Re: Explaining for broadening of peaks due to a shift of theta in theta-two theta scanning?
Such an offset of the theta (omega) axis violates the para-focusing condition of the Bragg-Brentano geometry. You will get diffracted intensity from positions far below and above the gonimeter axis, i.e. far outside the focusing circle. The only option to reduce this effect is a reduction of the divergence of the primary beam. Without parallel beam optics, you can just reduce the opening of the equatorial slit, of course causing significant loss of intensity. Reinhard Kleeberg Huy LE-QUOC schrieb: Dear Rietvelders, To avoid the gigantic peaks of Si substrate (which are too dominant over peaks of phases in investigation on a thin film of 3 micron), we have tried to take a scan theta-two theta with a shift of 3 degree for theta (i.e. instead of theta-2theta corresponding to 5-10 degree at the beginning, I have set theta=8 degree and 2theta=10). In fact, we have been able to reduce dramatically intensity of Si peaks but the broadening of all peaks in the diffractogram is increased comparing to the "normal" scan without shift of theta. We have also tried to rotate the sample around its perpendicular axis (angle Phi) to find the appropriate Phi where the peaks of Si are slightly decreased and found that the broadening of peaks is the same as in a "normal" theta-2theta scan. Does anyone have any ideas about this increased broadening of peaks during a theta-2theta scan with theta shifted ? By the way, do you know others ways, besides the razing incidence, to avoid the dominant peaks of substrate over the thin film ? Thanks a lot in advance for your any helps. Best regards, --- Huy LE-QUOC, Doctorant LPSC/UJF-Grenoble INP-CNRS, Centre de Recherche Plasmas-Matériaux-Nanostructures Institut Néel/CNRS, Département "Matière Condensée, Matériaux et Fonctions" 53 rue des Martyrs, Grenoble 38026, FRANCE Phone: +33 4 76 28 40 38 Fax: +33 4 76 28 40 11
Re: Explaining for broadening of peaks due to a shift of theta in theta-two theta scanning?
Dear Huy, as it was pointed out in previous letter by Joerg Bergmann, line broadening is caused by violation of theta-2theta relationship. More info can be found in the following articles: 1. R. Berthold. Z. Angew. Phys. 7 (1955) 443. 2. H. Toraya, J. Yoshino. J. Appl. Cryst. 27 (1994) 961. Best regards, Eduard.
Re: Explaining for broadening of peaks due to a shift of theta in theta-two theta scanning?
Besides Joerg's suggestion of mis-cut substrates (which may be too expensive for use for thin film growth experiments) you could use Si wafers cut to (100). The first allowed peak in that direction is (400), which is at about 70 degrees 2theta for Cu K-alpha. That will still reflect any bremsstrahlung radiation from your x-ray tube, which can make a significant background. If you have a monochromator in your optics, that will cut it down, but you can still get artifacts, such as lambda/2 radiation reflecting from the (400) appearing to be a peak at the (forbidden) Si (200) position. Or, maybe you can find a compromise between the Si substrate peak and defocusing with a smaller value of omega (theta - 2theta/2) than 3 degrees. Another possibility, if you are ready to rearrange your diffractometer, is to make the source-sample and sample-detector distances different, so that source, sample, and detector are on the focusing circle with theta not half of 2theta. I wonder if any of the manufacturers provide this geometry? ^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~ Peter W. Stephens Professor, Department of Physics and Astronomy Stony Brook University Stony Brook, NY 11794-3800 fax 631-632-8176
Re: Explaining for broadening of peaks due to a shift of theta in theta-two theta scanning?
Am Freitag, den 19.02.2010, 11:21 +0100 schrieb Huy LE-QUOC: > Dear Rietvelders, > > To avoid the gigantic peaks of Si substrate (which are too dominant over > peaks of phases in investigation on a thin film of 3 micron), we have > tried to take a scan theta-two theta with a shift of 3 degree for theta > (i.e. instead of theta-2theta corresponding to 5-10 degree at the > beginning, I have set theta=8 degree and 2theta=10). In fact, we have > been able to reduce dramatically intensity of Si peaks but the > broadening of all peaks in the diffractogram is increased comparing to > the "normal" scan without shift of theta. > > We have also tried to rotate the sample around its perpendicular axis > (angle Phi) to find the appropriate Phi where the peaks of Si are > slightly decreased and found that the broadening of peaks is the same as > in a "normal" theta-2theta scan. > > Does anyone have any ideas about this increased broadening of peaks > during a theta-2theta scan with theta shifted ? The Theta-Theta-geometry is a method for focussing X-Rays, you will loss the focus by rotating the sample off the theta-theta set-up. There are available special cut Si plates with a surface normal avoiding all possible reflections. Joerg > By the way, do you know others ways, besides the razing incidence, to > avoid the dominant peaks of substrate over the thin film ? > > Thanks a lot in advance for your any helps. > > Best regards, > > --- > Huy LE-QUOC, > Doctorant > LPSC/UJF-Grenoble INP-CNRS, Centre de Recherche > Plasmas-Matériaux-Nanostructures > Institut Néel/CNRS, Département "Matière Condensée, Matériaux et Fonctions" > 53 rue des Martyrs, Grenoble 38026, FRANCE > Phone: +33 4 76 28 40 38 > Fax: +33 4 76 28 40 11 > > >