Optical second-harmonic electroreflectance from Ag(111)

Second-order nonlinear optical properties of the Ag(111)/electrolyte interface in the presence of self-assembled monolayers containing conjugated pi systems. I. Alpha-functionalized terthiophene films on Ag(111)

The nonlinear optical properties of self-assembled monolayers obtained from bonding two different alpha-functionalized terthiophenes (alpha-T3) to (111) silver electrode surfaces have been investigated using second harmonic generation (SHG). The two (alpha-T3) compounds used were functionalized with alkane chains of different lengths (C8 and C4), and each was terminated with a thiol anchoring group. A nitrile group was attached to the terminal thiophene ring of the (alpha-T3) compound with the C4 chain. The orientation of the polarization of the incident beam was changed systematically and gradually between "p" and "s" orientation and the SH signal (isotropic and anisotropic contributions) analyzed in both directions ("P" and "S"). The symmetry of the system was reduced by the presence of the adlayers from C3v to C3. The dependence on the applied potential and the incident wavelength has also been studied. The relative magnitudes and phases of the various second-order tensor elements have been estimated and compared with the values for a bare surface. A resonance process in the (alpha-T3) pi moiety has been investigated, and from this, the effective "band-gap" energies of the organic semiconductor SAMs (i.e., the energy difference between the pi-pi bands) have been estimated.

LOCALIZED OPTICAL PHENOMENA AND THE CHARACTERIZATION OF MATERIALS INTERFACES

▪ Abstract  This review focuses on the characterization of interfaces, specifically on the optical methods of characterization that utilize some form of spatial localization to circumvent the special problems accruing to interfaces. Experiments utilizing radiation in only the infrared through the ultraviolet regions of the electromagnetic spectrum are considered. We specifically exclude the vast and important array of experimental techniques that utilize the vacuum ultraviolet and X-ray spectral regions. In addition, the interfaces considered are those composed of solids with liquids, thin films, and other solids, thus largely ignoring the literature of ultrahigh vacuum surface science.