Band mapping and frontier orbitals at the interface thin native SiO2/organics

Maria Benedetta Casu; Paolo Imperia; Sigurd K. Schrader

doi:10.1117/12.453252

3 March 2003 Band mapping and frontier orbitals at the interface thin native SiO₂/organics

Maria Benedetta Casu, Paolo Imperia, Sigurd K. Schrader

Proceedings Volume 4800, Organic Light-Emitting Materials and Devices VI; (2003) https://doi.org/10.1117/12.453252
Event: International Symposium on Optical Science and Technology, 2002, Seattle, WA, United States

Abstract

The properties of the interface Si<111>/SiO₂/low molecular compound were studied by means of ultraviolet photoelectron spectroscopy (UPS). The investigated material, an amphiphilic derivative of 2,5-diphenyl-1,3,4-oxadiazole (NADPO), is also of interest in photonics, because it can be used as active material in opto-electronic or electro-optic devices. The UPS measurements were performed at the beam line Seya F2.2 in HASYLAB (Hamburg, Germany). The photoelectrons were collected with a Vacuum Generators ADES 400 angle resolving spectrometer system at room temperature. The photoelectron spectra were measured with an angle of incidence of 45 degrees in normal emission for various incident energies and for an incident photon energy, E_inc, of 24 eV in off normal emission. We investigated the interface properties depending on the number of monolayers (2, 4, 6, 8) of well oriented Langmuir-Blodgett films, monitoring the frontier orbital position, with particular regard to the highest occupied molecular orbital energy position. The obtained results give evidence that the band structure is depending on the thickness of the organic layer at the interface Si<111>/SiO₂/NADPO. We also monitored the development of the energetic position of the highest occupied molecular orbital (HOMO) from that of the monolayer towards the "true" HOMO energy position of the thin film, where the word "true" is related to the actual interface properties of the films and not to a single monolayer (ML) or a double layer. As a matter of fact the 2 ML spectra show a different behaviour than those of thicker films since the 2 ML system is strongly influenced by the substrate while the spectra of thicker films are de-coupled from the electronic structure of the substrate.

Citation Download Citation

Maria Benedetta Casu, Paolo Imperia, and Sigurd K. Schrader "Band mapping and frontier orbitals at the interface thin native SiO₂/organics", Proc. SPIE 4800, Organic Light-Emitting Materials and Devices VI, (3 March 2003); https://doi.org/10.1117/12.453252

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KEYWORDS

Interfaces

Thin films

Oxides

Photoemission spectroscopy

Ultraviolet radiation

Metals

Silicon

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