr+, HeCd lasers for ex situ micro-Raman investigations and in situ Raman monitoring (UHV chamber for (organic) molecular beam deposition)Variable angle spectroscopic ellipsometer, J. A. Woollam, (240nm-1700nm) -FTIR spectrometer Bruker IFS 66 / Vertex 80vUHV chambers for - in situ I-V / C-V measurements and electron spectroscopies (ARUPS, IPES)Deposition chamber for - in situ ellipsometry and reflection anisotropy spectros-copyMOKE spectrometer, electromagnet (1.7T), magneto-optical cryostat (1.5K, 8T) -
s c i e n t i f i c c o o p e r a t i o n Institute of Semiconductor Physics, 630090 Novosibirsk, Russia -ISAS Berlin and BESSY -IRTG “Materials and Concepts for Advanced Interconnects” -Institute of Electron Physics, Uzhhorod, Ukraine -National Academy of Sciences of Ukraine -
s e r v i c e Metrology of thin films by (magneto-)optical spectroscopies -
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rESEarch
o r g a n i c / i n o r g a n i c i n t e r f a c e s The research work of Semiconductor Physics group focuses on the detailed understanding of organic/inorganic inter-faces phenomena, their electronic and chemical as well as geometrical and electrical properties. Ultra-thin organic molecular semi-conducting layers are prepared by molecu-lar beam deposition in UHV on inorganic substrates and
investigated in situ. Experimental techniques include high resolution angle resolved photoemission spectroscopy, in-verse photoemission spectroscopy and several optical char-acterisation methods, e. g. Raman spectroscopy and refl ec-tion anisotropy spectroscopy, and MOKE spectroscopy.
Combined VB-PES and IPES measurements of the perylene derivative PTCDI with the charge density contours of the HOMO and LUMO on top of the fi gure.
s y n t h e s i s a n d o p t i c a l i n v e s t i g a t i o n o f n o v e l s e m i c o n d u c t o r s e l f - a s s e m b l e d q u a n -t u m d o t s t r u c t u r e s Quantum dots are attractive systems for new electronic, photonic, or opto-electronic devices. Accurate control of the size, shape, and position of the dots together with a deeper understanding of their infl uence on fi nal device properties is, however, crucial for the exploitation of these nanostructures in quantum devices. In this research fi eld the Semiconductor Physics group has long term collabora-
tion with the Institute of Semiconductor Physics in Novo-sibirsk. In the Russian institute high quality quantum dot structures are prepared. These structures are optically char-acterised in Chemnitz, e. g. by means of Raman spectros-copy. The high yield of joint research activities is displayed in more than 50 papers.
InAs QDs embedded in GaAs
- Kompetenznetzwerk für Nanosystemintegration: http://www.nanett.org/- DFG Research Unit “Towards Molecular Spintronics”: http://www.tu-chemnitz.de/physik/RU_TMS/- International Research Training Group - “Materials and Concepts for Advanced Interconnects and Nanosystems”: http://www.zfm.tu-chemnitz.de/irtg/- Solarfabrik 2020: http://www.solarfabrik2020.de/- BMBF: Solar Cells from Silicon in Solution- AIF ZIM “High Temperature Measurement Sensor”: http://www.corant.de
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c o n t a c tReichenhainer Strasse 70 · Institute of Physics · P162Phone: +49 371 531 21750Fax: +49 371 531 [email protected]/physik/CHEMPHYS/
c H e M I c a l P H y s I c sProf. Dr. Robert Magerle
r e s e a r c h f i e l d sStructure and properties of polymeric materials on the nanometer scale. Our -current research focus is on block copolymers, semicrystalline polymers, and biological materials.
