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Projects / Programmes source: ARIS

Dependency of the interfacial charge carrier dynamics on the coupling strength in heterostuctured systems using resonant photoemission and the core-hole clock method

Research activity

Code Science Field Subfield
1.02.00  Natural sciences and mathematics  Physics   

Code Science Field
P260  Natural sciences and mathematics  Condensed matter: electronic structure, electrical, magnetic and optical properties, supraconductors, magnetic resonance, relaxation, spectroscopy 

Code Science Field
1.03  Natural Sciences  Physical sciences 
Keywords
physics of surfaces, synchrotron light studies, inner-shell excitations, charge carrier dynamics, He atom scattering, X-ray absorption, X-ray resonant photoemission, core-hole clock method
Evaluation (rules)
source: COBISS
Researchers (1)
no. Code Name and surname Research area Role Period No. of publicationsNo. of publications
1.  29515  PhD Gregor Kladnik  Physics  Head  2014 - 2016  77 
Organisations (1)
no. Code Research organisation City Registration number No. of publicationsNo. of publications
1.  1554  University of Ljubljana, Faculty of Mathematics and Physics  Ljubljana  1627007  34,275 
Abstract
Organic molecules are promising candidates as building blocks for the next generation of electronic devices. Advantages of reduced size, ordered self-assembly, functional tunability with chemistry and ease of synthesis make molecular electronic devices very attractive. To realize such devices, it is essential to understand the fundamental physics and chemistry at the nano-meter scale. One of the key issues concerning the organic molecular device performances concerns the transport of charge carriers through organic assemblies and also across the interfaces between organic-inorganic and hetero-organic assemblies. Synchrotron based spectroscopies offer a suitable approach to measure electronic properties of extended organic assemblies. The project will take advantage of the long-term cooperation with University of Trieste and the Laboratory TASC CNR-IOM and access to the ALOISA beamline at the Elettra synchrotron with its research infrastructure. Special interest will be given to amino and thiol functionalized molecules like pyridines, amino benzenes, amino acids, etc. and pi-conjugated systems of polycyclic aromatic hydrocarbons. These molecules can be used as a bridging layer between the metal substrate and other complex organic molecules and present possible candidates for further development of organic based nano-electronic devices. Along these systems also organic molecule functionalization of graphene as a promising candidate for future nano-devices is planned. Crystalline surfaces of solid substrates will act as 2D templates for synthesis and characterization of organic assemblies in form of ordered monolayers with narrow size distribution and uniform adsorption configurations. Electronic structure of such molecular assemblies will then be directly probed by X-ray photoemission and X-ray absorption experiments. Moreover, with the use of resonant photoemission and the core-hole clock method the excited carrier dynamics in molecular films will be studied with unprecedented time and spatial resolution. The aim of this project is to study charge carrier dynamics in controlled molecular films grown on metallic substrates in-situ under ultrahigh vacuum conditions. Fast charge transport across specific atomic sites within organic molecules adsorbed on Au, Ag and Cu substrates will be determined from core-hole-clock experiments. Likewise, still rare reports of dynamic charge transfer from the substrate to the adsorbed molecules to date demand an extensive and systematic investigation of the conditions that lead to the observed charge dynamics, which is of paramount importance to the understanding of basic natural phenomena in surface science. Furthermore, in collaboration with groups from Columbia University, New York, complementary measurements of the single molecule conductance as well as prototype device efficiency using the same organic system will be performed and related to our results. Using the core-hole clock method will enable us to access electron transfer dynamics in the sub-femtosecond timescale, and the details of molecular coupling to the metal will be characterized in detail by X-ray photoemission and X-ray absorption techniques. Additionally, the project will reveal the impact of the experimental geometry parameters (e.g. X-ray polarization direction, molecular adsorption geometry, etc.) on the resonant photoemission intensity and the core-hole clock method which has not been studied in detail yet and should therefore present an important scientific contribution. Finally, the experimental results of the spectroscopic measurements will be further corroborated with state-of-the-art numerical methods in collaboration with different groups from Italy and, if needed, new computational methods based on the observed processes in the performed experiments will be developed.
Significance for science
