Probing Metal/Organic Interfaces Using Doubly-Resonant Sum Frequency Generation Vibrational Spectroscopy

Determining the Orientation of Chemical Functional Groups on Metal Surfaces by a Combination of Homodyne and Heterodyne Nonlinear Vibrational Spectroscopy

“…This is because metals often have large electronic (vibrationally nonresonant, NR) contributions to the SFG signal that constructively or destructively interfere with the SFG generated from the organic functional groups on IR resonance. , This interaction is much the same as achieved with an external phase reference (the local oscillator, LO) in a heterodyne experiment. Several studies have made use of this in the analysis of SFG data. ,− Explicit measurement of the phase has several advantages over reliance on implicit phase interpretation, primarily the result of being able to independently characterize, control, and modulate the LO magnitude and phase. In this work we illustrate that while heterodyne SFG measurements excel at measuring the phase of bare metals and of organic layers adsorbed onto dielectric substrates with no appreciable NR response, there are challenges associated in phase characterization of organics on metals.…”

Direct probing of charge carrier behavior in multilayered organic light-emitting diode devices by time-resolved electric-field-induced sum-frequency generation spectroscopy

“…In this context, we have recently reported our observations of the vibrational spectra of the component layers in multilayer OLEDs with a drive voltage application using direct current (DC) electric-field-induced sum-frequency generation (EFI-SFG) spectroscopy. 14) Through measurement of the EFI-SFG spectra under double resonance conditions, molecular selectivity is greatly enhanced, 15,16) and it becomes possible to extract information regarding the specific organic layer of interest. This technique was further applied to both pristine and aged OLEDs, and we were successful in determining the behavior of each component material of the multilayer OLEDs through identification of the vibrational spectra of the component molecules.…”

Rearrangement of the molecular orientation of Alq3 in organic light-emitting diodes under constant current aging investigated using sum frequency generation spectroscopy

“…In second-harmonic generation (SHG) measurements, the SHG of Alq 3 films does not arise from electric field effects, but instead is ascribed to the electric-dipole mechanism due to the orientational ordering of the permanent dipole of the meridional isomer of the Alq 3 molecules [12]. The thickness-dependent SFG intensity of the Alq 3 deposited films also supports this argument [13]. It has been suggested by Kondakov et al.…”

“…In other words, this permanent dipole alignment against the surface normal induces an imaginary negative charge at the ␣-NPD/Alq 3 interface. Consequently, the uniaxial dipole alignment of Alq 3 with respect to the surface normal is the primary cause of the thickness dependence of the Alq 3 SFG signal intensities [13]. Furthermore, the thicknessdependent SFG peak strengths derived from Alq 3 in these OLEDs clearly indicate that the orientation of the permanent dipole is maintained in the real devices.…”