Excimer laser induced electrical conductivity and nanostructures in polymers

[摘要] The generation of substantial electrical conductivity in high temperature polymers and thin film C$sb{60}$ by means of KrF (248 nm) excimer laser irradiation has been investigated. Formation of both laser ablated surface structures and laser induced electrically conducting wires in polymers with nanometer dimensions is also demonstrated.The electrical conductivity of polymers has been changed by up to 18 orders of magnitude by laser irradiation, obtaining values exceeding 10 $Omegasp{-1}$ cm$sp{-1}$. The conducting material consists of graphitized carbon clusters whose size varies from 2-50 nm. The conduction mechanism is phonon assisted variable range hopping. The large change in the electrical conductivity is an example of a three dimensional percolative metal-insulator phase transition. The critical volume fraction is determined to be $Phisb{m c}$ = 0.30 $pm$ 0.05 and the critical exponent is t = 2.2 $pm$ 0.4.The electrical conductivity of thin film C$sb{60}$ has been altered by more than seven orders of magnitude with laser irradiation, obtaining values of 1 $Omegasp{-1}$ cm$sp{-1}$. The threshold for KrF laser ablation of C$sb{60}$ is determined to be 20 $pm$ 2 mJ/cm$sp2.$Modification of the surface morphology and the electrical conductivity of polymers with high spatial resolution using excimer lasers has also been achieved. Using holographic techniques with a KrF excimer laser, periodic lines structures with periods ranging from 166 nm to 950 nm were ablated into polyimide (Kapton$sp{m TM})$ and polybenzimidazole (PBI). The nonlinear nature of laser ablation permits linewidths as small as 30 nm to be obtained, exceeding the resolution expected from linear optics. These experiments establish a new spatial resolution limit for laser ablation and illustrate the dependence of resolution on material properties. This technique was combined with the ability to modify the electrical conductivity of polymers to produce an array of permanently electrically conducting wires in polyimide with a 0.5 $mu$m width and a 0.9 $mu$m period. The electrical conductivity of these submicron wires exceeded 1 $Omegasp{-1}$ cm$sp{-1}.$

[发布机构] Rice University

[效力级别] Electrical