The synthesis of poly(9,9-dioctylfluorene) conjugated polymer nanowires using the method of melt-assisted wetting of nanoporous alumina membrane templates is reported. Polymer nanowires exhibiting blue photoluminescence emission with diameters of approx. 300 nm are obtained. Absorption and photoluminescence spectra of nanowire mats indicate that the nanowires consist of the semi-crystalline form of the polymer. Single wires exhibit active waveguide behavior whereby excited luminescence propagates towards and out-couples at the tips of the nanowires. Spectra of out-coupled emission exhibit multiple modes with mode spacing corresponding to longitudinal Fabry-Pérot cavities of equivalent lengths to those of the nanowires. Above a threshold incident pump energy spectral collapse to a single blue shifted peak with instrument limited line width occurs characteristic of single mode lasing.

The influences of self-assembled-monolayers (SAMs) modifications on the gold electrodes in organic field effect transistors are studied using benzen-thiols (BzTs) having amino (NH2), nitro (NO2) and methyl (CH3) substituents and pentacene as an organic semiconductor. The field effect transistor (FET) characteristics are found to be very sensitive to the preparation condition of the SAMs modified surfaces. This can be rationalized in terms of the barriers against carrier injections made by SAMs and this situation can be monitored using a surface contact-angle method. The enhancement in the field effect mobilities μ is observed when the SAMs modifications to the electrodes are applied, and this could be caused by the higher efficiency of carrier injection attained by the hole transfer from SAMs to pentacene molecules.

Spin injection from GaAs(100) to organic semiconductor copper phthalocyanine (CuPc) has been investigated experimentally with spin-resolved two-photon photoemission (SR-2PPE) spectroscopy. With SR-2PPE, the dynamics of both electron and spin relaxation have been studied with femtosecond time resolution. The spin-polarized electrons are originally generated in GaAs through optical pumping and injected into CuPc. We observed an enhancement in spin polarization at the interface after initial CuPc deposition. This demonstrates that interface spin scattering is insignificant, which is similar to our previous result of spin injection at CuPc/Co interface. The spin polarization dropped when the CuPc film became thick, an effect attributed to bulk attenuation in CuPc. The lifetime of the unoccupied orbits in CuPC was also studied with red-blue excitation of photon energy 1.56 eV and 3.12 eV, respectively. There was a strong asymmetry in the time-resolved spectra, and an unexpected long lifetime when the lower unoccupied orbital was excited. A simple explanation of this phenomenon will be discussed.

Organic thin film transistors(OTFTs) were simulated by a SPICE model adopted in hydrogenated amorphous TFTs(a-Si:H). The gate voltage-dependent mobilities were assumed to fit the representative current-voltage characteristics. The optimal fitting procedures were suggested to compare the experimental data with the mathematical expressions used in the amorphous TFTs. Each SPICE parameter explains the gate dependent mobilities in OTFTs originating from the distribution of trap sites for the hopping conduction.

Scanning tunneling microscopy (STM), atomic force microscopy (AFM) and near-edge x-ray absorption fine structure (NEXAFS) have been used to study the structure of tetracene films on hydrogen-passivated Si(001). A distinct growth morphology change that occurs around a few monolayers of film thickness was characterized. This coverage-dependent film structural phase transition leads to a molecularly ordered film structure commensurate with the crystalline substrate.

Recently, low molecular organic non-volatile memories have been developed as a next generation of non-volatile memory because of nano-meter device-feature size and nano-second access and store-time. We developed a non-volatile memory fabricated with the device structure of Al/ α-NPD/Al nano-crystals surrounded by Al2O3/α-NPD/Al, where α-NPD is N,N'-bis(1-naphthyl)-1,1'biphenyl4-4”diamine. One layer of Al nano-crystals with ∼20 nm-width ∼20 nm length was uniform produced between α-NPD layers, confirmed by 1.2MV high voltage transmission-electron-microscope. This device showed Vth of 3.0 V, Vprogram of 4.3 V, and Verase of 6.3 V. Particularly, this device exhibited an excellent non-volatile memory behavior performing the bi-stability (Iprogrm/Ierase) of >1×102, program/erase cycles of >1×105 and multi-levels. In addition, previous reports about low molecular organic non-volatile memories have showed a bad reproducible memory characteristic. However, this issue was completely solved via isolating Al nano-crystals embedded in α-NPD by O2 plasma oxidation. The uniformity of Vth, Vp, and Ve were 9.91%, 6.94% and 7.92%, respectively. Furthermore, the effect of buffer or barrier layer on non-volatile memory characteristics was investigate to examine the control ability for Vth, Vp, and Ve. The 0.5-nm LiF showed a barrier layer behavior suppressing the bi-stability of non-volatile memory. Otherwise, 15-nm CuPc exhibited a buffer layer behavior enhancing the bi-stability of nonvolatile memory.

