Nanophotonics group

The nanophotonics research group, lead by Prof. Tapio Niemi, conducts applied and theoretical research on nanophotonic structures and develops novel nanofabrication methods. Our research includes the fields of plasmonics, metamaterials, resonant nanostructures and nanoparticles.

Tapio Niemi Professor

Janne Simonen Senior Researcher

Juha Kontio Researcher

Chunlei Tan Researcher

Outi Hyvärinen Researcher

Turkka Salminen Researcher

Contents

• Recent research areas
• • Metallic nanocones by UV-nanoimprint lithography
  • Second harmonic generation in silicon nitride films
  • Resonant waveguide gratings
  • Fabrication of nanoparticles by pulsed laser ablation in liquids
  • Active plasmonics and low-loss metamaterials
  • Nanostructures by laser interference lithography
• Projects
• Publications
• Contact

Recent research areas

Metallic nanocones by UV-nanoimprint lithography

Metallic nanostructures with sharp features are highly useful in plasmonics as they are very efficient in concentrating incident light, in a sense acting as optical antennas. A so-called lightning rod effect that also works in macroscale is mostly responsible for this, but particle plasmon resonances can also play a key role.

We have developed a cost-effective method for fabricating large arrays of metallic nanocones by nanoimprint lithography [Microelectr. Eng. 2010]. The method can be adapted to work with different materials and also more complex geometries are possible.

We have demonstrated that our gold cones can enhance second-harmonic generation by two orders of magnitude compared to an array of non-sharp reference cones [Opt. Lett. 2009]. We have also shown that a bridged double-cone structure was found to increase tip-enhanced Raman signal from crystal violet molecules by nearly an order of magnitude [Opt. Express 2010]. Moreover, our cones were used to demonstrate a novel second-harmonic generation imaging method [Nano Lett. 2012].

This work is partly done in collaboration with the Nonlinear Optics Laboratory at TUT and the University of Eastern Finland in project, REDMETA, funded by the Academy of Finland.

Contacts: Juha Kontio, Janne Simonen.

Second harmonic generation in silicon nitride films

Second harmonic generation is an optical process where light of frequency f interacts with a material and produces light of frequency 2f, double frequency or half the wavelength of the original incident light. This effect is highly useful in active optical components, such as electro-optic modulators and frequency converters.

Silicon nitride (SiN) is a CMOS compatible material that is widely used on the silicon-on-insulator (SOI) platform. It is thought to be amorphous and centro-cymmetric with no second order nonlinear response. However, we have observed that our PE-CVD-produced silicon nitride films have an effective second-order suspectibility 60 times higher than what has been previously reported [Appl. Phys. Lett. 2012].

This work is done in collaboration with the Nonlinear Optics Laboratory at TUT in project REDMETA, funded by the Academy of Finland.

Contacts: Outi Hyvärinen, Janne Simonen.

Resonant waveguide gratings

Resonant waveguide gratings (RWG) consist of a waveguide and a surface grating that diffracts light both into and out of the waveguide mode for a particular angle of incidence. Significantly, RWGs can also lead to strong local fields within the structure, enhancing light-matter interaction in processes such as two-photon fluorescence or second-harmonic generation (SHG).

We have demonstrated SHG enhancement by a factor of about 1000 from a purely dielectric sub-wavelength RWG compared to a thin-film of the same material of comparable thickness and in optimum geometry.

Moreover, we have shown that a broadband mirror for the IR wavelength region comprising a subwavelength grating made of germanium, a dielectric material with a very high refractive index. The reflectivity of the mirror was over 95% for the wavelength range between 2245 and 3080 nm [Opt. Lett. 2010].

This work is partly done in collaboration with the Nonlinear Optics Laboratory at TUT and the University of Eastern Finland in project REDMETA, funded by the Academy of Finland.

Contacts: Outi Hyvärinen, Juha Kontio, Janne Simonen.

Fabrication of nanoparticles by pulsed laser ablation in liquids

Pulsed laser ablation is used to produce nanoparticles by evaporation of materials that are submerged in liquids. The method can be used to fabricate e.g. metal, oxide and semiconductor nanoparticles. Possible application areas include sensors, light sources, photovoltaics, plasmonics and fluorescent labeling.

Nanoparticles can be formed in pure solvents, such as water or alcohols. This allows the production of pure nanoparticles, free from undesirable residue chemicals that often deteriorate the quality of nanoparticles produced by chemical synthesis.

During the process, nanoparticles produced by laser ablation in liquids are very reactive. The addition of reactants or conjugating molecules into the process solvent enables single-step production of complex nanoparticles, such as surface-passivated GaAs-nanocrystals [Opt. Mater. Express 2012] and gold/silicon core/shell nanoparticles [Phys. Chem. Chem. Phys. 2013].

The research focuses on four different areas:

• the physical processes involved in the formation of the particles
• up-scaling of the production process
• investigation of  the (optical) properties of the particles
• development of device applications

In our current European Regional Development Fund-funded project a steering group consisting of members from TUT and industrial partners is set up to support networking and seeking application possibilities for this technology.

