@ Isuru Lakmal. Just to add a view simulation: different thickness of CdS (50 and 100nm) and roughness (both 1 nm and 1.0/0.5 nm).

As mention by Prof Martens, you need to scan as low as possible. Make sure you align your film correctly. Check the tube-stage-detector alignment, specially if you dont have the xyz-stage.

Hi, thickness between 20-30 nm is considered good.

Thank you so much Muhammad Asad Iqbal for the information. So this might be the reason behind not having proper fringes pattern. Because layer thickness of my samples are so much greater than this range.

According to own x-ray reflectivity measurements in the 9keV regime the thickness values mentioned by Muhammad Asad Iqbal are ok. But you may go somewhat higher (up to ~ 100nm). But your fringe resolution depends on the angular resolution of your x-ray set up and in addition the fringe visibility depends on the x-ray attenuation of your film.

At which photon energy your are operating and which atomic numbers you are dealing with in the film?

Type of substrate ?

you are welcome Isuru Lakmal

Thank you Gerhard Martens for your advice.

Can you advise me using below information?

XRD machine : Bruker D8 ADVANCE

X-Ray tube : Cu (1.5418A)

Photon energy : 8keV

Layer material : CdS (Cd=48, S=16)

Substrate : Borosilicate

Angle range : 1°-10°

Increment : 0.02°

Machine settings look quite ok....

but Cd (quite high atomic number; Z=48) in the layer will easily attenuate the refracted beam. I expect that you can 'see' only a slight shoulder (if at all) instead of a series of sharp distinct fringes.

additional remark:

In the ppt (around page 21 )of the following link you can see some samples of fringe pattern as a function of the layer thickness (supporting the thickness range already mentioned above; but pay attention: R is given in log scale):

https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&ved=2ahUKEwjkjs2y0ZPkAhXusaQKHQguBlwQFjADegQIABAC&url=http%3A%2F%2Fwww.eng.uc.edu%2F~beaucag%2FClasses%2FCharacterization%2FReflectivityLab%2FColorado%2520State%2520Univ%2520XRR.pdf&usg=AOvVaw0V1mGH6GYc0VE-A9aaK52m

Thank you so much Gerhard Martens for your valuable information. As you mentioned, there are no sharp distinct fringes and for your reference I have attached the XRR pattern. It seems like XRR is not much suitable for my thick samples.

Thanks again.

It depends on your resolution in Q space. Q = 4 * pi * sin (theta).

The thickness you can measure is 2*pi/delta_Q.

delta_Q is the width of the fringes you measured.

In your sample system two materials show up:

CdS ; density about 4,8g/cm³

borosilicate; density about 2,23 g/cm³;

critical angle of total x-ray reflection (at Cu k-alpha) for these materials are at about 0,64° (in 2theta) for CdS and at about 0,43° for borosilicate.

None of these structures are seen in your reflection curve.

I do not understand them...

Perhaps your 2theta scale may have an offset of about 2,3°; the difference of about 0,2° is seen in your XRR.....

but neverthelass curious at the moment.

Next idea: does the CdS layer covers all of the surface of your substrate without holes?

Thank you very much Yizhou Lu for your information.

I really appreciate your concern about my problem Gerhard Martens .

Visually I could observe that the deposited CdS layer covers all of the surface and I have done four samples up to now. All the results have same behaviour.

I have discussed with my supervisor about the things we discussed here and he told me that he will provide me a CdS thin film which has thickness about 100 nm (measured by SEM).

According to your suggestions, first I'll do the all calibrations in XRD machine (detector calibration, Z scan, Rocking). Then I'll perform a XRR with the thickness known sample. Previously I have started the scanning from 1° and this time I'll start with 0° for more details.

After I observe the results I'll update you and we can check whether this problem occurred due to XRD machine calibrations or higher thickness.

Thank you again.

