We fabricated stand-alone trilayers (3L) and their heterostructures of MoS2 and WS2 on Al2O3 substrates. In particular, two kinds of heterostructures with different stacking sequences (i.e., 3L-MoS2/3L-WS2 and 3L-WS2/3L-MoS2) were prepared for comparison. The light-induced surface potential change suggested that the internal electric field along the thickness direction was present in the stand-alone (MoS2 and WS2) and heterostructure samples. Relative peak shifts of the Raman spectra supported the presence of the internal field in our samples. Physical origins to induce the internal electric field will be discussed in the presentation.
A nanostructure-based plasmonic biochip with the same size as standard 96-well plates for backside reflection-type biosensing was proposed and validated through analyses of biological interactions. The capped gold nanoslit arrays were fabricated on a polycarbonate plastic film using a rapid hot embossing nanoimprint lithography process. The optical properties of capped gold nanoslits with different structure parameters in backside reflection geometry were studied; their refractive index (bulk) and surface (thickness) sensitivities were verified. By changing the cavity length, the coupling between a broadband cavity resonance and a narrowband surface plasmon resonance mode results in an asymmetric Fano resonance in the reflection spectra. The coupling mode is able to enhance the thickness sensitivity by a factor of 2.4 with wavelength interrogation. The bulk and thickness sensitivities were 454 nm/RIU and 1.14 nm/nm, respectively. The protein-protein interaction experiments verified the sensing capabilities and high sensitivity of the capped nanostructures; a limit of detection (LOD) of 2 ng/mL IgA was achieved. Such a multi-well plate with backside reflection-type geometry, decoupling the optical paths, allows for sensing with opaque, bubbly or highly scattering liquids and benefits multiple sensing applications in the biotechnology and agricultural products.
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