nanosyd - annual report 2009

Annual Report 2009

Nano Centre SouthThe Mads Clausen Institute

Alsion 2, 6400 SønderborgDenmark

Preface 3The team 2009 4The partners 6Achievements 8Facilities 10Projects 14Publications 44Activities 50How to find us 52

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Table of content

NanoSYD

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Preface

NanoSYD is a nanotechnology centre at the Mads Clausen Institute at the Faculty of Engi-neering, University of Southern Denmark. It is located in Alsion, an educational and cul-tural building complex in Sønderborg near the Danish/German border. NanoSYD hosts the SDU cleanroom as well as optical and surface science laboratories. This is the third issue of the annual reports for NanoSYD.

NanoSYDs vision is

to bridge education, research and development in nano- and microtechnologies to develop nano- and microtechnology based innovative photonic and electromechanical devices. NanoSYDs mission is

to benefit the academic and industrial Southern Denmark with access to state-of-the art micro- and nanofabrication facilities including experimental and theoretical nanoscience- and technology.

In 2009 NanoSYD has improved safety issues for the cleanroom and has seen traffic in the cleanroom mainly for educational and research purposes. A new Interreg IVa project has started that combines research and educational competences between Universities of Applied Sciences Kiel and Flensburg, and SDU Sønderborg.

On the research and development side NanoSYD has focused activities in its third year on

- microfluidic platform generation- surface microstructure controlled growth of nanoaggregates - electroluminescence from organic materials - developing new methods for nanofiber growth- optical sensor development

In its third year again the number of staff at NanoSYD has increased. The presentations in the present report reflect this positive development, which I hope will continue in 2010.

Horst-Günter RubahnProfessor, Head of Centre

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NanoSYD

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Permanent Horst-Günter Rubahn Prof., Head of Nano Centre South Morten Willatzen Prof., Head of Mathematical Modelling Frank Balzer Associate professor Vladimir G. Bordo from 01.02. Associate professor Jens Ebbecke Associate professor

Technical & administrative Zora Milde Centre Secretary Martin W. Nørgaard Cleanroom technician Mogens Petersen Engineer Reiner Hübel Cleanroom technician

Assistant professors & Postdocs Jakob Kjelstrup-Hansen Assistant professor Benny Lassen Assistant professor Manuela Schiek Assistant professorSøren Madsen Assistant ProfessorJonathan Brewer Postdoc, afilliated to MEMPHYS, OdenseMihaela Albu from 15.03. Postdoc James Hoyland from 01.08. Postdoc Morten Madsen from 26.08. PostdocRalf Frese Postdoc

PhD studentsDaniele Barettin PhD student Kirill Bordo PhD student Christian Maibohm PhD student Roana de Oliveira-Hansen PhD student Luciana Tavares PhD student Kasper Thilsing-Hansen PhD student Casper Kunstmann-Olsen PhD student Anders Pors from 01.07. PhD studentLars Duggen PhD student

Research assistants Xuhai LIU from 15.07. Research assistantStefan Johansen from 01.08. Research assistantLasse Johansen from 01.11. Research assistant

Visiting scientistsLeszek Jozefowski several visits Visiting scientist Natasha Lopes Guest student Henri Boudinov from 01.08. until 31.10. Guest lecturer Ivonne Wallmann from 15.08. until 04.09. Visiting scientistAndreas Schäfer from 15.08. until 04.09. Visiting scientist

ANNUAL REPORT 2009

The team 2009

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Laser LaboratoriumGöttingen, Germany Contact person: Jürgen Ihlemann

University of Applied Sciences IMSTKiel, Germany Contact person: Mohammed Es-Souni

Christian-Albrechts University Multicomponent Materials Chair and Physics DepartmentKiel, Germany Contact persons: Franz Faupel and Michael Bauer

University of Oldenburg Center for Interface Science (CIS)Germany Contact person: Katharina Al-Shamery

Tyndall Institute Contact person: Eoin O’ReillyCork, Ireland

University of Milano-Bicocca Institute of PhysicsItaly Contact person: Gian Paolo Brivio

Kaunas University of Technology Institute of Physical ElectronicsLithuania Contact person: Sigitas Tamulevicius

Universidad National de Mexico Contact person: Rafael Bario

Jagiellonian University Faculty of PhysicsCracow , Poland Contact person: Marek Szymonski

P. N. Lebedev Physical Institute Contact person: Alexander UskovMoscow, Russia

Russian Academy of Sciences General Physics InstituteMoscow, Russia Contact person: Vladimir G. Bordo Lund University Physics DepartmentSweden Contact person: Andreas Wacker

Wright State University Physics DepartmentOhio, Dayton, USA Contact person: Lok C. Lew Yan Voon

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NanoSYD

PartnersUniversities and Research Institutes

Kepler University Linz Institute for Organic Solar Cells (LIOS) & Linz, Austria Institute of Semiconductor Physics Contact persons: Serdar Sariciftci and Helmut Sitter

Technical University of Graz Institute of PhysicsAustria Contact persons: Roland Resel and Franz Kappel

University of Porto Allegre Physics InstituteBrazil Contact person: Henri Boudinov

Wilfried Laurier University Mathematical Modelling GroupOntario, Canada Contact person: Roderick Melnik

Universidad de los Andres Contact person: Angela CamachoColombia

Aalborg University Department of Physics and NanotechnologyDenmark Contact persons: Thomas G. Pedersen and Kjeld Pedersen

Danish Technological Institute Microtechnology and surface analysis Copenhagen, Denmark Contact person: Leif Højslet Christensen

Technical University of Denmark DTU Nanotech and DTU PhotonicsCopenhagen, Denmark Contact persons: Jesper Mørk, Peter Bøggild, and Antti-Pekka Jauho

University of Southern Denmark BMB, IFK, SENSEOdense, Denmark Contact persons: Luis Bagatolli, Per Morgen, John E. Østergaard

Federal Agency for Materials Polymer DepartmentResearch and Testing Contact person: Heinz SturmBAM Berlin, Germany

Paul Drude Institute NanoacousticsBerlin, Germany Contact person: Paolo Santos

University of Bochum Chemistry DepartmentGermany Contact person: Christof Wöll

University of Bonn Kekulé Institute of Organic Chemistry and Biochemistry Germany Contact person: Arne Lützen

University of Applied Sciences FB TechnikFlensburg, Germany Contact person: Helmut Erdmann

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CompaniesBiomodics, Lyngby, Denmark; Bioneer A/S, Hørsholm, Denmark; Danfoss, Nordborg, Denmark; Diramo A/S, Nordborg, Denmark; Ibsen Photonics A/S, Farum, Denmark; Optaglio S.R.O., Czech Republik; PAJ Systemteknik A/S, Sønderborg, Denmark; Stensborg A/S, Roskilde, Denmark

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OctoberThe new peer reviewed journal ‘Nanoscale’, publishing experimental and theoretical work from nanoscience to nanotechnology, accepted the article “Pinning of organic nanofiber surface growth” written by Roana Melina de Oliveira Hansen, Jakob Kjelstrup-Hansen, and Horst-Günter Rubahn

From October 27 onwards, the first lecture series (Ringvorlesung) between Fachhochschule Flensburg and Uni-versity of Southern Denmark in Sonderborg took place.

NovemberProfessor Katharina Al-Shamery gave her inaugural lecture titled “Nano meets photon” at campus Sonderborg on Friday, November 13.

On November 19. - 20., University of Southern Denmark hosted the DOPS (Dansk Optisk Selskab) Annual Meeting.

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MarchHorst-Günter Rubahn’s book ‘Basics of Nanotechnology’ was reviewed in the Journal for Nanophotonics, Vol. 3, from March 17, 2009.

MayOn May 22, Danmarks Radio broadcasted a piece on TV-Avisen about a new invention for copy protection, which was developed in the research project ‘Nanolabelling’, lead by University of Southern Denmark’s nanotechnologycenter NanoSYD.

JuneIn the beginning of June, a new book on organic thin films: Interface Controlled Organic Thin Films has been published by H.-G. Rubahn, H. Sitter, G. Horowitz, and K. Al-Shamery in Springer Proceedings in Physics 129.

JulyProfessor Katharina Al-Shamery, a renowned professor of chemistry at the university in Oldenburg, has accepted to be honorary professor at the Mads Clausen Institute (MCI), University of Southern Denmark. Hereby the University of Southern Denmark strengthens its focus on organic molecular nanotechnology. Through a number of years, Katharina Al-Shamery has cooperated with Professor Rubahn, NanoSYD on development and extension of the research field of nanotechnology.

JulyOn July 16 and 17 2009, the science centre Phänomenta hosted the nanoTruck, a touring roadshow truck full of nanotechnology. Phänomenta in Flensburg is Germany’s first independent science centre, located at the Northern Gate of Flensburg. In the big premises, it is possible to test, and to experience the laws of technology and natural science on approx. 150 mostly interactive experiments. In connection with the visit of the nanoTruck, the premises of the Phänomenta were put to NanoSYDs disposal in order to present various examples on nanotechnology in our everyday life, different microscopes, and lasers. In addition to several talks about the technology, its future and potential, a partly interactive, online connection to the cleanroom at campus Sønderborg was established.

