Johannes Wiedersich - Academia.edu (original) (raw)
Uploads
Papers by Johannes Wiedersich
Physical Review B, 2001
ABSTRACT
Spectrochimica Acta Part B: Atomic Spectroscopy, 2004
Future generations of microelectronic devices will require both, ever-decreasing critical dimensi... more Future generations of microelectronic devices will require both, ever-decreasing critical dimensions and shrinking tolerance on those dimensions. The rising costs and complexity associated with lithographically created structures at the nanometer length scale opened opportunities for alternative techniques. Following this track, self-assembly in physical systems might play a key role in future technological applications. Self-assembling materials are characterized by spontaneous formation of nanometer-scaled structures. In addition long-range order or domains are installed.
Physical Review Letters, 1999
Accurate measurements of the dependence of low-frequency Raman scattering on the scattering angle... more Accurate measurements of the dependence of low-frequency Raman scattering on the scattering angle were performed in two silica glasses. By a comparison of spectra measured at a large scattering angle (close to back scattering) and a small one (close to forward scattering), we for the first time observed a q dependence of the low-frequency light scattering in glasses. From the magnitude of the effect, the vibration correlation length is estimated and compared with results from the picosecond optical technique; a reasonable agreement is found. [S0031-9007 09266-2] PACS numbers: 64.70.Pf, 63.20.Pw
Journal of Physics: Condensed Matter, 1999
We present dielectric relaxation (DS) and light scattering (LS) data of several glass formers. Re... more We present dielectric relaxation (DS) and light scattering (LS) data of several glass formers. Relaxational features are compiled which are not yet properly taken into account by current models. (i) We distinguish two types of glass formers. Type A systems do not show a slow β-process whereas type B systems do. A full line-shape analysis of ε(ω) is presented (10 −2 Hz < ν < 10 9 Hz). In type A systems the evolution of the high-frequency wing of the α-process is the most prominent spectral change while cooling and leads to an essentially constant loss at T < T g . The analysis of ε(ω) of type B systems is carried out within the Williams-Watts approach and we focus on the temperature dependence of the β-relaxation strength. (ii) Concerning fast relaxations below T g as revealed by LS (10 9 Hz < ν < 10 13 Hz) we identify relaxation with a low-frequency power-law behaviour. No indication of a crossover to a white noise spectrum as previously reported and discussed within MCT is found. Analysing this relaxation we recourse to the model of thermally activated transitions in asymmetric double well potentials. We show that the model works well in some cases and the distribution of barrier heights may be extracted, but in other systems pronounced deviations occur. † Corresponding author. 0953-8984/99/SA0147+10$19.50
Journal of Non-Crystalline Solids, 2007
Applying tandem-Fabry-Perot interferometry together with a double monochromator, depolarized ligh... more Applying tandem-Fabry-Perot interferometry together with a double monochromator, depolarized light scattering spectra were measured in order to investigate the fast relaxation processes and vibrations in molecular, ionic and polymeric glasses in the 1-5000 GHz range covering temperatures from the glass transition temperature T g down to some 10 K. In addition to the boson peak, the spectra reveal quasi-elastic contributions that we attribute to (i) a nearly constant loss in the frequency range below ffi10 GHz and (ii) a power-law contribution with positive exponent a at higher frequencies. In the majority of glasses the latter may be attributed to thermally activated dynamics in asymmetric double well potentials as previously found for the light scattering spectra in silica. Following the Gilroy-Phillips model the exponent a shows a master curve as a function of T/V 0 for the various glasses, where V 0 specifies the width of the exponential distribution of barriers g(V), i.e., g(V) / exp(ÀV/V 0 ). The parameter V 0 is found to be $T g /2 in most cases. The relative strength of the dynamics in asymmetric double well potentials and the nearly constant loss contribution is different in the glasses studied.