M e t h o d sScanning force microscopy, -Nanotomography: volume imaging based on scanning probe microscopy, -Scientific image processing. -
e q u i p m e n t4 scanning probe microscopes (JPK NanoWizard I and II, Veeco MultiMode) with -accessories for imaging in liquids, at elevated temperatures (up to 240°C), and automated Nanotomography imaging.2 optical microscopes with digital imaging. -1 rotary microtome (Leica RM2265) with freezing attachment for cutting at low -temperatures (-150°C).Thin film preparation laboratory including snow jet for substrate cleaning, -spincoater, and ovens.Setup for annealing in solvent vapor. -
Microstructure of a cylinder forming block copolymer. Nanotomog-raphy volume image reconstructed from a series of tapping-mode scanning force microscopy phase images. From: R. Magerle, Phys. Rev. Lett. 85, 2749 (2000); © 2000 American Physical Society
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rESEarchs e m i c r y s t a l l i n e p o l y m e r s Semicrystalline polymers, like polyethylene and polypro-pylene, are widely used polymeric materials. Their prop-erties can be controlled through synthesis and processing conditions. The material`s microstructure is an important parameter and can be imaged with Nanotomography. An example is the structure of a screw dislocation in a crystal-line lamella (see figure). Before volume imaging, the for-mation of the dislocation has been observed with in-situ
scanning force microscopy (SFM). With a micro-tensile test setup we track with SFM the deformations of individual crystals during deformation of the material. The data pro-vide a detailed view on the micromechanics of the material on the scale of 10 - 1000 nm. The data are expected to pro-vide a better understanding of the mechanical properties of semicrystalline polymers.
Screw dislocation in a crystalline lamella of elastomeric polypropylene. From: M. Franke, N. Rehse, Macromolecules 41, 163 (2008); © 2008 American Chemical Society.
M e s o s c a l e d y n a m i c s o f b l o c k c o p o l y m e r sWith in-situ tapping mode scanning force microscopy we observe how microdomain patterns rearrange at the sur-face of a fluid block copolymer film. We study the processes during long-range ordering, terrace formation and forma-tion of surface reconstructions. Our scanning force micros-copy time-laps movies show with 10 nm spatial resolution
the mesoscale dynamics and fluctuations during structural phase transitions and phase boundaries between differ-ently ordered phases. Computer simulations based on dy-namic density functional theory (MesoDyn) capture the experimental observations in stunning detail.
Nucleation and growth of a perforated lamella phase. Snapshots from an scan-ning force microscopy movie. From: A. Knoll et al., Nature Materials 3, 886 (2004).
B i o l o g i c a l m a t e r i a l s Biological materials have a complex hierarchical structure ranging from the molecular scale over the nano- and mi-crometer scale up to the macroscopic length scale. From the materials science point of view, bone can be considered as a composite material of inorganic hydroxyl apatite par-ticles embedded in an organic collagen matrix. We study the structure of human bone and aim establishing routine
imaging of native human bone based on Nanotomography. The imaging of mechanical properties with scanning force microscopy is of particular interest for understanding the structure property relationship of bone. For this purpose we develop suitable preparation, etching and imaging techniques based on scanning probe microscopy.
Microstructure of human bone imaged with bimodal amplitude modulation scanning force microscopy.
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c o n t a c t Reichenhainer Strasse 70 · Institute of Physics · P 165 Phone: +49 371 531 33035 Fax: +49 371 531 21819 [email protected] www.tu-chemnitz.de/physik/OSMP/
o P t I c a l s P e c t r o s c o P y a n d M o l e c u l a r P H y s I c s Prof. Dr. Christian von Borczyskowski
r e s e a r c h f i e l d s Optical Spectroscopy and Microscopy on Molecular and Complex Materials -
n a n o a s s e m b l i e s & s u p r a m o l e c u l a r s t r u c t u r e s Supramolecules -Quantum dots -
s i n g l e m o l e c u l e p r o b e s i n s o f t m a t t e r Diffusion, spectral diffusion -Polymers, liquid crystals, organic liquids -Thin films, interfaces -
f u n c t i o n a l m i c r o - a n d n a n o s t r u c t u r e s Self assembled molecules -Nanolithography -Organic Semiconductors -
l a s e r I n d u c e d P l a s m a Plasma Dynamics -Plasmagenerated Materials -
M e t h o d s (Time resolved) Optical Spectroscopy -Single Quantum System Detection -Nano-Optical Microscopy -AFM- Microscopy incl. Kelvin Probe Microscopy -Laser Interferometry -
s c i e n t i f i c c o o p e r a t i o n DFG Research Group “Driven diffusion in nanoscaled materials”; Inst. of Astro- -physics, Jena; National Academy of Science, Minsk; University Lyon; University of Buenos Aires; Dep. of Materials Engineering Science, Osaka; Inst. of Applied Physics, Gießen; Inst. of Physical Chemistry & Electrochemistry, Hannover; IZM Fraunhofer Institute, Berlin, Chemnitz; Moscow Inst. for Physics and Technol-ogy; Princeton University; TU München; University Lübeck
OSMP Group January 2011
Freezing single molecule dynamics on interfaces and in polymers
Wide fi eld microscopic imageof single molecules
Photoluminescence blinking of single molecules
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s i n g l e M o l e c u l e P r o b e s i n s o f t M a t t e r Individual fl uorescent dye molecules are used as probes for nanoscale structure and dy-namics in various soft materials, such as liquids, polymers or liquid crystals.Typical single molecule observables, such as mobility, excited state lifetime, lumines-cence polarization or intensity fl uctuations are used by us as reporters on the spatial and temporal heterogeneity in this class of materials. Since many properties of soft materials are closely related to thermal fl uctuations and heterogeneities we are able to contribute to central questions in the fi eld.
