# How can a monochromatic X-Ray tube produce a spectrum in XPS?

I thought that if we use monochromatic source, we can only get one peak, if it exists.

Because Photoelectric Effect allows only the electron that have the corresponding frequency(energy level) that can be excited.

appreciate your help to rectify my understanding.

Because the X-rays, in the Photoelectron spectroscopy device, excite the electrons from the individual core levels out and as we know the electrons from the individual core levels reside in different energy levels. Thus the amount of energy left after the electrons overcome the individual energy barrier of each level is different since they derive all their energy from a single source (The single source). The equation goes like this

$$KE=h\nu -E_f-E_b$$

Where $E_b$ is the binding energy of every electronic level under consideration and $E_f$ is the Fermi level height of the material under scrutiny with respect to vacuum. Since $E_b$ is different for different electronic levels, hence $KE$ of the electrons are different which result in different peaks.

• Said otherwise, the photoelectric effect applies to each bound state of the system. Ordinarily this means just the conduction band and valence band, but at xray energies there are many core states that before accessible. – KF Gauss Jul 30 '17 at 22:53
• "the electrons from the individual core levels reside in different energy levels." This is the part that I am asking about. monochromatic source can excite only the electrons with corresponding energy level, right? since it is monochromatic, then there should be only 1 energy level that corresponds with the radiation frequency of the monochromatic source. – Codelearner777 Jul 31 '17 at 2:14
• @Codelearner777 No, suppose the frequency of the source is $\nu$, then any level with energy $E$ can be excited such that $$E\leq h\nu$$ Moreover, I wouldn't use the word excited, I'd use extracted. – ubuntu_noob Jul 31 '17 at 14:24

Monochromatic X-rays produce electrons from a multiplicity of orbitals, producing a range of electron kinetic energies. One can analyze the outgoing electron energy to produce a spectrum. It's a spectrum of Xray photon energy minus binding energy of the electron, so for a fixed Xray energy, it's the electron binding energy that is represented.

Over a small range of energies, you can give monochromatic excitation and analyze the output electrons' individual energy. Over a larger range, the 'monochromatic excitation' from a synchrotron source can be swept through a range of frequencies. There is a significant improvement in Xray absorption efficiency for electron binding energies at or slightly above the incident Xray energy, so sweeping the Xray source energy is useful.