Optical Transmission through thin films.

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Discussion Overview

The discussion revolves around determining the thickness of a 1nm nickel coating on zirconium using optical transmission and reflection data. Participants explore various methods and challenges associated with measuring such thin films, including the limitations of available equipment and techniques.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant inquires about using light transmission data to ascertain the thickness of the nickel coating, noting the lack of access to AFM for direct measurement.
  • Another participant questions whether the transmission coefficient is known as a function of wavelength and expresses skepticism about obtaining useful data from a reflectance spectrum at 1nm thickness.
  • A suggestion is made to use reflection and transmission spectra to determine the thickness, with a recommendation to illuminate the sample with a laser to observe interference patterns.
  • A counterpoint is raised that interference fringes would not be observable due to the thinness of the film relative to the wavelength of light.
  • One participant acknowledges the wavelength of light as several hundred nm, reinforcing the argument against observing fringes.
  • A participant mentions finding data online for transmission versus wavelength for thicker films and considers fitting a function to predict the thickness of their film.
  • Concerns are raised about the accuracy of measurements due to potential error bars encompassing both 1nm and 0nm thicknesses.
  • Another participant shares a similar experience with measuring thin nickel films on an Al203 substrate, noting challenges with the transmission/reflection technique and possible interference from surface adsorbates.
  • Interest is expressed in the AFM technique for measuring film thickness, with a request for clarification on its operation.
  • A participant humorously reflects on their shift from hands-on science to a managerial role, questioning their earlier suggestion about interference fringes.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of using optical methods to measure the thickness of the 1nm film, with some suggesting potential techniques while others highlight significant limitations. The discussion remains unresolved regarding the best approach to accurately determine the film thickness.

Contextual Notes

Participants note limitations related to the thinness of the film, the wavelength of light, and the potential impact of surface adsorbates on measurement accuracy. There is also uncertainty regarding the applicability of certain techniques given the film's thickness.

G01
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Hello everyone.

I have some zirconium that is coated with 1nm of Ni. Now, here's the problem: I don't know if the coating is actually 1nm and have to find out. I don't have access to our AFM today, so I can't use that. But I do have light transmission data from the sample. i.e. I know the percentage of light the coating transmits and the percentage reflected. If there any way I can use this to find the thickness of the metal film. Are there data tables somewhere that have information, such as optical transmission vs. thickness or something like that? Any help finding this information would be greatly appreciated.
 
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When you say you know the transmission coefficient, do you mean that you know it as a function of wavelength? Over what window? Anyway, at 1nm, I doubt you'll get anything useful out of a reflectance spectrum.

If you have access to a thermal/e-beam evaporator, you may be able to work with the thickness monitor - but for that, you'll first need the substrate without the film.
 
Do you know the thickness of the zirconium? From the two reflection spectra and the transmission spectrum, you should be able to find the thickness. Even better, illuminate with a laser and see the interference spectrum at off normal incidence, the spacing of the fringes will guide you in determining th ethickness.
 
Dr Transport said:
Even better, illuminate with a laser and see the interference spectrum at off normal incidence, the spacing of the fringes will guide you in determining th ethickness.
Will not work - there will be no fringes. Thickness of film = 1nm, wavelength of light = several nm.
 
More like several hundred nm for wavelength of light. But of course that just reinforces your point all that much more, Gokul.
 
Thanks for the advice guys! I'm think I may have found some data on google for %T vs. wavelength for different thicknesses, but all the data points are thicker than my films. Maybe I can plug some values for the wavelength I care about into excel and fit a function to them. Then I could use the function to predict my films thickness...
 
G01 said:
Thanks for the advice guys! I'm think I may have found some data on google for %T vs. wavelength for different thicknesses, but all the data points are thicker than my films. Maybe I can plug some values for the wavelength I care about into excel and fit a function to them. Then I could use the function to predict my films thickness...
Methinks, more than anything else, you attempt will be foiled by your error bars (i.e., that 1nm as well as 0nm will lie within the error bar).
 
I have had a very similar problem to this, I needed to varify thickness of thin Ni films on an Al203 substrate. The films are of the order you mentioned, I tried using a the transmission/reflection technique (F20 instrument by Filmetrics) but they tell me the films are really too thin for this. However I did get results within the region of the films but they all seemed much thicker, this was possibly due to surface adsorbates which I am am keen to measure the thickness of.

I'm interested in the AFM technique you mentioned, how does this work? I know what an AFM is, but how can you get it to determine film thicknesses?
 
Gokul43201 said:
Will not work - there will be no fringes. Thickness of film = 1nm, wavelength of light = several nm.

What was I thinking?, I been working as a program manager too long, time to get back to doing real science.
 
  • #10
gareth said:
I'm interested in the AFM technique you mentioned, how does this work? I know what an AFM is, but how can you get it to determine film thicknesses?
Put sample on its side - cleave/cut - image.
 

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