Orientation dynamics of single molecules on SiOx surfacesDiff usion tracks of single molecules
M a n i p u l a t i o n a n d a n a l y t i c s o f s u r f a c e s a n d I n t e r f a c e s Self-assembled monolayers covalently linked on silicon and silicon oxide are used for ad-justment of surface properties as hydrophobicity or selective anchoring sites. The prop-erties are investigated by water contact angle measurement, atomic force microscopy and by optical methods. Structuring on the nanometer scale by atomic force microscope followed by selective binding e.g. by electrostatic interactions of optical active materials opens the way to functional nanostructures. Spatial, spectral and time-resolved optical methods are used for characterization of the prepared nanostructures.
AFM lithographyAFM lithographie of silicon oxide
I n t e r f e r o m e t r y o n l a s e r i n d u c e d P l a s m a Picosecond laser pulses at the wavelength of 1064 nm have been focused onto cop-per cathodes in coincidence with electric fi elds to produce laser-induced breakdown in vacuum. At high power densities formation of local regions with high pressures and temperatures have been investigated in cathode micro-volumes. As a result of an inten-sive energy deposition in a small volume a strongly coupled cathode micro-plasma was formed, of which the properties varied during non-stationary processes of heating and hydrodynamic motion over a wide range of the phase diagram : from a Fermi-like to an ideal plasma. Calculation of metal plasma
for a cathode micro-plasmaLaser induced plasma bullets
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c o n t a c tReichenhainer Strasse 70 · Institute of Physics · P307Phone: +49 371 531 37636Fax: +49 371 531 [email protected]/physik/TPSM/
s I M u l at I o n o f n e w M at e r I a l sProf. Dr. Angela Thränhardt
r e s e a r c h f i e l d sModelling and design of new semiconductor materials -Optical properties of semiconductor heterostructures -Non-equilibrium effects in semiconductor heterostructures and lasers -Laser modelling -Exciton hopping in semiconductors -
M e t h o d sMany-body theory -Numerical solution of differential equations -Monte Carlo simulation -Close collaboration with experiment -
e q u i p m e n tHigh performance Linux cluster CHiC (use) -Compute cluster Trinity - + (use)32 Core high performance SMP-workstation -
s c i e n t i f i c c o o p e r a t i o nThe University of Arizona, Arizona Center of Mathematics and Optical Sciences -Center, Tucson, Arizona, USASandia National Laboratories, Albuquerque, New Mexico, USA -Lakehead University, Thunder Bay, Ontario, Canada -Ruhr-Universität Bochum -Philipps-Universität Marburg -
I n d u s t r i a l c o o p e r a t i o nOsram Opto Semiconductors GmbH, Regensburg -
Gain in different semiconductor materials
Schematic semiconductor band structureSchematic semiconductor band structure
Our group (May 2009)
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Eg
k
hL0
h(+ )g L 0
h(- )g L 0
Valence band
Conduction band
M o d e l l i n g a n d d e s i g n o f n e w s e m i c o n d u c t o r m a t e r i a l sFor the design of novel semiconductor devices, a theoreti-cal prediction of their optical properties is very useful. This allows to minimise the number of iterations in the optimi-sation and thus the cost of the development of a new struc-ture. The theory, however, has to be free of fit parameters depending on the experimental conditions, necessitating a many-body theory with high numerical complexity. Us-
ing the semiconductor Bloch equations and approximat-ing phonon and Coulomb scattering in second Born and Markov approximation, predictions as to the gain and laser losses as well as other optical properties of semiconduc-tor heterostructures may be made. Alternatively, for highly disordered materials we perform an analysis of the optical properties based on exciton hopping.
