 HAYDAU MEETING |
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| Abstracts of the Workshop "Nanostructures" held at Haydau Monastery from Sept. 18th to Sept. 21st 1997 in the series "Haydauer Hochschulgespräche" sponsered by the Otto-Braun-Fonds Organized by R. Kassing (Tech. Physics) |
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| [1] | Manipulation and Characterisation of Surfaces on the Atomic Scale | Th.Schimmel |
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| [2] | Correlation between nano-scale structural, electronic and magnetic properties of thin films by scanning probe microscopy and spectroscopy | R.Wiesendanger |
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| [3] | Surface characterization by static and dynamic proximal probes | H.Fuchs |
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| [4] | Ultimate Limits in the Miniaturization of Chemical and Biochemical Sensors | C.Ziegler, W.Göpel |
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| [5] | Odor, Drug, and Toxin Analysis with Neuronal Networks in vitro: Extracellular Array Recording of Network Responses | C.Ziegler, G.W.Gross, A.Harsch, W.Göpel |
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| [6] | Integrated Analytical Microsystems – Small Volumes and High Speed | A.Manz |
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| [7] | Near Field Optical Technology for Nano/Atom Photonics | M.Ohtsu |
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| [8] | Integrated Proximal Probes for High Resolution Imaging of Surfaces | E.Oesterschulze |
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| [9] | Scanning tunneling microscopy of insulators and biological material based on lateral conductivity of ultrathin water films adsorbed to surfaces | R.Guckenberger, M.Heim |
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| [10] | Biomolecules at Work: Recent Observations with the Atomic Force Microscope | A.Engel, D.Fotiadis, S.Scheuring, D.J.Müller |
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| [11] | Microscopy and Spectroscopy on Single Molecules | J.Wrachtrup |
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| [12] | Near-field optical microscopy of single fluorophores and genetic material | N.F.van Hulst, M.F.Garcia-Parajo, J.-A. Veerman, S.J.T.van Noort, A.G.T.Ruiter |
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| [13] | Peptide Nanotubes: A New Class of Functional Biomaterials | R.Ghadiri |
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| [14] | Chemical and morphological scanning probe analysis of polymers and micropatterned protein coated substrates | C.Roberts |
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| [15] | Self Assembly of 2-d purine and pyrimidine crystals – A combined STM, LEED, TDS and Molecular Modelling study | W.M.Heckl, J.E.Freund, M.Edelwirth, R.Schloderer, S.J.Sowerby |
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Th.Schimmel
(Universität Karlsruhe, Institut für Angew. Physik, Karlsruhe)
Scanning probe microscopes are not only useful for characterising surfaces with high spatial resolution. The sharp tips of the scanning tunneling, scanning force and lateral force microscopes can also be used as local sensors and as nano-tools for carrying out experiments or for performing surface modification on the atomic scale. In this way, time-stable atomic-scale structures can be generated, modified and deleted under environmental conditions. Chemical reactions can be induced locally with the AFM tip and crystal growth can be monitored in situ and in real time. Forces and interactions can be investigated in the (sub)atomic scale and the phenomenon of energy dissipation due to friction can be studied quantitatively on a microscopic scale.
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R.Wiesendanger
Institute of Applied Physics and Microstructure Research Center, University of Hamburg, Hamburg
To study the relationship between structural, electronic and magnetic properties is one of the fundamental issues in thin film magnetism. This requires experimental techniques offering high spatial resolution combined with high sensitivity. Recent advances in scanning probe microscopy and spectroscopy have led to novel insight into the correlation between different physical properties of thin magnetic films at the nanometer scale.
We will present and discuss recent data obtained by UHV-STM/STS and UHV-MFM on thin transition and rare-earth metal films starting form the submonolayer up to the multiple monolayer coverage regime. It will be shown that the physical properties of ultra-thin magnetic films depend drastically on their atomic-scale structure. As a consequence, atomic-scale control of the growth of ultra-thin films is required in order to determine their electronic and magnetic properties in a precise way.
