研究目的
Investigating the implications of using materials structured at multiple length scales in the design of spectrally uniform photodetectors and exploring unusual ways to control the flow of light using hierarchical structures.
研究成果
Hierarchical structuring of materials offers unconventional ways to control the flow of light and to subsequently improve optoelectronic design. A simple self-assembly based hierarchical structure is used as a platform for photodetectors. Mechanical strain augmented fabrication offers a facile way to obtain multiperiodic structures on a ‘bench-top’ and multi-periodicity is seen to demonstrate the best spectral uniformity in the fabricated photodetectors. The underlying unusual multiscale process consists of a wavelength dependent coupling of scattered light from nano-structured domains to planar domains, which can necessarily occur only in hierarchical structures.
研究不足
The implications of hierarchical designs in the area of photonics and optoelectronics are yet to be fully understood. The fabrication of multiperiodic structures using self-assembly and mechanical strain-augmented nanofabrication was hitherto a challenge.
1:Experimental Design and Method Selection:
The optical transport through complex hierarchical structures is modelled in the frequency domain by solving the Maxwell’s equations in a Finite Element environment using COMSOL Multiphysics. Hierarchically structured transparent substrates are prepared using commonly available moldable epoxies. A layer of monodisperse discontinuous polystyrene nanoparticles (400 nm diameter) on a silicon substrate acts as the master template in a two-step molding process.
2:Sample Selection and Data Sources:
A 300 nm thick TiO2 high index waveguide is built on this substrate by RF sputtering. A solution processed polymer photodetector is built on the multiscale waveguide.
3:List of Experimental Equipment and Materials:
Polystyrene nanoparticles, PDMS, epoxy, TiO2, PH1000, PEDOT:PSS, PTB7:PC71BM, Al.
4:Experimental Procedures and Operational Workflow:
An inverse template is prepared by casting PDMS on the master. The PDMS which obeys the macro-geometry of a mechanical test element is strained to tweak the nano-structures. Under strain, epoxy is cast on the inverse template and cured for 24 hours to obtain the hierarchically structured multiperiodic substrates.
5:Data Analysis Methods:
The optical and optoelectronic behavior of the devices are measured through transmittance, reflectance, quantum efficiency spectroscopy.
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