13 June 2005 Local measurements by noise in dynamic force microscopy
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The micromechanical cantilevers have become a powerful tool for the study of forces on nanoscale and serves as the heart of the Atomic Force Microscope (AFM) and of all the Scanning Force Microscopes designs on this basic idea. These micromechanical cantilevers are forced to not negligible thermomechanical oscillations at room temperature induced by the thermal noise, which is a Brownian motion. These oscillations impose a fundamental limit to the accuracy of force detection setups in AFM. However these thermomechanical oscillations can be analyzed in order to obtain information about the tip-sample interaction. Several publications have been presented in the last years describing the evolution of the resonant frequency of the microcantilevers through the spectral power density in the case of non-contact behavior or by studying liquids or gas samples, with the standard optical lever technique. They have observed that it is impossible to detect the resonant frequency by this way in the case of contact with hard samples. Here we report on the investigation of mechanical sample properties by analysis of the thermomechanical noise of the first symmetric eigenmodes of a rectangular microcantilever. The presented work is the first study demonstrating the possible detection of the first flexural vibration modes of the microcantilever in contact with hard samples, by optical probing of the thermomechanical noise. By Analyzing the spectral density of the thermomechanical fluctuations attributed to the first symmetric flexural vibrational modes of the surface-coupled cantilever, the longitudinal stiffness of the tested sample can be obtained.
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Pascal Vairac, Pascal Vairac, Bernard Cretin, Bernard Cretin, Benjamin Joly, Benjamin Joly, } "Local measurements by noise in dynamic force microscopy", Proc. SPIE 5856, Optical Measurement Systems for Industrial Inspection IV, (13 June 2005); doi: 10.1117/12.612639; https://doi.org/10.1117/12.612639

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