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Proximal probe microscopies have displayed great versatility in analysing material surfaces from a wide range of fields and with varying properties. While static force microscopy allows to investigate local mechanical properties and intermolecular forces, dynamic SFM can be applied to differenciate between topography and specific material properties even on very soft materials.
The performance of an SFM operated in the dynamic mode at high oscillation amplitudes is determined by the reponse of the system to a given set of interaction forces between the probing tip and the sample surface. Measuring the oscillation amplitude and the phaseshift between the driving force and the cantilever response as a function of the tip-sample distance and calculating the corresponding forces, provides a means to characterize the interaction between the probing tip and the sample surface (Dynamic Force Spectroscopy) [1].
Modifying the effective quality factor of the oscillating cantilever, i.e. changing the system response, provides a means to influence the transition form the attractive to the partly repulsive interaction regime. Increasing the sensitivity forces the dynamic system to stay in the attractive regime and thereby leads to a significantly improved image quality when scanning on soft sample surfaces.
Recently, we introduced a SNOM based on a metal coated tetrahedral tip that is used as a light emitting probe and simultaneously as an STM tip [2]. In mixed metal films, silver grains are distinguished from gold grains at a lateral resolution in the 10 - 1 nm range by their specific near-field contrast. Plasmons excited on the faces as well as on the edges of the metal coated probe is thought to be the cause for light compression to the nanoscopic dimensions of the tip, responsible for the high lateral resolution. SNOM at molecular resolution exploiting local plasmon exitation of the probe for contrast enhancement is a challening perspective of SNOM with the tetrahedral tip.
[1] D. Krueger, B. Anczykowski, H. Fuchs, Ann.Phys. 6 (1997) 341–363
[2] J. Koglin, U.C. Fischer, H. Fuchs, Phys.Rev. B 55 (12), 7977–7984, 1997
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Christiane Ziegler, Wolfgang Göpel
(Institute of Physical and Theoretical Chemistry and Center of Interface Analysis and Sensors, University of Tübingen)
A survey is given on "top-down" (microstructure) and "bottom-up" (chemical synthesis) approaches to design chemical and biochemical sensors.
Particular emphasis is put on new materials and transducers for molecular recognition with current and future devices. These convert chemical information into electronic signals by making use of suitable "key-lock" structures. The design requires the control of atomic structures of chemically sensitive materials under either thermodynamically (equilibrium-) or kinetically (flow-) controlled conditions. This in turn requires the molecular understanding of the recognition and signal transduction mechanisms both of which are deduced from comparative microscopic, spectroscopic, and sensor test studies on "prototype devices".
Selected examples illustrate this approach for different chemically sensitive materials. These include electron conductors, ion conductors, mixed conductors, molecular cages, polymers, and biomolecular function units. Particular emphasis is put on the discussion of ultimate limits in the miniaturization of future devices.
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Christiane Ziegler1, Guenter W. Gross2, Annette Harsch1,2
and Wolfgang Göpel1 (1) Institute for Physical and Theoretical Chemistry, University of Tübingen, Tübingen
(2) Department of Biological Sciences and Center for Network Neuroscience, Universiy of North Texas, Denton, TX 76203, USA
Neurons, by virtue of intrinsic electrophysiological mechanisms, represent transducers that report the dynamics of cell death, receptor-ligand interactions, alterations in metabolism, and generic membrane perforation processes. In cell culture, mammalian neurons form fault tolerant, spontaneously active systems with great sensitivity to their chemical environment and generate response profiles that are often concentration and substance specific. Changes in action potential patterns are usually detected before morphological changes and cell damage occur which provides sensitivity and reversibility. Such biological systems can be used to rapidly screen for novel pharmacological substances, toxic agents, and for the detection of certain odorants.
Existing simple culture preparations can already be employed effectively for the detection of chemical compounds. Here, spontaneously active murine spinal cord cultures were used which were coupled to an array of 64 transparent microelectrodes. The importance of a tailored interface between cell axons and the electrode will firstly be addressed.
