Supplemental online materials
Physical deoxygenation of graphene oxide paper surface and facile in situ
synthesis of graphene based ZnO films
Jijun Ding,1 Minqiang Wang, 1,a) Xiangyu Zhang,1 Chenxin Ran,1 Jinyou Shao2
and Yucheng Ding2
1Electronic
Materials Research Laboratory, Key Laboratory of Ministry of Education, School of Electronic and Information
Engineering; International Centers for Dielectric Research, Xi’an Jiaotong University, Xi’an 710049, China
2State
a)
Key Laboratory of Manufacturing Systems Engineering, Xi’an Jiaotong University, Xi’an 710049, China
Electronic mail: mqwang@mail.xjtu.edu.cn.
Contents
S1 The principle of magnetron sputtering
S2 Raman spectra
S3 SEM and polarizing microscopy images
S1 The principle of magnetron sputtering
The physical details of interaction between the plasma, ZnO and the GO film are
explained below. During magnetron sputtering process, the sputter gas is a typical inert gas
such as argon (Ar). Plasma contains Ar+ ions, the electrons and ZnO molecules. The electrons
(e1-) accelerated and moved in an ascending spiral by electric and magnetic fields will collide
with Ar atoms to produce Ar+ ions and new secondary electrons (e2-). The extra Ar+ ions
created as a result of these collisions will be accelerated by electric field to sputter ZnO target.
The sputtered atoms or molecules with neutral charge are unaffected by the magnetic trap and
will be deposited on the substrates to form films. However, large numbers of electrons not
only collide with Ar atoms, but they are accelerated to bombard the substrates (GO paper).
These electrons are captured by oxygen-containing functional groups in GO paper surface.
Especially at higher sputtering power (300 W) and longer sputtering time (1h), more
electrons are captured by GO paper resulting in deoxygenation of the functional groups.
S2 Raman spectra
Figure S1(a) shows Raman spectra of rGO-ZnO with different sputtering power under
the 514.5 nm excitation source. Raman spectrum of GO paper exhibit the regular two peaks
at 1350 and 1587 cm−1 corresponding to the D and G peaks, respectively.1,
2
G band
corresponds to an E2g mode of graphite and is related to the vibration of sp2-bonded carbon
atoms. 3 In this work, all the intensity ratios of IG/ID (～1.0) hardly change, which can be
attributed to sp2 hybridized structures in GO are not destroyed during sputtering process. The
ID/IG value of rGO-ZnO should be higher than that of GO, provided that the electrons reacts
with sp2 C in GO during magnetron sputtering. Therefore, the nearly similar values of GO
and rGO-ZnO suggest that deoxygenation occurs at the original sp3 C sites in GO, that is, the
C sites connect with the oxygen-containing groups.4 In addition, the C/O of samples should
be utilized to evaluate the deoxygenation degrees. The C/O values of GO and rGO-ZnO are
48.3/51.7 and 74.1/25.9, respectively. This suggests that most of the residual
oxygen-containing groups could be removed by magnetron sputtering. The detailed
deoxygenation depth is determined by the electron energy and the base materials. Owing to
the relatively loose and disorder structure of the GO paper, the deoxygenation depth is still an
urgent issue.
FIG. S1. (a) Raman spectra of rGO-ZnO with different sputtering power, (b) Raman spectra
of as prepared GO and the rGO-ZnO after HCl treatment.
In addition, the intensity of these peaks is enhanced by 105% at the sputtering power of
300 W, which is similar to previous report about GO reduction assisted by Au nanoparticles
or fluorinating agent.
5,6
This indicates that GO is deoxygenated to form rGO and occurs an
interaction or bond between ZnO and rGO. 5 For the sake of comparison, Raman spectra of as
prepared GO and the rGO-ZnO after HCl treatment are shown in Figure S1(b). The rGO-ZnO
after HCl treatment also shows a disordered (D) band at 1350 cm−1 and a crystalline (G) band
at 1587 cm−1, and the intensity ratio of the G to the D band IG/ID was 1.041, which is larger
than that of as prepared GO paper (1.025).
S3 SEM and polarizing microscopy images
FIG. S2. (a) The cross-sectional SEM images and photograph of as prepared GO paper.
Polarized microscopy images of (b) as prepared GO paper and rGO-ZnO (c) before and (d)
after HCl treatment.
Figure S2(a) shows the cross-sectional SEM images and photograph of as prepared GO
paper. The curled sandwich structure of GO paper is observed in the cross-sectional SEM
images. The photograph of GO paper indicates that the diameter of samples is about 3 cm.
Figure S2(b-d) compared polarizing microscopy images of as prepared GO paper with
rGO-ZnO before and after HCl treatment. Compared with GO paper, either rGO-ZnO before
or after HCl treatment darken the color and shows the more homogeneous layered platelets
composed of curled nanosheets. We believe that the deoxygenation play a key role in
generating the fascinating-structural surface.
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