Staff directory Nikolaos Kehagias



  • All-optical radio-frequency modulation of Anderson-localized modes

    Arregui G., Navarro-Urrios D., Kehagias N., Torres C.M.S., García P.D. Physical Review B; 98 (18, 180202) 2018. 10.1103/PhysRevB.98.180202. IF: 3.813

    All-optical modulation of light relies on exploiting intrinsic material nonlinearities [V. R. Almeida, Nature 431, 1081 (2004)NATUAS0028-083610.1038/nature02921]. However, this optical control is rather challenging due to the weak dependence of the refractive index and absorption coefficients on the concentration of free carriers in standard semiconductors [R. A. Soref and B. R. Bennett, Proc. SPIE 704, 32 (1987)PSISDG0277-786X10.1117/12.937193]. To overcome this limitation, resonant structures with high spatial and spectral confinement are carefully designed to enhance the stored electromagnetic energy, thereby requiring lower excitation power to achieve significant nonlinear effects [K. Nozaki, Nat. Photonics 4, 477 (2010)1749-488510.1038/nphoton.2010.89]. Small mode-volume and high-quality (Q)-factor cavities also offer an efficient coherent control of the light field and the targeted optical properties. Here, we report on optical resonances reaching Q∼105 induced by disorder on photonic/phononic-crystal waveguides. At relatively low excitation powers (below 1mW), these cavities exhibit nonlinear effects leading to periodic (up to ∼35 MHz) oscillations of their resonant wavelength. Our system represents a test bed to study the interplay between structural complexity and material nonlinearities and their impact on localization phenomena and introduces a different functionality to the toolset of disordered photonics. © 2018 American Physical Society.

  • Design of a Multifunctional Nanoengineered PLLA Surface by Maximizing the Synergies between Biochemical and Surface Design Bactericidal Effects

    Nerantzaki M., Kehagias N., Francone A., Fernández A., Sotomayor Torres C.M., Papi R., Choli-Papadopoulou T., Bikiaris D.N. ACS Omega; 3 (2): 1509 - 1521. 2018. 10.1021/acsomega.7b01756. IF: 0.000

    Nanotechnology, the manipulation of matter on atomic, molecular, and supramolecular scales, has become the most appealing strategy for biomedical applications and is of great interest as an approach to preventing microbial risks. In this study, we utilize the antimicrobial performance and the drug-loading ability of novel nanoparticles based on silicon oxide and strontium-substituted hydroxyapatite to develop nanocomposite antimicrobial films based on a poly(l-lactic acid) (PLLA) polymer. We also demonstrate that nanoimprint lithography (NIL), a process adaptable to industrial application, is a feasible fabrication technique to modify the surface of PLLA, to alter its physical properties, and to utilize it for antibacterial applications. Various nanocomposite PLLA films with nanosized (black silicon) and three-dimensional (hierarchical) hybrid domains were fabricated by thermal NIL, and their bactericidal activity against Escherichia coli and Staphylococcus aureus was assessed. Our findings demonstrate that besides hydrophobicity the nanoparticle antibiotic delivery and the surface roughness are essential factors that affect the biofilm formation. © 2018 American Chemical Society.

  • Fabrication and replication of re-entrant structures by nanoimprint lithography methods

    Kehagias N., Francone A., Guttmann M., Winkler F., Fernández A., Torres C.M.S. Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics; 36 (6, 06JF01) 2018. 10.1116/1.5048241. IF: 1.314

    In this work, the authors present and demonstrate a simple method to fabricate and mass replicate re-entrant structures. The method consists of the direct imprinting of polymer mushroomlike microstructures produced by a combination of photolithography and nickel up-plating process. In particular, they have studied the conditions to generate highly robust mushroomlike topographies and their topographical impact on the replication process. They discuss all the imprinting conditions suitable to replicate such topographies using both ultraviolet light assisted nanoimprint lithography (UV-NIL) and thermal NIL methods in two polymer films, poly(methyl methacrylate) and polypropylene, and a hybrid (organic-inorganic) UV light curable photoresist, namely, Ormocomp. Re-entrant topographies have been widely studied for liquid/oil repelling and dry adhesive properties, whereas in their experiments, they have proved evidence for their amphiphobic potential. © 2018 Author(s).

