Download Report

Electronic Supplementary Material (ESI) for Nanoscale.
This journal is © The Royal Society of Chemistry 2015
Supplementary Material:
Nanosized graphene crystallite induced strong magnetism in pure carbon films
Chao Wang, Xi Zhang and Dongfeng Diao*
Institute of Nanosurface Science and Engineering,Shenzhen University, Shenzhen518060, China
*E-mail:[email protected]
Realization of Low Energy Electron Irradiation
Low energy electron irradiation technique is illustrated in Figure S1. Mirror confinement magnetic
field was generated by a set of concentric magnetic coils. Two electron cyclotron resonance zones
are located symmetrically at the magnetic mirror positions (indicated by grey dash lines), thus
electrons are restricted between the resonance zones and oscillate along the magnetic field lines
while doing Larmor movement (red spirals).
Fig S1. Illustration of low energy electron irradiation technique in ECR plasma. Electron oscillation
occurred between magnetic mirrors, which were indicated by grey dash lines. Electrons were
extracted from Ar plasma at the magnetic mirror position, and driven by bias voltage to irradiate the
substrate surface. Cylinder target (only a part showing in the figure) was sputtered to generate carbon
atoms for film deposition.
In order to extract electron from the plasma, substrate was located near magnetic mirror position.
The exact position of substrate was fixed at the point where the floating voltage was zero, which was
derived from plasma diagnosis results [33]. Thereafter, a positive bias voltage was applied on the
substrate, which generated an electric field force. The electrons were driven towards the substrate by
the electric field force, realizing electron irradiation. The irradiation energy E was determined by
substrate bias voltage U,
𝐸 = |𝑒𝑈|
(1)
where e is elementary charge.
By controlling Ar gas pressure, electron irradiation density can be changed. The electron
irradiation density was derived from substrate current is, since
𝑖𝑠 =
𝜌𝑒𝑠
𝑣
(2)
where s is substrate area, and v is electron velocity. By substituting electron dynamic energy
1
𝐸 = 𝑚𝑣2
2
(3)
into Eq.(1) and Eq.(2), then electron irradiation density can be obtained below,
𝑁=
𝑖𝑠
𝑚
𝑒𝑠 2𝑒𝑈
(4)
where s is substrate area, and m is electron mass. According to the above methods, different electron
irradiation energies and densities can be selected during film deposition.
Fig. S2 Plan view transmission electron microscope (TEM) image of carbon films deposited under electron
irradiation energy of 80, 100, 250 and 300 eV, respectively. The 80 and 100 eV sample contained graphene
nanocrystallite, while the 250 and 300 eV sample contained graphite-like structure.
Plasma Mass Spectrometry test
In order to further eliminate the influence of impurities inside the film, inductively coupled plasma mass
spectrometry (ICP-MS) was introduced to measure the impurities concentration. The mainly impurity
concentrations are shown in the following Table S1.
Table S1. Impurity contents in the film. The results are mean values from two replicate measurements.
Element
Atomic ppm
Element
Atomic ppm
Al
18.39
Fe
48.86
P
5.53
Co
0.76
Ti
1.39
Ni
6.60
V
0.19
Cu
367.52
Cr
19.32
Zn
1.90
Mn
5.25
Pb
0.44
It can be seen that the total amount magnetic metallic impurities (Fe, Co and Ni) are less than 60
ppm. Even they behave as a bulk ferromagnetic material, their maximum contribution to the
magnetic moment in our samples would be less than 3× 10-6 emu, a twentieth of the original signal.
So the intrinsic impurities are not the sources of paramagnetic behavior of film.
Table S2. Saturation magnetization Ms and residue magnetism Br of sample A-H
Sample number
E-I density cm-3
E-I energy eV
Ms emu/g
Br memu/g
A
1011
10
0.017
1.7
B
1011
50
0.075
4.2
C
1011
150
0.27
34
D
1011
200
0.12
16
E
1010
10
0.008
0.7
F
1010
50
0.04
15.8
G
1010
250
0.37
28.1
H
1010
300
0.14
4.4