Magnetic force microscopy

The remarkable outbreak of nanotechnologies and among these of nanobiotechnologies has been allowed by the invention, development, continuous improvement of different techniques and instrumentations for the imaging of materials and systems at the nanoscale. Among such techniques, atomic force microscopy (AFM) represents a well established technique for the imaging of a wide range of samples as it requires minimal sample preparation and allows one to image the samples in air, liquid environment, or vacuum. In AFM, the sample is imaged by scanning it using a sharp tip placed at the end of a micromachined cantilever, the deflection of which is monitored through an optical lever system. The sample morphology can be reconstructed by recording the cantilever deflection during the scanning (contact mode) and in this case the interaction between the tip and the sample surface is continuous during the scanning. In order to reduce the tip-sample interaction time and thus the possibility of damaging the sample and contaminating the tip, which are serious limitations when imaging soft samples like polymers or biological materials, the sample morphology can be reconstructed also by monitoring the oscillation amplitude of the cantilever set into vibration. In this second case, the tip-sample interaction is limited to a fraction of the period of oscillation of the cantilever (intermittent contact or tapping mode). The unique possibility of ‘touching’ instead that ‘seeing’ the surface offered by AFM has stimulated the development of a wide number of techniques for the characterization of different functional properties beyond the topographical reconstruction. Indeed, force spectroscopy, qualitative imaging, and quantitative mapping can be performed to characterize mechanical, electric, electromechanical, magnetic, chemical, thermal properties surfaces and materials with nanometrical lateral resolution. Among these techniques, magnetic force microscopy (MFM) has been proposed for the imaging of magnetic domains at the nanoscale. Although the