Guohua Hu

SERS Detection and Removal of Mercury(II)/Silver(I) using Oligonucleotide-Functionalized Core/Shell Magnetic Silica Sphere@Au Nanoparticles

Heavy metal ions, such as Hg(2+) and Ag(+), pose severe risks in human health and the environment. For sensitive detection and selective removal of Hg(2+) and Ag(+) ions, here, we demonstrate a surface-enhanced Raman scattering (SERS)-active platform by employing the oligonucleotide-functionalized magnetic silica sphere (MSS)@Au nanoparticles (NPs). This system exploits mismatched T-Hg-T and C-Ag-C bridges to capture Hg(2+) and Ag(+) ions, exhibiting excellent responses for Hg(2+) ions in the range of 0.1-1000 nM and for Ag(+) in the range of 10-1000 nM. The assay is highly selective for the target ions and does not respond to other metal ions. Additionally, the Hg(2+) and Ag(+) ions in this system can be effectively removed from surrounding solutions by an external magnetic field or through spontaneous precipitation. Moreover, more than 80% of the MSS@Au NPs can be easily recycled with the help of cysteine. We anticipate that the designed strategy could be extended to other analytes that can bind to DNA molecules with a high affinity, and can be used in many potential applications such as environmental renovation, toxin detection, and groundwater analysis.

Theoretical analysis of a nanoscale plasmonic filter based on a rectangular metal-insulator-metal waveguide

A compact and nanometric surface plasmon polariton (SPP) band-pass filter based on a rectangular ring resonator composed of metal–insulator–metal waveguides is proposed. Using the finite difference time domain method, the effects of the structure parameters on the transmission characteristics of this SPP band-pass filter are analysed in detail. The results show that the proposed SPP filter has narrow transmission peaks and the corresponding resonance wavelengths can be linearly tuned by altering the resonators cavity length. Moreover, the transmission ratios of the pass bands can be tuned by changing the coupling gaps between the input/output MIM waveguides and the resonator. Also the metal loss and dispersion effects on the filter responses are included. The simple band-pass SPP filter is very promising for high-density SPP waveguide integrations.

Resonant Mode Analysis of the Nanoscale Surface Plasmon Polariton Waveguide Filter with Rectangle Cavity

The resonant mode characteristics of the nanoscale surface plasmon polaritons (SPP) waveguide filter with rectangle cavity are studied theoretically. By using the finite difference time domain method, both the band-stop- and band-pass-type rectangle SPP filters are analyzed. The results show that the whispering gallery mode (WGM) and the Fabry–Perot (FP) mode can be supported by the rectangle SPP resonator. Furthermore, both traveling-wave mode and standing-wave mode can be realized by the WGM, while only standing-wave mode can be introduced by the FP mode. The traveling-wave mode can only be realized by the square-shaped SPP resonator, and the traveling-wave mode is splitted into two standing-wave modes by transforming the cavity shape from square to rectangle. Also, the effects of the cavity shape, cavity size, and coupling gap size on the transmission spectra of the SPP resonators are analyzed in detail. This simple SPP waveguide filter is very promising for the high-density SPP waveguide integrations.

Plasmon induced transparency in metal–insulator–metal waveguide by a stub coupled with F-P resonator

A simple and compact metal?insulator?metal (MIM) stub coupled with Fabry?Perot (FP) resonator is proposed to realize the plasmonic analogue of electromagnetically induced transparency. By the coupling between the stub and the FP resonator, a narrow transmission peak is formed in the broad stop-band of the stub resonator. By combining the magnetic field distributions and the plasmon hybridization theory, the physical mechanism is presented, which is the mode splitting caused by the evanescent coupling between the plasmonic resonators. And the effects of the structure parameters on the transmission characteristics of the coupled system are analyzed in detail. Also, double plasmon induced transmission peaks can be realized by simply adding a second FP resonator into the system. The proposed compact and simple plasmonic structure may have potential applications in nanoscale filter and slow-light devices.

