We demonstrate controllable shift of the threshold voltage and the turn-on voltage in pentacene thin film transistors and rubrene single crystal field effect transistors (FET) by the use of nine organosilanes with different functional groups. Prior to depositing the organic semiconductors, the organosilanes were applied to the SiO2 gate insulator from solution and form a self assembled monolayer (SAM). The observed shift of the transfer characteristics range from -2 to 50 V and can be related to the surface potential of the layer next to the transistor channel. Concomitantly the mobile charge carrier concentration at zero gate bias reaches up to 4 × 10 12 /cm 2 . In the single crystal FETs the measured transfer characteristics are also shifted, while essentially maintaining the high quality of the subthreshold swing. The shift of the transfer characteristics is governed by the built-in electric field of the SAM and can be explained using a simple energy level diagram. In the thin film devices, the subthreshold region is broadened, indicating that the SAM creates additional trap states, whose density is estimated to be of order 1 × 10 12 /cm 2 .

We calculated the uni-univalent ion distributions around the oligonucleotide d(AT)5.d(AT)5 in the A, B and wrinkled D conformation using the Metropolis Monte Carlo method. All atoms were included in the oligonucleotide model with partial charges and hard sphere radii assigned to each atom. The univalent counter- and coions were modeled as hard spheres with radius 0.3 nm. The solvent was assigned a dielectric constant of 80, corresponding to a temperature of 298K. The counterion distribution surrounding each of the conformers and the distribution surrounding an impenetrable cylinder, were calculated for four salt concentrations. We found significant counterion density in the major groove of the A DNA while fewer counterions occupied the grooves of B DNA. In the wrinkled D DNA, where groove occupancy is sterically hindered, the ion distributions were identical to the distributions surrounding the impenetrable, cylindrical model. This suggests that excluded volume effects significantly influence the details of the ion distributions near the oligomer, while the detailed charge distributions of the oligomer affects the ion distributions only minimally. Although substantial variation in counterion density was observed near the oligomers of differing conformations, the total number of counterions located within a cylinder surrounding the oligomer bounded radially by 2.4 nm was independent of the conformation of the oligomer. Therefore, for this model system, the local univalent counterion distributions are extremely sensitive to the geometry of the oligonucleotide whereas the extent of neutralization of the oligoanion is insensitive to the conformation of the oligomer.

For second‐order nonlinear optics, a supramolecularly ordered non‐centrosymmetric structure is required. Additionally, well‐ordered organic semiconducting thin films possess superior electronic properties compared to their amorphous counterparts. Herein, we firstly highlight that the design of nonlinear molecules and their functionalization for good molecular orientation (e.g., H‐bonding) is an important method in which to induce supramolecular ordering during subsequent growth. Secondly, we demonstrate a range of growth strategies (e.g., oblique‐incidence molecular beam deposition, hot‐wall deposition) for the growth of molecularly ordered thin films. Thirdly, we discuss various organic supramolecularly ordered material systems (4‐[trans(pyridin‐4‐ylvinyl)] benzoic acid, 5‐bromo‐5′‐formyl‐2,2′‐bithiophene‐4‐nitrophenyl hydrazone, tris(8‐hydroxyquinoline) aluminum) and observe the effects of molecular orientation on their nonlinear optical and optoelectronic properties.

due to substrate effects or changes in particle size due to coalescence.[11] Studies on the Ag particle geometry will be published at a later date.It is important to mention that although the discussion in this communication has been limited to binary MOMLs composed of Alq 3 and silver, other MOML systems utilizing various combinations of different metals and/or organic materials have been found to exhibit similar properties. Work done on some of these systems will be addressed in future publications.In conclusion, the morphology and chemical structure of metal±organic mixed layers composed of Alq 3 and Ag are investigated using a variety of characterization techniques. The results reveal a morphology of small silver metal particles embedded in an organic Alq 3 matrix. Further results show that these layers exhibit light-absorption properties characteristic of the plasmon resonance modes of small silver metal particles. Integration of these light-absorbing metal±organic mixed layers as part of the Black Cathode OLEDs leads to the lower reflectance properties of the novel cathode. This reduction in reflectance, of~8±40 or more, results in a greatly improved contrast for OLED displays. ExperimentalThe metal±organic mixed layers (MOMLs) studied in this paper are fabricated on various substrates. For TEM, carbon-coated copper grid substrates are used for the top-view imaging while Mylar substrates are used for the cross-sectional imaging. For XPS, indium tin oxide (ITO)-coated glass substrates are used. For optical absorption studies, quartz substrates are used. The MOML films are fabricated by thermal vapor deposition in vacuum, by the co-evaporation of Alq 3 and silver at a base pressure of about 10 ±6 torr. . All films are~200 nm in thickness. TEM bright-field images and SAED patterns are obtained using a Philips CM20 (S)TEM with an accelerating voltage of 120 kV. The SAED patterns are analyzed using process diffraction [13]. High-resolution XPS spectra are obtained using a Kratos Axis Ultra X-ray photoelectron spectrometer with a spherical mirror analyzer and a monochromatized Al Ka incident beam. A Schimadzu UV-160 spectrophotometer is used for the UV-visible absorption measurements. Thin films based on acentric supramolecular assemblies of organic conjugated molecules are very attractive for a multitude of information-processing and photonic applications, such as high-speed electro-optic modulation, optical switches, terahertz wave generation, holographic storage, anisotropic charge transport, self-assembled molecular nanowires, or nonlinear optical waveguides for integrated frequency conversion using low-power semiconductor lasers.[1±6] The main characteristics of the desired organic thin films for frequency conversion and telecommunication applications are: i) they must be non-centrosymmetric, and, therefore, show second-order nonlinear optical effects; ii) their thickness must be of the order of one micrometer, able to support waveguiding; iii) they must be homogenous and of good optical quality over large d...