Electronic transport properties through thiophenes on switchable domains

The electronic transport of electrons and holes through stacks of $\alpha$,\ome ga-dicyano-$\beta$,$\beta$'-dibutyl- quaterthiophene (DCNDBQT) as part of a nov el organic ferroic field-effect transistor (OFFET) is investigated. The novel ap plication of a ferroelectric instead of a dielectric substrate provides the poss ibility to switch bit-wise the ferroelectric domains and to employ the polarizat ion of these domains as a gate field in an organic semiconductor. A device conta ining very thin DCNDBQT films of around 20 nm thickness is intended to be suitab le for logical as well as optical applications. We investigate the device proper ties with the help of a phenomenological model called multilayer organic light-e mitting diodes (MOLED), which was extended to transverse fields. The results sho wed, that space charge and image charge effects play a crucial role in these org anic devices

Current without bias and diode effect in shuttling transport of nanoshafts

A row of parallely ordered and coupled molecular nanoshafts is shown to develop a shuttling transport of charges at finite temperature. The appearance of a cu rrent without applying an external bias voltage is reported as well as a natura l diode effect allowing unidirectional charge transport along one field directi on while blocking the opposite direction. The zero-bias voltage current appears above a threshold of initial thermal and/or dislocation energy

Sucrose Monoester Micelles Size Determined by Fluorescence Correlation Spectroscopy (FCS)

One of the several uses of sucrose detergents, as well as other micelle forming detergents, is the solubilization of different membrane proteins. Accurate knowledge of the micelle properties, including size and shape, are needed to optimize the surfactant conditions for protein purification and membrane characterization. We synthesized sucrose esters having different numbers of methylene subunits on the substituent to correlate the number of methylene groups with the size of the corresponding micelles. We used Fluorescence Correlation Spectroscopy (FCS) and two photon excitation to determine the translational D of the micelles and calculate their corresponding hydrodynamic radius, Rh. As a fluorescent probe we used LAURDAN (6-dodecanoyl-2-dimethylaminonaphthalene), a dye highly fluorescent when integrated in the micelle and non-fluorescent in aqueous media. We found a linear correlation between the size of the tail and the hydrodynamic radius of the micelle for the series of detergents measured

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

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