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Cathodoluminescence-based characterization method is developed for examining the organic semiconductor materials for organic light emitting device (OLED) applications. It is shown that [e.sup.-]-beam excitation has created singlet and triplet excitons similar to the carrier injection of an OLED device.

The synthesis, structural characterization and properties, investigation of the electrochemical, photophysical, electron transport, and light-emitting device properties of a series of five new diphenylanthrazoline molecules is presented. The high electron affinities and the robust thermal stability exhibited by the new compounds suggest that they have promising electron-transport properties of light-emitting diodes (LEDs).

Organic semiconductors based on [pi]-conjugated oligomers and polymers constitute the active elements in new generations of plastic (opto)electronic devices. The performance of these devices depends largely on the efficiency of the charge-transport processes; at the microscopic level, one of the major parameters governing the transport properties is the amplitude of the electronic transfer integrals between adjacent oligomer or polymer chains. Here, quantum-chemical calculations are performed on model systems to address the way transfer integrals between adjacent chains are affected by the nature and relative positions of the interacting units. Compounds under investigation include oligothienylenes, hexabenzocoronene, oligoacenes, and perylene. It is shown that the amplitude of the transfer integrals is extremely sensitive to the molecular packing. I interestingly, in contrast to conventional wisdom, specific arrangements can lead to electron mobilities that are larger than hole mobilities, which is, for instance, the case of perylene.

Electron transfer at molecule-metal interfaces is discussed based on a two-photon photoemission study of electron transfer between a molecular resonance and a metal surface. The important roles of molecular-metal wavefunction mixing, polarization, intermolecular band formation, and localization in interfacial electron transfer have been shown.

Research into high-performance bottom electrode organic thin-film transistors is presented.

Research is presented concerning the development of organic complementary circuits which include three-bit row decoders, 48-stage shift registers and simple inverters. Silicon photolithographic techniques were used to construct the circuits.

Doped conducting organic materials were studied to determine injection and space charge limited currents.

A rare class of semiconductors made of single-component pure organic materials are described. Research discuses the preparation of N',N'-dicyanopyrazinonaphthoquinodiiminides along with a fused pyrazine ring from cognate quinones.

Pentacene organic thin film transistors were studied with regard to the flicker (1/f) noise.

A new study investigates transport in n+(p+) c-Si/AlQ/metal junctions.

The electrical behavior of a pi-conjugated oligo(phenylene ethynylene) which resembles a resonant tunnelling diode is explained using density functional theory.

Quantum kinetic equations for electron transport in semiconductors were derived and the field-dependent collision integral was evaluated for impact ionization.

The influence of the deep Mg acceptor on band bending in GaN-based devices is examined.

In-(perylene-3,4,9,10-tetracarboxylic dianhydride) (PTCDA), an organic semiconductor, was measured using angle-resolved ultraviolet photoelectron spectroscopy with synchrotron radiation, to observe the origin of the band gap state.

A new study investigates unidirectional chaotic synchronization of injection-locked semiconductor lasers in the gigahertz range.

Organic waveguide laser structures constructed of transparent indium-tin-oxide electrodes and thin organic films are described.

Research was conducted to examine the electroluminescence (EL) performance of organic light emitting diodes (OLEDs) with a thick doped hole transport layer (DHTL). The basic cell structure is an anode/DHTL/HTL/emitter layer/cathode. Results indicate that the combination of a hole transport polycarbonate polymer and a tris (4-bromophenyl) amiium hexachroloantimonate as a dopant can form thick DHTL with yield an excellent EL performance. The EL characteristics of doped OLEDs are presented.

Research was conducted to examine cathode preparation using sputter deposition. The objectives were to investigate radiation effects on organic light emitting diodes (OLEDs) and to fabricate an efficient and stable OLED with a sputter-deposited cathode. Results revealed that the devices had good operational stability with a half lifetime greater than 3800 h at 20 mA/cm2.