The surface electronic structures of conjugated regio regular and regio random poly (3- hexylthiophene) (rr-P3HT and rra-P3HT) thin films were studied by near edge X-ray absorption fine structure spectroscopy, ultraviolet photoelectron spectroscopy and Penning ionization electron spectroscopy (PIES). The distribution of the surface electronic states was controlled on rr-P3HT and rra-P3HT thin films with different molecular ordering by varying the coating process and PIES was adopted to observe the electronic states existing outside the surface.

High quality BaTiO3 thin film epitaxially grown on a Nb-doped SrTiO3 (BTO/Nb-STO) substrate by a laser ablation technique is employed as a high-k gate insulator for a field-effect transistor of a rubrene single crystal in order to search for the possibility of high carrier accumulation. The high dielectric constant of 280 esu for the prepared BaTiO3 thin film accumulates 0.1 holes/rubrene-molecule, which is 2.5 times as high as the maximum carrier number of 0.04 holes/rubrene-molecule attained in the case of SiO2 gate insulator. Important parameters of rubrene single crystal FETs on BTO/Nb- STO are also described in comparison with those on SiO2/doped-Si.

We report on the effects of modifying the gate dielectrics by spin coating of HMDS, PVP and PVA which cause different surface energy and surface roughness owing to the different functional groups. In changing the surface state with applying various surface treatments, I-V and C-V measurements of the OTFTs were performed. The PVP-coated OTFTs, which has smoother and lesser amount of OH-groups on the gate dielectric surface, showed enhanced pentacene growth and nearly free hysteresis behavior than that of the HMDS and PVA-coated OTFTs.

A gold and aluminum layer was investigated as an anode for organic light-emitting devices (OLEDs). By pretreating the ultrathin aluminum layer in an oxygen (O2) plasma, the hole injection from the metal anode to the organic layer was greatly enhanced. The fabricated OLEDs demonstrated improved current density and luminance characteristics as compared with other devices using a gold anode and an aluminum layer not treated with an oxygen plasma.

We investigated luminescent properties of rare-earth metal complexes and phosphor-rescent molecules doped in a conducting polymer. Electroluminescent (EL) properties in combination of red emissive europium complex of tris(di-benzoylmethane)-mono(4,7-diphenyl-phenanthroline) europium (III) (Eu(dbm)3phen) and blue phosphorescent molecule of bis[(4,6-difluoro-phenyl)-pyridinato-N,C2'] (picolinate) iridium (III) (FIrpic) doped in poly(N-vinyl-carbazole) (PVK) and a new rare-earth complex tris(hexafluoroacethylacetonato) (phenan-throline) samarium(III) [Sm(hfa)3(phen)2] have been investigated as an EL emitter. White EL has been obtained from mixed layer of Eu(dbm)3phen and FIrpic, and EL from Sm complex has been obtained. Energy transfer and the emission mechanisms have been discussed.

Classical and ab-initio calculations were carried out on bulk defects and surfaces of the carbon allotrope Fcc-C22. The results revealed a number of possible defects with spin polarization and one with antiferromagnetic character. The surfaces were shown to be able to host magnetic polarization. Extrinsic light dopants (H and N) were shown to introduce spin polarization for small dopant concentration and to metallize the systems for large concentrations.

We demonstrate here functional polymeric particle synthesis by employing a microfluidic approach. The functional polymer is MIP system (molecularly imprinted polymer), which can be produced by “molecular imprinting”, a general protocol for the preparation of “synthetic receptor or binding sites” with specific recognition for targeted organic molecules. The recognition of complex molecules and biological entities is a necessary component for fabricating chemical sensors, diagonostic bio-sensors, and for drug delivery systems. We have obtained homogeneous MIP's microparticles, which may have high affinity receptor sites only by fabricating a microreactor.

We prepared quasi single crystalline pentacene monolayer films on Bi-terminated Si(111) by using bunched steps on vicinally-cut surfaces as an orientation template. Band dispersion in the conduction plane of pentacene was clearly observed by angle-resolved photoelectron spectroscopy.

Here we present a concept to improve the field effect transistor performance of P3HT in terms of threshold voltage stability as well as the stability in ambient atmosphere by introducing a strong acceptor dopant in the main polymer chain. In our concept the direct introduction of the acceptor dopant in the polymer main chain ensures the strucural stability against diffusion processes. P3HTs with different contents of acceptor molecules which are fixed linked in the main chain of the polymer , have been synthesized using the McCullough Grignard metathesis method. As acceptor unit has been integrated tetrafluorbenzene (TFB). The introduced dopant amount has been varied in order to obtain an optimum between the processability of the polymers and the resultant transistor performance.

