I have a free-standing thin film, amorphous carbon, that is a few nm thick. I'd like to get a more precise measurement. Any suggestions? It would be OK to destroy the film. I am going to try metal coating it and looking at a cross section in TEM, optical reflectance, and transferring it onto a substrate for AFM. I'd appreciate any input from someone who's done such a measurement before.
Hello Larry,
Depending on what you want to get.
for thickness of the film, a profilometer would be helpful.
AFM gives 3D surface topography.
TEM shows a picture from the cross section. SEM would have good figures for details.
XPS presents the chemical components.
Wish this help you.
For a few nm I'm assuming films) do some AFM with the same scratching on a blank substrate to ensure that the needle doesn't dig into your substrate. If you can get a clean edge on film via whatever deposition process your using would of course be a lot better. A less obvious solution might be nano indentation assuming the hardness of your substrate and film are different enough.
Dear Larry,
IF your carbon film can be brought up to a TEM grid and viewing such in the TEM you perhaps will find some "minimal fold" within this carbon film. If yes, you could use the so called "minimal fold method" for measuring thickness:
e.g.: > (citation from: FIALA & HARRIS, J.Micr. 202,Pt3,pp. 468-472,2001, open access @ http://synapses.clm.utexas.edu/pubs/2001%20J%20Microscopy%20Fiala%20Harris%20Cylindrical%20diameters%20method.pdf )
Original reference: SMALL J. V. (1968): Measurement of Section Thickness.
In: Abstracts of the Fourth European Regional Conference on Electron Microscopy, Rome, Vol. 1, pp. 609–610.
Another reference perhaps of interest to you would be:
Karlsson G.: Thickness measurements of lacey carbon films,
J Microsc. 2001 Sep;203(Pt 3):326-328:
Abstract:
>>
If you have online access:
http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2818.2001.00930.x/pdf,
otherwise: cf. http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2818.2001.00930.x/abstract;jsessionid=4F9DDAC08D5F0527A21A729B41C5A405.d02t04
best regards and good luck,
Wolfgang
If you plan to put it in the TEM anyways, forget the trouble with preparing a cross-section. Look at it in to view and use EELS to measure the relative thickness. This, together with the inelastic scattering length, give you a good estimate of the thickness.
And all those measurements are part of DigitalMicrograph, the most common TEM software.
I have done some thickness measurement on silicon nitride free standing films with grazing x-ray reflectometry. It provides very precise measurements : about 0.1nm precision for thickness about 80nm (see APPLIED OPTICS 41, 5905 (2002)). XRR should give good results for film thickness down to few nm.
Nano indents or Dikdek give precisely the value of thickess to + or- 10 Angstrum. You can transfer it to a substrate and view AFM at interface
Larry, The easiest way it to prepare the sample with scratch then image it using the AFM , depending on the thickness the AFM Z displacements is about 6-8 Micron, then you can see how thick the sample is from image analysis, If the sample is easy to tear, Increasing the setpoint of the AFM and turning off the fast scan axis will give a scratch, if it scratch then imaging the scratch will tell you the thickness.
If you have a nano indentor, you can also scratch the film and image it after using the same instrument.
Dear Larry,
Probably one of these answers did help you already. But for nano-topography measurements i made good experiences with vertical scanning interferometry.
Hi Larry,
I have personal experience with measuring the thickness of free standing thin films of amorphous carbon with/without metal coating (as I have worked on preparing high-resolution electron microscopy holey-carbon grids). I will suggest you to use a calibrated AFM for precise thickness measurement (very high lateral as well as vertical resolution).
Method: Take an ultra flat substrate (such as mica, silicon wafer or glass-cover slip) and place an EM grid (usual thickness 12-15 micron) on it. Then transfer the free standing film over this substrate. EM grid will act as a mask during transfer of the film on the substrate. After transfer, remove the EM grid (generally, it can be removed by moving the substrate upside-down). Now you have a ready substrate for thickness measurement of film by AFM over the masked area. Depending on the mesh size of the EM grid, you can easily have multiple places with clear edges of film for perfect thickness measurement. (This method is much much easier than scratching a film by stylus or cantilever to find the edge of the film to determine thickness).
Coated film before or after transfer can also be checked through the same way.
If you see any problem using this method, please write me as I have worked on many thin films using this method.
Good luck!
Dear Larry,
Probably one of these answers did help you already. But for thickness measurement in nano-range I made good experiences with ellipsometry, if you need space-resolved data you can use imaging ellipsometry.
A lot of good suggestions have been made already.
I've never looked at free-standing a-C films, but have measured thickness of a lot of amorphous carbon films on e.g. silicon, glass, metallic substrates.
On glass, the easiest way was probably using a UV-Vis-NIR spectrometer (Aquila nkd-8000). http://www.aquila-instruments.com
This is quite good for film thickness calculations, and can measure reflectance and transmittance simultaneously, and can also enable calculation of refractive index, dispersion, extinction coefficient, and even bandgap (via Tauc method).
AFM, ellipsometry and cross-sectional SEM as already suggested can all be useful too, although perhaps in the case of SEM (as Thomas suggested), films of as little as 10nm thickness might be difficult to resolve.
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