Received: 3 July 2018 Revised: 15 August 2018 Accepted: 18 August 2018

DOI: 10.1002/sia.6553

RESEARCH ARTICLE

Sputtering yield for Na and Cl ions on a graphene and SiC

membrane in the reverse osmosis method
Sanaa Rochd | Meriem El Marsi | Soufiya Mizani | Latifa Salama | Souad Lahlou |

Rachida Moultif | Aouatif Dezairi

Condensed Matter Physics Laboratory,

Faculty of Science Ben M'sik, Hassan Π Graphene is a single layer thick consisted by honeycomb‐packed sp2 carbon atom;
University of Casablanca, Casablanca,
nanoporous graphene holds great promise in the application of filtration such as
Morocco
Correspondence reverse osmosis method using a semipermeable membrane to remove ions, molecules,
Sanaa Rochd, Condensed Matter Physics and larger particles from drinking water. The movement of molecules and ions can
Laboratory, Faculty of Science Ben M'sik,
Hassan Π University of Casablanca, B. P 7955, caused by a collision between the ions, molecules, and the graphene, so we can talk
Av. D. El Harty, Casablanca 20663, Morocco. about the sputtering. In this work, we have studied the sputtering yield by Na and
Email: rochd.sanaa91@gmail.com
Cl ions to examine the potential and the challenges of osmosis membrane from
graphene in order to predict the performance of the graphene membrane for use in
the reverse osmosis method.

KEY W ORDS

graphene membrane, reverse osmosis method, SiC membrane, sputtering yield

1 | I N T RO D U CT I O N heat of sublimation of the target material; it is relatively sensitive to

the nature of the bombarding ions.8 Transport of ions in matter (TRIM)
The need for fresh water is growing. Worldwide, 1 billion people lack is a simulation program that employs Monte Carlo algorithm to simulate
access to safe drinking water. To provide fresh water, particularly in sputtering process.9 This software is based on the approximation of the
dry areas, much research has been conducted to find effective cascades of binary collisions, thanks to statistical models that are based
methods for removing salt from seawater and brackish water.1 Several on the Monte Carlo method, that allow rapid calculations of the
research topics are interested in different methods of desalination. spraying efficiency and sometimes the behavior of the emitted atoms.10
However, reverse osmosis (RO) is the most widely used desalination The most regularly encountered codes or programs in the literature are
technology globally.2 Thus, the biggest challenge would be making SRIM11 and TRIDYN,12 but we also find other close programs such as
(RO) desalination affordable for poorer countries. Unarguably, the cap- MARLOWE13 or OKSANA.14
ital investment and operating costs of (RO) plants must be further In previous research, we found that graphene is a good choice to
reduced to achieve this electricity (energy), labor, and chemical make use as a membrane in RO because it is the strongest, thinnest, and
up about 87% of the total RO cost.3 Hence, the developments in most chemically robust. This is why researchers from all disciplines
membrane material and module optimization can significantly contrib- began to explore this material in the next generation of this
ute to the reduction of all three aspects. membrane.15-19 In addition, metal‐organic frameworks (MOFs) such
It is known that the nanoporous material is a material of the order as zeolites have also been examined for desalination technology.20
of 1 nm. Previous work also supported the hypothesis that The conduction of ion‐water solution through two discrete bundles
nanomaterials could have a much higher permeability. In particular, of armchair carbon and silicon carbide nanotubes as useful mem-
studies of synthetic nanofluids and nanostructures such as carbon branes for water desalination is studied.21 Salt rejection for water
nanotubes (CNTs) suggest that water inside such structures may exhibit was also studied in the systems with pristine graphene monolayers.22
4
hyper drinking to flow at higher speeds. Other, sputtering is a process Cohen‐Tanugi and Grossman15 studied a hydrogenated and hydrox-
whereby atoms are ejected from a solid target material due to the bom- ylated graphene pores.
bardment of the target by energetic particles.5-7,16 Threshold energy is Some calculations suggest that graphene might experience
the minimum ionic energy required for sputtering; it depends on the 45 times greater stress for a given pressure.23 Also, Cohen‐Tanugi

Surf Interface Anal. 2018;1–5. wileyonlinelibrary.com/journal/sia © 2018 John Wiley & Sons, Ltd. 1
2 ROCHD ET AL.