August NanoSYD has received a grant from Veluxfonden of 125.000 DKK for a 3 months visiting professorship. From August to November 2009, Henri Budinov from University of Porto Alegre in Brazil visited the nanotechnology group in the framework of a cooperation on microstructure formation in the cleanroom.

On the occasion of the workshop “Smart Materials” in Kiel, a special issue of Applied Physics A was published in August, with M. Es-Souni and H.-G. Rubahn as guest editors: Applied Physics A, Vol 96, Number 3/August 2009, Special Issue “Smart Materials” (pp 537-614). http://springerlink.com/content/100501

September‘Nanotechnology: today and tomorrow’ was the topic of plenary talks given in Odense at the Alumni Day on September 12., and on the NetworkING Day on September 26.

The Summer School 2009 took place in Milano, at the University of Milano Bicocca, from September 14 - 19, 2009.

AchievementsANNUAL REPORT 2009

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Fields of Interest

Nano and micro technology devices based on

• Advanced sensing platforms

• Micro and nano fluidics

• Lighting, lasing, sensing, frequency-transforming, wave guiding photonic elements, and combina-tions of those

• Micro electro mechanical systems (MEMS)

• Ultrasonic components (theory)

• Development of integration strategies based on

• Fluidic alignment

• Soft lithography for transfer printing

• Nanolithographies

• Single element manipulation

NanoSYD

Facilities

The Cleanroom at NanoSYD

The cleanroom at NanoSYD has educational, research, and processing purposes. It is equipped for processing 4 inch silicon wafers. The equipment pool is especially suited for bulk micromachining of mechanical micro and nano structures featuring double-sided lithography and deep silicon etching capabilities. This enables the fabrication of, e.g., membranes and other sophisticated silicon platforms. In addition, it allows the fabrication of hot embossing stamps for, e.g., micro fluidic applications.Patterning can be accomplished on a wafer scale by photo and nanoimprint lithography, and on smaller substrates with electron beam lithography. Silicon nitride and poly-silicon can be deposited by low-pressure chemical vapour deposition, and silicon dioxide can be grown by thermal oxidation. Electron beam evaporation, and both DC and RF sputtering facilitates the deposition of various metals and insulators. Soft materials can also be deposited. Silicon, silicon dioxide, and silicon nitride are processed by wet chemical etching. In addition, a reactive ion etcher enables us for deep silicon etching of high aspect ratio structures.The characterisation equipment includes scanning electron microscopy, atomic force microscopy, ellipsometry, and various optical microscopy techniques, interference microscopy included. Back-end processing includes dicing and wire bonding. The complete equipment list can be found on www.sdu.dk/nanosyd.

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Nano Optics Laboratory (Basement, below the cleanroom)

This laboratory is equipped with an ultrafast laser source, a scanning near field optical microscope, spectrometers, a liquid helium cold finger and a laser scanning microscope. Additional laser tables allow one to set up further optical experiments for performing, e.g., goniometric measurements.

Microscopy Laboratory (Block A, 3rd floor)

A combined inverted epifluorescence and atomic force microscope is the main equipment of this laboratory. A second epifluorescence microscope with accompanying spectrometers allows for high resolution, spectrally resolved optical images of surfaces and surface structures.

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NanoSYD

The Optics and Surface Science Laboratories

The laboratories are complementary to the cleanroom facilities. They focus on thin film deposition and photonics technology, with special emphasis on laser materials treatment, spectroscopy, microfluidics, and near field optical technologies.

Surface Science Laboratory (Block A, 3rd floor)

This laboratory hosts ultrahigh and high vacuum thin film deposition apparatus with state-of-the-art surface characterisation equipment. Ultrathin films and nanoaggregates from metals, semiconductors, and dielectrics can be grown, but focus is on the growth of discontinuous organic thin films. The laboratory also hosts stations for micromanipulation of nanoaggregates, for electrical measurements, and for spectroscopy, as well as an excimer laser materials treatment station. Development of infrared light based sensors as well as microfluidic lab-on-chip technology, are performed in separated sections. A mechanical workshop is associated to, the laboratory.

FacilitiesANNUAL REPORT 2009

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Upcoming research 2010 The developed model will be further applied for metal nanowires as well as for nanoholes/nanowires in a metal film. The transmission properties of such systems will be also investigated.

Papers [1] V.G. Bordo, Model of Fabry-Pérot-type electromagnetic modes of a cylindrical nanowire. Phys. Rev. B 81, 035420, 2010.

The NW response function plotted versus the di-mensionless NW length and wavelength for a NW with εNW = 6 surrounded by vacuum. Only the even modes are shown.

The effective phase shift on reflection from the NW end plotted versus the dimensionless propaga-tion constant. εNW = 6.

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NanoSYD

Theory of Fabry-Pérot modes of a cylindrical nanowire

Vladimir Bordo

General introduction

Being an optical resonator, a nanowire (NW) enhances electromagnetic waves of certain frequencies which are determined by the resonator length and which are known as Fabry-Pérot modes. A commonly used approximation is to consider the confinement of the electromagnetic field in the NW waveguide and reflections at the NW ends as two completely independent problems. In the present work we have developed a rigorous theoretical approach which allows one to determine the NW Fabry-Pérot modes for an arbitrary NW length, diameter and electromag-netic wave wavelength.

Research results

We have derived an integral equation for the electromagnetic field amplitudes which are the solutions of Maxwell’s equations satisfying the boundary conditions at the whole NW surface simultaneously. The condition that this equation has non-trivial solutions determines the NW Fabry-Pérot modes.

The case of an elongated NW when its length, L, exceeds sufficiently its diameter, 2a, has been considered in detail. For such a NW the integral equation is reduced to a set of linear algebraic equations and the Fabry-Pérot modes can be found from the roots of its determinant. In particular, the Fabry-Pérot modes of a single-mode NW which supports only the fundamental mode HE11 are determined by the roots of the determinant of a 4x4 matrix.

In the latter case the result can be represented in the form which resembles the formula for classical Fabry-Pérot interferometer:

β L=mπ-φ(β),

where β is the mode propagation constant, m is a positive integer and the function φ(β) can be said to be an ef-fective phase shift on reflection from the NW end. The latter quantity can be calculated from the NW response function.

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Projects

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Upcoming research 2010

An appropriate nanofiber transfer method has been developed, which enables nanofiber transfer from the growth substrate mica to a polymeric (PDMS) substrate, where the nanofibers should remain straight and without breaks. Further, a method for transferring the nanofibers from the PDMS substrate to an arbitrary device substrate will be investigated. In addition, a nanostencil lithography substrate should be developed for depositing material on sensitive substrates. This stencil consists of a thin, perforated silicon nitride membrane supported by a silicon substrate. The coating, transfer and deposition techniques are particular important for future applications, where transferred nanofibers will be deposited on electrodes on a pre fabricated device substrate to establish the desired electrical contact to enable electrical rather than optical excitation of nanofiber light emission.

Papers

[1] L.Tavares, J. Kjelstrup-Hansen, H.-G. Rubahn, H. Sturm, Reducing bleaching effects in organic nanofibers by bilayer coating. In preparation.

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NanoSYD

Coating of organic nanofibers for largely reduced photobleachingLuciana Tavares


Para-hexaphenylene (p-6P) organic nanofibers emit polarized, blue light upon UV excitation with peaks of the emitted light at 3.09, 2.94, 2.77 and 2.62 eV and a spatially anisotropic distribution of the emitted light. However, the nanofibers exhibit a characteristic photoinduced reaction during illumination with UV light that causes a decrease in luminescence intensity (bleaching) and that is partly attributed to photooxidation. Systematic experi-ments were performed with the aim of identifying an appropriate coating material to stop the bleaching reaction. It was found that the most promising coating material combination results in a significant reduction of bleaching without significantly affecting the emission spectrum.

Research results

SiOx coatings result in a huge luminescence peak at 500 nm but after about 7 minutes of UV irradiation, the spectra exhibit a reduction of this peak and the spectral features look more similar to that of the uncoated p-6P nanofibers. However, the luminescence intensity still decays relatively fast. Al2O3 coatings generate a large peak around 500 nm and even after prolonged UV illumination the spectra do not change and it has not been possible to identify the characteristic peaks from p-6P nanofibers. Bi-layer polymer / oxide coatings show different behav-iors. PMMA A4 / 200 nm SiOx appears to be the best coating.

ANNUAL REPORT 2009

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Polymer stamp with nanofibers

device substrate

device substrate with nanofibers

Only a weak bleaching has been observed even after about 40 minutes UV illumination and the p-6P standard spectrum has been to a large degree recovered after UV exposure. Raman measurements have shown the charac-teristic peaks from p-6P nanofibers even after coating with PMMA A4 / 200 nm SiOx which is a strong hint that the local atomic arrangement of the nanofibers has not been affected by this bi-layer coating.

