I want to know how workfunction of a metal can be modulated by gas adsorption like in the case of H2 adsorption , work function of Pd gets changed. Can anyone please explain the detailed mechanism?
Thank you
Anwesha
Hi Anwesha.
If you deposite an element with a high polarizability on any surface the work function of the surface will be decreased due to an electrical field, formed by the surface dipoles arizen. The typical example is an alkali metal deposition on metal (semiconductor) surfaces. For a cover less then 20-30 at.% the electric field of dipoles and the corresponding work function shift is proporcional to the dipole moment of the surface dipole and the concentration of the dipoles. Them, after the concentration of 30% the de-polarizong effect starts and the work function change became more complex function. Detailes about that you can find by using "Tooping model" key worlds.
In the case of gas molecules adsorption the results is not so evident. It strongly depends on what a chem-adsorbtion or a phys-adsorption takes place. Then, if the molecule decomposes after adsorption or no. And etc. I did not see any model in literature about that.
In general in the case of chem-adsorption another material (oxide, carbide, nitride, hydrid...) will be formed and the work function of thi material can be used.
In the case of phys-adsorption, the work function chamge effect is too low, because of a low polarizability of most molecules of gases. A rough estimation can be done with the formula in the webpage above mentioned by Dr.Karaman.
Regards.
Dear Anwesha,
Chemisorption is characterized by high binding energies. The surface chemical bond results from charge transfer or charge redistribution involving the surface and the absorbate. High adsorption energies are found for transition metals, due to their incomplete d-bands. Notice the range of energies for hydrogen adsorption (around 2.5 eV) and oxygen adsorption (4 to 10 eV).
For more on this topic, please see the following link:
http://www.virginia.edu/ep/SurfaceScience/Adsorption.html
Hoping this will be helpful,
Rafik
Hi Anwesha.
If you deposite an element with a high polarizability on any surface the work function of the surface will be decreased due to an electrical field, formed by the surface dipoles arizen. The typical example is an alkali metal deposition on metal (semiconductor) surfaces. For a cover less then 20-30 at.% the electric field of dipoles and the corresponding work function shift is proporcional to the dipole moment of the surface dipole and the concentration of the dipoles. Them, after the concentration of 30% the de-polarizong effect starts and the work function change became more complex function. Detailes about that you can find by using "Tooping model" key worlds.
In the case of gas molecules adsorption the results is not so evident. It strongly depends on what a chem-adsorbtion or a phys-adsorption takes place. Then, if the molecule decomposes after adsorption or no. And etc. I did not see any model in literature about that.
In general in the case of chem-adsorption another material (oxide, carbide, nitride, hydrid...) will be formed and the work function of thi material can be used.
In the case of phys-adsorption, the work function chamge effect is too low, because of a low polarizability of most molecules of gases. A rough estimation can be done with the formula in the webpage above mentioned by Dr.Karaman.
Regards.
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