Nano Focus: Change in material boosts prospects of ultrafast single-photon detector
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no Focus Change in material boosts prospects of ultrafast singlephoton detector
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y swapping one superconducting material for another, B. Baek and colleagues at the National Institute of Standards and Technology (NIST) have boosted the efficiency of an ultrafast single-photon detector while also extending light sensitivity to longer wavelengths. The new tungsten-silicon alloy could make the ultrafast detectors more practical for use in quantum communications and computing systems and emerging applications such as remote sensing. The detector, made of superconducting nanowires, is one of several sensor designs developed or used at NIST to register individual photons. The original, uncoated nanowire detector uses wires made of niobium nitride and has a detection or quantum efficiency of less than 10% when coupled to a fiber. As reported in the June 21 online edition of Applied Physics Letters (DOI:10.1063/1.3600793), the tungsten-
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VOLUME 36 • AUGUST 2011
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These nanoparticles were then freeze-dried 200 μm and stored at different temperatures (freezer, refrigerator, and room temperature) for between one and three months. Their ability to be taken up by the cells was then re-tested. According to Green, after six months in storage, the effectiveness dropped by about half, but there was virtually no change in efBrain cancer cells produce a green fluorescent protein. DNA encoded to produce the protein was delivered to the fectiveness after three cancer cells by freeze-dried polymer-DNA nanoparticles. months of storage at Credit: Stephany Tzeng. room temperature. Furthermore, the tion with, and even instead of brain team found that certain nanoparticles surgery,” said A. Quiñones-Hinojos, an had a particular affinity for brain tumor associate professor of neurosurgery and cells over healthy brain cells. oncology at Johns Hopkins. “I could imagine particles based on this technology being used in conjunc-
silicon alloy version has an efficiency of 19–40% over a broad wavelength range of 1280–1650 nm, including bands used in telecommunications. The limitations are due mainly to imperfect photon absorption, suggesting that, with further design improvements, detector efficiency could approach 100% reliably, the researchers said. Niobium nitride is difficult to make into nanowires that are narrow, long, and Colorized micrograph of an ultrafast single-photon detector made of superconducting nanowires. Electron beam sensitive enough to work lithography is used to pattern the nanowires (colorized well. The researchers selectvertical lines) on a thin film of tungsten-silicon alloy, which produces more reliable signals than the niobium nitride ed the tungsten-silicon alloy material used previously. Credit: Baek/NIST. mainly because it has higher energy sensitivity, resulting er energy sensitivity, tungsten-silicon in more reliable signals. A photon breaks nanowires can have larger dimensions more electron pairs in the tungsten(150 nm wide versus 100 nm or less for silicon alloy than in niobium nitride. The n
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