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(Color online) (a) Illustration of the microcavity reflectance spectrum redshift upon binding. (b) Simulation of microcavity spectrum redshift as a function of coating layer optical thickness for different pore sizes. The inset illustrates the coating of a thin layer on the pore wall. (c) Redshift of the spectra with subangstrom coating thickness.
[(a) and (b)] Top view and cross sectional scanning electron microscopy (SEM) images of a mesoporous silicon microcavity with pore size etched in (100) -type silicon wafers using a solution of 15% hydroflouric acid (HF) in ethanol; [(c) and (d)] Top view and cross sectional SEM images of a macroporous silicon microcavity with pore size etched in (100) -type silicon wafers using a solution containing 5.5% HF in water. These PSi microcavities consist of two Bragg mirrors (a periodic stack of layers with two different porosities and quarter-wavelength optical thickness) and a defect layer (half-wavelength optical thickness).
(a) Redshift increase as the concentration of APTES increases for both mesoporous and macroporous silicon microcavities. The redshift saturates when one monolayer of APTES is formed inside the pores. (b) Redshift increase due to the binding of a two-layer coating made of glutaraldehyde and APTES. A fixed amount of glutaraldehyde was applied to sensors that were treated with different APTES concentrations. The redshift saturates when two layers of molecules completely coat the pores.
Redshift of microcavities due to the presence of a thin coating layer as a function of pore size and layer thickness. The solid curves are the calculated redshifts as a function of the pore size using and thick coating layers with . The data points are the measured redshift for mesoporous and macroporous microcavities after coating of APTES and . The error bars are from multiple trials.
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