| We present results on the interaction of a cantilever in the thermal oscillations regime with the force gradients near various kind of surfaces. As is well known, the power density spectrum of a cantilever freely oscillating in the absence of external modulation shows the thermal amplitude and resonance frequency of its flexural modes. As the tip approaches a surface, a frequency shift in the amplitude and resonance frequency of the thermally excited flexural modes is measured as a function of the tip-sample separation, until jump-to-contact sets in. After jump-to-contact, the power density spectrum of the cantilever fluctuations changes due to the fact it has a supported end. A comparison with available models permits to identify the flexural modes in the two situations (we detect four flexural modes for the free end cantilever and two for the supported end cantilever) and to extract information about the interaction force gradients. The mean vibration amplitude in the various flexural modes is in the range of 10-100 pm at room temperature, according to the stiffness of the cantilever. Finally, we describe the acquisition techniques and background requirements for the instrumentation. |
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