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