Contrast in EFM phase images

Melania Reggente posted on Fri, Jul 4 2014 4:58 AM

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Dear All,

my name is Melania Reggente. I am a PhD student at Sapienza University of Rome. I’m working with EFM using ICON microscope with NanoScopeV. While the acquisition of EFM images is straightforward, I’m having some problems with the interpretation of EFM phase images and I need some assistance. 

I’m using a conductive sample with a sort of array of tips. The tip is conductive. I’ve checked the electric contact between the tip and sample. Now, when imaging such a sample, in EFM phase images the tips are brighter than flat areas. The effect is actually electric as the contrast increases when increasing the tip-sample bias voltage. What seems actually not physical is the sign of the contrast. Indeed, in correspondence of the tip the field should be more intense, leading to bigger tip-sample electrostatic force which should be attractive. So, I expected that the tips were darker in phase images which is actually the opposite of what I observe. Also, I did similar measurements using another AFM instrument – the overall quality of which is really much lower than that of ICON – but the contrast I observe is the “correct” one (tips darker than the flat areas).

I wonder if I’m doing something wrong, maybe in the settings.

Looking forward to receiving your indication.

Sincerely yours,

Melania Reggente