Bragg profile is also known as RCP-Rocking Curve Profile or RSP-Reciprocal Space Profile. Let us examine this difference between the substrate (usually CZ grown) and an epitaxial structure grown on it using MBE. We’d appreciate your erudite & honest analyses, critique and suggestions for improvement!
A. Instrumental profile for GaAs (004) theoretically computed using the Bruker Leptos System:
http://www.flickr.com/photos/85210325@N04/9319044423/lightbox/
B. Experimental profile of GaAs (004) substrate contrasted with the theoretical GaAs (004):
http://www.flickr.com/photos/85210325@N04/9430820747/
C. Experimental profile of GaSb (004) substrate contrasted with the theoretical GaAs (004):
http://www.flickr.com/photos/85210325@N04/10502940644/
D. Experimental (004) profile of MBE grown 0.5µm epitaxial structure with 25nm period of InAsSb/InAs SL (super lattice) on GaSb (001) substrate:
http://www.flickr.com/photos/85210325@N04/10653618416/
http://www.youtube.com/watch?v=9SHH2GJ8IYE&list=PL7032E2DAF1F3941F
Attached is an excellent basic reference by Dr. Scott Speakman of MIT and important for all of us pursuing XRD as a viable tool for Quantitative Nano Structural Microscopy. The data displayed in this reference is predominantly using the conventional 0D point/scintillation detector. This type of conventional rocking curve data is an average of a sampling area usually ranging from 1X1mm^2 to 1X10mm^2. In contrast, the data I'm displaying is from a 25mm sampling area segmented into 76um Pixels. Besides, the data itself has an Omega resolution of less than 0.4 Arc Sec (for GaAs). I'm yet to see data in literature that is comparable in resolution other than that we had published in the late 1980's. In fact, I'm eager to find the conventional XRD rocking curve for any GaAs wafer compared with the theoretically expected profile. If anyone else is aware of such publications that I may have missed, please post or send PDF files to [email protected].
This is a link for the parallel LinkedIn discussion:
http://www.linkedin.com/groupItem?view=&gid=2683600&type=member&item=5815413009861873664&commentID=5815528858086043648&qid=27ae3d8d-eb70-498f-8cef-6a8ec9cdb411&trk=groups_most_recent-0-b-cmn&goback=%2Egde_2683600_member_5815413009861873664%2Egmr_2683600%2Egde_2683600_member_5815413009861873664%2Egmr_2683600#commentID_5815528858086043648
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CDkQFjAB&url=http%3A%2F%2Fprism.mit.edu%2Fxray%2F3%2520Introduction%2520to%2520HRXRD.pptx&ei=IY6kUorRB8S1sATP1oDQAQ&usg=AFQjCNHhHGOiaj7bT8wNeQ5OQlt9jj74dQ&sig2=ikngYaeDhk-18FTFSz5-xg&bvm=bv.57752919,d.cWc
Attached is an excellent basic reference by Dr. Scott Speakman of MIT and important for all of us pursuing XRD as a viable tool for Quantitative Nano Structural Microscopy. The data displayed in this reference is predominantly using the conventional 0D point/scintillation detector. This type of conventional rocking curve data is an average of a sampling area usually ranging from 1X1mm^2 to 1X10mm^2. In contrast, the data I'm displaying is from a 25mm sampling area segmented into 76um Pixels. Besides, the data itself has an Omega resolution of less than 0.4 Arc Sec (for GaAs). I'm yet to see data in literature that is comparable in resolution other than that we had published in the late 1980's. In fact, I'm eager to find the conventional XRD rocking curve for any GaAs wafer compared with the theoretically expected profile. If anyone else is aware of such publications that I may have missed, please post or send PDF files to [email protected].
This is a link for the parallel LinkedIn discussion:
http://www.linkedin.com/groupItem?view=&gid=2683600&type=member&item=5815413009861873664&commentID=5815528858086043648&qid=27ae3d8d-eb70-498f-8cef-6a8ec9cdb411&trk=groups_most_recent-0-b-cmn&goback=%2Egde_2683600_member_5815413009861873664%2Egmr_2683600%2Egde_2683600_member_5815413009861873664%2Egmr_2683600#commentID_5815528858086043648
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CDkQFjAB&url=http%3A%2F%2Fprism.mit.edu%2Fxray%2F3%2520Introduction%2520to%2520HRXRD.pptx&ei=IY6kUorRB8S1sATP1oDQAQ&usg=AFQjCNHhHGOiaj7bT8wNeQ5OQlt9jj74dQ&sig2=ikngYaeDhk-18FTFSz5-xg&bvm=bv.57752919,d.cWc
I consider that bulk crystals have 3D "equivalent" dispersors positions and thus their characteristic XRD 2theta intensities and positions according to cell lattice space group and type of atomic dispersors. But in an specific or oriented growth some intensities can be enhanced or diminished depending on the orientation of growth this could be j k or l or fractional. When orientation is through one or two dimensions the reflections related to the growth are enhanced in intensity due to a major amount of atomic dispersors in that or those preferred directions. The differences in 2theta positions are more related to defects or the presence of other atoms or molecules present into the net or crystal. Hope this helps in analyses of XRD diffractograms.
Though the growth is epitaxy, certainly other planes would appear as the film composition is different from the substrate-Eliminating the substrate contribution one can other planes
The predominant difference between the GaSb substrate (http://www.flickr.com/photos/85210325@N04/10502940644/) and the SL epi (004) reflection (http://www.flickr.com/photos/85210325@N04/10653888653/#!) is the "shape" of the profiles. The GaSb substrate (004) RCP is virtually an "identical fit" (pseudo-Voigt or Pearson VII) with the GaAs (004) theoretical RCP (http://www.flickr.com/photos/85210325@N04/9319044423/lightbox/) whereas the MBE epi RCP is a near perfect Lorentzian shape (symmetric). WHY?
REMINDER! Panalytical Seminar TODAY Dec 10th 10AM EST on "XRR".
http://www.linkedin.com/groupItem?view=&gid=2683600&type=member&item=5813241314594033664&qid=e32442aa-e39c-4a67-af1f-dce3ea8b7e1f&trk=groups_most_recent-0-b-ttl&goback=%2Egde_2683600_member_5816121106070806531%2Egmr_2683600%2Egde_2683600_member_5813241314594033664%2Egmr_2683600
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