Electronic state calculation for hydrogenated graphene with atomic vacancy Electronic state calculation of hydrogenated graphene and hydrogenated graphene vacancy Kusakabe Lab. M1 Gagus Ketut Sunnardianto

Contents 1. 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 Atomic nature Spectrum of carbon atom Crystal nature Bonding & hybridized energy bands of graphene

Unique properties of graphene 1.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….? Daniel R.Cooper et al, ISRN Condensed matter physics, 2012 Monolayer graphene produced by Mechanical exfoliation. Large sample With length of 1mm on Si/SiO 2

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. Pristine 2. Hydrogenation (cleaning) 3. Annealing 4. Ar Sputtering 5. Hydrogenation 6. Annealing 7. 2 nd Ar Sputtering 8. 2 nd Hydrogenation

 Graphene is a revolution material for hydrogen storage, Keyvan 3.  Experimentally, Capaz et.al 1 observed the charge transfer from hydrogen to graphene around In a recent experiment by Kudo et al 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 vacancy consisting 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 charge in hydrogenated graphene by Löwdin charge analysis to know the charge transfer and to understand the evolution of the electronic structure through density of states upon hydrogenation Research scopes Research objectives

 Based on Density Functional Theory (DFT)  Generalized Gradient Approximation (GGA)  VASP code (  Quantum espresso code (Löwdin charge analysis)  Force convergen criterion : F ≤ 1.0 x [Ry/a.u]  PAW potentials to describe ionic potentials  the energy cut off of 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 (Average) Graphene+H Graphene+H Graphene+H L ö wdin charge analysis

Graphene+H Pristine Fermilevel Dirac point Density of States (DOS)

Graphene+H Fermilevel

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 A B C Material Charge Tranfer (Average) Graphene_Vac+H Graphene_Vac+H Graphene_Vac+H Graphene_Vac+H (per vac) L ö wdin charge analysis

Graphene_Vacancy Graphene_Vacancy+H Fermilevel Density of States (DOS)

Graphene_Vacancy+H Fermilevel

 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 p z 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