Contacts: Turkka Salminen, Tapio Niemi.

Active plasmonics and low-loss metamaterials

A major disadvantage of using metals in plasmonics and metamaterials is their inherent absorption losses. Bringing the technology from the research labs to applications requires that the losses be reduced considerably. On the other hand, plasmonic nanostructures can be of considerable help in extracting light out of devices such as organic light-emitting diodes (OLEDs).

One route for loss-reduction is to introduce light amplifying media, i.e. gain into the components. Together with the Nanophotonics Laboratory at RIKEN, Japan, we have been involved in studies concerning plasmon-enhanced OLEDs [Appl. Phys. Lett. 2007] and plasmonic lasers [Opt. Comm. 2011].

On the other hand, the natural approach at ORC is to incorporate III-V semiconductor quantum wells and dots. This work is done in project ACEPLAN funded by ERA-NET NanoSci-E+ program. The partners are prof. Ortwin Hess from Imperial College London and Dr. Antonella Bogoni from the Integrated Research Center for Photonic Networks and Technologies, CNIT.

Contacts: Outi Hyvärinen, Janne Simonen.

Nanostructures fabricated by laser interference lithography

Laser interference lithography (LIL) is a maskless technique with high efficiency and low cost. It is ideal for the fabrication of periodic patterns on a large scale.  We have proved, both theoretically and experimentally, that LIL can also make graded structures [New J. Phys. 2008]. The focusing effect of a graded photonic crystal was analyzed theoretically [Opt. Comm., accepted].

Moreover, 'direct writing' was realized on GaAs-related wafers [Nanotechnology 2009] and Si wafers when a high-power pulse laser was used. As no resist is needed in the process the processing time is reduced.

This work is conducted within the Marie Curie IRSES project Laser Nanoscale Manufacturing (LaserNaMi) that focuses on staff exchange between partners in EU and China.

Contacts: Chunlei Tan, Tapio Niemi.

Projects

• ACEPLAN (EU ERA-NET NanoSci-E+): Active plasmonics and lossless metamaterials.
• LaserNano (Pirkanmaan liitto): Laser based fabrication and modification of nanomaterials.
• NEREUS (Academy of Finland): Negative refraction in semiconductor and photonics crystal metamaterials.
• Produla (Tekes): Photonics production platform.
• REDMETA (Academy of Finland): Resonance-domain metamaterials for subwavelength optics.

>> Full project list of ORC.

