Pin-Tso Lin

Plasmonic Coupling in Gold Nanoring Dimers: Observation of Coupled Bonding Mode

We investigate the optical properties of gold nanoring (NR) dimers in both simulation and experiment. The resonance peak wavelength of gold NR dimers is strongly dependent on the polarization direction and gap distance. As the gold NR particles approach each other, exponential red shift and slight blue shift of coupled bonding (CB) mode in gold NR dimers for longitudinal and transverse polarizations are obtained. In finite element method analysis, a very strong surface plasmon coupling in the gap region of gold NR dimers is observed, whose field intensity at the gap distance of 10 nm is enhanced 23% compared to that for gold nanodisk (ND) dimers with the same diameter. In addition, plasmonic dimer system exhibits a great improvement in the sensing performance. Near-field coupling in gold NR dimers causes exponential increase in sensitivity to refractive index of surrounding medium with decreasing the gap distance. Compared with coupled dipole mode in gold ND dimers, CB mode in gold NR dimers shows higher index sensitivity. This better index sensing performance is resulted form the additional electric field in inside region of NR and the larger field enhancement in the gap region owing to the stronger coupling of collective dipole plasmon resonances for CB mode. These results pave the way to design plasmonic nanostructures for practical applications that require coupled metallic nanoparticles with enhanced electric fields.

One-dimensional photonic crystal nanobeam lasers on a flexible substrate

We demonstrate a one-dimensional (1D) photonic crystal (PhC) nanocavity laser composed of hybrid PhC mirrors on a suspended nanobeam (NB) with very small device footprint of 8.5 × 0.57 μm2. The 0th-order mode lasing action with low threshold of 280 μW is observed. Via the optical glue stamping process, the devices are directly transferred onto a flexible polypropylene substrate. Single mode lasing action with effective threshold of 17 μW is achieved. The robust lasing properties of the device with different bending radii R from ∞ to 2.5 mm are obtained. Via finite-element method, we also theoretically address that the lasing wavelength is almost invariant when R > 1.0 mm. This flexible 1D PhC NB laser will be a good candidate for efficient nanolaser in future flexible photonic integrated circuits with ultrahigh component density.

Optical sensing of square lattice photonic crystal point-shifted nanocavity for protein adsorption detection

We propose a point-shifted D0 nanocavity formed by locally modulating four central air holes in square lattice photonic crystal for optical sensing application. Three defect modes in this nanocavity, including monopole, whispering-gallery, and dipole modes, are identified in experiments. We also apply a chemical treatment on InGaAsP surface to form a 1-octadecanethiol linking monolayer, which enables the following protein adsorption. In experiments, the wavelength shifts of lasing modes in the D0 nanocavity due to the protein adsorption are observed and agree with the simulation results. This can be a practical tool for label-free molecule detection in biomedical researches.

Enhancement and inverse behaviors of magnetoimpedance in a magnetotunneling junction by driving frequency

The magnetoimpedance effect was employed to study magnetotunneling junction (MTJ) with the structure of Ru(5nm)∕Cu(10nm)∕Ru(5nm)∕IrMn(10nm)∕CoFeB(4nm)∕Al(1.2nm)-oxide∕CoFeB(4nm)∕Ru(5nm). A huge change of more than ±17000% was observed in the imaginary part of the impedance between the magnetically parallel and antiparallel states of the MTJ. The inverse behavior of the magnetoimpedance (MI) loop occurs beyond 21.1MHz; however, the normal MI at low frequency and the inverse MI at high frequency exhibit the same magnetization reversal as checked by the Kerr effect. The reversal in MI was due to the dominance of magnetocapacitance at high frequency.

Photonic crystal horizontally slotted nanobeam cavity for silicon-based nanolasers.

We theoretically propose and investigate a TM-polarized one-dimensional photonic crystal nanocavity with a horizontal SiO2 slot on a suspended silicon nanobeam via the three-dimensional finite-element method. The ultrahigh quality factor and ultrasmall effective mode volume of 1.5×10(7) and 0.176 half-wavelength cubic of the horizontally SiO2-slotted nanocavity show strong possibilities for realizing an erbium-doped SiO2 nanolaser. This horizontal SiO2 slot structure can be precisely formed via the sputtering process and further transformed into an air slot via selective wet etching for optical index and biomolecule sensing.