  • In-line metrology for roll-to-roll UV assisted nanoimprint lithography using diffractometry

    Kreuzer M., Whitworth G.L., Francone A., Gomis-Bresco J., Kehagias N., Sotomayor-Torres C.M. APL Materials; 6 (5, 058502) 2018. 10.1063/1.5011740. IF: 4.127

    We describe and discuss the optical design of a diffractometer to carry out in-line quality control during roll-to-roll nanoimprinting. The tool measures diffractograms in reflection geometry, through an aspheric lens to gain fast, non-invasive information of any changes to the critical dimensions of target grating structures. A stepwise tapered linear grating with constant period was fabricated in order to detect the variation in grating linewidth through diffractometry. The minimum feature change detected was ∼40 nm to a precision of 10 nm. The diffractometer was then integrated with a roll-to-roll UV assisted nanoimprint lithography machine to gain dynamic measurements in situ. © 2018 Author(s).

  • Integrated 3D hydrogel waveguide out-coupler by step-and-repeat thermal nanoimprint lithography: A promising sensor device for water and pH

    Francone A., Kehoe T., Obieta I., Saez-Martinez V., Bilbao L., Khokhar A.Z., Gadegaard N., Simao C.D., Kehagias N., Sotomayor Torres C.M. Sensors (Switzerland); 18 (10, 3240) 2018. 10.3390/s18103240. IF: 2.475

    Hydrogel materials offer many advantages for chemical and biological sensoring due to their response to a small change in their environment with a related change in volume. Several designs have been outlined in the literature in the specific field of hydrogel-based optical sensors, reporting a large number of steps for their fabrication. In this work we present a three-dimensional, hydrogel-based sensor the structure of which is fabricated in a single step using thermal nanoimprint lithography. The sensor is based on a waveguide with a grating readout section. A specific hydrogel formulation, based on a combination of PEGDMA (Poly(Ethylene Glycol DiMethAcrylate)), NIPAAm (N-IsoPropylAcrylAmide), and AA (Acrylic Acid), was developed. This stimulus-responsive hydrogel is sensitive to pH and to water. Moreover, the hydrogel has been modified to be suitable for fabrication by thermal nanoimprint lithography. Once stimulated, the hydrogel-based sensor changes its topography, which is characterised physically by AFM and SEM, and optically using a specific optical set-up. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.


  • Design of Hierarchical Surfaces for Tuning Wetting Characteristics

    Fernández A., Francone A., Thamdrup L.H., Johansson A., Bilenberg B., Nielsen T., Guttmann M., Sotomayor Torres C.M., Kehagias N. ACS Applied Materials and Interfaces; 9 (8): 7701 - 7709. 2017. 10.1021/acsami.6b13615. IF: 7.504

    Patterned surfaces with tunable wetting properties are described. A hybrid hierarchical surface realized by combining two different materials exhibits different wetting states, depending on the speed of impingement of the water droplets. Both "lotus" (high contact angle and low adhesion) and "petal" (high contact angle and high adhesion) states were observed on the same surface without the need of any modification of the surface. The great difference between the capillary pressures exerted by the microstructures and nanostructures was the key factor that allowed us to tailor effectively the adhesiveness of the water droplets. Having a low capillary pressure for the microstructures and a high capillary pressure for the nanostructures, we allow to the surface the possibility of being in a lotus state or in a petal state. © 2017 American Chemical Society.

  • Hierarchical surfaces for enhanced self-cleaning applications

    Fernández A., Francone A., Thamdrup L.H., Johansson A., Bilenberg B., Nielsen T., Guttmann M., Sotomayor Torres C.M., Kehagias N. Journal of Micromechanics and Microengineering; 27 (4, 045020) 2017. 10.1088/1361-6439/aa62bb. IF: 1.794

    In this study we present a flexible and adaptable fabrication method to create complex hierarchical structures over inherently hydrophobic resist materials. We have tested these surfaces for their superhydrophobic behaviour and successfully verified their self-cleaning properties. The followed approach allow us to design and produce superhydrophobic surfaces in a reproducible manner. We have analysed different combination of hierarchical micro-nanostructures for their application to self-cleaning surfaces. A static contact angle value of 170 with a hysteresis of 4 was achieved without the need of any additional chemical treatment on the fabricated hierarchical structures. Dynamic effects were analysed on these surfaces, obtaining a remarkable self-cleaning effect as well as a good robustness over impacting droplets. © 2017 IOP Publishing Ltd.


