The Mudcat Café TM
Thread #59418 Message #1642650
Posted By: Amos
06-Jan-06 - 12:35 AM
Thread Name: BS: The Mother of all BS threads
Subject: RE: BS: The Mother of all BS threads
Since I first heard of Drexler' and Feynman and their vision of building with the very very small, I have dreamed of a day when the entire energy budget of a home would be met by the ambient impact of solar, wind, noise, vibration, cosmic rays and what have you on the structure of the house itself.
So -- to me, anyway -- this may be important,. Because it could not only lead to a major step toward energy independence for the US, but also untie millions of poorer cultures from their energy-driven shackles:
os Alamos National Laboratory scientists have discovered that a phenomenon called carrier multiplication, in which semiconductor nanocrystals respond to photons by producing multiple electrons, is applicable to a broader array of materials that previously thought. The discovery increases the potential for the use of nanoscrystals as solar cell materials to produce higher electrical outputs than current solar cells.
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In papers published recently in the journals Nature Physics and Applied Physics Letters, the scientists demonstrate that carrier multiplication is not unique to lead selenide nanocrystals, but also occurs with very high efficiency in nanocrystals of other compositions, such as cadmium selenide. In addition, these new results shed light on the mechanism for carrier multiplication, which likely occurs via the instantaneous photoexcitation of multiple electrons. Such a process has never been observed in macroscopic materials and it explicitly relies on the unique physics of the nanoscale size regime.
According to Richard Schaller, a Los Alamos scientist on the team, "Our research of carrier multiplication in previous years was really focused on analyzing the response of lead selenide nanocrystals to very short laser pulses. We discovered that the absorption of a single photon could produce two or even three excited electrons. We knew, somewhat instinctively, that carrier multiplication was probably not confined to lead selenide, but we needed to pursue the question."
Lead project scientist Victor Klimov explains, "Carrier multiplication actually relies upon very strong interactions between electrons squeezed within the tiny volume of a nanoscale semiconductor particle. That is why it is the particle size, not its composition that mostly determines the efficiency of the effect. In nanosize crystals, strong electron-electron interactions make a high-energy electron unstable. This electron only exists in its so-called 'virtual state' for an instant before rapidly transforming into a more stable state comprising two or more electrons."
Full article can be found here.
In other news of great interest, University of Iowa researchers have found a star orbiting a "medium-sized" black hole -- about 1,000 times more massive than the sun -- in the nearby starburst galaxy M82, a development that may help explain how medium-sized black holes form and evolve, according to a paper to be published in the Jan. 5 issue of Science Express, the online version of the journal Science. Full story at http://www.physorg.com/news9605.html.
And in an investigation smacking of forensic detective work, scientists have measured the rate of star death and rebirth in our galaxy by combing through the sparse remains of exploded stars from the last few million years. They conclude the Milky Way produces seven new stars a year.
Full story here.