... in addition to what Edward has mentioned above, the peak at ca. 32.5 degree is due to the forbidden (200) reflection. So the problem seems to be solved :-)

Best regards, Dirk

Are the extra peaks minor or major peaks?

Any surface treatment was performed before the XRD analysis?

If they were minor peaks that can NOT be indexed for a known phase then they are most likely originated from:

1- Surface reorganization as reported by:

Article Seeing the invisible laser markings

2- Different issues related to the reflection, symmetry, satellite, and so on as well explained in an answer of a previous question on RG:

https://www.researchgate.net/post/Single_crystalline_Silicon_XRD

They are minor compared to (400) peak.

M. Gaidi You have not shared details of your XRD, but my guess would be that you are seeing "contamination" of your incident XRD spectrum, by which I mean you are not using strictly monochromatic k-alpha radiation. Again, I don't know your setup, but I would guess you have some tungsten L-line radiation (from tungsten that has plated on your XRD tube target from the tungsten filament) and possibly some K-beta radiation from incomplete elimination of the beta spectrum (from either your monochromator or filter).

An easy check for these hypotheses is to calculate the wavelengths, assuming the peaks are ALL from the Silicon 400 peak. Then look up what characteristic lines these wavelengths correspond to.

Andrew

Three of the peaks are for sure from Si(400):

69deg is Cu K-alpha

66deg is W L-alpha

62 deg is Cu K-beta

I think 32deg peak is also from Si(400).

... in addition to what Edward has mentioned above, the peak at ca. 32.5 degree is due to the forbidden (200) reflection. So the problem seems to be solved :-)

Best regards, Dirk

Thanks all for your helpful comments. The XRD spectrum is attached to my previous message as PDF file. last question if (200) is a forbidden reflection, it should not show up. correct?

As suggested by Edward. I confirmed his idea: The three observed peaks at 62, 66 and 69 correspond to the (400) one but related to three different wavelengths.

69deg is Cu K-alpha

66deg is W L-alpha

62 deg is Cu K-beta

Dear M. Gaidi ,

The observation of the forbidden 200 peak is caused by the multiple diffraction which is explained in the attached file. More details regarding the forbidden 200 peak in Si is given in:

Article High-resolution characterization of the forbidden Si 200 and...

you may find more discussion regarding forbidden reflections in the following link:

https://www.researchgate.net/post/What_is_meant_by_forbidden_reflection_in_X-ray_diffraction

Hi,

As I came to know the extra peaks from single crystalline Si is form of contamination from source and involving some forbidden reflections. For specific hkl (e.g. 400) one knows the d value (1.35765) given lattice parameter (5.4307) of Si. Now from X ray source the radiations coming can be CuKa1 (n=1, wavelength-1.5406) giving peak at 2theta value ¬69. If you input value for CuKa1 (n=2, wavelength-0.7703) it gives peak at 2theta ¬32.96. Similarly you can get 2 theta values for CuKa2 (wavelength=1.5444) , CuKb1 (1.3922), WLa1 (1.4764), WLa2 (1.4874), WLB1 (1.2818), WLB2 (1.2446), WB3 (1.2627), WLy1 (1.0986), which will give 2theta values as 69.3285, 61.68966, 65.87497, 66.42896, 56.33581, 54.56229, 55.42341, 47.73071.

Though I am not sure what is the reason of visibility of these forbidden reflection, which seems to be independent of presence/absence of monochromator.