| 1. |
- Plogmaker, Stefan
(författare)
-
Techniques and Application of Electron Spectroscopy Based on Novel X-ray Sources
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The curiosity of researchers to find novel characteristics and properties of matter constantly pushes for the development of instrumentation based on X-radiation. I present in this thesis techniques for electron spectroscopy based on developments of X-ray sources both in time structure and energy. One part describes a laser driven High-Harmonic Generation source and the application of an off-plane grating monochromator with additional beamlines and spectrometers. In initial experiments, the source is capable of producing harmonics between the 13th and 23rd of the fundamental laser 800 nm wavelength. The intensity in the 19th harmonic, after monochromatization, was measured to be above 1.2·1010 photons/second with a repetition rate of 5 kHz. The development of a chopper system synchronized to the bunch clock of an electron storage ring is also presented. The system can be used to adjust the repetition rate of a synchrotron radiation beam to values between 10 and 120 kHz, or for the modulation of continuous sources. The application of the system to both time of flight spectroscopy and laser pump X-ray probe spectroscopy is shown. It was possible to measure triple ionization of Kr and in applied studies the valence band of a laser excited dye-sensitized solar cell interface. The combination of the latter technique with transient absorption measurements is proposed.The organic molecule maleic anhydride (MA) and its binding configuration to the three anatase TiO2 crystals (101), (100), (001) has been investigated by means of Xray Photoelectron Spectroscopy (XPS) and Near Edge X-ray Absorption Fine structure Spectroscopy (NEXAFS). The results provide information on the binding configuration to the 101 crystal. High Kinetic Energy Photoelectron Spectroscopy was used to investigate multilayers of complexes of iron, ruthenium and osmium. The benefit of hard X-rays for ex-situ prepared samples is demonstrated together with the application of resonant valence band measurements to these molecules.
|
|
| 2. |
- Bhatt, Pramod, 1979-
(författare)
-
Fabrication and study of inorganic and organic thin film magnets
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thin film magnets are very important for many kinds of electronic devices and play a crucial role to achieve optimum performance. Therefore an intense level of research is going on all around the world to fabricate advanced electronics devices using both new inorganic and organic thin-film magnets. Historically, most magnetic materials used for technological applications are based on inorganic materials and have been studied extensible up to now. Recently, however, organic or molecular magnets have opened a new prospective of thin film magnets which have begun to show promise, offering the possibility of light-weight flexible materials and devices that include magnetic functionality.The research presented in this thesis is hence divided into two parts, where inorganic and organic magnets in thin films form were studied. The Ti/Ni multilayer system is studied as an inorganic magnet in the first part, whereas M(TCNE)x thin films were studied in the second part with M= Fe, Ni and TCNE is tetracynoethelene, an organic compound, and x~2.The Ti/Ni multilayer is a potential candidate for industrial applications and also features solid-state amorphisation. Because of various interesting scientific and technological aspects of Ti/Ni multilayer structures, many structural properties and subsequent thermal stability studies have been extensively reported in the literature, but surprisingly few reports are available on the corresponding electronic and magnetic properties. The work in the present thesis is therefore focused on synthesis and systematic investigation of structural, electronic and magnetic properties of as prepared as well as annealed Ti/Ni multilayer structures and to establish correlation between them.The second part of the thesis deals with organic-based molecular magnets of the M(TCNE)x type, where x~2, M = Fe, Ni and TCNE = tetracynoethelene. Fe(TCNE)x and Ni(TCNE)x have for the first time been fabricated as thin films, free of oxygen- and precursor-induced defects. The films were fabricated in situ under ultra high vacuum conditions using our group’s recently developed fabrication techniques for organic-based molecular magnets. The previously unknown electronic structure of these thin film magnets are presented in the thesis. Room temperature magnetic ordering was observed for thin films of Ni(TCNE)2, in stark contrast to earlier versions of the material (fabricated with the old methods and hence containing various defects). Room temperature magnetic ordering for a similar system, Ni2(TCNE), previously has been reported by another group, but it is clear that more studies are necessary to completely resolve the underlying mechanisms for the magnetic properties seen in these materials.
