Benzylphosphonic acids with various fluorine substitutions are designed and synthesized. They are used to modify ITO such that the work function can be tuned over a range of 1.2 eV while keeping the surface energy relatively constant. The experimentally measured work function changes are also compared to and agree well with those estimated from DFT calculations.

Indium tin oxide (ITO) is currently the most widely used transparent electrode in organic light-emitting devices and solar cells as well as in liquid-crystal displays. The electronic and geometric structure of the interface formed between the ITO surface and the organic overlayer strongly affects the charge injection characteristics and the overall efficiency of the organic electronic devices. 1 Controlling the composition of this interface can be challenging, since there is often a complex mixture of the stoichiometric oxide, hydroxides, and even oxy-hydroxides in the near surface region, whose ratios strongly depend upon the source of the ITO, cleaning and activation procedures, and modification protocols using chemisorption of small molecules. 2 Chemical modification of an ITO surface via smallmolecule organic adsorbates provides a means for tuning interfacial charge injection and constitutes a promising route toward increasing device efficiency in both organic light emitting diodes and solar cells. 2c Among various smallmolecule compounds capable of self-assembling on OHterminated surfaces, phosphonic acids (PAs) are especially promising for surface modifications of various oxides including ITO, since they form robust monolayers without the need to resort to cross-linking, as is common, for example, in silane surface modification. 2a,b Several binding scenarios have been proposed for PA adsorption on transition metal oxide surfaces, which differ in the number of oxygen atoms bound to the surface and the involvement of hydrogen bonding. The type of adsorption mode can change the orientation of the modifier and the net surface dipole at the ITO/modifier interface, which can be important in determining both wettability and effective surface work function; therefore, it is important to be able to describe the possible adsorption modes and to differentiate among them.Typical proposed PA adsorption modes on metal oxides are shown in Scheme 1. The predominant adsorption modes depend on the type of oxide surface as well as on the reaction conditions. For example, modes (a) (monodentate) and (b) (bidentate + electrostatic) have been suggested for PA adsorption on TiO 2 , 4a Al 2 O 3 , 6a and BaTiO 3 , 7b while tridentate mode (d) has been proposed to dominate on ZrO 2 5 and SiO 2 . 8 PA adsorption on ITO has been described to occur via multiple modes, with a predominance of bidentate and tridentate modes (c) and (d), as indicated by a combination of X-ray photoelectron spectroscopy (XPS) and FT-IR studies. 3a,c There remains some uncertainty in the reported spectroscopic studies, in particular XPS studies, that have been used to discern among PA adsorption modes due to a lack of precise knowledge of the spectroscopic features specific to each binding mode.Here, we present what we believe to be the first theoretical characterization, based on density functional theory (DFT), (1) (a) Ishii, H.; Sugiyama, K.; Ito, E.; Seki, K. AdV. Mater. 1999, 11, 605-625. (b) Salaneck, W.; Seki, K.; Kahn, A.; Pireaux, J.-J., Eds. Con...

The past decade has witnessed an explosion of techniques used to pattern polymers on the nano (1-100 nm) and submicrometre (100-1,000 nm) scale, driven by the extensive versatility of polymers for diverse applications, such as molecular electronics, data storage, optoelectronics, displays, sacrificial templates and all forms of sensors. Conceptually, most of the patterning techniques, including microcontact printing (soft lithography), photolithography, electron-beam lithography, block-copolymer templating and dip-pen lithography, are based on the spatially selective removal or formation/deposition of polymer. Here, we demonstrate an alternative and novel lithography technique--electrostatic nanolithography using atomic force microscopy--that generates features by mass transport of polymer within an initially uniform, planar film without chemical crosslinking, substantial polymer degradation or ablation. The combination of localized softening of attolitres (10(2)-10(5) nm3) of polymer by Joule heating, extremely non-uniform electric field gradients to polarize and manipulate the soften polymer, and single-step process methodology using conventional atomic force microscopy (AFM) equipment, establishes a new paradigm for polymer nanolithography, allowing rapid (of the order of milliseconds) creation of raised (or depressed) features without external heating of a polymer film or AFM tip-film contact.