Effect of SAM physisorbed on graphene - some questions

  • #1
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Hello everyone! :)

I'm sorry that I'm posting something that might be obvious, but I'm still struggling to capture all the concepts behind the fundamental physics of this model.

Let's say, I have a 2D sheet of graphene, on which, theres a physisorbed layer of molecular dipoles (vdW bonding, no covalent bonds). Eventhough graphene is semi-metal, I consider it in this model as a metalic surface, sicne theres no band-gap = can I do that? I'm not 100% sure, but I think I can.

I understand that these dipoles can (when aligned in the same direction) modulate the workfunction of a surface when aligned: my vision is that there's a desk capacitor with an electric field between the poles of the dipole, and the electron that want to escape the material also has to get through this extra field, which either increases or decreases the energy needed depending on the direction. Is this (simplified) view right?

Okay, so, this modifies the work function of the surface. The work function is linked to the difference between Fermi level and vacuum level, and since it changes, the only variable in this equation is the Fermi level - does that mean the Ef changes with the adsorbed dipoles? Isnt Fermi level shifting equivalent to doping? But doping = charge transfer, right? From the scientific works I read, they generally agree that there can be a charge transfer during adsorption, but some say it's only during chemisorption. Can there be a charge transfer (=doping?) during physisorption, when the molecules are bound only by noncovalent interaction?
And, if the dipoles in the layer orient randomly (that means if they try to minimize the energy), will they still induce some change to the properties of the surface?

Hope it's not too many questions at once. I tried my best at grasping the concepts, read scientific works, some books, but failed to find a source that would 100% answer all my questions. Many thanks to anyone who can clarify some of these questions!
Have a great day, :-)
Matt
 

Answers and Replies

  • #2
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Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
 

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