Günther Leising - Academia.edu (original) (raw)
Papers by Günther Leising
Sub-ps transient differential transmission spectroscopy is used to study the photoexcitation dyna... more Sub-ps transient differential transmission spectroscopy is used to study the photoexcitation dynamics of a blue emitting ladder-type oligophenyl in bulk film. The observed spectral features are ascribed to singlet excited states and polarons. The time traces of these features reveal the dynamics of charge-carrier generation from singlets via a migration-assisted dissociation mechanism.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films
Paper published as part of the special topic on 2018 Special Collection on Atomic Layer Depositio... more Paper published as part of the special topic on 2018 Special Collection on Atomic Layer Deposition (ALD) This paper was selected as an Editor's Pick ARTICLES YOU MAY BE INTERESTED IN Plasma enhanced atomic layer deposition of aluminum sulfide thin films
physica status solidi (a)
The Journal of Chemical Physics
The evaporation of quinacridone from a stainless steel Knudsen cell leads to the partial decompos... more The evaporation of quinacridone from a stainless steel Knudsen cell leads to the partial decomposition of this molecule in the cell, due to its comparably high sublimation temperature. At least one additional type of molecules, namely indigo, could be detected in the effusion flux. Thermal desorption spectroscopy and atomic force microscopy have been used to study the co-deposition of these molecules on sputter-cleaned and carbon-covered silicon dioxide surfaces. Desorption of indigo appears at temperatures of about 400 K, while quinacridone desorbs at around 510 K. For quinacridone, a desorption energy of 2.1 eV and a frequency factor for desorption of 1 × 10 19 s −1 were calculated, which in this magnitude is typical for large organic molecules. A fraction of the adsorbed quinacridone molecules (∼5%) decomposes during heating, nearly independent of the adsorbed amount, resulting in a surface composed of small carbon islands. The sticking coefficients of indigo and quinacridone were found to be close to unity on a carbon covered SiO 2 surface but significantly smaller on a sputter-cleaned substrate. The reason for the latter can be attributed to insufficient energy dissipation for unfavorably oriented impinging molecules. However, due to adsorption via a hot-precursor state, the sticking probability is increased on the surface covered with carbon islands, which act as accommodation centers.
MRS Proceedings, 1999
ABSTRACTOligo (p-phenylene vinylene)s OPV were synthesized having cyanobiphenyloxy-groups bonded ... more ABSTRACTOligo (p-phenylene vinylene)s OPV were synthesized having cyanobiphenyloxy-groups bonded to the vinylene double bonds via alkylene spacers. A Pd(0)-reaction was used to synthesize the oligomers starting with the dibromo-substituted benzene and the alkenyloxy-biphenyl-nitrile. The orientation of the mesogens by a magnetic field and their influence on the orientation of the main chain was investigated by means of neutron diffraction ND. Data on the photophysics of the oligomers were gained using several spectroscopic methods such as UV/VIS, polarized optical microscopy POM, SEC, 1H-NMR, FT-IR.
Science And Technology For Photonic And Optoelectronic Application, 2001
Organic Materials for Photonics, 1993
Intrinsically Conducting Polymers: An Emerging Technology, 1993
MRS Proceedings, 1999
ABSTRACTDespite the fast-paced new developments and improvements of applications incorporating co... more ABSTRACTDespite the fast-paced new developments and improvements of applications incorporating conjugated organic materials, rather little effort is made to obtain well-defined structures and thin films of these in order to exploit the highly anisotropic properties (e.g. conductivity, polarized light emission) of most conjugated organic materials. It has been shown that oligomers, which can easily be evaporated under ultrahigh vacuum conditions, exhibit heteroepitaxial growth on various substrates. Depending on the nature of the interaction of the organic molecules with the substrate different orientations can be obtained, as well as by simply changing the conditions of evaporation. Therefore, by going from amorphous or polycrystalline structures to highly textured or single crystalline ones new insights into the physical properties of the materials can be expected, and also new applications. We studied the formation of well-defined films of the electroluminescent oligomer p -sexiph...
