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We have measured the specific heat of the antiferromagnetic spin-1 chain compounds NENP and ${\mathrm{Y}}_{2}$${\mathrm{BaNiO}}_{5}$ diluted with Zn, at temperatures between 0.1 and 15 K and magnetic fields up to 9 T. We find that the defect-related Schottky anomaly in ${\mathrm{Y}}_{2}$${\mathrm{BaNi}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Zn}}_{\mathit{x}}$${\mathrm{O}}_{5}$ is better described by assuming the defects are S=1, rather than free S=1/2, the latter proposed to exist within the valence-bond-solid model of finite S=1 chains. The relationship of these results to electron-spin-resonance data for NENP, which imply free S=1/2 defects is discussed.

The muon-spin-relaxation (\ensuremath{\mu}SR) technique has been used to study the internal field modulation dynamics of fluxons in crystals of \ensuremath{\kappa}-[BEDT-TTF${]}_{2}$Cu[NCS${]}_{2}$ (${\mathit{T}}_{\mathit{c}}$\ensuremath{\approxeq}10.5 K). The data exhibit a strong field dependence for applied fields in the range 129 Oe\ensuremath{\le}\ensuremath{\Vert}${\mathbf{H}}_{\mathrm{ext}}$\ensuremath{\Vert}\ensuremath{\le}4 kOe, which is attributed to a combination of vortex motion, finite core size effects, and pinning. In low fields (\ensuremath{\Vert}${\mathbf{H}}_{\mathrm{ext}}$\ensuremath{\Vert}=129 Oe), the data exhibit a flux-pinning transition at ${\mathit{T}}_{\mathit{x}}$\ensuremath{\sim}5 K, as evidenced by a peak in the second moment of the local field distribution at \ensuremath{\sim}5 K accompanied by an enhanced minimum in the first moment at the same temperature. In higher fields (\ensuremath{\Vert}${\mathbf{H}}_{\mathrm{ext}}$\ensuremath{\Vert}=750 Oe, 3 kOe, and 4 kOe), where the effects of motion and pinning are minimized, the symmetry of the underlying gap function is confirmed as s wave. Corrections for finite fluxon core, finite mean free path, and flux-lattice disorder were applied in determining the London penetration depth, ${\ensuremath{\lambda}}_{\mathit{L}}^{(\mathit{b}\mathit{c})}$(0)=7680\ifmmode\pm\else\textpm\fi{}700 \AA{}.

The synthesis and properties of 2-(3,4-dicyanocyclopenta-2,4-dienylidene)-1,3-dithiole 2have been, previously reported. NMR spectral data of that compound imply a large contribution of the dipolar form to its electronic structure. Two-solvent diffusion recrystallization, in the presence of O2, yields the title compound 3, the crystal structure of which is reported here. This appears to be the first crystal structure of a compound containing the dicyanocyclopentadiene moiety. The space group is P1–, and the lattice parameters are a= 8.3617(19), b= 11.1196(23). c= 12.8159(20)A, α= 96.587(15)°, β= 103.103(15)°, γ= 109.917(16)° and V= 1066.9(4)A°3 for Z= 2. We also discuss a plausible mechanism for the formation of compound 3, and its spectral properties.

The synthesis and properties of 2-(3,4-dicyanocyclopenta-2,4-dienylidene)-1,3-dithiole 2have been, previously reported. NMR spectral data of that compound imply a large contribution of the dipolar form to its electronic structure. Two-solvent diffusion recrystallization, in the presence of O2, yields the title compound 3, the crystal structure of which is reported here. This appears to be the first crystal structure of a compound containing the dicyanocyclopentadiene moiety. The space group is P1–, and the lattice parameters are a= 8.3617(19), b= 11.1196(23). c= 12.8159(20)A, α= 96.587(15)°, β= 103.103(15)°, γ= 109.917(16)° and V= 1066.9(4)A°3 for Z= 2. We also discuss a plausible mechanism for the formation of compound 3, and its spectral properties.

