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Thin film/XRD question.

  1. Aug 23, 2009 #1
    I am trying to produce a thin film of VO2 using reactive ion sputtering and am having some issues. The main one is that I have no clue what is being deposited and exactly how think it is.

    I have been depositing the film on both Si(100) and glass slides. When I take a XRD scan of both substrates it appears as though the only thing there is the substrate, I.E. a peak at about 70 degree for Si and a amorphous region around 20-30 degrees.

    My thoughts on this are as follows. First, there has to be something on the substrates since the glass is obviously tinted and the Si looks a little different also as compared to a bare wafer. If there is something there shouldnt i somehow see it on a scan from 10-70 degrees(which Im not). I have done a very fine scan of the substrae and still no results. The reaction conditions in the paper I'm copying seem to suggest that I should expect a deposition rate around 10nm/min which should have yielded 200nm, the elipsometry only seems to show 20-30nm and a refractive index around 1.5-1.8 when it should be more like 2.2. This seems to suggest That while i have something its not VO2, but shouldnt it show up on XRD and a peak somewhere?

    So why would something not show up on the XRD(using simiens D5005)?
    I would guess that it is amorphous and sortof gets lost in the glass area but nothing shows on the Si so that doesn't seem to be the case. beside that i would thing that that you would atleast see something.
     
  2. jcsd
  3. Aug 24, 2009 #2

    If the film is amorphous on Si too, how can we see the film with XRD except the crystalline peaks of Si that you see. I would suggest to check up with Raman spectroscopy which will show you the amorphous film.
     
  4. Aug 24, 2009 #3
    So if the film is amorphous wouldn't that mean that its is made up of a bunch of different crystals oriennted differently? If so would'nt the XRD instead of picking up a single peak for say a (100) or a (110) it would pick up multiple peaks such as (110), (010),(020) and so on. Or is it that the peaks from those are so small that they are not seen. I appologize I am not a matsci guy although I am slowly becoming one.
     
  5. Aug 25, 2009 #4
    In amorphous film, the crystals are oriented randomly whereas in crystalline material, its highly periodic which is required for constructive interference to take place. You might have known of superposition of waves. When two waves are in phase, we get the resultant wave as the algebraic sum of amplitude of waves at each point. When they are in phase completely, the resultant wave will have bigger amplitude adding up of two waves. When the phase difference increases, the amplitude decreases and when its 180 deg out of phase, the amplitude will be very very small and we will have desctructive interference.

    The peaks we get in XRD is due to superposition of scattered waves from the crystals. Unless they are arranged in some order, we cant see constructive interference as the scattered waves wont be in phase and so no peaks. May be very very small peaks but that would be just like noise.

    Try to reduce the incident angle (I hope thats how we say, may be I am wrong, we fix it 2 deg, 5 deg and so on). Higher the angle, higher the depth of scanning. May be try lower angle as your film is very thin so it scans the surface.
     
  6. Aug 25, 2009 #5
    thanks, that is sort of what i thought may be happening but being so new to this was unsure. I'm going to be training in on a RBS machine next week which will help me figure out where to go with this deposition process.
     
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