Ultrafast terahertz photoconductivity of bulk heterojunction materials reveals high carrier mobility up to nanosecond time scale

The few-picosecond (ps) decay of terahertz (THz) photoconductivity typically observed for conjugated polymer:fullerene blends (at excitation fluencies ~10(15) photons/cm(2) per pulse) is shown to be a result of charge pair annihilation for two polymer:PCBM blends. At a factor of 100 lower excitation density, the THz decay is in the hundreds of ps time scale, implying that very high carrier mobility (~0.1 cm(2) V(-1) s(-1)) prevails for long time after charge formation, of importance for free charge formation in organic solar cells.     

Mechanistic modeling of arsenic retention on natural red earth in simulated environmental systems

Arsenic retention on natural red earth (hereafter NRE) was examined as a function of pH, ionic strength, and initial arsenic loading using both macroscopic and spectroscopic methods. Proton binding sites on NRE were characterized by potentiometric titrations yielding an average pH(zpc) around 8.5. Both As(III)- and As(V)-NRE surface configurations were postulated by vibration spectroscopy. Spectroscopically, it is shown that arsenite forms monodentate complexes whereas arsenate forms bidendate complexes with NRE. When 4相似文献   

Non-electroactive electrode coatings formed by electrochemical polymerization

Platinum and gold electrodes are coated with thin, adherent polymer layers by the oxidation of divinylbenzene, 4-vinylpyridine, or phenol, and by the reduction of N-methyl-4-vinylpyridinium salts. All depositions are performed in acetonitrile electrolytes. The neutral polymer coatings derived from the first three monomers affect the cyclic voltammetry of reversible redox couples by controlling the rate of diffusion to the electrode surface. The neutral form of a redox couple penetrates the coating more rapidly than the charged form. Extreme negative potentials cause a marked swelling of the coatings; the swelling is partially reversible. An anomalous prewave appears for ferrocene oxidation. The cationic polymer coating derived from N-methyl-4-vinylpyridinium traps ferrocyanide electrostatically.     

Enhancement and quenching of fluorescence of metal chelates of 8-hydroxyquinoline-5-sulfonic acid

Fluorescence enhancement of 8-hydroxyquinoline-5-sulfonic acid complexes of Mg, Ca, Sr, Ba, Al, Zn and Cd were studied in micellar and hydroorganic solvents. Al is extraordinarily amenable to both types of fluorescence enhancement, an order of magnitude to two order of magnitude enhancement of fluorescence intensity has been observed with aqueous hexadecyltrimethylammonium chloride (HTAC) and certain mixed aqueous-organic solvents. Fe(III) appears to be an unusually powerful fluorescence quencher in these systems — the effect is noticeable in low micromolar concentrations and is greatly amplified by cationic surfactants such as HTAC.     

Pulsed reagent introduction through a membrane reactor for flow-injection systems

A method of intermittent reagent introduction, functionally equivalent to stop-go pumping, is described. A pneumatically pressurized reagent reservoir is used to deliver liquid through a high-speed on/off valve to the outer channel of an annular tube assembly. Except for this single entry point, the outer channel is otherwise sealed. The inner flow channel bearing the principal flow stream contains a short microporous membrane tube. When the reagent delivery valve is activated, reagent flows radially inward through the membrane into the principal flow stream.