Approximately 0.5% of nonmagnetic divalent ions Zn, Cd, and Hg have been alternatively substituted for Ni in the linear chain of antiferromagnetically coupled ${\mathrm{Ni}}^{2+}$ (S=1) spins in [Ni(${\mathrm{C}}_{2}$${\mathrm{H}}_{8}$${\mathrm{N}}_{2}$${)}_{2}$(${\mathrm{NO}}_{2}$)]${\mathrm{CIO}}_{4}$ (NENP). While at low temperature the pure NENP shows no EPR signal, the doped NENP shows identical EPR spectra corresponding to the fractional spin S=1/2 states at the ``open'' ends of the Ni chains adjacent to the nonmagnetic substitutions.

Crystals of C60 or C70 cocrystallized with n-pentane grow as elongated, ten-sided columns. X-ray diffraction shows ordering of C60 or C70 molecules along the column and a remarkable tenfold symmetry normal to the column. The ratio of the x-ray-diffraction vectors of the two lowest-order diffraction spots is nearly equal to the “golden ratio,” τ. Despite these similarities with decagonal, quasicrystalline order, the diffraction indicates crystalline order with a twinned unit cell.

The kinetics of the sorption characteristics of seven different solvents has been measured at 22°, 40°, and 50°C in several cured epoxies. In addition to water, the organic solvents methanol, acetone, isopropanol, ethyl acetate, 1,2-dichloroethane, and toluene were examined. The resin, diglycidyl ether of bisphenol A, was cured with four hardeners, each one resulting in a different epoxy material. The curing agents include triethylenetetramine, nadic methylanhydride, dicyandiamide and m-phenylenediamine, all commonly used substances. Data were analyzed using Fick's diffusion equation. In general, three types of behavior were observed, Fickian diffusion, Case II diffusion, and anomalous diffusion. Fickian or anomalous behavior dominated at all temperatures. Diffusion was both material and solvent dependent. The anomalous nature of isopropanol was noted. Although chemically similar to methanol and about the same size, as acetone, isopropanol is sorbed at a much lower rate. A combination of physical and chemical effects appeared to be responsible for the observations in the epoxies. Diffusion coefficients were estimated for all penetrants and were mostly in the range of 10−9 to 10−11 cm2/s. Where appropriate, apparent activation energies for diffusion were calculated from the kinetic curves.

We report the first direct measurement of the effective magnetic penetration depth in oriented single crystals of {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2}, with {ital T}{sub {ital c}}(5 G){approx}9 K. Results yield an effective in-plane value of {lambda}{sub {ital e}{ital f}{ital f}}{sup {ital b}{ital c}}(0){approx}9800 A (for {ital H}{sub ext}{approx}3 kG), and a temperature dependence consistent with conventional {ital s}-wave pairing. Comparison with the London penetration depth, {lambda}{sub {ital L}}(0) (estimated to be {approx}5100 A), indicates a tendency toward dirty-limit superconductivity, with the ratio of coherence length over mean free path of {xi}{sub 0}{sup {ital b}{ital c}}/{ital l}{sub {ital b}{ital c}}{approx}2.7. From our results, it appears unnecessary to invoke any unconventional pairing schemes to explain the superconductivity in this material.

Dans la phase metallique, la magnetoconductivite est proportionnelle a Hα ou α est inferieur a 2, et α decroit lorsque le champ magnetique tourne autour de l'axe c * . Dans les etats d'onde de densite de spin induite par champ, il y a une augmentation des anomalies aux transitions de phase lorsque le champ tourne

In pure oxygen at moderate temperatures of 200 °C, an fcc C60 transforms into amorphous carbon‐oxygen compounds and the icosahedral C60 molecular structure is destroyed. The maximum oxygen uptake of pure C60, O/C60, is 12. Isothermal TGA transformation curves are sigmoid‐shaped with the kinetic exponent n∼5/2 which conforms with a two‐dimensional nucleation and growth mode. The heat of formation for the carbon‐oxygen compounds is 90 kcal/mol O, and the formation energy for the reaction: 60C (graphite)→C60 molecule is estimated to be ∼600 kcal/mol.

