A brighter future for silicon aerocrystals.What would it be like to hold in one's hand In one's possession or keeping. At one's risk, or peril; as, I took my life in my hand s>. See also: Hand Hand a solid, crystalline object composed almost entirely of empty space - a material so sparse in structure that it appears nearly as faint as the air itself? Such wispy wisp n. 1. A small bunch or bundle, as of straw, hair, or grass. 2. a. One that is thin, frail, or slight. b. A thin or faint streak or fragment, as of smoke or clouds. 3. , ethereal ethereal /ethe·re·al/ (e-ther´e-il) 1. pertaining to, prepared with, containing, or resembling ether. 2. evanescent; delicate. e·the·re·al adj. 1. masses - almost like a solid, translucent version of beer foam - do exist. Since their appearance in 1931, these aerogels have intrigued scientists, who search for efficient ways to make and use them in a wide variety of electronic and optical applications. Now, Leigh T. Canham, a physicist at the Defense Research Agency in Malvern, England, and his colleagues report a new method of drying that improves the production and quality of an aerogel aerogel, any of a group of extremely light and porous solid materials; the lightest is less than four times as dense as dry air. Aerogels are produced from certain gels (see colloid) by heating the gel under pressure, which causes the liquid in the gel to become relative made of highly porous silicon Porous Silicon (pSi) is a form of the chemical element silicon which has an introduced nanoporous holes in its microstructure, rendering a large surface to volume ratio in the order of 500m2/cm3. . Known as silicon aerocrystals, these materials have garnered much interest in the world of computers and electronic communications because of their ability to give off light. With their 95 percent porous structure, such crystals exhibit "strong photoluminesence," making them potentially useful as thin films for optical-electronic devices. The chemists describe their results in the March 10 NATURE. When a wet, porous material dries by evaporation, the changeover of the liquid to a vapor can cause stresses and strains that "induce cracking, shrinkage, and even complete disintegration of delicate solid skeletons," says Canham. "Think of the way a riverbed cracks as it dries," he explains. Using supercritical drying Supercritical drying is a process to remove liquid in a precisely controlled way, similar to freeze drying. It is useful in the production of microelectromechanical systems and the drying of spices, and is commonly used in the production of aerogel. - in which carbon dioxide carbon dioxide, chemical compound, CO2, a colorless, odorless, tasteless gas that is about one and one-half times as dense as air under ordinary conditions of temperature and pressure. gas is warmed to 40 degrees C and pressurized pres·sur·ize tr.v. pres·sur·ized, pres·sur·iz·ing, pres·sur·iz·es 1. To maintain normal air pressure in (an enclosure, as an aircraft or submarine). 2. to 100 atmospheres - the scientists can remove liquid from the material's pores and avoid the fractural contractions that ordinarily accompany drying. Compared to silicon aerocrystals dried by evaporation, which showed heavy cracking, the specially dried crystals revealed no cracks when examined with electron microscopes, both scanning tunneling and scanning transmission, Canham and his colleagues report. While this kind of drying has come into wide use in preparing biological and ceramic materials, it has only now proved useful for making highly porous silicon. Moreover, the supercritically dried aerocrystals showed that they could generate light more efficiently than similar crystals dried by evaporation, the researchers say, The reason, they contend, lies in the fact that smaller crystal "skeletons" survive the drying process. Supercritical drying, they add, makes possible efficiencies that "would not otherwise be achievable." |
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