Research was conducted to examine four organic-organic heterointerfaces which were formed by depositing bathocuproine on Alq3, N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1' biphenyl-4,4' diazine, 4,4'-N,N'-dicarbazolyl-biphenyl and copper phthalocyanine. No evidence was found of dipoles at the interfaces which imply that the vacuum levels align in all four cases.

Research was conducted to examine the space charge distribution of organic-molecular-beam-deposition titanylphthalocyanine (TiOPc) films on metal electrodes using surface potential calculation. A spectrometer and an atomic force microscopy were used to investigate the profile and thickness of the TiOPc films. Results indicate that the space charges are excessive electrons transferred from metals and 90% of them concentrate on the metal-TiOPc interface at a range of 10 nm.

A study clarified the relationship between geometry and electronic structure and the effects of hole and electron injection in tris(8-hydroxyquinolino)aluminum (Alq3) interacting with individual atoms of Li, Al and Ca. It also analyzed the similarities and differences between the two geometrical isomers of Alq3. Understanding the nature of the chemical bonding of the systems investigated in this experiment is essential for gaining a microscopic understanding of light emitting diodes based on Alq3 and its derivatives. Experimental results are discussed.

A study on proposed significant device geometries for efficient organic light-emitting diodes (OLEDs) based on 8-hydroxyquinoline aluminum investigated the role of charge transfer in OLEDs using a synthesized soluble quinacridone derivative. Spectral measurements show that more emission originates from the soluble quinacridone derivative dopant for electroluminescence than for photoluminescence at a specified doping level.

The development of organic photovoltaic solar cells is discussed. A self-organized free base 5,10,15,20-tetrakis(4-n-octylphenyl) porphyrin (H2TOPP) is prepared to act as an intrinsic film. It is sandwiched between a titanium dioxide thin film and a zinc 5,10,15,20-tetra (4-carboxyphenyl) porphyrin (ZnTCPP) (p-type) thin film which is also an excellent sensitizer for titanium dioxide. It is shown that the H2TOPP acts as an intrinsic semiconductor and than ZnTCPP acts as a p-type semiconductor.

A substantial amount of research interest has been directed toward organic field effect transistors and their applications in integrated circuit creation. A systematic study of the gate bias dependence of the field-effect mobility in thee oligothiophenes was therefore conducted. A method which relies on drain current at low drain voltage was developed to determine the field effect mobility of these oligothiophenes. Experimental details and findings are discussed.

The influence of discrete trap levels on organic light emitting diodes under the space charge limited conditions was investigated. The interactions of the free, discrete and exponential trap charges in single- and double-carrier devices were examined. The abrupt transitions in the current-voltage properties usually associated with the discrete trap levels in single-carrier devices may disappear in double-carrier devices such as the organic light emitting diodes.

The high density excitation dynamics in waveguides of a ladder-type poly(p-phenylene) (LPPP) conjugated polymer are studied. Results show that amplified spontaneous emission causes a rapid depletion of the excited state at excitation densities over 1.6 x 10(super 18)/cu cm in LPPP films deposited on a glass substrate. For LPPP films deposited on an indium-tin-oxide substrate, bimolecular excitation annihilation was the dominant recombination channel for excitation densities over 10(super 18)/cu cm.

A study was conducted to characterize the preparation of a unique iron(III) phthalocyanine/TiO2 photocatalyst. The Philips PW 1050 powder diffractometer was utilized to obtain the X-ray diffractograms of the calcined samples. The adsorption isotherm was then examined based on the Langmuir theory. Experimental results indicated that the photocatalyst supported improved photocatalytic activities for the degradation of organic pollutants.

The formation of interfaces between the organic semiconductor 4,4'-N,N'-dicarbazolyl-biphenyl (CBP) and metals Au, Ag and Mg have been investigated using ultraviolet photoemission spectroscopy. When CBP was deposited on a metal surface an interface dipole of a magnitude almost independent of the metal work function was formed.

