Spin-Selective Transmission in Chiral Folded Metasurfaces.

Controlling the spin angular momentum of light (or circular polarization state) plays a crucial role in the modern photonic applications such as optical communication, circular dichroism spectroscopy, and quantum information processing. However, the conventional approaches to manipulate the spin of light require naturally occurring chiral or birefringent materials of bulky sizes due to the weak light-matter interactions. Here we experimentally demonstrate an approach to implement spin-selective transmission in the infrared region based on chiral folded metasurfaces that are capable of transmitting one spin state of light while largely prohibiting the other. Due to the intrinsic chirality of the folded metasurface, a remarkable circular dichroism as large as 0.7 with the maximum transmittance exceeding 92% is experimentally demonstrated. The giant circular dichroism is interpreted within the framework of charge-current multipole expansion. Moreover, the intrinsic chirality can be readily controlled by manipulating the folding angle of the metasurface with respect to the cardinal plane. Benefiting from its strong chirality and spin-dependent transmission characteristics, the proposed folded metasurface may be applied to a range of novel photon-spin selective devices for optical communication technologies and biophotonics.

Fabrication of nanopores for biomacromolecule detection.

Nanopores embedded in a thin membrane with diameter below 10 nm are suitable for the biomacromolecule detection. For such purpose, in this study, we developed a technique of how to obtain small nanopores in silicon nitride films using a focused-ion-beam (FIB) system. By changing the process parameters, such as the beam current, the film thickness of the membrane and the ion beam exposure time, the diameter of the nanopore can be tuned. Under an optimized condition, high quality nanopores with diameter as low as 6 nm was fabricated on a 7 nm thick membrane. Our result suggests that FIB direct writing technique might be a suitable approach for biomacromolecule detector fabrication.

Transport comparison of multiwall carbon nanotubes by contacting outer shell and all shells.

Carbon nanotubes, particularly multiwall carbon nanotubes (MWCNTs) can serve as interconnects in nanoelectronic devices and integrated circuits because of their extremely large current-carrying capacity. Many experimental results about the transport properties of individual MWCNTs by contacting outer shell or all shells have been reported. In this work, a compatible method with integrated circuit manufacturing process was presented to compare the transport property of an individual multiwall carbon nanotube (MWCNT) by contacting outer shell only and all shells successively. First of the Ti/Au electrodes contacting outer shell only were fabricated onto the nanotube through the sequence of electron beam lithography (EBL) patterning, metal deposition and lift-off process. After the characterization of its transport property, focused ion beam (FIB) was used to drill holes through the same nanotube at the as-deposited electrodes. Then new contact to the holes and electrodes were made by ion-induced deposition of tungsten from W(CO)6 precursor gas. The transport results indicated that the new contact to all shells can clear up the intershell resistance and the electrical conductance of the tube can be improved about 8 times compared to that of by contacting outer shell only.

The morphology of DNA solution in an open fluidic channel studied by non-contact AFM.

The morphologies of pure buffer solution and DNA-containing solution in an open fluidic channel with rectangle cross section (1 microm in width and 150 nm in depth) have been explored using non-contact AFM. A remarkable feature is that a uniform nano-scale trench (approximately 15 nm deep and 14 microm long) on the surface of the DNA solution has been observed. The presence of two neighboring stretched DNA molecules near the solution surface may be responsible for the configuration of the nanotrench. This new phenomenon of partially stretched DNA molecules is likely to be useful for the future designing of fluidic devices, and for the manipulation and study of single DNA molecules.