Though peripheral halogen substitution is a known strategy to lower the lowest unoccupied (LUMO) and highest occupied (HOMO) molecular orbital energy levels of planar molecular semiconductors, this strategy has not been explored in conformationally contorted systems. We demonstrate that substitution of peripheral hydrogens with fluorine and chlorine can effectively lower the energy levels of contorted hexabenzocoronene (cHBC) despite its nonplanar conformation. The HOMO energy level lowers comparably with fluorine and chlorine substitution. Due to chlorine’s ability to accommodate more electron density than fluorine, chlorination lowers the LUMO energy level more effectively compared to fluorination (31–60 meV/F versus 53–83 meV/Cl), resulting in a narrowing of the optical bandgap. We find the preference for electron transport to increase with increasing halogenation of cHBC. As an example, thin-film transistors fabricated with 8F-8Cl-cHBC demonstrated electron mobilities as high as 10–2 cm2/(V s) and solar cells with 8F-8Cl-cHBC and poly­(3-hexylthiophene), P3HT, showed power-conversion efficiencies as high as 1.2%.

In this paper, the electrical transport of Au nanoparticle/SrTiO(3) nanointerfaces has been studied. The fabrication method detailed creates atomically smooth SrTiO(3) substrate and controlled Au nanoparticle morphologies to create two unique interfaces. The two interfaces are identifiable in atomic force microscope images allowing us to compare variations in the electronic structure using scanning force spectroscopy. By combining AC imaging with scanning force spectroscopy, the interfaces are effectively probed and left undisturbed. The ideality factor and Schottky barrier height are obtained and compared with one orientation exhibiting deviations from thermionic emission theory while the other showing strong similarities to large area Schottky contacts. It is thus shown that controlling the interface structure is of utmost importance to controlling nanoscale Schottky barriers.

We have measured the electronic structure at Au nanoisland--niobium doped SrTiO3 interfaces over a range of contact diameters. Electron transport processes at the interface transition from thermionic emission dominated to tunneling dominated, leading to ohmic behavior at small sizes. The transition increases at a much higher rate than is generally expected, emphasizing the need for precise control of nanoscale dimensions for reproducible effects in nanoscale electronic devices.

The structural details of ferroelectric surfaces influence the effect of ferroelectric polarization on surface chemistry, and it is important to understand and control defect functionality as well as identify adsorption sites in ferroelectric materials. Ferroelectric domain polarization has been found to have a significant effect on surface properties and interactions. Here, both the structure and the presence of local electric fields are examined simultaneously. The surface structure and ferroelectric domain orientation are controlled while molecular adsorption effects are quantified. We use scanning tunneling microscopy (STM) to determine the surface and electronic effects of polarization-gas interactions on a model ferroelectric surface, BaTiO3 (001).

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