Unusual semimetallic behavior of carbonized ion-implanted polymers

Abstract

We report a comprehensive charge transport study of ion-implanted rigid rod and ladder polymers p-phenylenebenzobisoxazole, p-phenylenebenzobisthiazole, and benzimidazobenzophenanthroline. The three pristine materials are strong and stable polymers with a room temperature conductivity RT ϳ10 Ϫ12 S/cm. After high dosage ion implantation using Kr ϩ , a carbonized and conducting layer forms on the surface of the film samples with RT Ͼ10 2 S/cm. The experimental results suggest that this carbonized layer is semimetallic with unusual properties. The observed dc conductivity follows (T)ϭ 0 ϩ⌬(T), where ⌬(T) is weakly temperature dependent and interpreted within the model of weak localization and electron-electron interaction effects. The model reveals that the interaction effect is three dimensional for the experimental temperature range ͑3-300 K͒, whereas the weak localization effect undergoes a dimensional crossover at ϳ60 K from three to two-dimensions with decreasing temperature. The magnetoconductance, thermoelectric power, and microwave dielectric constant results are all in agreement with this semimetallic model. In addition, all these results consistently point to an enhanced interaction effect at low temperatures due to the reduced dimensionality of the localization effect. It is concluded that a sp 2 rich and three-dimensional interconnected carbon network reformed upon ion implantation of the densely packed pristine polymers is responsible for the semimetallic behavior.

Anisotropic weakly localized transport in nitrogen-doped ultrananocrystalline diamond films

“…Hence, understanding the interplay of dimensionality ͑2D to 3D͒ associated with the structural anisotropy of these novel materials appears to be rather crucial to interpret the proper transport mechanism at different temperatures and under the influence of external ͑magnetic͒ fields. [9][10][11][12] For heavily doped UNCD films ͑obtained from 10-20 % N 2 in source gases͒, on the basis of evaluation of temperature dependences of conductivity as well as magnetoresistance ͑MR͒, contributions from weak localization ͑WL͒, and also from variable-range hopping ͑VRH͒ transport ͑strong local-ization͒ to the net conductivity have been considered. 4 WL correction to conductivity in the GB regions is proposed as a dominant mechanism, especially at very low temperatures although the details of film microstructures in connection with mechanisms including 2DWL to 3DWL interplay and electron-electron ͑e-e͒ interaction effect in both dimensions have not been elucidated.…”

Investigation of Quantum Effects in Carbonaceous Materials Near the Metal-Insulator Transition by Means of THz Photoconductivity

“…This can be explained by layered structure of the pregraphitic carbon. The difference in magnitude of the Thouless length, characterizing the localization correction, and the Coulomb interaction characteristic length accounts for the difference in dimensionality of the two quantum effects [3].…”

Fabrication of embedded conductive layer in polymer by plasma immersion ion implantation

“…Sample I shows smaller cluster size while sample II shows an evaluation to larger cluster sizes of about 30 nm. In addition, XRD analysis was conducted to show that there exist some Ni nanocrystallites which can correlate well to the CAFM images [27,28].…”