Sulfur nanocomposites with insecticidal effect for the control of Bactericera cockerelli.

The purpose of this research was to synthesize nanocomposites consisting of sulfur nanoparticles coated with eucalyptus and rosemary essential oils to determine the insecticidal effect in the control of nymphs of paratrioza (Bactericera cockerelli (Sulc) (Hemiptera: Triozidae)) in potato crops. A solution of thiosulfate was reduced to elemental sulfur, and the sulfur nanoparticles were coated with eucalyptus and rosemary essential oils with the three concentrations of 0.25%, 0.5%, and 0.75%. The samples were characterized by UV-visible spectroscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and scanning electron microscopy. The insecticidal efficacy of the nanocomposites was evaluated in the entomology laboratory 24, 48, and 72 h after application. Furthermore, efficacy was compared to the commercial insecticide thiamethoxam (0.25%) and a control. The results show that eucalyptus nanocomposites with oil concentrations of 0.25%, 0.5%, and 0.75% and rosemary nanocomposites with an oil concentration of 0.5% have an insecticidal efficacy of 100% for the control of insect nymphs 24 h after application. The insecticidal efficacy of rosemary nanocomposites with oil concentrations of 0.25% and 0.75% increases over time and reaches 100% at 24 and 72 h, respectively. The synthesized nanocomposites are more effective in controlling nymphs of paratrioza than the commercial insecticide thiamethoxam; thus, they could be used for the development of new insecticides.

Electron Doping of Proposed Kagome Quantum Spin Liquid Produces Localized States in the Band Gap.

Carrier doping of quantum spin liquids is a long-proposed route to the emergence of high-temperature superconductivity. Electrochemical intercalation in kagome hydroxyl halide materials shows that samples remain insulating across a wide range of electron counts. Here we demonstrate through first-principles density-functional calculations, corrected for self-interaction, the mechanism by which electrons remain localized in various Zn-Cu hydroxyl halides, independent of the chemical identity of the dopant-the formation of polaronic states with attendant lattice displacements and a dramatic narrowing of bandwidth upon electron addition. The same theoretical method applied to electron doping in cuprate Nd_{2}CuO_{4} correctly produces a metallic state when the initially formed polaron dissolves into an extended state. Our general findings explain the insulating behavior in a wide range of "doped" quantum magnets and demonstrate that new quantum spin liquid host materials are needed to realize metallicity borne of a spin liquid.

Optically induced metastability in Cu(In,Ga)Se2.

Cu(In,Ga)Se2 (CIGS) is presently the most efficient thin-film photovoltaic technology with efficiencies exceeding 22%. An important factor impacting the efficiency is metastability, where material changes occur over timescales of up to weeks during light exposure. A previously proposed (V Se -V Cu ) divacancy model presents a widely accepted explanation. We present experimental evidence for the optically induced metastability transition and expand the divacancy model with first-principles calculations. Using photoluminescence excitation spectroscopy, we identify a sub-bandgap optical transition that severely deteriorates the carrier lifetime. This is in accordance with the expanded divacancy model, which predicts that states below the conduction band are responsible for the metastability change. We determine the density-capture cross-section product of the induced lifetime-limiting states and evaluate their impact on device performance. The experimental and theoretical findings presented can allow assessment of metastability characteristics of leading thin-film photovoltaic technologies.

Surface origin of high conductivities in undoped In2O3 thin films.

The microscopic cause of conductivity in transparent conducting oxides like ZnO, In{2}O{3}, and SnO{2} is generally considered to be a point defect mechanism in the bulk, involving intrinsic lattice defects, extrinsic dopants, or unintentional impurities like hydrogen. We confirm here that the defect theory for O-vacancies can quantitatively account for the rather moderate conductivity and off-stoichiometry observed in bulk In{2}O{3} samples under high-temperature equilibrium conditions. However, nominally undoped thin-films of In{2}O{3} can exhibit surprisingly high conductivities exceeding by 4-5 orders of magnitude that of bulk samples under identical conditions (temperature and O{2} partial pressure). Employing surface calculations and thickness-dependent Hall measurements, we demonstrate that surface donors rather than bulk defects dominate the conductivity of In{2}O{3} thin films.

Magnetism without magnetic ions: percolation, exchange, and formation energies of magnetism-promoting intrinsic defects in CaO.

We investigate theoretically the prospects of ferromagnetism being induced by cation vacancies in nonmagnetic oxides. A single Ca vacancy V(0)(Ca) has a magnetic moment due to its open-shell structure but the ferromagnetic interaction between two vacancies extends only to four neighbors or less. To achieve magnetic percolation on a fcc lattice with such an interaction range one needs a minimum of 4.9% vacancies, or a concentration 1.8 x 10(21) cm(-3). Total-energy calculations for CaO show, however, that due to the high vacancy formation energy even under the most favorable growth conditions one can not obtain more than 0.003% or 10(18) cm(-3) vacancies at equilibrium, showing that a nonequilibrium vacancy-enhancement factor of 10(3) is needed to achieve magnetism in such systems.