Ion beam irradiation of saturated polymers leads to the formation of new carbonaceous materials exhibiting enhanced electrical conductivity and increase of the optical absorption, which shifts gradually from the near UV to the visible. Different techniques, such as the analysis of the gas evolved from the polymer during irradiation, RBS and ERDA show the loss of the more volatile elements which results from the dissociation of the molecular structure. The consideration of different types of polymers indicates that some specific structural elements are preserved and that unsaturated bonds appear at high fluences, which are responsible for the loss of the insulating properties of polymers. The chemical bond modifications are discussed in view of infrared spectroscopy and ESCA, which shows the formation of graphite-like phases in polyimide and explains the high level of conductivity reached in this type of polymers. The appearance of conducting properties cannot be described by a simple model of carbonization and are governed both by the molecular structure of the parent polymer and the beam conditions. The behaviour of polyimide will be considered more in details because of the remarkable level of conductivity ( σ = 10 3 S/cm) and heat stability reached upon irradiation with heavy ions, which render this type of surface processing very efficient in order to produce conductive polymers.

Relation between structure and electronic properties of ion irradiated polymers

Organic Semiconductors for new electronic devices

Advances in n-Type Organic Thermoelectric Materials and Devices

A field effect transistor has been fabricated with organic semiconductors: scandium diphthalocyanine and nickel phthalocyanine. The electrical characteristics are studied in air atmosphere. The influence of the diphthalocyanine film thickness has been detected.

Field-effect transistor with diphthalocyanine thin film

A vast array of semiconductor applications relies on the ability to dope the materials by the controlled introduction of impurities in order to achieve desired charge carrier concentration and conduction type. In this way, various functional metal/semiconductor or semiconductor/semiconductor junctions can be constructed for device applications. Conjugated polymers are organic semiconductors that can be electrochemically doped to form a dynamic p−n junction. The electronic structure and even the existence of such a polymer p−n junction had been the subject of intense scrutiny and debate. In this work, the formation of the world’s largest frozen polymer p−n junction and its light-emission are visualized. With a pair of micromanipulated probes, we mapped the potential distribution of the p−n junction under bias across the entire interelectrode gap of over 10 mm. Site-selective current−voltage measurements reveal that the polymer junction is a graded p−n junction, with a much more conductive p region than n r...

Direct Imaging and Probing of the p−n Junction in a Planar Polymer Light-Emitting Electrochemical Cell

We have recently shown that specific and stable n or p doping may be obtained on poly(paraphenylene) providing moderate implantation conditions with appropriate ions are used. Here we describe a pn+ -junction made in intrinsic insulating poly(paraphenylene) (σ <10−12 Ω −1 cm−1) by implantation (E ⋍ 50keV) of alkali metal ions (essentially caesium for n doping) and halogen (iodine for p doping).

pn + junction in an implanted electroactive polymer: poly(paraphenylene)

A study of the Seebeck coefficient has shown that doping of polyparaphenylene by ion implantation makes it possible to obtain an electronically doped semiconductor at low energy: n-type with alkali metal ions and p-type with halide ions. At the highest energies (E > 100 keV) the p-type conductivity is due to the creation of defects by irradiation. Generally the semiconductor obtained is degenerate with a Seebeck coefficient close to that obtained by chemical doping. Study of the mechanisms of conduction suggests plots of log σ = (T−l/n); the greater n is, the better is the agreement between the experimental curve and theory. Representation of the conductivity is proposed according to Mott's theories, which are applicable to amorphous semiconductors and involve several conduction processes in the temperature space. For the variable-range-hopping (VRH) mechanism at low temperature, two parameters, α−1 (representing the spatial separation of hopping sites) and N(EF) (the density of states at the Fermi Level) are obtained.

Coefficient seebeck et méanismes de conduction dans les polymères (PPP) electroactifs dopés par implantation ionique

L’effet de la temperature d’implantation a ete essentiellement considere pour les basses temperatures : la mobilite des porteurs n’est finalement que legerement amelioree par rapport a celle obtenue a temperature ambiante.

Effet de la température d'implantation sur les propriétés électriques du PPP

La microanalyse SIMS nous a permis de verifier que l’on peut obtenir un elargissement et un deplacement vers la surface des couches implantees a une seule et meme energie, si les irradiations sont effectuees a travers une couche de resine autodeveloppable (par le faisceau d’ions).

Effet d’une résine autodéveloppable sur la position du profil d’implantation dans des films de PPP

Films of poly(paraphenylene) were synthesized by electroreduction and doped by ion implantation. Evolution of concentration profiles upon annealing was followed by Secondary Ion Mass Spectroscopy on n-doped with Cs or Na or on p-doped with I samples. Experimental depth and lateral profiles indicated that diffusion was rather slow, if any, even at temperatures as high as 270°C. However in some cases plateaus were observed in the profiles which may be accounted for by some “grain boundaries” diffusion. This process was tentatively explained by the very slow diffusion of ions from the crystalline microdomains followed by a fast one at the interface between these crystallites.

B. Ratier

Papers

pn + junction in an implanted electroactive polymer: poly(paraphenylene)

Coefficient seebeck et méanismes de conduction dans les polymères (PPP) electroactifs dopés par implantation ionique

Effet de la température d'implantation sur les propriétés électriques du PPP

Effet d’une résine autodéveloppable sur la position du profil d’implantation dans des films de PPP

Ion Implanted Polyparaphenylene: Modifications of Lateral and in Depth Concentration Profiles upon Annealing