The expected Kiessig fringes will show up in the angular dependence of the reflection curve around and above the critical angle of total reflection. This angle is for CdS at about 0,64°(in 2theta), as mentioned above. Thus starting at 1° will make no sense.

Therefore you should concentrate on the very low angular regime, from quite below 0,6°and up to1° and a bit more......

Please carefully adjust the knife edge in order to prevent primary x-rays impinging on the detector at those low angles.

Please have a look at the answers of a related question; the attached documents may help you to align your system....

https://www.researchgate.net/post/How_to_measure_a_film_thickness_using_XRR_on_a_D8_Brucker

Especially the link given there by Philipp Hoenicke, which provides film reflectivity curves, is very usefull:

http://henke.lbl.gov/optical_constants/layer2.html

I have put in the data of your 100nm CdS film (borosilicate substrate set to SiO2); the results are presented in the attachement.

You see that the x-ray attenuation of the CdS film very easily kills the fringes.

Please note that the angular scale is theta scale (not 2theta)

@ Isuru Lakmal. Just to add a view simulation: different thickness of CdS (50 and 100nm) and roughness (both 1 nm and 1.0/0.5 nm).

As mention by Prof Martens, you need to scan as low as possible. Make sure you align your film correctly. Check the tube-stage-detector alignment, specially if you dont have the xyz-stage.

Maykel Manawan ,

by the way, which software do you have used?

Additional remark, the pattern presented by Maykel are presented in the log scale. So Isuru, please be carefull when having a look at your measured pattern in linear scale. You may overlook your expected fringes...

Thank you Maykel Manawan for your information. I have used XYZ stage. But there might be problems in aligning process. And also I have started the scan from 1°. So I'm going to check all mistakes in aligning process and redo the scan from ~0°.

Prof Gerhard Martens; I've used Panalytical XRR for the simulation. I also use Leptos.

Isuru Lakmal; cud u attach the picture of ur sample?

Maykel Manawan ,

Still I didn't get SEM images of my samples. Once I get them, I'll upload here. For your reference I have attached camera photos.

Thank you.

Looks homogeneous but we need SEM to see the topography.

You have to do the omega scan and off-specular scan to check the surface roughness if there's still no fringes.

Are you use a parallel beam configuration?

Maybe you have to do GIXRD to check the phase. Omega of 0.3 deg, theoretically gave u 126 nm of penetration depth on CdS (100% packing density).

Maykel Manawan ,

I have performed the 2Theta-Omega scan and I don't have knowledge about Omega scan. Could you please explain me about that.

Yes I have used a parallel beam configuration with Goebel Mirror.

I have done GIXRD previously and matched for Hexagonal.

Below I mentioned the machine settings.

X-Ray beam: 40kV, 25mA

Twin Primary: Goebel Mirror

No hight limiting slit (0.2mm)

Sample stage: XYZ stage

Twin Secondary: Motorized Slit (4.0mm)

Cu attenuator

No solar slit (2.5mm)

Detector: SSD160 (0D mode with 0.1 opening)

One of the link provided by Gerhard Martens contains an procedure of XRR (attached below) which said that I have to use hight limiting slit. But I haven't used that. So when I perform the test again, I planed to add that also.

I want to give the results of my next approach quickly. Unfortunately our postgraduate institute of science have only one XRD and there is a huge list of pending powder samples. Once they have finished those, they will mount the XYZ stage and start my sample. Then I'll update you ASAP.

Thank you.

Isuru Lakmal Which omega scan did u do? perhaps you can post your data here, and I will try to do the analysis.

Perhaps u can post ur data if u not mind.

Maykel Manawan ,

I have used XYZ stage which can not rotate through omega axis. I have performed rocking to aligned with the tilt of the sample. So I think I haven't add any offset to the omega. So I think it should be Specular scan. And also the simulation spectrum given by the LEPTOS is similar to the spectrum shows in the Specular scan.

For your reference I have attached the raw, udx and origin files.