Vishnu V. Patel

Ultralow-k dielectrics prepared by plasma-enhanced chemical vapor deposition

Carbon-doped oxide materials (SiCOH films) with ultralow dielectric constants have been prepared by plasma-enhanced chemical vapor deposition (PECVD) from mixtures of SiCOH precursors with organic materials. The films have been characterized by Rutherford backscattering and forward recoil elastic scattering analysis, Fourier transform infrared spectroscopy and index of refraction measurements, and measurement of step heights in the films. The electrical properties of the films have been measured on metal–insulator–silicon structures. By proper choice of the precursor and deposition conditions, the dielectric constants of the SiCOH films can be reduced to values below 2.1, demonstrating the extendibility of PECVD-prepared carbon-doped oxides as the interconnect dielectrics for future generation of very large scale integrated chips.

Characterization of diamondlike carbon by infrared spectroscopy

Comparison of Fourier transform infrared (FTIR) absorption spectroscopy, high resolution 13C nuclear magnetic resonance spectroscopy, and hydrogen evaluation by forward recoil elastic scattering (FRES) measurements shows that FTIR cannot be used to determine the carbon hybridization or total hydrogen content of diamondlike carbon films (DLC). FTIR absorption reflects only the optically active hydrogen in the DLC and, using it together with FRES, it can provide an estimate of the unbound hydrogen contained in the films. The fraction of unbound hydrogen can reach values of up to ∼50%.

Comparative behavior of electrodes coated with thin films of structurally related electroactive polymers

Abstract General methods are described for the synthesis of electroactive polymers and the preparation of uniform, stable, polymer-coated electrodes. The electrochemical behaviour of thin films of eight different functionalized polystyrenes, differing in the identity and amount of attached electroactive species, and polyvinylferrocene is presented. A wide range of electrochemical properties can be observed by varying parameters such as film thickness, nature of the bound redox couple, extent of polymer functionalization and oxidation state. The deviations from ideal surface behavior are investigated in detail. These are shown to be consequences of cooperative electronic interactions, structural reorganization or uncompensated resistance within the film, depending upon the material. The film resistance varies greatly among the polymer films studied and is shown, in some cases, to be a sensitive function of the extent of oxidation and prior treatment of the film. This variable resistance is shown to be a consequence of slow ion transport through the film. The mechanism of electron transport in such materials is considered and a model of the metal/polymer/electrolyte interface is proposed.

Polymer‐modified electrodes: a new class of electrochromic materials

A new class of organic polymeric thin‐film electrochromic materials is described. We show that the new polymer‐modified electrodes change color reversibly in permanent thin‐film form without the electrodeposition characteristics of organic liquid state systems such as the viologens. The polymer films exhibit good switching speeds (τ⩽100 ms), possess intrinsic memory, and show no chemical degradation or adhesion loss in preliminary life tests (104 cycles). It is demonstrated that several important electrochromic parameters can be varied by chemical modification of the polymeric material.

Morphological stabilization of polymer-coated electrodes by electrochemical cross-linking

Abstract Electrochemical oxidation of N-phenyl-pyrazoline, N-alkylated carbazole and N-alkylated phenylhydrazone derived linear polymer films results in the formation of polymer-bound benzidine-type dimer species. The presence of these dimers, which are formed from the anodically generated cation radical precursors, was detected by the electrochemical and spectroscopic changes in the films following oxidation. In addition, we show that formation of this dimeric species must occur between non-nearest neighbors since the resulting electroactive polymer films are insoluble, with the electrochemically induced (dimer) cross-links leading to stabilization of film morphology.

Organic Conductors as Electron Beam Resist Materials

Conducting organic π‐donor halide complexes such as tetrathiafulvalene bromide were discovered to act as electron beam resists, which display a unique combination of useful properties. Exposure of sublimed films to an electron beam generates the neutral π donor and the halogen which is subsequently lost from the film. Depending on exposure conditions, either negative (solvent developed) or positive (in‐situ developed) resist images with a resolution of the order of 0.5 μ can be generated. The strongly absorbing (UV,vis.) and highly conducting (∼10/Ω cm) films were found to become transmitting and insulating upon electron beam irradiation.

Chemistry of geminal-dithiolates derived from cyano-substituted tetrathiafulvalenes

Tetracyanotetrathiafulvalene reacts with two equivalents of thiol salts (RS−) to give 1,2-dicyano-1,2-di RS ethene and a geminal dithiolate intermediate which reacts with a variety of reagents to provide novel tetrathioethene derivatives, such as reaction with 3-chloro-2-butanone and acid to give dimethyldicyanotetrathiafulvalene.

‘Organic metals’: synthesis of dithiolylidenetetrathiapentalenones and their higher analogues

Reaction of the tetrathiapentalene-2,5-dione (1) and 4,5-dimethoxycarbonyl-1,3-dithiole-2-thione (2) with trimethylphosphite in refluxing benzene provides, along with the expected self-coupled products, the dithiolylidenetetrathiapentalenone (4; R = CO2Me) and its higher analogue (6; R = CO2Me).

Bis-1,3-dithiole chemistry: Synthesis of compounds containing the 4,4′bis-(1,3-dithiole) unit

1,4-Dibrom-butan-2,3-dion (I) kondensiert mit dem Xanthogenat (II) zu einem Disubstitutionsprodukt (III), das mit konz. Schwefelsaure zu (IV) cyclisiert wird.

Triselenathiafulvalenes: a novel sulphur–selenium interchange on trimethyl phosphite coupling of substituted 1,3-diselenole-2-thiones

Coupling using trimethyl phosphite of 4,5-dimethoxycarbonyl- and 4,5-ditrifluoromethyl-1,3-diselenole-2-thiones unexpectedly gave only tetramethoxycarbonyl- and tetratrifluoromethyl-triselenathiafulvalene respectively, while self-coupling of 4,5-dimethyl-1,3-diselenole-2-thione provided a mixture (85:15) of tetramethyltetraselenafulvalene and tetramethyltriselenathiafulvalene.