@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}
}
@misc{DiFlorioBruendermannYadavallietal.2013,
  author    = {Di Florio, Giuseppe and Br{\"u}ndermann, Erik and Yadavalli, Nataraja Sekhar and Santer, Svetlana and Havenith, Martina},
  title     = {Polarized 3D Raman and nanoscale near-field optical microscopy of optically inscribed surface relief gratings},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-95233},
  pages     = {1544 -- 1554},
  year      = {2013},
  abstract  = {We have used polarized confocal Raman microspectroscopy and scanning near-field optical microscopy with a resolution of 60 nm to characterize photoinscribed grating structures of azobenzene doped polymer films on a glass support. Polarized Raman microscopy allowed determining the reorientation of the chromophores as a function of the grating phase and penetration depth of the inscribing laser in three dimensions. We found periodic patterns, which are not restricted to the surface alone, but appear also well below the surface in the bulk of the material. Near-field optical microscopy with nanoscale resolution revealed lateral two-dimensional optical contrast, which is not observable by atomic force and Raman microscopy.},
  language  = {en}
}
@article{YadavalliSaphiannikovaLomadzeetal.2013,
  author    = {Yadavalli, Nataraja Sekhar and Saphiannikova, Marina and Lomadze, Nino and Goldenberg, Leonid M. and Santer, Svetlana},
  title     = {Structuring of photosensitive material below diffraction limit using far field irradiation},
  series = {Applied physics : A, Materials science \& processing},
  volume    = {113},
  journal   = {Applied physics : A, Materials science \& processing},
  number    = {2},
  publisher = {Springer},
  address   = {New York},
  issn      = {0947-8396},
  doi       = {10.1007/s00339-013-7945-3},
  pages     = {263 -- 272},
  year      = {2013},
  abstract  = {In this paper, we report on in-situ atomic force microscopy (AFM) studies of topographical changes in azobenzene-containing photosensitive polymer films that are irradiated with light interference patterns. We have developed an experimental setup consisting of an AFM combined with two-beam interferometry that permits us to switch between different polarization states of the two interfering beams while scanning the illuminated area of the polymer film, acquiring corresponding changes in topography in-situ. This way, we are able to analyze how the change in topography is related to the variation of the electrical field vector within the interference pattern. It is for the first time that with a rather simple experimental approach a rigorous assignment can be achieved. By performing in-situ measurements we found that for a certain polarization combination of two interfering beams [namely for the SP (a dagger center dot, a dagger") polarization pattern] the topography forms surface relief grating with only half the period of the interference patterns. Exploiting this phenomenon we are able to fabricate surface relief structures with characteristic features measuring only 140 nm, by using far field optics with a wavelength of 491 nm. We believe that this relatively simple method could be extremely valuable to, for instance, produce structural features below the diffraction limit at high-throughput, and this could significantly contribute to the search of new fabrication strategies in electronics and photonics industry.},
  language  = {en}
}
@article{LindeYadavalliSanter2013,
  author    = {Linde, Felix and Yadavalli, Nataraja Sekhar and Santer, Svetlana},
  title     = {Conductivity behavior of very thin gold films ruptured by mass transport in photosensitive polymer film},
  series = {APPLIED PHYSICS LETTERS},
  volume    = {103},
  journal   = {APPLIED PHYSICS LETTERS},
  number    = {25},
  publisher = {AMER INST PHYSICS},
  address   = {MELVILLE},
  issn      = {0003-6951},
  doi       = {10.1063/1.4850595},
  pages     = {4},
  year      = {2013},
  abstract  = {We report on conductivity behavior of very thin gold layer deposited on a photosensitive polymer film. Under irradiation with light interference pattern, the azobenzene containing photosensitive polymer film undergoes deformation at which topography follows a distribution of intensity, resulting in the formation of a surface relief grating. This process is accompanied by a change in the shape of the polymer surface from flat to sinusoidal together with a corresponding increase in surface area. The gold layer placed above deforms along with the polymer and ruptures at a strain of 4\%. The rupturing is spatially well defined, occurring at the topographic maxima and minima resulting in periodic cracks across the whole irradiated area. We have shown that this periodic micro-rupturing of a thin metal film has no significant impact on the electrical conductivity of the films. We suggest a model to explain this phenomenon and support this by additional experiments where the conductivity is measured in a process when a single nanoscopic scratch is formed with an AFM tip. Our results indicate that in flexible electronic materials consisting of a polymer support and an integrated metal circuit, nano-and micro cracks do not alter significantly the behavior of the conductivity unless the metal is disrupted completely. (C) 2013 AIP Publishing LLC.},
  language  = {en}
}
@article{YadavalliLindeKopyshevetal.2013,
  author    = {Yadavalli, Nataraja Sekhar and Linde, Felix and Kopyshev, Alexey and Santer, Svetlana},
