The Nanoscale World

# Direction of current in C-AFM

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5 Posts
Points 58
weil posted on Tue, Mar 1 2011 11:36 PM

Hi!

We are using C-AFM to create a current map based on piezoelectric effect by applying different deflection setpoint. Although we could get a contrast in the current map, we are not sure about the direction of the current (flowing into the sample from the tip or flowing out the sample into the tip) based on the current map. Hence, may I know if we could tell the direction of the current based on the contrast on current map? Thanks!

The current map shows negative and positive current values in the software "nanoscope analysis 1.2", but i am skeptical about this. We are using an Multimode SPM with C-AFM application module and no voltage bias was applied during the experiment.

• | Post Points: 14

replied on Wed, Mar 2 2011 3:14 PM
Verified by weil

Maybe a good experiment is to put a resistor (MOhm or so) in between the the tip and sample. That way you can actually verify the tip-sample voltage and convince yourself about the direction of current by performing e.g. an I/V curve.

Stefan

• | Post Points: 11

#### All Replies

replied on Wed, Mar 2 2011 3:14 PM
Verified by weil

Maybe a good experiment is to put a resistor (MOhm or so) in between the the tip and sample. That way you can actually verify the tip-sample voltage and convince yourself about the direction of current by performing e.g. an I/V curve.

Stefan

• | Post Points: 11
55 Posts
Points 831
Chunzeng Li replied on Thu, Mar 3 2011 1:36 PM

The C-AFM polarity convention with Multimode is: positive current means the current is flowing from the sample to the tip. Another way to say this is: if you use a positive sample bias, you would read a posistive current.

When you say there is "no" bias applied, ideally that means 0 V. But no system is ideal, there is always some noise in the system to make the actual bias fluctuating around 0 resulting in small negative or psoitive bias. You can see then your current can go either way: from tip to sample or vice versa. To avoid this ambiguity, it is adviceable to use a bias, for instance, bigger than 10mV.

Chunzeng

5 Posts
Points 58
weil replied on Thu, Mar 3 2011 8:59 PM

Thanks for the suggestion and opinions. Our sample is an insulator (the resistivity is around 10e15), so at first we thought the bias wont make much different to the measurement we are doing. In fact, very little change has been observed even we applied a -12volt sample bias. I guess we would try to connect an external circuit to measure the voltage output. Again, thanks for the help.

• | Post Points: 12
replied on Fri, Mar 4 2011 3:48 PM

You are welcome. good luck with your experiments.

Stefan

• | Post Points: 10
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