and Grossman24 have studied the resistance of the graphene mem- 3 | CALCULATION DETAILS
brane by performing a deformation stress by applying the mechanical
deformation rate. Graphene is one of the most rigid materials (modulus approximately
In the vast majority of cases, sputtering is caused by a momentum 1 TPa) and the strongest (resistance approximately 100 GPa).28 There-
transfer process.25 In this work, the computer simulation program fore, we will study its sputtering yield by bombarding it with Na and Cl
SRIM‐2013 was employed to calculate the sputtering yields of both ions with energy that goes from 0 to 100 eV range, and we will then
graphene and SiC membranes by low‐energy Na and Cl ions bombard- measure its impact on the graphene and SiC membrane. We carried
ment. Moreover, the comparison between these membranes was elu- out simulations by the Monte Carlo SRIM that uses the binary collision
cidated in this paper. approximation (BCA), applied to ion‐solid interactions (software pack-
age created by J.F. Ziegler and J.P. Biersack)15; these calculations are
made in two different cases, when the ions are normal on the surface,
2 | S P U TT ER I N G T H EO RY
and also for different angles of incidence. The number of ions
impacting is 100 000.
Sputtering yield is the average number of atoms removed to incident
particle, as stated in the following equation:
• Graphene membrane: Density = 2.26 g/cm3; thickness = 3.605 Å.

atoms removed • SiC membrane: Density = 2.2871 g/cm3; Thickness = 9 Å.

Y¼ : (1)
incident particle

The collision on target atoms causes the recoil atoms to overcome sur-
face binding energy, which can be expressed as sputtering yield26: 4 | RESULTS AND DISCUSSION

YðE0 ; θ0 Þ ¼ ⋀ FD ð0; E0 ; θ0 Þ: (2) In this section, we present numerical simulations of the sputtering
yields of graphene and SiC membrane as a function of energy, thick-
As that ⋀ is factor associated with target material, and FD is the
ness, and density of membrane, then according to the angle of inci-
surface binding energy that can be expressed by26
dence of Na and Cl ions.
First of all, we notice in Figure 1 sputtering yields at normal inci-
FD ð0; E0 ; θ0 Þ ¼ α N Sn ðE0 Þ: (3)
dence as a function of projectile energy E of the two Na and Cl ions;
we note here that the sputtering yield in the case of the Na ion is
As that Sn(E0) is a nuclear‐stopping cross section, and α is the cor-
greater by comparing it with the sputtering yield in the case of the
rection factor, which is a function of the mass ratio between
Cl ion. They also have a different threshold energy. Concerning Na
bombarding target mass to the mass of the particle projectile M2/M1,
ion, we observe in this figure at the beginning the absence of the
and θ0 is initial angle of incidence, and N is atomic density of the tar-
sputtering yields, by increasing the energy of bombardment of the
get, so it can be described as sputtering yield.26
ion from 22 eV to 100 eV, the sputtering yields will increase. We also

Y ðE; ηÞ ¼ ⋀α N Sn ðE0 Þ (4) notice that the efficiency coefficient of the sputtering yield is very low
(from 0 to 0.04). On the other hand, in the case of the Cl ion, we
As ƞ is a generic parameter of energy. To accurately calculate the observe in this figure at the beginning the absence of sputtering yields,
sputtering yield, it can be used for nuclear‐stopping cross section, as by increasing the energy of bombardment of the ion from 37 eV to
given by the Sn(E0) equation.27 100 eV, the sputtering yields will increase. We also notice that the
efficiency coefficient of the spray is very low (from 0 to 0.025).
8:462 Z1 Z2 h i
Sn ðEÞ ¼
 Sn ðεÞ 10−15 eV:cm2 (5)
ð1 þ M2 =M1 Þ Z10;23 þ Z20;23

As Z1 and Z2 the atomic numbers for each of the incident particle

and material target bombard, respectively, and that ε its reduced
energy, which is given by the following equation.26

32:53 M2 E
ε¼
: (6)
Z1 Z2 ð1 þ M2 =M1 Þ Z0;23
1 þ Z0;23
2

Sn(ε) limits the decline in the nuclear cross section. The energy
unit of the ion incident E is keV, and pack of ions energy ε ≤ 30. It
is described by the following equation.26

