In addition to the Debye-Waller correction, you have additional attenuation from the Lorenz and Geometry factor (specific for your powder diffraction geometry) that convolutes with the DB apodization.
Meaning: the 400 will be more attenuated relative to 200 if you correct only for DBW. A peak shift is not explained this way, because larger B and LPG only affect intensity. A cell change should affect both reflections similarly (Bragg). The whole intensity thing falls apart if you have in addition preferred orientation effects, but I do not know enough about your sort of experiment to say whether this is possible. Can monolayers warp or something like anisotropically expand? Best, BR From: CCP4 bulletin board <CCP4BB@JISCMAIL.AC.UK> On Behalf Of Kamil Krawczyk Sent: Thursday, December 24, 2020 15:22 To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Relationship of crystallographic planes and reflections, e.g. (200) and (400) Hi all, Thanks for the insight so far! To give better information re: the system, I am studying quantum dot monolayers. Yes, these diffractograms are powder diffraction images that have been condensed into 1D diffractograms. This is under the condition of laser photoexcitation, and while some signal is thermal (e.g. typical Debye-Waller type decrease of intensity which can be well characterized), I am just trying to better understand the anomalous effects and get a better picture of how the (400) and (200) reflections, and they're relevant atomic coordinates, are related. I can't imagine it being due to dynamic scattering effects as this is a monolayer and my coherence length of my electrons is great! Thanks again! On Wed, Dec 23, 2020 at 7:12 AM Jon Cooper <jon.b.coo...@protonmail.com <mailto:jon.b.coo...@protonmail.com> > wrote: Hello, when you say the (4, 0, 0) intensity goes down, I was wondering what is actually changing? Likewise for the shift in (2, 0, 0). If every atom lay in a particular diffraction plane, they would all scatter in phase and the diffraction from that plane would be nice and strong! The relative phase of each atom's scattering is dictated by the distance from the plane, right ;-? Diffractogram sounds like proper physics. Best wishes, Jon. C. Sent from ProtonMail mobile -------- Original Message -------- On 22 Dec 2020, 22:26, Kamil Krawczyk < kamil.krawczyk7...@gmail.com <mailto:kamil.krawczyk7...@gmail.com> > wrote: Hi all, As an experimental physicist slowly becoming more acquainted with crystallography, I have a bit of clerical issue visualizing this particular problem in my head: For example, the 400 and 200 reflections in a diffractogram are related to the 100 family of crystallographic planes; I'd imagine, that in real space, the higher order plane (e.g. the 400) corresponds to atoms 'closer' to the center of the crystal/unit cell. I have an interesting observation where I am seeing the 400 peak intensity go down (likely due to increased RMS motion), whereas the 200 reflection does not really change in its intensity. Furthermore, I see a shift in the 200 peak, implying an expansion (a shift to lower q), but no abnormal change in the 400 peak position. What I am having a really hard time wrapping my head around is how these two events can be occurring simultaneously; I would naively say that since the 400 reflection is showing an increased RMS, the 400 peak should likely shift - not the 200. Does anybody have an easy way to visualize this? I am trying to look at crystallographic vectors in VESTA on a model system, but sadly have not been able to see the light just yet. Thank you! And sorry for dropping all the parentheses on reflection names, it saved me some typing :p ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB <https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1> &A=1 This message was issued to members of www.jiscmail.ac.uk/CCP4BB <http://www.jiscmail.ac.uk/CCP4BB> , a mailing list hosted by www.jiscmail.ac.uk <http://www.jiscmail.ac.uk> , terms & conditions are available at https://www.jiscmail.ac.uk/policyandsecurity/ _____ To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB <https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1> &A=1 ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 This message was issued to members of www.jiscmail.ac.uk/CCP4BB, a mailing list hosted by www.jiscmail.ac.uk, terms & conditions are available at https://www.jiscmail.ac.uk/policyandsecurity/
