X-ray photoelectron spectroscopy and dark DC conductivity of argon-ion implanted organic films over a wide temperature range

Films of metal-free phthalocyanine (MFPC) and 1,8-dihydrodibenzo[b,i]-[1,4,8,11]tetra-aza-[14]-annulene (TAA) were studied. The compounds were deposited by vacuum sublimation on to: (i) quartz substrates for UV-vis spectroscopy; (ii) Teflon disks for reflection measurements; (iii) stainless steel stubs for x-ray photo-electron spectroscopy (XPS); and (iv) interdigitated platinum electrodes on alumina for electrical conductivity measurements. The transmission UV, visible and IR spectra of the compounds were unchanged following bombardment by 10 kV argon ions, indicating that any damage caused was confined to only a thin surface layer. The x-ray photoelectron spectra of both of the compounds were substantially modified following bombardment by 10 kV argon ions. In both cases the hydrocarbon-type carbon levels increased, the intensities of the nitrogen peaks were decreased, and a new peak due to implanted argon was observed, indicating severe damage to the surface of the films. The electrical conductivities of all samples exhibited increases of up to six orders of magnitude following argon-ion exposure. On the basis of the XPS results and the form of the conductivity against temperature curves, it was concluded that the damaged surface was composed substantially of amorphous carbon. (author)