@article{KoenigSanter2012, author = {K{\"o}nig, Tobias and Santer, Svetlana}, title = {Visualization of surface plasmon interference by imprinting intensity patterns on a photosensitive polymer}, series = {Nanotechnology}, volume = {23}, journal = {Nanotechnology}, number = {48}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0957-4484}, doi = {10.1088/0957-4484/23/48/485304}, pages = {7}, year = {2012}, abstract = {We report on sub-wavelength structuring of photosensitive azo-containing polymer films induced by a surface plasmon interference intensity pattern. The two surface plasmon waves generated at neighboring nano-slits in the metal layer during irradiation interfere constructively, resulting in an intensity pattern with a periodicity three times smaller than the wavelength of the incoming light. The near field pattern interacts with the photosensitive polymer film placed above it, leading to a topography change which follows the intensity pattern exactly, resulting in the formation of surface relief gratings of a size below the diffraction limit. We analyze numerically and experimentally how the depth of the nano-slit alters the interference pattern of surface plasmons and find that the sub-wavelength patterning of the polymer surface could be optimized by modifying the geometry and the size of the nano-slit.}, language = {en} } @article{KoenigSanter2012, author = {K{\"o}nig, Tobias and Santer, Svetlana}, title = {Stretching and distortion of a photosensitive polymer film by surface plasmon generated near fields in the vicinity of a nanometer sized metal pin hole}, series = {Nanotechnology}, volume = {23}, journal = {Nanotechnology}, number = {15}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0957-4484}, doi = {10.1088/0957-4484/23/15/155301}, pages = {8}, year = {2012}, abstract = {Here we demonstrate how a surface plasmon (SP) generated near field pattern in the vicinity of a nano-scale pin hole can be used to generate reversible topography changes in a photosensitive polymer film above the opening. This can be achieved by simply changing the polarization state of the plasmon generating incoming light. In the case of linear polarization, the near field intensity pattern causes the film to laterally expand/contract according to the direction of the polarization. For circular polarization, two pronounced rims corresponding to maxima in the topography are observed. In all cases, the topographical variation is in close agreement with the SP intensity distribution computed from finite difference time domain simulation. Our results demonstrate the versatility of using SP near fields to imprint a variety of structures into photosensitive polymer films using only a single metallic mask.}, language = {en} } @article{KoenigSekharSanter2012, author = {K{\"o}nig, Tobias and Sekhar, Y. Nataraja and Santer, Svetlana}, title = {Surface plasmon nanolithography impact of dynamically varying near-field boundary conditions at the air-polymer interface}, series = {Journal of materials chemistry}, volume = {22}, journal = {Journal of materials chemistry}, number = {13}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {0959-9428}, doi = {10.1039/c2jm15864g}, pages = {5945 -- 5950}, year = {2012}, abstract = {It is well-known that surface plasmon generated near fields of suitably irradiated metal nano-structures can induce a patterning in an azobenzene-modified photosensitive polymer film placed on top. The change in the topography usually follows closely and permanently the underlying near field intensity pattern. With this approach, one can achieve a multitude of morphologies by additionally changing light intensity, polarization and the kind of metal used for nano-structuring. In this paper, we demonstrate that below a critical value of the polymer film thickness, the receding polymer material induces a change in refractive index of the glass-metal-polymer system, modifying the near field intensity distribution and causing a back-reaction on the flow of polymer material. This has a profound influence on the smallest size of topographical features that can be imprinted into the polymer.}, language = {en} } @article{KoenigYadavalliSanter2012, author = {K{\"o}nig, Tobias and Yadavalli, Nataraja Sekhar and Santer, Svetlana}, title = {Near-Field induced reversible structuring of photosensitive polymer films Gold versus silver nano-antennas}, series = {Plasmonics}, volume = {7}, journal = {Plasmonics}, number = {3}, publisher = {Springer}, address = {New York}, issn = {1557-1955}, doi = {10.1007/s11468-012-9339-3}, pages = {535 -- 542}, year = {2012}, abstract = {We report on reversible structuring of photosensitive azo-containing polymer films induced by near-field intensity patterns emanating from illuminated nano-scale metal structures fabricated by colloidal lithography. Two different sets of these nano-antennas, consisting of either gold or silver, were investigated with respect to their ability to induce topography changes in a photosensitive polymer film placed above. Using in situ recorded atomic force microscopy micrographs of polymer topography changes during UV irradiation, we find that the response of the polymer film differs for the two metals at similar geometries of the metal nanostructures. The maximum topography change is stronger for Ag antennas as compared to the Au pattern, whereas the latter material revealed a pronounced splitting of topography maxima into two, a phenomenon less visible in the case of Ag. Finite difference time domain simulations of the electromagnetic field distribution in the vicinity of the metal structures confirm this remarkable observation. The local intensity is twice as large for the Ag as compared to the Au structures, and in each case, a splitting of the intensity pattern results, with a stronger modulation for Au. For both metals, the topography change was found to be reversible between a patterned and a flat by repeated change of irradiation conditions.