In the second part, the three strategies which have been investigated in pilot experiments will be introduced:
One particular example will be stressed in detail: The glycine receptor blocker strychnine reliably generated increased multichannel bursting at 5 – 20 nM and regular, coordinated bursting above 5 mM. By artificial neural network analysis a quantitative interpretation of the data was possible for the first time.
These results indicate that cultured neuronal networks are practical systems that can be used for the detection and identification of a great variety of chemical substances.
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Andreas Manz
Imperial College, Zeneca/SmithKline Beecham Centre for Analytical Sciences,
London, England
Miniaturised analysis systems have a number of advantages, e.g., faster analysis time, better separation efficiency, lower reagent consumption. However, real samples to be analysed eventually contain particles or compound that adsorb to walls. The micron sized, high efficiency electrophoresis systems, for example, use single channels of 5 to 50 µm diameter. In these dimensions, the surface to volume ratio is relatively large. Adsorption processes dominate, and therefore, sample preparation prior to analysis becomes a necessity.
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M.Ohtsu
Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226, Japan
We review recent progress of our works on near field optics. We focus on presenting the results of
Based on these results, we try to demonstrate that near field optical technology can be used to a variety of applications in the field of photonics dealing with nano-materials and/or atoms, which can be called nano/atom photonics.
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Integrated Proximal Probes for High Resolution Imaging of Surfaces
Egbert Oesterschulze
University of Kassel, Institute of Technical Physics
Since the invention of scanning force microscopy (SFM) by Binnig et al. in 1986 scanning probe microscopy (SPM) has become a promising and wide spread technique in those cases of surface investigations, where highest lateral resolution is necessary. Another challenging aspect regarding the potential of SPM is the possibility to integrate various sensors in a single probe; thus allowing to measure simultaneously different physical quantities with the same probe. To reach this aim, appropriate probe concepts have to be developed, which on the other hand have to be realized by reproducible technological processes. Well established in microelectronic device fabrication for years, micromachining is the most appropriate technique for this purpose.
This contribution focuses on the design and micromachined fabrication of active and passive near-field probes for high frequency scanning electrical force microscopy (HFSEFM), scanning thermal microscopy (SThM), and scanning near-field optical microscopy (SNOM). Probe concepts presented include the possibility of sensor combination. To meet the requirements of the specific SPM technique the properties of different probe materials were exploited, e.g. silicon, gallium arsenide, and diamond. In case of HFSEFM passive silicon and GaAs cantilevers provided with a waveguide structure were fabricated, characterized and employed for voltage contrast imaging of electronic devices. A heterodyne technique was applied to extend the frequency range of this non destructive technique into the microwave range. For SThM active silicon and GaAs cantilevers with in the tip integrated Schottky diodes have been developed. The temperature sensitivity of about 3mV/K which is about two decades higher in comparison to thermocouples, should allow to get access to temperature variations down to a µK scale if transient signals are detected. Varying the fabrication process these diode probes can also be applied as miniaturized photodiodes for SNOM applications. This would allow not only to simplify the experimental set-up but also to open the possibility of parallel processing applying an array of cantilevers. A passive probe approach for SNOM employs a hollow metal tip with a miniaturized aperture at its apex. A lateral resolution in transmission imaging of about a tenth of a wavelength was obtained which underlines the suitability of aperture cantilever probes. Furthermore polarization microscopy was performed for the investigation of ferro-magnetic domain structures of optical transmitting thin Garnet films on glass substrates.
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Reinhard Guckenberger and Manfred Heim
Max-Planck-Institut für Biochemie, D-82152 Martinsried, Germany
Scanning Tunneling Microscopy (STM) allows to image surfaces even down to atomic resolution, at least for many flat surfaces. The only prerequisite is sufficient electrical conductivity of the specimen. This means, however, that insulators cannot directly be imaged by STM. Similarly, it is very difficult to use STM for studying biological materials thicker than about 1nm because they usually lack conductivity. We found, however, that STM imaging of biological samples can reliably be done in humid air at very low tunneling currents (below 1 pA). Even hydrophilic surfaces of insulators (e.g. mica and glass) can be imaged by STM. The observed conductivity of the specimens in humid air is related to a very thin water film adsorbed to the specimen surface. Measurements on mica and silicon dioxide show a very strong dependence of surface conductivity on humidity. The corresponding surface adsorbed water films are surprisingly thin with thicknesses below 2 layers of water molecules. Besides application for STM imaging, the unexpected high conductivity of ultrathin water films is of fundamental interest in itself.