  title     = {Soft matter beats hard matter - rupturing of thin metallic films induced by mass transport in photosensitive polymer films},
  series = {ACS applied materials \& interfaces},
  volume    = {5},
  journal   = {ACS applied materials \& interfaces},
  number    = {16},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1944-8244},
  doi       = {10.1021/am4006132w},
  pages     = {7743 -- 7747},
  year      = {2013},
  abstract  = {The interface between thin films of metal and polymer materials play a significant role in modern flexible microelectronics viz., metal contacts on polymer substrates, printed electronics and prosthetic devices. The major emphasis in metal polymer interface is on studying how the externally applied stress in the polymer substrate leads to the deformation and cracks in metal film and vice versa. Usually, the deformation process involves strains varying over large lateral dimensions because of excessive stress at local imperfections. Here we show that the seemingly random phenomena at macroscopic scales can be rendered rather controllable at submicrometer length scales. Recently, we have created a metal polymer interface system with strains varying over periods of several hundred nanometers. This was achieved by exploiting the formation of surface relief grating (SRG) within the azobenzene containing photosensitive polymer film upon irradiation with light interference pattern. Up to a thickness of 60 nm, the adsorbed metal film adapts neatly to the forming relief, until it ultimately ruptures into an array of stripes by formation of highly regular and uniform cracks along the maxima and minima of the polymer topography. This surprising phenomenon has far-reaching implications. This is the first time a direct probe is available to estimate the forces emerging in SRG formation in glassy polymers. Furthermore, crack formation in thin metal films can be studied literally in slow motion, which could lead to substantial improvements in the design process of flexible electronics. Finally, cracks are produced uniformly and at high density, contrary to common sense. This could offer new strategies for precise nanofabrication procedures mechanical in character.},
  language  = {en}
}
@article{YadavalliSanter2013,
  author    = {Yadavalli, Nataraja Sekhar and Santer, Svetlana},
  title     = {In-situ atomic force microscopy study of the mechanism of surface relief grating formation in photosensitive polymer films},
  series = {Journal of applied physics},
  volume    = {113},
  journal   = {Journal of applied physics},
  number    = {22},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {0021-8979},
  doi       = {10.1063/1.4809640},
  pages     = {12},
  year      = {2013},
  abstract  = {When photosensitive azobenzene-containing polymer films are irradiated with light interference patterns, topographic variations in the film develop that follow the local distribution of the electric field vector. The exact correspondence of e.g., the vector orientation in relation to the presence of local topographic minima or maxima is in general difficult to determine. Here, we report on a systematic procedure how this can be accomplished. For this, we devise a new set-up combining an atomic force microscope and two-beam interferometry. With this set-up, it is possible to track the topography change in-situ, while at the same time changing polarization and phase of the impinging interference pattern. This is the first time that an absolute correspondence between the local distribution of electric field vectors and the local topography of the relief grating could be established exhaustively. Our setup does not require a complex mathematical post-processing and its simplicity renders it interesting for characterizing photosensitive polymer films in general.},
  language  = {en}
}
@phdthesis{Yadavalli2014,
  author    = {Yadavalli, Nataraja Sekhar},
  title     = {Advances in experimental methods to probe surface relief grating formation mechanism in photosensitive materials},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-71213},
  school      = {Universit{\"a}t Potsdam},
  year      = {2014},
  abstract  = {When azobenzene-modified photosensitive polymer films are irradiated with light interference patterns, topographic variations in the film develop that follow the electric field vector distribution resulting in the formation of surface relief grating (SRG). The exact correspondence of the electric field vector orientation in interference pattern in relation to the presence of local topographic minima or maxima of SRG is in general difficult to determine. In my thesis, we have established a systematic procedure to accomplish the correlation between different interference patterns and the topography of SRG. For this, we devise a new setup combining an atomic force microscope and a two-beam interferometer (IIAFM). With this set-up, it is possible to track the topography change in-situ, while at the same time changing polarization and phase of the impinging interference pattern. To validate our results, we have compared two photosensitive materials named in short as PAZO and trimer. This is the first time that an absolute correspondence between the local distribution of electric field vectors of interference pattern and the local topography of the relief grating could be established exhaustively. In addition, using our IIAFM we found