22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Hydrogen plasma on graphene: the effect of ions energy distributions
A. Felten1, D. McManus2, C. Rice3, L. Nittler1, J.J. Pireaux1 and C. Casiraghi3
1
Research Center in Physics of Matter and Radiation (PMR), University of Namur, Namur, Belgium
2
School of Physics and Astronomy, University of Manchester, U.K.
3
School of Chemistry and Photon Science Institute, University of Manchester, U.K.
Abstract: In this work, we correlate the modifications induced on monolayer graphene
with the hydrogen ions energy distributions obtained by mass spectrometry. We show that
the H+, H 2 + and H 3 + ions energy depend strongly on the sample position, pressure, and
plasma power. Strong variations in the modification of graphene are observed by Raman
spectroscopy.
Keywords: hydrogen, mass spectrometer, graphene
1. Introduction
Plasma hydrogenation of graphene has been proposed
as a tool to modify the properties of graphene and leads to
new range of application for this 2D material. However,
hydrogen plasma is a complex system and controlled
hydrogenation of graphene suffers from a lack of
understanding of the plasma chemistry. The presence of
different species, such as electrons, ions and radicals,
combined with the fact that various types of plasma
systems and experimental conditions are used, makes
plasma treatments quite complex to understand and
difficult to compare. For instance, the results of graphene
modification vary from one study to the other [1-3]. In
most of the studies on hydrogenation of graphene, the
densities and energies of the different species present in
the plasma chamber are not known or just guessed based
on previous works. It is thus very difficult to interpret the
modification induced on graphene and to use plasma
hydrogenation as a tool to precisely functionalize
graphene.
Fig. 1. Side view of the plasma chamber with head of the
mass spectrometer inserted on the right side.
3. Results
We studied the hydrogenation of monolayer graphene
by Raman spectroscopy depending on the plasma
conditions (exposure time, pressure, power, and position
inside the chamber) [4]. Raman spectroscopy is a
powerful tool to detect and quantify defects introduced in
the graphene lattice [5, 6]. Fig. 2 (black curve) shows the
Raman spectrum of pristine graphene with its
characteristic G and 2D peaks. After treatment, the
Raman spectrum exhibit new defect activated peaks
(named D and D’ peaks). The amount of defects can be
quantified by using the integrated ratio of D and G band
intensities, I(D)/I(G). Fig. 2 presents the Raman spectra
of graphene treated at two different pressures: 0.06 mbar
(red curve) and 0.3 mbar (blue curve). The higher D peak
in the red curve indicates that stronger modification of the
graphene happens at lower pressure.
2. Experimental
Graphene was mechanically exfoliated on 90 nm
The graphene sheets were
SiO 2 /Si substrate.
hydrogenated in a home-made plasma chamber using
inductively coupled RF plasma at 13.56 MHz. An
energy-filtered mass spectrometer (Hiden EQP-300) was
connected to the chamber in order to detect the densities
and energies of ions present in the plasma. Fig. 1 shows a
schematic picture of the plasma chamber.
Fig. 2. Raman spectra of hydrogen plasma treated
monolayer graphene under the following conditions:
10 W, 30 s, inside the discharge and 0.3 mbar (blue) or
0.06 mbar (red). The black curve shows Raman spectra
of pristine graphene.
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We then correlated the modification induced on the
flakes with the hydrogen ions energy distributions (IEDs)
obtained by mass spectrometry . We show that the IEDs
of H+, H 2 + and H 3 + can change considerably depending
on the experimental conditions: we varied the plasma
pressure and power, and moved the mass spectrometer
head to different positions inside the plasma chamber [4].
For example, Fig. 3 shows the H+ IEDs for increasing
power (5-30W). The maximum energy of the H+ ions
varies from ~38 eV at 5 W to ~62 eV at 30 W. This
increase of kinetic energy comes along with an increase
of the concentration of the species.
Fig. 3. H+ Ion energy distributions during hydrogen
plasma 0.06 mbar, 30s, inside the discharge and for
increasing power.
4. Conclusions
Our study provides a better understanding of the impact
of H ions energies and fluxes on graphene surface
modification. Knowing the exact plasma chemistry, one
could use hydrogen plasma treatment to either: clean
graphene from residual polymers, without destroying it;
functionalize graphene or etch it away layer-by-layer.
Furthermore, based on our measurements we speculate
that, under specific plasma parameters, protons should
possess enough energy to penetrate the graphene sheet.
5. Acknowledgment
AF is supported by the Belgian fund for scientific
research (FNRS). CC acknowledges the EPSRC grant
EP/K016946/1 (graphene-based membranes).
6. References
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Shen, S. Wang and J. Lin. ACSnano, 3, 1781 (2009)
[2] M. Jaiswal, C.H. Lim, Q. Bao, C.T. Toh, K.P. Loh
and B. Ozyilmaz. ACS nano, 5, 888 (2011)
[3] A. Felten, A. Eckmann, J.J. Pireaux, R. Krupke and
C. Casiraghi. Nanotechnol., 24, 355705 (2013)
[4] A. Felten, C. Rice, L. Nittler, J.-J. Pireaux and
C. Casiraghi. Appl. Phys. Lett., 105, 183104 (2014)
[5] A. Eckmann, A. Felten, A. Mishchenko, L. Britnell,
R. Krupke, K.S. Novoselov and C. Casiraghi.
Nanoletters, 12, 3925 (2012)
[6] A. Eckmann, A. Felten, I. Verzhbitskiy, R. Davey
and C. Casiraghi.
PRB, 88, 035426 (2013)
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