Fullerens

It is quite a task  to perform experiments on diffraction on the limit of massive matter waves, namely with the smallest footballs of the world. The group of Prof. Anton Zeilinger in Vienna succeeded to produce a fullerene beam and to diffract it on an extremely fine grating.

Fullerenes are molecules, which consist of 60 (C60) or 70 (C70) carbon atoms arranged in polyeder. The molecule C60 has a mass of 720 atomic units and shows a shape identical to that of a football, consisting of 12 pentagons and 20 hexagons. The beam of C60 molecules is extracted at approx. 600 °C from an oven, collimated by two slits and diffracted on a grating. Finally the scattered "balls" are optically stimulated to emit radiation and thus can be detected.

 

Experimental set-up for diffraction tests with matter waves consisting of C60-"footballs".


The molecular beam is extracted from an oven at a velocity of approx. 210 m/s, which corresponds to a de Broglie wavelength of only 2.5 pm (pm = 10-12 m, or one billionth mm). The used gratings are made from silicon nitride, which has slits of 50 nm width and pitch of 100 nm (nm = 10-9 m). It is quite difficult to manufacture such a fine structured grating that matches the short wavelength. The distances between the slits are still 40.000 times larger than the wavelength of the molecular beam. At this extreme ratio of the wavelength to the lattice size we find that the angle between the center and the 1st diffraction maximum is only 1.4*10-3 degrees, which corresponds to only 0.03 mm at a distance of 1.25 m on the detection plane.

The figure compares the results with and without a grating. The bottom plot shows the width of the original molecular beam, which also has a certain velocity distribution and contains a number of "uncompleted" molecules like for example C59. The top plot shows the clear diffraction pattern when the grating is inserted.

The C60 molecules are the ever-heaviest particles, which were successfully used in the diffraction experiments to study the de Broglie matter waves.