Hi Kamil, Ok this gives a better picture of the experiment. Although electron density contribution to diffraction is a bit more complicated than what I said in my previous email, in essence though the diffracting angles of 200 and 400 are indeed related as you said, with sin(theta) equal to lambda/2d and lambda/2(d/2), respectively. Therefore a shift of the 200, which implies distortion of the original unit cell (or change in wavelength), should also mean a shift of 400. I cannot see why that would not be the case; even the presence of anomalous signal as you suggested should cause changes to intensity and phase of the reflection but not to the scattering angle? At least not to only one of either 200 or 400? Perhaps other may have an explanation for ... once their Christmas lunch is over!
BW, D > On 24 Dec 2020, at 23:23, Kamil Krawczyk <[email protected]> wrote: > > > 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 <[email protected]> >> 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 < [email protected]> 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&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/ >> > > To unsubscribe from the CCP4BB list, click the following link: > https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&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/
