Development of localized surface plasmon resonance (LSPR) sensors for label-free biodetection draws considerable
attention because of the potential of these sensors to provide simplified detection schemes, improved detection limits,
and high-density multiplexed array configurations. In this paper, we present our recent results on the theoretical and
experimental development of LSPR label-free biosensors based on nanohole and nanopillar arrays. First, we
theoretically compare the analytical performance metrics of wavelength modulated SPR and LSPR platforms for
biological recognition with surface-immobilized bioreceptors (e.g. antibodies and aptamers). Further, we discuss our
results on the application of a focused ion beam (FIB) technique to fabricate arrays of nanoholes and nanopillars in Au
films, investigate the origin and type of FIB-induced surface contamination, and demonstrate an efficient way for its
elimination. Next, we evaluate the refractive index (RI) response sensitivity of FIB-fabricated arrays of nanoholes (443
- 513 nm/RIU) and nanopillars (423 nm/RIU) in Au films. Further, we demonstrate the opportunities that are available
from the multivariate spectral analysis of plasmonic nanostructures for improvement of sensor system performance.
Finally, we present typical simulation results of predicting RI sensitivity of plasmonic nanostructures using finite-difference
time-domain technique (FDTD) and discuss the remaining challenges of simulation techniques for design of
LSPR sensors.
The influence of two monolayer (ML)-thick AlAs under- and overlayers on the formation and properties of self-assembled InAs quantum dots (QDs) has been studied using transmission electron microscopy, photoluminescence (PL) and electroluminescence. The main purpose of this work was to achieve high internal quantum efficiency of the active medium and temperature stability of the laser diodes. Single and multiple layers of 2.0-2.4ML InAs QDs with various combinations of under- and overlayers were grown on GaAs (001) substrate by molecular beam epitaxy inside a AlAs/GaAs short-period superlattice. It was found that a 2.4-ML InAs QD layer with GaAs underlayer and 2-ML AlAs overlayer exhibited the lowest QD surface density of 4.2x1010 cm-2 and the largest QD lateral size of about 19 nm as compared to the other combinations of cladding layers. This InAs QD ensemble has also shown the highest room temperature PL intensity with a peak at 1210 nm and the narrowest linewidth, 34 meV. Fabricated edge-emitting lasers using triple layers of 2.2-ML InAs QDs with AlAs overlayer demonstrated 120 A/cm2 threshold current density and 1230 nm emission wavelength at room temperature. Excited state QD lasers have shown high thermal stability of threshold current up to 130 degree(s)C.
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