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mica/p6P mica/p6P/PMMA A4/200 nm SiOx - at the beginning of UV illumination mica/p6P/PMMA A4/200 nm SiOx - after 40 minutes UV illumination

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In the low-SAW-power regime, the attenuation of the SAW is used as a highly sensitive and non-invasive probe for persistent photoconductivity effects in ZnCdSe/ZnSe QWs. These effects are observed over long time-scales exceeding several minutes at low temperatures (see Fig. 2). By varying the optical excitation energy and power and temperature we show that these effects arise from carriers photogenerated by interband excitation which are trapped in random potential fluctuations in the QWs related to compositional fluctuations. Furthermore, effects related to defect levels in the bandgap can be excluded and a transition of the conduction mechanism with tem-perature from a hopping to a percolation regime is observed.

Figure 2: SAW attenuation of the third SAW harmonic (f3 = 345 MHz) at T = 35 K, before, during and after optical excitation. Inset: ZnCdSe/ZnSe heterostructure on a LiNbO3 substrate with IDT.

Papers

[1] D. A. Fuhrmann, A. Wixforth, A. Curran, K. A. Prior, J. Morrod, R. J. Warburton, J. Ebbecke, Surface acoustic wave mediated exciton dissociation in a ZnCdSe/LiNbO3 hybrid, Appl. Phys. Lett. 94, 193505 (2009).

[2] D. A. Fuhrmann, H. J. Krenner, A. Wixforth, A. Curran, K. A. Prior, R. J. Warburton, and J. Ebbecke, Non-invasive probing of persistent conductivity in high quality ZnCdSe / ZnSe quantum wells using surface acoustic waves, submitted to J. of Appl. Phys.

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NanoSYD

Surface acoustic wave dynamics in ZnCdSe Quantum WellsJens Ebbecke


Surface acoustic waves (SAW) are a highly versatile tool to probe and manipulate optical and electronic properties of materials. Examples in the field of low-dimensional semiconductor heterostructures include charge convey-ance and spectroscopy of high-mobility electron systems and optically active systems as Quantum Wells (QWs) and Quantum Dots. However, most of these investigations focused on the most advanced III-V semiconductor compounds due to their piezoelectricity which allows for the use of interdigital transducers (IDTs) to excite and detect SAW. Despite the fact that most II-VI semiconductors are also weakly piezoelectric still SAW-based studies are very limited.The core of this project is to dissociate and transport optically excited excitons by high-power SAWs and in the low-power regime to probe the carrier dynamics in the QW by the SAW.

Research results

By making use of epitaxial lift-off, ZnCdSe QWs are transferred onto a LiNbO3 substrate in order to employ its enhanced piezoelectric properties (see Fig. 1). The photoluminescence emission of this hybrid structure is characterized and the influence of a SAW with large amplitude on the free exciton and bound exciton emission is investigated. The excitons can be dissociated by the piezoelectric field and the resulting electrons and holes are transported out of the lens focus by the travelling SAW. These “high-acoustic power” experiments with the ZnCdSe/LiNbO3 hybrid system are encouraging for future optical applications at elevated temperatures.

Figure 1: Schematic sketch of the epitaxial liftoff technique and the measurement setup: ZnCdSe QWs were grown on a GaAs substrate on top of a sacrificial MgS layer. Using a selective etchant solution the MgS layer can be removed and the top layers were transferred onto a LiNbO3 substrate with prestructured IDTs.

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NanoSYD

Functional Nanofibers from customized Organic Semiconduc-torsManuela Schiek, Andreas Schäfer*, Ivonne Wallmann*1

**permanent address: Kekulé Institute of Organic Chemistry and Biochemistry, University of Bonn, Germany

General introduction Nanofibers, nanowires and nanotubes established their reputation in basic and applied research within the field of nanotechnology. Organic compounds are interesting candidates because of their structural flexibility and suitability for controlled bottom-up growth. Especially rod-like organic semiconductors such as (functionalized) para-phenylenes, alpha-thiophenes and their co-oligomers form mutually well aligned lying nanofibers on an appropriate growth substrate. Controlled growth of upright standing nanofibers is also possible by solution assisted wetting of porous alumina templates. This has so far only been demonstrated for non-carbon based semiconductors.

Research results

Novel organic semiconductors have been implemented for the nanofiber growth. The usually rod-like shaped organic semiconductors consist of thiophene, phenyl and/or naphthyl units with optional addition of functional groups. Two approaches have been studied for the nanofibers growth: (1) vapour deposition in high vacuum onto a freshly cleaved muscovite mica substrate and (2) solution assisted wetting of a porous alumina template. In case of vapour deposition onto the mica substrate lying nanofibers are formed built up of lying molecules. The nanofibers are mutually aligned displaying heights and width of a few hundred nanometers and a length of a few or a couple of ten micrometer. Fig. 1 (a) shows nanofibers from a naphthyl-thiophene co-oligomer on muscovite mica. The nanofibers emit green, polarized fluorescence light after excitation with UV-light. Their dimensions and mutual alignment are controlled by process parameters like substrate temperature and deposition rate. The fluorescence microscopy image (top) and the SEM image (bottom), Fig. 1 (b) displays upright standing nanofibers from a blue fluorescent, functionalized phenyl-thiophene co-oligomer after liberating from the commercial alumina growth template. They are grown by a solution assisted wetting process. The fiber’s dimensions are given by the pore sizes, which are here 200 nm in width and 16 micrometer in length.

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Figure 1: (a) Fluorescence microscopy image (58 x 43 µm²) shows lying nanofibers from a naphthyl-thiophene co-oligomer; (b) shows a fluorescence microscopy image (top) and a SEM-image (bottom) of upright standing nanofibers from a functionalized phenyl-thiophene co-oligomer.


In order to achieve control over the dimensions of upright standing nanofibers custom-made alumina templates will be used. The nanofiber properties can be adjusted by implementing different, customized organic semiconductors. The features will be optimized for implementing the fibres in photovoltaic devices.

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Another advantage of PDMS is that it is possible to engineer its refractive index through UV exposure. It is hoped we can use this property to produce waveguides and other optical structures on the surface of the chip, delivering laser light directly to the cells and receiving fluorescence signals from the cells. This will be part of the next stage of the program which is to develop the optical and electronic systems for the chips. Most importantly we will be examining alternatives to the sensitive but expensive PMTs traditionally used as detectors in flow cytometry.

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NanoSYD

Lab-on-chip flow cytometry

James Hoyland, Casper Kunstmann-Olsen


With increasing public concern for food safety and quality, the food processing industry has an urgent need for contaminant detection technologies. Flow cytometry is a well established and highly sensitive technique for analyzing and identifying cells and other biological components in fluids using lasers. However, at present flow cytometers are bulky, expensive and require highly skilled operators. In an industrial setting, samples would have to be sent away for measurement. A faster and more cost effective approach would be if operators within a food processing facility could measure samples either in-line within processes or with a minimum of preparation. This project is dedicated to realizing that through an integrated lab-on-a-chip solution. The final chip will integrate microfluidics, optics and electronics into a single detection platform.

Research results

The primary material chosen for the chips is PDMS, better known as ‘silicone’. The microfluidic channel struc-tures are produced by molding the PDMS over a photolithographically produced “master”. We can produce high quality chips in this manner. The SEM image shows an intersection of two channels in one of our chips. Flow cytometry works by analyzing one cell at a time at high throughput rates. In order to do this the stream of fluid containing the cells must be focused to concentrate the cells into a single line. We achieve this on our chips by using two sheath streams to compress the central sample stream. The microscope image shows this process, the sample stream has been dyed red for clarity.Finally use optical fibers embedded in the chip to deliver the laser light used to analyze the cells and to receive the signals from the cells. As a model we use fluorescent microspheres to test the system. The picture shows the beads in one of the channels. To the left can be seen one of the embedded fibers used to detect the fluorescence. We have also tested spiral mixing structures to enable staining of cells “on chip”.

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Optically the nanotubes show blue-greenish fluorescence when excited with UV-light and their spectra resemble that of a single crystal of the same material with additional broadening due to their polycrystalline nature. A frac-tion of the nanotubes also show waveguiding behavior, but so far we have only observed waveguiding from tubes which are a part of a bundle of nanotubes. The underlying mechanisms controlling this have to be further inves-tigated. Controlling the waveguiding properties will make the nanotubes interesting for application in nano optics. Preliminary work with two-photon fluorescence and higher-harmonic imaging of the nanotubes has been done with a laser scanning microscope, built at NanoSYD. Continuation of this work is hoped to shed light on fun-damental questions like non-linearity, waveguiding and the connection between morphology and optical activity. Suspended nanotubes in liquid have allowed us to measure the anisotropy of the fluorescent emission. When UV excited the nanotubes look like small rotating flash lights and show an anisotropic ratio of 3 or higher between the side and the end of the tube. A high anisotropy ratio indicates a well ordered molecular packing in the nanotubes which is in good agreement with the polycrystalline nature seen in the TEM images.

