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 Fitting the BRUS equation to a graph
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Paddel

Germany
2 Posts

Posted - 07/26/2016 :  08:54:50 AM  Show Profile  Edit Topic  Reply with Quote  View user's IP address  Delete Topic
Origin 8.1G on Windows 7

Hi and Thanks to everyone who will take their time to help me with this.

The BRUS equation is a formula with which you can quantisize the quantum size effect in nano particles. I have a set of data and want to use this equation to fit the graph.

E(bandgap, bulk)-(h*c/lambda)=(h²/8R²)*((1/(me*m))+(1/(mh*m)))-((1.8e²)/(4pi*Eps*Eps0*R))

, wherein E(bandgap, bulk) is the bandgap energy of the material, h is Planck's constant, c is the speed of light, lambda is the wavelength of the absorption spectrum, R is the particle size, me is the effective mass of the elctron and mh is the effective mass of the hole (both of which are multiples of the electron mass m), e is the charge of an electron, pi is the number pi, Eps is the permittivity of the material and Eps0 is the permittivity of vacuum.
R is the value I want to know, so it is the y-axis. lambda is the value I am measuring in my spectra so it is the x-axis. So R is the dependant variable and lambda is the variable. Constants are h, c, m, e, Eps0 and of course pi.
I have tried to form the explicit function, sipmlify it and fit it, but that did not work. I have tried to use the implicit form but I cannot get it to work. Now I hope that someone here can give me some useful information or code that I can use.
Thanks.
Patrick

Paddel

Germany
2 Posts

Posted - 07/29/2016 :  08:09:47 AM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
The simplfied explicit function is

R=(A/(sqrt(E-(h*c/(l*1E-09))*2*A+B^2)+B))*1E9

A=h²/4 *((1/(me*m))+(1/(mh*m) is set as a parameter as well as
B=(1.8e²)/(4*pi*Eps*Eps0). E is also a parameter. h and c are Planck's constant and the speed of light which I set as constants.
So I now have 3 parameters and Origin still cannot do anything.
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