@article{YadavalliLoebnerPapkeetal.2016,
  author    = {Yadavalli, Nataraja Sekhar and Loebner, Sarah and Papke, Thomas and Sava, Elena and Hurduc, Nicolae and Santer, Svetlana},
  title     = {A comparative study of photoinduced deformation in azobenzene containing polymer films},
  series = {Soft matter},
  volume    = {12},
  journal   = {Soft matter},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {1744-683X},
  doi       = {10.1039/c6sm00029k},
  pages     = {2593 -- 2603},
  year      = {2016},
  abstract  = {In this paper two groups supporting different views on the mechanism of light induced polymer deformation argue about the respective underlying theoretical conceptions, in order to bring this interesting debate to the attention of the scientific community. The group of Prof. Nicolae Hurduc supports the model claiming that the cyclic isomerization of azobenzenes may cause an athermal transition of the glassy azobenzene containing polymer into a fluid state, the so-called photo-fluidization concept. This concept is quite convenient for an intuitive understanding of the deformation process as an anisotropic flow of the polymer material. The group of Prof. Svetlana Santer supports the re-orientational model where the mass-transport of the polymer material accomplished during polymer deformation is stated to be generated by the light-induced re-orientation of the azobenzene side chains and as a consequence of the polymer backbone that in turn results in local mechanical stress, which is enough to irreversibly deform an azobenzene containing material even in the glassy state. For the debate we chose three polymers differing in the glass transition temperature, 32 degrees C, 87 degrees C and 95 degrees C, representing extreme cases of flexible and rigid materials. Polymer film deformation occurring during irradiation with different interference patterns is recorded using a homemade set-up combining an optical part for the generation of interference patterns and an atomic force microscope for acquiring the kinetics of film deformation. We also demonstrated the unique behaviour of azobenzene containing polymeric films to switch the topography in situ and reversibly by changing the irradiation conditions. We discuss the results of reversible deformation of three polymers induced by irradiation with intensity (IIP) and polarization (PIP) interference patterns, and the light of homogeneous intensity in terms of two approaches: the re-orientational and the photo-fluidization concepts. Both agree in that the formation of opto-mechanically induced stresses is a necessary prerequisite for the process of deformation. Using this argument, the deformation process can be characterized either as a flow or mass transport.},
  language  = {en}
}
@article{PapkeYadavalliHenkeletal.2014,
  author    = {Papke, Thomas and Yadavalli, Nataraja Sekhar and Henkel, Carsten and Santer, Svetlana},
  title     = {Mapping a plasmonic hologram with photosensitive polymer films: standing versus propagating waves},
  series = {ACS applied materials \& interfaces},
  volume    = {6},
  journal   = {ACS applied materials \& interfaces},
  number    = {16},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1944-8244},
  doi       = {10.1021/am503501y},
  pages     = {14174 -- 14180},
  year      = {2014},
  abstract  = {We use a photosensitive layer containing azobenzene moieties to map near-field intensity patterns in the vicinity of nanogrids fabricated within a thin silver layer. It is known that azobenzene containing films deform permanently during irradiation, following the pattern of the field intensity. The photosensitive material reacts only to stationary waves whose intensity patterns do not change in time. In this study, we have found a periodic deformation above the silver film outside the nanostructure, even if the latter consists of just one groove. This is in contradiction to the widely accepted viewpoint that propagating surface plasmon modes dominate outside nanogrids. We explain our observation based on an electromagnetic hologram formed by the constructive interference between a propagating surface plasmon wave and the incident light. This hologram contains a stationary intensity and polarization grating that even appears in the absence of the polymer layer.},
  language  = {en}
}
@article{KoenigPapkeKopyshevetal.2013,
  author    = {K{\"o}nig, Tobias and Papke, Thomas and Kopyshev, Alexey and Santer, Svetlana},
  title     = {Atomic force microscopy nanolithography fabrication of metallic nano-slits using silicon nitride tips},
  series = {Journal of materials science},
  volume    = {48},
  journal   = {Journal of materials science},
  number    = {10},
  publisher = {Springer},
  address   = {New York},
  issn      = {0022-2461},
  doi       = {10.1007/s10853-013-7188-x},
  pages     = {3863 -- 3869},
  year      = {2013},
  abstract  = {In this paper, we report on the properties of nano-slits created in metal thin films using atomic force microscope (AFM) nanolithography (AFM-NL). We demonstrate that instead of expensive diamond AFM tips, it is also possible to use low cost silicon nitride tips. It is shown that depending on the direction of scratching, nano-slits of different widths and depths can be fabricated at constant load force. We elucidate the reasons for this behavior and identify an optimal direction and load force for scratching a gold layer.},
  language  = {en}
}