Chung-Lun Wu

Magnetic susceptibility reduction method for magnetically labeled immunoassay

In addition to synthesizing biofunctionalized magnetic nanopaticles for the purpose of magnetically labeling biomolecules, a system to measure the ac magnetic susceptibility of the labeled sample was developed. When a targeted biomolecule was mixed with magnetic fluid possessing biofunctionalized magnetic nanoparticles, portions of magnetic nanoparticles agglomerated to form clusters due to the association with the targeted biomolecule. Due to the formation of magnetic clusters, the measured ac magnetic susceptibility reduced. The relationship between the mixed-frequency ac magnetic susceptibility reduction and the amount of the detected biomolecule was established.

Time-Evolution contrast of target MRI using high-stability antibody functionalized magnetic nanoparticles: an animal model

In this work, high-quality antibody functionalized Fe3O4 magnetic nanoparticles are synthesized. Such physical characterizations as particle morphology, particle size, stability, and relaxivity of magnetic particles are investigated. The immunoreactivity of biofunctionalized magnetic nanoparticles is examined by utilizing immunomagnetic reduction. The results show that the mean diameter of antibody functionalized magnetic nanoparticles is around 50 nm, and the relaxivity of the magnetic particles is 145 (mMċs)-1. In addition to characterizing the magnetic nanoparticles, the feasibility of using the antibody functionalized magnetic nanoparticles for the contrast medium of target magnetic resonance imaging is investigated. These antibody functionalized magnetic nanoparticles are injected into mice bearing with tumor. The tumor magnetic-resonance image becomes darker after the injection and then recovers 50 hours after the injection. The tumor magnetic-resonance image becomes the darkest at around 20 hours after the injection. Thus, the observing time window for the specific labeling of tumors with antibody functionalized magnetic nanoparticles was found to be 20 hours after injecting biofunctionalized magnetic nanoparticles into mice. The biopsy of tumor is stained after the injection to prove that the long-term darkness of tumor magnetic-resonance image is due to the specific anchoring of antibody functionalized magnetic nanoparticles at tumor.

Mutlicolor electroluminescent Si quantum dots embedded in SiO x thin film MOSLED with 2.4% external quantum efficiency

The enhanced recombination and external quantum efficiency (EQE) of the multi-color metal-oxide-semiconductor light-emitting diodes (MOSLEDs) made on the SiOx film with buried Si quantum dots (Si-QDs) grown by plasma-enhanced chemical vapor deposition are demonstrated. By shrinking Si-QD size from 4.2 to 1.8 nm with increasing RF plasma power from 20 to 50 W, these MOSLEDs enhance the maximal electroluminescent (EL) power from 0.1 to 0.7 μW. This is mainly attributed to the enhanced recombination rate by enlarging the overlap between electron and hole wave-functions. As evidence, the photoluminescent lifetime is significantly shortened from 5 µs to 0.31µs due to the enhanced direct recombination in smaller Si-QDs. The corresponding power-current slope and EQE are observed to increase from 0.09 to 5.7 mW/A and from 1.9 × 10(-5) to 2.4%, respectively. The EL enhancement originates from shorter wavelength and stronger carrier confinement within Si-QDs with smaller size, as confirmed by the increased barrier height at the ITO/SiOx:Si-QD interface from 1.05 to 3.62 eV. The smaller and denser Si-QDs result in a current endurance to operate the MOSLED at breakdown edge with highest power conversion efficiency, thus providing a maximal blue-light EL power at 0.7 μW with the highest EQE of 2.4%.

Effect of InGaAs capping layer on the properties of InAs/InGaAs quantum dots and lasers

We report the effects of In0.33Ga0.67As capping layers on the structural and optical properties of InAs self-organized quantum dots grown by gas-source molecular-beam epitaxy. With different deposition methods for the InGaAs capping layer, the quantum-dot density can be adjusted from 2.3×1010 to 1.7×1011 cm−2. As-cleaved 3.98-mm-long diode laser using triple stacks of InAs quantum dots with the capping layer grown by GaAs/InAs sequential binary growth demonstrates an emission wavelength of 1305 nm and a threshold current density of 360 A/cm2. A ground-state saturation gain of 16.6 cm−1 is achieved due to the high dot density.

Si-Rich

The nonstoichiometric ITO/n-SiC/i-SiC/p-Si/Al light-emitting diodes (LEDs) with dense Si quantum dots (Si-QDs) embedded in the Si-rich Si_xC_1-x -based i-SiC layer are demonstrated. The Si-rich Si_xC_1-x films with buried Si-QDs are grown by the plasma-enhanced chemical vapor deposition with varying substrate temperatures. After the annealing process, the average Si-QD size in the Si-rich Si_0.52C_0.48 film is 2.7 ± 0.4 nm with a corresponding volume density of 1.43 × 10¹⁸ cm^-3. By increasing the deposition temperatures from 300°C to 650°C, the turn-on voltage and turn-on current of the ITO/n-SiC/i-SiC/p-Si/Al LEDs are found to decrease from 13 to 4.2 V and from 0.63 to 0.34 mA, respectively. In addition, these Si-rich Si_xC_1-x LEDs provide the maximal electroluminescent (EL) power intensity increasing from 1.1 to 4.5 μW/cm². The yellow (at 570 nm) EL emission power of the ITO/n-SiC/i-SiC/p-Si/Al LEDs reveals a saturated phenomenon due to the Auger effect. The dissipated energy by the lattice thermal vibration contributes to a decayed EL emission power at higher biased currents. The corresponding power-current slope is observed to enhance from 0.45 to 0.61 μW/A with the substrate temperature increasing to 650°C.