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A. Engel, D. Fotiadis, S. Scheuring and D.J. Müller
M.E. Müller Institute for Microscopy, Biozentrum, University of Basel.
In spite of progress in the 3D crystallization of membrane proteins only a small number of structures are solved. During 2D crystallization in the presence of lipids the membrane protein is reconstituted in its native environment, the lipid bilayer. Thus, the biological activity is restored, and functional states of the protein can be studied by electron crystallography and atomic force microscopy. The static 3D atomic structure is calculated from projections and diffraction patterns of 2D membrane protein crystals recorded with the electron microscope (EM), while their surface topography is measured with the atomic force microscope (AFM). The latter allows dynamic changes to be monitored at subnanometer resolution.
Recent results from bacteriorhodopsin and bacterial porin (OmpF) acquired with the atomic force microscope will be discussed. Bacteriorhodopsin of Halobacterium salinarium, is a light-driven proton pump packed into highly ordered two-dimensional (2-D) crystals, the purple membranes. The structure of bacteriorhodopsin has been solved by electron crystallography revealing seven closely packed alpha helices that surround the photoactive retinal. A similar arrangement of seven alpha helical membrane spanning segments has been observed for halorhodopsin and rhodopsin. This feature also appears to represent a common motif of the G protein-coupled receptor family.
Besides electron microscopy, X-ray diffraction, neutron diffraction, and more recently scanning tunneling microscopy and atomic force microscopy have been used to the study purple membrane. We have established conditions to reproducibly acquire topographs of purple membranes at subnanometer resolution using the AFM and have identified the cytoplasmic surface. We have also demonstrated that subnanometer force-induced conformational changes of bacteriorhodopsin can be directly visualized by this microscope.
Porin OmpF represents a channel forming protein that facilitates the diffusion of hydrophilic molecules (Mr < 600) across the outer membrane of the Escherichia coli cell. The trimeric structure solved by X-ray crystallography revealed monomers comprising a barrel made of 16 antiparallel b-strands. Reconstituted 2D crystals of porin OmpF have been imaged at high resolution with the AFM. Two conformations of the extracellular surfaces have been observed, which we now have systematically studied under different ionic strength and pH, operating the AFM under conditions that warrant preservation of the native structure. The results suggest that these changes are physiologically relevant and may reflect a mechanism to protect the periplasmic space.
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J. Wrachtrup
TU Chemnitz
The combination of microscopy and spectroscopy has forstered considerable progress in single molecule spectroscopy. Single molecules and macromolecular complexes can now be localised under different environmental conditions. In such studies the behaviour of different dye molecules on surfaces are studied with respect to their intra- and intermolecular relaxation rates. It proves that the temporal stability of single molecules is extremely sensitive to temperature and contaminations on the surfaces. The studies pave the way for detailed investigations on complex macromolecular structures like light harvesting complexes in photosynthetic reaction centres. On the other hand, with the same type of methods detailed local spectroscopy on inorganic compounds like diamond can be carried out. Such investigations enable experiments on single defect centres which prove to be excellent probes for the local structure of the surrounding lattice.
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N.F. van Hulst, M.F. Garcia-Parajo, J.-A. Veerman, S.J.T. van Noort & A.G.T.
Ruiter
Applied Optics group & MESA Research Institute, Department of Applied Physics, University of Twente
Single fluorescent molecules, chromosomes and DNA have been studied using an aperture type near-field optical microscope with tuning fork shear force feedback.