|
|
| 3. |
- Greczynski, Grzegorz, 1973-
(författare)
-
Photoelectron spectroscopy studies of conjugated polymer surfaces and interfaces for organic-based light emitting devices
- 2001
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since the initial discovery of metallic conductivity in doped polyacetylene in 1977, which lead to the Nobel Prize in Chemistry year 2000, the field of conducting polymers has expanded tremendously. Today, research developments in this area cover transistors, photodiodes and light emitting diodes (LEDs). The latter one was initiated by the first report on electroluminescence in conjugated polymer that appeared in 1990 by the group of Prof. R. H. Friend in Cambridge. After a decade from this discovery the first polymer-based LEDs are approaching the stage of commercial manufacturing. The low-cost processing and attractive device characteristics make them strong competitors for the inorganic LED-industry.The focus of the work presented in the papers in this thesis is the characterization of the electronic structure of some conjugated polymers used in polymer-LED, as well as different types of interfaces often occurring in real structures (metal-polymer, polymer-metal, metal-insulator-polymer, etc.) and interface materials. The analysis technique that was used for these investigations was almost exclusively photoelectron spectroscopy with both X-ray photons (XPS) and ultraviolet light (UPS), occasionally some measurements were also done employing synchrotron radiation. These two methods XPS and UPS are the complementary techniques and enormous amount of information concerning the valence band electronic structure and electronic core levels can be obtained at the same time. This combination has proven to be especially powerful when applied to the investigations of interfaces formed between conjugated polymers and various metals where the undergoing changes can be mapped step by step in situ while building the metal contact under ultra high vacuum (UHV). The later issue is of great importance for applications in LEDs, where the device characteristic depends strongly on the character of interfaces between emissive polymer layer and injecting electrodes.
|
|
| 4. |
- Hahlin, Maria, 1975-
(författare)
-
Electronic and Molecular Surface Structures of Dye-Sensitized TiO2 Interfaces
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The dye-sensitized solar cell is a promising solar cell technology. In these systems the key process for light to electricity conversion is molecular in nature and is initiated in dye molecules adsorbed at a semiconducting surface. This thesis focuses on the electronic and molecular surface structure of the dye/TiO2 interface, and the experimental results were obtained from surface sensitive X-ray based electron spectroscopic methods. Two families of dyes, triarylamine based organic dyes and ruthenium based inorganic dyes, were investigated. The effect of dye structural modications on the interfacial properties was studied, such as the surface concentrations, dye molecular surface orientation, molecular interactions, and energy level matching. Also, the impact of additional parameters such as the incorporation of coadsorbents and the solvents used for dye sensitization were studied and complementary photoelectrochemical characterization was used to demonstrate functional properties corresponding to changes in the molecular layers. The experiments provided information on how specic structural modications change the frontier electronic structure. The results also showed that the adsorption of the organic dye leads to submolecular electronic changes, and that the dye surface orientations in general favor effcient energy conversion. Moreover, effects of solvents and coadsorbents, on both energy level matching between the dye and the TiO2 substrate and the surfacemolecular structure were quantied.