Chemical Physics Letters, 2015
The origins of specific polymorphic phases within thin films are still not well understood. The p... more The origins of specific polymorphic phases within thin films are still not well understood. The polymorphism of the molecule dioctyl-terthiophene is investigated during the presence of a silicon-oxide surface during the crystallisation process. It is found that a monolayer of molecules forms two-dimensional crystals on the surface. In the case of thicker films crystalline islands are formed, A comparison of the three polymorphic phases observed within thin films and the thermodynamically more stable single crystal phases reveals distinct differences which can be related to an adaption of the molecular packing with the flat surface of the substrate.
Photonics, Devices, and Systems IV, 2008
ABSTRACT Today's most common approach for solid state lighting relies on the conversion o... more ABSTRACT Today's most common approach for solid state lighting relies on the conversion of a portion of the blue light emitted from the LED die by an inorganic phosphor material. Although this concept, at a first glance, seems to be rather simple, the appropriate shape of the color conversion element (CCE) in white LED light sources turns out to have essential significance for the quality of the white light (especially in terms of angular homogeneity). In this contribution we discuss recent developments and novel coating concepts for LEDs that excel in terms of spatial homogeneity of the emission and variability of the color temperature, which on the one hand can be attributed to the application of Silicate based phosphors, a beneficial class of luminescent materials for LED application, and on the other hand on optimized CCE geometries, which were obtained by numerical calculations with the help of state-of-the-art simulation tools.
BioMEMS and Nanotechnology, 2004
Nanoimprinting is a low cost method to fabricate features from mum down to the nm-range. Differen... more Nanoimprinting is a low cost method to fabricate features from mum down to the nm-range. Different nanofabrication techniques, namely hot embossing, UV-nanoimprinting as well as micro-contact printing will be discussed. Recently achieved results with nanoimprinting methods will be demonstrated.
Physik in unserer Zeit, 2000
ABSTRACT
MRS Proceedings, 1999
ABSTRACTIn this contribution we compare experimental investigations (of photoluminescence, absorp... more ABSTRACTIn this contribution we compare experimental investigations (of photoluminescence, absorption and modulation spectroscopy) for a number of novel dye molecules to quantum-chemical simulations. The investigated materials contain phenylene-, phenylenevinylene-, naphthylene- and anthrylene units linked either by saturated or non saturated bonds. In the first part of the paper we give a short overview of the principal optical properties of the investigated molecules including a discussion of exciton localization effects. The latter can be accomplished by studying the geometry modifications in the excited state relative to the ground state. To do so, we couple the Austin Model 1 (AM1) approach to a multi-electron configuration interaction technique (MECI). The optical spectra are subsequently obtained from the Intermediate Neglect of Differential Overlap (INDO) Hamiltonian combined with a Single Configuration Interaction (SCI) approach. In the main section of this contribution we ...
MRS Proceedings, 1999
ABSTRACTWe determined the internal electric field distribution in light emitting electro-chemical... more ABSTRACTWe determined the internal electric field distribution in light emitting electro-chemical cells (LECs) and light emitting diodes (LEDs) based on methyl substituted poly(paraphenylen) (mLPPP) by performing electroabsorption measurements as a function of an external bias voltage. Based on these results we outline the working principle of both types of devices. In the case of the LEC we observed an abrupt increase in the EA signal above a threshold voltage of about 2V which we attributed to junction formation due to in-situ electrochemical doping. For single layer LEDs we found the behavior expected for metal/insulator/metal/structures, i.e. the electric field drops linearly over the bulk polymer and no space-charge regions were observed.These findings are important for improving the performance of organic electroluminescent devices.
MRS Proceedings, 2002
ABSTRACTThe realization of a polymeric injection laser diode is an important aim in organic elect... more ABSTRACTThe realization of a polymeric injection laser diode is an important aim in organic electronics. A crucial step towards this goal lies in the understanding and fabrication of feedback structures for lasers. Such feedback structures may be fabricated either in the substrate or directly in the active polymer layer.Soft Lithography has proven itself as a useful tool to pattern a wide variety of materials. Typically one uses elastomeric molds (stamps) to pattern materials and structures whereby dimensions as low as 30 nm can be achieved.Different types of Soft Lithographic processes are applied to produce optical feedback structures for optically pumped laser arrays.
