On-going research activities

Here is listed the current research activities in the SEM group.

[1] Optical effects in polymers


The NanoPlast project is a HTF funded (Danish National Advanced Technology Foundation) project including partners from university and industry, where the goal is to create polymer components with functional surfaces using injection molding. The role of the SEM group is to design and demonstrate surfaces with optical functionalities such as anti reflection and structural color phenomena. The very big challenge is to create convincing effects in low index media while being limited by the condition that the structures must be suitable for injection molding.

Contact Person: Jeppe Clausen, jepcl@fotonik.dtu.dk

Related publications:
[1] A.B. Christiansen, J. Clausen, N.A. Mortensen, and A. Cristensen, "Minimizing scattering from antireflective surfaces replicated from low-aspect-ratio black silicon", Appl. Phys. Lett., 101, 131902 (2012).
[2] J. Clausen, A.B. Christiansen, J. Garnaes, N. A. Mortensen, and A. Kristensen, "Color effects from scattering on random surface structures in dielectrics", Opt. Express, 20, 4376 (2012).

[2] Advanced optical nanostructure for energy harvesting
plasmonics nanostructureThe project is to experimentally demonstrate advnaced optical nanostructure for energy harvesting, particularly focusing on plasmonic nanostructures for photovoltacis. The project will combine design, fabrication, and characterization of plasmonic improved thin film solar cell, and will have main focus on the experimental fabrication and characterization the effects of the plasmonic nanostructures on model cell performance. The project will be conducted in collaboration between the Department of Micro- and Nanotechnology and the Department of Photonics Engineering and it will be in strong synergy with the CASE (www.case.dtu.dk) initiative on enhancing catalysis and sustainable energy.

Contact Person: Xiaolong Zhu, xizhu@fotonik.dtu.dk

Related publications:
[1] X. Zhu, S. Xiao, L. Shi, X. Liu, J. Zi, O. Hansen, and N. A. Mortensen, "A stretch-tunable plasmonic structure with a polarization-dependent response", Opt. Express, 20, 5237 (2012).
[2] X. Zhu, F. Xie, L. Shi, X. Liu, N. A. Mortensen, S. Xiao, J. Zi, and W. Choy, "Broadband enhancement of spontaneous emission in a photonic-plasmonic structure", Opt. Lett., 37, 2037 (2012).
[3] X. Zhu, C. Zhang, X. Liu, O. Hansen, S. Xiao, N. A. Mortensen, and J. Zi, "Evaporation of water droplets on "lock-and-key" structures with nanoscale features", Langmuir, 28, 9201 (2012).
[4] X. Zhu, Y. Ou, V. Jokubavicius, M. Syvajarvi, O. Hansen, H. Ou, N.A. Mortensen, and S. Xiao, "Broadband light-extraction enhanced by arrays of whispering gallery resonators", Appl. Phys. Lett., 101, 241108 (2012). 

[3] Graphene plasmonics
grapheneThe field of graphene plasmonics is a novel, emerging research field at the intersection of condensed matter physics and photonics or more precisely, at the intersection between graphene physics and plasmonics. This field offers the promise of tunable plasmonic excitations - a tunability that is unavailable in the e.g. the widely studied field of metal plasmonics. In this project, we aim to study the properties of graphene plasmons theoretically in a range of finite and semi-infinite structures and to investigate potential applications in nanosensing and optoelectronics.

Contact Persons: Thomas Christensen, tomch@fotonik.dtu.dk, Xiaolong Zhu, xizhu@fotonik.dtu.dk

Related publications:
[1] X. Zhu, W. Yan, N.A. Mortensen, and S. Xiao, "Bends and splitters in graphene nanoribbon waveguides", Opt. Express, 21, 3486 (2013). 
[2] X. Zhu, W. Yan, P.U. Jepsen, O. Hansen, N.A. Mortensen, and S. Xiao, "Experimental observation of plasmons in a graphene monolayer resting on a two-dimensional subwavelength silicon grating", Appl. Phys. Lett., 102, 131101 (2013). 

[4] Graphene-reinforced Surface enhanced Raman Spectrocopy
SERSSurface enhanced Raman spectroscopy (SERS) is powerful for sensitive structural detection of bio-chemical compounds. Generally, nanostructured noblemetal substrates support SERS, but the nano-scale topography also challenges the sensing platform in terms of reproducibility, quenching, clean-ability, oxidation, and long-term mechanical stability. We address this need by exploring the concept of graphene-reinforced SERS substrates.

Contact person: Xiaolong Zhu, xizhu@fotonik.dtu.dk

Related publication:
X. Zhu, L. Shi, M.S. Schmidt, A. Boisen, O. Hansen, J. Zi, S.Xiao, and N. A. Mortensen, Enhanced light-matter interaction in graphene-coved gold nanovoid array, Nano Lett. 13, 4690 (2013).