![Research paper thumbnail of Light scattering spectra of fast relaxation in B[sub 2]O[sub 3] glass](https://attachments.academia-assets.com/46269307/thumbnails/1.jpg)
](The Journal of Chemical Physics, 2000
Light scattering spectra of B 2 O 3 glass were measured in the frequency range 20-7000 GHz at tem... more Light scattering spectra of B 2 O 3 glass were measured in the frequency range 20-7000 GHz at temperatures in the range of 15-300 K and are compared with those previously obtained for Ca 0.4 K 0.6 ͑NO 3 ͒ 1.4 ͑CKN͒. The low-frequency contribution of the fast relaxation susceptibility spectrum is found to show a power-law behavior with an exponent ␣ϭ0.6, the latter being temperature independent in contrast to the finding in other inorganic glasses such as silica and CKN. Possible explanations of the spectral shape in B 2 O 3 are considered.
The Journal of Chemical Physics, 2000
This contribution presents a systematic light scattering study of a series of boron oxide glasses... more This contribution presents a systematic light scattering study of a series of boron oxide glasses which are characterized by different thermal histories. The thermal treatment was obtained by annealing the samples close to the glass transition temperature for times of several hours. Both low-frequency ͑0.1-30 cm Ϫ1 ͒ and high-frequency ͑5-1600 cm Ϫ1 ͒ spectra were monitored by using a tandem Fabry-Perot interferometer and a Raman spectrometer, respectively. The low-frequency spectra include quasielastic contributions and the boson peak. It was found that different thermal histories lead to pronounced changes in the low-frequency spectrum. The position of the boson peak shifts to higher frequencies and the magnitude of the quasielastic contribution decreases as a function of annealing time. Both quantities correlate linearly with the density of the samples ( ϭ1.804-1.866 g/cm 3 ͒. On the other hand, the high-frequency modes do not show discernible changes. In particular, no alteration of the modes which correspond to the boroxol ring is found, indicating that the fraction of boroxol rings is constant within 2% accuracy. Taking the boson peak as a manifestation of medium-range order, we conclude that annealing the glass influences the intermediate-range order rather than the short-range order.
The Journal of Chemical Physics, 2003
ABSTRACT
Analytical and Bioanalytical Chemistry, 2010
A combination of microbeam grazing incidence small angle X-ray scattering (μGISAXS) and imaging e... more A combination of microbeam grazing incidence small angle X-ray scattering (μGISAXS) and imaging ellipsometry is introduced as a new versatile tool for the characterization of nanostructures. μGISAXS provides a local lateral and depth-sensitive structural characterization, and imaging ellipsometry adds the position-sensitive determination of the three-dimensional morphology in terms of thickness, roughness, refractive index, and extinction coefficient. Together μGISAXS and imaging ellipsometry enable a complete characterization of structure and morphology. On the basis of an example of buildup of nanostructures from monodisperse colloidal polystyrene nanospheres on a rough solid support, the scope of this new combination is demonstrated. Roughness is introduced by a dewetting structure of a diblock copolymer film with one block being compatible with the colloidal nanoparticles and one block being incompatible. To demonstrate the potential for kinetic investigations, μGISAXS and imaging ellipsometry are applied to probe the drying process of an aqueous dispersion of nanospheres on such a type of rough substrate.
Advanced Functional Materials, 2011
... 2011, XX, 110 Matthias A. Ruderer , Shuai Guo , Robert Meier , Hsin-Yin Chiang , Volker Körs... more ... 2011, XX, 110 Matthias A. Ruderer , Shuai Guo , Robert Meier , Hsin-Yin Chiang , Volker Körstgens , ... Absorption and photoluminescence measure-ments complement the structural analysis. MA Ruderer , S. Guo , R. Meier , H. Chiang , Dr. V. Körstgens , Dr. J. Wiedersich , Prof. ...
The Journal of Chemical Physics, 2007
The authors compared the spectral response of Zn-substituted horseradish peroxidase in a glycerol... more The authors compared the spectral response of Zn-substituted horseradish peroxidase in a glycerol/water solvent to hydrostatic pressure at 2 K and ambient temperature. The low temperature experiments clearly demonstrate the presence of at least three different conformations with drastically different elastic properties. However, the main conformation, which determines the fluorescence spectrum at ambient temperature, did not show any significant difference between low and high temperature and pressure. The authors conclude that the local compressibility of the heme pocket of the protein depends only very weakly on temperature.
