Electron spin resonance studies on defects in phosphorus ion-implanted C60 films

Abstract

Abstract Paramagnetic defects produced by phosphorus ion implantation of C 60 films and the influence of annealing on dangling bonds defect center have been studied by electron spin resonance (ESR) to improve the properties of P + -implanted C 60 films for solar cell applications. The films implanted at room temperature reveal the presence of a paramagnetic defect center, which originated from the carbon dangling bonds, with g =2.0036±0.0004. The volume concentration of the defect center increases with the implantation dose, from approximately 4.5×10 21 to 4.6×10 22 cm −3 for the lowest implantation dose of 1×10 13 P + ions cm −2 and the highest implantation dose of 5×10 15 P + ions cm −2 , respectively. The increase in dose also causes a narrowing of the line width (from 2.6 to 2.15 G) although the g -value of the single Lorentzian line remains unchanged. The narrowing is attributed to exchange (motional) interaction. The ESR results imply that no significant graphitization has occurred as a result of implantation. Furthermore, upon annealing at a temperature of 773 K the spin defect density is reduced by a factor of 3.5, while the g -value remains centered at the same magnetic field. This reduction is due to a reconstruction of the less stable spin defect sites. The originality of this paper is that it is the first ESR study of defects produced by phosphorus implantation of C 60 films.