1.7 A practical introduction to x-ray absorption spectroscopy  (Page 5/5)

Sample preparation

As was described in last section, there are diluted solid samples, which can be prepared onto big substrates or concentrate solid samples which have to be prepared in thin films . Both methods are following described.

Liquid and gases samples can also be measured, but the preparation of those kind of sample is not discussed in this paper because it depends in the specific requirements of each sample. Several designs can be used as long they avoid the escape of the sample and the material used as container does not absorb radiation at the energies used for the measure.

Method 1

1. The materials needed are showed in [link] : Kapton tape and film, a thin spatula, tweezers, scissors, weigh paper, mortar and pestle, and a sample holder. The sample holder can be made from several materials, as polypropylene, polycarbonate or Teflon.

   

2. Two small squares of Kapton film are cut. One of them is placed onto the hole of the sample holder as shown [link] a. A piece of Kapton tape is placed onto the sample holder trying to minimize any air burble onto the surface and keeping the film as was previously placed [link] b. A side of the sample holder is now sealed in order to fill the hole ( [link] ).

   

   

3. Before fill the sample holder, make sure your sample is a fine powder. Use the mortar to grind the sample ( [link] ).

   

4. Fill the hole with the powder. Make sure you have extra powder onto the hole ( [link] a). With the spatula press the powder. The sample has to be as compact as possible ( [link] b).

   

5. Clean the surface of the slide. Repeat the step 2. Your sample loaded in the sample holder should look as [link] .

   

Method 2

1. The materials needed are showed in [link] : Kapton tape, tweezers, scissors, weigh paper, mortar and pestle, tape and aluminum foil.

   

2. Aluminum foil is placed as the work-area base. Kapton tape is place from one corner to the opposite one as shown [link] . Tape is put onto the extremes to fix it. In this case yellow tape was used in order to show where the tape should be placed but is better use Scotch invisible tape for the following steps.

   

3. The weigh paper is placed under the Kapton tape in one of the extremes. Sample is added onto that Kapton tape extreme ( [link] ). The function of the weigh paper is further recuperation of extra sample.

   

4. With one finger, the sample is dispersed along the Kapton tape, always in the same direction and taking care that the weigh paper is under the tape area is being used ( [link] a). The finger should be slid several times making pressure in order to have a homogeneous and complete cover film ( [link] b).

   

5. The final sample covered Kapton tape should look like [link] . Cut the extremes in order to a further manipulation of the film.

   

6. Using the tweezers, fold the film taking care that is well aligned and there fold is complete plane. [link] a shows the first folding, generating a 2 layers film. [link] b and [link] c shows the second and third folding, obtaining a 4 and 8 layers film. Sometimes a 4 layers film is good enough. You always can fold again to obtain bigger signal intensity.

   

Bibliography

• B. D. Cullity and S. R. Stock. Elements of X-ray Diffraction , Prentice Hall, Upper Saddle River (2001).
• F. Hippert, E. Geissler, J. L. Hodeau, E. Lelièvre-Berna, and J. R. Regnard. Neutron and X-ray Spectroscopy , Springer, Dordrecht (2006).
• G. Bunker. Introduction to XAFS: A practical guide to X-ray Absorption Fine Structure Spectroscopy , Cambridge University Press, Cambridge (2010).
• S. D. Kelly, D. Hesterberg, and B. Ravel in Methods of Soil Analysis: Part 5, Mineralogical Methods , Ed. A. L. Urely and R. Drees, Soil Science Society of America Book Series, Madison (2008).