Schematic of the interface formation between a metal and an organic semiconductor and the PES measurement. VL, FL, and and , , and represent the vacuum level, the Fermi level, and the work function of the sample and spectrometer, respectively. , , and represent the depletion width, the interfacial dipole, and the hole injection barrier, respectively.
(Color online) UPS spectra (KE scale) of clean Co and pentacene deposited on Co at different thicknesses of pentacene (5, 15, and ).
(Color online) The evolution of the energy levels (normalized) with increasing pentacene thickness: a) secondary electron cutoff (SEC), (b) HOMO level, and (c) C energy level. The vertical dashed lines represent the values of SEC, HOMO, and C , respectively, at a thickness of .
(Color online) The binding energy shifts of the energy levels: HOMO, “a,” “b,” C , and VL, as a function of the deposited pentacene thickness. The shifts are expressed as , where represents the pentacene thickness. Note the flipped BE scale. Two distinct regimes are observed: low coverage up to and high coverage for thicknesses higher than .
(Color online) C energy level parameters: binding energy (BE), full width at half maximum (FWHM), and intensity as a function of pentacene coverage.
(Color online) (a) UPS spectra of Co deposited on pentacene in the HOMO-FL region. Starting from the bottom: spectrum of clean Co, spectrum of pentacene on Co, and spectra with increasing Co thickness deposited atop. The labels indicate the Co thickness. (b) The time evolution of the spectrum in the HOMO level region at Co coverage. (c) The attenuation of the intensity of the C level of pentacene as a function of the top Co layer thickness investigated in three similar samples.
(Color online) (a) C energy level shift as a function of Co overlayer thickness, extracted from XPS. (b) VL (SEC) shift, extracted from UPS. Added to figure is a guide to the eyes which qualitatively represents the similar evolution of the energy levels in all the samples. Energy level shifts are expressed as , where is the thickness of the Co layer.
Complete band diagram for a layered structure. Lowest unoccupied orbital of pentacene is not included.
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