Transient gain in a multiquantum well structure for differ-ent densities, theory (solid) and experiment (dashed).
l a s e r d y n a m i c s a n d n o n - e q u i l i b r i u m e f f e c t sMost laser theories assume an equilibrium distribution of the carrier system due to the fast scattering of the high density system. But especially high power applications and optically pumped structures, e.g. semiconductor disk lasers, demand a more elaborate theory. Modelling the full
dynamics of the carrier system demands a high numerical effort, yet allows to simulate the full temporal dynamics of the system. We remark strong effects of the temporal shape of the optical pump pulse, i.e. the chirp of the in-cident pulse.
Time-resolved emission of a vertical cavity surface emitting laser (VCSEL), depend-ing on the chirp of the optical pump. The inset shows the integrated emission.
o p t i c a l p r o p e r t i e s o f i n d i r e c t s e m i c o n d u c t o r sA microscopic model for the calculation of the optical prop-erties of Silicon and Germanium heterostructures is being developed. Even though a number of simulations have been performed in this area, most are based on simple single-particle models. The proliferation of optical Silicon
devices, e.g. modulators, necessitates the improvement of their theoretical treatment. Also, the optical gain in indi-rect materials is thought to principally differ from the gain in direct materials. This result of simple theories needs to be verified in a many-body calculation.
Phonon-assisted optical interband transition in an indirect semiconductor
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c o n t a c t Reichenhainer Strasse 70 · Institute of Physics · P 208 Phone: +49 371 531 21870 Fax: +49 371 531 21959 [email protected] www.tu-chemnitz.de/physik/KSND/
c o M P l e X s y s t e M s a n dn o n l I n e a r d y n a M I c s Prof. Dr. Günter Radons
r e s e a r c h f i e l d s Lyapunov instabilities of extended dynamical systems -Anomalous diffusion processes -Dynamical systems with hysteresis -Systems with varying delay -Formation of localized modes and coherent structures -Time series analysis of complex systems -
M e t h o d s Smart brain-work -Analysis of complex systems and problem solving -Numerical and analytical tools of nonlinear dynamics and disordered systems -Time-series and data analysis -Parallel and high-perfomance computing -
e q u i p m e n t Compute cluster with 48 Opteron Dual Core processors -Compute cluster with 96 Opteron Dual Core processors (Theoretical Physics) -CHiC (Chemnitz University of Technology) -JUGENE (Forschungszentrum Jülich) -Jump cluster (Forschungszentrum Jülich) -
s c i e n t i f i c c o o p e r a t i o n s Max Planck Institute for the Physics of Complex Systems, Dresden -Queen Mary, University of London, School of Mathematical Sciences -Sächs. Forschergruppe 877 (From Local Constraints to Macroscopic Transport) -Max Planck Institute for Plasmaphysics, Garching -Technical University of Lublin, Department of Applied Mechanics -CEA-Saclay, France -Fraunhofer Institutes (IPA, IWU, EMI) -
I n d u s t r i a l c o o p e r a t i o n s Robert Bosch AG, Stuttgart -Airbus Deutschland GmbH, Hamburg -
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ly a p u n o v i n s t a b i l i t i e s o f e x t e n d e d d y n a m i c a l s y s t e m s The modern theory of nonlinear dynamics is of great im-portance for the understanding of the fundamentals of statistical mechanics. We are mainly interested in the Ly-apunov instabilities of extended dynamical systems and
possible implications for their macroscopic behavior. The systems we deal with include coupled map lattices, Ham-iltonian lattice models, partial diff erential equation (PDE) systems and glass formers.
Lyapunov spectral gap
d y n a m i c a l s y s t e m s w i t h h y s t e r e s i s Many systems ranging from magnetic materials to shape memory alloys, or fl uids in porous structures, and certain friction models show complex hysteretic behavior in the sense that besides major loops, subloops and non-local memory eff ects are observed. The most prominent phe-
nomenological model to account for such eff ects is the so-called Preisach model. Our main interest lies in the investigation of general properties of dynamical systems with hysteresis.
Return map for tent map under hysteresis
s y s t e m s w i t h v a r y i n g d e l a y Delay diff erential equation with constant delay are nowa-days well understood. In real applications, ranging from machining operations such as turning or milling to the evo-lution of biological systems, the delay is actually time- or
state-dependent. Such systems are much less understood. Our research aims at a deeper understanding especially of stability issues in dependence on the delay characteristics.
