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- เผยแพร่เมื่อ 28 ต.ค. 2021
- Download the pdf notes at edmerls.com/xps-spectra/
00:16 Photoelectric effect, which was discovered by Albert Einstein in 1905
Photoelectric Effect says that “When electromagnetic radiation, such as light, hits a material, electrons from the surface are emitted out.”
01:10 The basic equation for the ejection of electrons from the surface by electromagnetic radiation becomes, h𝑣 = BE + KE + 𝜙
02:23 Instrument: First thing is source of radiation Mg ka and Al Ka. Actually only one source can emit both the radiation.
05:56 Lenses, we use electrostatic lenses to collect the emitted electrons which are focussed to the entrance slit of the analyser. Lens and the slit system decides the area of the simple from where we want to collect the electrons. Or area of the sample to be analysed.
06:20 Analyzer, most of the commercial xps instruments are having hemispherical analyser, which is made up of two hollow hemicylindrical electrodes. Outer sphere is negatively charges and inner sphere is positively charged. Generally ejected electrons travel in straight line but when they enter in hemispherical analyser, they feel attraction from positive electrode, and repulsion from negative electrode. Because of this electric field the straight line path of electron is now bend in the direction of electrodes. Now it is important to note that if constant voltage difference is applied across two hemispherical electrodes, the electron with high velocity of kinetic energy will be bended to a lesser extent and will collide with the outer wall of the path. And if the ejected electron have low velocity or kinetic energy they will be bended to a larger extent and they will hit the inner wall of analyser.
That means only certain electrons with a fix velocity or kinetic energy will travel exactly through the path and will be allowed to pass through the exit slit. Rest of the electron with lower or higher kinetic energy will be lost in hemispherical path. This is quite important because by varying the applied voltage across two electrodes we can pass the electrons of certain kinetic energy, this means now we can separate electrons as per their kinetic energy.
08:38 Electrons coming out of the exit slit are counted with electron multiplier tube or channeltron.
So finally the number of electrons counted and the kinetic energy of electron from the analyser is send to the computer, which plot a graph of Kinetic energy in x axis and number of electrons counted in y axis.
In modern instruments, KE is converted into BE by computer, so the graph or spectrum becomes BE Vs Electron counts.
09:19 One important aspect of the instrument is presence of gas molecules in air in the path of X-ray. The gases present in air can also absorb the x ray and also the ejected electrons will collide with the gas molecules in their path, this will reduce the KE of ejected electrons. To avoid this complete instrument is maintained under Ultra high vacuum which is around 1 x10 -10 mbar pressure.
With simple rotary pump we can reach unto 10 -3 mbar, in addition if we can combine turbo molecular pump it can generate 10-8 mbar. But at this level of vacuum also water molecules sticking to the chamber are not removed, so we can do baking of the chamber. During Baking, chamber is heated upto 120C for about 24 hrs, at this temperature water molecules sticking on the surface gets vaporised and can be pumped with turbo molecular pump. After doing all, still hydrogen molecules remain inside the chamber, as the hydrogen molecules are very small they can not be removed by turbo molecular pump. So we need titanium sublimation pump. Titanium sublimation pump evaporates metallic titanium inside the chamber which is very reactive and the residual hydrogen reacts with the evaporated titanium and stick to the walls of the chamber. In this way we can reach unto the required vacuums of 1 x 10-10 mbar.
So that was all about the basic principle and instrumentation of XPS, In next video we will discuss the spectrum in more details, till than Thanks for watching this video and if you have any doubt, you can ask me in comment box.
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Thats the quality of a great teacher ,
10 min. Video everything explained in easy words .
Great ❤️
You earned my respect. Thanks a lot, and please make more videos with the same pattern and quality.
Thank YOU VERY MUCH SIR.. you made my day..Very clear explanation and now I understand the basic principle of XPS
Brilliant Explanation!!
It is very, very helpful for us. Thank you so much.
Great video, clear explanation on how it works. Can you further explain why XPS is a good method to measure density of state (DOS) of a crystal? For DOS, one needs to sum over electrons with all momenta. But if the incident light and outgoing electrons are fixed, thus the momenta are fixed, how come the detect collect electrons with all momenta? Can the sample freely rotate by arbitrary angles during the measurement?
There is a little mistake at 0:20 Albert Einstein didn't discover the photoelectric effect...He gave the right explanation of the effect. The Nobel prize was for the right explanation of the effect and not for his discovery. The photoelectric effet was known, but nobody before Albert Einstein could give a right explanation to it. All the rest is very well explained, thank you very much for your efforts.
Superb explanation sir, finally iam understanding this topic , keep it up sir
Thank you sir.very nice explaination
Thank you so much. I enjoyed learning. Very nice explanation 🥰🥰
Thank you 🤗
It is really helpful
It was an amazing video, thankss
Superb explanation:)
Super explanation
Excellent sir
Sir, can you share me the ppt , it will help me to explain further, I am a xps analyst in CSIR lab from last 4 year, Thank you..
Thanks a lot !!
Thank you
Sir, why the core level electrons are ejected not the valence one and how do we comes to know that these are core level electrons not the valence, can't we characterise the surface with valence electrons? Please reply
molecular mass of my coating is 254g/mol. Nitrogen inside is 28g/mol. XPS analysis shows 0,5%N in sample. How can i estimate amount of coating on sample in %?
What if the binding energy of core electron is more than the incident energy? Can it be detected?
It will not be detected
Sir notes?
Sir please send ppt in this video
Great video with clear explanation and easy to understand. Make more videos on Raman spectroscopy and FTIR.
Sir notes mill sktai hai
Superb
Thanks 🤗!!
Dear Edmels sir, i would like to ask you to get permission from you?. Can i use this figure my presentation and feature to use my manuscript. i should wait for your nice replay. thank you
Yes you can..
👍
❤
Dear sir can you send me the ppt of this video please ?
Khuda ka wasta hy yar ....kya photo electric effect einstein ny discover keya hy? Matlab kuch b.