Doped fullerenes

Y2 Cg2 denotes two Y atoms inside a Cg2 fullerene [19], Thus far, only small quantities of endohedrally-doped fullerenes have been prepared and only limited investigations of endohedrally-doped crystalline materials have been reported but steady progress is being made both in synthesis and in properties measurements [20]. 

As is well known, many experimental smdies have been made extensively to search for a possibility of encapsulation of atoms by hollow fullerenes since the discovery of Cgo by Kroto et al. [143]. These methods, however, usually require high tempratures and high pressures, or ion implantation. The yields are also as low as 0.4—10 %. In this sense, the efficiency in our case is much higher and the required conditions are much milder with collison energy of 2 eV. However, the boron substimtion is a bottle neck, although Smalley and co-workers successfully synthesized boron-doped fullerenes [144]. 

It is very likely that PF6 occupies the Van de Waals gap between the SWNTs in a similar way than in graphite intercalation compounds [6] and in anion-doped fullerenes [7]. Because of lower surface area between... 

Since alkali metal doped fullerenes are conductors, and low-temperature superconductors, one wonders if the curved polynuclear hydrocarbons might exhibit a similar behavior. 

The discovery of superconductivity [105] in alkali metal doped attracted the attention of a broad cross-section of the scientific community. The composition of the first alkali metal doped fullerene was determined to be [106,107]. In this compoimd, the transition to a superconducting state occurs at = 19.3 K [106]. In a short time, a large variety of alkali metal fullerides M Cgo have been synthesized and studied with respect to their solid-state properties [1, 106-114]. Thereby, the stoichiometries of as well as the alkali metal with M = Na, K, Rb, Cs have... 

Prassides K (2000) Polymer and dimer phases in doped fullerenes. In Andreoni W (ed) The physics of fullerene-based and fullerene-related materials. Kluwer Academic, Boston... 

The A-potential model multiwalled doped fullerene onions 19... 

The 5-potential model of single-walled doped fullerenes 19... 

Photoionization of doped fullerene anions Coulomb confinement resonances 38... 

To date, since the photoelectron spectroscopy of doped fullerenes has been difficult to perform, numerous theoretical studies of photoionization spectra of atoms encaged in doped fullerenes, performed at various levels of approximations, [15-46], have been prevalent. Consequently, to aid emerging experiments and new theories on gas phase doped fullerenes, a review of the theoretical findings and predictions that have been accumulated in this area of research so far is very timely. This is precisely the aim of the present paper. 

The extension of the above described model from neutral doped single-walled fullerenes A Cn to charged doped fullerenes A C Z is pretty straightforward [28]. To account for the effects of a charged shell Cfz, one reasonably assumes that the extra charge z is evenly distributed over the entire outer surface of C . Correspondingly, the entire model potential Vn(r) in the case of charged C z is... 

For neutral doped fullerene onions A C6o C24o, A C6o C24o Cs4o, etc., the confining potential Vn of a multiwalled cage is replaced by a linear combination of corresponding single-walled potentials V [32]... 

An alternative simple modeling of doped fullerenes, specifically, A C6o, was developed initially in [34]. It was then used extensively in a number of photoionization studies of thus encaged atoms [34 41], The method is based on approximating the C60 cage by a spherical potential V(r) which differs from zero only within an infinitesimally thin wall of a sphere of radius RC/ the latter being considered the C60 radius, Rc = 6.639 au [47] ... 

The present paper has focused on novel systems, doped fullerenes, with the emphasis on their photoionization spectra. While the photoionization problem of gas phase doped fullerenes has been experimentally addressed only recently in pioneering works [12,13], there has been much more activity on the theoretical side of the problem this has far outstripped experiment. In the present paper, only those results obtained on the basis of simple semiem-pirical models, the A-potential [15,20-22,27-33,43,44] and 5-potential [34-41] models have been highlighted. Surprisingly, even within the framework of these simple models a rich variety of novel effects, particularly the confinement resonances and their manifestations in the photoionization spectra of doped fullerenes has been unraveled. Although the approximations made are indisputably reasonable for trusting the existence of, and trends in, the predicted confinement resonances, and thereby urging their experimental... 

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