Hi, Looking at the attached file, my opinion is that this effect is caused by a quite large divergent (or both divergent and anti-scattering) slits. It is not normal to have over 1000 counts at 5 degrees 2-theta. This could be due either by a portion of incident beam or by a scattering from the sample holder. It is not clear if your XRD is equipped with variable slits. If yes, William is correct - try to adjust them properly. I was working some years ago with variable slits diffractometer and as I remember I had hard time trying to collect good quality data below 3 degrees 2-theta. Now I have a fixed slits goniometer and I am easily getting pretty good patterns even below 1 degree 2-theta - by appropriate setting of the slits. I think this is one important benefit of using fixed slits - the higher quality of low theta scans. Dear Chuisy, with appropriate slits arrangement, at 5 degrees 2-theta you should have almost horizontal background level and every peak should be well displayed on the pattern. So, if you have fixed slit system - try with smaller divergent and anti-scattering slits. It would be better if you use as a test sample something that provides peaks below 5 degrees in order to check and control the quality of peaks appearance on the pattern while adjusting the slits. Don't forget: for good quality low theta data it is critical to have a large sample width (or length - depends on the view). My sample holders for low theta data collection are rectangular shaped 18x35 mm with different depths. The beam must be kept as much as it is possible within the sample area. Good luck, Srebri
/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\ Dr. Sr. Petrov, PXRD Analyses, Dept. of Chemistry, University of Toronto Tel/Fax: (416)-978-1389. ----- Original Message ----- From: "William Bisson" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Thursday, June 03, 2004 6:21 AM > Dear Chuisy, > > The broad bump you are experiencing at low angle may be to do with the > slits. One has to be careful with these new XRD machines which have > variable slits, to make sure the divergent and the anti-scattering slits > are equal and if you choose to keep the slits fixed, which usually results > in a broad peak, the footprint is small. However, this will result in poor > high angle data. > > It does require a deal of playing around with the slits to see what each > of the effects are. The main purpose of variable slits is to have > consistant data throughout a range of 2Theta, which it will do, however, > it does make refinement just that little harder, having to take into > account changing slit width over 2Theta. If anyone has any good tips on > this matter, I would be very interested to know. > > Regards > William Bisson > > On Thu, 3 Jun 2004 [EMAIL PROTECTED] wrote: > > > Dear all, > > > > We are recently installing a XRD, and there is a huge peak occurred in the > > 3-7deg (2T) which is masking the useful signals from the sample. How can we > > eliminate the big peak there? > > > > We use 40kW, 30mA CuKa x-ray, divergent and receving slits are used, > > > > many thanks, > > > > stephen Chui > > > > > >
