Interface formation of Mg with DiMePTCDI studied by Raman spectroscopy

Abstract

PACS 68.35.Ja, 78.30.Jw Metal/organic interfaces play an important role in the performance of organic based devices. In this work the interface formation between Mg and N,N'-DiMethyl-3,4,9,10-Perylene Tetra Carboxylic DiImide (DiMePTCDI) films grown on sulphur-passivated GaAs (100) substrates is investigated in situ by Raman spectroscopy. The Raman spectra are taken in a backscattering geometry at room temperature under resonance conditions with the 488 nm (2.54 eV) Ar + laser line. They reveal that when Mg is deposited onto a 15 nm DiMePTCDI layer the external phonon modes are preserved up to large metal coverages. Since these modes are a fingerprint of the molecular crystal, their preservation indicates a low diffusion of Mg into the DiMePTCDI layer. Concerning the internal molecular modes, the Mg deposition induces a breakdown of selection rules which is proposed to originate from a dynamical charge transfer between the DiMePTCDI molecules and the metal. Above 0.3 nm nominal thickness of Mg the line-shape of the molecular breathing mode at 221 cm -1 develops an asymmetric tail towards higher frequencies. A similar effect is observed for the bands that occur at 1291 cm -1 and 1606 cm -1 but the asymmetry appears at the low frequency side. This line-shape asymmetry is likely to be related to a Fano resonant coupling between the molecular vibrational modes and the electronic continuum of states of metallic clusters formed above 0.3 nm Mg coverage.

New Approach for Analyzing the Vertical Structure of Polymer Thin Films Based on Surface-Enhanced Raman Scattering

“…Moreover, it can be seen that for the F8BT there is an additional peak that appears (∼1520 cm –1 ) when the spectrum is taken on gold. The new peak is an IR mode that becomes active in the presence of the metal. , The second polymer, PFB, has only one peak in this region ∼1603 cm –1 . , …”

“…The new peak is an IR mode that becomes active in the presence of the metal. 23, 24 The second polymer, PFB, has only one peak in this region ∼1603 cm −1 . 15,27 After studying the fingerprints of the SERS effect on each polymer we studied two structures that are common for organic photovoltaic devices made from polymers, namely bilayer and blend structure of F8BT and PFB.…”

“…A different SERS technique is used when the aim of the study is to investigate the interaction between organic materials and metals that are evaporated on top of them as reported by Paez et al , and by Davis and Pemberton. , In these studies, a thin layer of metal was evaporated on top of the organic layer while monitoring changes in the Raman spectra as a function of the evaporated material and its thickness. One of the findings of these studies is that when the evaporated metal is gold or silver (noble metals) and they do not chemically interact with the material the only observed effect is the enhance the Raman signal.…”

“…A different SERS technique is used when the aim of the study is to investigate the interaction between organic materials and metals that are evaporated on top of them as reported by Paez et al 24,25 and by Davis and Pemberton. 26,27 In these studies, a thin layer of metal was evaporated on top of the organic layer while monitoring changes in the Raman spectra as a function of the evaporated material and its thickness.…”

The modeling of dynamical degradation process for operating organic light emitting diode

“…Surfaces and Interfaces of a degraded OLED have been observed by using atomic force microscopy (AFM) and scanning electron microscopy (SEM) [1]. Several major approaches for investigating interfacial properties of OLED include secondary ion mass spectrometry (SIMS) for qualitative and surface analysis [2], X-ray photoelectron spectroscopy (XPS) for chemical and qualitative analysis [2,3], Raman scattering for interface analysis [4,5]. Gap states at organic/electrode interfaces were scrutinized by these microscopic and destructive approaches.…”