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A virtual NC − AFM machine has been built using the Matlab language. The virtual NC − AFM is identical to a real hybrid machine built with Digital Instruments and Omicron blocks. The role of every subset is described in detail, and special attention is paid to the parameters of the Automatic Gain Control (AGC) which controls the amplitude of the oscillations. The virtual machine is a powerful tool, that allows to solve, without any approximation, non linear coupled differential equations describing the physics of the tip-surface interaction. The machine is then used to study the frequency shift and damping signal in the approach-retract mode. Two types of situations are analyzed: the first one corresponds to the case where no dissipative force is introduced in the tip-surface interaction, the second one deals with dissipative forces. These last ones are here introduced by assuming a mechanical deformation of the surface under the tip. Interesting results are then obtained, in particular the fact that unstability may occur under some particular conditions. Most of the results obtained by simulation are then compared with those of analytical models already published in the literature.

International audience; no abstract

International audience; no abstract

International audience; no abstract

International audience; Using sub-picosecond CARS experiment we observed direct photolysis of liquid nitromethane after pulse excitation at 299 nm. We measured the dynamic behaviour under excitation of three main ground state Raman lines at 917 cm-l, 1400 cm-l and 2968 cm-1. We deduced an excited state lifetime of 1.1 +/- 0.3 ps and we measured a photolysis quantum yield at 299 nm of 24% +/- 5%. Using "pump-probe" experiments we observed the evolution of excited states of eight nitro-stilbene derivatives including 2,4,6,2',4',6'-hexanitro-stilbene (HNS). In the studied compounds important non-radiative desexcitation channels have been observed and their possible role on explosive process is discussed.

no abstract

International audience; no abstract