Atomic force microscopy characterization of stable faces in cubic C60 and hexagonal C60, 2CCl4 single crystals

Well-developed surfaces of crystals of pure C-60 grown in various experimental conditions have been examined by atomic force microscopy. To our knowledge, macroscopic "pure" faces of bulk crystals have not been studied by near-field microscopies. The crystals obtained by sublimation or by rapid evaporation of C-60 solutions in toluene have a fee structure. By slow evaporation of fullerene C-60 solution in CCl4 at room temperature, a stable solvate C-60, 2CCl(4) crystallizes in a simple hexagonal system, with a flat large (0001) surface. The morphological habits of the fee crystal show macroscopically well-defined (100) and (111) faces, with some examples of faces which cannot be attributed unambiguously. For the first time, AFM images have been obtained for all these faces. In every case, molecular resolution has been achieved. The (100) face of the fee crystal, which has been shown by SEM to accumulate impurities, appears at a molecular scale to be constituted by a juxtaposition of micro domains, each of which having all the angle and distance characteristics of the (100) face. The AFM images demonstrate directly that the molecular arrangement is the same on the (111) face of the fee crystal of pure C-60 as on the (0001) face of the hexagonal crystal of the C-60, 2CCl(4) solvate. Measurements on AFM images of a face that could not be indexed give results which induce us to assign tentatively this surface to the (311) face of the crystal.