Jacques Simon

Columnar Mesophases From Metal and Metal-Free Derivatives of Phthalocyanine

Abstract A series of phthalocyanine octasubstituted derivatives were studied using optical microscopy and X-ray diffraction. Some of them were metal-free; the rest contained various metal atoms such as copper, zinc or manganese in the center of the aromatic cores. For most of the derivatives, the substituents consisted of eight peripheral decyloxymethyl chains; for one there were six of these plus two cyano groups attached to the same benzene ring; for another, there were short “polyethylene oxide” chains. All the samples considered in this work exhibited columnar mesophases with hexagonal packing of the columns, stable in a wide range of temperatures.

Molecular material‐based junctions: Formation of a Schottky contact with metallophthalocyanine thin films doped by the cosublimation method

A new method for obtaining thin films of doped molecular materials in a complete absence of oxygen is described. It consists in simultaneously subliming under vacuum the electroactive compound—a metallophthalocyanine—and the electron acceptor or electron donor doping agent. The extent of doping is controlled by the relative rates of sublimation. The ac and dc electrical properties of thin films are determined under high vacuum as to eliminate the influence of oxygen which has been previously shown to be of the utmost importance. Both p‐ and n‐type dopings have been achieved; the increase of conductivity reaches six orders of magnitude for p‐type doping with dichlorodicyanoquinone (DDQ). For the first time a rectifying contact between doped phthalocyanine thin films and aluminum has been observed in strict absence of oxygen.

Polycondensation in Mesomorphic Phases: Spinal Columnar Liquid Crystals Based on Octasubstituted Phthalocyanine Siloxane Derivatives

Abstract Within the liquid crystalline domain, dihydroxysilicon(IV) octakis(dodecyloxymethyl) phthalocyanine is polycondensed to give a distribution of polysiloxanes. These latter form a mesophase with lamellar order. For the first time polycondensation has been carried out in a columnar mesophase and a new type of oligomeric mesogen has been obtained. The term spinal columnar liquid crystal is proposed to designate such a mesophase.

Bipolar junction formation in the case of molecular materials

The standard model of junction formation based on delocalized electronic levels is highly inappropriate in the case of molecular materials that are constituted of individual molecular units subsequently condensed into a material. A model is proposed to describe the electrical characteristics arising at interfaces between p‐ and n‐doped molecular materials. Two antagonistic forces will govern the amount of charge transfer giving rise to the space‐charge region (i) the driving force is given by the difference in redox potentials between the electron donor and the electron acceptor (ii) the opposite force is due to ion‐ion repulsions between ionized impurities. A numerical calculation permits the estimation of the characteristics of the space‐charge region and demonstrates that minute amounts of impurities must be present within the materials; doped insulators, therefore, cannot lead to well‐behaved devices.

Role of Oxygen in the Space Charge Layer Formation in Organic-Metal Junctions: Trans-Polyacetylene and Metallo-Phtha-Locyanine

Abstract Junctions based on trans-polyacetylene and different metallo-phthalocyanines have been studied. The dark conductivity as a function of the frequency and of the applied voltage of sandwich cells of the type M1/t-(CH)x/M2 or M1/MPc/M2 demonstrate that these different organic materials present very similar properties. If all these compounds show an apparent Schottky behavior, the standard model cannot be applied. The properties of the space charge region below the surface charge layer are dramatically different from those found in monocrystalline inorganic semiconductors (constant thickness, constant capacity and variable equivalent resistance on applied voltage). The O2 adsorption is clearly shown to be responsible of the formation of the depletion layer. Indeed O2 not only acts as a dopant of t-(CH)x and MPc but is also responsible for the formation of the space charge region near blocking electrodes with trapped charge carriers. The I-V relationship seems to indicate Frenkel Poole mechanism of ch...

Lutetium Bisphthalocyanine: The First Molecular Semiconductor

Berzelius, in 1823, isolated silicon, the first inorganic semiconductor. This material showed unusual conduction properties. The electrical conduction is thermally activated with an activation energy of 1.12 eV, the density of intrinsic carriers is low, of the order of 7.1 109/cm3, approximately one carrier per 1013 atoms. However, the corresponding mobilities are high:

Basic Notions of Solid State Physics

{\mu_e} = 1350 c{m^2}/V.s.,\quad {\mu_n} = 480 c{m^2}/V.s.

Molecular Semiconductors: Photoelectrical Properties and Solar Cells

([1,2]) The intrinsic conductivity of silicon is therefore around 10-6 Ω-1 cm-1. This latter value may be reached only for extremely pure materials because of the very low concentration of intrinsic carriers. Ti, Zr or V for example affect the electrical properties of silicon for concentrations exceeding 0.001 ppm [2]. This ensemble of electrical properties leads to the definition of a class of materials whose conduction is situated between those of insulators (inferior to 10-7–10-8 Ω-1 cm-1) and those of metals (102 Ω-1 cm-1 or higher). It is worth pointing out that the criterion of overall conductivity for defining an inorganic semiconductor in fact reflects a low density of charge carriers associated with a high mobility. In 1948, Bardeen, Schockley and Brattain opened the field of microelectronics by fabricating the first transistor based on another semiconductor: a single crystal of germanium. The material, the semiconductor, had found its main function, the fabrication of devices associated with electronics finalities.