Publications

1. C. Tan, J. Simonen, and T. Niemi, “Hybrid waveguide-surface plasmon polariton modes in a guided-mode resonance grating,” Opt. Commun. 285(21-22), 4381-4386 (2012) [doi:10.1016/j.optcom.2012.07.027].
2. T. Salminen, M. Honkanen, and T. Niemi, “Coating of gold nanoparticles made by pulsed laser ablation in liquids with silica shells by simultaneous chemical synthesis,” Phys. Chem. Chem. Phys. (2012) [doi:10.1039/C2CP42999C].
3. T. Salminen, J. Dahl, M. Tuominen, P. Laukkanen, E. Arola, and T. Niemi, “Single-step fabrication of luminescent GaAs nanocrystals by pulsed laser ablation in liquids,” Opt. Mater. Express 2(6), 799–813 (2012) [doi:10.1364/OME.2.000799].
4. T. Ning, H. Pietarinen, O. Hyvärinen, J. Simonen, G. Genty, and M. Kauranen, “Strong second-harmonic generation in silicon nitride films,” Appl. Phys. Lett. 100(16), 161902–161902–4 (2012) [doi:10.1063/1.4704159].
5. G. Bautista, M. J. Huttunen, J. Mäkitalo, J. M. Kontio, J. Simonen, and M. Kauranen, “Second-Harmonic Generation Imaging of Metal Nano-Objects with Cylindrical Vector Beams,” Nano Lett. 12(6), 3207–3212 (2012) [doi:10.1021/nl301190x].
6. Y. Bai, J. Feng, Y.-F. Liu, J.-F. Song, J. Simonen, Y. Jin, Q.-D. Chen, J. Zi, and H.-B. Sun, “Outcoupling of trapped optical modes in organic light-emitting devices with one-step fabricated periodic corrugation by laser ablation,” Organic Electronics 12(11), 1927–1935 (2011) [doi:10.1016/j.orgel.2011.08.004].
7. C. Tan, T. Niemi, C. Peng, and M. Pessa, “Focusing effect of a graded index photonic crystal lens,” Opt. Commun. 284(12), 3140–3143 (2011) [doi:10.1016/j.optcom.2011.02.067].
8. F. H’Dhili, T. Okamoto, J. Simonen, and S. Kawata, “Improving the emission efficiency of periodic plasmonic structures for lasing applications,” Opt. Commun. 284(2), 561–566 (2011) [doi:10.1016/j.optcom.2010.09.052].
9. S. Rao, M. J. Huttunen, J. M. Kontio, J. Makitalo, M.-R. Viljanen, J. Simonen, M. Kauranen, and D. Petrov, “Tip-enhanced Raman scattering from bridged nanocones,” Opt. Express 18(23), 23790–23795 (2010) [doi:10.1364/OE.18.023790].
10. J. M. Kontio, J. Simonen, J. Tommila, and M. Pessa, “Arrays of metallic nanocones fabricated by UV-nanoimprint lithography,” Microelectr. Eng. 87(9), 1711–1715 (2010) [doi:10.1016/j.mee.2009.08.015].
11. J. Tommila, V. Polojärvi, A. Aho, A. Tukiainen, J. Viheriälä, J. Salmi, A. Schramm, J. M. Kontio, A. Turtiainen, et al., “Nanostructured broadband antireflection coatings on AlInP fabricated by nanoimprint lithography,” Solar Energy Materials and Solar Cells 94(10), 1845–1848 (2010) [doi:10.1016/j.solmat.2010.05.053].
12. T. Salminen, M. Hahtala, I. Seppälä, P. Laukkanen, and T. Niemi, “Picosecond pulse laser ablation of yttria-stabilized zirconia from kilohertz to megahertz repetition rates,” Appl. Phys. A 101(4), 735–738 (2010) [doi:10.1007/s00339-010-5931-6].
13. J. M. Kontio, J. Simonen, K. Leinonen, M. Kuittinen, and T. Niemi, “Broadband infrared mirror using guided-mode resonance in a subwavelength germanium grating,” Opt. Lett. 35(15), 2564–2566 (2010) [doi:10.1364/OL.35.002564].
14. J. M. Kontio, H. Husu, J. Simonen, M. J. Huttunen, J. Tommila, M. Pessa, and M. Kauranen, “Nanoimprint fabrication of gold nanocones with ~10 nm tips for enhanced optical interactions,” Opt. Lett. 34(13), 1979–1981 (2009) [doi:10.1364/OL.34.001979].
15. T. Okamoto, J. Simonen, and S. Kawata, “Plasmonic crystal for efficient energy transfer from fluorescent molecules to long-range surface plasmons,” Opt. Express 17(10), 8294–8301 (2009) [doi:10.1364/OE.17.008294].
16. T. Salminen, M. Hahtala, I. Seppälä, T. Niemi, and M. Pessa, “Pulsed laser deposition of yttria-stabilized zirconium dioxide with a high repetition rate picosecond fiber laser,” Appl. Phys. A 98(3), 487–490 (2009) [doi:10.1007/s00339-009-5482-x].
17. C. Tan, C. S. Peng, J. Pakarinen, M. Pessa, V. N. Petryakov, Y. K. Verevkin, J. Zhang, Z. Wang, S. M. Olaizola, et al., “Ordered nanostructures written directly by laser interference,” Nanotechnology 20(12), 125303 (2009) [doi:10.1088/0957-4484/20/12/125303].
18. T. Okamoto, J. Simonen, and S. Kawata, “Plasmonic band gaps of structured metallic thin films evaluated for a surface plasmon laser using the coupled-wave approach,” Phys. Rev. B 77(11), 115425–115428 (2008) [doi:10.1103/PhysRevB.77.115425].
19. C. Tan, C. S. Peng, V. N. Petryakov, Y. K. Verevkin, J. Zhang, Z. Wang, S. M. Olaizola, T. Berthou, S. Tisserand, et al., “Line defects in two-dimensional four-beam interference patterns,” New J. Phys. 10(2), 023023 (2008) [doi:10.1088/1367-2630/10/2/023023].
20. B. K. Canfield, H. Husu, J. Kontio, J. Viheriälä, T. Rytkönen, T. Niemi, E. Chandler, A. Hrin, J. A. Squier, et al., “Inhomogeneities in the nonlinear tensorial responses of arrays of gold nanodots,” New J. Phys. 10(1), 013001 (2008) [doi:10.1088/1367-2630/10/1/013001].
21. J. Feng, T. Okamoto, J. Simonen, and S. Kawata, “Color-tunable electroluminescence from white organic light-emitting devices through coupled surface plasmons,” Appl. Phys. Lett. 90(8), 081106–3 (2007) [doi:10.1063/1.2645149].
22. J. Viheriala, T. Niemi, J. Kontio, T. Rytkonen, and M. Pessa, “Fabrication of surface reliefs on facets of singlemode optical fibres using nanoimprint lithography,” Electronics Letters 43(3), 150–151 (2007).
23. A. Tukiainen, J. Viheriälä, T. Niemi, T. Rytkönen, J. Kontio, and M. Pessa, “Selective growth experiments on gallium arsenide (1 0 0) surfaces patterned using UV-nanoimprint lithography,” Microelectronics Journal 37(12), 1477–1480 (2006) [doi:10.1016/j.mejo.2006.05.030].

>> Full publication list of ORC.

Contact

For more information of our research contact Prof. Tapio Niemi or the researchers for the topics described above.