I have seen many answers to the question on how to determine the band gap of a semi-conductor, but that always implies the use of UV-Vis Spectroscopy. However, the problem with this method is that the material we want to analyze the Band Gap of (aluminum waste from a beverage/soda can) is not a film but rather something that is opaque and will evidently just end up absorbing all of the light it is subject to. Please help us, it's part of our research requirement for us to graduate.
Dear Angelica Marie K Carbonell :
There may be another way of calculation the bandgap Eg of a solid material besides of doing it via UV-vis absorption spectroscopy.
Is your sample a bulk material, right ?
Lets first look the attached diagram for moment
I'm not familiarized with this method but I know that it is possible to compute the Eg measurint other electronic parameters of the solid as the , Fermi Level, Work Function, the Ionization Energy, Electron Affinity, etc.
For example: if you know the Ionization energy (I.E. in the diagram) and the Electron Affinity, then, from the diagram Eg = I.E. - E.A or: the (W.F - E.A.) + F.L. = Eg as well.
So the problem reduces on how to measure experimentally some of these parameters of the material.
And the answer is gonna be UPS and XPS.
For instance, is possible to measure the Valence Band Edge with UPS. For the Work Function, there is a method with XPS to compute this property. and I know that by combining UPS and XPS techniques is possible to measure the Fermi Level, but I'm sorry, As I said I'm not familiarized with these methodologies, but I know they exist, is just about getting a little deep into these techniques and search some papers where you can find this is applied to some material science.
Wish you Luck !
Kind Regards !
Dear Angelica,
you have different interactions of light with matter. Opaque means, that the light is scattered. This influences the direction of propagation (k-vector). If you look through a window, normally you can see a picture behind this window. If the window is opaque, the light is deflected and you cannot see a clear picture. This doesn`t mean, that the absorption characteristic is changed. Absorption is an inelastic process. I would try to carry out an absorption measurement. Of course, it can be, that the properties responsible for opacity can influence the absorption characteristic. But the gap is probably the same.
I would try to carry out an absorption measurement.
With Regards
R. Mitdank
Sir Rüdiger Mitdank , thank you for your input! We did try to subject it to an absorption test via UV-Vis, however we came up with just a consistent absorption, throughout the whole wavelength interval it was subject to, which would not provide us with values that could construct a Tauc plot wherein we could compute the value of the gap from. Would there be any other method you could suggest in order to achieve such values? Thank you in advance!
You are right, it is a difficult task, if the scattering centers themself influence the absorption near the band edges.
If the material allows to produce p- and n-type material, than you could try to measure the contact potential difference by Kelvin probe measurements. This could give a rough estimation of the gap.
With Regard
R. Mitdank
Dear Angelica Marie K Carbonell for the opaque material you may use Diffuse Reflectance Spectroscopy (DRS). There is Kubelka-Munk theory explaining how to recalculate the band gap from the diffuse reflectance spectrum. You may find many papers concerning Kubelka-Munk theory. For examle: W. Wedland and H. Hecht, Reflectance Spectroscopy (Interscience, New York, 1966). End take a look at the attachment.
If the semiconductor is intrinsic you could try measuring it electrically, the resistivity vs Temp can be fitted to determine eV.
Sir Curtis Guild
,I wanted to ask you what method is good in order to pulverize aluminum samples, and what procedures come with regards to placing the samples in the cuvette, such as what exactly to do, dissolve the metal in solution? Or maybe mix it with the powder barium sulfate? Thank you in advance!
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