Voltage on a quadrant photodiode used with an AFM

In summary, the operation of an AFM in tapping mode involves the use of a quadrant photo-diode to measure the deflection of the laser beam as the tip travels over a single carbon nano-tube on a flat surface. The changing voltage of the piezoelectric actuator corresponds to different heights and affects the voltage on the photo-diode in each quadrant. Understanding the setup and drawing a sketch is necessary before finding relevant equations for the system.
  • #1
Phantoful
30
3

Homework Statement


An AFM uses a quadrant photo-diode to measure the deflection of the laser beam. Sketch the voltage in quadrants A, B, C and D as the tip travels on top of a single carbon nano-tube resting on a flat surface when the AFM is operating on tapping mode.
DDI7esS.jpg

Homework Equations


Not sure what to use, or if this is a conceptual problem.
λ= 1.2 / V1/2
λ = h/p

The Attempt at a Solution


I know that the AFM (and the piezoelectric actuator) would have a changing voltage to account for different heights and such, but how does that relate to what voltage is on the photo-diode? How can there be a specific voltage for each quadrant, I'm not getting that.
 

Attachments

  • DDI7esS.jpg
    DDI7esS.jpg
    74.2 KB · Views: 571
Physics news on Phys.org
  • #2
Did you draw a sketch of the setup? Before finding relevant equations you'll have to understand what leads to a different current in the quadrants.
 

1. What is a quadrant photodiode and how is it used with an AFM?

A quadrant photodiode is a type of semiconductor device that is used to measure the position of a laser spot on a surface. It is often used in conjunction with an Atomic Force Microscope (AFM) to detect changes in the surface height as the tip of the AFM probe moves over the sample.

2. How does the voltage on a quadrant photodiode relate to the position of the AFM probe?

The voltage on a quadrant photodiode is directly proportional to the position of the AFM probe on the sample surface. As the probe moves, the laser spot on the photodiode will shift, resulting in a change in voltage output.

3. What factors can affect the voltage output of a quadrant photodiode on an AFM?

The voltage output of a quadrant photodiode can be affected by several factors, such as the intensity of the laser, the angle at which the laser hits the photodiode, and any interference or noise in the system. Environmental factors such as temperature and humidity can also impact the voltage output.

4. How is the voltage signal from a quadrant photodiode processed and interpreted in an AFM?

The voltage signal from a quadrant photodiode is processed by a computer or data acquisition system attached to the AFM. This signal is then converted into a 2D image of the sample surface, with changes in voltage corresponding to changes in height.

5. Can the voltage on a quadrant photodiode be used to measure other properties besides surface height?

Yes, in addition to measuring surface height, the voltage on a quadrant photodiode can also be used to measure other properties of a sample, such as surface roughness and surface charge. This is because changes in these properties can also affect the voltage output of the photodiode.

Similar threads

Quadrant photodiode selection advice
    • Electrical Engineering
Replies
1
Views
1K
Textbooks on Condensed Matter Physics
    • Science and Math Textbooks
Replies
19
Views
17K

Hot Threads

Recent Insights

Back
Top