}, language = {en} } @article{MalyarGorinStetsyuraetal.2012, author = {Malyar, I. V. and Gorin, D. A. and Stetsyura, S. V. and Santer, Svetlana}, title = {Effect of a nanodimensional polyethylenimine layer on current-voltage characteristics of hybrid structures based on single-crystal silicon}, series = {Journal of electronic materials}, volume = {41}, journal = {Journal of electronic materials}, number = {12}, publisher = {Springer}, address = {New York}, issn = {0361-5235}, doi = {10.1007/s11664-012-2266-4}, pages = {3427 -- 3435}, year = {2012}, abstract = {In this paper the study of the tunneling current-voltage (I-V) characteristics of silicon surfaces with n- and p-type conductivity as a function of roughness in the presence of an adsorbed insulating layer of polyethylenimine (PEI) is presented. A new approach is proposed for analysis of the tunnel current-voltage characteristics of a metal-insulator-semiconductor structure based on the combination of two models (Simmons and Schottky). Such joint analysis demonstrates the effect of surface states and evaluates changes in the band bending and electron affinity after the deposition of the polyelectrolyte layer on the semiconductor surface. As a result, we are able to differentiate between the equilibrium tunnel barrier (q phi (0)) and the barrier height (q phi (B)). It is shown that the deposition of the polymer leads to an increase of the equilibrium tunnel barrier by more than 250 meV, irrespective of the roughness and the conductivity type of the silicon substrate. The PEI deposition also leads to changes in the barrier height (less than 25 meV) that are smaller than the equilibrium tunnel barrier changes, indicating pinning of the Fermi level by the electron surface states that are energetically close to it. These surface states can trap charge carriers, a process leading to the formation of a depletion region and band bending on the semiconductor surface. Moreover, the change in the barrier height q Delta phi (B) depends on the conductivity type of the semiconductor, being positive for n-type and negative for p-type, in contrast to q Delta phi (0), which is positive for all substrates. The change is explained by capture of electrons preferably from the semiconductor space-charge region in the presence of a cationic polyelectrolyte, e.g., PEI.}, language = {en} } @inproceedings{SchuhPruckerLomadzeetal.2012, author = {Schuh, Christian and Prucker, Oswald and Lomadze, Nino and Kopyshev, Alexey and Santer, Svetlana and Ruehe, Juergen}, title = {Nanogradient polymer brushes}, series = {Abstracts of papers : joint conference / The Chemical Institute of Cananda, CIC, American Chemical Society, ACS}, volume = {243}, booktitle = {Abstracts of papers : joint conference / The Chemical Institute of Cananda, CIC, American Chemical Society, ACS}, publisher = {American Chemical Society}, address = {Washington}, issn = {0065-7727}, pages = {1}, year = {2012}, language = {en} } @article{ZakrevskyyRichterZakrevskaetal.2012, author = {Zakrevskyy, Yuriy and Richter, Marcel and Zakrevska, Svitlana and Lomadze, Nino and von Klitzing, Regine and Santer, Svetlana}, title = {Light-controlled reversible manipulation of microgel particle size using azobenzene-containing surfactant}, series = {Advanced functional materials}, volume = {22}, journal = {Advanced functional materials}, number = {23}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1616-301X}, doi = {10.1002/adfm.201200617}, pages = {5000 -- 5009}, year = {2012}, abstract = {The light-induced reversible switching of the swelling of microgel particles triggered by photo-isomerization and binding/unbinding of a photosensitive azobenzene-containing surfactant is reported. The interactions between the microgel (N-isopropylacrylamide, co-monomer: allyl acetic acid, crosslinker: N,N'-methylenebisacrylamide) and the surfactant are studied by UV-Vis spectroscopy, dynamic and electrophoretic light scattering measurements. Addition of the surfactant above a critical concentration leads to contraction/collapse of the microgel. UV light irradiation results in trans-cis isomerization of the azobenzene unit incorporated into the surfactant tail and causes an unbinding of the more hydrophilic cis isomer from the microgel and its reversible swelling. The reversible contraction can be realized by blue light irradiation that transfers the surfactant back to the more hydrophobic trans conformation, in which it binds to the microgel. The phase diagram of the surfactant-microgel interaction and transitions (aggregation, contraction, and precipitation) is constructed and allows prediction of changes in the system when the concentration of one or both components is varied. Remote and reversible switching between different states can be realized by either UV or visible light irradiation.}, language = {en} }