Difference between Voltage Bias in STM/STS vs. Electrochemical Cell

[DannyL]

Hello Everyone,
I am a student studying electrochemistry – specifically energy storage devices. I have been familiarizing myself with various techniques to characterize the electrode surfaces. In particular, I am interested Scanning Tunneling Microscopy (STM) / Scanning Tunneling Spectroscopy (STS).

It appears that STM/STS can be used to measure the band-gap of semi-conductors by taking the derivative of the i-V curve in order to obtain a plot of “differential conductance” as a function of bias voltage. Where the potential region where dI/dV equals zero is taken to be the band-gap.

Usually when I see the term “voltage”, I think of an electrochemical cell (anode, cathode, electrolyte). However, the voltage between an anode and cathode in solution is referenced to some redox couple (vs. SHE or Li/Li+ or Ag/AgCl, for example).

In STM/STS, I know that the voltage bias is between the tip and the sample. However, no electrolyte is involved. Therefore, I cannot convert between potential scales (for example SHE => Li/Li+).

I would like to study semi-conducing materials as potential electrodes for energy storage. However, when I apply a potential to these materials (for example to intercalate lithium) I need to know that the potential range will not be within the band-gap.

My question is:
How can I compare the voltage bias measured using STM/STS against the applied voltage of an electrochemical cell?

Thanks!
Dan

 

[eljose79]

Dear Dan,

Thank you for your interest in electrochemistry and energy storage devices. I am glad to hear that you are familiarizing yourself with various techniques for characterizing electrode surfaces, including Scanning Tunneling Microscopy (STM) and Scanning Tunneling Spectroscopy (STS).

You are correct in your understanding that STM/STS can be used to measure the band-gap of semi-conductors by taking the derivative of the i-V curve to obtain a plot of "differential conductance" as a function of bias voltage. This technique is commonly used to study the electronic properties of materials, including semiconductors.

In terms of comparing the voltage bias measured using STM/STS against the applied voltage of an electrochemical cell, there are a few things to consider. Firstly, it is important to keep in mind that the voltage bias in STM/STS is between the tip and the sample, whereas the voltage in an electrochemical cell is between the anode and cathode. This means that the voltage scales are not directly comparable.

However, one way to compare the two is to use the work function of the material being studied. The work function is the minimum energy required to remove an electron from the surface of a material. This can be measured using STM/STS and can serve as a reference point for comparing the voltage scales.

Another approach is to use a reference electrode in your STM/STS measurements. This can be a metal electrode, such as platinum or gold, which can be used to establish a reference potential. This reference potential can then be used to convert between potential scales, such as SHE, Li/Li+, or Ag/AgCl.

I hope this helps answer your question. Good luck with your studies and research on energy storage devices.