Controllable synthesis of fullerene nano/microcrystals and their structural transformation induced by high pressure

Abstract

Fullerene molecules are interesting materials because of their unique structures and properties in mechanical, electrical, magnetic, and optical aspects. Current research is focusing on the construction of well-defined fullerene nano/microcrystals that possess desirable structures and morphologies. Further tuning the intermolecular interaction of the fullerene nano/microcrystals by use of pressure is an efficient way to modify their structures and properties, such as creation of nanoscale polymer structures and new hybrid materials, which expands the potential of such nanoscale materials for direct device components. In this paper, we review our recent progress in the construction of fullerene nanostructures and their structural transformation induced by high pressure. Fullerene nano/microcrystals with controllable size, morphology and structure have been synthesized through the self-assembly of fullerene molecules by a solvent-assisted method. By virtue of high pressure, the structures, components, and intermolecular interactions of the assemblied fullerene nano/microcrystals can be finely tuned, thereby modifying the optical and electronic properties of the nanostructures. Several examples on high pressure induced novel structural phase transition in typical fullerene nanocrystals with C60 or C70 cage serving as building blocks are presented, including high pressure induced amorphization of the nanocrystals and their bulk moduli, high pressure and high temperature (HPHT) induced polymerization in C60 nanocrystals, pressure tuned reversible polymerization in ferrocene-doped C60/C70 single crystal, as well as unique long-range ordered crystal with amorphous nanoclusters serving as building blocks in solvated C60 crystals, which brings new physical insight into the understanding of order and disorder concept and new approaches to the design of superhard carbon materials. The nanosize and morphology effects on the transformations of fullerene nanocrystals have also been discussed. These results provide the foundation for the fabrication of pre-designed and controllable geometries, which is critical in fullerenes and relevant materials for designing nanometer-scale electronic, optical, and other devices.

Morphological modifications of C60 crystal rods under hydrothermal conditions*

“…[1][2][3][4][5][6][7][8][9][10][11][12] On the other hand, their engineering unique properties are strongly dependent on the ability to control the structure, size and morphology of fullerene materials, which remain a crucial issue in fullerene nanoscience and nanotechnology as well as applications. [13] Therefore, investigation on preparation of crystalline fullerenes with controllable morphology is of great interest from both a fundamental and a practical point of view.…”

Intermolecular bonding in C70 at high pressure and temperature

“…For both materials dimers react with each other and with remaining monomers at high temperatures and pressures such that larger units are formed. For C70, only disordered oligomers are expected, as discussed above, while for C60 ordered or disordered oligomers or polymers may be formed depending on the actual pressure-temperature conditions in the experiment [1][2][3][4][5][6][7]26].…”

“…While there is a very extensive literature on the high pressure properties and structures of C60 (see reviews in Refs. [1][2][3][4][5][6][7]), including in-depth studies of both the dimer and of several well defined one-, two-and three-dimensional polymers, there is only a small number of studies on C70. There are valid reasons for this: C70 was initially much more expensive than C60 and more difficult to obtain in reasonably pure form, and although the basic physical properties of the two fullerenes are rather similar the lower symmetry of both the molecule and the crystal structure(s) makes both structural and spectroscopic work much more complicated for C70 than for C60.…”

“…While dimerization and polymerization in C 60 has already been well investigated [1][2][3][4][5][6][7]26], intermolecular bonding in C70 is still basically unexplored and the discussion above shows that there are strong reasons to investigate the high pressure intermolecular bonding reaction in C70 further. In a recent paper [26] the formation of intermolecular bonds in C60 was mapped as a function of pressure (up to 2 GPa) and temperature (up to 750 K) using a simple method based on Raman scattering.…”