Svetlana Santer

Universität Potsdam, Potsdam, Brandenburg, Germany

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Publications (53)195.67 Total impact

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    ABSTRACT: Realization of all-optically controlled and efficient DNA compaction is the major motivation in the study of interactions between DNA and photosensitive surfactants. In this article, using recently published approach of phase diagram construction [Y. Zakrevskyy, P. Cywinski, M. Cywinska, J. Paasche, N. Lomadze, O. Reich, H.-G. Löhmannsroben, and S. Santer, J. Chem. Phys. 140, 044907 (2014)], a strategy for substantial reduction of compaction agent concentration and simultaneous maintaining the light-induced decompaction efficiency is proposed. The role of ionic strength (NaCl concentration), as a very important environmental parameter, and surfactant structure (spacer length) on the changes of positions of phase transitions is investigated. Increase of ionic strength leads to increase of the surfactant concentration needed to compact DNA molecule. However, elongation of the spacer results to substantial reduction of this concentration. DNA compaction by surfactants with longer tails starts to take place in diluted solutions at charge ratios Z < 1 and is driven by azobenzene-aggregation compaction mechanism, which is responsible for efficient decompaction. Comparison of phase diagrams for different DNA-photosensitive surfactant systems allowed explanation and proposal of a strategy to overcome previously reported limitations of the light-induced decompaction for complexes with increasing surfactant hydrophobicity.
    The Journal of chemical physics. 10/2014; 141(16):164904.
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    ABSTRACT: The contraction/swelling transition of anionic PNIPAM-co-AAA particles can be manipulated by light using interactions with cationic azobenzene-containing surfactant. In this study the influence of pHbuffers and their concentrations, the charge density (AAA content) in microgel particles as well as the spacer length of the surfactant on the complex formation between the microgel and surfactant is investigated. It is shown that the presence of pH buffer can lead to complete blocking of the interactions in such complexes and the resulting microgel contraction/swelling response. There is a clear competition between the buffer ions and the surfactant molecules interacting with microgel particles. When working in pure water solutions with fixed concentration (charge density) of microgel, the contraction/swelling of the particles is controlled only by relative concentration (charge ratio) of the surfactant and AAA groups of the microgel. Furthermore, the particle contraction is more efficient for shorter spacer length of the surfactant. The onset point of the contraction process is not affected by the surfactant hydrophobicity. This work provides new insight into the interaction between microgel particles and photo-sensitive surfactants, which offers high potential in new sensor systems.
    Polymer 10/2014; 55:6513-6518. · 3.77 Impact Factor
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    Nataraja Sekhar Yadavalli, Svetlana Santer
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    ABSTRACT: When azo-modified photosensitive polymer films are irradiated with light interference patterns, topographic variations in the film develop that follow the E ⃗-field vector distribution resulting in the formation of surface relief grating (SRG). The exact correspondence of the E ⃗-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. Here, we report on 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).[1–3] 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.[4] This is the first time that an absolute correspondence between the local distribution of E ⃗-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 with characteristic features measuring only 140 nm, by using far field optics with a wavelength of 491 nm.[2] 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).[5–7] 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 E ⃗-field distribution in the interference pattern even when the magnitude and the kinetic of the strain are kept constant. The stresses developed during the polymer deformation appear to be so strong that even multi-layered graphene (thickness-10 nm) is deformed conveniently along SRG.[8] 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 a formation of bonding layer that confirms the transduction of light induced stresses in the polymer layer to a metal film.[9, 10] [1] N. S. Yadavalli and S. Santer. J. Appl. Phys. 113, 224304 (2013) [2] N. S. Yadavalli, M. Saphiannikova, N. Lomadze, L. M. Goldenberg, and S. Santer. Appl. Phys. A 113, 263 (2013) [3] G. Di Florio, E. Bründermann, N. S. Yadavalli, S. Santer, and M. Havenith. Soft Matter 10, 1544 (2014) [4] N. S. Yadavalli, M. Saphiannikova, and S. Santer. Appl. Phys. Lett. (2014) – accepted for publication [5] N. S. Yadavalli, F. Linde, A. Kopyshev, and S. Santer ACS Appl. Mater. Interfaces 5, 7743 (2013) [6] F. Linde, N. S. Yadavalli, and S. Santer. Appl. Phys. Lett. 103, 253101 (2013) [7] N. S. Yadavalli and S. Santer. ACS Division of Polymeric Materials: Science & Engineering 107, 213 (2012) – ISBN: 9781622762071 [8] G. Di Florio, E. Bründermann, N. S. Yadavalli, S. Santer, and M. Havenith. Soft Materials (2014) – revised [9] N. S. Yadavalli, J.-F. Moulin, D. Korolkov, M. Krutyeva, and S. Santer. MLZ Annual Report: Soft matter, 54 (2013) – Scientific Highlight [10] N. S. Yadavalli, D. Korolkov, J-F Moulin, M. Krutyeva, and S. Santer. ACS Appl. Mater. Interfaces (2014) – revised
