electronic properties of hydrogenated ... - senhri journal

Senhri Journal of Multidisciplinary Studies, Vol. 4, No. 2 (July - December 2019), p. 72-79

© SJMS, 2019 72

Senhri Journal of Multidisciplinary Studies

A Journal of Pachhunga University College

(A Peer Reviewed Journal)

https://senhrijournal.ac.in

DOI: 10.36110/sjms.2019.04.02.008

ISSN: 2456-3757

Vol. 04, No. 02

July-Dec., 2019

Open Access

ELECTRONIC PROPERTIES OF HYDROGENATED

HEXAGONAL BORON NITRIDE (h-BN): DFT STUDY B. Chettri

1,2, P. K. Patra

2, Sunita Srivastava

3,4, Lalhriatzuala

1, Lalthakimi Zadeng

5 &

D. P. Rai1*

1Physical Sciences Research Center (PSRC), Department of Physics, Pachhunga University

College, Aizawl, Mizoram, India 2Department of Physics, North-Eastern Hill University (NEHU), Shillong, Meghalaya, India

3Department of Physics, Panjab University, Chandigarh, Punjab, India

4Department of Physics, Guru Jambheshwar University of Science and Technology, Hisar,

Haryana, India 5Department of Physics, Mizoram University, Aizawl, Mizoram, India

*Corresponding Author: [email protected]

Dibya P. Rai: https://orcid.org/0000-0002-3803-8923

Keywords: BN monolayer, hydrogenated, band gap, metallic, adsorption energy.

Introduction

The exfoliation of ultrathin 2D

carbon sheet called graphene from the bulk

graphite has given the new direction in the

field of digital technology (Novoselov et al.,

2004). However, the implementation of

graphene as the novel electronic material in

the advancement of new technology has

plenty of draw backs due to the absence of

band gap. The nanoscale materials

ABSTRACT

In this work, we have constructed the hydrogenated hexagonal boron nitride (h-BN) by

placing hydrogen atom at different surface sites. The possibility of hydrogen adsorption on

the BN surface has been estimated by calculating the adsorption energy. The electronic

properties were calculated for different hydrogenated BNs. The theoretical calculation was

based on the Density Functional Theory (DFT). The electron-exchange energy was treated

within the most conventional functional called generalized gradient approximation. The

calculated band gap of pure BN is 3.80 eV. The adsorption of two H-atoms at two

symmetrical sites of B and N sites reduces the band gap value to 3.5 eV. However, in all

other combination the systems show dispersed band at the Fermi level exhibiting conducting

behavior. Moreover, from the analysis of band structure and Density Of States we can

conclude that, the hydrogenation tunes the band gap of hexagonal boron nitride.

https://senhrijournal.ac.in/

https://doi.org/10.36110/sjms.2019.04.02.008

mailto:[email protected]

https://orcid.org/0000-0002-3803-8923


© SJMS, 2019 73

exhibiting graphene like properties with

finite band gap can be a perfect replacement.

The exfoliation of 2D graphene like

materials from the same group element can

be crucial. In this regard, 2D Boron Nitride

(BN) with hexagonal lattice looks promising

as the presence of sp2 hybridized B-N bonds

is same as the C-C bond in graphene (Wang

et al., 2017; Fujimoto, 2017). The other

reason being the finite value of band gap,

low density, great thermal conductivity,

chemically stable, high tensile strength etc.

The most common methods like Chemical

Vapor Deposition (CVD) and segregation

method (Ortiz et al., 2018; Shi et al., 2010)

are used to exfoliate 2D graphene like

hexagonal materials namely, BN, ZnS, ZnO,

CdO, Silicene, Germanene, transition metal

chalcogenides (TMDs), etc., (Lalrinkima et

al., 2019; Mak et al., 2010; Rai et al., 2018;

Kaur et al., 2016) from wurtzite structures.

They are used as anti-oxidation layer (due to

its thermal conductivity), lubricants, in the

field of nanoelectronics, cosmetics etc.,

(Wang et al., 2017; Fujimoto, 2017). Its

large band gap is studied to be utilized as

non-conducting substrate in electrical

applications (McCulloch et al., 2000). BN

has also been extensively used for

performance FETs (Meric et al., 2010),

substrate of graphene based FETs (Meric et

al., 2010) as well as metal decorated BN for

hydrogen storage (Zhang et al., 2017).

