Inhomogeneous electronic structure of copper phthalocyanine film measured with microspot photoemission spectroscopy

Abstract

We have applied photoemission microspectroscopy to copper phthalocyanine film grown on a polycrystalline copper with a lateral resolution of 0.3μm and an energy resolution of 30meV. The photoemission band due to the highest occupied molecular orbital peaked at the binding energy of either 1.6 or 1.2eV depending on the sample positions, while the work functions were 4.3 and 4.5eV for the respective positions. The band was intense when the binding energy was low. The results demonstrate that a large inhomogeneity exists in the interface electronic structure.

Intrinsic emittance reduction of copper cathodes by laser wavelength tuning in an rf photoinjector

“…A purely theoretical estimation of the intrinsic emittance is difficult. For the work function of copper, values in the literature range from 4.3 [27] to 4.6 eV [28]. This value is influenced by crystal structure, surface roughness, impurities and contamination and, as a result, varies from cathode to cathode.…”

Interfacial electronic structure of copper phthalocyanine on a gold surface studied by synchrotron radiation photoemission

“…In the existing literature, the onset of the highest occupied molecular orbital ͑HOMO͒ in a thin CuPc layer occurs sooner than that in bulk with a magnitude of a few tenths of an eV. 6,14 This structure is not due to the filling of the lowest unoccupied molecular orbital ͑LUMO͒, since it coexists with the bulk HOMO level for a given CuPc thickness. Data from inverse photoemission, which defines the unoccupied electronic structures, show an early rise in the onset of the principal peak for a thin layer.…”

Laser-based photoemission micro-spectroscopy for occupied and unoccupied states of inhomogeneous surfaces

“…This is an advantage of the present light source. We have assigned that the substrate area for (a) is polycrystalline and the area for (b) and (c) is the (1 1 1) surface [8]. CuPc molecules are considered to be standing at polycrystalline area and are lying flat on the (1 1 1) surface.…”

“…By focusing coherent VUV radiation at a wavelength of 140 nm (8.86 eV photon energy), our micro-spot ultraviolet photoemission spectroscopy (micro-UPS) achieved 0.3 lm-lateral resolution and 30 meV-energy resolution [4][5][6][7]. We apply micro-UPS to a thin film of copper phthalocyanine (CuPc) deposited on a polycrystalline copper substrate, demonstrating the high lateral/energy resolutions can successfully reveal inhomogeneous electronic structures [8]. A promising method to probe the unoccupied states, but not frequently applied to organic films, is the two-photon photoemission (2PPE) spectroscopy in which the first photon excites an electron to a normally unoccupied state, and the second photon stimulates photoemission from the unoccupied intermediate state [3,9,10].…”