Photo-switchable molecules such as azobenzene are of high interest for “smart” surfaces. Such “smart” surfaces respond to external light excitation by changing their macroscopic properties. The absorbance of light on a single normal path through a layer of azobenzene immobilized on a surface is small and thus a high excitation light intensity is required. We investigate the enhancement of the local energy density using periodically nanostructured surfaces in a high refractive index material. Such photonic crystals support quasi-guided modes visible as resonances in the reflection as well as in the transmission light spectrum. These guided modes have field contributions decaying exponentially in the near field of the photonic crystal. Azobenzene immobilized on the photonic crystal surface will experience a significantly increased light intensity compared to non-resonant surfaces. We performed finite-difference time-domain (FDTD) calculations for determination of resonance positions and electric field strengths in compound grating structures. By superimposing two single-period gratings a photonic crystal can be designed supporting multiple guided mode resonances suitable to switch azobenzenes between the trans and cis isomer. To accomplish this, the central wavelength of the guided mode resonances should be in a range of λcis= 350 – 370 nm to initiate transition tothe cis isomer and λtrans= 420 – 450 nm generating the trans isomer. Additionally, the impact of the periods, the duty cycle of each period and the distance between the two superimposed periods on the electrical field strength propagating on the surface are investigated and compared to non-resonant surfaces.
|Publication status||Published - 2016|
|Event||Photonic and Phononic Properties of Engineered Nanostructures VI: SPIE OPTO - The Moscone Center, San Francisco, CA, United States|
Duration: 13. Feb 2016 → 18. Feb 2016
|Conference||Photonic and Phononic Properties of Engineered Nanostructures VI|
|Location||The Moscone Center|
|City||San Francisco, CA|
|Period||13/02/2016 → 18/02/2016|