Figure 2: Nomalized waveguided intensity of two Tms-tbf nanotubes inside a 8 µm wide bundle. The attenuation of the waveguided intensity is fitted with a single exponential decay. The solid line in the figure shows the UV-excitation profile.


Nanotubes from different organic compounds can be seen as the first step towards fabrication of core shell struc-tures. By filling the nanotubes, in another growth step, with either another organic compound or metal colloids we can fabricate core shell structures which have intriguing new properties, which could be used as active material in light harvesting devices, nano optical components or as sensors.

Papers

[1] Maren Rastedt, Templat gesteuerte Erzeugung organischer Nanofasern/-röhrchen. Diploma thesis, Oldenburg 2008.[2] Frauke Kutscher, Neuartige molekulare mehrwandige Nanoröhren. Bachelor Thesis, Oldenburg.

NanoSYD

Growth and characterization of organic nanotubes

Christian Maibohm, Maren Rastedt*1

1*Institut für Reine und Angewandte Chemie, Carl von Ossietzky Universität Oldenburg, 26111 Oldenburg, Arbeitsgruppe Al-Shamery.


Template assisted growth of nanostructures offers an easy way of processing a large variety of materials. We have been using the technique to fabricate small tube like structures of organic molecules. When the tubes are freed from the template, their optical and morphological properties are investigated.

Research results

Nanotubes of Tbf (Tetrabenzo[a,c,g,i]fluorene) and 17-Tms-tbf (17-Trimethylsilyl-tetrabenzo[a,c,g,i]fluorine) were fabricated via template assisted growth from a receipt developed and published by Maren Rastedt [1] and further investigated by Frauke Kutscher [2]. The method utilizes holes in porous alumina templates as scaffold for the structures. Powder of the respective organic molecules is placed on the template and heated in a furnace, where temperature and heating time are the critical growth parameters. After cooling the template is removed, which makes the nanotubes accessible, using an alkaline solution and this solution can then be drop casted on a substrate. The used templates controls the characteristic dimensions of the tubes which is up to 60 µm in length and from 100 to 300 nm in outer diameter. The wall thickness is controlled by the heating time and type of organic compound.

Figure 1: SEM image of template assisted growth of Tbf nano-tubes, where the porous alumina template is partly removed with a 10% NaOH solution.

After removal of the template the nanotubes are investigated for both morphological and optical characteristics. TEM images have shown that the tubes are polycrystalline, while combined FIB and SEM images show that the tube structure runs along the full length of the structure, which has been tested by cutting the tube with the FIB at different places.

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It is planned to continue the fabrication of nanofiber arrays for solar cell applications, using different organic sub-stances. Further improvement of the anodization procedure, including two-step anodization and electropolishing of the initial substrates, will be also tried.

Papers

[1] K.V. Bordo, M. Es-Souni, S. Habouti, M. Schiek, H.-G. Rubahn, Mesoporous thin film templates for the synthe sis of nanowires and nanotubes, 3rd International Workshop on Smart Materials & Structures, Kiel, Germany, August 19-21, 2009. Book of abstracts.

[2] K.V. Bordo, M. Es-Souni, S. Habouti, M. Schiek, H.-G. Rubahn, Mesoporous thin templates for the synthesis of nanowires and nanotubes, Chemistry and Physics of Materials for Energetics. A European School in Materials Science. Milano, Italy, September 14-19, 2009. Book of abstracts.

NanoSYD

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Nanofibers and Nanotubes by Template Wetting

Kirill Bordo


The method of template wetting allows one to fabricate highly ordered arrays of 1D structures from different ma-terials. The structures obtained can be used, e.g., in solar cells and other electronic devices. The project is devoted to the fabrication of organic nanofibers and nanotubes on different substrates, by means of template wetting. It also includes the preparation of porous anodic alumina films which are subsequently used as templates.

Research results

A number of porous anodic alumina (PAA) films on silicon substrates (see Figure 1) have been produced. The procedure has been optimized for the case of oxalic acid as an electrolyte. Several supported porous templates with the use of sulphuric acid as an electrolyte have also been made. Free-standing PAA membranes for the fur-ther fabrication of metallic nanorods by means of electrochemical deposition have been produced. A new anodi-zation device which allows to work with strong acids at different temperatures has been installed at Alsion.

Some of the obtained PAA films were used for the fabrication of organic nanofibers by means of template wet-ting. In particular, nanofiber arrays from dioctyl substituted polyfluorene (PF8) and zinc phthalocyanine (Zn Pc) were fabricated (see Figure 2).

Figure 1. SEM image of a PAA template on a silicon substrate

Figure 2. SEM image of a ZnPC nanofiber array fabricated by means of template wetting

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Figure 4. ZnPC nanofiber array from a thin ano-gised film on silicon.

Figure 3. Polyfluorescent nanotubes.

2 examples of fabricated tubes and fibres

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Figure 2a shows an optical microscope image of a p6P thin film sample biased with Vd = -Vs = 30 V and a AC gate voltage with an amplitude of 75 V and a frequency of 200 kHz. Clear blue light is emitted from the edges of the source and drain electrodes. The electroluminescence spectrum in figure 2b is recorded to confirm that the blue light is from the p6P material. This EL together with a reference photoluminescence spectrum is normalized to enable a direct comparison of peak positions. When biased in a DC configuration, the p6P thin film showed nice p-type behaviour with a hole mobility around 1×10 cm²/Vs and an onset voltage of -30 V. The nanofibers also exhbited p-type characteristics, but the output curves suffered high noise, from which the mobility was hard to determine.

Figure 2: (a) Optical microscope image of the EL output of a 60 nm p6P thin film biased with Vds = 60 V and a sinusoidal gate voltage with an amplitude of 75 V and a frequency of 200 kHz. (b) Normalized PL and EL spectra from a p6P thin film.


Other organic semiconductors could be investigated based on the bottom contact structure, as well as alternating configurations, such as top-contacts and top gate structure. A self-assembled monolayer (SAM) could be used to modify the metal electrode to improve charge carrier injection hereby leading to more intense electrolumines-cence. The transferring method of p6P nanofibers should be improved, which can maintain excellent properties of nanofibers after transferring.

Papers [1] Kjelstrup-Hansen, Norton, da Silva Filho, Brédas, and Rubahn, Charge transport in oligo phenylene and phenylene–thiophene nanofibers, Organic Electronics,Vol. 10, p. 1228 (2009).

[2] Kjelstrup-Hansen, Liu, Henrichsen, Thilsing-Hansen, and Rubahn, Conduction and electroluminescence from organic continuous and nanofiber thin films, accepted for publication in Physica Status Solidi (a).

[3] Liu, Wallmann, Boudinov, Kjelstrup-Hansen, Schiek, Lützen, and Rubahn, Electroluminescence of Naphthyl End-Capped Oligothiophenes by Alternating-Current Voltage in an Organic Light-emitting Field-Effect Transistor Con figuration, submitted to Organic Electronics.

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Conduction and electroluminescence from organic thin films andnanofibers

Jakob Kjelstrup-Hansen and Xuhai Liu


Phenylene-based oligomers are of particular interest due to their ability to self-assemble into elongated, crystalline nanostructures – nanofibers. Such nanofibers can emit highly anisotropic, polarized light upon UV light exposure and can function as optical waveguides and random lasers, while chemical functionalization of the molecular building blocks can enable the tailoring of the nanofiber properties for particular applications. The connection of metal electrodes to nanofibers enables the probing of their electrical properties and constitutes a significant step towards the realization of a sub-micron organic LED. In this study, we investigate electrical and light-emission properties of both nanofibers and thin films in a field-effect transistor (FET) configuration.

Research results

Two types of devices have been investigated: FETs based on (I) non-crystalline thin films and (II) crystalline nanofibers. The FET device substrate was made by standard microfabrication techniques. It consists of a highly n-doped silicon substrate, which acts as the FET backgate electrode. The gate oxide is a 200 nm thermally grown silicon dioxide layer, upon which an interdigitated array of gold source and drain electrodes are prepared by pho-tolithography, metal evaporation, and lift-off. The thin film devices were fabricated by vacuum depositing p6P molecules directly onto the device substrates, while the nanofiber devices was prepared by transferring pre-made nanofibers from the growth template mica onto the device substrate. The FET device platform and a diagram of the electrical circuit used when biasing the device with an AC gate voltage for light emission experiments are shown in figure 1.

Figure 1: FET device platform consisting of a highly doped silicon substrate acting as the backgate. On top of a silicon dioxide film, gold source and drain electrodes function as bottom contacts to the organic material, p6P (shown in the upper right corner).

