General substitution rules for non-periodic rhomb tilings are derived. From the requirement that ... more General substitution rules for non-periodic rhomb tilings are derived. From the requirement that all substitution tiles consist of a discrete number of prototiles, it follows that a substitution tile with angle s*pi/n must be built out of pairs of prototiles with angles (s+t)*pi/n and (s-t)*pi/n, except if t=0. In addition, we require that a discrete number of prototile edges must fit between the beginning and endpoint of the substitution tile edge. By comparing the total area of the discrete number of prototiles constituting the substitution tile and the total area derived from the assumed edge shape, a set of substitution rules is derived. The generalization involves the introduction of prototiles with a negative area or subtraction tiles.
The radical anions in TCNQ salts are generally stacked in chains, isolated from each other by the... more The radical anions in TCNQ salts are generally stacked in chains, isolated from each other by the diamagnetic cations. Consequently the electronic system may be regarded as one dimensional. One of the basic problems in these materials is to which extent the valence electrons are correlated. The degree of correlation is determined by the ratio of the transfer integrals and the electron electron interactions. In the F.S.R.-spectra of some TCNQ salts lines have been observed which must be attributed to triplet excitons, showing that correlation effeccs are important. These triplet excitons may be regarded as bound electron-hole pairs. ... Zie: Summary
ABSTRACT In an attempt to obtain wustite Fe1-xO as epitaxial films on MgO(100), NO2-assisted mole... more ABSTRACT In an attempt to obtain wustite Fe1-xO as epitaxial films on MgO(100), NO2-assisted molecular-beam epitaxy was applied. At low NO2 fluxes, the low-energy electron diffraction and reflection high-energy electron diffraction images indeed indicate the formation of a rocksaltlike structure. In addition, Mössbauer spectroscopy provides evidence for the formation of a phase that is paramagnetic at room temperature. However, the layers are not pure oxides but are well-ordered oxynitrides with composition Fe1-xO1-yNy. The nitrogen atoms occupy substitutional sites on the oxygen-anion sublattice. Similarly, at slightly higher NO2 fluxes, magnetitelike oxynitride films with composition Fe3+deltaO4-yNy are obtained. By correlating x-ray photoelectron spectroscopy spectra with the intensity oscillation periods observed during reflection high-energy electron diffraction, it is possible to derive the complete stoichiometry of the films. We propose that the abrupt incorporation of nitrogen atoms only occurs if the atomic oxygen provided by the NO2 flux is insufficient to form a stoichiometric Fe3O4.
In specific-heat measurements of the solid electrolyte (C5H5NH)Ag5I6, the disordering of the silv... more In specific-heat measurements of the solid electrolyte (C5H5NH)Ag5I6, the disordering of the silver ions shows up in the form of a Schottky-type anomaly. A model calculation of the site occupancies of the Ag+ ions and the excess specific heat reproduces the main features of the gradual transition to the solid-electrolyte state in this compound and proves that correlations between Ag+ ions play an important role. Single-crystal conductivity measurements were carried out both along and perpendicular to the hexagonal axis. The large anisotropy of the conductivity at low temperatures ascertains that the motion of the Ag+ ions through the channels provided by the c sites is much easier than the motion via pathways involving m sites. In addition, the specific-heat measurements show the existence of a second-order phase transition which is probably associated with the orientational disordering of the pyridinium ions. Finally, single-crystal conductivity results of (C5H5NH)5Ag18I23 are pres...
Using the MgO/Ag(100) interface as a model system, we demonstrate that Coulomb and charge-transfe... more Using the MgO/Ag(100) interface as a model system, we demonstrate that Coulomb and charge-transfer energies in oxide layers deposited on a highly polarizable medium like a metal, are reduced from their bulk values, by as much as 1.8 eV and 2.5 eV, respectively. The use of efficient image potential screening may provide a new method to alter various transition temperatures
Summary form only given. CoO/Fe3O4 bilayers and multilayers show exchange-biasing i.e. the hyster... more Summary form only given. CoO/Fe3O4 bilayers and multilayers show exchange-biasing i.e. the hysteresis loop of the Fe3O4 layers is shifted by the presence of anti ferromagnetic CoO layers. Recent neutron diffraction measurements clarified to a great extent the temperature and magnetic field dependent behavior of the CoO part of these superlattices. A magnetic domain wall in the CoO layer, which
General substitution rules for non-periodic rhomb tilings are derived. From the requirement that ... more General substitution rules for non-periodic rhomb tilings are derived. From the requirement that all substitution tiles consist of a discrete number of prototiles, it follows that a substitution tile with angle s*pi/n must be built out of pairs of prototiles with angles (s+t)*pi/n and (s-t)*pi/n, except if t=0. In addition, we require that a discrete number of prototile edges must fit between the beginning and endpoint of the substitution tile edge. By comparing the total area of the discrete number of prototiles constituting the substitution tile and the total area derived from the assumed edge shape, a set of substitution rules is derived. The generalization involves the introduction of prototiles with a negative area or subtraction tiles.