    Polydays 2014, TU Berlin, Eugene Wigner Building, EW 201-­‐202, Hardenbergstr. 36; 10/2014
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    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, since the deformation takes place without photo-fluidization; the polymer is in a glassy state throughout. However, until now there has been no attempt to characterise 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 propert
    Nano Letters 09/2014; 14:5754-5760. · 13.03 Impact Factor
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    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 trans-cis 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.
    Applied Physics Letters 08/2014; 105(5):051601. · 3.52 Impact Factor
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    ABSTRACT: AbstractIn 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.
    Soft Materials 08/2014; · 1.43 Impact Factor
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    ABSTRACT: We use a photosensitive layer containing azobenzene moieties to map near field intensity patterns in the vicinity of nano grids 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 paper 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 nano grids. 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.
    ACS Applied Materials & Interfaces 07/2014; · 5.90 Impact Factor
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    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 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 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 kinetic 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 metal layer within the polymer resulting in a formation of bonding layer that confirms the transduction of light induced stresses in the polymer layer to a metal film.
    ACS Applied Materials & Interfaces 07/2014; · 5.90 Impact Factor
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    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.
    Soft Matter 02/2014; 10(10):1544-54. · 4.15 Impact Factor
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    Nataraja Sekhar Yadavalli, Svetlana Santer
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    ABSTRACT: There is a growing interest on having an integrated electronic functionality over three dimensional large area surfaces for over decade (viz., paper like thin displays on furniture, interconnects, robot sensor skin, intelligent medical bandages or surgical tools etc).1-4 Flexible polymer substrates sandwiched with electronic circuitry are increasingly in use for developing these applications. Understanding the perturbation of polymer substrate and the deforming behaviour of metallic thin films supposed to be the crucial challenges during the design of deformable electronics to avoid mechanical and electrical failure of the integrated and functionalized structures. Despite significant importance, studying the deformation of nanoscale metallic thin films below 50 nm remains a challenge. In the current investigation, we developed a method to apply optomechanical stress locally at nanoscopric scale to study the deformation of thin metal films of 5–50 nm. Further, the method also useful to probe the molecular level forces developed during the mass transport of the photosensitive polymer films under light irradiation. It is well known that the photosensitive polymer thin films containing azo-benzene groups, reacts strongly to light irradiation. During the irradiation with light interference pattern, photosensitive polymer film topography deforms and result in the formation of surface relief grating (SRG).5,6 SRG formation is a suitable phenomenon due the mass transport of polymer occurring in regular and periodic fashion across the polymer surface to apply optomechanical stress locally. Metallic films with a thickness varying between 5 to 50 nm are deposited on photosensitive polymer films and under suitable irradiation conditions, we observed and studied an interesting regular and irregular metallic film deformation and rupturing behaviour at different interfering beam conditions (±45 and RL) and the metal film thicknesses.7 We also studied the electrical conductivity behaviour of such deformed conductive metal films. 1. V. J. Lumelsky, M. S. Shur, and S. Wagner, IEEE Sensors J. 1, pp. 41–51 (2001). 2. J. Jones, S.P. Lacour and S. Wagner. MRS Proceedings, 863, B10.9 (2005). 3. I. Sample, New Scientist 170, 23 (2001). 4. J. Engel, J. Chen, C. Liu, B. R. Flachsbart, J. C. Selby, and M. A. Shannon, Mater. Res. Soc. Symp. Proc. 736 , pp. D.4.5.1-D4.5.6 (2003). 5. N. S. Yadavalli, and S. Santer. J Appl. Phys. 113, 224340 (2013). 6. N. S. Yadavalli, M. Saphiannikova, N. Lomadze, L. M. Goldenberg, and S. Santer. Appl. Phys. A 113, 263-272 (2013). 7. N. S. Yadavalli, F. Linde, A. Kopyshev and S. Santer. ACS Appl. Mater. Interfaces 5, 7743-7747 (2013).
    2nd International Symposium on "Integration of Molecular Components in Functional Macroscopic Systems", Hannover, Germany; 01/2014
