NIST Glassy Carbon Absolute Intensity SRM
NIST absolute intensity SRM 3600 - Absolute Intensity Calibration Standard for Small-Angle X-Ray Scattering - is officially certified Glassy Carbon SRM, replacement of all of the Glassy carbons provided by me for the last ~12 years. This SRM has been calibrated (also) on our USAXS instrument and then tested and certified by use of other instruments. This SRM costs $513 and is available from NIST web site. I strongly encourage everyone to buy their own certified standard for their needs. This SRM can and should be used exactly the same way as my prior Glassy carbon artifacts, as it is the same material and same calibration method, just more complex, careful, and guarranteed by NIST.
Glassy Carbon samples measured using USAXS instrument
Jan Ilavsky, 2011-May-27
About 100 samples of Glassy carbon 1mm material are currently used throughout the World with SAXS instruments (desktop as well as synchrotron). Some are also used with SANS instruments, even though some interesting issues with dependence of sample transmission on neutron wavelength are still under investigation. If you need sample for your own use, please contact me via e-mail with your needs.
Jan Ilavsky, 2016-08-01 : I used to provide these samples (when available) for free - and there is about 160 pieces in use - but since now the NIST SRM is available for purchase, i encourage everyone to buy the NIST SRM 3600 (see above).
Anyone using my Glassy carbon srtandard is kindly asked to cite the following publication (which is Open Access on the journal web site!):
Fan Zhang, Jan Ilavsky, Gabrielle Long, John Quintana, Andrew Allen, and Pete Jemian, "Glassy Carbon as an Absolute Intensity Calibration Standard for Small-Angle Scattering," Metallurgical and Materials Transactions A 41 (5), 1151-1158 (2010).
Calibrating using this standard
I get a lot of questions how to calibrate using this standard... New movie (2015) is in the new location - Youtube channel ... the old movie is here : 20 minute movie and here is short summary:
- Measure glassy carbon as sample for whatever time Tc you need and reduce it as sample using your reduction method. Set for now Calibration Coefficient (Cf) = 1. You need to know the thickness (=1mm) and transmission (~0.85 for Cu wavelength, but measure it!). Calculate constant Cf by diving MY dataI sent you by Your data. This is correction factor which puts your instrument on the absolute scale.
- The easiest way to get the scaling factor is by using "Data manipualtion I" from irena package, which has ability to "autoscale" two data sets using the curve between the cursors. USAXS data do contain some flat background, so they will likely deviate at high q. Select only part of data which has similar shape.
- Next calculate Calibration Constant Cf:
- Now measure yoru sample, reduce with its own thickness and own transmission with Cf from above to put this on absolute scale.
- If you need to measure sample at differen ttimes, you need to correct Cf for time:
Cf(new time) = (originalGlassy Carbon measurement time / new sample measurement time) * Cf
Hope this explains it.
Absolute intensity conversion
For details of the conversion of raw intensity to absolute units of differential scattering cross-section per unit volume per solid angle, please consult:
- Fan Zhang, Jan Ilavsky, Gabrielle Long, John Quintana, Andrew Allen, and Pete Jemian, "Glassy Carbon as an Absolute Intensity Calibration Standard for Small-Angle Scattering," Metallurgical and Materials Transactions A 41 (5), 1151-1158 (2010).
- Pete Jemian's 1990 PhD thesis, http://www.jemian.org/pjthesis.pdf, page 51, equation 83.
Glassy Carbon samples were cut into smaller pieces, each is identified by name (Adam, Bob, H1, G15…). If you have samples marked with one of the letters below, you can find your data below, if you have others, send me e-mail and I''ll send you your data.
ASCII data are Q [1/A], Intensity [cm2/cm3], and error:
Glassy Carbon L
Glassy Carbon M
Glassy Carbon N
Some additional comments (from 2004, so they are bit old):
Five samples of glassy carbon manufactured by Alpha Aesar were measured using USAXS and are used around the APS as secondary intensity standard. This web page lists the results obtained for the glassy carbon samples on USAXS instrument. Data available here are fully desmeared and corrected, with absolute intensity calibration using USAXS standard-less absolute calibration method. The sample thickness is 1 mm.
The samples were denoted A, B, C, D, and E. Number of measurements were obtained on each sample to compare stability of measurements and samples together.
The following graph shows reproducibility within one sample (sample denoted A).
As you can see, 3 measurements on one sample (in different places) are quite reproducible. Error bars (errors are available in files for download) are not displayed for clarity. Generally we have found out, that within one sample any variations of scattered intensity are likely caused by small changes in the sample thickness. These data were confirmed and better documented by use of DND CAT pinhole camera.
The following graph shows comparison of 5 available glassy carbon samples:
As you can see, there is significant difference in scattered intensity for the 5 different samples – especially at smaller Qs (below 0.1 A-1).