0:5 lnð1 þ 1383εÞ FIGURE 1 The graphene sputtering yield under the Na and Cl ions
Sn ðεÞ ¼ : (7)
ε þ 0:0132ε0:21226 þ 0:19593ε0:5 bombardment as a function of energy
ROCHD ET AL. 3

Concerning Figure 2, it illustrates the sputtering yields as a func-

tion of the angle of incidence for the two Na and Cl ions. Here, we
observe that the two curves have the same shape except that the
sputtering yield is greater for the Na ion. In the matter of Na ion, we
see that the sputtering yield is increasing when the angle of incidence
is about 20° to 55° and is decreasing when the angle of incidence is
about 75° to 90°. About Cl ion, we notice that the sputtering yield
is increasing when the angle of incidence is about 30° to 70° and is
decreasing when the angle of incidence is about 70° to 90°.
Second, we see in Figures 3 and 4 sputtering yield under the Na
and Cl ions bombardment as a function of the angle of incidence
and energy. We find that the sputtering yield with the angle of inci-
dence 60° is large relative to the angle of incidence 30° and 0°.
Figure 5 treats the graphene sputtering yield under the Na and Cl
ions bombardment as a function of the thickness of the membrane; we
notice here that the sputtering yield decreases by increasing the thick- FIGURE 4 The graphene sputtering yield under the Cl ion
ness of the membrane, but when the thickness reaches 6 Å, the bombardment as a function of the angle of incidence and energy

FIGURE 2 The graphene sputtering yield under the Na and Cl ions FIGURE 5 The graphene sputtering yield under the Na and Cl ions
bombardment as a function of the angle of incidence bombardment as a function of the thickness of the membrane

sputtering yield will stop to decrease, and it will become stable. So

by increasing the thickness of the membrane, we obtain a stronger
and more resistant membrane against the sputtering.
Figure 6 illustrates the sputtering yield as a function of the density
of the graphene membrane; we show two different regimes. Initially
(density < 1 g/cm3), the sputtering yield assumes a steep increase.
Then, for longer density (density| > 1 g/cm3), the sputtering yield
levels off, and a plateau regime is reached faster. Therefore, it is better
to have a small density to avoid the sputtering.
We notice in Figures 7 and 8 an increase of sputtering yield as a
function of energy, but it is important in the case of SiC membrane
by comparing it with the graphene membrane.
In general, we can decompose the curve of the sputtering yield as
a function of the energy of the incident ions into three large regions,
the portion of the sputtering yield threshold where the incident parti-
FIGURE 3 The graphene sputtering yield under the Na ion cle has a very low energy that causes the ejection of the particle of the
bombardment as a function of the angle of incidence and energy target, the part where the sputtering yield increases with the energy
4 ROCHD ET AL.

of the incident particle until it reaches its maximum in the range 60° to
76°, and the part where the sputtering yield decreases at very high
energy due to the ion reflection.29
Finally, we can deduce that the sputtering yield is very low at the
angle of incidence of 0° and high at the angle of incidence of 60°. So
the graphene membrane needs a specific angle of incidence to pulver-
ize. And we deduce that the increase of thickness protects the mem-
brane against the sputtering yield. Rather, the increase of density
favored the pulverization.

5 | CO NC LUSIO N

Among the desalination methods of seawater, there is the method of

RO. This method requires the use of a membrane, and since there is
an increase in pressure, this will cause a bombardment of the
FIGURE 6 The graphene sputtering yield under the Na and Cl ions graphene membrane by the Na and Cl ions.
bombardment as a function of the density of the membrane In our study, a graphene membrane is used. Therefore, to know
that this membrane supports the bombardment of Na and Cl ions,
we calculated its sputtering yield coefficient as a function of ion ener-
gies and as a function of the angle of incidence.
We notice that the sputtering yield is not very important in the
most angle of incidence, but it is important in the range 60° to 76°
and that the graphene membrane is less sprayable than the SiC
membrane. So we conclude that the graphene membrane is solid
because it only pulverizes for some specific angle of incidence. In
addition, it can be said that the graphene is performing and it is a
good choice to use as a membrane in RO. And we note that the
increase in membrane thickness is a positive parameter against
sputtering and it is better to have a small density to avoid
the sputtering.

ORCID
Sanaa Rochd http://orcid.org/0000-0002-0826-2844

FIGURE 7 The sputtering yield of the graphene and SiC membrane

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