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    ABSTRACT: Recently, photosensitive surfactants have re-attracted considerable attention. It has been shown that their association with oppositely charged biologically important polyelectrolytes, such as DNA or microgels, can be efficiently manipulated simply by light exposure. In this article, we investigate the self-assembly of photosensitive surfactants as well as their interactions with DNA by calorimetric and spectroscopic methods. Critical micelle concentration (CMC), standard micellization enthalpy, entropy, and Gibbs energy were determined in different conditions (ionic strengths and temperatures) for a series of cationic surfactants with an azobenzene group in their tail. It is shown, that aggregation forces of photosensitive units play an important role in the micellization giving the major contribution to the micellization enthalpy. The onset of the aggregation can be traced from shift of the absorption peak position in the UV-visible spectrum. Titration UV-visible spectroscopy is used as an alternative, simple, and sensitive approach to estimate CMC. The titration UV-visible spectroscopy was also employed to investigate interactions (CAC: critical aggregation concentration, precipitation, and colloidal stabilization) in the DNA-surfactant complex.
    The Journal of Chemical Physics. 01/2014; 140(4):044906.
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    ABSTRACT: In this paper, we investigate interactions and phase transitions in polyelectrolyte-surfactant complexes formed between a cationic azobenzene-containing surfactant and two types of polyelectrolytes: natural (DNA) or synthetic (PAA: poly acrylic acid). The construction of a phase diagram allowed distancing between four major phases: extended coil conformation, colloidally stable compacted globules, colloidal instability range, and surfactant-stabilized compact state. Investigation on the complexes' properties in different phases and under irradiation with UV light provides information about the role of the surfactant's hydrophobic trans isomers both in the formation and destruction of DNA and PAA globules as well as in their colloidal stabilization. The trans isomer shows much stronger affinity to the polyelectrolytes than the hydrophilic cis counterpart. There is no need for complete compensation of the polyelectrolyte charges to reach the complete compaction. On contrary to the findings previously reported in the literature, we demonstrate - for the first time - complete polyelectrolyte compaction which occurs already at 20% of DNA (and at 50% of PAA) charge compensation. The trans isomer plays the main role in the compaction. The aggregation between azobenzene units in the photosensitive surfactant is a driving force of this process. The decompaction can be realized during UV light irradiation and is strongly influenced by the interplay between surfactant-surfactant and surfactant-DNA interactions in the compacted globules.
    The Journal of Chemical Physics. 01/2014; 140(4):044907.
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    ABSTRACT: I n microfabrication processes, ultra-thin metallized polymers are commonly prepared using physical vapor deposition of a metal film on the polymer surface. During the deposition process, it is often expected that the metal layer will defuse into the polymer surface, thereby creating a bonding/sandwich layer near the metal/polymer interface. In this work, we demonstrate the presence of a diffused metal layer and its thickness using neutron reflectometry and also discuss the electrical conductivity and mechanical properties of these metallized polymers.
    MLZ annual report 2013. 01/2014;
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    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.
    Applied Physics Letters 12/2013; 103(25):253101. · 3.52 Impact Factor
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    ABSTRACT: We report on a change in the properties of monomolecular films of polyelectrolyte molecules, induced by illuminating the silicon substrate on which they adsorb. It was found that under illumination the thickness of the adsorbed layer decreases by at least 27% and at the same time the roughness is significantly reduced in comparison to a layer adsorbed without irradiation. Furthermore, the homogeneity of the film topography and the surface potential is shown to be improved by illumination. The effect is explained by a change in surface charge density under irradiation of n- and p-type silicon wafers. The altered charge density in turn induces conformational changes of the adsorbing polyelectrolyte molecules. Their photo-controlled adsorption opens new possibilities for selective manipulation of adsorbed films. This possibility is of potential importance for many applications such as the production of well defined coatings in biosensors or micro-electronics.
    Langmuir 12/2013; · 4.38 Impact Factor
