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Advanced Photon Source

Beamline 11-BM: High Resolution Powder Diffraction

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11-BM Frequently Asked Questions

» Why is the beamline called "11-BM"?
The APS is divided into 34 Sectors, numbered clockwise around the synchrotron ring. Our instrument is located in Sector 11.

The "BM" means that the beamline obtains its synchrotron x-rays from a bending magnet. Each APS sector contains one or more beamlines receiving radiation from a bending magnet (BM) or an insertion device (ID). Multiple beamlines (and optic hutches) in each sector also receive a letter suffix (e.g. 11-ID-C). Technically, the 11-BM experimental hutch is named 11-BM-B, and no user measurements are performed in the A hutch.

» Do I need to write a proposal to use 11-BM mail-in service? Is this complicated?
To use the 11-BM mail-in service, at least one member of your research team will need to register as an APS user (if they have not so previously) and submit a General User Proposal. More information is available (including registration and proposal examples) at the 11-BM Mail-In Introduction page.

Both the registration and proposal processes are relatively quick and straightforward. Rapid access proposals are generally shorter and less detailed than standard on-site or extended experiment proposals. A short abstract paragraph, and brief answers to a few questions concerning your experiment are appropriate for rapid access mail-in proposals. An example of a rapid access user proposal for the 11-BM mail-in service is available here (PDF document).

» My laboratory has a powder diffractometer. What are the advantages of collecting data at 11-BM?
A synchrotron radiation source provides many advantages when collecting powder diffraction data.

The shorter wavelength of the synchrotron x-ray beam provides greater structural information on your sample, by enabling more observations over a wider Q range (especially for smaller d-spacings). Compared with common laboratory radiation sources, the shorter wavelength used at 11-BM greatly reduces or eliminates fluorescence problems for most samples. Furthermore, any remaining fluorescence is rejected by the analyzer crystals used in 11-BM's detection system.

The extremely high flux and resolution of 11-BM affords users a level of sensitivity and detail not possible with a laboratory based instrument. The high resolution data allows more peaks to be resolved, which is essential for correct pattern indexing. The high sensitivity enables the observation of weak peaks above the background. Both factors lead to a greater level of detail in the resulting crystal structure solutions.

The higher operating energy generally reduces sample absorption. This enables the use of transmission geometry diffraction for nearly all samples, even those containing high-Z elements. When coupled with a rotating capillary stage like that found at 11-BM, the transmission measurement often eliminates preferred orientation in samples, a common problem with many lab-based refection geometry instruments. Uncertainties resulting from surface absorption corrections, zero-point shifts, and sample height displacements are also eliminated by collecting your powder diffraction data at 11-BM.

Some laboratories have variable temperature stage attachments for their diffractometer; your institution may not. 11-BM offers its mail-in users a range of sample collection temperatures. This may be an extremely quick and cost-effective solution for the occasional non-ambient temperature powder scans needed for your research.

» Our group has never used a synchrotron before - is it appropriate to use the APS for our research?
Absolutely! From its conception, one intent of 11-BM and its rapid access program has been to attract new synchrotron users and expand the APS user community. Powder x-ray diffraction has the potential to attract a wide audience, as it is a common technique used across a wide range of scientific disciplines.

See the answer just before this for examples of how using 11-BM could benefit your research, and the following question for more about the goal of the mail-in service.

» I only have 1 or 2 samples, is that OK?
No problem at all! In fact, the 11-BM mail-in service as been primarily developed for users with a limited number of samples. Our goal is to promote superior crystallographic science across a wide user community by providing convenient and timely access to world-class powder diffraction data.

Previously, it would have been prohibitively complicated and expensive to travel to a synchrotron in order to collect a high-resolution diffraction pattern on one sample; the 11-BM mail-in service is designed to eliminate the cost and hassle associated with routine synchrotron powder diffraction measurements.

» What is the cost of the mail-in service?
The 11-BM mail-in program is a free service offered to all non-proprietary users. We are funded by the APS and the U.S. Department of Energy's Office of Science. This free service is also available to international researchers working outside of the United States.

The APS does not charge for any beam time supporting research that is intended be published in the open literature. Users are expected to notify the APS of publications containing work conducted at the APS. Proprietary users are charged an hourly fee for APS beamtime (including 11-BM mail-in sample) to recover facility costs. More information is available here.

» How many samples can I send for the rapid access program?
Rapid access proposals are limited to 8 hours (1 shift) of beamtime per proposal. A standard 11-BM ambeint temperature scan takes ~ 1 hour, so for many mail-in users the answer here is 8 samples. However, non-standard scans may take longer than 1 hour; this time will be subtracted from your 8 allocated hours of beamtime accordingly. On-site users and non-rapid access mail-in users are typically awarded more than 1 shift of beamtime.

» Can I collect at non-ambient temperatures on 11-BM? What temperature range is possible?
The 11-BM Mail-in service allows rapid access users to perform a limited number of scans at select non-ambient temperatures. Extended non-ambient experiments or parametric studies are better performed as on on-site user. More Information about 11-BM sample environments is available here.

» The data format I need is not offered by 11-BM, what can I do?
It is not practical to support every possible powder diffraction format. We have tried to include some of the most common ones here. Let us know if you feel we missed a common format. If the format you need is not listed, check to see if your software also supports one of these common formats. Many formats are quite similar: occasionally a file can be "fixed" or "converted" by using a simple text editor to make small changes to the file or file header. Note it is also possible to obtain your data as a simple comma separated .csv file and manually convert as needed.
Also try the free program CMPR which opens GSAS (.fxye) files from 11-BM, and can be used to view your data and convert to a several popular alternative formats.

» My software opens format "X", but why doesn't work with "X" format from 11-BM?
Try changing the file extension, this is often a simple and quick solution. For example, all the following are valid and common file extensions for a certain GSAS format: ".gsas", ".raw", ".gsa" and ".gs" - but different software packages may not recognize one or more of these extensions.

It is likely someone else has encountered this problem before. The Rietveld Mailing List Archive, or the CCP14 website on Rietveld and Powder Diffraction Software are good places to look for help.

» I observe small peak(s) in my pattern at low 2θ angles which are not from my sample, what is this?
The 11-BM polyimide (Kapton) capillaries add a small but measurable background contribution to the pattern (in addition to general air scatter). Its relative contribution to the overall pattern depends in part on how well your sample diffracts. At ~ 30 KeV (λ ~ 0.46 Å), Kapton shows a small peak at 2θ of ~ 2° (d ≈ 15.5 Å) and a broader bump centered at 2θ of ~ 5° (d ≈ 5 Å).

View an 11-BM background scan of diffraction data collected on an empty Kapton capillary here. These patterns are also available for download here.

» What is "Q", and how does it relate to 2θ or d spacing?
Technically, Q is a vector that descibes the momentum transfer of scattering. Its magnitude is defined as follows:
Q = [4πsin(θ)] / λ
or rewritten as :
Q = 2π / d
In practice, Q is convenient way to discuss and plot powder diffraction data independent of the wavelength (λ) of each particular data set or instrument. When plotted in Q, a diffraction pattern from 11-BM can be matched up with a scan from a Cu Kα source lab diffractometer. The same could be achieved by using d-spacing, but this over emphasizes the areas of the pattern with primarily low angle scattering. Plotting in Q is generally a more practical approach.

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