Turning process
a n o m a l o u s d i f f u s i o n p r o c e s s e s Recently it has been recognized that many transport pro-cesses do not show standard or normal diff usion, but be-have anomalously. Our research on anomalous diff usion processes is motivated by stability considerations in plasma
physics, by the experimental observation of molecular dif-fusion in thin fl uid layers at solid surfaces, and more gener-ally, by questions of transport in disordered environments.
Two-layer diff usion process
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c o n t a c t Reichenhainer Strasse 70 · Institute of Physics · P 302 Phone: +49 371 531 21910 Fax: +49 371 531 21919 [email protected] www.tu-chemnitz.de/physik/THUS/
t H e o r y o f d I s o r d e r e d s y s t e M s Prof. Dr. Michael Schreiber
r e s e a r c h f i e l d s Disordered quantum systems (Anderson localization, Coulomb glass) -Quantum and molecular dynamics -Quasicrystals -Formation of correlations and structure -Nanostructures and interfaces -
M e t h o d s Solution of large-scale eigenvalue problems especially for sparse matrices -Analysis of eigenvalue spectra and wave functions (multifractal analysis, -participation ratio, etc.)Random matrix theory (level spacing distribution) -Quantum master equations for density matrices (molecular wires) -Density functional methods (molecules, molecular crystals, inorganic semicon- -ductors)Empirical tight-binding approach (inorganic semiconductors, nanotubes, -metal-nonmetal interfaces)
e q u i p m e n t Compute Cluster with 86 Opteron Dual Core processors -Compute Cluster with 96 Opteron Quad Core processors, InfiniBand intercon- -nect, 816 GB total memory and 24TB external raid storage
s c i e n t i f i c c o o p e r a t i o n Research center Forschungszentrum Dresden-Rossendorf -Jacobs University Bremen -Leibniz Institute for Solid State and Materials Research Dresden -Max-Planck-Institute for Physics of Complex Systems, Dresden -Technical University Munich -University of Tartu (Estonia) -University of Warwick (England) -
Group members and research collaborators
Ensemble of disordered icecream containers (long term study)
Static charge susceptibility for the two-dimensional Hubbard model
Anomalously localized state at the transition of the Anderson model of localization. Box sizes correspond to probabilities.
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0 50 100 150 200 250 300 350 400
lattice site
ln t = 24
ln t = 18
ln t = 12
ln t = 6
ln t = 0 |ϒ(t)|
d i s o r d e r e d q u a n t u m s y s t e m s The transition between metallic and insulating phases (MIT) of a solid exhibits a variety of interesting phenom-ena. Fundamentally, the MIT can be well described by a variation of disorder in the sample or/and of interactions between charge carriers. We study a purely disorder-driven MIT using the Anderson model of localization discretized on a lattice, where disorder is contained as potential disor-der on the sites and as topological disorder in the links be-
tween sites. In a disordered potential exceptional statistical fl uctuations lead to so-called anomalously localized states that appear in the metallic phase and also at the MIT. We fi nd that these states can infl uence the behaviour of the critical properties. Topological disorder is investigated for quasicrystalline structures and samples with sites connect-ed according to a small-world network. The MIT is located numerically and characterized by its critical parameters.
Quantum diff usion of a wave packet Υ(t) in a one-dimensional silver mean quasicrystal
s e m i c o n d u c t o r s p e c t r o s c o p y The spectroscopic properties of inorganic and organic ma-terials are investigated with complementary microscopic approaches. For molecules and molecular materials the coupling between electronic excitations and internal vibra-tions plays a key role. Therefore microscopic models for the optical response have to account for the coupling between excitons and internal vibrations.
We have recently investigated the photoluminescence (PL) of H-passivated tetrahedral silicon nanocrystals up to a di-ameter of 2.5 nm by using a time-dependent DFT method. From a comparison of our calculations with measured PL bands obtained on clusters with known size distribution, we fi nd an agreement of the PL energies within better than 0.2 eV.