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Single entities have been isolated by either dropcasting the wires, or by initiating the whole precipitation process in a droplet of chloroform+PTCDI-C8 directly on a substrate surface. Examples for both bunches of wires as well as isolated ones are shown in the AFM images in Fig. 2. Typical widths of the wires are 100 – 200 nm, typical heights 20 – 40 nm.


Obviously none of the samples show aligned wires. However, first experiments on shear-force assisted alignment have been successful. Growth via precipitation will be compared to growth by organic molecular beam deposition for more relevant organic semiconductors.

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Figure 2: AFM images of PTCDI-C8 nanowires dropcasted onto a glass surface. Both, areas with a high number density (b) and a low number density (c) of wires can be fabricated.

Organic Nanowires Self-Assembled in Solution

Frank Balzer, Manuela Schiek


Semiconducting organic nanowires can be fabricated by different methods. Organic molecular beam deposition onto crystalline substrates, filling of mesoporous templates, and the AFM-induced built-up from small crystallites are just a few ways. If one is interested in large numbers of nanowires without any waste of material and if mutual alignment of the wires is not a major concern, self-assembly from solution can generate large quantities of well defined wires within a few seconds.

Research results

The well known, n-conducting N,N’-Dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) molecule (Sigma-Aldrich), Fig. 1(a), serves as a model molecule. In first experiments it’s wire growth by precipitation and the deposition of the formed wires onto a solid surface are investigated. A PTCDI-C8 solution in chloroform has a slightly orange color, Fig. 1(b). Adding methanol promotes precipitation, where all of the molecules assemble via π-π interactions into nanoscopic wires, Fig. 1(c).

Both under white light and under UV-illumination (excitation wavelength 365 nm) the wires appear red, Fig. 1(d). Typical lengths are between a few micrometers and a few ten micrometers.

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Figure 1: The n-conducting PTCDI-C8 molecule (a) dissolved in chloroform (b), and after addition of methanol (c). Adding methanol leads to the precipitation of billions of red nanowires. Five of them are shown in the optical microscope image (d).

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Figure 1: In (a) and (b) visualization of the local direction of the molecular transition dipoles within nanofiber samples from para-hexaphenylene and from MOP4, respectively, are shown. The corresponding distribution of transition dipole orientations, (c) and (d), show that in both cases to different orientations are present within the samples.


In 2010 this technique will be applied to more nanofiber systems from different molecules, fabricated under dif-ferent conditions and with different methods to optically identify homogeneously grown samples.

Papers

[1] R. Resel, T. Haber, O. Lengyel, H. Sitter, F. Balzer, H.-G. Rubahn, Origins for epitaxial order of sexiphenyl crystals on muscovite (001), Surf. Interface Anal. 41 (2009) 764.

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Textures in Nanofiber Films and Single Fibers

Frank Balzer


Imaging of the degree of molecular order within needle-like organic crystallites is of paramount importance for, e.g., a basic understanding of the needles’ formation mechanism. Any type of transport property such as charge carrier mobility is also crucially depending on the local crystal structure and the number of grain boundaries. In this project the polarization state of emitted light from the needles after UV-excitation is analyzed. With sub-micrometer resolution the local molecule orientation is deduced.

Research results

For the polarization analysis the fiber samples are illuminated with UV-light under an optical microscope with a polarizer in front of the imaging part. The sample is rotated by a motorized rotational stage, and a series of im-ages is taken. Fourier analysis of such a series of images provides the direction of the average molecular transition dipole for each image pixel. In Figure 1 examples for two different samples are shown: a dense film of para-hexa-phenylene fibers (a), and isolated fibers from a methoxy-functionalized para-quaterphenylene (MOP4) (b). Colors code the local direction of the molecules’ transition dipole. In (c) and (d) the corresponding total distribution of directions is presented.

For para-hexaphenylene two different molecule orientations are known to exist within a sample [1]. These two orientations are clearly visible in the total distribution of directions (c). The spatially resolved image demonstrates that the abundance of the two orientations is not related to different fibers, but may change even within a single fiber. In the case of MOP4 also two different molecule orientations are observed, see Figure 1 (d). Here these two orientations are clearly related to different growth directions of the fibers, Figure 1 (b). However, even within the fibers slight variations of molecule orientations are detected.

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Figure 1 The influence of hydrostatic and shear strain deformation potentials on conduction and valence band states.

Upcoming research 2010The general theory on electromechanical coupling effects and bandstructures of quantum-confined structures is continued in the mathematical modelling group and intensified on the comparison of k•p theories with atomistic-based models.

Papers

[1] L. C. Lew Yan Voon and M. Willatzen, The k•p Method - Electronic Properties of Semiconductors, Springer, Berlin (ISBN 978-3-540-92871-3), 445 pages, August 2009.

[2] L. C. Lew Yan Voon and M. Willatzen, Electronic Structure of Semiconductor Nanostructures: k•p Techniques, Review Paper, In Press, Encyclopedia of Nanoscience and Nanotechnology (2009).

[3] B. Lassen, R.V.N. Melnik, and M. Willatzen, Spurious solutions in the multiband effective-mass theory applied to low-dimensional nanostructures, Comp. Phys. Comm. 6(4), 699-729 (2009).

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The k•p Method – Electronic Properties of Semiconductors

Morten Willatzen and Lok C. Lew Yan Voon*1

1* Lok C. Lew Yan Voon is permanently employed at Wright State University, Ohio, USA. Lok was a guest professor at MCI during August 2009.


General introduction: A general theory of the envelope-function approximation method, also known as the k•p method, applied to semiconductor crystals is presented. The most famous k•p models derived since the mid-fifties are discussed, initially limited to bulk semiconductors but later extended to quantum-confined semiconductor heterostructures. The power of group theory is demonstrated in the computation of eigenstate degeneracies for the most important crystal structures: Diamond, zincblende, and wurtzite (hexagonal). Several unpublished results are presented for the first time, in particular, a multiband derivation of the spin-splitting Hamiltonian for wurtzite semiconductors. An extensive treatment of the so-called Burt-Foreman method to quantum-confined structures is given.

Research results

k•p results include the Luttinger-Kohn envelope function approximation for the upper valence band states in the presence of impurities and external magnetic fields. The full symmetry discussions, essential for k•p bandstruc-ture calculations, are given in details and implications for eigenstates and degeneracies outlined. Continuation to provide a 15-band k•p model for bulk diamond structures including the derivation of all matrix elements based on Cardona and Pollak’s original paper (we note that derivations of matrix elements are not included in the original paper by Cardona and Pollak). Recent full-zone extensions by Fishman et al. to zincblende structures are next discussed.

The general symmetry-based discussions of external electric fields, magnetic fields, strain effects are next pre-sented based on the Pikus-Bir theory and further discussed by Rössler et al. and Cho. We extend the methods of Cho and Pikus-Bir to derive the general bandstructure properties of the Gamma-7, -8, and -9 double-group representations of wurtzite. Special attention is given to the A,B,C upper valence states and the lower conduction states. Detailed bandstructure discussions of impurity effects, electric- and magnetic fields, strain (refer to Fig. 1), exciton effects, and spin-splitting effects in bulk zincblende, and wurtzite structures follow next. These studies are also carried out for diamond structures when relevant.

Substantial discussions are devoted to the Burt-Foreman model with derivations of the so-called exact envelope function approximation for heterostructures. The influence of quantum-confinement effects on eigenstate sym-metries and properties is described. Again, discussions of the importance of external fields in quantum-confined heterostructures are given.

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In figure 1 results of semi-coupled and fully-coupled continuum models are compared with VFF results. In the semi-coupled model the strain fields were found decoupled from the electric field, followed by a calculation of the electric potential taking into account the thus found strain fields. From these results, it is seen that the three models agree reasonably well, however, the discrepancy lead to a difference in the allowed electronic energies of around 100 meV. This is especially due to the discrepancies in the electric potential.


At present we are working on optimizing the VFF code by considering periodic boundary conditions which is a non-trivial matter for strain calculations. The optimized code is required in order to be able to consider larger quantum dots. Furthermore, we are going to investigate the impact of changing the concentration profile inside the quantum dot. This is relevant because quantum dots are never grown with a homogeneous concentration profile. In these extensions we will both consider zinc blende and wurtzite structures.

Papers

[1] D. Barettin, S. Madsen, B. Lassen, and M. Willatzen, Comparison of wurtzite atomistic and piezoelectric con tinuum strain models: Implications for the electronic band structure, Superlattices and Microstructures (2009), doi:10.1016/j.spmi.2009.10.002.

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Atomistic and continuum piezoelectric models for wurtzite and zinc blende quantum dots: Implications for the electronic band structure

Daniele Barettin, Søren Madsen, Benny Lassen and Morten Willatzen


We compare continuum and atomistic models for the electromechanical fields in wurtzite GaN/AlN quantum dots and their relative impact on the electronic band structure. Qualitative agreement between atomistic strain cal-culations and continuum elastic models for a wurtzite hexagonal quantum-dot structure is demonstrated; however, significant quantitative discrepancies of up to 100 meV are observed. A smaller difference of approximately 15 meV is found between fully coupled and semi-coupled continuum models.

