The B 1s exciton spectrum of the wide-band-gap semiconductor c-BN has been studied by resonant photoemission spectroscopy. The core-exciton band is found with a binding energy of about 1.2 eV. The constant-initial-state spectra for the valence-band features indicate that the B 1s exciton is the intermediate state for the resonant photoemission from the valence band. A satellite is found below the lower valence band by the resonant photoemission at B 1s exciton. The energy distribution curves of the valence band are qualitatively in agreement with the energy-band density-of-states curves but the discrepancy is conspicuous for the conduction band. The remarkable Fermi-level shift is found between p-type and n-type c-BN in accord with the rigid-band model, in spite of the large band-bending e8'ect.
This paper reports on the development of compact surface plasmon resonance (SPR) sensors for mobile robot olfaction. Underwater robots benefit from olfactory sensing capabilities in various tasks including the search for unexploded ordnance and undersea wreckage. Although the SPR-based chemical sensor is a promising sensing platform, the cumbersome optical setup has been limiting its use on mobile robots. The proposed sensor employs a periodic metal structure formed on a self-assembled layer of polystyrene particles of 200 nm in diameter. With the grating of this size, SPR can be excited even with a simple LED light source. The change in the absorbance is simply measured using a photodiode. Demonstration of the proposed SPR sensor is provided by mounting the sensors on an underwater crayfish robot that autonomously searches for a chemical source. The fabricated sensor shows linear response to ascorbic acid for a concentration range from 20 to 80 mM. Responses of the bare and thiol-coated gold nanostructure to different chemical substances are presented to show the change in the selectivity of the sensor by the coating. Discussions are made on the importance of sample collection for the sensor to attain sensitive chemical detection on a mobile robot.
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