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Electronic Supplementary Information

Graphene-based gas sensor: metal decoration effect and

application to a flexible device

Byungjin Choa*, Jongwon Yoonb, Myung Gwan Hahma, Dong Ho Kima, Ah Ra Kima,

Yung Ho Kahngc, Sang Won Parka, Young-Joo Leea, Sung-Gyu Parka, Jung-Dae Kwona,

Chang Su Kima, Myungkwan Songa, Yongsoo Jeonga, Kee-Seok Nama, Heung Cho Kob

aAdvanced Functional Thin Films Department, Surface Technology Division, Korea

Institute of Materials Science (KIMS), Changwon, Gyeongnam 641-831, Republic of

Korea, *E-mail: bjcho@kims.re.krbSchool of Materials Science and Engineering, Gwangju Institute of Science and

Technology (GIST), Gwangju 500-712, Republic of KoreacDepartment of Physics Education, Chonnam National University, Gwangju 500-757,

Republic of Korea

Contents

A. Fabrication process of graphene based gas sensor devices

B. 4-probe Hall measurement

C. AFM image and line profile of graphene film

D. Operating temperature dependency of sensing characteristics

E. Comparison of sensing performance for non-patterned and patterned graphene

F. Bending performance of graphene based devices

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry C.This journal is © The Royal Society of Chemistry 2014

A. Fabrication process of graphene based gas sensor devices

GrapheneSiO2/Si or PI substrate

Metal NPs

(a) (b)

(c) (d)

Cleaning of substrate Transfer of graphene film

Deposition of Au/Ti electrodes Deposition of metal NPs

Fig. S1 Sequential process of graphene based gas sensor devices. (a) Cleaning process of

substrate (hard SiO2/Si or flexible PI substrate). (b) Transfer process of graphene film grown

on Ni film to the prepared substrates. (c) Deposition of Au/Ti (100/7 nm) electrodes using a

shadow mask with IDE array structure. (d) Decoration process of metal NPs (Pd or Al NPs)

on graphene film using a thermal evaporator.

B. 4-probe Hall measurement

Table S1 Comparison of several electrical parameters extracted from Hall measurement of

Graphene, Pd:Graphene, and Al:Graphene.

Device Typeμ

(cm2/Vs)

n

(1/cm3)

ρ

(Ω/cm)

Rs

(Ω/)

RH

(cm3/C)

Graphene p 400 2.94 × 1019 5.31 × 10-4 531 0.213

Pd:Graphene p 374 3.22 × 1019 5.17 × 10-4 517 0.194

Al:Graphene p 536 1.37 × 1019 8.49 × 10-4 849 0.455

*Type of carrier, mobility, carrier concentration, resistivity, sheet resistance, and hall

coefficient are denoted as Type, μ, n, ρ, Rs, and RH, respectively.

C. AFM image and line profile of graphene film

0 1 2 3 4 5

0

5

10

15

He

ight

(nm

)

Distance (m)

(b)(a)

1 µm

Fig. S2 (a) AFM morphological image and (b) line profile of graphene film.

D. Operating temperature dependency of sensing characteristics

27 50 100 150 200-1.0

-0.8

-0.6

-0.4

-0.2

0.0

S

ensi

tivity

(%)

Temperature (oC) 20

40

60

80

100

120

140

Rec

over

y (%

)

0 5 10 15 20 25 30 35-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

27 C 50 C 100 C 150 C 200 C

Sens

itivity

(%)

Time (min)

NO2 1.2 ppm(a) (b)

Fig. S3 (a) Transient sensing characteristics of Graphene device under NO2 1.2 ppm at the

operating temperature ranging from 27 to 200 °C. (b) Sensitivity and recovery characteristics

of Graphene device as function of the operating temperature.

E. Comparison of sensing performance for non-patterned and patterned graphene

-2

-1

0

1

2

Sens

itivity

(%)

Gr Pd:Gr Al:Gr

Gr Pd:Gr Al:Gr

NO2 gas NH3 gas

Gr Pd:Gr Al:GrGr Pd:Gr Al:Gr

NO2 gas NH3 gas

5 ppm-6-5-4-3-2-10123

Se

nsitiv

ity (%

)

(a)

(b)

5 ppm

Fig. S4 Gas sensing performance of Graphene, Pd:Graphene, and Al:Graphene devices

compared under 5 ppm gas concentration of NO2 or NH3 for (a) non-patterned and (b)

patterned graphene. The insets of Fig. S4(a) and (b) are top view images of non-patterned and

patterned graphene device, respectively.

F. Bending performance of graphene based devices

Fig. S5 (a) Resistance change as function of bending radius. (b) Resistance change as

function of bending cycles.