Research results

Semiconductor wurtzite and zinc blende heterostructures are important materials for optoelectronic applications. An important aspect in this context is the influence of electromechanical field interactions and their combined effects on the band structure and eigenstates of quantum dots. Since the linear continuum mechanics model does not contain the full crystal symmetry it shows a higher degree of symmetry than atomistic models. In order to quantitatively address the importance of strain, a comparison of the continuum mechanics and valence force field strain models is made and implications for electrons are investigated for a hexagonal shaped GaN/AlN quantum dot.

Figure 1: The zz strain component (left), the electric potential (middle), and the effective potential (right) along the centerline for a hexagonal shaped quantum dot.

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All important sub-systems (laser diode, acoustic cell, signal acquisition, data processing) have been analyzed sepa-rately to gather the performance measurement independent of cross correlations. The performance of total sys-tem has been investigated, too. The experiments have been concentrated on interference effects with the electrical background and also on systematic concentration measurements. The photoacoustic response recorded for differ-ent n-heptane concentrations and corrected for electrical interferences is presented in the figure below.

The investigations show that in its current configuration the PA sensor has a detection limit for n-heptane in air at atmospheric pressure of ~0.1 parts in 10 by volume (ppmv).


In the next stage we plan to apply photocatalytic oxidation (PCO) using nano-sized semiconductors likeTiO , when the oil molecules are disassembled into carbon dioxide and water.The resulting carbon dioxide will be deter-mined using photoacoustic detection.

Papers

[1] M. Albu, R.N. Frese, N.E. Lopes, L. Duggen, M. Willatzen, H.-G. Rubahn, Photoacoustic detection of gaseous n-heptane using a 1725 nm laser diode. In preparation.

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Figure 1: Corrected photoacoustic signal for different n-heptane concentrations.

Sensor Element Platform – Detection of Contaminations in Compressed Air Systems

Mihaela Albu, Ralf Frese, Natasha Lopes


The project objective is to develop an in-situ sensor element platform for detection of contaminations (oil va-pour, droplets, aerosols etc.) in compressed air covering the ISO 8573 standard. The measuring principle behind the sensor is photoacoustic. Photoacoustics has the obvious advantage of being a selective method that can be applied to both molecular oil recognition and particle detection, is a simple technology and is potentially of high sensitivity. The photoacoustic effect is based on the resonant absorption of light by a sample and the transfer of the excitation energy into heat via inelastic collisions of gas molecules. A modulated irradiation of the sample causes periodic pressure variations that can be detected by a microphone and measured using a lock-in technique.

Research results

In order to achieve the specified objective, the initial investigations have been focused on the photoacoustic detec-tion of n-heptane in air at atmospheric pressure. The experiments have been carried out using the opto-mechani-cal setup presented below. The light source utilized was a laser diode FLO-950 (1725 nm, 300 mW). The shape of the photoacoustic cell is of importance and was optimized by theoretical considerations.

Opto-mechanical setup: LD – laser diode; PC – passive cooler; BS – beam splitter; L1, L2 – focusing elements; M1, M2, M3 – gold coated laser mirrors; HeNe – helium neon laser; PA – photoacoustic cell; MIC – microphone; PM – power meter.

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The micron-sized ridges are fabricated by optical lithography on a silicon (100) surface with subsequent gold deposition (55 nm). It has been demonstrated, how growth of almost mutually parallel nanofibers, perpendicular to the long ridge axes, can be obtained on these surfaces. In order to obtain this alignment, it has been shown, that a high surface temperature (around 440 K) and narrow ridges (below 10 µm) are needed. A comparison between growth on ridges and in between the titanium pinning lines shows, that the alignment effect is similar on the two different surfaces. Figure 2 shows a plot of the orientational distribution and length of nanofibers grown on 2.5 µm ridges and in between titanium pinning lines (with 2.5 µm separation distance) at a surface temperature of 435 K and 433 K, respectively.

Figure 2: Comparison between (a) orientational and (b) length distributions of nanofibers grown on 2.5 µm wide ridges and nano-scale pinning lines (with 2.5 µm separation distance), respectively.

The standard deviation of the orientational distribution is 24.1 degrees for the nano-scale pinning lines and 25.6 degrees for the micron-size ridges. Note that the length of the nanofibers is limited by the ridge width or the distance between the pinning lines, i.e. 2.5 µm. This method therefore leads to a control of both the orientation and the length of the nanofibers.


The ability to achieve such controlled growth opens a wide range of possible applications including fabrication of polarization controlled light emitting arrays and nanofiber growth between electrodes for direct electrical connec-tion in organic LEDs. Currently we are investigating the nanofibers electrical properties, by growing them on gold electrodes fabricated on silicon oxide. In certain cases, the nanofibers are growing across the electrodes, which makes it possible to directly measure the nanofibers electrical mobility. The substrate fabrication using nanoim-print lithography is also going to be reached in the coming year.

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Papers[1] Roana Melina de Oliveira Hansen, Jakob Kjelstrup-Hansen and Horst-Günter Rubahn; Pinning of organic nanofiber surface growth. Nanoscale, 2010, 2, 134-138.

[2] Morten Madsen, Roana Melina de Oliveira Hansen, Jakob Kjelstrup-Hansen and Horst-Günter Rubahn, Controlled growth of organic nanofibers on nano- and micro-structured gold surfaces. Proc. SPIE. 7406, 7406R (2009).

[3] Morten Madsen, Jakob Kjelstrup-Hansen and Horst-Günter Rubahn, The surface microstructure controlled growth of organic nanofibres. Nanotechnology 20, 115601 (2009).

Controlled growth of organic nanofibers on micro- and nano-structured gold surfaces

Roana Melina de Oliveira Hansen and Morten Madsen


Nanofibers made from para-hexaphenylene (p6P) molecules hold unique optoelectronic properties, which make them interesting candidates as elements in electronic and optoelectronic devices. Typically, these nanofibers are grown by physical vapor deposition of p6P molecules on specific single-crystalline substrates (muscovite mica), on which long, mutually parallel nanofibers are formed. However, the lack of ability to further process these substrates restrains their use in devices. It has been shown that p6P nanofibers can be formed on thin gold films, but without the alignment observed for nanofibers grown in mica. We demonstrate how metal nanostructures (fabricated by electron-beam and optical lithography) can be used to guide the molecules surface diffusion leading to controlled growth of nanofibers with specific length, position and orientation.

Research results

P6P molecules are deposited on the gold surfaces containing either nanoscaled titanium pinning lines or micron sized ridges. The molecules diffuse on the structured gold surface until they reach an edge, i.e. a titanium pinning line or a ridge edge, where they nucleate, causing the nanofiber to grow from there. In the case of the titanium pinning lines, the experiments were done under different substrate and growth condi-tions, such as different pinning line dimensions, pitch distances, p6P thicknesses and substrate temperature during deposition. The different conditions lead to different observables, as can be seen on figure 1. A systematic inves-tigation was made, changing the conditions to obtain different observable results.

Higher substrate temperatures during molecular deposition lead to longer and better aligned fibers. The lines aspect ratio is also influent, since higher and thinner lines give better results (also concerning orientation and length control). The pitch distance between lines is in some cases determining the fibers length, if the substrate temperature is high enough to create fibers bridg-ing between two lines.

Figure 1 (a and b) SEM images of p6P nanofibers grown on sputtered gold with titanium pinning lines (width of 250 nm and height of 25 nm) at substrate temperatures of 418 K (a) and 448 K (b), respectively. The distances between the lines are 2.5 µm (1), 5 µm (2) … 17.5 µm (7); (c and d) orientational distributions for the fibers growing between lines at a pitch distance of 10 µm (4) for substrate temperatures of 418 K (c) and 448 K (d), respectively. Here, 90 degrees refers to the long fiber axes being perpendicular to the pinning lines.

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Kasper Thilsing-Hansen


Organic nanofibers grown on mica, shows promising properties such as waveguiding, lasing and semi-conducting. One of the key challenges is to transfer these nanofibers from their growth substrate (mica) onto any desired ap-plication structure, such as organic field effect transistor (OFET) or nanolabels used as security makers in counter fighting.

Research results

Organic nanofibers made of parahexaPhenyl (p6P) grown by molecular beam epitaxy (MBE) on a fresly cleaved mica substrate, have been successfully transferred from their growth substrate mica and onto both a silicon sub-strate and a polyethylene (PET) film. The transfer is made by stamping the nanofibers from mica to for example a pre-fabricated OFET structure in a controlled environment i.e. at air temperature of 33°C and humidity of 70-75%RH. By keeping the stamp temperature below the drew point, small water droplets are condensing at the stamp surface. When the stamp is pressed onto the nanofiber mica substrate, the water droplets releases the na-nofibers from the mica and the nanofibers are transferred onto the stamp (OFET) see figure 1. The fluorescence image (figure 2) shows nanofibers stamped onto a 100x100 µm² elevated Si/SiO square, with top electrodes (gold) evaporated afterwards. The silicon substrate works as backgate and the two gold electrodes works as source and drain, hereby the desired OFET structure is reached.