Rigorous research is in progress on h-BN as

a gas sensor. DFT study shows a promising

gas sensing ability of the h-BN in the

presence of external electric field (Zhang et

al., 2017). Chen et al., (2010) performed

DFT study using Vienna ab initio simulation

package (VASP) of the hydrogenation on

boron nitride nanoribbons and it was

observed that depending upon the

percentage of hydrogenation, there was

transition from semiconductor-half-metal-

metal (Chen et al., 2010). Rad & Ayub

(2016) using Gaussian 09 suite studied the

ability of nickel decorated BN nano-cluster

for hydrogen molecule storage. Li et al.,

(2008) also performed ab initio calculations

on the hydrogenated boron nitride nanotubes

using the SIESTA package where they

showed the possibility of tuning the

magnetic properties of the boron nitride

nanotubes upon hydrogenation and also by

creating defects (Li et al., 2008). Increase in

population have increased the demand for

fossil fuels. Fossil fuels being limited in

nature, also contributes in the environmental

pollution. Hydrogen has many advantages

over the fossil fuel due to its light weight,

high energy density and produces water

upon combustion meaning it doesn’t

contribute in the environmental pollution

(Bromley, 2002). The major problem for

hydrogen to be utilized as an energy carrier,

lies in its storage. The present techniques are

risky and not cost effective.

In quest for promising hydrogen

storage materials, we have carried forward

our work with h-BN monolayer. In this

paper, we have investigated the hydrogen

adsorption ability at different sites by

calculating the adsorption energy at different

sites. Also, we have calculated the energy

band structures, DOS to highlight the effect

of the hydrogenation on the electronic and

structural properties of h-BN monolayer.

Materials and Methodology

A 2D graphene like hexagonal

monolayer structure has been constructed


© SJMS, 2019 74

from Boron and Nitrogen atoms by taking

the experimental lattice constant a=b=2.502

Å (Caldwell et al., 2019). The hydrogen

atoms are adsorbed at different surficial

sites, as shown in Fig. 1. The B and N atom

has taken the hexagonal lattice and are

allowed to extend in x-y plane. However,

the transverse repetition of BN layers along

the z-axis has been terminated by taking the

vacuum of 10 Å. The vacuum along z-axis

has been introduced to break the transverse

symmetry which prevent the inter layer

interaction. The hexagonal structure was

optimized by conjugate gradient (CG)

method till HF-force reaches 0.01 eV/Å.

The calculated optimized lattice constant is

found to be a=b=2.486 Å which is consistent

with the experimental one (Caldwell et al.,

2019). The electronic structure calculations

was carried out by a DFT-based

computational code “SIESTA” which works

with pseudo-potential and numerical nano-

orbitals (NAOS) (Soler et al., 2002). The

most common functional like generalized

gradient approximation (PBE-GGA) is used

for exchange correlation of valence

electrons. To calculate the band structure,

hybrid functional are considered as more

accurate. As, the hybrid functional are

expensive, so we performed our calculations

using PBE-GGA which provides the result

in close range. The first Brillouin zone was

sampled with optimized k-mesh 8x8x1in

Monkhorst-pack scheme. The adsorption

energy has been calculated from Eq. (1):

𝐸𝑎𝑑 =−1

2 𝐸𝑠𝑦𝑠 − 𝐸𝑠𝑙𝑎𝑏 + 𝑛𝐸𝑎𝑡𝑜𝑚 - (1)

Where 𝐸𝑠𝑦𝑠 is the energy of total

system, 𝐸𝑠𝑙𝑎𝑏 is the energy of monolayer

BN , n is the number of adsorbed atoms and

𝐸𝑎𝑡𝑜𝑚 is the energy of single hydrogen

atom.

Results & Discussion

The optimized lattice constant was

used for the calculation of electronic

properties. We have considered number of

h-BN monolayer with hydrogen atom at

different atomic sites. We have studied ten

hydrogenated BN monolayers with H-atoms

at different sites on the surface. The

adsorption energy were also calculated for

different hydrogenated BN monolayers.

Since PBE-GGA underestimates the band

gap, we have found a band gap of 3.8eV

which is less than the reported value for pure

BN monolayer which lies in the range of

3.6-6.2eV which are obtained theoretically

using first principle study based on Density

Functional Theory (DFT) using different

approximations on Vienna ab initio

simulation package, Spanish Initiative for

Electronic Simulation with Thousands of

Atoms, QUANTUM EXPRESSO as well as

from different experimental techniques like

laser-induced fluorescence measurements,

Ultraviolet Lasing of Hexagonal Boron

Nitride, luminescence excitation

spectroscopy etc., (Solozhenkoa et al., 2001;

Fan et al., 2011; Zupan & Kolar, 1972;

Lopatin & Konusov, 1992; Watanabe et al.,

2004; Kaloni & Mukherjee, 2011; Schuster

et al., 2018; Gao, 2012; Zhou et al., 2010;

Elias, 2019; Ba et al., 2017; Beiranvand &

Valedbagi, 2015; Topsakal et al., 2009). The

formation of band gap in monolayer BN is

mainly due to the contribution of B-p and N-

p orbitals similar to graphene. The sp2

hybridization gives strong covalent bond as

a result the system BN monolayer does not

interact with the host elements very easily.


