Scanning eddy current dynamometer with 100 mm resolution

We report on a new contactless scanning probe technique to probe thin metallic films. The scanning eddy current dynamometer ~SECD! is based on the measurement of the force generated by a magnetic tip oscillating in close proximity to a conducting thin film glued to a high-Q mechanical oscillator. By measuring the resonant motion induced in the mechanical oscillator, the eddy current force on the sample can be determined. The size of the magnetic field profile from our tip limits the spatial resolution of the instrument to ' 100 mm. This spatial resolution is demonstrated by scanning the magnetic tip over inhomogeneities in metallic films. For a homogeneous metallic film much larger than 100 mm the force measured by the SECD is directly proportional to the conductance of the film. In this configuration the equivalent noise conductance of the eddy current dynamometer is Dsh'30 V . By exploiting the boundary conditions on the induced current density in the conducting film, cracks much smaller than 100 mm in a metallic film can be detected. To demonstrate this property, a 2.5 mm wide slit is detected using the SECD. © 2000 American Institute of Physics. @S0034-6748~00!00608-0#