Research on the impact of coupling of organic molecules with various inorganic/organic substrates on the ultrafast charge transfer is essential to understanding the processes at these interfaces, especially in the light of the development of the next generation advanced electronic devices. Molecular electronic components are very attractive because of the advantages of smaller size (miniaturization), self-assembled growth, ability of chemical functionalization and simple synthesis. A comprehensive experimental and theoretical study provided insight into the physical processes of charge transfer in the investigated heterostructured layers, which is crucial in the design of new organic molecules based electronic nano-devices. To achieve this, one of the few available experimental methods, which allows the study of charge transport in molecular systems on a ultrafast time scale, i.e., resonant photoemission spectroscopy (RPES) and the core-hole clock (CHC) method was employed. An extensive and systematic study of the impact of the experimental layout, i.e., the X-ray polarization direction, electron emission angle and the molecular orientation on the surface, on the intensity of the RPES signal and thus on the derived charge transfer times was conducted for the first time. The research results have an important influence on the choice of the experimental layout in the RPES measurements and the CHC method in the future. Among other things, the applied experimental methods enable the determination of ultrafast charge transfer pathways and directions in the studied molecular systems on various substrates, like graphene and graphene nanoribbons, due to the methods' atomic site selectivity. Moreover, it also allows insight into the charge transfer from the substrate to the adsorbed molecular films which, together with the corresponding charge carrier dynamics model, permitting the interpretation of fundamental physical processes at the nano-scale. In this regard we were the first to quantitatively assess the dynamic charge transfer from the substrate to the molecules. In addition to the new experimental findings in the wider field of surface science and physics itself, also development of new theoretical and numerical models has been achieved in collaboration with theoretical groups, which further illuminate the observed processes at the quantum level. The research has therefore contributed to several new scientific insights into the physical processes on the nanoscale, which are key in the development of new nanoelectronic devices as well as in other scientific fields, such as electrochemistry, pharmacy and biotechnology, especially in the light of understanding the role of inter-molecular coupling on the charge carrier dynamics.
Significance for the country
The main significance of the project for Slovenia is the determination of important candidates for use in the development of new advanced nano-electronic components, such as photovoltaic cells and other active electronic components, in understanding the processes and importance of transfer and transport of electric charge in chemistry and in complex organic systems used for pharmaceutical and biotechnology purposes. This project could importantly contribute to further development of various industries in Slovenia such as pharmaceutical, chemical and photovoltaic industry. The project will provide insight into the basic understanding of quantum processes on the nanoscale and thereby offer technical and development-oriented businesses tools and knowledge to optimize/improve their products and production processes, which is crucial for success in the global international market. Moreover, with the ongoing development of nanoelectronic devices based on organic molecules lower production costs, reduced environmental pollution and opening of new opportunities for the creation of new businesses and thus new jobs for mostly highly educated staff can be expected. In addition, the project has a significant impact not only on the integration of Slovenian scientists and the Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana with international cooperations and work efforts at the highest level, but also on the visibility and the scientific impact of Slovenia and the Slovenian achievements in the field of surface physics due to the continuation and strengthening of existing international collaborations with renowned research teams from the U.S. and Europe. During the course of the project access to and transfer of foreign knowledge to the Slovenian research area was enabled, as well as networking of Slovenian scientists with excellent foreign researchers, which is nowadays of utmost importance in modern science. Futhermore, due to access to the most advanced experimental methods and devices (non-existent in Slovenia) at the Elettra (Italy) and SLS (Swiss) synchrotron facility, it is also possible to promote surface science research areas among the students of the Department of Physics at the University of Ljubljana within the framework of diploma/masters/doctoral theses and with this to educate new scientific staff in Slovenia in the important developing field of nanotechnology.
Most important scientific results Annual report 2015, final report
Most important socioeconomically and culturally relevant results Annual report 2015, final report
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