Achieving Anisotropy in Metamaterials made of Dielectric Cylindrical Rods

We show that anisotropic negative effective dispersion relation can be achieved in pure dielectric rod-type metamaterials by turning from the symmetry of a square lattice to that of a rectangular one, i.e. by breaking the rotation symmetry of effective homogeneous medium. Theoretical predictions and conclusions are verified by both numerical calculations and computer based simulations. The proposed anisotropic metamaterial, is used to construct a refocusing slab-lens and a subdiffraction hyperlens. The all-dielectric origin makes it more straightforward to address loss and scaling, two major issues of metallic structures, thus facilitating future applications in both the terahertz and optical range.Comment: Accepted for AP

Electroosmotic flow in single PDMS nanochannels

The final publication is available at Nanoscale, 2016,8, 12237-12246 via https://dx.doi.org/10.1039/C6NR02937JThe electroosmotic flow (EOF) velocity in single PDMS nanochannels with dimensions as small as 20 nm is investigated systematically by the current slope method in this paper. A novel method for the fabrication of single nanochannels on PDMS surfaces is developed. The effects of channel size, ionic concentration of the electrolyte solution and electric field on the EOF velocity in single nanochannels are investigated. The results show that the EOF velocity in smaller nanochannels with overlapped electric double layers (EDL) is proportional to the applied electric field but is smaller than the EOF velocity in microchannels under the same applied electric field. The EOF velocity in relatively large nanochannels without the overlap of EDLs is independent of the channel size and is the same as that in microchannels under the same applied electric field. Furthermore, in smaller nanochannels with overlapped EDLs, the EOF velocity depends on the ionic concentration and also on the channel size. The experimental results reported in this paper are valuable for the future studies of electrokinetic nanofluidics

Fabrication of polydimethylsiloxane (PDMS) nanofluidic chips with controllable channel size and spacing

The final publication is available at Lab Chip, 2016,16, 3767-3776 via http://dx.doi.org/10.1039/C6LC00867DThe ability to create reproducible and inexpensive nanofluidic chips is essential to the fundamental research and applications of nanofluidics. This paper presents a novel and cost-effective method for fabricating a single nanochannel or multiple nanochannels in PDMS chips with controllable channel size and spacing. Single nanocracks or nanocrack arrays, positioned by artificial defects, are first generated on a polystyrene surface with controllable size and spacing by a solvent-induced method. Two sets of optimal working parameters are developed to replicate the nanocracks onto the polymer layers to form the nanochannel molds. The nanochannel molds are used to make the bi-layer PDMS microchannel–nanochannel chips by simple soft lithography. An alignment system is developed for bonding the nanofluidic chips under an optical microscope. Using this method, high quality PDMS nanofluidic chips with a single nanochannel or multiple nanochannels of sub-100 nm width and height and centimeter length can be obtained with high repeatability

Electrokinetic motion of single nanoparticles in single PDMS nanochannels

The final publication is available at Springer via http://dx.doi.org/10.1007/s10404-017-1848-0Electrokinetic motion of single nanoparticles in single nanochannels was studied systematically by image tracking method. A novel method to fabricate PDMS-glass micro/nanochannel chips with single nanochannels was presented. The effects of ionic concentration of the buffer solution, particle-to-channel size ratio and electric field on the electrokinetic velocity of fluorescent nanoparticles were studied. The experimental results show that the apparent velocity of nanoparticles in single nanochannels increases with the ionic concentration when the ionic concentration is low and decreases with the ionic concentration when the concentration is high. The apparent velocity decreases with the particle-to-channel size ratio (a/b). Under the condition of low electric fields, nanoparticles can hardly move in single nanochannels with a large particle-to-channel size ratio. Generally, the apparent velocity increases with the applied electric field linearly. The experimental study presented in this article is valuable for future research and applications of transport and manipulation of nanoparticles in nanofluidic devices, such as separation of charged nanoparticles and DNA molecules