Interaction of small molecules with grapheen supported on metal substrates: A first principles study
Download as PPTX, PDF2 likes2,492 views
The document presents a first principles study of the interaction between small molecules and graphene supported on metal substrates, focusing on the electronic structure of the graphene/ni(111) interface and the impact of water molecule adsorption. It employs density functional theory (DFT) to calculate binding energies and analyzes how various factors, such as substrate type and mechanical strain, can modify the band gap of graphene. Future research plans include exploring electronic structure variations in different substrate materials and the corrosion control properties of graphene-coated materials.
![14
Functional
• The functional described in Hohenberg-Kohn
theorem
푬 휳풊 = 푬풌풏풐풘풏 휳풊 + 푬푿푪[{휳풊}]
• Known term
푬풌풏풐풘풏 휳풊 = −
ℏퟐ
ퟐ풎
∗휵ퟐ휳풊풅ퟑ 풊 풓 +
휳풊
푽 풓 풏(풓)풅ퟑ풓 +
풆ퟐ
ퟐ
풏 풓 풏(풓′)
|풓−풓′ |
• Hence total energy functional
풅ퟑ풓풅ퟑ풓’+푬풊풐풏
푬 풏 = 푻풔 풏 + 푽푯 풏 + 푽풆풙풕 풏 + 푬풙풄[풏]](https://image.slidesharecdn.com/finalfinalfinal-141117082214-conversion-gate02/85/Interaction-of-small-molecules-with-grapheen-supported-on-metal-substrates-A-first-principles-study-14-320.jpg)
![19
Results and Discussions
• Binding energy of graphene-Ni interface :
푬푮−푴 = 푬풕풐풕[푮 푴] − 푬풕풐풕[푴] − 푬풕풐풕[푮]
• Adsorption energy of water :
푬풂풅풔 = 푬풕풐풕 푯ퟐ푶 − 푮 푴 − 푬풕풐풕 푮 푴 − 푬풕풐풕[푯ퟐ푶]
• For graphene-nickel interface:
Orientation Equilibrium height(Å) Binding energy
(eV)
Top-fcc 2.1 0.317
Top-hcp 2.1 0.287
Fcc-hcp 3.0 0.269](https://image.slidesharecdn.com/finalfinalfinal-141117082214-conversion-gate02/85/Interaction-of-small-molecules-with-grapheen-supported-on-metal-substrates-A-first-principles-study-19-320.jpg)
Interaction of small molecules with grapheen supported on metal substrates: A first principles study
- 1. Interaction of small molecules with graphene supported on metal substrates: A first principles study Mihir Ranjan Sahoo 12PH09008 School of Basic Sciences IIT Bhubaneswar 1
- 2. Outline • Introduction • Motivation • Objectives • Methodology • Result and Discussion • Future plans • References 2
- 3. Introduction to Graphene • One atom thick planar sheet of carbon atoms • Honeycomb like structure • C-C bond length 1.42 Å • Thinnest, lightest and strongest material • Zero band gap leads to highly conductive. • High electron mobility • High Mechanical Strength Primitive Cell 3
- 4. band structure of graphene Valence band and conduction band touches at K and K’ in Brillouin zone. Zero band gap. Linear energy-momentum relation. Mass less fermions- Dirac particles. K K’ Brillouin zone 4 K K’ K’ K
- 5. • In spite of various novel properties, Graphene has limitation for using in some applications such as digital electronics, transistors due to its zero band gap. • For electronic switch high on/off ratio is required . For this a material having non zero band gap is necessary. 5
- 6. Inducing bandgap in graphene • Putting graphene on different substrates • Adsorption of atoms/molecules on graphene layer • By giving mechanical strain. • By increasing layers of graphene such as bi-layered or trilayered graphene • Cutting graphene in smaller dimensions such as nanoribbon. 6
