Nanoblades Fabricated from Magnesium
- PDF / 754,902 Bytes
- 2 Pages / 576 x 783 pts Page_size
- 16 Downloads / 207 Views
technique called replica molding. Then they fasten commercially available quantum dots to the surface of the plastic. “We designed the photonic crystal to efficiently capture the light from an ultraviolet laser and to concentrate its intensity right within the surface where the quantum dots are located,” said Cunningham, who also is affiliated with the university’s Beckman Institute, the Micro and Nanotechnology Laboratory, and the Institute for Genomic Biology. “Enhanced absorption by the quantum dots is the first improvement we made.” Enhanced, directed emission from the quantum dots is the second improvement. Quantum dots normally give off light in all directions. However, because the researchers’ quantum dots are sitting on a photonic crystal, the energy can be channeled in a preferred direction, such as toward a detector. The group reported an enhancement of fluorescence intensity by a factor of up to 108 as compared to quantum dots on an unpatterned surface. “The enhanced brightness makes it feasible to use photonic crystals and quantum dots in biosensing applications from detecting DNA and other biomolecules, to detecting cancer cells, spores, and viruses,” Cunningham said. “More exotic applications, such as personalized medicine based on an individual’s genetic profile, may also be possible.”
of intensive research for use in sensors to detect, for example, molecular forces. The researchers used an rf circuit to cool a 200 mm × 14 mm × 1500 µm silicon cantilever vibrating at its natural resonant frequency of 7000 cycles/s (see Figure 1). The scientists cooled it from room temperature (~23°C) to –228°C. Other research groups have used optical techniques to chill microcantilevers to lower temperatures, but the rf technique may be more practical in some cases, because the equipment is smaller and easier to fabricate and integrate into cryogenic systems. By extending the rf method to higher frequencies at cryogenic temperatures, researchers hope eventually to cool a cantilever to its “ground state” near absolute zero (–273°C), where it would be essentially motionless and quantum behavior should emerge.
Radio Wave Cooling Offers New Twist on Laser Cooling Visible and ultraviolet laser light has been used for years to cool trapped atoms and, more recently, larger objects by reducing the extent of their thermal motion. Now, by applying a different form of radiation for a similar purpose, K.R. Brown and D.J. Wineland of the National Institute of Standards and Technology (NIST), J. Chiaverini of Los Alamos National Laboratory, and their colleagues have used radio waves to dampen the motion of a miniature mechanical oscillator containing more than a quadrillion atoms. Described in the September 2007 issue of Physical Review Letters (DOI: 10.1103/ PhysRevLett.99.137205), this demonstration of rf cooling of a relatively large object may offer a new tool for exploring the elusive boundary where the familiar rules of the everyday, macroscale world give way to the bizarre quantum behavior seen in the smallest particles o
Data Loading...
