We investigate ambipolar charge transport in organic field-effect transistors ͑OFETs͒ with copper-phthalocyanine ͑CuPc͒ as active material. It is shown that charge carrier mobilities can be increased by at least one order of magnitude using the long-chain alkane tetratetracontane ͑TTC͒ as a passivation layer on top of silicon dioxide. TTC and CuPc films are characterized by atomic force microscopy and x-ray diffraction. TTC forms a highly crystalline layer that passivates electron traps on the SiO 2 surface very efficiently and serves as a template for the growth of CuPc films with significantly improved crystallinity. High electron mobilities comparable to the values reported on single crystals are reached. We show that the contact resistance for hole transport as determined by the transmission line method can be reduced considerably by using organic charge-transfer complexes as top contacts in OFETs based on CuPc.
This paper presents results for a new acoustic emission crack source model based on a finite element modelling approach which calculates the dynamic displacement field during crack formation. The specimen modelled is statically loaded until conditions for crack growth as defined by a failure criterion are fulfilled. Subsequently, crack growth is modelled by local degradation of the material stiffness utilizing a cohesive zone element approach. The displacements due to crack growth generate the acoustic emission signal and allow detailed examination of the principles of acoustic emission sources operation. Subsequent to crack growth signal propagation is modeled. The signal propagation is modeled superimposed on the static displacement field. The presented model comprises a multi-scale and multi-physics approach to consider the signal propagation from source to sensor, the piezoelectric conversion of the elastic wave to an electric signal and the interaction to the acquisition electronics. Validation of the modeling approach is done by investigating the acoustic emission signals of micromechanical experiments. Using a specifically developed load stage, carbon fiber filament failure and matrix cracking can be prepared as model sources. A comparison of the experimental signals to the modeled signals shows good quantitative agreement in signal amplitude and frequency content. A comparison between the present modeling work and analytical theories demonstrates the substantial differences not considered in previous modeling work of acoustic emission sources.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.