Metallodielectric Multilayer Stacks Show Enhanced Ultrafast Optical Nonlinear Response
- PDF / 991,581 Bytes
- 1 Pages / 576 x 783 pts Page_size
- 49 Downloads / 216 Views
Nano-Imprint Mold and Direct Imprinting Technique Creates Single Sub-20-Nanometer-Wide, Centimeter-Long Nanofluidic Channel Many leading-edge applications in biochemical sensors and microfluidics require isolated, continuous fluidic channels, with lengths on the order of a cm, and widths on a 20-nm scale. Traditional nanolithographic tools are challenged by the strict limits on line edge roughness (to prevent clogging) over the desired centimeter-long channel length, which is much larger than typical writing fields. X. Liang and colleagues at Princeton University have demonstrated a novel direct imprinting technique to fabricate a single fluidic channel of uniform width (11–50 nm) and over 1.5 cm long. As reported in the December 2007 issue of Nano Letters (p. 3774; DOI: 10.1021/nl072253x), the researchers first created the nano-imprint mold. They grew about 10 nm of SiO2 on a (110)oriented silicon-on-insulator wafer, then lithographically patterned a 0.5 cm × 1.5 cm rectangle in the SiO2. The long edge was aligned to the {111} crystallographic axis in Si. An anisotropic KOH-based etch of the silicon, using the silicon dioxide as a mask and the underlying insulator as a stop layer, created a mesa with vertical sidewalls of {111} planes. The much slower etching rate in the directions versus the < 110 > directions ensured that the sidewalls were nearly atomically smooth, despite the severe edge roughness of the original etch mask. Subsequently, the SiO2 was stripped away. A thin layer of SixNy was then deposited uniformly and conformally, by low-pressure chemical vapor deposition, over the entire wafer surface including the sidewalls. The
thickness of this film defined the channel width. An anisotropic reactive ion etch (RIE), acting in the vertical direction, removed the SixNy on all horizontal surfaces while leaving some on the relatively tall sidewalls. By selectively etching away the remnants of the Si mesa, the long “fin” of SixNy was isolated and became the protrusion of an imprint mold. During the imprinting step, the mold was pressed into a UV-curable material layer. The resulting nanochannel could be used directly or as an etching mask to transfer the channel into an underlying substrate (e.g., SiO2) using RIE. The researchers characterized the channel dimensions using scanning electron microscopy and completed a nanofluidic device by fabricating a pair of liquid reservoirs at each end. They passed water containing a fluorescent marker through the nanochannel and also flowed DNA in solution (which stretched as it passed into and through the device). “This approach to creating and precisely placing a single long, narrow and continuous nanofluidic channel removes a key obstacle to developing many innovative biological and chemical sensors such as single-strand DNA sequencers,” Liang said. RICH LOUIE
Metallodielectric Multilayer Stacks Show Enhanced Ultrafast Optical Nonlinear Response
In the December 1, 2007 issue of Optics Letters (p. 3435), G. Ma and S.H. Tang of Shanghai University in China and the Natio
Data Loading...
