Carbon organic semiconductor

Other types of carbon (amorphous or transitional forms with turbostratic structure) consist of fragments of graphitelike regions cross-linked to a three-dimensional polymer by carbon chains. Unlike graphite, the transitional forms are organic semiconductors with electrical properties determined by delocalized rr-electrons. 

Research is also focussed on alternative materials for photocells based either on elements which are more efficient than silicon but dearer, or on organic semiconductors and carbon nanostructures, which are much cheaper but less efficient than even the poorest quality silicon. Each approach has its attractions and its drawbacks. 

Concentration of antistats in plastics is mostly 0.1 to 2 %. Special grades of electroconducting (EC) carbon black are used in PO at levels higher than 10 % (Accorsi and Yu, 1998). Other conducting fillers incorporating antistatic effects, such as metals or organic semiconductors (e.g. polypyrrole) are not commonly used in plastics for contact with food. 

The signal travels through a thick, or even molecularly thin, semiconductor that connects these electrodes it could be an inorganic semiconductor (doped Si, doped Ge), an organic conducting polymer (polyaniline, polythiophene, polyacetylene), a carbon nanotube, or an organic semiconductor (sexithiophene). 

To illustrate the use of PIXE and micro-PIXE in the study of breakdown phenomena in polyethylene high voltage cable insulation and other related topics we will describe a few typical measurements, first the study by standard PIXE of impurities in the organic semiconductor H2PC and in the carbon black semicon used in high voltage cables. Examples of the use of the microbeam to study some electrical and water trees as well as the diffusion of impurities from the semicon into polyethylene under typical electric field and humidity conditions will be given. 

A summary of ordered macroporous materials with different compositions is given elsewhere.Many compositions have been made, ranging from oxides, polymers, " and carbons, to semiconductors and metals. The wall structures of macroporous materials can be amorphous, crystalline, with mesopores or micropores, organically modified, or with surface catalysts. ... 

Chapter 2 provides a summary of the chemical physics of organic semiconductor operation. It explains why carbon is so special and how its unique properties lend it to the formation of an unusual class of semiconductor materials. 

If we look at a popular organic semiconductor, say pentacene, the hydrogen atoms which surround the carbon backbone are less electronegative than the carbon backbone itself and lend some electron density to the delocalized pi-electron cloud. The electron rich conjugated molecule has difficulty accepting another electron, but is able to lose an electron with relative ease. As a consequence, positive charge carriers dominate transport in pentacene thin films. 

Fig. 3.1. Some of the more common repeating functional units in conjugated organic materials. Most organic semiconductors and conductors are made from fused or linked elements like these, which are rich in sTj hybridized carbon atoms and delocalized pi electrons. It should be noted that chemical synthesis of organic semiconductors and conductors is often not performed using these materials as starting ingredients.

Fig. 4.10. Schematic side and top view of the electron cloud in a small molecule electron-rich organic semiconductor (e.g. an ohgothophene or an acene). Because hydrogen is more electronegative than carbon the peripheral hydrogens attract the pi electrons leading to a herringbone stacking. The higher permittivity of neighboring standing molecules leads to the nearly vertical orientation for the first few deposited layers.

FET behavior in LB physisorbed multilayers of conducting polymers were seen, as was FET behavior in thin-film organic semiconductors, e.g., sexithiophene. The assembly of SWCNT in the Fet1 2-24j limited to "Pasteur s method" of studying the one SWCNT that fortuitously landed across the "right" Au electrodes. This is a major shortcoming of aU carbon nanotube-based devices. 

Keywords Luminophores Organic systems Inorganic systems Dendrimers Nanoparticle systems Nanoclusters Carbon nanoparticles Semiconductor nanocrystals Quantum dots... 

Electrical conductivity measurements have been reported on a wide range of polymers including carbon nanofibre reinforced HOPE [52], carbon black filled LDPE-ethylene methyl acrylate composites [28], carbon black filled HDPE [53], carbon black reinforced PP [27], talc filled PP [54], copper particle modified epoxy resins [55], epoxy and epoxy-haematite nanorod composites [56], polyvinyl pyrrolidone (PVP) and polyvinyl alcohol (PVA) blends [57], polyacrylonitrile based carbon fibre/PC composites [58], PC/MnCli composite films [59], titanocene polyester derivatives of terephthalic acid [60], lithium trifluoromethane sulfonamide doped PS-block-polyethylene oxide (PEO) copolymers [61], boron containing PVA derived ceramic organic semiconductors [62], sodium lanthanum tetrafluoride complexed with PEO [63], PC, acrylonitrile butadiene [64], blends of polyethylene dioxythiophene/ polystyrene sulfonate, PVC and PEO [65], EVA copolymer/carbon fibre conductive composites [66], carbon nanofibre modified thermotropic liquid crystalline polymers [67], PPY [68], PPY/PP/montmorillonite composites [69], carbon fibre reinforced PDMS-PPY composites [29], PANI [70], epoxy resin/PANI dodecylbenzene sulfonic acid blends [71], PANI/PA 6,6 composites [72], carbon fibre EVA composites [66], HDPE carbon fibre nanocomposites [52] and PPS [73]. 

Polymers from Thiophen Derivatives.—The bifunctionality of thiophen and its potential availability in large quantities at a low price has for many years attracted the interest of polymer chemists. However, progress has been slow. 2,5-Dichlorothiophen has been polymerized to a solid in 93% yield on treatment with aluminium chloride and cupric chloride in carbon disulphide. The product is believed to be poly-5-chloro-2,3-thienylene. Thiophen-2,5-dicarboxylic hydrazide was prepared by the reaction of thiophen-2,5-dicarbonyl chloride with the corresponding dihydrazide and then cyclodehydrated to poly-(thienylene-[2,5]-alt-l,3,4-oxadiazolylene-[2,5]-amer) (258) by polyphosphoric acid. This polymer could also be obtained directly from thiophen-2,5-dicarboxylic acid and hydrazine in oleum. The polymers produced were investigated in view of their thermal stability and as polymeric organic semiconductors. The same research... 

In the organic semiconductor family there are two major classes small molecular weight materials and polymers. Both of them have the common property of a conjugated TT-electron system that is formed by the pz-orbital of sp2-hybridized carbon atom (Fig. 25.2). 

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