Compared to the p-type semionducting polymers the n-type organic materials are markedly less developed. Recently an interesting solution to this task has been proposed in the form of a conjugated ladder-type poly (benzo-bisimidazobenzo-phenanthroline) (BBL) showing either ambipolar or n-type field effect properties dependent upon the sample preparation and processing. However this rigid-chain ladder polymer is not soluble in the common organic solvents resulting in a rather complicated technological transfer. We report the significant improvement of the BBL-processing utilizing aqueous colloidal dispersions and their OFET-application. The resultant devices demonstrate ambipolar electronic transport with charge carrier mobilities in the range of 10−5 cm2/Vs without specific optimization procedures..

In this work, an accurate capacitance-voltage (C-V) model of organic Schottky diode is proposed. By taking the interface trap of the Schottky barrier into account, the capacitance model was derived from the junction and interface capacitance as a function of operation voltage. The model successfully describes the turn-around capacitance characteristic of Al/poly(3-hexylphiophene)(P3HT)/poly(3,4-ethylenedioxythiophene)poly(styrene sulfonate)(PEDOT:PSS)/IZO Schottky diode in the forward bias region. The simulated capacitances are in good agreement with our experimental data.

We have investigated the charge carrier transport properties of polycrystalline films fabricated with discotic and calamitic liquid crystals. The polycrystalline films of these liquid crystals exhibiting particular textures under a polarized microscope, i.e., hexagonal and co-circular patterns for discotic and calamitic liquid crystals, respectively, which indicate that the molecular alignment in the liquid crystalline phase is well preserved exhibit clear hole transport along with molecular stacks even in a 15 μm thick film, judging from transient photocurrents by time of flight method. The hole mobilities are over 0.1 cm2/Vs at room temperature. These results indicate formation of fewer grain boundaries across conduction channels. On the other hand, the carrier transport properties in the polycrystalline films of non-liquid crystalline molecules with the same molecular shape exhibit no particular patterns as described and photocurrents are annihilated in the bulk as a function of time, indicating many deep trap sites in grain boundaries. The present results indicate that the liquid crystalline molecule is a good candidate for preparing quality organic polycrystalline semiconductor thin films in opto-electronic applications.

The influence of charge carrier traps on charge carrier transport is studied in a small molecule organic semiconductor model system by means of an optical time-of-flight method. The model system consists of the hole transport material N,N'-di(1-naphtyl)-N,N'-diphenylbenzidine (α-NPD, sometimes denoted as α-NPB) either undoped or doped with various concentrations of the small molecule 4,4',4”-tris-[N-(1-naphtyl)-N-(phenylamino)]-triphenylamine (1-NaphDATA), which is known to create hole traps in α-NPD.

In case of undoped α-NPD, non-dispersive hole transport is observed and the hole mobility is determined as 6·10−4cm2/Vs in the examined electric field range, being in good agreement with published data. Depending on the intensity of the laser light employed for optical charge carrier generation, current transients both in the space-charge regime and in the small signal case are obtained. In the small signal case the current transients do not exhibit the expected flat current plateau before the characteristic kink that marks the transit time, but feature a cusp instead. A tentative mechanism for its formation is proposed.

The influence of the trap concentration on charge carrier transport is studied by introducing 1-NaphDATA as a molecular dopant. It is demonstrated that the hole transport in α-NPD can be controlled by varying the doping concentration of 1-NaphDATA. Increasing the trap concentration, a transition from non-dispersive transport in undoped α-NPD to non-dispersive but trap-controlled transport with reduced mobility and further to dispersive transport is observed.

The structure and polymorphism of pentacene thin films on SiO2 substrate were investigated by grazing incidence x-ray diffractometry (GIXD). The in-plane GIXD patterns were successfully obtained from vacuum deposited ultra-thin films of a few monolayers thick. The two-dimensional lattice constants were determined for both thin-film and bulk phases from the observed GIXD patterns. Considering the obtained unit cell parameters, the mechanism of the transformation between polymorphs was discussed using the classical nucleation theory.

We report a synthetic method for shifting the pKa for the deprotonaton of polyaniline by the formation of non-covalent complexes between polyaniline and a polyanion. Depending on the choice of the polyanion and the condition of the synthesis, we can control the pKa value for the dedoping reaction to spread the pH range from 5.5 to 9.0. From a systematic study of the structural influence on the pKa values, we have verified that the electrostatic stabilization of the polaron is the origin for this unusually large pKa shift.