  • Residual layer-free Reverse Nanoimprint Lithography on silicon and metal-coated substrates

    Fernández A., Medina J., Benkel C., Guttmann M., Bilenberg B., Thamdrup L.H., Nielsen T., Sotomayor Torres C.M., Kehagias N. Microelectronic Engineering; 141: 56 - 61. 2015. 10.1016/j.mee.2014.11.025. IF: 1.197

    In this work we demonstrate that Reverse Nanoimprint Lithography is a feasible and flexible lithography technique applicable to the transfer of micro and nano polymer structures with no residual layer over areas of cm2 areas on silicon, metal and non-planar substrates. We used a flexible polydimethylsiloxane stamp with hydrophobic features. We present residual layer-free patterns imprinted using a commercial poly(methylmethacrylate) thermoplastic polymer over silicon, nickel and pre-patterned substrates. Our versatile patterning technology is adaptable to free form nano structuring and has coupling to adhesion technologies. © 2014 Elsevier B.V. All rights reserved.


  • Embedded inkjet printed silver grids for ITO-free organic solar cells with high fill factor

    Burgués-Ceballos, I.; Kehagias, N.; Sotomayor-Torres, C.M.; Campoy-Quiles, M.; Lacharmoise, P.D. Solar Energy Materials and Solar Cells; 127: 50 - 57. 2014. 10.1016/j.solmat.2014.03.024. IF: 5.030

  • Hypersonic phonon propagation in one-dimensional surface phononic crystal

    Graczykowski, B.; Sledzinska, M.; Kehagias, N.; Alzina, F.; Reparaz, J.S.; Sotomayor Torres, C.M. Applied Physics Letters; 2014. 10.1063/1.4870045. IF: 3.515

  • Order quantification of hexagonal periodic arrays fabricated by in situ solvent-assisted nanoimprint lithography of block copolymers

    Simão, C.; Khunsin, W.; Kehagias, N.; Salaun, M.; Zelsmann, M.; Morris, M.A.; Sotomayor Torres, C.M. Nanotechnology; 2014. 10.1088/0957-4484/25/17/175703. IF: 3.672


  • Fabrication of highly ordered sub-20 nm silicon nanopillars by block copolymer lithography combined with resist design

    Salaun, M.; Zelsmann, M.; Archambault, S.; Borah, D.; Kehagias, N.; Simao, C.; Lorret, O.; Shaw, M.T.; Sotomayor Torres, C.M.; Morris, M.A. Journal of Materials Chemistry C; 1 (22): 3544 - 3550. 2013. 10.1039/c3tc30300d. IF: 6.108

  • Lasing in nanoimprinted two-dimensional photonic crystal band-edge lasers

    Reboud, V.; Romero-Vivas, J.; Lovera, P.; Kehagias, N.; Kehoe, T.; Redmond, G.; Sotomayor Torres, C.M. Applied Physics Letters; 2013. 10.1063/1.4790646. IF: 3.794

  • Metallic nanoparticles enhanced the spontaneous emission of semiconductor nanocrystals embedded in nanoimprinted photonic crystals

    Reboud, V.; Lévêque, G.; Striccoli, M.; Placido, T.; Panniello, A.; Curri, M.L.; Alducin, J.A.; Kehoe, T.; Kehagias, N.; Mecerreyes, D.; Newcomb, S.B.; Iacopino, D.; Redmond, G.; Torres, C.M.S. Nanoscale; 5 (1): 239 - 245-245. 2013. 10.1039/c2nr32134c. IF: 6.233

  • Robust spin crossover platforms with synchronized spin switch and polymer phase transition

    Novio, F.; Evangelio, E.; Vazquez-Mera, N.; González-Monje, P.; Bellido, E.; Mendes, S.; Kehagias, N.; Ruiz-Molina, D. Scientific Reports; 3 2013. 10.1038/srep01708. IF: 2.927

  • Soft-graphoepitaxy using nanoimprinted polyhedral oligomeric silsesquioxane substrates for the directed self-Assembly of PS-b-PDMS

    Borah, D.; Simao, C.D.; Senthamaraikannan, R.; Rasappa, S.; Francone, A.; Lorret, O.; Salaun, M.; Kosmala, B.; Kehagias, N.; Zelsmann, M.; Sotomayor-Torres, C.M.; Morris, M.A. European Polymer Journal; 49 (11): 3512 - 3521-3521. 2013. 10.1016/j.eurpolymj.2013.08.011. IF: 2.562


  • Enhanced light extraction in ITO-free OLEDs using double-sided printed electrodes

    Reboud, V.; Khokhar, A.Z.; Sepúlveda, B.; Dudek, D.; Kehoe, T.; Cuffe, J.; Kehagias, N.; Lira-Cantu, M.; Gadegaard, N.; Grasso, V.; Lambertini, V.; Sotomayor Torres, C.M. Nanoscale; 4 (11): 3495 - 3500. 2012. .