|
|
| 5. |
|
|
| 6. |
- Johansson, Erik, 1977-
(författare)
-
Interfaces in Dye-Sensitized Oxide / Hole-Conductor Heterojunctions for Solar Cell Applications
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nanoporous dye-sensitized solar cells (DSSC) are promising devices for solar to electric energy conversion. In this thesis photoelectron spectroscopy (PES), x-ray absorption spectroscopy (XAS) and photovoltaic measurements are used for studies of the key interfaces in the DSSC.Photovoltaic properties of new combinations of TiO2/dye/hole-conductor heterojunctions were demonstrated and their interfacial structures were studied. Three different types of hole-conductor materials were investigated: Triarylamine derivatives, a conducting polymer and CuI. The difference in photocurrent and photovoltage properties of the heterojunction due to small changes in the hole-conductor material was followed. Also a series of dye molecules were used to measure the influence of the dye on the photovoltaic properties. Differences in both the energy-level matching and the geometric structure of the interfaces in the different heterojunctions were studied by PES. This combination of photovoltaic and PES measurements shows the possibility to link the interfacial electronic and molecular structure to the functional properties of the device.Three effective dyes used in the DSSC, Ru(dcbpy)2(NCS)2, Ru(tcterpy)(NCS)3 and an organic dye were studied in detail using PES and XAS and resonant core hole decay spectroscopy. The results gave information of the frontier electronic structure of the dyes and how the dyes are bonded to the TiO2 surface.Finally, the hole-conductor mechanism in a conducting polymer was investigated theoretically using semi-empirical and ab-initio methods.
|
|
| 7. |
- Kristensen, Emma, 1976-
(författare)
-
Characterization of Surfaces Designed for Biomedical Applications
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In order to develop blood biocompatible materials a heparin surface and a phosphorylcholine (PC) functionalized polymer surface were characterized using photoelectron spectroscopy (PES). The formation of the heparin surface was studied by quartz crystal microbalance with dissipation monitoring (QCM-D). This heparin surface consists of heparin conjugates deposited on a conditioning layer, applied once or twice. The PC functionalized polymer, poly(trimethylene carbonate), was linked to a silicon substrate through 3-amino- propyltrimethoxysilane (APTMS), also studied using PES. Synchrotron radiation based PES showed that the thicker heparin film resulted in complete coverage of the substrate, while the thinner did not. This could explain the difference in blood biocompatibility between the two films, as observed by others. It was also found that the heparin chains bend down towards the substrate (under vacuum). For the thinner heparin film the modifications, resulting from extensive irradiation of the sample, were studied with synchrotron radiation based PES. This was done at a pressure of about 10-7 mbar and in 0.5 mbar water vapor. It was found that the modification is slower under water vapor than at low pressures and that the damaged film incorporates water upon exposure.The heparin coating was found to be stable and wear resistant enough to still be present on artificial heart valves after three weeks testing in circulating plasma. It then had about the same antithrombin uptake as a non-tested surface. The film was, however, partly destroyed by the durability test and plasma proteins were deposited. The PC functionalized, APTMS linked polymer was found to be much shorter than could be expected from random reactions. One plausible explanation is an interaction between the PC group and the silane surface, favoring aminolysis close to the PC group. This is consistent with our finding that the PC group bends down towards the surface.
|
|
| 8. |
- Mahrov, Boriss, 1977-
(författare)
-
Studies of Semiconductors Modified with Nanoscale Light Absorbers for Solar Cell Application
- 2004
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recently, materials such as hole conductors (CuI, CuSCN) and light absorbers (Ru-complexes, CuInS2) have been actively investigated for application in nanocrystalline solar cells. In this thesis combinations of these materials have been studied.In the first part of the thesis, various methods were applied to characterize the electronic structure and photoconversion mechanism of the dye molecule Ru(dcbpyH2)2(NCS)2 when combined with materials for the use in photovoltaic devices. Specifically, the adsorption and electronic structure of the dye molecules adsorbed to semiconductors were investigated by means of photoelectron spectroscopy. The results indicate a chemical bond between the dye molecules and the hole conductors (CuI, CuSCN) via the NCS- groups. In addition, preparation of a TiO2/Ru-dye/CuI solid state model system was studied in situ. These experiments showed a partial breaking of the TiO2-dye bond caused by CuI evaporation. Photovoltage measurements were also performed. These investigations showed a shift in the light absorption threshold of the dye molecules adsorbed onto the hole conductors (CuI and CuSCN), indicating new defect states at the dye/CuSCN interface. Also, charge accumulation and transport in solar cells with CuSCN were compared to liquid electrolyte cells. Measurements showed that the lifetime and transport time of electrons in solar cells with CuSCN are much shorter than in electrolyte cells.In the second part of the thesis, the deposition of CuInS2 onto various metal oxides by spray pyrolysis has been studied with x-ray diffraction and photoelectron spectroscopy. The measurements showed that the morphologies of the substrates play a significant role in the formation of CuInS2 layers. Also, the presence of CdS at TiO2 has a positive influence on the formation of CuInS2.
