Local contact potential difference of molecular self-assemblies investigated by Kelvin probe force microscopy

Abstract

Self-assembled pi-conjugated oligomer nanowires have been investigated by frequency modulation atomic force microscopy and amplitude modulation Kelvin probe force microscopy under ultra high vacuum. The distance dependence of the contact potential difference (CPD) has been analyzed by combining high resolution imaging with distance-spectroscopy measurements. It is shown that the apparition of a damping contrast characterizes the onset of short range electrostatic (SRE) forces, which are responsible for the occurrence of local CPD (LCPD) modulations correlated with the molecular lattice. By working at the onset of the damping contrast, the tip-surface separation can be adjusted to minimize the contribution of SRE forces to the measured CPD. VC 2011 American Institute of Physics. [doi:10.1063/1.3662850]Funding Agencies|French "Recherche Technologique de Base" Program||SERC (Swedish e-Science Research Center)|

High-Resolution Kelvin Probe Force Microscopy Imaging of Interface Dipoles and Photogenerated Charges in Organic Donor–Acceptor Photovoltaic Blends

“…(a,b) Chemical structures of the electron donor (FG1, a) and acceptor ([70]­PCBM, b) molecules. (c) Single FG1 molecule in its most stable conformation, as determined from molecular mechanics calculations . The main molecular dipole D at the fluorenone core is highlighted by an arrow.…”

“…The main molecular dipole D at the fluorenone core is highlighted by an arrow. (d) Single FG1 molecular stack (top view).…”

“…These blends are based on an oligothiophene−fluorenone oligomer 25 (FG1, see Figure 1a) and [6,6]-phenyl C70 butyric acid methyl ester ([70]PCBM, Figure 1b). Due to the liquidcrystalline properties of the electron donor 25 FG1, the sample morphology can be tuned via in situ (under UHV) sample annealing (see Supporting Information, Figure S1), resulting in samples for which nanometer-sized [70]PCBM clusters are buried in the subsurface of a matrix of self-assembled π-stacked FG1 molecular wires 26 (Figure 1d). These extremely flat samples constitute model systems for high-resolution KPFM investigations, thanks to the highly homogeneous nature of the surface layer which reduces the risk of cross-talk effects between the topographic and CPD channels.…”

“…This organization in well-ordered lamellae appears to be promoted by the annealing process. Molecular mechanics and dynamics simulations have shown 26 that FG1 can form two-dimensional monolayers of polar or nonpolar π-stacked self-assemblies, for which the orientation of the molecular dipole alternates or is identical from one π-stacked wire to the next. In the D−A blends, however, the exact nature of the three-dimensional supramolecular assembly remains unknown, and both kind of structures (alternate and nonalternate) may coexist in the donor matrix.…”

Direct Utilization of Photoinduced Charge Carriers to Promote Electrochemical Energy Storage

“…It can be seen that the surface potential in the light is much more evenly distributed that that in the dark, suggesting a prompt kinetic for charge transfer. [ 17a,32 ]…”