The potential barrier heights at interfaces between poly-(p-phenylene vinylene) (PPV) and mixtures of polyaniline doped with camphorsulfonic acid (PAni-CSA) and poly-(methylmethacrylate) (PMMA) were quantitatively evaluated. Measurement of barrier heights considered the temperature dependence of tunneling current measurements. The results showed that the value of the {PAni-CSA/PMMA}/PPV potential barrier height was generally not affected by the PAni-CSA concentration in the mixture.

The construction of interfaces between magnesium and the organic molecular semiconductor tris(8-hydroxy-quinoline) aluminum (Alq3) was investigated through ultraviolet photoemission spectroscopy. The morphology and electronic structure of Mg-on-Alq3 and Alq3-on-Mg interfaces were contrasted. The energy of the Alq3 molecular levels was obtained for both cases with respect to a reference Fermi level as a function of interface formation.

Research was conducted to investigate the electronic structures of evaporated films of five organic-light emitting and carrier-injecting materials for organic electroluminescent devices. Ultraviolet photoemission spectroscopy was used in studying light-emitting materials tris(8-hydroxyquinolino) aluminum an 1,2,3,4,5-pentaphenylcyclopentadiene, a hold injecting material and electron-injecting materials. Results reveal the correlation between the ionization threshold energies.

Research was conducted to study ultraviolet photoemission spectroscopy of the electronic structure of organic-organic heterojunctions established between the standard electron-transport emissive material tris(8-hydroxy-quinoline)aluminum and two hole-transport materials. The measurements were carried out in an ultrahigh vacuum system characterized by analysis and organic deposition chambers. Results showed the existence of substantial charge transfer-induced dipoles at the interfaces.

Experiment was conducted to examine the fabrication of efficient green light-emitting diodes using a side-chain random polymer based on a high electron affinity (EA) naphthalimide moiety (PNI). Results suggest that the electroluminescence quantum efficiency is not limited by Al cathodes as for poly(p-phenylene vinylene) which is attributed to the increased EA. Findings also indicate that PNI generates higher efficiencies at high currents and longer lifetimes.

The current-voltage (I-V) characteristics of an inorganic semiconductor (IS)|metal Schottky diode are largely determined by the potential barrier height [Φ.sub.b] at the interface. Small barrier heights yield ohmic contacts, and [...], Although in principle semiconductor-metal (Schottky) diodes should be tunable by changing the work function of the metal, such flexibility cannot be achieved in a single device and in practice is often limited by interfacial states that cause Fermi-level pinning. A tunable diode is reported based on a hybrid inorganic-organic, n-indium phosphide|poly(pyrrole)|nonaqueous electrolyte architecture. By electrochemically manipulating the work function of the conjugated polymer poly(pyrrole), the turn-on voltage (more precisely, the forward bias potential required to pass a particular current) of the diode can be continuously and actively tuned by more than 0.6 volt. The work highlights a distinguishing feature of conjugated polymers relative to more traditional semiconductor materials, namely, the ability of dopant ions to permeate conjugated polymers, thereby enabling electrochemical manipulation.

An experiment is conducted to evaluate compensation between silicon (Si) and carbon (C) isoelectronic implantations in n-type and vanadium (V) implantations in p-type 6H-SiC. This is achieved due to the chemically active nature of the V implant and the lattice damage formed by Si and C implantations. Maximum resistivity values were computed for both SiC and V implants.

Vapor deposition was utilized to fabricate light emitting devices with a sandwich structure: metal/EC6T/indium-tin-oxide, using end-capped sexithiophene (EC6T) as active organic material. Intensity and current of electroluminescence (EL) of the EC6T layers were measured as a function of voltage for various metals (Ca, Mg, Al, In, Ag) in a wide range of temperatures (4-300 K) and thicknesses of the EC6T layers (40-350 mm).

Raman spectroscopy research shows that the deposition temperature of heavily doped GaN buffer layers on sapphire substrates is a strong determinant of the presence of free carriers in GaN layers. Infrared measurements provide information for Raman spectra calculations. An inhomogeneous concentration of electrons on the scale of hexagonal microcrystallites were observed.