MRS Proceedings, 1999
ABSTRACTThe application of ele ctroactive organic materials in devices (light emitting diodes, ph... more ABSTRACTThe application of ele ctroactive organic materials in devices (light emitting diodes, photovoltaic cells) often requires electrodes with a low workfunction. Commonly, aluminum or alkaline earth metals are used, which usually exhibit strong interaction with the organic material, such as the formation of new covalent bonds or doping. This results in a strong modification of the electronic structure of the organic/metal interface, and in most cases does not yield the energy level alignment expected for the unreacted interface. As a n alternative to the above-mentioned metals we propose the use of samarium, with a workfunction of 2.7 eV, for the following reason: we have studied the interface formation between Sm and p -sexiphenyl (6P, which exhibits intense blue electroluminescence), with ultraviolet photoelectron spectroscopy. Sm was deposited stepwise onto thin films of 6P in ultrahigh vacuum, and the photoelectron spectra were recorded after each step. We did not find any i...
Nanofabrication: Technologies, Devices, and Applications II, 2005
ABSTRACT The availability of reliable ultrafast laser systems and their unique properties for mat... more ABSTRACT The availability of reliable ultrafast laser systems and their unique properties for material processing are the basis for new lithographic methods in the sector of micro- and nanofabrication processes such as two-photon 3D-lithography. Beside its flexibility, one of the most powerful features of this technology is the true 3D structuring capability, which allows fabrication with higher efficiency and with higher resolution compared to a sequential layer-by-layer structuring and build-up technique. Up to now, the two-photon method was mainly used for writing 3D structures quasi anywhere inside a bulk volume. In combination with a sophisticated and versatile machine vision support, the two-photon 3D-lithography is now targeting for micro- and nano-optical applications and the integration of optical and photonic components into optical microsystems. We report on a disruptive improvement of this lithographic method by means of an optical detection system for optical components (e.g. laser diode chips / LEDs and photo diodes) that are already assembled on an optical micropackage. The detection system determines the position coordinates of features of the optical microsystem in all three dimensions with micrometer resolution, combining digital image processing and evaluation of back reflected laser light from the surface of the system. This information is subsequently processed for controlling the fabrication of directly laser written optical and photonic structures inside and around such an optical microsystem. The strong advantage of this approach lies in its adaptation of laser written structures to existing features and structures, which also permits to compensate for misalignments and imperfections of preconfigured packages.
Sub-ps transient differential transmission spectroscopy is used to study the photoexcitation dyna... more Sub-ps transient differential transmission spectroscopy is used to study the photoexcitation dynamics of a blue emitting ladder-type oligophenyl in bulk film. The observed spectral features are ascribed to singlet excited states and polarons. The time traces of these features reveal the dynamics of charge-carrier generation from singlets via a migration-assisted dissociation mechanism.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films
Paper published as part of the special topic on 2018 Special Collection on Atomic Layer Depositio... more Paper published as part of the special topic on 2018 Special Collection on Atomic Layer Deposition (ALD) This paper was selected as an Editor's Pick ARTICLES YOU MAY BE INTERESTED IN Plasma enhanced atomic layer deposition of aluminum sulfide thin films
physica status solidi (a)
The Journal of Chemical Physics
The evaporation of quinacridone from a stainless steel Knudsen cell leads to the partial decompos... more The evaporation of quinacridone from a stainless steel Knudsen cell leads to the partial decomposition of this molecule in the cell, due to its comparably high sublimation temperature. At least one additional type of molecules, namely indigo, could be detected in the effusion flux. Thermal desorption spectroscopy and atomic force microscopy have been used to study the co-deposition of these molecules on sputter-cleaned and carbon-covered silicon dioxide surfaces. Desorption of indigo appears at temperatures of about 400 K, while quinacridone desorbs at around 510 K. For quinacridone, a desorption energy of 2.1 eV and a frequency factor for desorption of 1 × 10 19 s −1 were calculated, which in this magnitude is typical for large organic molecules. A fraction of the adsorbed quinacridone molecules (∼5%) decomposes during heating, nearly independent of the adsorbed amount, resulting in a surface composed of small carbon islands. The sticking coefficients of indigo and quinacridone were found to be close to unity on a carbon covered SiO 2 surface but significantly smaller on a sputter-cleaned substrate. The reason for the latter can be attributed to insufficient energy dissipation for unfavorably oriented impinging molecules. However, due to adsorption via a hot-precursor state, the sticking probability is increased on the surface covered with carbon islands, which act as accommodation centers.
