electronic state calculation for hydrogenated graphene with atomic vacancy electronic state...
TRANSCRIPT
Electronic state calculation for hydrogenatedgraphene with atomic vacancyElectronic state calculation of hydrogenated
graphene and hydrogenated graphene vacancy
Kusakabe Lab. M1Gagus Ketut Sunnardianto
Contents1. Introduction
2. Results and Discussion
3. Summary
- What is graphene?- Unique Properties of graphene- How to get graphene and graphene vacancy?-Motivation-Research scopes-Research objectives
- Calculation (DFT+Löwdin)- Simulation condition- Charge transfer value- DOS (Density of states)
Graphene
http://invsee.asu.edu/nmodules/carbonmod/bonding.html
Atomic nature
Spectrum of carbon atom
Crystal nature
Bonding & hybridized energy bands of graphene
Unique properties of graphene1. High electron mobility (electronic properties)
2. Robust but also very stretchable (mechanical properties)
3. Can adsorb and desorb various atoms and molecules (chemical properties)4. The thinnest material (one atom thick -> nearly transparent)
C. Lee, X. Wei, J. W. Kysar, & J. Hone, Science 321, 385 (2008) R. R. Nair, P. Blake, A. N. Grigorenko, K. S. Novoselov, T. J. Booth, T. Stauber, N. M. R. Peres, & A. K. Geim , Science 320, 1308 (2008).
How to get Graphene….?
http://nobelprize.org/nobel_prizes/physics/laureates/2010/press.htmlDaniel R.Cooper et al, ISRN Condensed matter physics, 2012
Monolayer graphene produced by Mechanical exfoliation. Large sample With length of 1mm on Si/SiO2
http://newsdesk.umd.edu/uniini/release.cfm?ArticleID=2390
Graphene vacancy
Prof. Fuhrer(University of Maryland): Graphene vacancy acts as tiny magnets, open the possibility of “Defect engineering” for spintronic application
Hydrogenated graphene vacancy
DOS of Pure graphene and graphene vacancy
DOS of pure graphene
DOS of graphene vacancy
Motivation
“It is not possible to determine the charge transfer value per hydrogen adsorption directly from our experiment because the sticking coefficient on graphene is unknown.”
Motivation
1. Pristine2. Hydrogenation (cleaning)3. Annealing4. Ar Sputtering5. Hydrogenation6. Annealing7. 2nd Ar Sputtering8. 2ndHydrogenation
Graphene is a revolution material for hydrogen storage, Keyvan3.
Experimentally, Capaz et.al1 observed the charge transfer from hydrogen to graphene around 0.161. In a recent experiment by Kudo et al2 @TITECH, they found a value around 0.6 per vacancy.
[1]. APCTP-POSTECH-AMS WORKSHOP, Pohang, September 3, 2010[2] Kudo, et al. 27aXJ-3, Spring Meeting of JPS (2013).[3] Inside Rensselaer Volume 4, Number 3, February 19, 2010
Motivation
The most promising materials suggested as a potential hydrogen storage media is carbon based materials such as graphene (Durgun et al, Zhao et al)
This study carried out calculation for hydrogenated graphene sheet consisting of 24 carbon atoms and hydrogenated graphene vacancyconsisting of 63 carbon atoms within the framework of DFT
The present study just focuses on charge transfer and the evolution of the density of states to understand the change in the character of hydrogenated graphene and hydrogenated graphene vacancy
The objectives of this research are to calculate the atomic chargein hydrogenated graphene by Löwdin charge analysis to know the charge transfer and to understand the evolution of the electronicstructure through density of states upon hydrogenation
Research scopes
Research objectives
Based on Density Functional Theory (DFT) Generalized Gradient Approximation (GGA) VASP code (https://www.vasp.at) Quantum espresso code (Löwdin charge analysis)
Force convergen criterion : F ≤ 1.0 x 10-5 [Ry/a.u] PAW potentials to describe ionic potentials the energy cut off of 36.75 Ry for the plane wave expansion K-points mesh 16X16X1 for scf calculation Charge transfer calculated using Löwdin analysis
Method
Calculation
Simulation condition
RESULT
Initial structure
Optimized structure
Initial structure
Optimized structure
Initial structure
Optimized structure
Hydrogenated graphene
v
Graphene+3H
C
Graphene+H
A
Graphene+2H
A
B
B
A
Material Charge Transfer
Charge Transfer(Average)
Graphene+H 0.2241 0.2241
Graphene+H2 0.20190.2019
0.2019
Graphene+H3 0.21640.17660.2208
0.2046
Löwdin charge analysis
Graphene+H
Pristine
Fe
rmi
leve
l
Dirac point
Density of States (DOS)
Graphene+H
7
13
19
16
10
17
22
Fe
rmi
leve
l
Initial structure
Optimized structure
Initial structure
Optimized structure
Initial structure
Optimized structure
Hydrogenated graphene vacancy
v
Graphene_Vacancy+H
Graphene_Vacancy+2H
Graphene_Vacancy+3H
A
A
B
ABC
Material Charge Tranfer
Charge Tranfer(Average)
Graphene_Vac+H 0.2051 0.2051
Graphene_Vac+H2
0.18600.1876
0.1868
Graphene_Vac+H3
0.16170.16290.1617
0.1621
Graphene_Vac+H3
0.4853(per vac)
Löwdin charge analysis
Graphene_Vacancy
Graphene_Vacancy+H
Fe
rmi
leve
l
Density of States (DOS)
Graphene_Vacancy+H
918
1021
2936
1320
Fe
rmi
leve
l
Our simulation show the value of charge transfer calculated by lowdin analysis was around 0.2e per hydrogen adsorbed and 0.5e per vacancy which was approximately comparable with experimental result by Kudo et al.
As for the DOS of hydrogenated graphene the Fermi level is shifted upward because of electrons doped from hydrogen to graphene structure, the sharp peak close to Fermi level is arise from pz orbital
As for the DOS of hydrogenated graphene vacancy, after monomer hydrogenation the value DOS at the Fermi level come from localized states of dangling bond is decrease.
Summary