You can actually probe fairly deep using XRR.  I published a paper studying the structure of amorphous diamond like carbon films that used XRR quite heavily, and went into much discussion.  You should be able to download it from my publication list on this site.  "Nanostructural characterization of amorphous diamondlike carbon films " Siegal et al, Phys Rev B, 61, 10,451 (2000).  I think you will find the discussions there useful.

Good luck.

The depth will depend on the film composition.  We published an in-depth paper in 2000 that used XRR to study the roughness and densities of different layers of amorphous diamond like carbon films.  You can download it on my page in this website.  "Nanostructural characterization of amorphous diamondlike carbon films " Siegal et al, Phys Rev B, 62, 10,451 (2000).

Good luck.

It depends on equipment type. In general the XRR may be used for 2000-3000A thick films. Thicker than 300nm is very hard (or impossible) to analyze.

In addition, please refer to this article which is very nice technical document concernig to XRR method.

http://maglab.iphy.ac.cn/XRD%E4%B8%93%E9%A2%98/X-ray%20thin-film%20measurement%20techniques_V_X-ray%20reflectivity%20measurement.pdf

Thanks a million Hayk & Michael!

The Pt. thin film along with all the buffer layers as shown in image below add up to no more than 1150 nm to the (001) Si substrate. Therefore, I shouldn't expect information about all the layers in the "sandwich" structure below using the XRR signal. 2000-3000A = 200-300nm. Therefore the 1um (1000nm) SiO2 layer would act as the substrate and I should not expect information from the Si substrate below the 1um SiO2 layer. Correct?

• What about the ability to use the 2D XRR signal to estimate film/surface characteristics topographically?
• Is there any literature supporting this type of "topographic" analysis using the 2D XRR signal?
• What about the ability to tilt the 2D detector to an acute angle w.r.t. the diffracted beam to spread the XRR signal across the 2D detector? Position # 3: -https://www.flickr.com/photos/85210325@N04/9311681113/in/album-72157632724094863/

Any existing literature reference or suggestions in this regard would be deeply appreciated from you experts in this field.

https://www.researchgate.net/post/Can_XRR_X-Ray_Reflectivity_be_implemented_in_the_Topographic_Mode_with_spatial_resolution_over_the_sample_surface_Is_there_value_for_such_analyses

The XRR intensity depends on materials absorption coefficient (depends on elements its made of).

So films/structures that are sufficiently thin, so that they allow the X Rays to be reflected back (from all the interfaces buried within the sample) to the X ray detector without getting absorbed, can only be success fully studied with XRR.

One way of improving the chances are by using high intensity sources.

typical thickness limits possible ~120 nm or less for low Z element films and 70 nm or less for metallic/ magnetic films/ higher Z materials.

Thanks Ravi!

Your answer, 70-120nm, is inconsistent with that of Michael's, 200-300nm. Got some literature references to support your suggestion?

The NIST 2000 SRM we utilized had a 25nm strained Si layer atop a 50nm Si-Ge thin film above the Si (001) substrate:  https://www.flickr.com/photos/85210325@N04/19886365571/

I remain open-minded :-)

When I was working on thin-polymer films. I used the NIST tables for penetration depth of X-rays. When I first started measurements, I was picking up indium tin oxide peaks from the substrate. By using the depth-tables and changing the incident angle of the X-rays, I was able  to minimize the signal for the ITO. A good reference for the basic maths is here: http://nvlpubs.nist.gov/nistpubs/jres/51/jresv51n2p95_A1b.pdf

Most of the XRR signal for the "flat sample" of NIST 2000 SRM extends for only 1.4 degree 2-Theta and half that for Omega. Just curious, how one can adjust the incident angle for varying penetration depth in this case :-)

https://www.flickr.com/photos/85210325@N04/19855146126/in/photostream/lightbox/

Dear Ravi 

Indeed - XRR is sensitive to a couple of hundred of nm typically. The figure you show above has a plateau at reflected intensity = 1 below some small angle 0.45 degrees or thereabouts. This is the critical angle for total external reflection - it's very small because the refractive index of solids is close to 1 for X-rays (similarly for neutrons). Below the critical angle, X-ray techniques are highly surface sensitive (a few nm - we can probe surface reconstructions etc.). But most of the information in the XRR is from above the critical angle! Remember XRR is not an "absorption" method like XAS or XMCD. This paper has some comparison of different depth-sensitivity magnetic techniques:

Depth-dependent magnetism in epitaxial MnSb thin films: effects of surface passivation and cleaning, Journal of Physics: Condensed Matter (2012), vol. 24, art. no. 146002

I hope that clarifies things a bit.

Regards

Gavin

Thanks Gavin!

Please send me a PDF file when possible.

Warm regards,

Ravi

[email protected]

P.S: Attached is something I found.

https://www2.warwick.ac.uk/fac/sci/physics/staff/academic/bell/proj/magstruc.pdf

Thickness, roughness and density are the 3 parameters quantifiable using LEPTOS. 

My question is straight forward: How do I compute the contributing depth in this case of XRR signal for NIST 2000 SRM with Cu KAlpha 1 and for the Pt. thin film sample as well?

Ravi, you may easily calculate the X-ray penetration depth by applying the Fresnel theory, using the optical constants of your material(s) for the X-ray energy of interest. Come back if you don't succeed in finding the correct equations. I think you'll probably find them either in the original literature (e.g. the famous Parratt Phys. Rev. Paper from 1954, or in adequate books (like the TXRF-book from Klockenkämper and coworkers)... Cheers, and all the best for 2016, Dirk

Here are some observations of NIST2000 XRR profiles integrated at various heights on the sample. There appears to be notable changes in these XRR profiles potentially indicating the changes in the thickness, flatness etc. topographically. Preliminary findings.

https://www.flickr.com/photos/85210325@N04/24088531293/in/dateposted-public/

Here are some sources I discovered while searching for "Parratt Phys. Rev. Paper from 1954" :-)

https://neutrons.ornl.gov/sites/default/files/beamline_04A_xray_neutron_reflectivity_tutorial.pdf

http://przyrbwn.icm.edu.pl/APP/PDF/89/a089z3p09.pdf

Between 250 to 350 nm.