Thread View: sci.materials
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Started by Swami srinivasan
Thu, 09 Apr 1992 00:10
Why do Fullerenes form in MBE?
Author: Swami srinivasan
Date: Thu, 09 Apr 1992 00:10
Date: Thu, 09 Apr 1992 00:10
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have a nagging question... Recently someone from Arizona (Hoffman's (?) group) came over to UNM to talk about fullerenes. He was once a grad student studying inter-galactic clouds or something like that, when Fullerenes were discovered. He mentioned that fullerenes can also be made by MBE growth. Being a compound semiconductors person, i am used to the concept of MBE being used to grow thin films/superlattices, etc. Except for some 3-D defects, the growth usually is uniform across the wafer (at that's what we try to do most of the time). How does a fullerene form? i would have expected a flat thin film of C to deposit. What makes the few atoms that first contact the substrate to grow upward, with the "prior" knowledge of C-60 geometry? How does the structure actually grow and under what special conditions (in an MBE)? Can these be grown with MOCVD? More generally, how do fullerenes form at all? There must be some particular feature about the bonding in this structure, that justifies the Carbon atoms forming the elaborate sphere. If i am correct, an ordered structure like that must entail lower entropy than just amorphous C; i.e., there must be energy put in during its formation to make it a preferred structure. So why does it happen? I hope these aren't silly questions. Any info/references will be welcome. i am curious about the topic and slowly getting interested, anticipating some non-linear optics applications. swami srinivasan ======================================================================= swaminathan srinivasan center for high tech materials univ. of new mexico, albuquerque cogito ergo sum swami@chtm.eece.unm.edu =======================================================================
Re: Why do Fullerenes form in MBE?
Author: Tapesh Yadav
Date: Thu, 09 Apr 1992 23:41
Date: Thu, 09 Apr 1992 23:41
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================= In article <phrjz0#@lynx.unm.edu> swami@chtm.eece.unm.edu (Swami srinivasan) writes: > > have a nagging question... > > He mentioned that fullerenes can also be made by MBE growth. > MBE process is news to me. Did you ask him for references? > How does a fullerene form? i would have expected a flat >thin film of C to deposit. What makes the few atoms that first contact >the substrate to grow upward, with the "prior" knowledge of C-60 >geometry? How does the structure actually grow and under what special >conditions (in an MBE)? Can these be grown with MOCVD? > Fullerenes do grow, quite profusely and in concentric helical pattern, on negative electrodes in electrode arc process. These fullerenes are being called bucky tubes - for their tubular shapes. Reference: S. Iijima, Nature, last year. I am not aware of C60 growing upward. C60 closes. C60, therefore has to begin, grow/extend and then end. Fullerenes are convex structures and follow Euler's theorem of geometry. They have to have 12 pentagons. Bucky tubes have all these pentagons at the tube ends. The growth of the bucky tubes therefore begins with pentagons. Pentagons lead to curvature. This curvature gives the first direction - "growth upward." The helical structure of the each bucky tube easily and elegantly permits self growth with prior knowledge - much like the DNA in life forms. Use some jelly beans/potato pieces with match sticks/tooth pick and play it out. See Iijima's bucky tube figures in Nature and in Science (last year sometime), to get hints. > More generally, how do fullerenes form at all? There must be > I hope these aren't silly questions. Any info/references will >be welcome. i am curious about the topic and slowly getting interested, >anticipating some non-linear optics applications. > > swami srinivasan Formation mechanism: different processes seem to suggest different hypothesis. For the graphite vaporisation processes: the hypothesis that is still not disproved is by Smalley et al. (See latest issue of Accounts of Chemical Research - special issue on buckministerfullerenes). Your anticipation on nonlinear optics applications is already racing towards reality. See recent issues of Nature (Mar or Feb). So don't get interested slowly. Plunge. There is too much fun in the global bucky olympics. T.Y. ---- tyadav@athena.mit.edu
Re: Why do Fullerenes form in MBE?
Author: Scott D. Berry
Date: Tue, 14 Apr 1992 07:39
Date: Tue, 14 Apr 1992 07:39
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In article <phrjz0#@lynx.unm.edu> swami@chtm.eece.unm.edu (Swami srinivasan) writes: > > have a nagging question... > > Recently someone from Arizona (Hoffman's (?) group) came over >to UNM to talk about fullerenes. He was once a grad student studying >inter-galactic clouds or something like that, when Fullerenes were >discovered. > > He mentioned that fullerenes can also be made by MBE growth. >Being a compound semiconductors person, i am used to the concept of >MBE being used to grow thin films/superlattices, etc. Except for >some 3-D defects, the growth usually is uniform across the wafer (at >that's what we try to do most of the time). > Are you sure that the fullerenes are formed in the MBE process? I do know of work involving the sublimation of fullerenes in MBE machines (where the "molecule" in MBE is the fullerene) to form single crystal thin films. As far as I know, you cannot form C60 and C70 from C atoms in a MBE environment. > How does a fullerene form? i would have expected a flat >thin film of C to deposit. What makes the few atoms that first contact >the substrate to grow upward, with the "prior" knowledge of C-60 >geometry? How does the structure actually grow and under what special >conditions (in an MBE)? Can these be grown with MOCVD? As I said above, I doubt it. >======================================================================= >swaminathan srinivasan >center for high tech materials >univ. of new mexico, albuquerque cogito ergo sum > >swami@chtm.eece.unm.edu >======================================================================= Grower of single crystal magnetic oxide materials (iron oxide, nickel oxide): Scott D. Berry Assistant Professor of Physics Florida State University 315 Keen Bldg, B-159, Tallahassee, FL 32306-3016 (904) 644-1218 INTERNET: berry@redbeard.physics.fsu.edu BITNET: berry@fsu
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