EFM phase shift signals mismatch in "scan" and "ramp" regimes

virggis posted on Mon, Mar 16 2015 11:23 AM

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Hi all,

I have a question about EFM measurements in "scan" and "ramp" modes. The strange thing is that EFM phase shift values in interleave (lift) mode on the same sample surface area are different. Below is the picture illustrating this mismatch. In the left side is the image of EFM phase difference distribution the surface of GaAs based device with p-n junction. Graph in the upper right corner is the cross section of the scan, the highlighted black dot is on the n-type region and light blue one is on the p-type region. When scanning  bias between the sample and SPM tip was -1V. After the scan point and shoot ramping was performed over the surface in the areas highlighted with the color dots in section graph. These ramp curves are shown in the lover right corner of the picture. In contrast to the phase shift values acquired in scan mode, the values of ramp mode (when bias = -1V ) significantly differs. Lift height in ramp mode was controlled by photodetector signal as feedback value. Is there some software problem, or the signals in phase channels in ramp and scan modes are not the same? For measurements the Dimension 3100/ Nanoscope IVa system was used with SCM-PIT probes. The software version NanosScope 6.14R1.