Hello friends....

As we know when we shrunk the size from bulk to nano the bandgap of the material increases......

But when we go from Graphite to Graphene, why there is no change in the bandgap

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Consider H to Zn. The band gap of H is more than that of Zn as Zn tends to have more no. of electrons(electron clouds)surrounding it. So, more electrons means, lesser band gap, as there is an increase in bands between the energy levels. When we see Graphene, it itself is a zero-gap semiconductor. Graphite is nothing but stacks of graphene layer, one over the other. Thus, producing no change in the band gap. 

I hope, this satisfies your query. Thanks!
For more info, please refer to the below link:
http://prb.aps.org/abstract/PRB/v74/i7/e075404

Thank you Madhulika Sinha for replying me.......

As you mentioned here, according to eletron affinity and electronegativity in periodic table the band structure will vary..........But if u consider bulk material...for example Gold (Au).....yellow in color but when we go on reduce the size the bandgap increases in the same way if we go from Stacked graphene to single layered graphene the bandgap should increase but it remains the same......

MADHULIKA SINHA said:

Consider H to Zn. The band gap of H is more than that of Zn as Zn tends to have more no. of electrons(electron clouds)surrounding it. So, more electrons means, lesser band gap, as there is an increase in bands between the energy levels. When we see Graphene, it itself is a zero-gap semiconductor. Graphite is nothing but stacks of graphene layer, one over the other. Thus, producing no change in the band gap. 

I hope, this satisfies your query. Thanks!
For more info, please refer to the below link:
http://prb.aps.org/abstract/PRB/v74/i7/e075404

Dear Sandeep,

As Madhulika mentioned that graphite is nothing but stacked graphene layers in 3D. There is indeed a change in band gap when u go from grahite to graphene but that is very small and not observable owing to very small band gap of graphite. It is mentioned in the reference provided by Madhulika. 

In case of Au, it is the quantum confinement effect which gives rise to different colors due to surface plasmon resonance.

SK

Thank you sir for replying me......

is this the answer which is mentioned in the reference......graphite shows a semimetallic behavior with a band overlap of about 41 meV. In contrast to a single graphene layer, we show that two graphene layers have a parabolic spectrum around the Fermi energy and are a semimetal like graphite; however, the band overlap of 0.16 meV is extremely small....

i.e., from 41 meV to 0.16 meV.......

Dr. Satender Kataria said:

Dear Sandeep,

As Madhulika mentioned that graphite is nothing but stacked graphene layers in 3D. There is indeed a change in band gap when u go from grahite to graphene but that is very small and not observable owing to very small band gap of graphite. It is mentioned in the reference provided by Madhulika. 

In case of Au, it is the quantum confinement effect which gives rise to different colors due to surface plasmon resonance.

SK

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