Interfacial electronic structures for TPD/metal (Au, Ag, and Ca) systems we
re investigated by Kelvin probe method (KP), ultraviolet photoemission spec
troscopy (UPS), X-ray photoemission spectroscopy (XPS), and metastable atom
electron spectroscopy (MAES). KP results showed that an abrupt vacuum leve
l shift occurred right at the interface, and no further shift was observed
by further deposition of TPD up to the thickness of about 100 nm. Similar a
brupt shift was also observed from the onset of the lower kinetic electron
energy in the UPS spectra. These results suggest that band bending does not
occur in the TPD/metal interface. From the MAES and XPS measurements, chem
ical interaction between TPD and Ca was observed, while the interaction bet
ween TPD and Au or Ag was weak. These results show that the origin of the v
acuum level shift for TPD/Ca is of more chemical nature, and is different f
rom that for TPD/Au or Ag systems. The highest occupied molecular orbital (
HOMO) and C Is levels of the TPD films gradually shifted by deposition of t
he TPD and their trends were different from the abrupt shift of the vacuum
level. We consider that such gradual shift is due to the final-state screen
ing effect in photoemission measurements, not due to the band bending in th
e space charge layer. (C) 2001 Elsevier Science B.V. All rights reserved.