© SJMS, 2019 75

Figure 1: Hexagonal Structure of (a) pure BN (b) H-atom at top of BN surface (c) H-atom

at top and bottom sides of both BN (H-green , B-blue , N-red)

Table 1: Experimentally and theoretically reported band gap value of pristine h-BN

monolayer. Other reported band gap values are provided in references.

Sl. No. Experimental and DFT Method Band Gap (eV) Reference

1 Fluorescence excitation spectra (Exp.) 4.02 (Solozhenkoa et al., 2001)

2 DFT using Projector Augmented Wave (PAW)

Potential and PW91 as functional. 4.64 (Topsakal et al., 2009)

However, we intend to study the adsorption

ability of BN monolayer by adding H-atoms

on the surface. Among ten hydrogenated BN

monolayers only two of them exhibit

semiconducting behavior in which H-atoms

are symmetrically placed at the top and

bottom. The calculated band gap of

hydrogenated BN monolayers are 3.5 eV

and 3.9 eV for B1N1 and B2N2

respectively. The result of Density Of States

and band structure shows that B1N1 and

B2N2 hydrogenated system shows the

nature of an insulator with finite band gap

3.5-3.9 eV [Fig. 2a & Fig. 3(a,b)]. The rest

of hydrogenated BN monolayer shows

metallic behavior due to the presence of

dispersed band around the fermi energy

[Fig. 2(b,c)]. The dispersed band around the

Fermi energy may be accounted by the H-

atoms having single electron which behave

like a free charge carriers on the surface of

the BN monolayer.

In order to examine the ground state

stability of the hydrogenated system we

have calculated the adsorption energy from

Eq. (1) by adding the H-atoms on the

surface at different atomic sites. The

adsorption energies for different

hydrogenated systems has been displayed in

Fig. 3d. The adsorption energy measures the

ability of BN monolayer as a host for

incoming H-atom. Moreover, the negative

value of adsorption energy gives the ground

state stability and predicts the suitable

location for H-atom to reside in the host BN

monolayer. Among all hydrogenated BN

monolayer that we have considered in our

study only two systems like B-t-b-c-N

(Hydrogen at top bottom and centre site) and

B-2N (Hydrogen at top, bottom of Boron)

has given the negative value of adsorption

energy resembling an exothermic process.


© SJMS, 2019 76

Figure 2: Total Density Of States - (a) pure BN (BN-black), 1H-atom each at the top of BN

(B1N1-red), 1H-atom each at the top & bottom of BN (B2N2-green) (b) 1H-atom

at B & 2H-atoms at N (B1N2-green), 2H-atoms at B (B2N-red), 2H-atoms at B &

1H-atom at N (B2N1-blue), 1H-atom at B & 2H-atoms at N (BN2-black) and (c)

2H-atoms at BN & 1H-atom at centre (2B-c-N2-black), 2H-atoms at BN & 2H-

atoms at top-bottom of centre site (2B-tb-N2-green) , 2H-atoms at BN & 3H-

atoms at top-bottom-centre (2B-tcb-N2-blue).

(a)

(b)

(c)

(d)

Figure 3: Band structure (a) 1H-atom each at the top of both BN (b) 1H-atom each at the

top & bottom of both BN (c) pure BN and (d) Adsorption energy of different

hydrogenated h-BN

Conclusion

We have calculated the electronic

properties of pristine BN monolayer and

hydrogenated BN monolayers from the first

principles calculation with generalized

gradient approximation as electron

exchange-correlation functional. The

calculated band gap for the BN was found to

be 3.8 eV. Also upon hydrogenationno

structural deformation was observed. Most

of the hydrogenated BN monolayers exhibit


© SJMS, 2019 77

metallic properties except for B1N1 and

B2N2 with paired symmetric hydrogen on

top and bottom. Our random sampling of

adsorption of H-atoms on the surface of BN

monolayer gives positive values. But still

there are few hydrogenated system with

negative value of adsorption energy which

predicts that BN monolayer is a suitable host

for adsorbing hydrogen atoms and the work

can be further expanded for its hydrogen

storage suitability by checking other

parameters like gravimetric density(weight

percentage) etc. Also, selective

hydrogenation can be considered as one of

the mechanism to tune the band gap of the

h-BN.

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electronic properties of hydrogenated ... - senhri journal

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