- 7. • Graphene was reported to be used as highly sensitive gas sensors. • Sensor property depends upon the change in resistivity by adsorption of molecules on graphene. • By adsorption of molecule, charge carrier concentration can be increased . • Two-dimensional crystal structure which having surface but no volume enhances effect of surface dopant. 7
- 8. Objectives • To study electronic structure of graphene/Ni(111) interface and compare how band gap of the system is different from pristine graphene. • To study how adsorption of water molecule on graphene-metal interface affects binding energy. • To know how insulating substrates affects electronic structure. 8
- 9. Methodology • Density functional theory (DFT) is method to find approximate solution of many body Schrodinger equation. • Hence, DFT was employed to perform first principle calculation. • Vienna Ab-initio Simulation Package (VASP) was used for DFT calculation. • VASP uses projector augmented wave (PAW) method and pseudopotential for first principles calculation. 9
- 10. 10 Z Z Z 1 1 2 B A i j ij A B AB N i j M A B A N i M A iA M A A N i i r R r H 1 1 1 , , 1 2 1 2 2 Many electron system Time independent Schrӧdinger equation Ĥѱ(r1,r2..ri…rN,RA,RB…..RM)= Eѱ(r1,r2,…ri…rN,RA,RB…..RM) The full molecular Hamiltonian ^
- 11. 11 Born-Oppenheimer Approximation • Mass of Nucleus is much larger than mass of electron. i.e. Mn>>me • Freeze the motion of nuclei. Nuclear Kinetic Energy Nuclear-nuclear Interaction 0 constant • Electron-nuclear potential acts as external potential. Z Electronic Hamiltonian ^ 2 1 1 H elec i T V V Ne ee N i j ij 1 1 1 , i j N i M A A iA N i r r 2
- 12. Background of DFT • Electron density states all physical properties of many body system instead of wavefunction. • Electron density n(r) : 풏 풓 = 풅ퟑ풓ퟐ 풅ퟑ풓ퟑ … … … 풅ퟑ풓푵 휳( 풓, 풓ퟐ, 풓ퟑ … 풓푵) ퟐ • Hohenberg-Kohn Theorem: 1. The ground state energy is a unique functional of electron density. 2. The electron density that minimizes overall functional is the true electron density. 12
- 13. 훁ퟐ + 퐕 퐫 + 퐕퐇 퐫 + 퐕퐗퐂 퐫 횿퐢 퐫 = ℇ퐢횿퐢(퐫) 13 Kohn-Sham Approach • Interacting Non-Interacting • Kohn-Sham Schrodinger equation − ℏퟐ ퟐ퐦 • Kohn-Sham Density 푵 풏 풓 = |휳풊(풓)|ퟐ 풊=ퟏ
- 14. 14 Functional • The functional described in Hohenberg-Kohn theorem 푬 휳풊 = 푬풌풏풐풘풏 휳풊 + 푬푿푪[{휳풊}] • Known term 푬풌풏풐풘풏 휳풊 = − ℏퟐ ퟐ풎 ∗휵ퟐ휳풊풅ퟑ 풊 풓 + 휳풊 푽 풓 풏(풓)풅ퟑ풓 + 풆ퟐ ퟐ 풏 풓 풏(풓′) |풓−풓′ | • Hence total energy functional 풅ퟑ풓풅ퟑ풓’+푬풊풐풏 푬 풏 = 푻풔 풏 + 푽푯 풏 + 푽풆풙풕 풏 + 푬풙풄[풏]
- 15. Exchange and Correlation • Local Density Approximation(LDA) : 푳푫푨 풏 = 풏 풓 ℇ풙풄(풏) 풅풓 푬푿푪 • Depends on Local density and derived from Homogeneous electron gas model. • Generalized Gradient Approximation(GGA): 푮푮푨 풏 = ℇ풙풄(풏)휵풏 풅풓 푬푿푪 • Depends on local density and its gradient. 15
- 16. Procedure for Self-Consistence Calculation 16
- 17. Calculation in VASP • Spin polarization Calculation • Exchange-Correlation potential-GGA • Supercell 2X2 • Energy cutoff 400 eV • 5X5X1 grid in kpoints for Brillouin zone sampling • 5 layers of Ni(111) • 15 Å vacuum 17
- 18. Why Ni(111) ? • Ni(111) surface –Hexagonal structure • ABC type Arrangement • Lattice Constant of Ni(111)= 3.52Å • Nearest C-C atom distance in Graphene = 1.42Å • Length calculated for C-C distance on Ni(111) surface = 1.43Å • 1% lattice mismatch. 18
