Hamburg 2001 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 31: Organische Halbleiter

HL 31.5: Vortrag

Donnerstag, 29. März 2001, 12:45–13:00, S16

Metal / Organic Interfaces Characterized by Raman Spectroscopy — •G. Salvan¹, Y. Sakurai², R. Scholz¹, T. U. Kampen¹, D. R. T. Zahn¹, H. Ishii², and K. Seki² — ¹Institut für Physik, TU Chemnitz, 09107 Chemnitz, Germany — ²Department of Chemistry, Graduate School of Science, Nagoya University, Japan

The silver deposition process onto two different organic films, i.e. 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) and tris-(8-hydroxyquinoline) aluminium (Alq₃) was monitored by means of Raman spectroscopy. An ultra high vacuum chamber aligned with a Raman set-up is equipped with cells for the thermal evaporation of both the metal and the organic materials. Thin organic films with thicknesses of ∼15 nm and ∼3 nm were deposited onto GaAs(100) and Ag(111)/Si(111) substrates, respectively. The films showed a drastic increase in the Raman response with increasing nominal Ag thickness, a clear indication of surface enhanced Raman scattering (SERS). The largest enhancement factors were observed for Alq₃ films.

Special interest was paid to the internal vibrational modes. Their intensities and frequency positions should be strongly affected by chemical reactions, and less drastically by charge transfer or symmetry lowering in the presence of an electromagnetic field in the metal. Slight changes in the relative intensities occurred in the case of the PTCDA films, whereas the intensities of Alq₃ modes were preserved upon the Ag deposition. Therefore it is concluded that the SERS effect arises mainly from the local fluctuations of the electromagnetic field in the granular Ag film covering the organic layer.