MRS Proceedings, 1999
ABSTRACTOligo (p-phenylene vinylene)s OPV were synthesized having cyanobiphenyloxy-groups bonded ... more ABSTRACTOligo (p-phenylene vinylene)s OPV were synthesized having cyanobiphenyloxy-groups bonded to the vinylene double bonds via alkylene spacers. A Pd(0)-reaction was used to synthesize the oligomers starting with the dibromo-substituted benzene and the alkenyloxy-biphenyl-nitrile. The orientation of the mesogens by a magnetic field and their influence on the orientation of the main chain was investigated by means of neutron diffraction ND. Data on the photophysics of the oligomers were gained using several spectroscopic methods such as UV/VIS, polarized optical microscopy POM, SEC, 1H-NMR, FT-IR.
Science And Technology For Photonic And Optoelectronic Application, 2001
Organic Materials for Photonics, 1993
Intrinsically Conducting Polymers: An Emerging Technology, 1993
MRS Proceedings, 1999
ABSTRACTDespite the fast-paced new developments and improvements of applications incorporating co... more ABSTRACTDespite the fast-paced new developments and improvements of applications incorporating conjugated organic materials, rather little effort is made to obtain well-defined structures and thin films of these in order to exploit the highly anisotropic properties (e.g. conductivity, polarized light emission) of most conjugated organic materials. It has been shown that oligomers, which can easily be evaporated under ultrahigh vacuum conditions, exhibit heteroepitaxial growth on various substrates. Depending on the nature of the interaction of the organic molecules with the substrate different orientations can be obtained, as well as by simply changing the conditions of evaporation. Therefore, by going from amorphous or polycrystalline structures to highly textured or single crystalline ones new insights into the physical properties of the materials can be expected, and also new applications. We studied the formation of well-defined films of the electroluminescent oligomer p -sexiph...
Chemical Physics Letters, 2015
The origins of specific polymorphic phases within thin films are still not well understood. The p... more The origins of specific polymorphic phases within thin films are still not well understood. The polymorphism of the molecule dioctyl-terthiophene is investigated during the presence of a silicon-oxide surface during the crystallisation process. It is found that a monolayer of molecules forms two-dimensional crystals on the surface. In the case of thicker films crystalline islands are formed, A comparison of the three polymorphic phases observed within thin films and the thermodynamically more stable single crystal phases reveals distinct differences which can be related to an adaption of the molecular packing with the flat surface of the substrate.
Photonics, Devices, and Systems IV, 2008
ABSTRACT Today's most common approach for solid state lighting relies on the conversion o... more ABSTRACT Today's most common approach for solid state lighting relies on the conversion of a portion of the blue light emitted from the LED die by an inorganic phosphor material. Although this concept, at a first glance, seems to be rather simple, the appropriate shape of the color conversion element (CCE) in white LED light sources turns out to have essential significance for the quality of the white light (especially in terms of angular homogeneity). In this contribution we discuss recent developments and novel coating concepts for LEDs that excel in terms of spatial homogeneity of the emission and variability of the color temperature, which on the one hand can be attributed to the application of Silicate based phosphors, a beneficial class of luminescent materials for LED application, and on the other hand on optimized CCE geometries, which were obtained by numerical calculations with the help of state-of-the-art simulation tools.
BioMEMS and Nanotechnology, 2004
Nanoimprinting is a low cost method to fabricate features from mum down to the nm-range. Differen... more Nanoimprinting is a low cost method to fabricate features from mum down to the nm-range. Different nanofabrication techniques, namely hot embossing, UV-nanoimprinting as well as micro-contact printing will be discussed. Recently achieved results with nanoimprinting methods will be demonstrated.
Physik in unserer Zeit, 2000
ABSTRACT
MRS Proceedings, 1999
ABSTRACTIn this contribution we compare experimental investigations (of photoluminescence, absorp... more ABSTRACTIn this contribution we compare experimental investigations (of photoluminescence, absorption and modulation spectroscopy) for a number of novel dye molecules to quantum-chemical simulations. The investigated materials contain phenylene-, phenylenevinylene-, naphthylene- and anthrylene units linked either by saturated or non saturated bonds. In the first part of the paper we give a short overview of the principal optical properties of the investigated molecules including a discussion of exciton localization effects. The latter can be accomplished by studying the geometry modifications in the excited state relative to the ground state. To do so, we couple the Austin Model 1 (AM1) approach to a multi-electron configuration interaction technique (MECI). The optical spectra are subsequently obtained from the Intermediate Neglect of Differential Overlap (INDO) Hamiltonian combined with a Single Configuration Interaction (SCI) approach. In the main section of this contribution we ...