We have observed rotational and translational diffusion of single molecules, both in polymer and covalently attached to amino-silanised glass, using a near-field scanning optical microscope with two polarisation detection channels [1,2]. In successive images the fluorescence of single molecules was followed over about one hour, with 10 ms integration time, until photo-dissociation. The position of single molecular fluorescence could be located with an accuracy of 1 nm. The orientation of the in-plane emission dipole of all molecules in one image could be directly determined with an accuracy of a few degrees, by simultaneous detection in two perpendicular polarisation directions. By rotating the excitation polarisation we could selectively excite different sets of molecules and compare their in-plane absorption and emission dipole orientation. Monitoring DiI molecules in PMMA over one hour we found rotation of less than 10 degrees for the majority of molecules, while incidental fast rotation and transition to a dark state occurs. The fluorescence intensity was observed to be molecule dependent, which is an indication for out-of-plane orientation and different local photophysical environment.
Fluorescence in situ hybridisation (FISH) labels on repetitive and single copy probes on human metaphase chromosomes have been imaged with a width of 80 nm, allowing their localisation with nanometer accuracy, in direct correlation with the simultaneously obtained topography [2,3].
Finally shear force imaging of double stranded DNA with a vertical sensitivity of 0.2 nm, based on tuning fork detection with phase feedback [4], will be presented. A DNA height of 1.4 nm is measured, which indicates the non-disturbing character of the shear force mechanism [5].
[1] A.G.T. Ruiter, J.-A. Veerman, M.F. Garcia-Parajo and N.F. van Hulst, J. Phys. Chem., Sep. 1997.
[2] N.F. van Hulst, M.F. Garcia-Parajo, M.H.P. Moers, J.-A. Veerman & A.G.T. Ruiter, J. Struct. Biol. (1997) in print.
[3] M.H.P. Moers, W.H.J. Kalle, A.G.T. Ruiter, J.C.A.G. Wiegant, A.K. Raap, J. Greve, B.G. de Grooth and N.F. van Hulst, J. Microscopy 182, (1996), 40–45.
[4] A.G.T. Ruiter, J.-A. Veerman, K.O. van der Werf and N.F. van Hulst, Appl. Phys. Lett. 71 (1997) 28.
[5] M.F. Garcia-Parajo, A.G.T. Ruiter, J.-A. Veerman and N.F. van Hulst, Ultramicroscopy, Proc. Near-field Optics 4, Nov. 1997.
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Reza Ghadiri
Departments of Chemistry and Molecular Biology and The Skaggs Institute for Chemical Biology
Design and synthesis of materials with predetermined structure and function require not only elaboration of highly efficient and convergent synthetic processes, but also the ability to direct specific and desired molecular recognition events. In other words, rigorous control over the inter- and intramolecular information transfer processes must be exercised. Toward that goal, our group has exploited self-assembling and self-organizing molecular processes for the construction of tubular peptide architecture. We will outline the design, synthesis, characterization, and functional properties of this new class of biomaterials.
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Clive Roberts
Laboratory of Biophysics and Surface Analysis, Department of Pharmaceutical Sciences, The University of Nottingham, Nottingham, U.K.
It is widely recognized that the control of a materials architecture and composition at the nanoscale will provide significant advantages across a wide range of applications. Related to this demand is the requirement for techniques to characterize the "nanoscale". At Nottingham, we are in particular interested in the implications of such new materials and methodologies for the evolution of novel biomaterials, biosensing devices and diagnostic techniques.
The advent of a new raft of scanning probe analysis modes, such as spatially resolved specific and non-specific molecular adhesion measurements and phase imaging, presents fresh opportunities in the characterization of biomaterial surfaces at the nanoscale.
We will illustrate this potential with examples of distinguishing between microdomains of a blend of biodegradable polymers and studies on protein adsorption and binding to a range of homogeneous and patterned polymeric and self-assembled monolayer substrates.
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M.F. Garcia-Parajo, J.-A.Veerman, S.J.T. van Noort, A.G.T. Ruiter and N.F.
van Hulst
Applied Optics Group & MESA Research Institute, Department of Applied Physics, University of Twente
The ability to detect single fluorescent molecules at ambient conditions combined with great advances in Genetic Engineering has opened new opportunities in DNA analysis and fundamental studies. In particular, the use of DNA-binding proteins and synthetic oligonucleotides, combined with high resolution & ultrasensitive optical techniques is leading to new genetic diagnostic methods and contributing to the understanding of molecular events involved in DNA transcription and gene regulation.
