If you've eliminated the possibility of target or sample impurities, the so-called Renninger Reflections would also be my guess. However, I also don't have the (picture of) data to observe. If the "continuous ring" [re: Andrew Payzant below] refers to a transmission photo of a powder, then it's not reasonable to suspect multiple diffraction from a very large crystal. Such a large crystal would manifest itself in a spot, and not a ring, wouldn't it? Frank May XRD since 1972 University of Missouri - St. Louis
________________________________ From: Whitfield, Pamela [mailto:[EMAIL PROTECTED] Sent: Wed 1/24/2007 1:05 PM To: [email protected] Subject: RE: Re: Strange peaks from grainy Si For some reason the original email never made it to me so I can't see the data - so apologies if this is way off base. However, it's not impossible for perfect single crystal material to produce forbidden reflections from multiple diffraction effects if the crystallites are big enough. Pam ________________________________ From: Andrew Payzant [mailto:[EMAIL PROTECTED] Sent: Wed 24/01/2007 12:58 PM To: Rietveld list Subject: Re: Strange peaks from grainy Si Peter, That is my guess too - either additional (weak) characteristic lines such as Mo-K beta, or contaminant lines such as W L, or, as you point out, some wavelength in the Bremmstrahlung that meets the Bragg condition for some silicon crystallites. However, I would not have expected a few large crystallites to yield a continuous ring, as appears in his CCD image, so perhaps there is another explanation. Andrew -- E. Andrew Payzant Senior R&D Staff Member High Temperature Materials Laboratory Oak Ridge National Laboratory 1 Bethel Valley Road PO Box 2008, MS 6064 Building 4515, Room 113 Oak Ridge, TN, 37831-6064 ph: (865) 574-6538 FAX: (865) 574-3940 web: <http://html.ornl.gov/dtpgrp/staff/payzant.html> <http://html.ornl.gov/dtpgrp/staff/payzant.html> ________________________________ From: <[EMAIL PROTECTED]> Reply-To: <[email protected]> Date: Wed, 24 Jan 2007 12:51:57 -0500 To: <[email protected]> Subject: Re: Strange peaks from grainy Si I'll mail you some fine Si powder if you send me your address. My best guess is that you have a relatively big lump of Si in your sample that happens to be lined up to make a bright spot from the bremstrahlung part of the spectrum. It happens to meet some Si Bragg reflection condition for some wavelength in the brems. spectrum. ^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~ Peter W. Stephens Professor, Department of Physics and Astronomy Stony Brook University Stony Brook, NY 11794-3800 fax 631-632-8176
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