- 19. 19 Results and Discussions • Binding energy of graphene-Ni interface : 푬푮−푴 = 푬풕풐풕[푮 푴] − 푬풕풐풕[푴] − 푬풕풐풕[푮] • Adsorption energy of water : 푬풂풅풔 = 푬풕풐풕 푯ퟐ푶 − 푮 푴 − 푬풕풐풕 푮 푴 − 푬풕풐풕[푯ퟐ푶] • For graphene-nickel interface: Orientation Equilibrium height(Å) Binding energy (eV) Top-fcc 2.1 0.317 Top-hcp 2.1 0.287 Fcc-hcp 3.0 0.269
- 20. 20 Graphene on Nickel(111) top-fcc top-hcp fcc-hcp Ni atom C atom
- 21. 21 Band Structure: (For only graphene) Fermi energy Energy (eV)
- 22. 22 Band Structure: (For only Ni(111)) Fermi energy Energy (eV)
- 23. 23 Band structure: (for graphene/Ni(111)) Energy (eV) ΔE=0.35 eV
- 24. 24 Up down pointing parallel Water on Graphene C atom O atom H atom
- 25. Adsorption energy and heights for different geometry Position Orientation Height in Å Adsorption Energy (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 orientation dependence 25
- 26. 26 Band Structure Pristine Graphene Water on graphene
- 27. Band Structure • Band structure of water on graphene is almost identical to pristine graphene due to weak interaction of water with graphene. • HOMO is located at -5.16 eV • LUMO is located at 0.89 eV • HOMO-LUMO gap of Isolated gas phase water is 6.18 eV. • Larger dipole moment associated with water molecules able to modify electronic properties of graphene. 27 6.05 eV
- 28. Water on Graphene/Ni interface • Graphene-nickel is arranged in top-fcc position. • Water lies above graphene surface on the centre of honeycomb structure and in pointing orientation. orientation Height of O atom(Å) Adsorption energy(meV) Top-fcc with centre-pointing 3.50 504 28
- 29. Future Plans • To study electronic structure modification of graphene on different substrates including insulating substrate. • To study how graphene coated materials control corrosion. • To study the electronic structure of metals such as aluminium and copper adsorbed on graphene. 29
- 30. References • Wallace P. R.:”The Band Theory of Graphite”. Phys. Rev. 71, 622, 1947. • Geim A. K., Novoselov K.S.: “The Rise of Graphene”. Nat. Matter, 6, p.183. 2007. • Geim A. K., Science, 324, 5934, 2009. • Allen M. J., et al., : “Honeycomb Carbon: A Review of Graphene”. Chem. Rev. 110, 2010. • Balandin A. A. , “Thermal properties of graphene and nanostructured carbon materials”, Science ,320 , p. 1308, 2008. • Boukhvalov D.W., Katsnelson M. I.: “Chemical functionalization of graphene”. J Phys. Condens. Matter, 21, p.344205, 2009. 30
- 31. • Kohn W., Becke A. D. , Parr R. G. , J. Phys. Chem. , 100(31), p. 12974-12980, 1996. • Kohn W., Sham L. J., Phys. Rev. 140, A1133, 1965. • Hohenberg P., Kohn W., Phys. Rev. 136, B864, 1964. • Perdew J. P. , Zunger A. , Phys. Rev. B. ,23, 5048, 1981. • Sham L. J., Kohn W. , Phys. Rev. 145, 561 , 1966. • Sham L. J., Schluter M. , Phys. Rev. Lett. , 51, p. 1888, 1983. • Kresse, G. "Software VASP, Vienna, 1999; G. Kresse, J. Furthmüller." Phys. Rev. B., 54.11, 1996. • Kresse G., Hafner J., Phys. Rev. B., 47, p. 558 , 1993 . 31
- 32. Acknowledgement • School of Basic Sciences, IIT Bhubaneswar. • DSC members. 32
- 33. 33