The Nanoscale World

STS curve using lock-in amplifier

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Ki-Rak Kim posted on Mon, Jan 24 2011 3:20 PM

 Dear all:

Now I am using scanning tunneling microscopy and added lock-in amplifier to get STS curve. I want to reduce noise and get dI/dV curve. I got some help from expert who had used STS about connection of lock-in amplified with STM system. I followed him as shown in the picture below, but my STM system does not work properly. I have some problem to operate STM after connection. The software (Nanoscope) always says that tip was engaged from the begining of experiment even the tip was not moved at all. When I turn the toggle switch (from Signal Access Module III, SAM III) of the 'bias' from left (input) to the right (output), the tip moves properly.

My questions are;
1) Is the connection good to use STM and STS? And can I get a dI/dV curve with this connection?
2) Why it always fails to engage the tip with toggle switch 'input'?
3) Which software should I use to get modified curve, Nonoscope or Acquire?
4) If I should use Acquire, which parameter I should choose to get dI/dV curve?
    X axis: I need bias voltage, but software has (Osc Freq, Osc Amplitude, DAC 1-4 voltage, and Digital port)
    Y axis: The need current depend on bias. But there are no current (amp).

Thank you very very much.
Ki-Rak Kim


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Bruker Employee

Dear Ki-Rak,

Can you send me the manual for the Lock-in Amplifier you are using, I'd like to know what exactly are ADC1, ADC2, A, OSC Out.

Here is my guess:

  • ADC1 is to read in the modulated data, in this case, tunneling current.
  • OSC Out is the AC drive signal, in this case, the dV.
  • "A" got be the measured oscillation amplitude, here, dI.

If the above is right, then you need to change your connection as follows:

  • Disconnect ADC2<->Bias Out (I suppose you want to use the Bias Out as the reference, but you do not need to as the ac drive is generated by the Lock-In amplifier)
  • Disconnect A<->In0 Out (looks like you are shorting the STM current with the dI)
  • Connect A<->AuxA input on the SAM (this is to feed you measured dI for Nanoscope to read and display; if AuxA is not available in the software, then you can try AuxB, or AuxC, or AuxD)

When you run I-V, one channel would still be Current vs Bias (I-V); the 2nd channel AuxA vs Bias (dI/dV - V).

The other thing you may try is: with the modified connection, toggle to "Bias Input" only after engage and when you are running I-V.

Try the above, and we go from there.

Best regards


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Bruker Employee

Dear Ki-Rak,

I read the manual of the lock-in amplifier (model Recovery 7265), my guesses about the signals are incorrect in my previous response, so please disregard it.

The connection diagrams you proposed is correct, albeit may be incompete.  It is possible to set it up for either or both Nanoscope or Aquire to read and display I~V and dI/dV~V curves. Lets focus on the former. The first and foremost is to make sure tip will engage the sample surface.

Connections between the Lock-in and SAMIII, based on your diagram:

  • Disconnect IN0 Output<->ADC1 (the connection is not wrong, but lets do this for now so to simplify the settings),
  • Disconnect Bias Output<->ADC2 (again, the connection is not wrong, but lets do this for now so to simplify the settings).
  • Connect CH1 to AuxA.

Settings on the Lock-in side:

  • Set in "Single Reference" mode and use INTERNAL reference, page 51 of the manual.
  • Set CH1, CH2 to be R and Ө respectively.
  • Set the Internal Oscillator frequency to be 1000Hz, and Amplitude 10mV (for initial testing, optimization can be made later).

Toggle switch positions on SAMIII:

  • Bias: Input
  • IN0: Output
  • AuxD: Input

Question and suggestions about your "Adder"

  • Where does your "Adder" get power (+/- 15V, ground) from?

Signal check / diagnosis: use a Oscilloscope to

  • Check the output of the adder to see whether it correctly adds the DC part (Bias from SAMIII) and AC part (the oscillation output from the Lock-in).
  • Check IN0 Output to see the tunneling current, when tip is far away (not engaged), current should stay near 0.

Our goal for this first step is to make sure tip will engage. We will get to data acqusition and display in the follow-up communication.



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Thank you very much, Dr. Li.

Your reply and phone call helped me a lot. I follwed your advice and finish to set it up. Now I can engage the tip properly.

But dI/dV curve still has a lot of noise. And there's no difference with and without lock-in amplifier.

I am going to talk to another technician from Veeco today. I hope I can solve every problems today.

Thank you again.

Ki-Rak Kim

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Top 25 Contributor
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Bruker Employee

Dear Ki-Rak,

Thanks for the update. I'd like to recap some points discussed during the phone call:

  • During imaging, please set the Oscillation Amplitude to "0" on the Lock-in, otherwise "noise" would appear in the image, a manifestation of current response to the modulated bias.
  • In STS (I-V) mode, never use "Feedback Type: Pixel", if you do, then the feedback will be on while Bias is ramped and modulated, it would try to adjust z position to cancell the change in current caused by the modulation in Bias. Instead, use "Feedback Type: Cycle or Ramp"
  • For STS display:
    • Channel1: Data Type: Current (I ~V)
    • Channel2: Data Type: AuxA (dI ~ V)
  • AuxA is represented in V by default, it should be in the unit of current. Here is how to change that: Microscope->Calibrate->Detectors: AuxA: 10nA/V (the same as the current sensitivity for STM)

To reduce the nosie on dI/dV, you can use a bigger Oscillation amplitude. Note, if the I-V is noisy, then dI/dV will be too.


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Dear Chunzeng,

I have the same problem about connecting like  Ki-Rak.

below is my Instrument and connect: 


  1. My microscopy is Nanoscope IIIa (mutillmode)
  2. SAM (DI).
  3. lock-in Amplifier: SR830 (If you need manual I can sent to you)
  4. adder (home made)
  5. sample: HOPG
  6. connecting by myself (refer to above your conversation) :
  • Connect
    • adder (bias output from SAM& SINE OUT form lock-in Amp) output<->bias input on the SAM   
    • In0 output on the SAM<-> A/I on the lock-in Amplifier
    • CH1 output<->AuxA input on the SAM
  • Toggle switch positions on SAM:
    • bias: input
    • In0: output
    • AuxA: input

For lock-in Amplifier setting:

 Oscillator frequency to be 3000Hz, and Amplitude 20mV

For STS display:

Channel1: current (I~V)

channel2: AuxA (dI/dV~V ?(I'm not sure...))


My questions are:

  1. The connection are correct?
  2. why STS display are just noise (channel 1: only horizontal sin wave; (channel 2 only noise )?
  3. If connection are correct, what setting should I check on my software(nanoscope 5.30r3sr3)?

Thank you a lot!




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