Since it was first evidenced in 1995, light-induced mass motion in layers of azobenzene-containing molecules has ledtodiverging interpretations, and it remains partly unexplained. In this paper, we discuss a light-driven randomwalk model where moving chromophores drag the molecule to which they are grafted. It consists in a diffusion motion of the azobenzene functions where each random step follows an isomerizing absorption. After a summary of the main characteristics of the motion, we present the hypotheses of the model and we show how it suits the experimental observations reported. In the frame of this model, where each azobenzene function is put in motion by light, we assess the distance over which an azobenzene-containing molecule can be dragged. We also estimate the energetic output of this dragging process. Finally, we discuss the microscopic origin of these molecular motors and we compare it to the model of thermal ratchets introduced by Feynman and extensively resorted to in Biology nowadays.

Mixed self-assembled monolayers SAMs Ž.consisting of n-alkylthiol andror 11-mercapto1-undecanol are produced and investigated by Scanning Tunnelling Microscopy STM Ž.in picoampere regime. Such systems allow the creation of surfaces with tuned chemical properties. We investigate both the qualities of the organic films and their electron transport properties. We evidence a contact regime and measure the decay lengths both in the film and in the tunnelling gap.

Gold atomic point contacts are prototype systems to evidence ballistic electron transport. The typical dimension of the nanojunction being smaller than the electron-phonon interaction length, even at room temperature, electrons transfer their excess energy to the lattice only far from the contact. At the contact however, favored by huge current densities, electron-electron interactions result in a nano hot electron gas acting as a source of photons. Using a home built Mechanically Controlled Break Junction, it is reported here, for the first time, that this hot electron gas also radiates in the infrared range (0.2eV to 1.2eV). Moreover, in agreement with the pioneering work of Tomchuk [1],we show that this radiation is compatible with a blackbody like spectrum emitted from an electron gas at temperatures of several thousands of Kelvin given by (kB.T e) 2 = α.I.V where α, I and V are respectively a fitting parameter, the current flowing and the applied bias.

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