Highest occupied molecular orbital of Si17H36(B3LYP/double-zeta)
I n t e r a c t i n g fe r m i a n d B o s e g a s e s Near Feshbach resonances it is possible to tune the interac-tion in ultra-cold Fermi and Bose gases. One can therefore vary the interaction in a Bose-Einstein condensate (BEC) or drive a Fermi gas through a transition from Cooper pairs in a BCS state to two-particle bound states which can also form a BEC. Our main interest of the group lies on the con-ditions for the formation of bound states, Cooper pairs or a
BEC. Especially the dependence of these conditions on the interaction is investigated. Calculations are done mainly analytically with a many-body Green functions technique for idealized potentials. Therefore also medium eff ects such as Bose enhancement and Pauli repulsion can be included. Furthermore the deformations of surfaces of superconduc-tors caused by vertex motion are investigated.
Phase diagram for bound states (BS) of an interacting Bose gas.
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c o n t a c tReichenhainer Strasse 70 · Institute of Physics · P210Phone: +49 371 531 21950Fax: +49 371 531 [email protected]/physik/CPHYS/
t H e o r e t I c a l a n d c o M P u t at I o n a l P H y s I c sProf. Dr. Karl Heinz Hoffmann
r e s e a r c h f i e l d sDynamics of Complex Systems -Spin Glasses -Energy Landscapes -Irreversible Thermodynamics -Quantum Thermodynamics -Anomalous Diffusion -Phase Transitions and Thermodynamic State Equations -Stochastic Optimization -
M e t h o d sMathematical Analysis -Algebraic Computing -High Performance Computing -Parallel Computing -
s c i e n t i f i c c o o p e r a t i o nSan Diego State University, USA, Complex Systems, Optimization -University of Western Ontario, Canada, Mathematics, Fractals -University of Southern Denmark, Denmark, Spin Glasses -University of Copenhagen, Denmark, Thermodynamics -Jadavpur University, India, Complex Systems, Fractals -University of Chicago, USA, Thermodynamics, Energy Landscapes -MPI Festkörperforschung Stuttgart, Complex Systems -
I n d u s t r i a l c o o p e r a t i o nBASF AG, Ludwigshafen, Thermodynamics -
Teaching Computational Science
Our group (January 2008)
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rESEarchc o m p l e x s y s t e m s a n d a n o m a l o u s d i f f u s i o nAn often-used picture for complex systems is that of a mountainous landscape, where the heights of the moun-tains represent the energy, which depends on the state in all the degrees of freedom. Typical examples of such com-plex systems are spin glasses, cluster of molecules with their thermal relaxation behavior, or anomalous diffusion processes in complex structures. Studying the dynamics of
complex systems means to overcome the problem of the enormous number of states. This number can be reduced considerably by coarse graining the state space. Often the resulting structure has a tree topology. The result is that Markov processes on tree structures are good modeling tools for the thermal relaxation of complex systems.
An example for complex systems: Hexadecan
s t o c h a s t i c o p t i m i z a t i o nStochastic optimization procedures try to provide solutions to optimization problems which have many local minima in their objective function. For these optimization prob-lems the usual steepest descent algorithms fail as they get easily caught in local minima. Therefore, we investi-gate controlled optimization dynamics using tools based
on theoretical physics concepts. Stochastic optimization procedures and especially simulated annealing have been used with growing success, to provide at least “good” solu-tions which are not too “far” apart from the desired global minimum. A typical field of application is the travelling salesman problem.
The “traveling salesman” problem
I r r e v e r s i b l e t h e r m o d y n a m i c sUsually, results of simple thermodynamics are obtained from the study of reversible processes. However, this con-tradicts the dynamics of the world we are living in. Existing heat engines, for example, never attain more than a frac-tion of the reversible Carnot efficiency. A number of ap-proaches - Finite-Time Thermodynamics and Endorevers-
ible Thermodynamics - have been developed to overcome that shortcoming and to provide better limits and bounds. Innovative theoretical techniques have been developed to model the performance of for instance automobile en-gines, refrigerators, heat pumps, solar cells, and chemical distillation processes.
A power-efficiency-graph of a heat engine
Publisher: Institute of Physics, Chemnitz University of Technology
Editors: AG Öffentlichkeitsarbeit, Institute of Physics
Layout: M/Ö; AG Öffentlichkeitsarbeit, Institute of Physics
Edition: APRIL 2011
Institute of Physics
Institute of Physics
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Institute of Physics
Faculty of Natural SciencesChemnitz University of Technology
Reichenhainer Strasse 7009126 Chemnitz Germany
Phone: +49 371 531 21500Fax: +49 371 531 21509
