3 March 2003 Band mapping and frontier orbitals at the interface thin native SiO2/organics
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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, Einc, 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.
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Maria Benedetta Casu, Maria Benedetta Casu, Paolo Imperia, Paolo Imperia, Sigurd K. Schrader, 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); doi: 10.1117/12.453252; https://doi.org/10.1117/12.453252
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