  • Polymer photonic band-gaps fabricated by nanoimprint lithography.

    Reboud, V. ; Kehoe, T.; Romero Vivas, J.; Kehagias, N.; Zelsmannd, M.; Alsina, F.; Sotomayor Torres, C.M. Photonics and Nanostructures - Fundamentals and Applications; 10: 632 - 635. 2012. .

  • Soft graphoepitaxy of hexagonal PS-b-PDMS on nanopatterned POSS surfaces fabricated by nanoimprint lithography

    Simao, C.; Francone, A.; Borah, D.; Lorret, O.; Salaun, M.; Kosmala, B. ; Shaw, M.T.; Dittert, B.; Kehagias, N.; Zelsmann, M.; Morris, M.A.; Sotomayor Torres, C.M. Journal of Photopolymer Science and Technology; 25(2): 239 - 244. 2012. .


  • Direct top-down ordering of diblock copolymers through nanoimprint lithography

    Salaün, M.; Kehagias, N.; Salhi, B.; Baron, T.; Boussey, J.; Sotomayor Torres, C.M.; Zelsmann, M. Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures; 29 2011. 10.1116/1.3662399.

  • Fine control of critical dimension for the fabrication of large bandgap high frequency photonic and phononic crystals

    Cuffe, J. ; Dudek, D.; Kehagias, N.; Chapuis, P.O.; Reboud, V.; Alsina, F. ; McInerney, J.G.; Sotomayor Torres, C.M. Microelectronic Engineering; 2011. .

  • Low temperature direct imprint of polyhedral oligomeric silsesquioxane (POSS) resist

    Kehagias, N.; Zelsmann, M.; Chouiki, M.; Francone, A.; Reboud, V.; Schoeftner, R.; Sotomayor Torres, C. Microelectronic Engineering; 2011. .

  • Surface-Directed Dewetting of a Block Copolymer for Fabricating Highly Uniform Nanostructured Microdroplets and Concentric Nanorings

    Farrell, R.A.; Kehagias, N.; Shaw, M.T.; Reboud, V.; Zelsmann, M.; Holmes, J.D.; Sotomayor Torres, C.M.; Morris, M.A. ACS Nano; 2011. .


  • Tuning the Intensity of Metal-Enhanced Fluorescence by Engineering Silver Nanoparticle Arrays

    Yang, B.; Lu, N.; Qi, D.; Ma, R.; Wu, A.; Hao, J.; Liu, X.; Mu, Y.; Reboud, V.; Kehagias, N.;Sotomayor Torres, C.M.; Yin Chiang Boey, F.; Chen, X.; Chi, L. Small; 2010. .


  • Inline metrology configuration for sub-wavelength diffraction using microscope optics

    T. Kehoe; V. Reboud; N.Kehagias; C.M. Sotomayor Microelectronic Engineering; 86 (04-juny): 1036 - 1039. 2009. .

  • Nanoimprinted plasmonic crystals for light extraction applications

    V. Reboud; N. Kehagias; T. Kehoe; G. Leveque; C. Mavidis; M. Kafesaki.; C.M. Sotomayor Microelectronic Engineering; 87: 1367 - 1369. 2009. 10.1016/j.mee.2009.12.030.

  • Stamp replication for thermal and UV nanoimprint lithography using a UV sensitive silsesquioxane resist

    N. Kehagias; V. Reboud; Girolamo; M. Chouiki; M. Zelsmann; J. Boussey; C.M. Sotomayor Microelectronic Engineering; 86: 1036 - 1039. 2009. 10.1016/j.mee.2009.01.052.

  • Tuning the intensity of metal enhanced fluorescence by engineering silver nanoparticle arrays

    B. Yang; N. Lu; D. Qi; Q. Wu; J. Hao; R. Ma; X. Liu; Y. Mu; V. Reboud; N. Kehagias; C. M. Sotomayor; F.Y. Chiang; X. Chen and L. Chi Small; 6 (9): 1038 - 1043. 2009. 10.1002/smll.200902350.


