Doping of C 60 Films Using High Energy Boron Ion Implantation
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ABSTRACT C60 films, which are deposited by partially ionized beam deposition (PIBD), are doped by 100 keV boron ion implantation at dose ranging from 3 *1014 to 1*1016 cm2 The implantation process has been studied using Fourier transform infrared spectroscopy (FTIR), Raman spectra and X-ray diffraction (XRD) analyses. Almost all C6 soccer-balls in the doped region in the films are found to be broken at dose of 1*1016 cm 2, while at dose less than 6*1014 cm 2 a few C60 molecules remain undestroyed and maintain the original structural properties.
L.INTRODUCTIONS The discovery of superconductivityat 18 K in potassium-doped C60[1] films has stimulated detailed investigations on doping of fullerenes, in theoretical and experimental aspects[2,3]. Alkali and alkali earth metals have been used for doping of fullerenes by several methods[1-3]. Chemical vapor doping of C60 is commonly used in which fullerenes powder with a few dopant are annealed in a closed environment. Kastner[4,5] proposed a new kind of doing method using high-energy (30keV) K' beam implantation to overcome the instability of doped films as exposed to atmosphere in which oxygen could possibly be incorporated into the films to change the desirable properties resulted from doping treatment. During the ion implantation process, an amorphous surface layer is formed while fullerenes molecules beyond this layer remain undestroyed[4,5]. In this paper, in an alterative way, fullerenes films are doped by boron species using high energy (100keV) B+ beam with dose ranging from 3* 1014 to 1*1016 cm2. Since boron ions are relatively small as compared to many other species usually used for doping technique such as K+, Ba+ and Cs+, the ion-induced damages in doped films should be less. Studies of B-doped fullerenes films could be useful to investigate the possibility and to find appropriate experimental conditions for ion-implantation doping in C60 films.
2. EXPERIMENTS C60 films are deposited by partially ionized beam deposition[6]. FTIR measurements are carried on FT-IR Spectrometer of Model IFS 113V. The Raman spectroscopy is carried out on a Spex-1403 Raman Spectrometer with an Ar+ laser at 100mW output at 5145A. The XRD is performed on Siemens D500 with Cu Ka radiation.
433 Mat. Res. Soc. Symp. Proc. Vol. 359 01995 Materials Research Society
3. RESULTS AND DISCUSSIONS TRIM calculationis used to estimate the depth distributionof boron species in the doped fullerenes film and the damages caused. The average depth range for B species Is about 3500 A, while the largest depth is about 4700 A. B-content is found to distributemostly In the region from 3000 to 4500 A. The depth profile for vacancyshows a high damage level in this same region. TRIM calculationsgave good agreements with experimental results in the investigationof doping of fullerenesfllms by high energy K +beams [4,5],exhibitinggood estimation of the depth profile of doping species in the resultingfilms. According to this analysis, fullerene films with thicknessof 5000 A deposited by PIBD are used for B
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