|
|
| 9. |
- Maibach, Julia, et al.
(författare)
-
Probing a battery electrolyte drop with ambient pressure photoelectron spectroscopy
- 2019
-
Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 10
-
Tidskriftsartikel (refereegranskat)abstract
- Operando ambient pressure photoelectron spectroscopy in realistic battery environments is a key development towards probing the functionality of the electrode/electrolyte interface in lithium-ion batteries that is not possible with conventional photoelectron spectroscopy. Here, we present the ambient pressure photoelectron spectroscopy characterization of a model electrolyte based on 1M bis(trifluoromethane)sulfonimide lithium salt in propylene carbonate. For the first time, we show ambient pressure photoelectron spectroscopy data of propylene carbonate in the liquid phase by using solvent vapor as the stabilizing environment. This enables us to separate effects from salt and solvent, and to characterize changes in electrolyte composition as a function of probing depth. While the bulk electrolyte meets the expected composition, clear accumulation of ionic species is found at the electrolyte surface. Our results show that it is possible to measure directly complex liquids such as battery electrolytes, which is an important accomplishment towards true operando studies.
|
|
| 10. |
- Watcharinyanon, Somsakul, 1978-
(författare)
-
Structure of Self-Assembled Monolayers on Gold Studied by NEXAFS and Photoelectron Spectroscopy
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Self-assembled monolayers (SAMs) provide well-defined and ordered films of molecules spontaneously chemisorbed on a surface. By designing molecules with desired functionalities, such molecular film can be interesting for a range of applications from molecular electronics to catalysis. Important parameters for SAM applications are the film structure and quality, which are dependent on the structure of molecular constituents, the substrate, and the self-assembly process. In this work, SAMs on Au(111) of a variety of functionalized molecules, with thiol and silane headgroups, have been studied using high-resolution X-ray photoemission spectroscopy (HRXPS), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, Infrared reflection absorption spectroscopy (IRRAS), contact angle measurements and Kelvin probe measurements. In particular, the effects of varying the size of the backbone, varying the headgroup, inclusion of a porphyrin tailgroup, different ways of deprotection of the headgroups, and mixed molecular layers have been investigated. The first part of thesis work is focused on SAMs of oligo(phenyleneethynylene) (OPE) derivatives. First the effect of the extent of the conjugated system on the structure of SAM was investigated. As the lateral π-system in the OPE backbone increases, molecular surface densities become lower and molecular inclinations larger. Subsequently, a bulky porphyrin tailgroup was added onto the OPE molecule. Porphyrin-functionalized OPE with several headgroups were compared and the thioacetyl anchor group was found to form a high quality SAM. In the second part of the work, the molecular orientation of thiol-derivatized tetraphenylporphyrin layers was studied. The geometry of the molecular layer and the number of linkers that bind to the gold surface depend strongly on preparation schemes, i.e. whether or not the acetyl protection groups on the thiol were removed before adsorption. Finally, mixed SAMs of a ferrocene-terminated alkanethiol and alkanethiols were studied. By diluting the ferrocene-functionalized molecules in unfunctionalized alkanethiols, the orientational order and the packing density improved. The geometrical structure and the fraction of the ferrocene-terminated molecules can be tuned by controlling the parameters in the preparation scheme.
|
|