Azobenzene (AB) and 4-nitroazobenzene (NAB) were covalently bonded to carbon surfaces by electrochemical reduction of their diazonium derivatives. The [N.sub.1s] features of XPS spectra of modified surfaces had intensities expected for monolayer coverage. However, the Raman spectra were significantly more intense than expected, implying an increase in scattering cross section upon chemisorption. A likely explanation is resonance enhancement of the carbon/adsorbate chromophore analogous to that reported earlier for dinitrophenylhydrazine (DNPH) chemisorption. Vibrational assignments indicate that the C-C vibration between azobenzene and the carbon surface is in the 1240-1280 [cm.sup.-1] region, and this conclusion is supported by spectra obtained from [13C]graphite. Observation of depolarization ratios for 4-nitroazobenzene and DNPH on graphite edge plane indicate that NAB is able to rotate about the NAB/carbon C-C bond, while chemisorbed DNPH is not. The partial multiple bond character of the DNPH linkage to graphite is consistent with the observation that the DNPH r system remains parallel to the graphitic planes.

The synthesis of functionalized analogs of 1,3,6,8-tetrakis (methylsulfanyl)pyrene with a 60% yield involves the steps of nitration, reduction, acetylation and bromination of pyrene in tandem. Oxidation of the acetamide analog with iodine yields a radical-cation salt that has an electron conductivity of 1 S per cm at room temperature. The formation of such radical-cation salts is not blocked by the replacement of the methylsulfanyl groups by an amide group, which acts as a lever for the addition of functionality to the molecule.

The electrical properties of homogenous organic semiconductive thin films grown by radio frequency plasma polymerization of 3,4,9,10-perylenetetracarboxcyclic dianhydride were investigated. The results showed that the conductivity of the samples prepared with a rf power of 60 W was lower by three orders of magnitude than those prepared with a rf power of 10 W. In addition, exposure to air decreased conductivity.

Ac and dc conduction through thin Langmuir-Blodgett films sandwiched between different metal electrodes was analyzed. The results showed that dc conduction changed from a linear to a nonlinear I/V characteristic. Heat annealing was observed to cause significant changes in conduction characteristics.

The recent interest in lasing action and stimulated emission in optically pumped thin films of small molecular weight organic semiconductors and polymers (1-5) is opening the door to a new [...], Lasing action in organic vertical-cavity surface-emitting laser (OVCSEL) structures is demonstrated. Optically pumped OVCSELs with an active layer composed of a thin-film organic semiconductor tris-(8-hydroxyquinoline) aluminum ([Alq.sub.3]) doped with DCM laser dye produced very narrow linewidth (0.2 ± 0.1 angstrom), high-power (3 watts) emission that could be varied in different devices from orange to red. The efficient energy transfer from [Alq.sub.3] to DCM results in a threshold input energy of 300 microjoules per square centimeter. An operational lifetime [is greater than] [10.sup.6] laser pulses was achieved for a device operated well above threshold in atmosphere. The linewidths above threshold are Fourier transform-limited and could potentially be narrowed further.

The application for full color displays of hybrid organic-inorganic GaN-based light-emitting diodes (LED) was examined. The LED was composed of two parts, namely, the GaN-based eletroluminescent part and the organic thin-film-based fluorescent part whose absorption of electroluminescence enabled fluorescing at a longer wavelength, thereby causing color conversion. Deposition at lower temperatures was also demonstrated to produce organic films with enhanced surface smoothness.

The differences in drain current and drain voltage characteristics of top and bottom contact organic thin film transistors (OTFTs) are studied by an OTFT devices simulator. The mechanism behind the intrinsic characteristics differences is the deficiency of carriers at the source-channel interface, which has resulted to a very high potential drop that the bottom contact devices suffer more.

The synthesis, structures, characterization, and applications of naphtho[1,2-b:5,6-b']dithiophene (NDT) and -diselenophene (NDS) derivatives to field-effect transistors (FETs) are presented. The results demonstrated the use of NDT and NDS as new potential heteroarene core structures for organic semiconducting materials.