In the caption to Figure 3 in the paper, the authors note that they use a different .... http://www.nobel.se/chemistry/laureates/1998/index.html. ⢠Is this the world's ...
Miniature Machines: "Pulling" Nanowires Angew. Chem. Int. Ed. 2003, 42, 2251-2253 thermodynamics • quantum chemistry • nanotechnology
Nanotechnology opens a window between engineering, physics and chemistry. Broadly defined, it is an area of research where the critical dimensions are on the order of 103 nm or less. Chemists might define nanotechnology more narrowly, as the design and construction of devices which are well defined on the molecular level. The ability to see and manipulate matter at the atomic level has changed dramatically over the last 25 years. My physical chemistry text made the point that you could not "see" an atom; ten years later, in 1989, scientists at IBM used atomic force microscopy to position Xe atoms on a Ni surface to spell "IBM" in what likely remains the world's smallest advertisement. Now researchers can assemble machines using structures such as quantum dots, nanotubes and nanowires. For example, CdSe-ZnS quantum dots have been used as in vivo labels to image blood vessels in mice [Science 2003, 300, 1434]. Carbon nanotubes have been used as building blocks in molecular electronics [Nature 1998, 393, 49]. Researchers in nanotechnology are interested in learning how to control the size and shape of nanomaterials and in characterizing their unique properties. Nanoscale materials can have very different optical and electronic properties relative to the bulk state. Gold nanorods, for example, have 10 million times the fluorescence intensity of bulk gold [Chem. Phys. Lett. 2000, 317, 517]. The authors of the paper considered here use a theoretical approach to understand how mechanical forces can result in the growth of single atom gold nanowires on a surface.
Nano comes from the Greek for dwarf: νανοσ.
Does anyone actually use nanowires? Well, Dr. Ock in Spiderman 2 claimed to use “nanowires” to connect his neural circuitry to a machine circuit. In fact, silicon nanowires have recently been used to build sensors for DNA. The sensors are designed to detect the presence of mutations in a cystic fibrosis gene. [Nano Letters 2004, 4, 51 -54]
© 2004 Michelle M. Francl. May be reproduced for use in an individual classroom. May not be sold or used in other collections without the express permission of the author. These materials were produced as part of “P-Chem with a Purpose,” funded by the National Science Foundation, grant DUE-0340873.
Miniature Machines Angew. Chem. Int. Ed. 2003, 42, 2251-2253
Towards "Mechanochemistry": Mechanically Induced Isomerizations of Thiolate-Gold Clusters Translated in a nano-second To a c.c. of poisonous nothing In a giga-death W.H. Auden in “About House” 1965
Daniel Kr_ger, Roger Rousseau, Harald Fuchs, Dominik Marx*
Questions and Problems The questions and problems below are based on the paper cited. They are meant to encourage you to read the paper critically, you may need to consult other articles in the literature to answer these question. If you were the editor of the journal, what questions might you have for the authors?
Engineers think that equations approximate the real world. Scientists think that the real world approximates equations. Mathematicians are unable to make the connection.
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1. How do the Au-Au bond energies in small clusters compare to those for CC bonds in molecules? in graphite? What, if anything, can you conclude about how the bulk compares to clusters? What does this mean for the conclusions the authors can draw in this study? 2. How is density functional theory (DFT) different from molecular orbital (MO) theory? Why do the authors use DFT rather than MO theory? 3. In the caption to Figure 3 in the paper, the authors note that they use a different sign convention than in an earlier paper by some of the same authors [Phys. Rev. Lett. 2 0 0 2 , 8 9 , 186402]. What are the different sign conventions? Does this matter? 4. The authors constrained one of the gold atoms to remain in the left-hand plane (see Figure 1 of the paper) as they pull the two planes apart. Identify that gold atom in structure A-I in Figure 2. Could another atom have been reasonably selected? In that case would the results of the authors' simulation be different? In what way? 5. The energy versus distance plot in Figure 3 of the paper is discontinuous. Would you expect it to be? Why or why not? 6. The authors don’t mention entropy. Should they? 7. Explain the equations the authors give for estimating the energies involved in the molecular rearrangements leading to the formation of a nanowire. 8. In the description of their model in the text of the paper,
Miniature Machines
the authors state that the authors state that zi=0 Å, yet Figure 1 seems to imply that zi>0 Å. Can you reconcile this apparent notational inconsistency? How long is the wire in the end (that is in structure E-II)? 9. Using the data in the table below, estimate the work done in pulling the 5 atom long gold wire. z/ Å
Force/n N
z/ Å
Force/n N
0.0 0.35 0.67 1.0 1.33 1.67 2.0 2.33 2.67 3.0 3.5 4.0 4.25
0.0 -0.25 -0.50 -1.0 -1.25 -1.4 -1.4 -1.5 -1.5 -1.6 -2.0 -1.25 -1.40
4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0
-0.75 +0.25 -0.3 -0.8 -1.8 -2.25 0.0 -0.25 -0.75 -1.0 -1.5 -1.5
10. The force required to elastically stretch a wire is given by − o F= EA o where A is the cross-sectional area of the wire, o is the length of the unstretched wire and the length of the wire after it is stretched. E is the elastic modulus, sometimes called Young's modulus. Using this equation, compute the force as a function of distance stretched for the gold nanowire as it is stretched from E-I to E-II. The elastic modulus for bulk pure gold is 7.448 x 1010 Pa. Compare the values obtained from this equation to those obtained in the paper. Is the behavior of the nanowire qualitatively or quantiatively different from that of the bulk?
Mildred Dresselhaus Professor of Physics and Electrical Engineering, MIT Mildred Dresselhaus's research interests include carbon nanotubes, bismuth nanowires and low dimensional thermoelectricity. She was the first woman to be tenured in engineering at MIT and was science advisor to President Clinton in 2000. Prof. Dresselhaus grew up in the Bronx during the Depression, and got her bachelor's degree from Hunter College. She spent a year at Cambridge on a Fulbright fellowship followed by a Ph.D. from University of Chicago in 1958. She has four children and is married to another scientist, Gene Dresselhaus. Want to know more? Read "Single Nanotube Raman Spectroscopy." Dresselhaus, M. S.; Dresselhaus, G.; Jorio, A.; Souza Filho, A. G.; Pimenta, M. A.; Saito, R.; Acc. Chem. Res. 2002; 35 1070.
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Miniature Machines Further Reading
• • The physicist's greatest tool is his wastebasket. Albert Einstein
• • • •
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"Molecular Machines", Accts. Chem. Res., vol. 34, no. 6 (2001). A special issue devoted to nanotechnology. Phillip Ball, Designing the Molecular World, Princeton University Press, 1994. pp. 38-53; 186-215. "C60: Buckminsterfullerene", H.W. Kroto, J.R. Heath, S.C. O'Brien, R.F. Curl, R.E. Smalley, Nature 1985 318, 162. The paper that began it all. In 1998 Walter Kohn shared the Nobel Prize in Chemistry for his work on density functional theory. See http://www.nobel.se/chemistry/laureates/1998/index.html Is this the world’s smallest advertisement? See IBM spelled in atoms at http://www.almaden.ibm.com/vis/stm/atomo.html. “Direct Ultrasensitive Electrical Detection of DNA and DNA Sequence Variations Using Nanowire Nanosensors”, Jong-in Hahm and Charles M. Lieber, Nano Letters 2004, 4, 51 –54. A nanosensor for biological applications.
