Nematic fluctuations in iron-oxychalcogenide Mott insulators

Nematic fluctuations occur in a wide range physical systems from biological molecules to cuprates and iron pnictide high-Tc superconductors. It is unclear whether nematicity in pnictides arises from electronic spin or orbital degrees of freedom. We studied the iron-based Mott insulators La2O2Fe2OM2M = (S, Se), which are structurally similar to pnictides. Nuclear magnetic resonance revealed a critical slowing down of nematic fluctuations and complementary Mössbauerr spectroscopy data showed a change of electrical field gradient. The neutron pair distribution function technique detected local C2 fluctuations while neutron diffraction indicates that global C4 symmetry is preserved. A geometrically frustrated Heisenberg model with biquadratic and single-ion anisotropic terms provides the interpretation of the low temperature magnetic fluctuations. The nematicity is not due to spontaneous orbital order, instead it is linked to geometrically frustrated magnetism based on orbital selectivity. This study highlights the interplay between orbital order and spin fluctuations in nematicity.

Fabrication and Characterization of 3-D Photonic Crystals of Various Microspheres by Electrophoretic Self-Assembly

Fabrication of high sphericity, monodispersed microspheres (100~600 nm) of various oxides (SiO2, TiO2, ZnO, In2O3, SnO2) via sol-gel process and polystyrene (PS) microspheres (200~400 nm) via emulsion polymerization is presented. A high colloidal stability suspension was obtained by adjusting the zeta potential of such spheres and pH of the colloid. The 3-D photonic crystal (PhC) templates of opaline structure on ITO-coated glasses and silicon wafers were easily formed under electrophoretic self-assembly (EPSA) of microspheres under the influence of exerting electrical forces. Different setups of counter-electrode were attempted to establish an electrical field. The lattice constant of an ordered opal structure by EPSA can also be tuned by the electrical field gradient. Interestingly various self-assembled 3-D structures of silica microspheres in either symmetrical curvilinear profile or triangular ridges can be produced through EPSA route using specific counter-electrode setups. The measured optic properties of such 3-D PhC templates manifest photonic bandgap (PBG) based on planar-wave expansion (PWE) simulation to verify the existence of real PBG in PhC samples with tunable nanostructures. The PS PhC templates are currently used to easily transform into inverse opal structure (IOS) by infiltrating sol of other oxides with high dielectric constant (e.g. ZnO or TiO2) and filled with metallic nanoparticles (Ni or Cu) by electrochemical deposition or chemical bath deposition (CBD).

Analytical modeling of reservoir effect on electromigration in Cu interconnects

Electromigration (EM) in Cu dual-damascene interconnects with extensions (also described as overhangs or reservoirs) ranging from 0 to 120 nm in the upper metal (M2) was investigated by an analytical model considering the work of electron wind and surface/interface energy. It was found that there exists a critical extension length beyond which increasing extension lengths ceases to prolong electromigration lifetimes. The critical extension length is a function of void size and electrical field gradient. The analytical model agrees very well with existing experimental results. Some design guidelines for electromigration-resistant circuits could be generated by the model.

Natural Electrotransformation of Lightning-Competent Pseudomonas sp. Strain N3 in Artificial Soil Microcosms

ABSTRACT The lightning-competent Pseudomonas sp. strain N3, recently isolated from soil, has been used to study the extent of natural electrotransformation (NET) or lightning transformation as a horizontal gene transfer mechanism in soil. The variation of electrical fields applied to the soil with a laboratory-scale lightning system provides an estimate of the volume of soil affected by NET. Based on the range of the electric field that induces NET of Pseudomonas strain N3, the volume of soil, where NET could occur, ranges from 2 to 950 m3 per lightning strike. The influence of DNA parameters (amount, size, and purity) and DNA soil residence time were also investigated. NET frequencies (electrotransformants/recipient cells) ranged from 10−8 for cell lysate after 1 day of residence in soil to 4 × 10−7 with a purified plasmid added immediately before the lightning. The electrical field gradient (in kilovolts per cm) also played a role as NET frequencies ranging from 1 × 10−5 at 2.3 kV/cm to 1.7 × 10−4 at 6.5 kV/cm.

Laboratory-Scale Evidence for Lightning-Mediated Gene Transfer in Soil

ABSTRACT Electrical fields and current can permeabilize bacterial membranes, allowing for the penetration of naked DNA. Given that the environment is subjected to regular thunderstorms and lightning discharges that induce enormous electrical perturbations, the possibility of natural electrotransformation of bacteria was investigated. We demonstrated with soil microcosm experiments that the transformation of added bacteria could be increased locally via lightning-mediated current injection. The incorporation of three genes coding for antibiotic resistance (plasmid pBR328) into the Escherichia coli strain DH10B recipient previously added to soil was observed only after the soil had been subjected to laboratory-scale lightning. Laboratory-scale lightning had an electrical field gradient (700 versus 600 kV m−1) and current density (2.5 versus 12.6 kA m−2) similar to those of full-scale lightning. Controls handled identically except for not being subjected to lightning produced no detectable antibiotic-resistant clones. In addition, simulated storm cloud electrical fields (in the absence of current) did not produce detectable clones (transformation detection limit, 10−9). Natural electrotransformation might be a mechanism involved in bacterial evolution.

Characterization of Photochemically or Electrochemically Reduced Blue Titanium Dioxide

Blue TiO2 which is formed under UV irradiation under inert gases in the presence of hole scavengers is characterized. The concentration of surface-trapped electrons which cause the blue colour was analytically determined after irradiation in the presence of methanol or other organic compounds. The saturation concentration is controlled by a dynamic equilibrium of photoreduction and reoxidation of the reduced surface sites which leads to H2 formation. The blue colour can also be produced by chemical or electrochemical reduction. Mobility of the surface-trapped electrons in an electrical field gradient is demonstrated. The reduced TiO2 is similar to a hydrogen titanium bronze.