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    ABSTRACT: In this paper we report on an opto-mechanical scission of polymer chains within photosensitive diblock-copolymer brushes grafted to flat solid substrates. We employe surface-initiated polymerization of methylmethacrylate (MMA) and t-butyl methacrylate (tBMA) to grow diblock-copolymer brushes of poly(methylmethacrylate-b-t-butyl methacrylate) following the atom transfer polymerization (ATRP) scheme. After the synthesis, de-protection of the PtBMA block yields poly(methacrylic acid) (PMAA). To render PMMA-b-PMAA copolymers photosensitive, cationic azobenzene containing surfactants are attached to the negatively-charged outer PMAA block. During irradiation with an ultraviolet (UV) interference pattern, the extent of photo-isomerization of the azobenzene groups varies spatially and results in a topography change of the brush, i.e., formation of surface relief gratings (SRG). The SRG formation is accompanied by local rupturing of the polymer chains in areas from which the polymer material recedes. This opto-mechanically induced scission of the polymer chains takes place at the interfaces of the two blocks and depends strongly on the UV irradiation intensity. Our results indicate that this process may be explained by employing classical continuum fracture mechanics, which might be important for tailoring the phenomenon for applying it to post-structuring of polymer brushes.
    Langmuir 10/2013; · 4.38 Impact Factor
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    ABSTRACT: There is a growing interest on having an integrated electronic functionality over three dimensional large area surfaces for over decade (viz., paper like thin displays on furniture, interconnects, robot sensor skin, intelligent medical bandages or surgical tools etc).1-4 Flexible polymer substrates sandwiched with electronic circuitry are increasingly in use for developing these applications. Understanding the perturbation of polymer substrate and the deforming behavior of metallic thin films supposed to be the crucial challenges during the design of deformable electronics to avoid mechanical and electrical failure of the integrated and functionalized structures. Despite significant importance, studying the deformation of nanoscale metallic thin films below 50 nm remains a challenge. In the current investigation, we developed a method to apply optomechanical stress locally at nanoscopric scale to study the deformation of thin metal films of 5–50 nm. Further, the method also useful to probe the molecular level forces developed during the mass transport of the photosensitive polymer films under light irradiation. It is well known that the photosensitive polymer thin films containing azo-benzene groups, reacts strongly to light irradiation. During the irradiation with light interference pattern, photosensitive polymer film topography deforms and result in the formation of surface relief grating (SRG).5,6 SRG formation is a suitable phenomenon due the mass transport of polymer occurring in regular and periodic fashion across the polymer surface to apply optomechanical stress locally. Metallic films with a thickness varying between 5 to 50 nm are deposited on photosensitive polymer films and under suitable irradiation conditions, we observed and studied an interesting regular and irregular metallic film deformation and rupturing behaviour at different interfering beam conditions (±45 and RL) and the metal film thicknesses.7 We also studied the electrical conductivity behaviour of such deformed conductive metal films. 1. V. J. Lumelsky, M. S. Shur, and S. Wagner, IEEE Sensors J. 1, pp. 41–51 (2001). 2. J. Jones, S.P. Lacour and S. Wagner. MRS Proceedings, 863, B10.9 (2005). 3. I. Sample, New Scientist 170, 23 (2001). 4. J. Engel, J. Chen, C. Liu, B. R. Flachsbart, J. C. Selby, and M. A. Shannon, Mater. Res. Soc. Symp. Proc. 736 , pp. D.4.5.1-D4.5.6 (2003). 5. N. S. Yadavalli, and S. Santer. J Appl. Phys. 113, 224340 (2013). 6. N. S. Yadavalli, M. Saphiannikova, N. Lomadze, L. M. Goldenberg, and S. Santer. Appl. Phys. A, (2013), DOI: 10.1007/s00339-013-7945-3. 7. N. S. Yadavalli, F. Linde, A. Kopyshev and S. Santer. ACS Appl. Mater. Interfaces 5, 7743-7747 (2013)
    Polymer Interphases, Frankfurt, Germany; 09/2013
  • DFG-SPP 1369, Frankfurt, Germany; 09/2013
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    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 due to excessive stress at local imperfections. Here we show that the seemingly random phenomena at macroscopic scales can be rendered rather controllable at sub-micron 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 nano-fabrication procedures mechanical in character.
    ACS Applied Materials & Interfaces 07/2013; · 5.90 Impact Factor
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    ABSTRACT: The effect of illumination on the thickness and roughness of monolayers of polycationic molecules of polyethyleneimine deposited from solution onto a silicon substrate was discovered and investigated. The super-bandgap illumination of the substrate during polyethyleneimine adsorption causes a decrease in both the roughness and integral thickness of the organic layer on n- and p-Si substrates.
    Technical Physics Letters 07/2013; 39(7):656-659. · 0.56 Impact Factor

Publication Stats

160 Citations
195.67 Total Impact Points

Institutions

  • 2011–2014
    • Universität Potsdam
      • Institute of Physics and Astronomy
      Potsdam, Brandenburg, Germany
    • University of Münster
      • Institute of Theoretical Physics
      Münster, North Rhine-Westphalia, Germany
  • 2004–2011
    • University of Freiburg
      • Department of Microsystems Engineering (IMTEK)
      Freiburg, Lower Saxony, Germany