[5] Active and passive mechanical structures

accousticFunctional mechanical materials combine disciplines from acoustics and elastodynamics to explore new material properties comprising striking wave phenomena. One task is the realization of an acoustic deaf material capable of absorbing sound from any direction with a wide spectral range. In this context we explore both ordered and random structures. Within this project we also aim at manipulating elastic waves by means of active piezoelectric structures to produce sound amplification with strong gain. Besides the ability to amplify sound we also study the possibility to engineer active systems with ultra high stiffness. Alongside our theoretical investigations we are accompanied by international experimental expertise.

Contact person: Johan Christensen, jochri@fotonik.dtu.dk

Related publications:
J. Christensen, V. Romero-García, R. Picó, A. Cebrecos, F.J. García de Abajo, N.A. Mortensen, M. Willatzen, and V.J. Sánchez-Morcillo, “Extraordinary absorption of sound in porous lamella-crystals” (submitted, 2013).
J. Christensen, Z. Liang, and M. Willatzen, “Metadevices for the confinement of sound and broadband double-negativity behavior” Phys. Rev. B, 88, 100301(R) (2013).
Z. Liang, M. Willatzen, J. Li and J. Christensen, "Tunable acoustic double negativity metamaterial", Sci. Rep. 2, 859 (2012).

[6] Quantum effects in nanoplasmonic metal structures 
quantum plasmonicsMiniaturization of photonic and plasmonic circuits is inevitable in the future, and there is therefore a need for a deeper understanding of the interaction between electromagnetic waves and matter, when objects are much smaller than the wavelength of the waves, i.e. on the order of 10 nm. The appearance of quantum mechanical effects in plasmons are anticipated at these size scales, and therefore the ability to experimentally probe and theoretically explain these quantum effects is of increasing importance. To this end, we use the superb spatial resolution capabilities of transmission electron microscopes at DTU Cen to probe the metallic nanostructures, while we theoretically include quantum effects in a semiclassical treatment based on the so-called hydrodynamic Drude model for the free electrons in metals. With this perfect combination, we are capable of calculating and measuring quantum mechanical effects in plasmons.

Contact Persons: Søren Raza, sraz@fotonik.dtu.dk,  Nicolas Stengers, niste@fotonik.dtu.dk.

Related publications:
[1] S. Raza, G. Toscano, A.-P. Jauho, M. Wubs, and N.A. Mortensen, "Unusual resonances in nanoplasmonic structures due to nonlocal response", Phys. Rev. B, 84, 121412 (R), 2011. 
[2] G. Toscano, S. Raza, A.-P. Jauho, N.A. Mortensen and M. Wubs, "Modified field enhancement in plasmonic nanowire dimers due to nonlocal response", Opt. Express, 20, 4176 (2012).
[3] G. Toscano, S. Raza, S. Xiao, M. Wubs,  A.-P. Jauho, S.I. Bozhevolnyi, and N.A. Mortensen, "Surface-enhanced Raman spectroscopy (SERS): nonlocal limitations", Opt. Lett., 37, 2538 (2012).
[4] G. Toscano, S. Raza, W. Yan, C. Jeppesen, S. Xiao, M. Wubs, A.-P. Jauho, S.I. Bozhevolnyi, and N.A. Mortensen, "Nonlocal response in plasmonic waveguiding with extreme light confinement", Nanophotonics, 2, 106 (2013). 
[5] S. Raza, T. Christensen, M. Wubs, S.I. Bozhevolnyi, and N.A. Mortensen, "Nonlocal response in thin-film waveguides: loss versus nonlocality and breaking of complementarity", Phys. Rev. B 88, 115401 (2013).

[7] Quantum optics of metamaterials
QOMetamaterials are engineered materials with optical properties often not occurring in nature. They have unit cells much smaller than an optical wavelength. Their optical properties can be described by effective parameters such as the effective refractive index. Most metamaterials are designed to interact with classical light. We study the use of metamaterials to transport and modify quantum states of light, for example squeezed light or single photons, and ask questions like: (1) Are the metamaterials also useful in quantum optics? (2) Do we need to modify the effective description of the metamaterial? (3) Are there new fundamental limits in the use of metamaterials in quantum optics?

Contact person: Martijn Wubs, mwubs@fotonik.dtu.dk

Related publication:
[1] E. Amooghorban, N.A. Mortensen, and M. Wubs, "Quantum optical effective-medium theory for loss-compensated metamaterials", Phys. Rev. Lett., 110, 153602 (2013).