MRS-I Announces XIth AGM
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laser. The Cluster/ particle beam is injected into a high vacuum Chamber and ionized using an excimer laser for time-of-flight mass spectroscopy. A beam chopper running synchronously with the CÖ 2 laser is used for size selection. High-resolution electron microscopy was used to reveal details of the crystalline structure of Sili con nanoparticles as a function of size. Huisken also described work on photoluminescence of the nanoparticles. Size selection is important for photoluminescence, and smaller nanoparticles result in a wider bandgap. A uv laser was used to excite the films and the photoluminescence was spectrally analyzed. Larger particles were seen to luminesce at a lower energy, or longer wavelength. An astrophysical connection was made in this Ses sion: A b r o a d red emission b a n d is observed in astronomical objects, for example in the Orion constellation. This has been attributed to photoluminescence of an interstellar dust grain component excited by the uv radiation from a nearby star. This astrophysical aspect was discussed also in a separate paper by O. Guillois (CEA, France) in Symposium I. Computational materials science, the topic of Symposium C, is showing a closer integration than before of the diverse m e t h o d o l o g i e s a n d progress t o w a r d hybrid methods. To study electronic struc ture and dynamics simultaneously, the Car-Parrinello technique has become a real "workhorse" and it is the method of choice for Systems of up to a few hundred atoms observed over time periods on the order of 10 ps. For larger Systems or longer times, tight-binding molecular d y n a m i c s is the preferred approach. Several scientists reported applications of these methods to novel fields such as biomolecules and pharmacological Systems, besides the more traditional materials (e.g., metals a n d semiconductors). Classical electronic band structure meth ods conrinue to be very useful tools yielding a great deal of information, from binding energies and activation barriers to excited states. Classical particle-based simulations, using the Monte Carlo (MC) or molecular dynamics (MD) approaches, increasingly rely on energetic Information obtained from first-principles calculations rather than resorting to a phenomenological description. With continuing advances in Computer power, MC and MD now permit the study of mesoscopic Systems and in some cases a p p r o a c h the scale of macroscopic objects. The largest System reported at the Symposium had over 5,000,000 atoms, with time-scales in MD simulations approaching milliseconds (on the order of tens of millions of time-steps). Spectacular though these numbers may be, only continuum methods permit stud-
ies of truly macroscopicaUy large Systems, over long time scales (in some cases rang ing on the order of centuries). Impressive work along those lines was reported for electromigration, metallic foams, and micromagnetism, to name a few. Here too, major progress has been made in the last few years. Clearly the main challenge in the years ahead will be
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