A new azobenzene-thiophene molecular switch is designed, synthesized, and used to form self-assembled monolayers (SAM) on gold. An "on/off" conductance ratio up to 7 x 10(3) (with an average value of 1.5 x 10(3)) is reported. The "on" conductance state is clearly identified to the cis isomer of the azobenzene moiety. The high on/off ratio is explained in terms of photoinduced, configuration-related changes in the electrode-molecule interface energetics (changes in the energy position of the molecular orbitals with respect to the Fermi energy of electrodes) in addition to changes in the tunnel barrier length (length of the molecules). First principles density functional calculations demonstrate a better delocalization of the frontier orbitals as well as a stronger electronic coupling between the azobenzene moiety and the electrode for the cis configuration over the trans one. Measured photoionization cross sections for the molecules in the SAM are close to the known values for azobenzene derivatives in solution.

We address in this paper the issue of quantitative charge imaging of individually charged semiconductor nanoparticles on conductive substrates by electric force microscopy ͑EFM͒. An analytical model is proposed for arbitrary tip and nanoparticle geometries to determine the amount of stored charges from the ratio R between the nanoparticle charge and capacitive force gradients. The quantitative character of the model is validated by extensive numerical calculations of EFM signals using various nanoparticle shapes, sizes, and aspect ratios, and different EFM tip geometries.

Unveiling the charge storage mechanism of vanadium nitride to defy the limits of on-chip micro-supercapacitors.