Fabrication of Suspended Microand Nanostructures Accomplished by Direct Drawing of Polymer Fibers
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delivered a lithium insertion capacity correlating to 8.6 mol lithium per mol WS2 nanotube whereas the lithium insertion capacity was 0.6 mol lithium per mol crystalline WS2. The researchers attribute the nanotube capability to its 1D topology and open structure. They further found that the WS2 nanotubes show stable cyclability over a wide voltage range (0.1–3.1 V vs. Li/Li+), so that batteries built with these materials will be tolerant for overcharge and overdischarge. Based on their results, the researchers said that WS2 nanotubes may be an attractive material for usage in electrochemical applications. In particular, they said, the capacity for storing Li is much enhanced in the nanotube modification of the material than the crystalline powder materials. MARKUS J. BUEHLER
Fabrication of Suspended Microand Nanostructures Accomplished by Direct Drawing of Polymer Fibers In designing and fabricating microand nanostructures, ease of fabrication is an important consideration. S. Harfenist,
R.W. Cohn, and co-workers at the ElectroOptics Research Institute and Nanotechnology Center in the University of Louisville have demonstrated a simple and versatile method for creating suspended micro- and nanostructures by direct drawing of fibers from liquid polymers. The novelty of this approach is that it offers control and flexibility of forming and simultaneously patterning polymer fibers as suspended bridges and networks of three-dimensional structures. As reported in the October 13 issue of Nano Letters (p. 1931), the researchers used tips attached to an atomic force microscope (AFM) or a computer-controlled micromill to draw fibers from a drop of poly(methyl methacrylate) (PMMA) electron beam resist placed on a substrate. The tip was dipped into the polymer drop several times until a fiber formed between the tip and the drop. The tip end of the fiber was drawn to a second drop of liquid polymer or adhered to a surface to form a polymer fiber that dries and solidifies into a suspended beam. The fibers produced were circular and uniform in diameter ranging
from under 50 nanometers to tens of microns and can be made to span lengths from a few microns to several centimeters. This approach can be modified to produce suspended fibers in parallel and to pattern and orient them into three-dimensional geometries. For example, a bead of liquid polymer applied and allowed to dry momentarily on the edge of a stiff sheet of plastic or a microscope glass slide before being quickly dragged over an array of sharp silicon tips results in fibers suspended along each row of tips (see Figure 1). In a different example, polymer fibers several centimeters long can be drawn by hand on the cleaved end of a glass optical fiber and can be repeatedly manipulated and coiled without breaking. Fibers have been formed at draw rates between 10 µm/s and 100 mm/s, depending upon experimental conditions. According to the researchers, polymer fibers formed and patterned by this approach may be applied as threedimensional templates for subsequent processin
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