MRS Proceedings, 1999
ABSTRACTWe determined the internal electric field distribution in light emitting electro-chemical... more ABSTRACTWe determined the internal electric field distribution in light emitting electro-chemical cells (LECs) and light emitting diodes (LEDs) based on methyl substituted poly(paraphenylen) (mLPPP) by performing electroabsorption measurements as a function of an external bias voltage. Based on these results we outline the working principle of both types of devices. In the case of the LEC we observed an abrupt increase in the EA signal above a threshold voltage of about 2V which we attributed to junction formation due to in-situ electrochemical doping. For single layer LEDs we found the behavior expected for metal/insulator/metal/structures, i.e. the electric field drops linearly over the bulk polymer and no space-charge regions were observed.These findings are important for improving the performance of organic electroluminescent devices.
MRS Proceedings, 2002
ABSTRACTThe realization of a polymeric injection laser diode is an important aim in organic elect... more ABSTRACTThe realization of a polymeric injection laser diode is an important aim in organic electronics. A crucial step towards this goal lies in the understanding and fabrication of feedback structures for lasers. Such feedback structures may be fabricated either in the substrate or directly in the active polymer layer.Soft Lithography has proven itself as a useful tool to pattern a wide variety of materials. Typically one uses elastomeric molds (stamps) to pattern materials and structures whereby dimensions as low as 30 nm can be achieved.Different types of Soft Lithographic processes are applied to produce optical feedback structures for optically pumped laser arrays.
MRS Proceedings, 1999
ABSTRACTThe application of ele ctroactive organic materials in devices (light emitting diodes, ph... more ABSTRACTThe application of ele ctroactive organic materials in devices (light emitting diodes, photovoltaic cells) often requires electrodes with a low workfunction. Commonly, aluminum or alkaline earth metals are used, which usually exhibit strong interaction with the organic material, such as the formation of new covalent bonds or doping. This results in a strong modification of the electronic structure of the organic/metal interface, and in most cases does not yield the energy level alignment expected for the unreacted interface. As a n alternative to the above-mentioned metals we propose the use of samarium, with a workfunction of 2.7 eV, for the following reason: we have studied the interface formation between Sm and p -sexiphenyl (6P, which exhibits intense blue electroluminescence), with ultraviolet photoelectron spectroscopy. Sm was deposited stepwise onto thin films of 6P in ultrahigh vacuum, and the photoelectron spectra were recorded after each step. We did not find any i...
Nanofabrication: Technologies, Devices, and Applications II, 2005
ABSTRACT The availability of reliable ultrafast laser systems and their unique properties for mat... more ABSTRACT The availability of reliable ultrafast laser systems and their unique properties for material processing are the basis for new lithographic methods in the sector of micro- and nanofabrication processes such as two-photon 3D-lithography. Beside its flexibility, one of the most powerful features of this technology is the true 3D structuring capability, which allows fabrication with higher efficiency and with higher resolution compared to a sequential layer-by-layer structuring and build-up technique. Up to now, the two-photon method was mainly used for writing 3D structures quasi anywhere inside a bulk volume. In combination with a sophisticated and versatile machine vision support, the two-photon 3D-lithography is now targeting for micro- and nano-optical applications and the integration of optical and photonic components into optical microsystems. We report on a disruptive improvement of this lithographic method by means of an optical detection system for optical components (e.g. laser diode chips / LEDs and photo diodes) that are already assembled on an optical micropackage. The detection system determines the position coordinates of features of the optical microsystem in all three dimensions with micrometer resolution, combining digital image processing and evaluation of back reflected laser light from the surface of the system. This information is subsequently processed for controlling the fabrication of directly laser written optical and photonic structures inside and around such an optical microsystem. The strong advantage of this approach lies in its adaptation of laser written structures to existing features and structures, which also permits to compensate for misalignments and imperfections of preconfigured packages.