The radical anions in TCNQ salts are generally stacked in chains, isolated from each other by the... more The radical anions in TCNQ salts are generally stacked in chains, isolated from each other by the diamagnetic cations. Consequently the electronic system may be regarded as one dimensional. One of the basic problems in these materials is to which extent the valence electrons are correlated. The degree of correlation is determined by the ratio of the transfer integrals and the electron electron interactions. In the F.S.R.-spectra of some TCNQ salts lines have been observed which must be attributed to triplet excitons, showing that correlation effeccs are important. These triplet excitons may be regarded as bound electron-hole pairs. ... Zie: Summary
ABSTRACT In an attempt to obtain wustite Fe1-xO as epitaxial films on MgO(100), NO2-assisted mole... more ABSTRACT In an attempt to obtain wustite Fe1-xO as epitaxial films on MgO(100), NO2-assisted molecular-beam epitaxy was applied. At low NO2 fluxes, the low-energy electron diffraction and reflection high-energy electron diffraction images indeed indicate the formation of a rocksaltlike structure. In addition, Mössbauer spectroscopy provides evidence for the formation of a phase that is paramagnetic at room temperature. However, the layers are not pure oxides but are well-ordered oxynitrides with composition Fe1-xO1-yNy. The nitrogen atoms occupy substitutional sites on the oxygen-anion sublattice. Similarly, at slightly higher NO2 fluxes, magnetitelike oxynitride films with composition Fe3+deltaO4-yNy are obtained. By correlating x-ray photoelectron spectroscopy spectra with the intensity oscillation periods observed during reflection high-energy electron diffraction, it is possible to derive the complete stoichiometry of the films. We propose that the abrupt incorporation of nitrogen atoms only occurs if the atomic oxygen provided by the NO2 flux is insufficient to form a stoichiometric Fe3O4.
In specific-heat measurements of the solid electrolyte (C5H5NH)Ag5I6, the disordering of the silv... more In specific-heat measurements of the solid electrolyte (C5H5NH)Ag5I6, the disordering of the silver ions shows up in the form of a Schottky-type anomaly. A model calculation of the site occupancies of the Ag+ ions and the excess specific heat reproduces the main features of the gradual transition to the solid-electrolyte state in this compound and proves that correlations between Ag+ ions play an important role. Single-crystal conductivity measurements were carried out both along and perpendicular to the hexagonal axis. The large anisotropy of the conductivity at low temperatures ascertains that the motion of the Ag+ ions through the channels provided by the c sites is much easier than the motion via pathways involving m sites. In addition, the specific-heat measurements show the existence of a second-order phase transition which is probably associated with the orientational disordering of the pyridinium ions. Finally, single-crystal conductivity results of (C5H5NH)5Ag18I23 are pres...
Using the MgO/Ag(100) interface as a model system, we demonstrate that Coulomb and charge-transfe... more Using the MgO/Ag(100) interface as a model system, we demonstrate that Coulomb and charge-transfer energies in oxide layers deposited on a highly polarizable medium like a metal, are reduced from their bulk values, by as much as 1.8 eV and 2.5 eV, respectively. The use of efficient image potential screening may provide a new method to alter various transition temperatures
Summary form only given. CoO/Fe3O4 bilayers and multilayers show exchange-biasing i.e. the hyster... more Summary form only given. CoO/Fe3O4 bilayers and multilayers show exchange-biasing i.e. the hysteresis loop of the Fe3O4 layers is shifted by the presence of anti ferromagnetic CoO layers. Recent neutron diffraction measurements clarified to a great extent the temperature and magnetic field dependent behavior of the CoO part of these superlattices. A magnetic domain wall in the CoO layer, which
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