The efficiency of the conduction of photocurrent in discotic liquid crystals is known to depend on the quality of the
columnar organization. Solvents have shown to be able to influence the formation of wire structures on substrates
promoting very long and ordered wired formations or bulkier structures depending on the affinity of the solvent with
parts of the molecular structure of discotics. Here we present a study on the effect of solvents when the liquid crystal is
confined between two substrates with the columns running perpendicular to them, geometry used in solar cells. We
focused on toluene and dodecane, solvents that have shown to promote on substrates the formation of aligned and long
nanowires and bulk large and isolated fibers, respectively. The phase transition behavior indicates that toluene does not
interfere with the columnar formation while dodecane strongly influence increasing the disorder in the structure.
The self-organization of discotic liquid crystal molecules in columns has enormous interest for soft nanoelectronic applications. A great advantage of discotic liquid crystal is that defects can be self-annealed in contrast to typical organic materials. Through the overlap of molecular orbitals, the aromatic cores assemble into long range ordered one-dimensional structures. Very thin structured films can be obtained by spin-coating from solution and the resulting morphologies are strongly dependent on the interaction between discotics and solvent molecules. Toluene produces films formed by very long nanowires, spontaneously aligned along a common direction and over fairly large areas. These nanostructured films are a result of the interplay between liquid crystal self-organization and solvent driven assembly. The ordered nanowire structures exhibit improvement in the electrical properties compared to misaligned structures and even to pristine HAT5, deposited without the aid of solvent. In this study we show that the toluene-based deposition of discotic liquid crystals is advantageous because it allows a uniform coverage of the substrate, unlike pristine HAT5 but also thanks to the type of induced structures exhibiting one order of magnitude higher conductivity, in the aligned nanowire films, compared to bare HAT5 ones.
The industry’s march towards higher transistor density has called for an ever-increasing number of interconnect levels in
logic devices. The historic transition from aluminum to copper was necessary in reducing timing delays while future
technology nodes presents an opportunity for new materials and patterning techniques. One material for consideration is
graphene, a single atomic layer of carbon atoms. Graphene is known to have excellent electrical properties , driving
strong interest in its integration into the wafer fabrication processes for future electronics , and its ballistic transport
properties give promise for use in on-chip interconnects . This study demonstrates the feasibility of a direct electron
beam lithography technique to pattern sub-5nm metallic graphene ribbons, without using a mask or photoresist, to act as
next generation interconnects. Sub-5nm monolayer and multilayer graphene ribbons were patterned using a focused
electron beam in a transmission electron microscope (TEM) through direct knock-on ejection of carbon atoms. These
ribbons were measured during fabrication to quantify their electrical performance. Multilayered graphene nanoribbons
were found to sustain current densities in excess of 109 A/cm2, orders of magnitude higher than copper, while monolayer
graphene provides comparable performance to copper but at the level of a single atomic layer. High volume manufacturing
could utilize wafer-size chemical vapor deposition (CVD) graphene  transferred directly onto the substrate paired with
a direct write multi-beam tool to knock off carbon atoms for patterning of nanometer sized interconnects. The patterning
technique introduced here allows for the fabrication of small foot-print high performance next generation graphene
interconnects that bypass the use of a mask and resist process.
We have investigated the charge ordering phenomenon from the temperature dependence of inverse susceptibility, resistivity, and thermoelectric power (TEP) for Bi1-xSrxMnO3 (BSMO) from 300 K to 700 K. At high temperatures, susceptibility follows Curie-Weiss law. The resistivity data indicate insulating behavior of BSMO. TEP (S(T)) value is negative and weakly temperature-dependent in the high temperature regime. The slope of TEP changes dramatically near the charge ordering temperature (ΤCO), indicating an increase of energy gap due to the charge ordering. In the vicinity of ΤCO, thermal hysteresis is observed in TEP data as well as in the resistivity data, which is consistent with the nature of the martensitic transition of the charge ordering phenomena. From this hysteretic behavior, we estimated ΤCO. As Sr concentration increases, ΤCO shifts to lower temperature from ΤCO ~ 490 K for x = 0.45 to ΤCO ~ 435 K for x = 0.8, and the thermal hysteretic behavior becomes less pronounced. The electrical transport properties have been discussed in terms of carrier localization due to charge ordering transition accompanied by the local lattice distortions.
The lattice effects on the magnetic and transport properties in La0.67-xGdxSr0.33CoO3 series are studied. The introduction of smaller Gd3+ ions leads to an enhanced mismatch between the La-O layer and the CoO2 layer and a decrease of the tolerance factor t. The spin-state of trivalent Co ion transits to low-spin state with the decrease of Co-O bond length. The doping of Gd3+ drives the system from the cluster-glass state to the spin-glass state and progressively decreases the Curie temperature. At high Gd3+ doping content, an interesting negative
magnetoresistance occurs at low temperature.
Thermoelectric power(TEP) mesurement has been carried out on the series of Pr0.5Sr0.5Mn1-xRuxO3 (0.0 ≤ x ≤ 0.1) under zero and 6 tesla magnetic fields. In Pr0.5Sr0.5MnO3, a large negative peak of TEP was observed below the ferromagnetic(FM) to antiferromagnetic(AFM) transition temperature, TN ~ 165K. Under H = 6 tesla, the magnitude of the negative TEP peak is slightly reduced with decrease of TN down to 105K. For Mn-site doped samples with Ru, however, the negative TEP peak is drasically suppressed by only 2% of Ru doping and completely disappears with further Ru doping. This indicates that the FM metallic state is induced more strongly by Ru substitution than by the magnetic field. In the paramagnetic(PM) regime above the Curie temperature, TC, it was found that TEP as well as resistivity for Pr0.5Sr0.5Mn1-xRuxO3 can be described by the polaronic transport mechanism. The systematic changes of TEP in the PM regime with variation of Ru concentration is discussed in relation to the effects of Ru doping at Mn sites which extends the FM phase at low temperatures and increases TC similarly to the application of magnetic field.
We report the magnetic field-induced superconductivity in Sr1- xKxBiO3 superconductors. A reentrant superconducting- normal resistive transition is observed in certain samples and, by applying the external magnetic field (H) or increasing the current (I), the reentrant normal state goes back to the zero resistivity: the recovery of superconductivity by applying H or increasing I. The magnetotransport of investigation on different samples reveals an interesting relation between the observed field-induced superconductivity and the normal state transport properties. Possible origins of this unusual phenomenon in Sr1-xKxBiO3 are discussed.