Electrical characterization and electroluminescence from these OFET structures.

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Large-scale transfer of organic nanofibers by soft stamping

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21 oC

Nanofibers on mica

33 oC

70 %RH

Structured surface

Water droplets

Figure 1: Principle of the soft transfer technique. Figure 2: Array of nanofibers transferred to a100x100 µm² Si square with top Au electrodes evaporated afterwards.

Figure 1: Principle of the soft transfer technique.

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Analysis of optical properties of strained semiconductor quantum dots for electromagnetically induced transparency, Phys. Rev. B, 80(2009)235304

D. Barettin, J. Houmark, B. Lassen, M. Willatzen, T. R. Nielsen, J. Mørk, and A.-P. Jauho

Crystal structure of 1,4´´´-dimethoxy-4,1´:4´,1´´:4´´,1´´´-quaterphenylene, Materials Letters. Vol. 63(2009)2399–2401

J. Iwicki, C. Naether, M. Schiek, A. Luetzen, H.-G. Rubahn, W. Krueger, K. Rossnagel, and L. Kipp

Nanoparticulate Dye-Semiconductor Hybrid Materials Formed by Electrochemical Self-Assembly as Electrodes in Photoelectrochemical Cells, Zeitschrift fuer Naturforsc-hung. Vol. 64a(2009)518-530

K. Nonomura, T. Loewenstein, E. Michaelis, P. Kunze, M. Schiek, J. Reemts, M. Y. Iwaya, M. Wark, J. Rathousky, K. Al-Shamery, A. Kittel, J. Parisi, D. Wöhrle, T. Yoshida, and D. Schlettwein

Popular Science

Nye teknikker indenfor mikrobiologisk analyse af fødeva-rer, Plus Proces 3(2009)8.

H. Erdmann and H.-G. Rubahn

Mikrobielle Analytik: Neue Entwicklungen für die Be-reiche Lebensmittel, Medizin und Umwelt, Mikrofluidik, October (2009)

H. Erdmann and H.-G. Rubahn

Hvem skal tage over efter mig? Forskning i vækst - fri forskning giver næring til vækstlaget. DFF vækst-huset (2009)20

Horst-Günter Rubahn

Peer-reviewed articlesThe Surface microstructure controlled growth of organic nanofibers, Nanotechnology, 20(2009)115601

M. Madsen, J. Kjelstrup-Hansen, and H.-G. Rubahn

Scanning Electron Microscopy of Semiconducting Nanow-ires at Low Voltages. Materials Science (Medziago-tyra) 15(2009)86

T. Tamulevicius, A. Sileikaite, S. Tamulevicius, M. Madsen, and H.-G. Rubahn

Crystal structure determination from two-dimensional pow-ders: A combined experimental and theoretical approach. Eur.Phys. J. Special Topics 167(2009)59

A. Moser, O. Werzer, H.-G. Flesch, M. Koini, D.-M. Smilgies, D. Nabok, P. Puschnig, C. Ambrosch-Draxl, M. Schiek, H.-G. Rubahn, and R. Resel

Temperature dependent analysis of three classes of fluores-cence spectra from p6P nanofiber films, J. Luminescence 129(2009)784

F. Balzer, A. Pogantsch, and H.-G. Rubahn

Nanoaggregates from Thiophene/Phenylene Co-Oligomers. J. Phys. Chem. C. 113 (2009)9601-9608

M. Schiek, F. Balzer, K. Al-Shamery, A. Lützen, and H.-G. Rubahn

Surface acoustic wave mediated exciton dissociation in a ZnCdSe/LiNbO3 hybrid. Applied Physics Letters 94(2009)193505

D.A. Fuhrmann, A. Wixforth, A. Curran, J.K. Mor-rod, K.A. Prior, R.J. Warburton, and J. Ebbecke

Para-hexaphenyl nanofiber growth on Au-coated porous alumina templates, Appl.Phys.A, 96(2009)591

M. Madsen, G. Kartopu, N. L. Andersen, M. Es-Souni, and H.-G. Rubahn

Charge Transport in Oligo Phenylene-Thiophene Nanofi-bers, Organic Electronics 10(2009)1228-1234

J. Kjelstrup-Hansen, J. E. Norton, D. A. da Silva Filho, J.-L. Bredas, and H.-G. Rubahn

Origins for epitaxial order of sexiphenyl crystals on musco-vite, Surf. Interface Anal. 41(2009)764-770

R. Resel, T. Haber, O. Lengyel, H. Sitter, F. Balzer, and H.-G. Rubahn

Organic nanofibers from thiopene oligomers, Thin solid Films 518, 130 - 137 (2009)

L. Kankate, F. Balzer, H. Niehus, and H.-G. Rubahn

Second-harmonic generation spectroscopy on organic nanofi-bers, Applied Physics B: Lasers and Optics, Vol. 96, 4(2009)821-826

K. Pedersen, M. Schiek, J. Rafaelsen, and H.-G. Rubahn

Self-Organized Growth of Organic Thiophene-Phen-ylene Nanowires on Silicate Surfaces, Chem. Mater. 21(2009)4759 - 4767

F. Balzer, M. Schiek, A. Lützen, and H.-G. Rubahn

Conversion of bound excitons to free excitons by surface acoustic waves, Phys. Rev. B 80(2009)165307

S. Völk, A. Wixforth, D. Reuter, A. D. Wieck, and J. Ebbecke

Spurious solutions in the multiband effectivemass theory applied to low-dimensional nanostructures, Comp. Phys. Comm. 6(4)(2009)699-729

B. Lassen, R.V.N. Melnik, and M. Willatzen

Electromagnetic-wave propagation along curved surfaces, Phys. Rev. A 80 (4)(2009)043805

M. Willatzen

Publications

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ProceedingsSelf-assembly of a thiophene/phenylene co-oligomer, SPIE 7393(2009)14


Controlled growth of organic nanofibers on nano-and micro-structured gold surfaces, SPIE 7406(2009)27

R.M. Oliveira, M. Madsen, J. Kjelstrup-Hansen, and H.-G. Rubahn

FEM Analysis of cylindrical resonant photoacoustic cells, Proceedings of ICPPP 15, J. Phys. Conf. Series, Leuwen, Belgium, July (2009)

L. Duggen, R. Frese, and M. Willatzen

Book articles

Organic Nanofibers from PPTPP, in ‘Interface Con-trolled Organic Thin Films’, H.-G. Rubahn, H. Sit-ter, G. Horowitz, and K. Al-Shamery, Eds., Spring-er Proceedings in Physics, Berlin Vol. 129(2009)11


Nanotechnology, in ‘Ullmann’s Encyclopedia of Industrial Chemistry’, Electronic Release, 7th ed., Wiley-VCH, Weinheim, (2009)

H.-G. Rubahn

Books

Interface controlled organic thin films, Springer Procee-dings in Physics 128, Berlin (2009)

H.-G. Rubahn, H. Sitter, G. Horowitz and K. Al-Shamery, eds.

The k•p Method - Electronic Properties of Semiconductors, Springer, Berlin, August 2009

L. C. Lew Yan Voon and Morten Willatzen

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NanoSYD

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ANNUAL REPORT 2009

Diffraction of a waveguide mode in a nanowire, Oral pre-sentation, PIERS, Moscow, Russia, August (2009)

V. G. Bordo

Optics of nanofibers, Oral presentation, Annual Meet-ing for The Danish Optical Society, Sønderborg, Denmark (2009)

V. G. Bordo

Light emitting organic nanofibers from thiophene oligomers, DOPS annual meeting (2009)

F. Balzer, L. Kankate, H. Niehus, M. Schiek, A. Lützen, K. Al-Shamery, and H.-G.Rubahn

Photoemission electron microscopy of organic nanofibers in interaction with plasmonic substrates, DOPS annual meeting (2009)

I. Leissner, M. Bauer, J. Kjelstrup-Hansen, and H.-G. Rubahn

Fluorescence detection of hydrodynamically focused micro-beads in microfluidic platforms, DOPS annual meeting (2009)

C. Kunstmann-Olsen, J. Hoyland, R. Frese, and H.-G. Rubahn

Organic nanofiber surface growth control, DOPS annual meeting (2009)

R. M. de Oliveira Hansen, J. Kjelstrup-Hansen, and H.-G. Rubahn

Light emitting organic nanofibers from thiophene oligomers, DOPS annual meeting (2009)

F. Balzer, L. Kankate, H. Niehus, M. Schiek, A. Lützen, K. Al-Shamery, and H.-G. Rubahn

Photoemission electron microscopy of organic nanofibers in interaction with plasmonic substrates, DOPS annual meeting (2009)

