Electronic structure of the organic semiconductor copper phthalocyanine and K-CuPc studied using photoemission spectroscopy

Abstract

The changes of the electronic structure of copper phthalocyanine ͑CuPc͒ caused by the intercalation with potassium are studied using core-level and ultraviolet photoemission spectroscopy. The analysis of the valenceband spectra allows the estimation of the energy gap relevant for transport, which is substantially larger than the energy gap obtained using optical methods, showing that solid CuPc has to be regarded as a correlated material. Furthermore, our experiments indicate that there is structural ͑polaronic͒ relaxation of the CuPc molecules upon charging and that the lowest unoccupied molecular orbital of CuPc is more concentrated in the central part of the phthalocyanine molecules.

Chemistry and electronic properties of a metal-organic semiconductor interface: In on CuPc

“…28 The valence band onset at 1.25 eV binding energy for the pristine CuPc film indicates that the initial E F position is located near the middle of the transport gap which has been reported to be 2.1-2.3 eV. 25,29 The mid gap position of E F is consistent with the intrinsic nature of the CuPc films as prepared in this study. Indeed, CuPc films grown in argon atmosphere or in high vacuum conditions of ϳ10 −6 Torr show p-type properties, which most probably reflects the non-negligible level of oxygen impurities, arising from such growth conditions.…”

“…The shoulder S C-1 and the feature S C-2 are the satellites of the C-1 and C-2 component, respectively. 21,22,[24][25][26][27] The analysis of the relative intensity of the C-1 to C-2 components, taking into account the satellites, leads to a number of 2.97, which is very closed to the theoretically expected value of 3.…”

On-Surface Reaction between Tetracarbonitrile-Functionalized Molecules and Copper Atoms

“…Whereas the spectrum of MOCN1 exhibits only one peak, at the same binding energy of Cu deposited on Au(111), the reaction is marked by the appearance of a new feature at about 935.4 eV, in good agreement with the binding energy of the Cu(II) copper peak measured for bulk CuPc and CuPc on Au(100). 36,37 This new feature cannot be explained by Au−Cu intermixing, 32 and we then interpret this peak as the signature of the CuPyc formation. The homogeneity of the CuPyc coordination network allows an accurate quantitative analysis of the Cu 2p 3/2 spectrum: the Cu(II):N:C ratio is about 1:31:98, which is consistent with the 1:32:96 ratio of the CuPyc molecule formed on the whole surface.…”

Indium on a copper phthalocyanine thin film: Not a reactive system

“…The spectra of pristine CuPc films resemble those reported previously. 16,30,31 Upon the first indium deposition, the C 1s and the N 1s core level shift by 0.18 eV toward higher BE, while the further indium evaporation produces a tiny gradual shift back toward lower BE. The behavior can be qualitatively rationalized being induced by a varying work function 32 ͑Fig.…”

“…2͒ consists of three peaks associated ͑going toward higher BEs͒ with benzene and pyrrole rings, and the shake-up of pyrrole rings, respectively, while the shake-up of the benzene rings is obscured by the pyrroleassociated feature located at about 286 eV. 31,33 The shakeups reflect inelastic energy-loss processes caused by -‫ء‬ intramolecular transitions. As the shake-ups should vanish if a reaction between a metal and a molecular film occurs, 17,18,22,30,31,34 in the present case, the persistence of shake-up features upon indium deposition suggests preserved pristine molecular structure in accordance with other studies of nonreactive systems such as Au/CuPc ͑Ref.…”