Vibrational resonance enhanced broadband multiphoton absorption in a triphenylamine derivative

Multiphoton absorption of 2,5-bis[4-(2-N,N-diphenylaminostyryl)phenyl]-1,3,4-oxadiazole was experimentally studied by using femtosecond laser pulses. This material demonstrates a very broad multiphoton absorption band of around 300nm width with two peaks of 1250 and 1475nm. The first peak results from the three-photon absorption process while the second is attributed to the vibrational resonance enhanced four-photon absorption process. Combination of these two processes provides a much broader multiphoton absorption band. In this letter, the analytical solution to nonlinear transmission of a three-photon absorption process is also given when the incident beam has a Gaussian transverse spatial profile.

High Performance Ridge Type PLZT Optical Switch With Offset Upper Electrode

(Pb,La)(Zr,Ti)O3 (PLZT) has a high electro-optical coefficient and is very attractive for optical waveguide switches with high speed, low driving voltage, and compact size. The 1 × 2 PLZT optical switch using ridge type Mach-Zehnder interference structure has been designed and fabricated. By introducing offset upper electrodes instead of the conventional top electrodes, the insertion loss of the fabricated 1 × 2 PLZT optical switch was decreased 9.8 dB significantly with a crosstalk of -25.3 dB and the driving voltage <;10 V.

Dielectrophoretic assembly of ZnO nanowires

The synthesis of zinc oxide (ZnO) nanowires is achieved by vapor phase transportation (VPT) method. The designed quartz tube, whose both ends are narrow and the middle is wider, is used to control the growth of ZnO nanowires. Dielectrophoresis (DEP) method is employed to align and manipulate ZnO nanowires which are ultrasonic dispersed and suspended in ethanol solution. Under the dielectrophoretic force, the nanowires are trapped on the pre-patterned electrodes, and further aligned along the electric field and bridge the electrode gap. The dependence of the alignment yield on the applied voltage and frequency is investigated.

Multilayer graphene electro-absorption optical modulator based on double-stripe silicon nitride waveguide

A graphene electro-absorption optical modulator based on double-stripe silicon nitride waveguide is proposed and analyzed. By embedding four graphene layers in the double-stripe silicon nitride waveguide and the graphene layers co-electrode design, the total metal-graphene contact resistance can be reduced 50% and as high as 30.6GHz modulation bandwidth can be achieved theoretically. The calculated extinction ratio and figure of merit are 0.1658dB/um and 9.7, respectively. And the required switching voltage from its minimum to maximum absorption state is 3.8180V and 780.50fJ/bit power consuming can be achieved. The proposed modulator can remedy the lack of high speed modulator on the passive silicon nitride waveguide.

Epitaxial growth and characterization of nonpolar a-plane AlGaN films with MgN/AlGaN insertion layers

MgN/AlGaN insertion layers were applied for the first time to the growth of nonpolar a-plane AlGaN epilayers by metal organic chemical vapor deposition technology. The full width at half maximum of the X-ray rocking curve for the a-plane AlGaN epilayers was reduced by approximately 50.6% and the root-mean-square roughness value of the surface was reduced by 74% by applying the MgN/AlGaN insertion layers with an optimized number of insertion pairs. These results reveal that the compressive strain within the a-plane AlGaN epilayers was effectively reduced, leading to significant improvements in crystalline quality and surface morphology. These improvements are very helpful in fabricating high-quality AlGaN-based ultraviolet light-emitting diodes.

Study of low-threshold and high-intensity random lasing in dye doped liquid crystals

Random lasers in dye-doped nematic liquid crystal (DDNLC) cells with different structures are studied. By choosing the cell gap and the cells rubbing methods, the DDNLC random laser obtains lower energy threshold. The DDNLC random laser energy threshold can also be decreased with an Al mirror as the external feedback from 4.2 μJ/pulse to 1.5 μJ/pulse. It is worth mentioning that the random laser shifts red and intensity increases with the Al mirror. The study of the DDNLC random laser with cell structure is aimed to obtain a low power consumption laser at a lower cost.