that for a certain polarization combination of two orthogonally polarized interfering beams namely SP (↕, ↔) interference pattern, the topography forms SRG with only half the period of the interference patterns. Exploiting this phenomenon we are able to fabricate surface relief structures below diffraction limit with characteristic features measuring only 140 nm, by using far field optics with a wavelength of 491 nm. We have also probed for the stresses induced during the polymer mass transport by placing an ultra-thin gold film on top (5-30 nm). During irradiation, the metal film not only deforms along with the SRG formation, but ruptures in regular and complex manner. The morphology of the cracks differs strongly depending on the electric field distribution in the interference pattern even when the magnitude and the kinetic of the strain are kept constant. This implies a complex local distribution of the opto-mechanical stress along the topography grating. The neutron reflectivity measurements of the metal/polymer interface indicate the penetration of metal layer within the polymer resulting in the formation of bonding layer that confirms the transduction of light induced stresses in the polymer layer to a metal film.},
  language  = {en}
}
@article{YadavalliKorolkovMoulinetal.2014,
  author    = {Yadavalli, Nataraja Sekhar and Korolkov, Denis and Moulin, Jean-Francois and Krutyeva, Margarita and Santer, Svetlana},
  title     = {Probing opto-mechanical stresses within azobenzene-containing photosensitive polymer films by a thin metal film placed above},
  series = {ACS applied materials \& interfaces},
  volume    = {6},
  journal   = {ACS applied materials \& interfaces},
  number    = {14},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1944-8244},
  doi       = {10.1021/am501870t},
  pages     = {11333 -- 11340},
  year      = {2014},
  abstract  = {Azo-modified photosensitive polymers offer the interesting possibility to reshape bulk polymers and thin films by UV-irradiation while being in the solid glassy state. The polymer undergoes considerable mass transport under irradiation with a light interference pattern resulting in the formation of surface relief grating (SRG). The forces inscribing this SRG pattern into a thin film are hard to assess experimentally directly. In the current study, we are proposing a method to probe opto-mechanical stresses within polymer films by characterizing the mechanical response of thin metal films (10 nm) deposited on the photosensitive polymer. During irradiation, the metal film not only deforms along with the SRG formation but ruptures in a regular and complex manner. The morphology of the cracks differs strongly depending on the electrical field distribution in the interference pattern, even when the magnitude and the kinetics of the strain are kept constant. This implies a complex local distribution of the opto-mechanical stress along the topography grating. In addition, the neutron reflectivity measurements of the metal/polymer interface indicate the penetration of a metal layer within the polymer, resulting in a formation of a bonding layer that confirms the transduction of light-induced stresses in the polymer layer to a metal film.},
  language  = {en}
}
@article{DiFlorioBruendermannYadavallietal.2014,
  author    = {Di Florio, G. and Bruendermann, E. and Yadavalli, Nataraja Sekhar and Santer, Svetlana and Havenith, Martina},
  title     = {Graphene multilayer as nanosized optical strain gauge for polymer surface relief gratings},
  series = {Nano letters : a journal dedicated to nanoscience and nanotechnology},
  volume    = {14},
  journal   = {Nano letters : a journal dedicated to nanoscience and nanotechnology},
  number    = {10},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1530-6984},
  doi       = {10.1021/nl502631s},
  pages     = {5754 -- 5760},
  year      = {2014},
  abstract  = {In this paper, we show how graphene can be utilized as a nanoscopic probe in order to characterize local opto-mechanical forces generated within photosensitive azobenzene containing polymer films. Upon irradiation with light interference patterns, photosensitive films deform according to the spatial intensity variation, leading to the formation of periodic topographies such as surface relief gratings (SRG). The mechanical driving forces inscribing a pattern into the films are supposedly fairly large, because the deformation takes place without photofluidization; the polymer is in a glassy state throughout. However, until now there has been no attempt to characterize these forces by any means. The challenge here is that the forces vary locally on a nanometer scale. Here, we propose to use Raman analysis of the stretching of the graphene layer adsorbed on top of polymer film under deformation in order to probe the strength of the material transport spatially resolved. With the well-known mechanical properties of graphene, we can obtain lower bounds on the forces acting within the film. Upon the basis of our experimental results, we can deduce that the internal pressure in the film due to grating formation can exceed 1 GPa. The graphene-based nanoscopic gauge opens new possibilities to characterize opto-mechanical forces generated within photosensitive polymer films.},
  language  = {en}
}
@article{YadavalliSaphiannikovaSanter2014,
  author    = {Yadavalli, Nataraja Sekhar and Saphiannikova, Marina and Santer, Svetlana},
