1. Water Adsorption on Graphene: A First principles study
Mihir Ranjan Sahoo
IIT, Bhubaneswar
2. Graphene as Gas Sensors:
•Graphene: highly sensitive gas sensor
•Increase in Graphene charge carrier/concentration induced by adsorbed gas molecule leads to highly sensitive sensors, even possibility of detecting individual molecules.
•Sensor property based on changes in resistivity due to molecules adsorbed on graphene sheet.
•Excellent sensor properties of graphene due to 2 important facts:
i) 2-D crystal structure with only surface and no volume, maximizes the effect of surface dopant.
ii)Highly conductivity and shows metallic conductance in the limit of zero conductance.
4. Water on Graphene
Position
Orientation
Height (in A)
Adsorption Energy
(in meV)
Centre
Up
3.70
36.22
Centre
Down
4.02
30
Centre
Parallel
3.55
36.80
Top
Up
3.70
33.87
Top
Down
4.05
28.95
Bridge
Up
3.70
32.45
Bridge
Down
4.05
29.87
Centre
Pointing
3.50
54.26
The Adsorption Energy has weaker Water-Orientation dependence.
Down
Pointing
Parallel
Up
5. Band Structure
Pristine Graphene
Water on Graphene with O atom Up
Water on graphene with one O-H is pointing
6. Band Structure
•Band Structure of water on graphene is almost identical to that of Pristine Graphene due to weak Interaction of water with Graphene.
•HOMO of water molecule is located at -2.62 eV relative to the Fermi level
•LUMO of water molecule is located at 3.31eV relative to the Fermi level.
7. Density of States
a)- HOMO of H2O
b) – LUMO of H2O
Main panel- DOS of H2O on Graphene
9. Orientation Vs Charge transfer
Orientation
Charge Transfer(e)
Up
0.021
Down
-0.009
Parallel
0.015
Pointing
-0.025
10. Adsorption of water on Graphene
•In Up Orientation , the HOMO plays dominant role, through a small mixing of graphene orbitals above the fermi level, and donates some charge to Graphene. (Donor)
•In Down and Pointing orientation,the LUMO of water interacts stronger with the surface, through a small mixing with the graphene orbitals below Dirac point, to accept some charge from graphene (Acceptor)
•Experimentally, water acts as acceptor, which is also energetically favorable condition in Center-Pointing position predicted in theoretical calculation.
