SPM equipment

The STM/AFM unit (Unversial SPC 400 SPM, Park Scifentific Instruments) consisted of an electronic unit which provided both the scan control for scanning the tip over the surface and an electronic feedback loop maintaining a constant working distance between tip sample. Additionally a four-electrode bi-potentiostat that was connected to the control unit was capable of setting the potentials of both tip and substrate independently. This system allowed minimization of the electrochemical current flowing through the tip and hence could reduce the overall noise superposed on the tunneling current.

All AFM and STM topographic images were obtained in the mode of constant interaction. The distance modulation measurements were recorded by modulating the z-position of the piezo with a sinusoidal signal having an amplitude and frequency of 1 - 5 A and 1.5 kHz respectively.

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