  title     = {Photosensitive response of azobenzene containing films towards pure intensity or polarization interference patterns},
  series = {Applied physics letters},
  volume    = {105},
  journal   = {Applied physics letters},
  number    = {5},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {0003-6951},
  doi       = {10.1063/1.4891615},
  pages     = {5},
  year      = {2014},
  abstract  = {In this paper, we report on differences in the response of photosensitive azobenzene containing films upon irradiation with the intensity or polarization interference patterns. Two materials are studied differing in the molecular weight: an azobenzene-containing polymer and a molecular glass formed from a much smaller molecule consisting of three connected azobenzene units. Topography changes occurring along with the changes in irradiation conditions are recorded using a homemade set-up combining an optical part for generation and shaping of interference patterns and an atomic force microscope for acquiring the kinetics of film deformation. In this way, we could reveal the unique behavior of photosensitive materials during the first few minutes of irradiation: the change in topography is initially driven by an increase in the azobenzene free volume along with the transcis isomerization, followed by the mass transport finally resulting in the surface relief grating. This study demonstrates the great potential of our setup to experimentally highlight puzzling processes governing the formation of surface relief gratings. (C) 2014 AIP Publishing LLC.},
  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{DiFlorioBruendermannYadavallietal.2014,
  author    = {Di Florio, G. and Bruendermann, E. and Yadavalli, Nataraja Sekhar and Santer, Svetlana and Havenith, Martina},
  title     = {Confocal raman microscopy and AFM study of the interface between the photosensitive polymer layer and multilayer graphene},
  series = {Soft materials},
  volume    = {12},
  journal   = {Soft materials},
  publisher = {Taylor \& Francis Group},
  address   = {Philadelphia},
  issn      = {1539-445X},
  doi       = {10.1080/1539445X.2014.945040},
  pages     = {S98 -- S105},
  year      = {2014},
  abstract  = {In this paper we report on the interaction between photosensitive azobenzene-containing polymer films and on top adsorbed graphene multilayers. The photosensitive polymer film changes its topography under irradiation with light interference patterns according to their polarization distribution. The multilayer graphene follows the deformation of the polymer film and stretches accordingly. Using confocal Raman microspectroscopy we can detect the appearance of additional peaks in the Raman spectrum of the photosensitive polymer film upon irradiation indicating a molecular interaction at the interface between the graphene multilayer and the polymer matrix. Multi-component analysis of the specific Raman bands shows that the interaction involves the graphene rings and the aromatic rings of the azobenzenes causing the strong adhesion between the two materials.},
  language  = {en}
}
@article{DiFlorioBruendermannYadavallietal.2014,
  author    = {Di Florio, Giuseppe and Bruendermann, Erik and Yadavalli, Nataraja Sekhar and Santer, Svetlana and Havenith, Martina},
  title     = {Polarized 3D Raman and nanoscale near-field optical microscopy of optically inscribed surface relief gratings: chromophore orientation in azo-doped polymer films},
  series = {Soft matter},
  volume    = {10},
  journal   = {Soft matter},
  number    = {10},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {1744-683X},
  doi       = {10.1039/c3sm51787j},
  pages     = {1544 -- 1554},
  year      = {2014},
  abstract  = {We have used polarized confocal Raman microspectroscopy and scanning near-field optical microscopy with a resolution of 60 nm to characterize photoinscribed grating structures of azobenzene doped polymer films on a glass support. Polarized Raman microscopy allowed determining the reorientation of the chromophores as a function of the grating phase and penetration depth of the inscribing laser in three dimensions. We found periodic patterns, which are not restricted to the surface alone, but appear also well below the surface in the bulk of the material. Near-field optical microscopy with nanoscale resolution revealed lateral two-dimensional optical contrast, which is not observable by atomic force and Raman microscopy.},
  language  = {en}
}
@article{YadavalliKoenigSanter2015,
  author    = {Yadavalli, Nataraja Sekhar and K{\"o}nig, Tobias and Santer, Svetlana},
  title     = {Selective mass transport of azobenzene-containing photosensitive films towards or away from the light intensity},
  series = {Journal of the Society for Information Display},
  volume    = {23},
  journal   = {Journal of the Society for Information Display},
  number    = {4},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {1071-0922},
  doi       = {10.1002/jsid.306},
  pages     = {154 -- 162},
  year      = {2015},