\hbox{Si}_{\rm x}\hbox{C}_{1 - {\rm x}}

The synthesis of few-layer graphene sheets on an ultra-thin nickel film-coated SiO2/Si substrate using hydrogen-free plasma-enhanced chemical vapor deposition (PECVD) with in situ low-temperature carbon dissolution is preliminarily demonstrated. The deposited carbon atoms are initially dissolved into the nickel matrix and subsequently precipitate out onto the nickel film surface. The threshold carbon dissolution temperature for synthesizing few-layer graphene is observed to be as low as 475 °C, and the critical thickness of the host nickel film is at least 30 nm. Due to the ultra-low solubility of the carbon atoms in the nickel film at a threshold temperature of 475 °C, the layer number in few-layer graphene can be precisely controlled. Raman scattering analysis indicates almost identical D and 2D peak intensities for nickel films with different thicknesses, whereas the G peak is enhanced with an increasing layer number of graphene which precipitates from thicker nickel films. Saturation of the G peak for the 50 nm thick nickel film is observed, due to the finite carbon dissolution within a limited deposition time, and results in a stabilized, high quality precipitated few-layer graphene. The linear transmittance of few-layer graphene at 550 nm increases from 83 to 93% when the deposition time is shortened from 600 to 100 s, which corresponds to a decrease of the graphene layer number from 8 to 3 layers. The Raman scattering peak ratio of ID/IG decreases from 1.8 to 0.2 and the G-band linewidth shrinks from 67 to 37.2 cm−1, providing strong evidence for the improved quality of few-layer graphene synthesized by hydrogen-free PECVD at the threshold temperature on an ultra-thin nickel host.

Light-Emitting Diodes With Buried Si Quantum Dots

A SiO2/SiOx/SiO2 strip-loaded waveguide with buried Si quantum dots is optically pumped to provide amplified spontaneous emission centered at 805 nm with spectral linewidth of 140 nm. By top-pumping the 350-nm-thick SiOx with He–Cd laser of 40 mW at 325 nm, the optical gain of 65 cm−1 and loss coefficient of 5 cm−1 are determined. Under a 785 nm small-signal injection diagnosis, the power-dependent gain curve fitting with gain-saturated amplifier model reveals a peak gain of 27 dB (not including waveguide loss) and a net power gain of 9.5 dB for the Si-rich SiOx waveguide amplifier with a length of 5 mm.

Hydrogen-free PECVD growth of few-layer graphene on an ultra-thin nickel film at the threshold dissolution temperature

Silicon photonic interconnection on chip is the emerging issue for next-generation integrated circuits. With the Si-rich SiNx micro-ring based optical Kerr switch, we demonstrate for the first time the wavelength and format conversion of optical on-off-keying data with a bit-rate of 12 Gbit/s. The field-resonant nonlinear Kerr effect enhances the transient refractive index change when coupling the optical data-stream into the micro-ring through the bus waveguide. This effectively red-shifts the notched dip wavelength to cause the format preserved or inversed conversion of data carried by the on-resonant or off-resonant probe, respectively. The Si quantum dots doped Si-rich SiNx strengthens its nonlinear Kerr coefficient by two-orders of magnitude higher than that of bulk Si or Si3N4. The wavelength-converted and cross-amplitude-modulated probe data-stream at up to 12-Gbit/s through the Si-rich SiNx micro-ring with penalty of −7 dB on transmission has shown very promising applicability to all-optical communication networks.

Saturated small-signal gain of Si quantum dots embedded in SiO2/SiOx/SiO2 strip-loaded waveguide amplifier made on quartz

Carrier retention and recombination in Si quantum dots (Si-QDs) embedded SiNx light emitting diode with dark-yellow emission of 93 nW and linear P-I slope of 1.2 mW/A at 80 μA bias are compared. The capacitance-voltage hysteresis of <0.5 V reveals low carrier density per Si-QD, and the 1 ms charge retention concludes only 4% carrier retention within ms time. The fast radiative recombination with electroluminescent (EL) response is shorter than the charge retention within Si-QDs, elucidating that the low Si-QD/Si3N4 interfacial barrier is not dominant for small EL quantum efficiency. Few injected carriers and Auger effect in Si-QDs fail to promote the external quantum efficiency.

Si-rich SiNx based Kerr switch enables optical data conversion up to 12 Gbit/s

Coil-like graft copolymers of poly(Am-co-B(1−m)) containing identical heterocyclic aromatic benzoxazole with trifluoromethyl-ethyl as the backbone and pendants of monohydroxl (Am) and/or bidecyloxyl (B(1−m)) on their phenylene ring were studied for luminescence properties. The copolymers were synthesized with molar fraction m ranging from 0, 0.25, 0.5, 0.75, to 1, and then dissolved and spun onto a Spectrosil® quartz slide or an indium-tin-oxide (ITO) substrate. The fluorescence properties of copolymers were investigated by ultraviolet–visible absorption covering 185 nm to 800 nm and photoluminescence (PL) emission excited at 363 nm. The PL results exhibited an excellent chromatic tuning, ranging from green to white emission as m decreased. Aluminum electron injectors were evaporated onto the copolymer/ITO unit making it into monolayer light-emitting diodes for current–voltage and electroluminescence (EL) responses. An emission threshold voltage of 6 V was achieved for all the monolayer copolymer devices....