Polymorphism in ferroic functional elements

The present study describes an approach for the scale-bridging modeling of ferroic materials as functional elements in micro- and nanoelectronic devices. Ferroic materials are characterized by temperature-dependent complex ordering phenomena of the internal magnetic, electronic, and structural degrees of freedom with several involved length and time scales. Hence, the modelling of such compounds is not straightforward, but relies on a combination of electronic-structure-based methods like ab-initio and density-functional schemes with classical particle-based approaches given by Monte-Carlo simulations with Ising, lattice-gas, or Heisenberg Hamiltonians, which incorporate material-specific parameters both from theory and experiment. The interplay of those methods is demonstrated for device concepts based on electroceramic materials like ferroelectrics and multiferroics, whose functionality is closely related with their propensity towards structural and magnetic polymorphism. In the present case, such scale-bridging techniques are employed to aid the development of an organic field effect transistor on a ferroelectric substrate generated by the self-assembly of field-sensitive molecules on the surfaces of ferroic oxides. Electronic-structure-based methods yield the microscopic properties of the oxide, the surface, the molecules, and the respective interactions. They are combined with classical particle-based methods on a scale-hopping basis. This combination allows to study the morphology evolution during the self-assembly of larger adsorbate arrays on the (defective) oxide surface and to investigate the interplay of low-temperature magnetic ordering phenomena with the ferroelectric functionality at higher temperatures in multiferroic oxides like the hexagonal manganites. The combination of density-functional data with classical continuum modelling also yielded a model Hamiltonian for the quick determination of the properties of a gate structure based on bio-functionalized carbon nanotubes.     

An intramolecular diene-carbene cycloaddition equivalence. The observation of a remarkable substituent effect on photorearrangement of tricyclo[4.3.0.05,7]non-3-en-2-ones

The preparation and photorearrangement of vinyl cyclopropanes 2a–c and pyrazolines 3a and 3c are presented.     

Tunable laser measurements of water vapor transitions in the vicinity of 5 μm

The present results confirm earlier tunable laser observations that the atmospheric widths of high rotational energy transitions are considerably narrower than previously predicted. Intensities, self-broadening coefficients, nitrogen and air shifts, and relative positions have also been measured.     

Tunable diode laser spectroscopy of CO2 in the 10- to 15-μm spectral region—Lineshape and Q-branch head absorption profile

The self-broadened and nitrogen-broadened absorption profiles of the Q-branch head of the 10⁰0 ← 01¹0 band of CO₂ near 618 cm^?1 were studied under high resolution (～10^?4 cm^?1) using tunable diode laser techniques. The intensity and linewidth of several lines in this Q branch, the ν₂ band, 10.4-μm and 9.4-μm laser bands have been measured accurately. The lineshape of a CO₂ line has also been measured to be Lorentzian within experimental accuracy to about 15 half-widths. Preliminary calculated Q-branch head absorption profiles agree reasonably well with the observed profiles.     

Breitlinien-NMR-Untersuchung der amorphen Komponente von Poly-(trans-1,4-butadien)- und Poly(4-methylpenten-1)-Kristallen, die mit Schwefelkohlenstoff benetzt sind

Ohne Zusammenfassung     

C60 on SiC nanomesh

A SiC nanomesh is used as a nanotemplate to direct the epitaxy of C60 molecules. The epitaxial growth of C60 molecules on SiC nanomesh at room temperature is investigated by in situ scanning tunneling microscopy, revealing a typical Stranski-Krastanov mode (i.e., for the first one or two monolayers, it is a layer-by-layer growth or 2-D nucleation mode; at higher thicknesses, it changes to island growth or a 3-D nucleation mode). At submonolayer (0.04 and 0.2 ML) coverage, C60 molecules tend to aggregate to form single-layer C60 islands that mainly decorate terrace edges, leaving the uncovered SiC nanomesh almost free of C60 molecules. At 1 ML C60 coverage, a complete wetting layer of hexagonally close-packed C60 molecules forms on top of the SiC nanomesh. At higher coverage from 4.5 ML onward, the C60 stacking adopts a (111) oriented face-centered-cubic (fcc) structure. Strong bright and dim molecular contrasts have been observed on the first layer of C60 molecules, which are proposed to originate from electronic effects in a single-layer C60 island or the different coupling of C60 molecules to SiC nanomesh. These STM molecular contrast patterns completely disappear on the second and all the subsequent C60 layers. It is also found that the nanomesh can be fully recovered by annealing the C60/SiC nanomesh sample at 200 degrees C for 20 min.     

Anisotropy contrast in phonon-enhanced apertureless near-field microscopy using a free-electron laser

We demonstrate the imaging of ferroelectric domains in BaTiO3, using an infrared-emitting free-electron laser as a tunable optical source for scattering scanning near-field optical microscopy and spectroscopy. When the laser is tuned into the spectral vicinity of a phonon resonance, ferroelectric domains can be resolved due to the anisotropy of the dielectric properties of the material. Slight detuning of the wavelength gives rise to a contrast reversal clearly evidencing the resonant character of the excitation. The near-field domain contrast shows that the orientation of the dielectric tensor with respect to the sample surface has a clear influence on the near-field signal.