Reflective low-sideband plasmonic structural colors

It is demonstrated experimentally that an aluminum (Al) nanowire grating structure on silicon substrates can produce low-side-band monochromatic peak when it reflects colored light in the transverse magnetic (TM) mode. The central wavelength of the reflection is shown to be sensitive to the incident angle, which leads to significant color shifts. Formation of the monochromatic peak is attributed to the surface plasmon resonance on the interface between Al and air, together with remarkable diffraction at shorter wavelengths and strong Fabry-Perot (F-P) resonance absorption by Al-surrounding nano-cavities and silicon substrate at longer wavelengths. In contrast, reflection in transverse electric (TE) mode does not show distinct wavelength selectivity due to the cut-off effect of the nano-cavities. The outstanding characters of the proposed structure with polarization dependence, high sensitivity to incident angle, high color rendering facilitate more compact and sophisticated color-filter-based devices for displays, anti-counterfeit, and sensing applications. In addition, the two-dimensional structure with thin grating thickness and high duty ratio tolerance is relatively easy for fabrication

Preparation and characterization of carboxyl-group functionalized superparamagnetic nanoparticles and t he potential for bio-applications

In this work, a method was developed to prepare monodispersed carboxyl-group functionalized magnetic nanoparticles. Nanosized maghemite (y-Fe2O3, 7.0 ± 1.0 nm) was synthesized using thermal co-precipitation method and subsequently coated with functional groups by one-step suspension copolymerization. The Fourier transform infrared spectroscopy study and thermogravitmetric analyses confirmed the successful functionalization of carboxyl groups on the surface of magnetic nanocrystals. The surface chemistry makes it possible for SPRI (solid phase reversible immobilization)-based DNA purification. Thus the nanoparticles were employed to isolate plasmid DNA from bacterial cell culture and the results demonstrated its applicability in DNA preparation

Modifying the STM Tip for the ' Ultimate ' Imaging of the Si(111)-7×7 Surface and Metal-supported Molecules

We report on high-resolution STM measurements with modified probe tips. First, both the rest atoms and adatoms of a Si(111)-7×7 surface are observed simultaneously. The visibility of rest atoms is dependent upon the sample bias voltage (less than –0.7 V) and is enhanced by sharpening the tip, which is rationalized by first-principles calculations. Second, a tip with a perylene molecule adsorbed at its apex is used to discriminate the molecular states and the metal states of the underlying Ag(110) surface, which is attributable to a mismatch between the energy levels of the functionalized tip and the adsorbates on silver. Lastly, high-resolution images of iron phthalocyanine (FePc) and zinc phthalocyanine (ZnPc) molecules on Au(111) are obtained by using an O2-terminated tip, and the images reveal rich intramolecular features arising from molecular orbitals that are not observed when using clean metallic tips

Broad bandwidth waveguide polarizer via grating mediated mode conversion

A polarization beam splitter (PBS) based on a four-layer slab waveguide is proposed, where a sub-wavelength grating is embedded between the waveguide core and the cladding. This grating not only affords Bragg momentum to tune the propagation constant of guiding modes but also converts the forward zero-order waveguide mode to the backward first one for a specific polarization. Thus, the incident light with polarization that satisfies the phase-matching condition is highly reflected in the waveguide, while other light with orthogonal polarization keeps intact and passes through it efficiently. Numerical simulations show that one can make the compact PBS for both polarizations with an extinction ratio higher than 35 dB, a waveband larger than 80 nm, a grating period tolerance of 20 nm, and a waveguide height tolerance of 80 nm. The revealed mode conversion mechanism via the sub-wavelength grating enriches the design of PBSs for integrated silicon waveguide chips