A three-dimensional reflectance scanning optical microscope based on the nonlinear optical phenomenon of second-harmonic generation is presented. A mode-locked Ti:sapphire laser producing <90-fs pulses at approximately 790 nm was used, and the images were constructed by scanning of an object, which possessed local second-order nonlinearity, relative to a focused spot from the laser. The second-harmonic light at approximately 395 nm generated by the specimen was separated from the fundamental beam by use of dichroic and interference filters and was detected by a photodiode. The technique was then used to characterize the distribution of second-order nonlinearity and microstructure of the nonlinear material lithium triborate.

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The kinetics of P680(+) reduction in oxygen-evolving spinach Photosystem II (PS II) core particles were studied using both repetitive and single-flash 830 nm transient absorption. From measurements on samples in which PS II turnover is blocked, we estimate radical-pair lifetimes of 2 ns and 19 ns. Nanosecond single-flash measurements indicate decay times of 7 ns, 40 ns and 95 ns. Both the longer 40 ns and 95 ns components relate to the normal S-state controlled Yz → P680(+) electron transfer dynamics. Our analysis indicates the existence of a 7 ns component which provides evidence for an additional process associated with modified interactions involving the water-splitting catalytic site. Corresponding microsecond measurements show decay times of 4 μs and 90 μs with the possibility of a small component with a decay time of 20-40 μs. The precise origin of the 4 μs component remains uncertain but appears to be associated with the water-splitting center or its binding site while the 90 μs component is assigned to P680(+)-QA (-) recombination. An amplitude and kinetic analysis of the flash dependence data gives results that are consistent with the current model of the oxygen-evolving complex.

Gold and silver nanoparticles functionalized at their surfaces with electron acceptor (TCNQ) and donor (TMPD) molecules were spray-deposited as thin films on highly ordered pyrolytic graphite (HOPG) substrates. Pure films and bilayer structures were investigated by means of scanning tunneling spectroscopy (STS). The pure films show symmetric current−voltage dependences, whereas the bilayer structures are characterized by a diode-like behavior with rectification ratios of up to 66 at ±75 mV for structures containing silver nanoparticles and 6.5 at ±1 V for analogous structures based on gold nanoparticles. Such properties have been previously described for molecular rectifiers containing electron acceptor and donor groups. Our results suggest that electronic structures of this type might be assembled alternatively through appropriate nanoscale architectures using sequential deposition of functionalized nanoparticles.