  • Fabrication of defect-free nanoimprinted photonic crystal for laser applications

    V Reboud; N Kehagias; M Striccoli; T Placido; A Panniello; M L Curri; M Zelsmann; F Reuther; G Gruetzner; C M Sotomayor Torres Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes; 47: 5139 - 5141. 2008. 10.1143/JJAP.47.5139.

  • Modification of spontaneous emission of (CdSe)ZnS nanocrystals embedded in nanoimprinted photonic crystals

    V. Reboud; N. Kehagias; M. Zelsmann; M. Striccoli; M. Tamborra; M. L. Curri; A. Agostiano; M. Fink; F. Reuther; G. Gruetzner; C. M. Sotomayor Torres Journal of Nanoscience and Nanotechnology; 8: 535 - 539. 2008. 10.1166/jnn.2008.A143.

  • Nanoimprint lithography and surface modification as prospective technologies for heterogeneous integration

    N Kehagias; W Hu; N Lu; L Chi; H Fuchs; A Genua; J A Alduncin; J A Pomposo; D Mecerreyes; C M Sotomayor Torres Physica Status Solidi (C) Current Topics in Solid State Physics; 5: 3671 - 3575. 2008. 10.1002/pssc.200780226 .

  • Residual layer thickness in nanoimprint: experiments and coarse-grain simulation

    N Kehagias; V Reboud; C M Sotomayor Torres; V Sorotin; A Svintsov; S Zaitsev Microelectronic Engineering; 85: 846 - 849. 2008. 10.1016/j.mee.2007.12.041.


  • Embedded nano channels fabricated by non-selective reverse contact UV nanoimprint lithography technique

    N. Kehagias; G. Chansin; V. Reboud; M. Zelsmann; C. Schuster; M. Kubenz; F. Reuther; G. Gruetzner; C. M. Sotomayor Torres Microelectronic Engineering; 10: 1016. 2007. .

  • Functional patterns obtained by nanoimprinting lithography and subsequent growth of polymer brushes

    A Genua; J. A. Alduncín; J. A. Pomposo; N Kehagias; V. Reboud; C. M. Sotomayor Torres; D. Mecerreyes Nanotechnology; 2007. 10.1088/0957-4484/18/21/215301.

  • Multicolor Emission on Prepatterned Substrates Using a Single Dye Species

    W. Hu; N. Lu; H. Zhang; Y. Wang; N. Kehagias; V. Reboud; C. M. Sotomayor Torres; J. Hao; W. Li; H. Fuchs; L. Chi Advanced Materials; 19: 2119 - 2123. 2007. 10.1002/adma.200602491.

  • Photoluminescence enhancement in metallic nanocomposite printable polymer

    V. Reboud; N. Kehagias; M. Striccoli; T. Placido; A. Panniello; M. L. Curri; M. Zelsmann; F. Reuther; G. Gruetzner; C. M. Sotomayor Torres Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures; 2007. .

  • Photoluminescence enhancement in nanoimprinted photonic crystals and coupled surface plasmons

    V. Reboud; N. Kehagias; M. Zelsmann; C. Schuster; M. Fink; F. Reuther; G. Gruetzner; C. M. Sotomayor Torres Optics Express; 2007. .

  • Reverse-contact UV nanoimprint lithography for multilayered structure fabrication

    N Kehagias; V Reboud; G Chansin; M Zelsmann; C Jeppesen; C Schuster; M Kubenz; F Reuther; G Gruetzner; C M Sotomayor Torres Nanotechnology; 2007. .

  • Spontaneous emission control of colloidal nanocrystals using nanoimprinted photonic crystals,

    V. Reboud; N. Kehagias; M. Zelsmann; M. Striccoli; M. Tamborra; M. L. Curri; A. Agostiano; M. Fink; F. Reuther; G. Gruetzner; C. M. Sotomayor Torres Applied Physics Letters; 90: 11114. 2007. .

  • Spontaneous emission of nanocrystals in nanoimprinted photonic structures

    V. Reboud; N. Kehagias; M. Zelsmann; M. Striccoli; M. Tamborra; M. L. Curri; A. Agostiano; M. Fink; F. Reuther; G. Gruetzner; C. M. Sotomayor Torres Microelectronic Engineering; 10: 1016. 2007. .

  • Two-dimensional polymer photonic crystal band-edge lasers fabricated by nanoimprint lithography

    V. Reboud; P. Lovera; N. Kehagias; M. Zelsmann; C. Schuster; F. Reuther; G. Gruetzner; G. Redmond; C. M. Sotomayor Torres Applied Physics Letters; 91: 15110. 2007. .