Methods to stabilize scanning tunneling microscope(STM)

In summary, when the STM becomes unstable, you should try varying the bias voltage, current, gain, time constant, and applying voltage pulses. However, you may find that nothing works, and the best solution is to vary the tip-to-sample distance.
  • #1
3
0
When the STM becomes unstable(large variations in the current), what procedures should I take in order to fix it?

I am new to the STM, but after a few month`s experience I notice that one of the main problems is stabilizing it.

When the tunneling current becomes unstable, I`ve tried to vary the bias voltage, current, gain, time constant, and applying voltage pulses. I find that applying pulses much higher than the bias voltage seems to be most effective.

However, there are times when nothing works, and the topographic image lines can vary in orders of tenths of nanometers, with no similarity in the left and right scan directions.

How much does sample preparation affect the STM measurement? I have to prepare my samples on HOPG in ambient conditions. To avoid contamination, I heat the sample after preparation of HOPG, then I dry in a vacuum dessicator. If there are more efficient methods, I`m willing to hear all advices.
 
Physics news on Phys.org
  • #2
Have you tried varying the tip-to-sample distance?

Zz.
 
  • #3
Yes, I`ve tried that a few times, but it did not work.

I suspect that it has something to do with sample preparations, because samples prepared in ultra high vacuum by evaporation seem to exhibit nice images with roughness less than 10 pm.
My samples are carbon nanotubes, thus they cannot be evaporated, all I can do is deposit them onto a substrate in ambient conditions.
Once in a while, I have been able to observe high resolution, but upon scanning twice in the same area, the images became unstable.
 
  • #4
Yesterday I found one method that worked.

The left-right scan image lines bared no resemblance and the roughness was in orders of tenths of nanometers.
At the time I was observing at 0.7 nA and 1.8 V. I increased the voltage to 3.00 V and the current to 2.0 nA. After scanning for sometime, part of the tip drops onto the substrate and the tip tracks it much more easily. I then slowly decrease the current, then the voltage back to normal scanning conditions, and moved to observe a clean area.

The system was more stable with height variations below 200 pm. I tried this a few more times when it became unstable, and although it did not yield the best results everytime, the system always became more stable.
 

What is a scanning tunneling microscope (STM)?

A scanning tunneling microscope (STM) is a scientific instrument that allows for the visualization and manipulation of individual atoms on a surface. It uses a sharp probe to scan a surface and measures the flow of electrons between the probe and the surface, creating a topographic image of the surface with atomic resolution.

Why is it important to stabilize an STM?

Stabilizing an STM is crucial for obtaining accurate and reliable results. Any vibrations or movements can affect the positioning and stability of the probe, leading to distorted images and inaccurate measurements. Additionally, stabilizing the STM allows for longer scan times and better control over the manipulation of individual atoms.

What are some common methods used to stabilize an STM?

There are several methods used to stabilize an STM, including vibration isolation systems, active feedback control, and temperature stabilization. Vibration isolation systems use mechanical or magnetic systems to reduce external vibrations. Active feedback control uses piezoelectric elements to make constant adjustments to the probe position, compensating for any movements. Temperature stabilization involves maintaining a constant temperature to reduce thermal drift.

How does active feedback control work in stabilizing an STM?

Active feedback control in an STM involves using piezoelectric elements to make small, constant adjustments to the probe position. These adjustments are based on the feedback from the STM's sensors, which detect any movements or vibrations. By constantly making adjustments, the probe position can be stabilized, allowing for more accurate and precise measurements.

What are some challenges in stabilizing an STM?

One of the main challenges in stabilizing an STM is reducing external vibrations from the surrounding environment. This can be especially difficult in a laboratory setting where there may be other equipment or people moving nearby. Additionally, temperature changes can also affect the stability of the STM, making temperature stabilization an important aspect of the stabilization process.

Similar threads

  • Quantum Physics
Replies
1
Views
863
Replies
1
Views
2K
  • Atomic and Condensed Matter
Replies
1
Views
4K
  • Introductory Physics Homework Help
Replies
1
Views
2K
  • Advanced Physics Homework Help
Replies
2
Views
2K
  • Introductory Physics Homework Help
Replies
1
Views
3K
Replies
1
Views
1K
Replies
8
Views
7K
Replies
5
Views
6K
  • Advanced Physics Homework Help
Replies
2
Views
4K
Back
Top