The ability to manipulate nanoscopic matter precisely is critical for the development of active nanosystems. Optical tweezers are excellent tools for transporting particles ranging in size from several micrometres to a few hundred nanometres. Manipulation of dielectric objects with much smaller diameters, however, requires stronger optical confinement and higher intensities than can be provided by these diffraction-limited systems. Here we present an approach to optofluidic transport that overcomes these limitations, using sub-wavelength liquid-core slot waveguides. The technique simultaneously makes use of near-field optical forces to confine matter inside the waveguide and scattering/adsorption forces to transport it. The ability of the slot waveguide to condense the accessible electromagnetic energy to scales as small as 60 nm allows us also to overcome the fundamental diffraction problem. We apply the approach here to the trapping and transport of 75-nm dielectric nanoparticles and lambda-DNA molecules. Because trapping occurs along a line, rather than at a point as with traditional point traps, the method provides the ability to handle extended biomolecules directly. We also carry out a detailed numerical analysis that relates the near-field optical forces to release kinetics. We believe that the architecture demonstrated here will help to bridge the gap between optical manipulation and nanofluidics.
We present a new solvent system which has the potential to overcome the manufacturing barriers associated with the currently used toxic high boiling point solvents.
Optoelectronic properties are unraveled for formamidinium tin triiodide (FASnI ) thin films, whose background hole doping density is varied through SnF addition during film fabrication. Monomolecular charge-carrier recombination exhibits both a dopant-mediated part that grows linearly with hole doping density and remnant contributions that remain under tin-enriched processing conditions. At hole densities near 10 cm , a strong Burstein-Moss effect increases absorption onset energies by ≈300 meV beyond the bandgap energy of undoped FASnI (shown to be 1.2 eV at 5 K and 1.35 eV at room temperature). At very high doping densities (10 cm ), temperature-dependent measurements indicate that the effective charge-carrier mobility is suppressed through scattering with ionized dopants. Once the background hole concentration is nearer 10 cm and below, the charge-carrier mobility increases with decreasing temperature according to ≈T , suggesting that it is limited mostly by intrinsic interactions with lattice vibrations. For the lowest doping concentration of 7.2 × 10 cm , charge-carrier mobilities reach a value of 67 cm V s at room temperature and 470 cm V s at 50 K. Intraexcitonic transitions observed in the THz-frequency photoconductivity spectra at 5 K reveal an exciton binding energy of only 3.1 meV for FASnI , in agreement with the low bandgap energy exhibited by this perovskite.
Reproducibility issues of perovskite materials and devices stem from their extreme sensitivity to fractional, quite possibly unintentional, deviations in the precursor solution stoichiometry.
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