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The 1,9-dithiophenalenylium cation has been prepared as a stable hexafluorophosphate salt, by reaction of 9-ethoxyphenalenone with phosphorus pentasulfide. The compound has been fully characterized and a M I N D 0 / 3 SCF MO calculation of the ground-state structure is reported. The compound is shown to undergo three one-electron reduction steps (without decomposition) the first two of which are reversible. Moderately highly conducting charge transfer salts are obtained with TCNQ derivatives. The 1,9-dithiophenalenyl radical has been prepared in solution by electrochemical and chemical reduction of 1,9-dithiophenalenylium hexafluorophosphate. The compound has been subjected to ESR, mass, and electronic spectral examination. The radical is found to be monomeric in solution in the temperature range between 18 and -95 OC. The observed ESR hyperfine splittings are consistent with the removal of spin density from the phenalenyl nucleus by disulfide substitution.Odd alternant hydrocarbons are unique in their ability to form stable cations, radicals, and anions' which are of very similar molecular geometry.2 They may therefore be of interest in the development of organic metals, where such characteristics have been suggested to be i m p~r t a n t .~-~ The chief obstacle to their utilization in this respect is the propensity of the neutrals radicals for dimerization-in fact we are not aware of any planar carbon-based radical which is wholly monomeric in solution and/or the solid state. The phenalenyl (PLY) (lb) Ib radical, while particularly stable, is known to dimerize at low temperatures in solution.5s6 W e therefore sought to stabilize the triad of oxidation states and particularly the radical in a way which would not seriously perturb the desirable electronic properties of the P L Y nucleus or inhibit intermolecular interactions in the solid state.The 1,2-dithiolyl system also provides a number of accessible oxidation states.j Thus the 3,5-diphenyl-l,2-dithiolylium cation (2a) has been shown to undergo three reduction steps;j again the neutral radical (2b) is found to be in equilibrium with 2b, R , = R, = P h ; R, = H f , R , = R, = P h ; R, = H 3 the dimer.' W e therefore sought to combine these two components (1 and 2) in the 1,9-dithiophenalenyl system (DTPLY) (4). W e felt that this species might be interesting in its own ' W ' s-s 4b right, as well as providing some insight into the effectiveness of incorporating sulfur into the PLY nucleus.t City University of New York Results and DiscussionSynthesis and Characterization of the 1,9-Dithiophenalenylium Cation (4a) and 1,9-DithiophenalenyI (4b). Our initial efforts to obtain 4a began with 9-hydroxyphenalenone (5),*-1° to which we applied the standard reagents for conversion of a @hydroxy ketone into a 1,2-dithiolylium salt.11%12 Presumably as a result of the very strong hydrogen bonding in this compound,1° the material was found to be inert to the usual procedures, except under particularly forcing conditions from which no characterizable products could be recove...

Epitaxial thinfilm ruby as an ionirradiation damage sensorThin films of 3,4,9, lO-perylenetetracarboxylic dianhydride (PTCDA) develop low electrical resistivity ( < 10-3 (J cm) after irradiation with 2-MeV Ar+ ions. Electron microscopy and diffraction show that vacuum-deposited films of this material consist, prior to ion-irradiation, of discrete crystalline grains ( -20-50 nm diameter) in which the molecules are disposed closely parallelto the substrate (average inclination _10°_15°). Upon irradiation with up to _10 14 Ar+ I cm 2 , the grains become progressively more defect-rioden and eventually amorphous. At that stage, the resistivity begins to decrease by -12 orders of magnitude at doses between _10 14 and -5 X 10 16 Ar+ Icm 2 , while the intergranular boundaries become diffuse and the grains begin to merge. The temperature dependence of resistivity in this regime is as exp(constlT 1/2), which is consistent with our morphological and structural results as it implies carrier hopping between conducting islands embedded in a nonconducting matrix. At the highest ion doses ( > 5 X 10 16 Ar+ Icm 2 ) the grains become connected into a rather uniform and featureless network akin to amorphous carbon, and the resistivity reaches its lowest value and becomes independent of temperature. The amorphous-carbon-like character of the highly irradiated material is evidenced not only by its diffraction pattern but also by its crystallization with a graphitic-type structure during annealing to 1200 °C. PACS numbers: 73.60. -n, 68.55. + b, 81.40.Rs, 61.65. + d Lovinger et a/. 478 [This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP: 130.88.90.110 On: Sun, 21 Dec 2014 05:04:25

We discuss the properties of organic-on-inorganic (OI) semiconductor contact barrier diodes. A model for charge transport is developed which suggests that thermionic emission over the organic/inorganic contact barrier dominates at low current densities, whereas space-charge effects dominate transport through the organic layer at high current densities. The effects of charge trapping in the organic layer are also considered. This model is applied to OI diodes using thin films of the prototypical aromatic compound; 3,4,9,10-perylenetetracarboxylic dianhydride, (PTCDA) vapor-deposited onto n- and p-Si substrates. Several electrical and optical properties of PTCDA are investigated to provide a basis for analyzing the OI diodes. Both ohmic and space-charge-limited transport are observed in the PTCDA. We discuss mobility, transient response, and photoresponse of the thin-film organic material. Also described are the general properties of organic-on-inorganic contact barrier diodes which employ PTCDA and related compounds on either p- or n-Si substrates. Comparisons between diode performance and the theory are made. The contact barrier diodes exhibit high breakdown voltages (≤230 V) and reverse dark currents limited by generation and recombination of carriers in the Si bulk. From the forward current-voltage characteristics, apparent OI contact barriers of φBp=(0.75±0.02) eV and φBn=(0.61±0.01) eV are formed with p- and n-Si substrates, respectively. The resulting diodes are superior, in many respects, to conventional Schottky diodes due to enhanced contact barriers and reduced edge effects.