I am doing research on nanoparticles using laser ablation method.I am varying different parameters and Xrd results show an increase in intensity with increase in laser fluence.
I don't know what this laser ablation is but an XRD peak is a kind of gaussian. when its intensity increases its width decreases which infers the increase in crystallite size. in case of nano particles the crystallite size can be same as of particle size....
maybe the crystallite size increases. the best way is post 2 different data as u mentioned.
I think I. Farrer is very close to the solution. When increasing the laser intensity the speed of the ablation process increases and thus the amount of nano particles going off the surface increases and thus the XRD interaction with the x-ray beam just in front of the film is stronger. In other words: there is a cloud of ablated particles just in front of the film, Its density depends on the laser intensity. Part of this cloud is seen by the x-ray beam in addition to the signals of the film. Partial volume effects could also play a role here, because the off-going particle cloud passes the x-ray interaction region, which is set up by the primary beam and the acceptance cone of the detector.
Definition of laser ablation is the process of removing material from a solid (or occasionally liquid) surface by irradiating it with a laser beam. At low laser flux, the material is heated by the absorbed laser energy and evaporates or sublimates. At high laser flux, the material is typically converted to a plasma. According to this definition, with increasing laser flux it means the temperature will be increase. Sometime when increasing the temperature, the coarsening material will also increase. The coarsening increase, the size particle increases. When temperature increase, the crystallization can also increase. Both of coarsening particle and increase of temperature can contribute to the height of intensity in XRD.
Do you perform XRD investigation while doing the laser ablation ? If yes you should look at the XRD peak heights after switching off the laser. If then the peak heights remain high Posman should be right in his answer with respect to coarsening effects.
Hi Tanzeeha,
there is another thing, which came me in mind: it is the huge temperature increase of the sample during laser ablation. There are two scenarios of the experiment: a) in situ laser ablation during XRD measurements or b) alternately doing XRD, laser ablation, XRD, laser ablation and so on. In the latter case (b) the sample has to be moved together with its sample holder between the two systems in order to provide reproducibility in mounting the sample in the XRD set-up.
In both cases the laser ablation passes a huge amount of heat into one of the surfaces of the sample. Here a very un-isotropic heat transfer takes place, which will cause strong temperature gradients into the sample and sample holder system and a displacement of the sample surface will show up as a consequence of a bending (caused by temperature gradients)of the sample and/or its support.
For case a) it is obvious, that then a displacement of the sample surface relative to the x-ray optical set-up will show up, which is stronger the higher the laser fluence is. For case b) I can imagine that strong temperature gradients may lead to non-reversible deformations of the sample/holder system, so that also here a sample displacement in the XRD set up will show up at the end; also fluence dependent.
If a displacement of the sample takes place during the XRD experiments there is always a change of x-ray flux showing up; which you see in your experiments here for example as a common increase of all diffraction-line intensities.
I think it is not trivial to create an experimental set up without exerting a sample displacement when a huge heat transfer into the sample system is performed like that of an ablation laser system. You should think of a clever normalizing routine. I hav’nt found a solution yet. Good luck.
You stated that you have got the answer. But I think we are all eager of knowing what is the 'real' answer in your case?
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