Junctions between metals and blends of conducting and biodegradable polymers (PLLA-PPy and PCL-PPy)

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• 作者：C.M. Boutry ; ^{clementine.boutry@micro.mavt.ethz.ch}  ; [Author Vitae] ; M. Mü ; ller ^{muemiche@student.ethz.ch}  ; [Author Vitae] ; C. Hierold ^{christofer.hierold@micro.mavt.ethz.ch}  ; [Author Vitae]
• 关键词：Conducting polymers ; Polypyrrole ; Biodegradable polymers ; Contact resistance ; Ideality factor ; Barrier height
• 刊名：Materials Science and Engineering ; C
• 出版年：2012
• 期刊代码：63_09284931
• 类别：ms
• 出版时间：1 August, 2012
• 卷：32
• 期：6
• 页码：1610-1620
• 文件大小：1410 K

摘要

The junctions between newly developed biodegradable conducting polymers (polylactide-polypyrrole PLLA-PPy and polycaprolactone-polypyrrole PCL-PPy) and metal electrodes (Au, Au/Cu, Ag, Ag/Cu, Cu, Cr/Au/Cu, Pd/Au/Cu, Pt/Au/Cu) were studied. The objective was to determine the composite/metal combination having the lowest possible contact resistance and ohmic characteristics. In a first step, different surface treatments, adhesion and metal layers were tested in order to evaluate the contact resistance. Then the current-voltage (IV) characteristics were measured and both ohmic and rectifying behaviour were observed depending on the polymer/metal junctions investigated. The surface treatments studied included an argon sputtering step and a grinding of the polymer surface with the objective of improving the contact between the metal electrode and the polymer. It was found that the most favourable conditions resulted from a process flow without argon sputtering, without grinding for PLLA-PPy and with a slight grinding for PCL-PPy. Moreover the most favourable metal electrodes for PLLA-PPy were Pd/Au/Cu, while the best compromise for PCL-PPy was to use Au/Cu. For the rectifying polymer/metal junctions, the standard thermionic emission model modified with a series resistance was successfully applied to the measured current-voltage IV characteristics. The saturation current density J₀, series resistance R, ideality diode factor n and barrier height 蠁_B were investigated. The Chot functions were computed for each rectifying junction and the corresponding threshold voltages were calculated. Finally the conductivity of both composites was evaluated as a function of temperature in the range of 30 掳C to 80 掳C. For PLLA-PPy a decrease of the resistivity was observed when the temperature was increasing, while no clearly recognisable pattern was identified for PCL-PPy in this temperature range. The electrical conductivity of the PLLA-PPy samples was found to follow the empirical Arrhenius model, and the difference between the Fermi energy E_F and the mobility edge E_C | E_F - E_C | as well as the conductivity at the mobility edge 蟽_C were evaluated. Moreover the electrical conductivity of the PLLA-PPy samples was found to follow the Mott variable range hopping (VRH) model, and the high temperature limit of conductivity 蟽₁ as well as the Mott characteristic temperature T₁ were calculated.