There should be no peak shift, as you still observe the lattice planes in Theta-2Theta geometry, only in other crystallites than in XRD. But as you have a thin film, you will observe some texture, which will lead to significantly different peak intensity ratios. It's also possible that you observe peaks that didn't appear in measurements done in normal XRD mode (locked-coupled).

 Dear Claus ,

so if I use from x-ray under 5 degree in thin film ,is it logical observe peak in 30 degree?

You can see peaks anywhere, when you push the detector far enough. The difference between XRD and GIXRD is as follows: in XRD, all diffraction intensity originates from lattice planes that are parallel to the sample surface. In GIXRD the lattice planes are tilted against the sample surface, and this tilt angle will be higher the higher the 2Theta position of the peak is. 

The main difference is the geometry: In GIXRD you have an asymmetric geometry with a small incident angle and a large exit angle, that may in certain cases be identical to 2Theta (if the incidence angle is very small). In conventional theta-2theta geometry, incidence angle (with respect to the sample surface) and exit angle (with respect to the sample surface) are identical, summing up to 2 theta!

Thus peaks at large exit angles in GIXRD are expected! Hope this helps, Dirk

  Dear Claus and Dirk,

Thanks.

All the best,Abbas

You may also get multiple scattering which can lead to a peak at a forbidden scattering angle. This is quite common in Silicon and other materials with very sharp darwin widths. For example a 1 1 1 and 1 1 -1 multiple reflection can lead to a reflection that seems to be a 2 2 0.

Dear  Lawrence و

Thanks.

your very welcome.

 Dear Dirk ,

as you know similar to GIXRD ,in the XRR the incident angle is small and  exit angle is large , but It is not possible  observe x-ray peaks in higher angle in the  XRR while in the GIXRD  it is possible observe x-ray peaks in higher angle .why?

Dear Claus ,

please suggest a book in the GIXRD field that cover your comments.

Regards,

Abbas

Dear Abbas,

if you simply increase your incidence angle in XRR (up to say 10 degrees or more) you will observe diffraction peaks - this is conventional XRD! Please find some examples in the attached files. In case 1, you will see Bragg peaks because of the presence of a supperlattice (see http://www-ssrl.slac.stanford.edu/content/science/highlight/2012-02-27/resonant-x-ray-reflectivity-study-perovskite-oxide-superlattices), in the second because of the internal structure of an organic layer (http://pubs.rsc.org/en/Content/ArticleLanding/2012/RA/c2ra20272g#!divAbstract). In both graphs you can see the transition of the XRR geometry (small incidence small exit angle and specular reflectivity) towards larger angles (decreasing intensity, and superimposed "Bragg-like" peaks!

Hope this clarifies your question, kind regards, Dirk

You could have a look at "Surface and Thin Film Analysis - a Compendium of Principles, Instrumentation, and Applications" by H. Bubert and H. Jenett. But in principle you only need basic geometry. Look at the attached image and the angles. If you fix the angle of the incident beam at a certain value and obtain a peak at some high detector angle, this diffraction will have taken place on lattice planes that are tilted against the sample surface in a way that incident and emergent angle are the same (with respect to the lattice plane). I would recommend to create a model from transparent slides and play around with the beam angles and crystal orientations, that might help in understanding the principle.

 Dear Dirk and  Claus ,

very thanks.

Regards,

Abbas

My first question is this, what is your sample mounted on. Is it glass? This was always the first question I would ask researchers when they came to me with anomalous data in the approximate range of 20-25 degree. 

 Dear Robert ,

yes.

That is consistent with Dirk's answer where you may be observing diffraction at higher incident angles. 

Dear Robert ,

It ( observing diffraction at higher incident angles ) depends on the type of material?

Dear Abbas,

Let's say that you observe this peak consistently, with different samples, different materials, then I would say it is an artifact with the sample holder. If the peak is unique to the sample, or say changes intensity like the RSC paper in Dirk's post, then it is a product of the film itself. Working with the conjugated polymers of my collaborator, I have seen those sorts of peaks before, though at lower angles of 2*theta. I had a sample of an organic film on an ITO coated slide and signal from the ITO started to appear at higher angles of incidence. In this case, a measurement was taken of the ITO slide to determine whether or not the signal we were observing was from the film of interest or the ITO. I mention sample holders merely because it was not something I had seen in any of the previous posts and sometimes, sometimes, it can cause a problem with analysis.

Dear Robert ,

Thanks.please suggect refrence .

Regards,A

 Dear Dirk and  Claus and Robert ,

Can you tell me about the number ofX-ray peak for single-crystal ?

Dear Abbas, the number of peaks you may observe is dependent on the crystal structure and orientation of your sample, as well as on your experiment. Especially the X-ray energy and the angular range accessible are important here. For example, if you use a smaller X-ray wavelength (higher energy) then all of your peaks will "move" to smaller diffraction angles. Attached please find a graph that we have measured recently. It shows a single crystal Si(111) wafer, and we employ the radiation from a conventional Cu anode, the incidence angle is fixed to about 20°, and we record the diffracted intensity with an energy-dispersive detector. Thus we make use of the Bremsstrahlung radiation for an energy-dependent diffraction experiment, keeping the geometry constant but varying the X-ray wavelength (energy). You may recognize many diffraction peaks, as well as you see that the background of the Cu K_alpha lines gives rise to additional peaks in the detected diffraction pattern. You will see that we were able to detect at least the (111), (333), (444) and (555) reflections, and there are indications as well for the (777). Using a higher energy (excitation energy of the anode), you may probably detect more peaks!

Hope this help! Cheers, Dirk

Dear  Dirk ,

thanks.

In addition to what you say, for example, single-crystal X-ray peaks are associated with higher-order reflections?

well some of them are! But take care - there are selection rules. The (222) for Si is e.g. a forbidden reflection!

Dear  Dirk ,

please tell me about selection rules more.why The (222) for Si is  a forbidden reflection?

Dear  Dirk ,

Is the peak density (number of peaks per 2θ angle) higher at low 2θ or at high 2θ in X-ray diffraction spectra? Why?