A ratio between the mass of fullerenes and the total mass of carbon soot defines fullerene yield. The yields determined by UV-Vis absorption are approximately 40%, 10-15%, and 15% in laser, electric arc, and solar processes. Productivity of a production process can be defined as a product between fullerene yield and flow rate of carbon soot. Interestingly, laser ablation technique has both the highest yield and the low productivity and, therefore, a scale-up to a higher power is costly. Thus, fullerene commercial production is a challenging task.
A pulsed high-energy laser beam may be employed to evaporate a graphite target, reducing the possibility of having fullerenes photochemically destructed (1). A double Nd-YAG laser beam, focused at 45° to the target surface, was used to ablate different targets of carbonaceous materials (2). Calculations based on this fullerene synthesis indicated the possibility of attaining fullerene yields of circa 70-80% (3). Expert knowledge on possible plasma regions of fullerene self-assembly was proposed to determine the necessary local conditions for fullerene formation (1). Herein, these aspects are viewed and considered as a unified issue.
We propose basic concept of the control system of fullerene synthesis by lasers. The designed algorithm links fullerene yield and production rate to laser characteristics. Based upon predictions that the time dependent evolution of the plasma/He interaction volume for laser ablation experiments essentially follows that for cathodic arc discharge experiments, the possible zones of formation of the large carbon molecules and the feasibility of a more efficient fullerene production by lasers are analyzed. On the basis of computational simulations, the optimized plasma zones providing a C60 yield of 70% and a production rate of 5.14 g/min (PHe = 240 Torr; power density = 7×109 W/cm2, T = 2700 K) from a graphite target are identified and displayed as time response.
Cathodic arc systems are suggested to be valuable tools in the determination of local conditions for fullerene formation. The development of a new methodology based on multilaser systems that could improve both yield and fullerene selectivity is suggested. Monitoring the power and wavelength of secondary lasers is suggested to control fullerene selectivity such as C60, C70, C76 or higher fullerenes. These laser capabilities are unmatched by the conventional electric arc processes. The choice of appropriate lasers is critical for the achievement of the objectives of control.
Acknowledgments. This work was partially supported by the Killam Trusts.
(1) P. Mitrasinovic and D. Koruga, "Laser-aided production of fullerenes," Tehnika, vol. 50, pp. NM13-NM20, 1995.
(2) É. Millon, J.V. Weber, J. Theobald, and J.F. Muller, "Laser ablation of carbonaceous materials: a method to produce fullerenes," C. R. Acad. Sci. Paris, vol. t. 315 Série II, pp. 947-953, 1992.
(3) P.M. Mitrasinovic, "Contribution to the development of the control system for fullerene commercial production by using high-energy lasers," MSc thesis, University of Belgrade, Belgrade, Yugoslavia, 27 June 1995.