Bruker Optics

Applications on Metamaterials and Reflection Unit for Electrochemical Applications

Applications on Metamaterials

IntroductionMetamaterials are artificial materials revealing properties which cannot be found in nature. They are assembled of individual elements from conventional materials that are typically arranged in periodic patterns on a microscopic scale. These individual elements themselves exhibit sub-wavelength sizes being smaller than the electromagnetic wavelength of the waves they affect.

Possible application areas for metamaterials could be op-toelectronics based on photonic crystals, microantennas based on plasmonic structures, TeraHertz devices, aero-space, and military/defense.

Opportunities given by FT-IR SpectroscopyAccording to the periodicity of the patterns applications may require access to a wide spectral ranges (NIR/VIS, MIR, and FIR) and hence flexible FT-IR spectrometers able to cover these spectral ranges are to favor. Since samples can be rather small (<1 mm) FT- IR microscopes can be very useful, e.g. to check homogeneity of samples.With its well-know and acknowledged FT-IR research spectrometer series VERTEX and microscope series HY-PERION (Fig. 1) Bruker offers an ideal combination.

Innovation with IntegrityTechnology

Arno Simon1, Michael Jörger1, Armin Gembus1 and Shigeru Shimada2, 1 Bruker Optik GmbH, Ettlingen, Germany2 Bruker Optics K.K., 104-0033 Tokyo, Japan

Fig. 3: NIR to Vis range (4,000-20,000 cm-1) from [1].Applications1. FT-IR characterization of Distributed Bragg Reflectors.Distributed Bragg Reflectors (DBR) are reflectors used in waveguides. Since DBRs can be designed such that the stop-band is located at the LASER wavelength they often serve as resonators in semiconductor LASERs. In analogy to metamaterials DBRs are formed from multiple layers of alternating materials or by periodic variations in the struc-ture of a dielectric waveguide. Both approaches result in a variation of the refractive index across the cavity.The stop-band position (Fig. 2) strongly depends on the layer stack and angle of incidence.

Fig. 1: Bruker VERTEX 80v FT-IR vacuum spectrometer with right-side coupled HYPERION 2000 FT-IR micro-scope.

Fig. 2: Reflectivity profile of a DBR (top) recorded using a perpendicular reflectance unit with parallel beam (bottom).

Stop band, R~100%:Light can not propa-gate through sample

2. Octave-wide photonic band gap in three-dimensional plasmonic Bragg structures and limitations of radiative cou-plings [1] measured on VERTEX 80v and HYPERION 2000 by R. Tauber and H. Giessen [Fig. 3].

Fig. 4: Reflection unit for electrochemical applications. The unit can be adapted to Bruker TENSOR or VERTEX series spectrometers.

Reflection Unit for Electrochemical Applications

The reflection unit for Bruker TENSOR and VERTEX series can be used to study chemical reactions in the presence of electric currents (Fig. 4)

Fig. 5: Setup for measurement with reflection unit for elec-trochemical applications.

References[1] R. Taubert et al., Nat. Commun. 3, 691 (2012).[2] Na Liu et al., Science 332, 1407 (2011).[3] N. Verellen et al., Nano Lett. 11 (2), 319-397 (2011).[4] J.-H. Cho et al., SMALL 7 (14) (2011).[5] J. Ye, M. Shioi et al., Appl. Phys. Lett. 97, 163106 (2010).

The reflection unit contains variable angle inserts for 30° or 60° angle of incidence each variable by ±5° and can be used with a polarizer. Depending on the chemical media being used and spectral range of interest following hemi-spherical window material are available CaF2, Si, Ge, ZnSe, and BaF2.A mount for a customer supplied electrochemical cell in-cluding a sealing between the window and cell is included.For automated measurements the spectrometer can con-trol a suited potentiostat via a CAN-ADI board (Fig. 5). The related script allows to record single channel curves at user-defined potentials and sets the potential back to a ref-erence potential before stepping to the next potential of in-terest in order to provide identical chemical conditions prior to any potential to be measured. For achieving equilibrated states a variable time constant can be introduced.