I. Leissner, M. Bauer, J. Kjelstrup-Hansen, and H.-G. Rubahn

Fluorescence detection of hydrodynamically focused micro-beads in microfluidic platforms, DOPS annual meeting (2009)

K. Kunstmann-Olsen, J. Hoyland, R. Frese, and H.-G. Rubahn

Organic nanofiber surface growth control, DOPS annual meeting (2009)

R. M. de Oliveira, J. Kjelstrup-Hansen, and H.-G. Rubahn

ThesisDirected growth of organic nanofibersDefended on: 26th August

Morten Madsen

Conference abstractsGrowth of organic PPTPP nanowires, spm workshop Bremen 2009

F. Balzer, M. Schiek, A. Lützen, and H.-G. Rubahn,

Growth of organic semiconductors on lithium niobate sur-faces, spm workshop Bremen 2009

M. Schiek, J. Ebbecke, F. Balzer, A. Lützen, and H.-G. Rubahn

Conduction and electroluminescence from organic continuous and nanofiber thin films. TNT Barcelona 2009

X. Liu, J. Kjelstrup-Hansen, K. Thilsing-Hansen, H. H.Henrichsen, and H.-G. Rubahn

Ambipolar light-emitting field-effect transistors based on or-ganic nanofibers and thin films, MRS fall meeting 2009

J. Kjelstrup-Hansen, LIU, X., K.Thilsing-Hansen, H. H.Henrichsen, and H.-G. Rubahn

Large-scale transfer of organic nanofibers by soft stamping, MRS fallmeeting 2009

K. Thilsing-Hansen, J. Kjelstrup-Hansen, and H.-G. Rubahn

Organic nanofiber surface growth control, Smart Materials 3 workshop, Kiel 2009

R. M. de Oliveira, J. Kjelstrup-Hansen, and H.-G. Rubahn

Electroluminescent Field-Effect Transistors based on organic nanofibers and thin films, Smart Materials 3 workshop, Kiel 2009

J. Kjelstrup-Hansen, LIU, X., K. Thilsing-Hansen, H. H. Henrichsen, and H.-G. Rubahn

Mesoporous thin film templates for the synthesis of nanow-ires and nanotubes, Smart Materials 3 workshop, Kiel (2009)

K. V. Bordo, M. Es-Souni, S. Habouti, M. Schiek, and H.-G. Rubahn

Fluorescence detection of hydrodynamically focussed micro-beads in microfluidic platforms, Materials for Energet-ics. European School for Materials Science, Milano 2009

C. Kunstmann-Olsen, J. Hoyland, R. Frese, and H.-G. Rubahn

Reducing bleaching effects in organic nanofibers by coat-ing, Materials for Energetics. European School for Materials Science, Milano 2009

L. Tavares, J. Kjelstrup-Hansen, H.-G. Rubahn, and H. Sturm

Mesoporous Thin Film Templates for the Synthesis of Nanowires and Nanotubes, Materials for Energetics. European School for Materials Science, Milano 2009

K. Bordo, M. Schiek, S. Habouti, M. Es-Souni, and H.-G. Rubahn

Band-mixing and strain effects in InAs/GaAs quantum ring, Oral presentation, PLMN09, Lecce (2009)

B. Lassen, M. Willatzen, and D. Barettin

Electron conductance in curved quantum structures, Poster presentation PLMN09, Lecce (2009)

M. Willatzen and J. Gravesen

Comparison of Wurtzite atomistic and piezoelectric con-tinuum strain models: Implications for optical properties, Poster presentation PLMN09, Lecce (2009)

D. Barettin, S. Madsen, B. Lassen and M. Willatzen

Optics of nanofibers, Oral presentation, 18th Interna-tional Laser Physics Workshop, Barcelona, Spain, July (2009)

V. G. Bordo

5150

21./25.09. Odense, Denmark, Dansk Naturvidenskabfestival, Tema: Byggesten (Nanotechnology and Nanochemistry)

M. Schiek

22.09. Vejle, Denmark, Vejen Gymnasium og HF, Danish Science Festival (Nanoteknologi med lysende molekyler)

J. Kjelstrup-Hansen

23.09. Kolding, Denmark, Kolding Gymnasium, Danish Science Festival (Nanoteknologi med lysende molekyler)

J. Kjelstrup-Hansen

26-09. SDU, Dimission TEK 2009 (Nanotechnology: today andtomorrow)


29.09. Velux visit, MCI, Alsion (Nanofibers for solar cells) Horst-Günter Rubahn02.10. NiNA workshop ISIT, Lübeck

(Nanophysics and nanoproducts cross border: the new nanotechnology centre Nano-SYD)


30.10. ROP board meeting, London (New developments in optics andnanophotonics) Horst-Günter Rubahn04.11. Tag der Chemie,Universität Oldenburg

(Nanotechnology cross border - from organic nanofibers to functional nanodevices)Horst-Günter Rubahn

17.11. Nordischer Abend, FH Flensburg (University of Southern Denmark - competences and possibilities)


20.11. Sønderborg, Denmark, Alsion, Annual meeting for the Danish Optical Society (Optics of Nanofibers)

V. Bordo

24.11. FH Flensburg, Ringvorlesung (From the really small to thereally important - promises of nanotechnology)


01.12. Boston, USA, Materials Research Society Fall Meeting (Ambipolar Light-emitting Field-effect Transistors Based on Organic Nanofibers and Thin FIlms)

J. Kjelstrup-Hansen

03.12. SDU, Alsion, ISIT visit (NanoSYD: nano- and microstructure activities)


NanoSYD

Activities03.02. Sønderborg, Denmark, Alsion, Diramo og renrumsekspertgruppe visit

(NanoSYD and cleanroom interests)Horst-Günter Rubahn

25.02. TI Nanobusiness - fra forskning til forretning(Nanosensors -ultrasmall sensing elements and ultrasmall sensing platforms)


20.03. Aarhus University, iNano (Nano at Alsion - new visions for functional materials)


25.03 Bundesdruckerei, Berlin (Nanofiber A/S: next generation anticounterfeit products)


30.04. Goslar, workshop “From the Witches Cauldrons of MaterialsScience” (Nanotechnology in Denmark)

Katharina Rubahn

30.04. Sønderborg, Denmark, Alsion, international partners (NanoSYD)

J. Kjelstrup-Hansen

13./14.05. Berlin, Germany (Hands-on Workshop: Quantitative Force Spectroscopy from Molecules and to Cells, JPK instruments)

Manuela Schiek

26.05. Sønderborg, Denmark, Alsion, MCI day (Det rene rum) Horst-Günter Rubahn25.06. Linz, Austria, Johannes Kepler University (Waveguiding in Nanofibers) V. Bordo

25.06. Linz, Austria, Johannes Kepler University (New developments in organic nanofiber technology)


16./17.07. Flensburg, Germany, Phänomenta (Selbstorganisation in der Nanowelt) F. Balzer16./17.07. Flensburg, Germany, Phänomenta

(Nanopartikel: Kolloide, Quantenpunkte, Ferrofluide)M. Schiek

16./17.07. Flensburg, Germany, Phänomenta (Nanoporöse Materialien: Poröse Aluminiumoxid-Membranen & Aerogele)

M. Schiek

16./17.07. Flensburg, Germany, Phänomenta (Nanochemie) M. Schiek21.07 FH Flensburg, press conference (Lab-on-chip Technik zur Qualitätskontrolle

in der Lebensmittel- und Bio-Industrie)Horst-Günter Rubahn

24.08. SDU, IFK, Odense, BioControl workshop (Surface induced self-assembly of organic nanoaggregates)


09.09. Barcelona, Spain, Trends in Nanotechnology conference (Conduction and electroluminescence from organic continuous and nanofiber thin filmshihiihihi

J. Kjelstrup-Hansen

12.09. SDU, Alumne dag 2009 (Nanotechnology: today and tomorrow) Horst-Günter Rubahn21.09. Vejen, Denmark, Vejen Gymnasium og HF, Danish Science Festival

(Nanoteknologi med lysende molekyler)J. Kjelstrup-Hansen

ANNUAL REPORT 2009

52

By plane:

- Fly to Copenhagen and take an internal flight directly to Sønderborg- Go to Hamburg/Lübeck, then by train to Flensburg, and by bus or taxi to Søndeborg

By train:

- Go to Hamburg, then by train to Flensburg, and by bus or taxi to Søndeborg.

How to find usANNUAL REPORT 2009

NanoSYD

University of Southern DenmarkAlsion 2DK-6400 SønderborgPhone +45 6550 1000www.sdu.dk

Phone +45 6550 1673www.sdu.dk/nanosyd

nanosyd - annual report 2009

Documents

research purposes

sdu cleanroom

nano centre souththe

postdoc morten madsen

nanotechnology centre

head of centre42nanosyd7

educational competences

postdoc james hoyland