Our approach involves the use of an aperture type near-field scanning optical microscope with tuning fork shear force feedback for the study of genetic material with high sensitivity (down to the single molecule detection limit) and super resolution physical mapping. At the chromosome level, we have used the technique for the detection of two-colour fluorescence in-situ hybridisation signals. Multiple sequence-specific probes are recognised, and their physical position visualised with nanometric accuracy and excellent optical resolution (down to 80 nm) [1]. At single molecular level, de-condensed DNA and small strands (less than 1000 bp) have been imaged using shear force microscopy based on tuning fork detection with phase feedback. The technique is used to accurately determine binding sites of proteins to the DNA with a vertical sensitivity of 0.2 nm and nanometric lateral resolution [2,3]. Single molecule fluorescence detection sensitivity is achieved on DNA strands labelled with one fluoresecence tag attached to the amino-modified 5’end of the strand. Single fluorophores are selectively excited according to their dipole orientation, and imaged using two channel fluorescence polarisation detection [2]. Due to the high sensitivity and long term stability of our set-up, mapping and colocalisation studies of sequence tagged sites are performed at individual molecular level.
[1] M.H.P Moers, W.H.J. Kalle, A.G.T. Ruiter, J.C.A.G. Wiegant, A.K. Raap, J. Greve, B.G. de Grooth and N.F. van Hulst, J. Microscopy 182 (1996), 40–45.
[2] M.F. Garcia-Parajo, J.-A. Veerman, A.G.T. Ruiter and N.F. van Hulst, Ultramicroscopy, Proc. Near-field Optics 4, Nov. (1997).
[3] N.F. van Hulst, M.F. Garcia-Parajo, J.-A. Veerman and A.G.T. Ruiter, J. Struct. Biol. (1997), in print.
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W. M. Heckl, J. E. Freund, M. Edelwirth, R. Schloderer, S. J. Sowerby
Institut für Kristallographie u. Mineralogie, Ludwig-Maximilians-Universität München
The experimental evidence for the spontaneous formation of two-dimensional monolayers of the purine and pyrimidine bases by a template directed self assembly process is reviewed [1]. Two dimensional molecular packing structure and monolayer preparation of nucleic acid bases on graphite (0001), MoS2 (0001) and Ag (111) have been studied using STM, LEED and thermal desorption spectroscopy (TDS) [2]. By combining real space images and diffraction data a close packed hydrogen bonded molecular network is proposed, where the substrate acts as a template. LEED data show patterns of reflexes which can be interpreted as a superposition of molecular domains, epitaxially grown on the trigonal surfaces. The energy minimized molecular arrangement could be determined by force field calculations. Because of the different substrate-adsorbate interaction (physisorption vs. chemisorption) molecular films were investigated on semiconductor and metal substrates resulting in a different molecular arrangement. For the first time DNA base layers were grown by OMBE. TDS measurements allow for the determination of preparation parameters and of the adsorption energy which can be compared to force field calculations.
2D-crystallisation is an example of non-equilibrium thermodynamics as it favours the synthesis of the reaction product by removing it from the chemical equilibrium expression. Therefore this experiments can serve as a model for prebiotic synthesis, where it would push prebiotic reactions in the direction of purine and pyrimidine base synthesis and allow the accumulation of these molecular species even from low yielding reactions.
The observation of enantiomorphism in the adenine monolayer, however, suggests that these structures may have played a more significant role in the origin of life.
[1] S.J. Sowerby and W.M. Heckl, "The Role of Self-assembled Monolayers of the Purine and Pyrimidine Bases in the Origin of life", Origins of Life and Evolution of the Biosphere, submitted
[2] J.E. Freund, M. Edelwirth, W.M. Heckl, Phys.Rev.B 55 (1997), 5394–5397
[3] S.J. Sowerby, W. M. Heckl et al., "Chiral symmetry breaking during molecular self-assembly of achiral purine molecules at the solid-liquid interface", Journal of Molecular Evolution 43 (1996), 419–424.
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