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Diffraction and Interference with Fullerenes:
Wave-particle duality of C60

The art of hitting the goal with every shot


"Wave-particle duality of C60"
Markus Arndt , Olaf Nairz, Julian Voss-Andreae, Claudia Keller,Gerbrand van der Zouw
and Anton Zeilinger
Nature 401, 680-682, 14.October 1999
              More recent experiments on fullerene interference: 
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Introduction to de Broglie Interferometry with large Molecules

Observation and application of matter waves has become one of the leading themes in the development of experimental physics in the 20th century. 

What we achieved

We have observed de Broglie wave interference of the buckminsterfullerene C60 with a wavelength of about 3 pm through diffraction at a SiNx absorption grating with 100 nm period. This molecule is the by far most complex object revealing wave behaviour so 
far. The buckyball is the most stable fullerene with a mass of 720 atomic units, composed of 60 tightly bound carbon atoms. 

Why should you care about it ?

It is intriguing that C60 can almost be considered to be a body obeying classical physics in view of its many excited internal degrees of freedom. Leaving the source, it has as much as 7 eV of internal energy stored in 174 vibrational modes, and highly excited rotational states with quantum numbers greater than 100. Fullerenes can emit and absorb blackbody radiation very much like a solid and they can no longer be treated as a simple few level system. 
Quantum interference experiments with large molecules, of the kind first reported here, open up many novel possibilities among them decoherence studies and nanolithography experiments.

A new kind of football game :-)

While the mass of a buckyball does not agree with the requirements for footballs (US: soccer balls) as defined by the International Football Association (FIFA) the symmetry and shape of this molecule actually does in all respects. 
Note that the ratio between the diameter of a buckyball (1 nm) and the width of our diffraction grating slits (50 nm) compares favorably with the ratio between the diameter of a football (22 cm) and the width of a goal (732 cm) according to FIFA standards. 
The distance between the source and the detector corresponds in this scaling to the distance between the Earth and the moon. 



Setup of the diffraction experiment

  • C60 powder is heated to ~ 600 ... 700°C in a resistively heated oven. 

  • The velocity distribution is very broad and faster than purely thermal. 

  • The molecular de Broglie wavelength is centered at ~ 2.5 pm. 

  • The de Broglie wave length is thus ~ 400 times smaller than the size of the particle 

  • (1nm diameter of the electron shell) 
  • The hot and divergent beam is collimated to a pencil of ~ 10µrad divergence. 

  • Buckyballs that pass the second slit are transversely cold 
  • The SiN diffraction grating has a nominal gap width of 50nm and a grating constant of 100nm 

  • After free evolution over 1m the molecules are detected via thermionic ionization by a tightly 

  • focused Argon ion laser beam at 24 W. 
  • The positive ions are counted by a secondary electron counting system. 


The velocity distribution


The most probable velocity of 210 m/s corresponds to a deBroglie wavelength for C60 of ldB = 2.5 pm !

The grating


The grating was manufactured by Tim Savas, working in the group of Henry Smith at MIT

A Look into the lab 

Experimental Results: Diffraction of C60 at a SiN grating

Interpretation of the diffraction curve

  • Interference fringes can clearly be seen 

  • Theory and experiment in good agreement although 

  • - molecules are highly excited, with internal T=600°C
    - molecules are fast and dispersed with external T=600°C
    - different isotopes present in the sample (12C60,12C5913C1, ...)
  • Fitted gap width smaller than design gap width 

  • - contaminations ?
    - van der Waals forces ?
  • contrast currently mainly limited by 

  • - collimation 
    - width of velocity distribution
    - variation of slit widths in the grating ?

Our Team (1999)

Julian Gerbrand Olaf  Markus Anton Claudia



- C60 Nobel Prize
- H. Kroto, Sussex
- R. Smalley, Rice
- H. Kuzmany, Wien
-E. Campbell, Göteborg
- E. Kolodney, Haifa
-L. Dunsch, Dresden
- Other groups active in fullerene research (1994)

Nanofabrication of SiN gratings:
- Henry Smith, MIT
- Tim Savas, MIT

Other groups currently working on interferometry with nanogratings:
- D. E. Pritchard, MIT
- J. P. Toennies, MPI für Strömungsforschung

Quantum Optics and Atom Optics:
- Quantum Optics and Atom Optics Link Collection (D. Rice)
- Institute of Physics: Highlights of the year (quantum precision)