Physical Review B, 2001
ABSTRACT
Spectrochimica Acta Part B: Atomic Spectroscopy, 2004
Future generations of microelectronic devices will require both, ever-decreasing critical dimensi... more Future generations of microelectronic devices will require both, ever-decreasing critical dimensions and shrinking tolerance on those dimensions. The rising costs and complexity associated with lithographically created structures at the nanometer length scale opened opportunities for alternative techniques. Following this track, self-assembly in physical systems might play a key role in future technological applications. Self-assembling materials are characterized by spontaneous formation of nanometer-scaled structures. In addition long-range order or domains are installed.
Physical Review Letters, 1999
Accurate measurements of the dependence of low-frequency Raman scattering on the scattering angle... more Accurate measurements of the dependence of low-frequency Raman scattering on the scattering angle were performed in two silica glasses. By a comparison of spectra measured at a large scattering angle (close to back scattering) and a small one (close to forward scattering), we for the first time observed a q dependence of the low-frequency light scattering in glasses. From the magnitude of the effect, the vibration correlation length is estimated and compared with results from the picosecond optical technique; a reasonable agreement is found. [S0031-9007 09266-2] PACS numbers: 64.70.Pf, 63.20.Pw
Journal of Physics: Condensed Matter, 1999
We present dielectric relaxation (DS) and light scattering (LS) data of several glass formers. Re... more We present dielectric relaxation (DS) and light scattering (LS) data of several glass formers. Relaxational features are compiled which are not yet properly taken into account by current models. (i) We distinguish two types of glass formers. Type A systems do not show a slow β-process whereas type B systems do. A full line-shape analysis of ε(ω) is presented (10 −2 Hz < ν < 10 9 Hz). In type A systems the evolution of the high-frequency wing of the α-process is the most prominent spectral change while cooling and leads to an essentially constant loss at T < T g . The analysis of ε(ω) of type B systems is carried out within the Williams-Watts approach and we focus on the temperature dependence of the β-relaxation strength. (ii) Concerning fast relaxations below T g as revealed by LS (10 9 Hz < ν < 10 13 Hz) we identify relaxation with a low-frequency power-law behaviour. No indication of a crossover to a white noise spectrum as previously reported and discussed within MCT is found. Analysing this relaxation we recourse to the model of thermally activated transitions in asymmetric double well potentials. We show that the model works well in some cases and the distribution of barrier heights may be extracted, but in other systems pronounced deviations occur. † Corresponding author. 0953-8984/99/SA0147+10$19.50
Journal of Non-Crystalline Solids, 2007
Applying tandem-Fabry-Perot interferometry together with a double monochromator, depolarized ligh... more Applying tandem-Fabry-Perot interferometry together with a double monochromator, depolarized light scattering spectra were measured in order to investigate the fast relaxation processes and vibrations in molecular, ionic and polymeric glasses in the 1-5000 GHz range covering temperatures from the glass transition temperature T g down to some 10 K. In addition to the boson peak, the spectra reveal quasi-elastic contributions that we attribute to (i) a nearly constant loss in the frequency range below ffi10 GHz and (ii) a power-law contribution with positive exponent a at higher frequencies. In the majority of glasses the latter may be attributed to thermally activated dynamics in asymmetric double well potentials as previously found for the light scattering spectra in silica. Following the Gilroy-Phillips model the exponent a shows a master curve as a function of T/V 0 for the various glasses, where V 0 specifies the width of the exponential distribution of barriers g(V), i.e., g(V) / exp(ÀV/V 0 ). The parameter V 0 is found to be $T g /2 in most cases. The relative strength of the dynamics in asymmetric double well potentials and the nearly constant loss contribution is different in the glasses studied.
