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- Jafari, Mohammad Javad, 1984-
(författare)
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Application of Vibrational Spectroscopy in Organic Electronics
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The rapid technological developments enforce us to live in an increasingly electronic world, and the revolutionary usage of conjugated polymers in electronics in the late 1970s accelerated these developments, based on the unique characteristics of conjugated polymers, such as low cost, easy processing, mechanical flexibility, large-area application and compatibility with a variety of substrates. Organic electronic devices are commercially available in the form of, for example, solar cells, transistors, and organic light-emitting diode (OLED) displays. Scientists work on electroactive polymers to enhance their chemical, electrical and mechanical properties, to improve parameters such as charge carrier mobility and doping capacity, in order to reach acceptable efficiency and stability to fabricate organic electronic devices. A comprehensive understanding of the changes in chemical structure, in response to external factors such as applied potential and temperature gradients, which can disturb the chemical equilibrium of the constituent materials, and of the conduction mechanisms of the operating devices, can help to enhance the performance of organic electronics devices. Vibrational spectroscopy is a powerful analytical method for in-situ monitoring of such chemical or electrochemical reactions and associated structural changes of conjugated polymers in a working device.In this thesis, Fourier-transform infrared (FTIR) spectroscopy has been used to study the structural changes in electroactive organic materials, in response to chemical or electrochemical reactions, and to study electrical and thermal conduction mechanisms in different organic electronic devices. FTIR microscopy was used to approach a realistic conduction mechanism by time-resolved chemical imaging of active materials in planar light-emitting electrochemical cells (LECs), investigated as an alternative to organic light emitting diodes (OLEDs). These chemical images are used for in-situ mapping of anion density profiles, polymer doping, and dynamic junction formation in the active layer under an applied bias. Results confirm the electrochemical doping model and help the systematic improvement of function and manufacture of LECs. Mixed ion-electron polymeric conductor materials such as PEDOT-PSS are used as active materials in organic thermoelectric generators (OTEGs), where charge carrier transport through the active layer promotes internal electrochemical reactions under a temperature gradient. FTIR microscopy and FTIR-attenuated total reflection (FTIR-ATR) were used to study thermoelectric and electrical properties of the conducting polymers. Recently, electrochemical supercapacitors have emerged as an alternative to conventional batteries, and polymeric materials are used to design polymer electrodes for renewable energy storage. To understand the charge transfer and structural changes of the polymer during the redox reaction, we have used FTIR-ATR as a tool for the in-situ spectroelectrochemical study of redox states in polypyrrole/lignin composites; we clarified the structural changes in the materials during charging and discharging of the composite. In further work, FTIR-ATR was also used for in-situ spectroelectrochemical studies of PEDOT:Cl, to monitor the effects of dissolved oxygen on PEDOT:Cl films, which are used as electrodes in renewable energy technologies. Further, time-resolved oxygen reduction reactions of PEDOT:Cl have been studied via polarization-modulation infrared reflection-absorption spectroscopy (PM-IRAS) to reveal chemical changes in electrochemically doped PEDOT upon exposure to oxygen.Taken together, these studies provide an advancement in the use of infrared spectroscopy as a tool to understand electroactive materials under wet conditions, and have provided detailed chemical and electrochemical information of materials and devices under operation, that is not easily accessible with other methods.
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| 2. |
- Langer, Judith, et al.
(författare)
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Present and Future of Surface-Enhanced Raman Scattering
- 2020
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 14:1, s. 28-117
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Forskningsöversikt (refereegranskat)abstract
- The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article. ©
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