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Nanonshells May Be Key to Next Wave of LightBased Technologies

first_imgAddThis Share CONTACT: Lia Unrau PHONE: (713)831-4793E-MAIL: [email protected] NANOSHELLS MAY BE KEY TO NEXT WAVE OF LIGHT-BASEDTECHNOLOGYNano-sized metal spheres may be thekey to the next wave of light-based technologies. Rice University researchers, led by Naomi Halas, professor ofelectrical and computer engineering, developed metal nanoshells–particles withan insulating core coated by a thin shell of gold–the “malted milk balls” ofthe nanoscale world. Nanoshells can absorb or scatter light at virtually anywavelength in the visible or infrared ranges depending upon the dimensions ofthe particle’s core and shell. Metal nanoshells may be embedded in solid-state materials andfilms, such as plastics or glasses, or attached directly to surfaces forspecial-purpose coatings. New products could include energy efficient paints andwindows, coatings for cars, airplanes or buildings, solar collection materials,or even fabrics. Metal nanoshells may also prove quite valuable in chemical andbiosensors and in optical switches. They have been used to enhance signals inRaman spectroscopy, a chemical monitoring technique extensively used inindustry.Their ability to absorb light is so great that if you put justone thousandth of an ounce of nanoshells into a quart of water, the water wouldbe completely opaque. The nanoshells currently range in size from 50 to 1,000nanometers in diameter; one nanometer is one-billionth of a meter.A key is that Halas and her team can control which wavelengthof light is absorbed or scattered by the nanoshells by controlling the particlesize and the ratio of the particle’s core and shell. The particles can be madeto absorb or scatter visible light, but more important, they can absorb orscatter light in the infrared. This range, particularly around the one micronwavelength, is of critical importance in many technological applications. Veryfew materials absorb light at this wavelength, and those that do are often quiteexpensive, difficult to produce, and contain hazardous or toxicelements.“The nanoshells act as an amazingly versatile optical componenton the nanometer scale: they may provide a whole new approach to opticalmaterials and components,” Halas says. Halas and graduate students Richard Averitt and Steve Oldenburgare studying the fabrication, properties and uses for these particles, and theyhave filed for a patent on this technology.Averitt has studied the optical properties of naturallyoccurring nanoshells–gold-terminated gold sulfide nanocrystals. He hasexplained their growth process and how their structure corresponds to theiroptical properties. During the past year, Oldenburg has developed a method ofassembling composite metal nanoshells with varying diameters and shellthicknesses that consist of glass cores and a gold shell.“We are pursuing strategies to get us out to the five micronrange in the infrared,” Halas says, “and we’re pretty confident that we can dothat by refining our current method. Using other techniques, I think we might beable to get out to 10 microns and beyond, into the far infrared.”Since the 15th century, craftsmen have embedded nanometer-sizedgold particles into glass to produce the brilliant red of stained glass windows.The remarkable optical properties of gold nanoparticles have been used in manytechnological applications ranging from optical filters to chemical sensors andbiological markers. In 1951 it was discovered theoretically that one could changethe color of small gold particles in a highly controlled manner by changingtheir shape from solid metal spheres to thin metal shells. Up until now,however, it has proven very difficult to make these particles. Halas and herco-workers have developed a highly reproducible method to fabricate metalnanoshells.In a recent article in Chemical Physics Letters, the teamoutlined the fabrication process of these nanoparticles and showed how theirstructure corresponds to their optical properties.This work is funded by the Office of Naval Research, theNational Science Foundation, NASA and the Robert A. Welch Foundation.###last_img

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