In Solution Stacking of Two-Dimensional Flakes
Benjamin
1
1
Knipfer ,
Dale
2
Brown ,
David
2
Estrada
Dept. of Material Science and Engineering, College of Engineering, University of Illinois at Urbana-Champaign
2Dept. of Material Science and Engineering, College of Engineering, Boise State University
Introduction
Materials and Methods
Since the isolation of single layer graphene, the twodimensional allotrope of carbon, in 2004, there has been an
abundance of interest in atomically thin materials. These 2Dlayered materials are characterized by strong in plane bonding
and weak Van der Waals forces between sheets.
To synthesize single and few-layered flakes for this study, we
performed exfoliation using a probe-tip sonicator. The
resulting solution was centrifuged and the supernatant
removed twice. Imaging was done using Raman Spectroscopy.
Figure 1. Depicted is
a Bernal stacking
pattern typical of
graphene exhibiting a
common 2D-layered
structure [1].
Results
Figure
3.
Probe
tip
sonication
creates
a
cavitation field in the
sample which destroys the
Van der Waals bonds
creating few layered 2D
flakes [4].
Currently, we are investigating different methods of
exfoliation for a higher yield of few-layered flakes with a
focus on lithium intercalation. With increased yield, restacked
flakes from different materials can be plasma sintered and the
resultant solid might have unique electronic and thermal
properties. One procedure for lithium intercalation is shown
below [6].
Figure 7. Raman mapping of flakes that were stacked with
acetone. The blue intensities are relative to the height of
graphene's G peak and the red intensities are relative to the
concentration of MoS2. The two are mapped over the same
location on the sample and share a common x-axis.
Figure
4.
After
sonication, the sample
was centrifuged for 5
minutes at 4500rpm.
The supernatant was
then centrifuged again
for 15 minutes at
4500rpm
and
the
supernatant
was
collected.
As we develop our knowledge of the exfoliation and
restacking of 2D-layered flakes, we expand our abilities to
create new layered materials with tunable atomic properties
from phonon dissipation to new electronic materials.
Aim
The method of depositing the sample onto the silicon wafers
appeared to be affecting the energy mismatch between the
flakes and the solvent, causing stacking. In order to show the
flakes were restacking from the acetone alone, the absorbance
of a sample was measured before and after the addition of
acetone relative to a control.
From this study, we showed our hypothesis to be accurate. It is
clear that acetone affects the restacking of the flakes.
However, how this affects the structure of graphene and MoS2
is not explicitly known. It is not known if this is diffusion
limited or if the stacking can be increased by changing the
interfacial energies to a higher degree.
- Can 2D flakes from cosolvent-exfoliated materials
be stacked in solution?
Background:
Changing the interfacial energies of the
flakes in solution causes the flakes to
quickly stack with the surrounding flakes.
Figure 8. Above shows the absorbance of the solutions with
and without acetone after centrifugation
Previous experiments have shown that
restacking of flakes has been done by
vacuum filtration [2] and adding acetone
to restack exfoliated flakes of a single
material [3].
After centrifuging both solutions for one hour, the acetone
solution showed a lower absorbance. Lower absorbance after
centrifugation indicates fewer, larger flakes left in the
solution, resulting in larger flake mass.
Figure 5. The sample is deposited on silicon and dried and
is then ready for Raman Spectroscopy [5]
A1g
G
E12g
2D
Figure 2. Visible exfoliated flakes using atomic force
microscopy. Scale bar: 200nm
D
Figure 6. Typical Raman spectra of MoS2 (left) and graphene
(right).
RESEARCH POSTER PRESENTATION DESIGN © 2012
www.PosterPresentations.com
Figure 9. Above shows a rough outline of the procedure that
will be used for lithium intercalation.
Conclusion
In this project, we hope to determine the following:
Hypothesis:
Current and Future Work
Discussion
Based on the absorption data, adding acetone to cosolvent
solutions of exfoliated flakes causes them to restack.
Additionally, when graphene and MoS2 solutions were mixed
in a 5:1 ratio, it was shown that everywhere a MoS2 flake was
found, it was stacked with graphene, further indicating
stacking.
This result is a step towards realizing the extent to which
restacked materials may be used; from thermal management to
photovoltaic applications. Understanding how to restack
flakes with a method that is easily scalable brings us one step
closer to restacked materials implemented into daily life.
Acknowledgements
Benjamin Knipfer was funded by the REU in Materials for
Energy and Sustainability grant number: 132G106257 and the
National Science Foundation. This experiment was hosted by
the Integrated NanoMaterials Laboratory at Boise State
University. Dale Brown helped guide the research. AFM
images were gathered by Katie and Kari Livingston.
Literature Cited
[1] Yacoby, A. (2011). Nature Physics.
[2] Loyta, M. et al. (2009). American Chemical Society.
[3]Anto Jeffery et al. (2014) The Journal of Physical Chemistry.
[4]”S. Berliner, II”. (2014) Consultant in Ultrasonic Processing
[5] J. Phys. Chem. C, 2011, 115 (46) pp 22761 - 22769
[6] Huang.H. et al. (2012) Journal of Materials Chemistry.