Carbon-13 NMR spectra of powder samples of pure C60 and of a mixture of C60 and C70 provide information about molecular motions in the solid state. At room temperature, C60 molecules rotate rapidly and isotropically. The transition from a rapidly rotating to a stationary (on the time scale of the experiment) system occurs over a temperature range from 120 K to 60 K, suggesting a distribution of activation energies. C70 molecules also rotate rapidly at room temperature, but more anisotropically.

We have grown crystals of the carbon structure C60 by sublimation. In contrast to solution-grown crystals, the sublimed crystals have long range order with no evidence of solvent inclusions. Sublimed C60 forms three dimensional, faceted crystals with a close-packed, face-centered cubic unit cell. We have refined a crystal structure using the “soccer ball” model of the C60 molecule. The results indicate that the C60 molecule has the expected spherical shape, however the data are not sufficiently accurate to unambiguously determine atomic positions.

The usefulness of a simple three-chamber apparatus for the growth of organic donor-acceptor salts has been demonstrated. Relatively large, well-formed crystals of one such salt, TTF-TCNQ, have been grown in this manner and exemplify the method.

Four compounds, N,N,N',N'-tetramethyl-p-phenylene diamine, N,N,N',N'-tetramethyl-benzidine, 4,4'-bis(dimethylamino)azobenzene and bis(4-dimethylaminophenylimino)sulfur (BAPIS) were examined electrochemically and spectroscopically. Each was shown to be a fairly good donor forming in its first oxidation state a radical-cation. The latter two materials surprisingly exhibited only single one-electron oxidations. Conformational flexibility about the -NSN- unit was studied by NMR spectroscopy and ab initio molecular orbital theory. The experimental ΔG* for a cis-trans to trans-cis interconversion in BAPIS was found to be 11.9 kcal/mole. The four donors all form 1:1 adducts with TCNQ. The compaction resistances of the complexes have been measured as a function of temperature. Of the four, (BAPIS)(TCNQ) appears to be a one-dimensional material. The other three complexes behave as typical mixed stack organic semiconductors.

Studies of multiline ESR spectra in ten organic charge-transfer salts give g-tensors which are characteristic of individual molecular ions containing sulphur, nitrogen and smaller atoms. Such nearly universal g-tensors are not found in three salts with molecules containing selenium. These conclusions are supported by some results at variable temperature and hydrostatic pressure.

We have prepared a series of 2,3-naphthalocyanine (H2NPc) compounds and examined their spectroscopic properties. All of them can be vacuum sublimed as thin films which absorb strongly in the near i...

comparaison entre le potentiel d'ionisation obtenu a partir du spectre de photoelectron UV et celui calcule par des methodes ab initio STO-3G

The preparation of high T/sub c/ superconductors, in most cases, proceeds by ceramic methodology from the metal oxides and carbonates. In this paper the authors show that the same materials can easily be derived, as well, from nitrates. Nitrates are a potentially useful class of starting materials because of their solubility and thus possible use in technologies that require the deposition of thin films of precursors to the high T/sub c/ superconductors. When the appropriate mixture of nitrate salts is prepared and ground together, then fired, first in air, and then in pure oxygen, the superconducting material results. Both the La/sub 1.85/Sr/sub 0.15/CuO/sub 4/ and Ba/sub 2/YCu/sub 3/O/sub 7/ materials have been prepared in this way. Their authenticities have been confirmed by comparison of their x-ray powder patterns and resistivity properties with those published for known materials. In addition the authors demonstrated that solutions of nitrate salts can be analyzed for purity by a simple spectroscopic method.

Poly(pyrrole) may be prepared by electrochemical or chemical systhesis, and under appropriate conditions, free-standing films of the oxidized material are produced, which exhibit relatively high conductivity and stability. This material provides an interesting contrast with the phosphazene polymers. Although the polyphosphazene are completely conjugated, all of the currently known materials are insulators; nevertheless the polyphosphazenes exhibit excellent mechanical and chemical stability properties. In the present study we report the synthesis of polybis(pyrrolyl)phosphazene (PBPP), a new polymer which incorporates certain features of both classes of materials. Subsequent electrochemical oxidation of PBPP leads to the deposition of electrically conducting fibrous black films at the anode.

