Surface-enhanced Raman scattering (SERS) spectra of azo dyes (methyl orange and p-methyl red) adsorbed on ZnO nanoparticles were observed. Hydrothermally synthesized ZnO nanoparticles were characterized by powder X-ray diffraction and X-ray photoelectron spectroscopy. The ZnO nanoparticle size, monitored with X-ray diffraction, was tuned by calcination to optimize SERS intensities. The observed SERS effect of azo dyes adsorbed on ZnO can be ascribed to charge-transfer resonance effect. Time-dependent density functional theory was used to calculate the optical spectra and interpret the chemical enhancement observed in the experiment. The SERS enhancement factors for methyl red on ZnO were boosted by nearly four times and twice with O 2 plasma and H 2 plasma, respectively. However, plasma treatment showed no effect on the enhancement factors of methyl orange on ZnO. We conclude that plasma-induced defect formation and band gap shift in ZnO and the coupling of energy levels between ZnO and azo dye molecules are responsible for the observed enhancement of SERS intensities.
Bluetooth is a popular wireless communication technique, providing connection between portable or stationary devices in close range. A procedure called pairing needs to be performed when two devices intend to connect with each other in order to form a trusted pair and generate secret keys to protect the link. There are several modes of Bluetooth pairing, and password-based is the most convenient and prevalent way. In this paper, we discover a potential vulnerability in the passwordbased pairing protocol of the latest Bluetooth v4.0 proposed in 2010, which makes password guessing possible. To cope with the problem, a new scheme is proposed which can mitigate the network threats, and is compatible with the hardware of legacy Bluetooth devices. Note that our modification does not affect Bluetooth users' custom. This makes it a suitable replacement for the new Bluetooth pairing protocol.
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