  abstract  = {Here, we report on two photosensitive amorphous polymers showing opposite behavior upon exposure to illumination. The first polymer (PAZO) consists of linear backbone to which azobenzene-containing side chains are covalently attached, while in the second polymer (azo-PEI), the azobenzene side chains are attached ionically to a polyelectrolyte backbone. When irradiated through a mask, the PAZO goes away from the intensity maxima, leaving behind topography trenches, while the direction of the mass transport of the azo-PEI polymer points towards the intensity maxima. This kind of behavior has been reported only for certain liquid crystalline polymers that exhibit in-phase reaction on illumination, that is, topography maxima coincides with the intensity maxima. Furthermore, flat nanocrystals placed on top of azo-PEI film was found to be moved together with the mass transport of the underlying polymer film as visualized using in situ atomic force microscopy (AFM) measurements. It was also demonstrated that the two polymer films respond differently on irradiation with the polarization and intensity interference patterns (IPs). To record the kinetic of the surface relief grating formation within two polymers during irradiation with different IPs, we utilized a homemade setup combining the optical part for the generation of IP and AFM. A possible mechanism explaining different responses on the irradiation of amorphous polymers is discussed in the frame of a theoretical model proposed by Saphiannikova et al. (J. Phys. Chem. B 113, 5032-5045 (2009)).},
  language  = {en}
}
@misc{LoebnerJelkenYadavallietal.2016,
  author    = {Loebner, Sarah and Jelken, Joachim and Yadavalli, Nataraja Sekhar and Sava, Elena and Hurduc, Nicolae and Santer, Svetlana},
  title     = {Motion of Adsorbed Nano-Particles on Azobenzene Containing Polymer Films},
  series = {Molecules},
  volume    = {21},
  journal   = {Molecules},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {1420-3049},
  doi       = {10.3390/molecules21121663},
  pages     = {397 -- 411},
  year      = {2016},
  abstract  = {We demonstrate in situ recorded motion of nano-objects adsorbed on a photosensitive polymer film. The motion is induced by a mass transport of the underlying photoresponsive polymer material occurring during irradiation with interference pattern. The polymer film contains azobenzene molecules that undergo reversible photoisomerization reaction from trans-to cis-conformation. Through a multi-scale chain of physico-chemical processes, this finally results in the macro-deformations of the film due to the changing elastic properties of polymer. The topographical deformation of the polymer surface is sensitive to a local distribution of the electrical field vector that allows for the generation of dynamic changes in the surface topography during irradiation with different light interference patterns. Polymer film deformation together with the motion of the adsorbed nano-particles are recorded using a homemade set-up combining an optical part for the generation of interference patterns and an atomic force microscope for acquiring the surface deformation. The particles undergo either translational or rotational motion. The direction of particle motion is towards the topography minima and opposite to the mass transport within the polymer film. The ability to relocate particles by photo-induced dynamic topography fluctuation offers a way for a non-contact simultaneous manipulation of a large number of adsorbed particles just in air at ambient conditions.},
  language  = {en}
}
@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}
}
@misc{LoebnerJelkenYadavallietal.2017,
  author    = {Loebner, Sarah and Jelken, Joachim and Yadavalli, Nataraja Sekhar and Sava, Elena and Hurduc, Nicolae and Santer, Svetlana},
  title     = {Motion of adsorbed nano-particles on azobenzene containing polymer films},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-400423},
  pages     = {11},
  year      = {2017},
  abstract  = {We demonstrate in situ recorded motion of nano-objects adsorbed on a photosensitive polymer film. The motion is induced by a mass transport of the underlying photoresponsive polymer material occurring during irradiation with interference pattern. The polymer film contains azobenzene molecules that undergo reversible photoisomerization reaction from trans- to cis-conformation. Through a multi-scale chain of physico-chemical processes, this finally results in the macro-deformations of the film due to the changing elastic properties of polymer. The topographical deformation of the polymer surface is sensitive to a local distribution of the electrical field vector that allows for the generation of dynamic changes in the surface topography during irradiation with different light interference patterns. Polymer film deformation together with the motion of the adsorbed nano-particles are recorded using a homemade set-up combining an optical part for the generation of interference patterns and an atomic force microscope for acquiring the surface deformation. The particles undergo either translational or rotational motion. The direction of particle motion is towards the topography minima and opposite to the mass transport within the polymer film. The ability to relocate particles by photo-induced dynamic topography fluctuation offers a way for a non-contact simultaneous manipulation of a large number of adsorbed particles just in air at ambient conditions.},
  language  = {en}
}
@misc{YadavalliLoebnerPapkeetal.2018,
  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 = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {458},
  issn      = {1866-8372},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-413510},
  year      = {2018},
  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 °C, 87 °C and 95 °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}
}