The Journal of Chemical Physics, 2000
Light scattering spectra of B 2 O 3 glass were measured in the frequency range 20-7000 GHz at tem... more Light scattering spectra of B 2 O 3 glass were measured in the frequency range 20-7000 GHz at temperatures in the range of 15-300 K and are compared with those previously obtained for Ca 0.4 K 0.6 ͑NO 3 ͒ 1.4 ͑CKN͒. The low-frequency contribution of the fast relaxation susceptibility spectrum is found to show a power-law behavior with an exponent ␣ϭ0.6, the latter being temperature independent in contrast to the finding in other inorganic glasses such as silica and CKN. Possible explanations of the spectral shape in B 2 O 3 are considered.
The Journal of Chemical Physics, 2000
This contribution presents a systematic light scattering study of a series of boron oxide glasses... more This contribution presents a systematic light scattering study of a series of boron oxide glasses which are characterized by different thermal histories. The thermal treatment was obtained by annealing the samples close to the glass transition temperature for times of several hours. Both low-frequency ͑0.1-30 cm Ϫ1 ͒ and high-frequency ͑5-1600 cm Ϫ1 ͒ spectra were monitored by using a tandem Fabry-Perot interferometer and a Raman spectrometer, respectively. The low-frequency spectra include quasielastic contributions and the boson peak. It was found that different thermal histories lead to pronounced changes in the low-frequency spectrum. The position of the boson peak shifts to higher frequencies and the magnitude of the quasielastic contribution decreases as a function of annealing time. Both quantities correlate linearly with the density of the samples ( ϭ1.804-1.866 g/cm 3 ͒. On the other hand, the high-frequency modes do not show discernible changes. In particular, no alteration of the modes which correspond to the boroxol ring is found, indicating that the fraction of boroxol rings is constant within 2% accuracy. Taking the boson peak as a manifestation of medium-range order, we conclude that annealing the glass influences the intermediate-range order rather than the short-range order.
The Journal of Chemical Physics, 2003
ABSTRACT
Analytical and Bioanalytical Chemistry, 2010
A combination of microbeam grazing incidence small angle X-ray scattering (μGISAXS) and imaging e... more A combination of microbeam grazing incidence small angle X-ray scattering (μGISAXS) and imaging ellipsometry is introduced as a new versatile tool for the characterization of nanostructures. μGISAXS provides a local lateral and depth-sensitive structural characterization, and imaging ellipsometry adds the position-sensitive determination of the three-dimensional morphology in terms of thickness, roughness, refractive index, and extinction coefficient. Together μGISAXS and imaging ellipsometry enable a complete characterization of structure and morphology. On the basis of an example of buildup of nanostructures from monodisperse colloidal polystyrene nanospheres on a rough solid support, the scope of this new combination is demonstrated. Roughness is introduced by a dewetting structure of a diblock copolymer film with one block being compatible with the colloidal nanoparticles and one block being incompatible. To demonstrate the potential for kinetic investigations, μGISAXS and imaging ellipsometry are applied to probe the drying process of an aqueous dispersion of nanospheres on such a type of rough substrate.
Advanced Functional Materials, 2011
... 2011, XX, 110 Matthias A. Ruderer , Shuai Guo , Robert Meier , Hsin-Yin Chiang , Volker Körs... more ... 2011, XX, 110 Matthias A. Ruderer , Shuai Guo , Robert Meier , Hsin-Yin Chiang , Volker Körstgens , ... Absorption and photoluminescence measure-ments complement the structural analysis. MA Ruderer , S. Guo , R. Meier , H. Chiang , Dr. V. Körstgens , Dr. J. Wiedersich , Prof. ...
The Journal of Chemical Physics, 2007
The authors compared the spectral response of Zn-substituted horseradish peroxidase in a glycerol... more The authors compared the spectral response of Zn-substituted horseradish peroxidase in a glycerol/water solvent to hydrostatic pressure at 2 K and ambient temperature. The low temperature experiments clearly demonstrate the presence of at least three different conformations with drastically different elastic properties. However, the main conformation, which determines the fluorescence spectrum at ambient temperature, did not show any significant difference between low and high temperature and pressure. The authors conclude that the local compressibility of the heme pocket of the protein depends only very weakly on temperature.