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(Color online) (a) Electron spin resonance (ESR) of Al|LiF|C60 (inverted deposition sequence) samples annealed at different temperatures. Only a signal for g = 2.001 is detected. (b) ESR signal of 35-nm C60 neat film, and with Al and LiF/Al electrodes deposited on top. Films with LiF demonstrate a strong signal with a g-value of 1.998, corresponding to C60-radical anion, while the remaining samples show a g = 2.001 signal.
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IRRAS spectra of LiF, C60, and LiF/Al with different deposition orders. The spectra are offset for clarity. A 260-nm Al film serves as the bottom reflection element in all cases. Asterisks mark the four vibrational modes of C60.
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We report our investigations on the chemical doping mechanisms induced by LiF|Al electrodes evaporated onto fullerene thin films.Electron spin resonance(ESR) and infrared reflection-absorption spectroscopy (IRRAS) are utilized to characterize C60|Al and C60|LiF|Al interfaces. ESR spectra show that deposition of LiF followed by Al generates C60 radical anions and also the presence of an additional paramagnetic species of lower concentration that is present in all C60films regardless of LiF. IRRAS clarifies the mechanism occurring at the C60|LiF|Al interface, showing that interaction between LiF and C 60 followed by deposition of Al causes LiF clusters to chemically dissociate.
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