Ahmed advanced the study of polymer conductors by using precise photoemission spectroscopy techniques to study transport at ultrahigh charge densities.
An international collaboration, including CSMB scientists Prof. Dr. Norbert Koch, Dr. Ahmed Mansour, and Dr. Andreas Opitz, has made a significant breakthrough in understanding the transport physics of conducting polymers.
Through their experiments, the team discovered that in p-type organic electrochemical transistors, it’s possible to completely deplete the valence band and even access deeper energy levels without causing damage. By introducing a second gate electrode, they could inject additional carriers, leading to surprising non-equilibrium transport behaviors.
Ahmed’s expertise enabled the team to explore the behavior of conducting polymers at extreme charge densities. Using x-ray photoemission spectroscopy (XPS), he was able to accurately quantify carrier concentrations, revealing up to 1.5 dopant ions per monomer unit in highly doped samples, to understand the electronic environment of the polymer and its interaction with dopant ions.
His ultraviolet photoemission spectroscopy (UPS) measurements provided additional insight into the electronic structure of the polymers, showing how doping shifts energy levels and affects charge transport. Ahmed’s analysis illustrated the transition from insulating to metallic states, highlighting the complete bleaching of the highest occupied molecular orbital (HOMO) at high doping levels.
Fig 2: UPS spectra of different molecules at various doping levels. Top right insets show a detailed view of the Fermi level.
These findings offer new strategies to enhance the transport properties of conducting polymers by exploiting these unique non-equilibrium states and opens up exciting possibilities for applications in fields like neuromorphic computing, bioelectronics, and thermoelectric devices.
Fig 1: Device structure
Fig 3: Seebeck–conductivity plot at 200 K.
blue → green → grey → red: doping from 0 to 1.5 ions/monomer
Nat. Mater. (2024)
Ahmed advanced the study of polymer conductors by using precise photoemission spectroscopy techniques to study transport at ultrahigh charge densities.
An international collaboration, including the three CSMB scientists Professor Norbert Koch, Ahmed Mansur, and Andreas Opitz, has made significant strides in understanding the transport physics of conducting polymers. It’s study reveals that in p-type organic electrochemical transistors, it is possible to deplete the valence band entirely and even access deeper bands without causing degradation. By introducing a second gate electrode, additional carriers can be injected, leading to surprising non-equilibrium transport behaviors.
Ahmed Mansur’s expertise enabled the team to explore the behavior of conducting polymers at those extreme charge densities. Using XPS, Ahmed was able to accurately quantify carrier concentrations, revealing up to 1.5 dopant ions per monomer unit in highly doped samples. This precision was critical to understanding the electronic environment of the polymer and its interaction with dopant ions.
UPS measurements provided additional insight into the electronic structure of the polymers, showing how doping shifts energy levels and affects charge transport. Ahmed’s analysis illustrated the transition from insulating to metallic states, highlighting the complete bleaching of the highest occupied molecular orbital (HOMO) at high doping levels. Ahmed’s precise UPS measurements were critical in elucidating these band-filling phenomena, providing deeper insights into the effects of doping on polymer electronic structures and contributing to a broader understanding of charge transport in conducting polymers.
These findings offer new strategies to enhance the transport properties of conducting polymers by exploiting these unique non-equilibrium states and open new avenues for enhancing the performance of conducting polymers, with potential applications in neuromorphic computing, bioelectronics, and thermoelectric devices.
Nat Commun 14, 5463 (2024).