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           COLLOQUIUM OF THE COMPUTATIONAL MATERIALS SCIENCE CENTER
                             College of Science
                      (CDS Department CSI 898-Sec 001)
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    STRUCTURE AND STABILITY OF SUSPENDED METAL MONOATOMIC CHAINS

                               Anwar Hasmy
 NIST Center for Theoretical and Computational Nanosciences, Gaithersburg, MD
         and INEST Group, Philip Morris USA, Richmond, VA  23234

Since the spectacular achievement of the ultimate thin wire (a suspended
linear gold atom chain), an intense research activity has been devoted to
determine the ubiquity of this phenomenon. Although formations of these
monatomic chains have been corroborated indistinctively through
high-resolution transmission electron microscopy observations and conductance
measurements on mechanically controllable break junctions composed of 5d metal
nanowires, results on 3d and 4d metals differ depending on the considered
technique. Moreover, the high stability exhibited by such chains still remain
a mysterious because quantum calculations predict a zigzag shape instead of
the visualized linear structure. I will present a systematic molecular
dynamics study based on the NRL tight-binding approximation to investigate the
breaking process of monovalent metal nanowires. Our results show that at low
temperature (4 K) gold, silver and copper exhibit linear and stable monatomic
chains, while at room temperature silver and copper chains become unstable by
overcoming a potential barrier that allow them to adopt the zigzag geometry.
The average number of atoms contained in these suspended atomic chains depend
on the temperature and the metal specie. Besides to clarify the controversy in
the literature on their formation in 3d and 4d metals, these findings give
insights on the advantages and limitations of detecting them through
conductance measurements on breaking nanowires.

                          November 20, 4:30 pm
                   Room 301, Research I, Fairfax Campus

Refreshments will be served at 4:15 PM.
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Find the schedule at http://www.cmasc.gmu.edu/seminar/schedule.html
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