Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Mathematics of radio engineering wikipedia , lookup
Electronic engineering wikipedia , lookup
Scattering parameters wikipedia , lookup
Two-port network wikipedia , lookup
Mechanical-electrical analogies wikipedia , lookup
Printed electronics wikipedia , lookup
Impedance matching wikipedia , lookup
Organic Nanofiber Impedance Spectroscopy Organic semiconductors constitute an important class of materials for electronic and opto-electronic devices such as organic field-effect transistors (OFETs) and lightemitting diodes (OLEDs). For example, organic semiconductors are used for flexible electronics and in organic flat panel displays. Typically, the organic semiconductor is processed into a thin film and electrical contact is realized through a pair of lithographically defined metal electrodes. However, this often results in ‘large’ devices with dimensions of several hundred micrometers or more. For future devices with a higher level of integration – such as microsystems for biochemical sensing - smaller devices with nanoscale dimensions are required. In the NanoSYD research group at the Mads Clausen Institute, we are working with a particular class of organic semiconducting nanofibers. The basic building block is a small molecule (such as hexaphenylene as seen in fig. 1a), which can be assembled into a nanofiber structure (fig. 1b) through a special self-assembly process. These nanofibers with cross sectional dimensions of the order of 100 nanometers have a range of interesting properties such a being semiconducting and able to emit and guide light. Among other things, our research is focused on fabricating nanoscale OFETs and OLEDs from nanofibers. This requires a detailed investigation of the electrical carrier injection and transport. One experimental technique for making such investigations is impedance spectroscopy, where the frequency dependence of the device impedance is examined. Figure 1 (a) Space-fill model of a para-hexaphenylene (p6P) molecule. (b) Top view of a p6P nanofiber structure model. The individual molecules are stacked in a nanofiber structure with a typical width between 100 and 400 nm, a typical height between 20 and 50 nm, and an as-grown length of typically some hundred micrometers. (c) Scanning electron microscope (SEM) image of a single p6P nanofiber contacted with two metal electrodes for electrical characterization. In this project, you will work on constructing a set-up for impedance spectroscopy measurements and use this to investigate the electrical properties of such nanofibers. The system consisting of one (or several parallel) nanofiber(s) between two metal electrodes can be considered as a one-port, which should be characterized within a bandwidth between a few Hz and a few tens of kHz. By fitting the measured impedance to an equivalent circuit model, it is possible to extract device parameters that can be used to investigate the carrier transport mechanism in detail. The project will involve the following tasks: Literature study of: o different measurement techniques for impedance spectroscopy o device modeling of organic semiconductor devices Realization and test of measurement set-up o Design, construct, and characterize a suitable measurement set-up for nanofiber impedance spectroscopy o Set-up and program a commercial lock-in amplifier (Labview programming) to compare with the constructed set-up o Determine appropriate comparison parameters (e.g. bandwidth, signal levels etc.) o Compare the performance of the two systems using different “known” components Investigate the nanofiber impedance frequency response and extract device model parameters Supervisors Jakob Kjelstrup-Hansen [email protected] Horst-Günter Rubahn [email protected]