Etude de la structure electronique, et des proprietes de l'etat fondamental, des diphenyl-3,7- et bis(dimethylamino)-3,7-dithia-1,5 tetrazocines-2,4,6,8, par des calculs ab initio STO-3G (+5D), et par spectrometrie photoelectronique RX; interpretation d'une conformation du cycle «courbe» avec de fortes interactions soufre-soufre transversales au cycle

Preparation de complexes stables de Ag(±), Cu(I), Mn(II) et Co(II). Etude RX du complexe de Co(II)

The non-polymeric organic compound: 3,4,9,10 - perylenetetracarboxylic dianhydride (PTCDA) has recently been observed to undergo a large increase in conductivity on irradiation with energetic particle beams. In this paper we discuss the unique properties of both the as-deposited and irradiated forms of PTCDA and related compounds. When the organic compounds are irradiated with 2 MeV Ar+; beams, their resistivity can be reduced over 14 orders of magnitude from ρ (300K) =; 1010 Ω-cm (as-deposited) to ρ (300K) = 5 × 10-4 Ω-cm using a maximum dose of 1017 ions/cm.2 The temperature dependence of the resistivity for doses 1016cm−2 follows ρ(T) ∝ exp (-const./ T1/2) consistent with conduction due to hopping of carriers between isolated, conducting islands formed furing the irradiation process. In addition, we report on studies of structural changes induced by particle irradiation. The unirradiated PTCDA was vacuum sublimed onto (100), 10 Ω-cm p-Si substrates yielding a rectifying contact barrier with a height of ϕB = 0.74 eV. The diodes thus formed undergo avalanche breakdown at Vg = 230V, and exhibit current densities at VB/2 of ≤50 μ A/cm.2 In addition, the forward current-voltage (IF-V) characteristics are strongly dependent on the contact metal used on the top PTCDA surface. The rectifying characteristics reported for the as-deposited material, coupled with the electronic and optical properties of irradiated PTCDA and related compounds suggest that these are interesting electronic materials whose potential device applications appear worthy of further study.

A series of experiments on solutions of long (C20H41I) and short (C2H5I) chain molecules has verified that the longer molecules form a host micelle for the shorter ones, which appear to interpenetrate the ordered C20− molecules to give an aggregate of similar external morphology. Further measurements on the two systems resulted in a technique to evaluate the contributions of close order I–I, C–C, and C–I terms in the intensity, and from this analysis the I–I superstructure scattering function could be isolated from the rest of the scattering. The scattering function fitted that of a hollow sphere of radius 17 A, as predicted from earlier experiments.

We have investigated the suitability of organic‐on‐inorganic (OI) semiconductor contact barrier diodes for use in deep level transient spectroscopy (DLTS) of III‐V semiconductors. The diodes are formed by vacuum deposition of a thin film of an organic molecular solid onto semiconductor samples as has been previously reported. DLTS measurements performed on n‐type GaAs using conventional Au Schottky barriers have been compared with those using OI diodes DLTS measurements have also been made on as‐grown p‐type GaAs and n‐type InP (upon which high quality conventional Schottky barriers cannot readily be fabricated) using OI diodes. OI devices can be made upon many semiconductors for which conventional Schottky barriers cannot be fabricated, require no sample heating, and can be easily removed without detrimental effects to the inorganic semiconductor material.

We have measured the magnitude of the conduction‐band discontinuities at heterojunctions for several compositions of InGaAsP grown lattice matched on InP. We find that the conduction‐band discontinuity (ΔEc) is related to the difference in band gaps (ΔEg) between the InGaAsP and InP layers via ΔEc =0.39(ΔEg). Thus, 40% of the band‐gap difference lies in the conduction band of this material system. The measurements were made on a series of composition of InGaAsP spanning the alloy range from In0.53Ga0.47As (with energy gap Eg =0.75 eV) to InP (Eg =1.35 eV) using capacitance‐voltage techniques. Depletion deep into the semiconductor layers was facilitated by the formation of organic‐on‐inorganic semiconductor contact barriers on the InGaAsP surface.