High-coercivity CoPt alloy films grown by sputtering

Co/sub x/Pt/sub 1-x/ alloy films (x=0.2/spl sim/0.4) were prepared by rf sputtering at substrate temperatures 150/spl sim/300/spl deg/C without a Pt underlayer and post annealing. The magnetic properties of the films showed strong dependence on the composition and substrate temperature. High coercivity (/spl sim/191 KA/m) and saturated remanence were achieved at conditions x=0.25 and 200/spl deg/C. In contrast to the previous observations, the high perpendicular magnetic anisotropy, in the current case, appeared not associated with the good CoPt (111) texture. An interpretation based on minor composition modulation in the films was proposed.

Efficient transportation of nano-sized particles along slotted photonic crystal waveguide

We design a slotted photonic crystal waveguide (S-PhCW) and numerically propose that it can efficiently transport polystyrene particle with diameter as small as 50 nm in a 100 nm slot. Excellent optical confinement and slow light effect provided by the photonic crystal structure greatly enhance the optical force exerted on the particle. The S-PhCW can thus transport the particle with optical propulsion force as strong as 5.3 pN/W, which is over 10 times stronger than that generated by the slotted strip waveguide (S-SW). In addition, the vertical optical attraction force induced in the S-PhCW is over 2 times stronger than that of the S-SW. Therefore, the S-PhCW transports particles not only efficiently but also stably. We anticipate this waveguide structure will be beneficial for the future lab-on-chip development.

All-optical controllable trapping and transport of subwavelength particles on a tapered photonic crystal waveguide

We propose that a tapered photonic crystal waveguide design can unify optical trapping and transport functionalities to advance the controllability of optical manipulation. Subwavelength particles can be trapped by a resonance-enhanced field and transported to a specified position along the waveguide on demand by varying the input wavelength. A simulated transport ability as high as 148 (transport distance/wavelength variation) is obtained by the waveguide with 0.1° tilted angle. Stable trapping of a 50 nm polystyrene particle can be achieved with input power of 7 mW. We anticipate that this design would be beneficial for future life science research and optomechanical applications.

Photonic crystal waveguide cavity with waist design for efficient trapping and detection of nanoparticles

For manipulating nanometric particles, we propose a photonic crystal waveguide cavity design with a waist structure to enhance resonance characteristic of the cavity. For trapping a polystyrene particle of 50 nm radius on the lateral side of the waist, the optical force can reach 2308 pN/W with 24.7% signal transmission. Threshold power of only 0.32 mW is required for stable trapping. The total length of the device is relatively short with only ten photonic crystal periods, and the trapping can occur precisely and only at the waist. The designed cavity can also provide particle detection and surrounding medium sensing using the transmission spectrum with narrow linewidth. The simulated figure of merit of 110.6 is relatively high compared with those obtained from most plasmonic structures for sensing application. We anticipate this design with features of compact, efficient, and versatile in functionality will be beneficial for developing lab-on-chip in the future.

Oscillating Voltage Dependence of High-Frequency Impedance in Magnetic Tunneling Junctions

Oscillating voltage (VOs), which depends on the frequency dependence of the magnetoimpedance (MI) effect, was applied to study a magnetic tunneling junction (MTJ) of Ru(5 nm)/Cu(10 nm)/Ru(5 nm)/IrMn(10 nm)/CoFeB(4 nm)/Al2 O3/CoFeB(4 nm)/Ru(5 nm) at frequencies up to 40 MHz. The MI ratio decreased as the VOs was increased. The MI ratio turned from positive to negative at a certain frequency. An equivalent circuit model was employed to analyze the results. The fact that MTJ can be regarded as the composition of a resistance component and two sets of parallel resistance (R) and capacitance (C) components in series has been utilized to describe the individual impedance contribution from the lead of cross pattern, barrier, and interface. The resistance (Rbarrier) and capacitance (Cbarrier) of the barrier effect are functions of VOs. The Rbarrier decreases as the VOs increases, However, C barrier behaves the opposite way. The tendency is for interfacial resistance Rinterface and interfacial capacitance Cinterface to have opposite results with increasing VOs . This work provides a detailed investigation of high-frequency transport behavior subjected to VOs, especially useful for MTJ characterization