Do you know semiconductors? your answer is no... "I will explain to you very easily" Part # 9

Hello friends, lovers of science, I disappeared some days from the page due to personal problems, but nothing that can not be solved.

Today I want to resume publishing the continuation of the post part # 8 previous publication where I was explaining in detail how to structurally characterize a semiconductor by powder X-ray diffraction technique. I speak to you in a general way about the equipment that we use in Laboratory of Structure and Engineering of Nanostructured Materials. In the same way how it is composed and how the equipment works, different tips to use the device, etc.

I also mentioned how we analyzed the diffractogram that we obtained after doing the sample sweep of the semiconductor compound, by means of the computer programs search-match and Dicvol2004.

Now entering fully into today's topic, I want to show you another computer program that I use to perform the qualitative analysis of the diffraction patterns, the search-match serves to identify each peak with its respective intensity and location in 2θ. The Dicvol2004 performs a complete analysis of the most intense peaks to show us which crystalline system a semiconductor compound belongs to, it also gives us the parameters of the unit cell and the miller indexes, but there is a small detail with this program, and it turns out that It is not very reliable to give us the real values ​​of the parameters of the structure, if not rather it is used is simply to determine to which crystalline system the compound belongs, and this is because we only take 10 peaks of the diffractogram.

There is another computer program and this one is perfect to determine the real values of the network parameters, miller indexes and the most important thing to be able to see if there is any additional phase not reported, which unlike the Dicvol2004 does not identify them .

How to perform a qualitative analysis through the NBS computer program.

The methodology is the same as the one we used with the Dicvol2004 program, it is an exe executable program.

The first thing we must do is get the program and open the folder.

We open the folder and we will get several files, but we select an input file and modify it, placing the name of the compound to be indexed, in this case it is copper-gallium-tellurium2.

Later we open the file and it will show us something like this:

This file shows all the peaks identified by us when making the qualitative analysis through the search-match, unlike the Dicvol2004 that we only write in the folder the 10 most intense peaks, in this program we will place all peaks identified, in order to do a complete indexing of the diffractogram and correctly determine the network parameters and possible appearance of additional phases.

We must bear in mind that at the time of recording each peak, it is important to be able to observe well its location on the x-axis, that is 2θ, so that the error is the least significant, and write them in the notes blog exactly as shown in the image, without spaces, without points, without commas, because otherwise at the moment of executing the file it will show us an error, since the algorithms of the program are determined in that way.

After writing down all the peaks identified, the next phase will be to execute the input folder in the NBS application, this will perform the sweep and will result in the creation of a new file in this case of output.

We open the application and place the name of the input file, as follows:

Press enter on your keyboard and automatically the program will index the peaks initially entered in the input file.

In the same NBS folder we will look for the file with the updated date and that will be the output file with the results of the indexing.

The file is opened and we visualize the results:

The image shows the real value of the parameters of the unit cell of the tetragonal system a = b and c, in the same way the volume of the sample.

Below in the same letter appears all the peaks entered in the file with their miller indexes assigned, other peaks also appear that we did not introduce initially but the program shows as results the appearance of new peaks, for us to confirm if they are really a phase additional we must take its location 2θ, and go back to the search-match and corroborate if it is a new peak, and this is done taking into account the intensity of the new peak with that of others already assigned by us, that is to say, we make a comparison of intensities.

As we can see I index the 33 peaks introduced by us initially.

Also at the end it shows the figure of merit which means that the greater the number, the better the indexing and the more reliable.

In this way we finish the qualitative analysis and we have the final results of our diffraction pattern.

References

• http://personales.upv.es/~avicente/curso/unidad3/determinacion.html
• https://es.wikipedia.org/wiki/Cristalograf%C3%ADa_de_rayos_X#Rayos_X
• https://www.upct.es/~minaeees/difraccion_rayosx.pdf
• User manual Dicvol2004 and NBS

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I hope you have enjoyed my experiment, if you have any doubts on the subject remember to leave your comment and my person will kindly try to clarify those doubts.

Carlos Pagnini