We report the first organic‐on‐inorganic contact barrier semiconductor transistor. InP field‐effect transistor similar to metal‐semiconductor field‐effect transistors was made by vacuum subliming a thin film of N, N’‐dimethyl 3,4,9,10‐perylenetetracarboxylic diimide onto Si‐implanted channel, forming a gate contact. Good pinch‐off characteristics and relatively small gate leakage current were obtained. The extrinsic transconductances for these devices are approximately 70–80 mS/mm, with a gate length of 1.5 μm and a channel carrier concentration in the high 1016 cm−3.

The pyrolysis of organic dianhydrides (e.g., 3,4,9,10‐perylenetetracarboxylic dianhydride) in an evacuated system results in the loss of hydrogen, CO, and CO2 and the deposition of a chemically inert, metallic‐appearing mirrolike film. The films are highly conducting (σRT250 Ω−1 cm−1) and can evidence either metallic or semiconducting behavior, depending on the preparation temperature. Superconducting films are obtained when niobium is used as a dopant. Preparation of films on doped silicon semiconductor chips results in the formation of p‐n junctions. ESR spectra exhibit a moderately strong line at g=2.0025. The resonance intensity remains almost constant to 20 °K, characteristic of a highly delocalized spin system.

Transparent, stable, electrically insulating, crystalline thin films of two aromatic organic dianhydrides, 3,4,9,10‐perylenetetracarboxylic dianhydride C24H8O6 and 1,4,5,8‐naphthalenetetracarboxylic dianhydride C14H4O6, were prepared by vapor deposition. On exposure to an electron beam dose of 0.05 C cm−2 the written areas of the films appeared visually blackened and were electrically conducting. This chemical transformation was found to be both dose and current density dependent. Fine lines with widths of 1000 A were prepared by electron exposure at just above writing threshold doses. The chemical and electrical properties of the materials formed upon e‐beam treatment were found to be notably different from those of the starting anhydrides and useful for semiconductor device fabrication.

Etude de la structure electronique, et des proprietes de l'etat fondamental, des diphenyl-3,7- et bis(dimethylamino)-3,7-dithia-1,5 tetrazocines-2,4,6,8, par des calculs ab initio STO-3G (+5D), et par spectrometrie photoelectronique RX; interpretation d'une conformation du cycle «courbe» avec de fortes interactions soufre-soufre transversales au cycle

Aus den Phenacylbromiden (I) erhalt man mit Dithiocarbaminat (II) die Substitutionsprodukte (III), die mit Tetrafluorborsaure zu (IV) cyclisiert und dann mit Boronat zu (V) reduziert werden.

Rectifying junctions prepared by vacuum deposition of 3,4,9,10-peryIenetetracarboxylic dianhydride (PTCDA) and related Compounds on both p- and n-type inorganic semiconducting wafers are used for their non-destructive evaluation. By evaporation of metal contact pads onto the organic layer, we can probe many of the fundamental bulk and surface properties of the semiconductor. The current-vol tage characteristics of these organic-on-inorganic (OI) devices on silicon are similar to those of abrupt junction diodes due to the higher OI contact barrier energies, and the absence of edge breakdown in these devices. For example, reverse breakdown voltages are governed by the semiconductor carrier concentration. On many III-V semiconductors qualitatively similar results are obtained. For example, high barrier energies have been observed on n-GaAs (0.64 eV) and p-GaAs (0.75 eV), and for the p-type material they are significantly higher than those achieved with conventional Schottky devices. Barrier heights are found to be dependent on the surface treatment given to the semiconductor prior to deposition of the organic film. Both current-voltage (I-V) and capacitance-voltage (C-V) measurements performed on devices over the wafer surface have permitted the generation of maps of the carrier concentrations and epitaxial layer thicknesses. Upon completion of such measurements, the organic layers with their metal contacts are removed with an aqueous base wash with no damage to the underlying semiconductor.