Herstellung und Charakterisierung von dreidimensionalen polymeren Nanostrukturen mit Hilfe der chemischen Elektronenstrahl-Nanolithographie
Zusammenfassung der Projektergebnisse
The major goals of the DFG-funded project were (i) a further development of Electron Beam Chemical Lithography (EBCL) on the basis of monomolecular resists and templates and related fabrication of 3D polymer nanostructures by surface-initiated polymerization (SIP) as well as (ii) the fabrication, design, and characterization of novel ultrathin free-standing polymer nanostructures. The above goals were achieved to the full extent. Two different EBCL approaches were utilized. The key idea of the first approach is electron-induced modification of a functional tail-group attached to an aromatic backbone of a molecule comprising self-assembled monolayer (SAM), which occurs simultaneously with cross-linking of the aromatic backbones ensuring the stability of the entire system. The key idea of the second approach - irradiationpromoted exchange reaction (IPER) - is a tuning of the extent and rate of the exchange reaction between the primary SAM and a potential molecular substituent by electron irradiation with a variable dose. In context of the first approach we studied the basic reasons for the high stability of aromatic SAMs under electron irradiation. Using a model system of cycloaliphatic compounds, we demonstrated that not the aromatic character but connectivity of the skeleton is the decisive factor for this stability. Further, we extended a class of materials which can be used for EBCL on the basis of aromatic SAM, introducing and studying in detail irradiation-induced modification of nitrile-substituted biphenylthiol monolayers. We demonstrated that these films are as suitable for EBCL as the well-known systems of nitro-substituted biphenylthiols (NBPT), based on the transformation of inert nitrile group into chemically active amine moiety. The effect of irradiation dose and energy of electrons on efficiency of cross-linking and nitro/nitrile-to-amine transformation were studied in detail, using SIP in the latter case. Using the above knowledge, we designed a novel procedure for the fabrication of freestanding, biocompatible, and ultrathin membranes on the basis of NBPT SAMs. To achieve the biocompatibility, we coupled these SAMs, with potentially protein-repelling poly(ethylene glycol) (PEGs) moieties. Preliminary, the SAMs were irradiated by electrons to activate the tail groups and to mediate cross-linking, necessary for the mechanical stability of the PEG-NBPT bilayer after its separation from the substrate. Along with SAM-based, PEGylated nanosheets, biocompatible films and membranes consisting of PEG only were fabricated. The key idea of the preparation procedure was to mix two complementary PEG components which polymerize spontaneously at an elevated temperature after their deposition by spin-coating or drop casting. The films exhibited very high stability, reversible hydrogel-like behavior, and an ability to adsorb nanoobjects dissolved in aqueous solutions. Composite films containing such nanoobjects (Au nanoparticles) reveal interesting and potentially useful optical properties. PEG films can also serve as a flexible platform for lithography and nanofabrication. Finally, within the IPER-EBCL approach, a controlled imbedding of thiolated single strand DNA (ssDNA) species into a protein-repelling matrix of oligo(ethylene glycol) substituted alkanethiols (OEG-ATs) was performed, resulting in mixed OEG-ATs/ssDNA films of variable composition or, in combination with EBL, in preparation of ssDNA patterns of a flexible form in a protein-repelling matrix. Using the OEG-ATs/ssDNA patterns fabricated by IPER-EBL as the templates, we grew them in the Z-dimension into 3D DNA nanostructures using surface-initiated enzymatic polymerization, which allowed us to sculpture complex DNA nanostructures. The obtained results are of significant scientific value and useful for potential applications in context of soft-matter nanofabrication, biotechnology, transmission electron microscopy (supporting membranes and matrix films), and sensor fabrication.
Projektbezogene Publikationen (Auswahl)
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Chemical nanolithography, Bunsenmagazin 1, 3-13 (2009)
W. Eck and M. Grunze
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Aromatic versus aliphatic: self-assembled monolayers of cyclic aliphatic thiols and their reaction towards electron irradiation, J. Phys. Chem. C 116, 13559–13568 (2012)
P. A. Waske, W. Eck, and M. Zharnikov
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Biocompatible nanomembranes based on PEGylation of cross-linked self-assembled monolayers, Chem. Mater. 24, 2965–2972 (2012)
N. Meyerbröker, Zi-An Li, W. Eck, and M. Zharnikov
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Fabrication of ssDNA/oligo (ethylene glycol) monolayers and complex nanostructures by irradiation promoted exchange reaction, Angew. Chem. Int. Ed. 51, 10303–10306 (2012)
M. N. Khan, V. Tjong, A. Chilkoti, and M. Zharnikov
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Modification of nitrile-terminated biphenylthiol selfassembled monolayers by electron irradiation and related applications, Langmuir 28, 9583–9592 (2012)
N. Meyerbröker and M. Zharnikov
