graphene-based dispersions for touch sensor fabrication
TRANSCRIPT
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Characteristics of spray-coated samples made with the graphene dispersions
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Thickness histogram by AFM Raman analysis
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Introduction
Acknowledgments
Resuls: grafene-based dispersions and devices
Liquid phase exfoliation (LPE) was usedto exfoliate graphite and leave thegraphene flakes in suspension.LPE can be done by several methods,e.g., ultrasonication, shear mixing, andball milling.
Process ConditionsConcentration
(g/ L)Lateral size
(nm)
Ultrasonication 11 h 0.29 - <1000 -
Shear mixing 10 h 0.44 0.49 <1000 <25
SM + US 10 h + 6h 2 2.77 <500 <20
Solvent: NMP Cyrene NMP Cyrene
• LPE dispersions of graphene flakes with controlled morphology can be used to prepare functional inks and pastes• A highly concentrated ink in cyrene (green solvent) was made by a combination of ultrasonication and shear mixing• Our approach allows large-area coverage and an extensive compatibility with several flexible substrates (such as polymers)• Our graphene-based touch sensor showed a suitable ratio of transmittance/conductivity, and a constant low attenuation level
[1] W. Kong et al., “Path towards graphene commercialization from lab to market”. Nature Nanotechnology 14
(2019) 927–938.
[2] Y. Hernandez et al., “High-yield production of graphene by liquid-phase exfoliation of graphite”. Nature
Nanotechnology 3 (2008) 563-568.
[3] A. Capasso et al., “Ink-jet printing of graphene for flexible electronics: An environmentally-friendly approach”.
Solid State Communications. 224 (2015) 53-63.
A.C. acknowledges the support of theEuropean Union’s Horizon 2020 researchand innovation program under the MarieSkłodowska-Curie grant agreement No.713640.
Size-selected graphene flakes were used to make inks and pastes with suitablefluidic properties, to be deposited by spray and blade coating.
We prepared graphene-based electrodes with various characteristics by spraycoating.
A combination of ultrasonication (US) and shear-mixing (SM) with tunedparameters allowed a high degree of control on the lateral size and thickness ofthe graphene flakes, and on the concentration of the dispersions.
International Iberian Nanotechnology Laboratory, Avenida Mestre José Veiga, 4715-330 Braga, Portugal
M. Monteiro, S. Tkachev, P. Alpuim, A. Capasso
Conclusion
Graphene-based and two-dimensional materials are approaching the industrialproduction stage with a sustained pace [1]. These materials can be processed insolution and deposited by several techniques to make components for manytechnologies, such as flexible electronics [2, 3]. However, graphene-baseddispersions are currently rather expensive and face some issues, such as alimited compatibility with substrates or the need for post-processing treatments.Here, we propose an approach to produce graphene-based dispersions with highyield and control on the material properties. Our approach is based on the use ofa combination of two solution-processing techniques (i.e., shear mixing and ultra-sonication) for the efficient exfoliation of natural graphite into graphene flakes.
References
Graphene-based dispersions for touch sensor fabrication
Finally, we fabricated a 10x10 cm2 graphene-based capacitive touch sensor byspray coating.
The dispersions were deposited by several techniques (i.e., spray coating, inkjetand screen-printing) on various substrates to fabricate films with desired levelsof transparency and conductivity.
The graphene dispersions in different solvents were characterized by Ramanspectroscopy, atomic force and transmission electron microscopy.
CE
CE
CT
Virtual ground
1x1
10x10
20x20
Coord. SNR (dB)
1x1 14,0
10x10 13,9
20x20 13,9
[email protected]@inl.int
Graphene dispersion Spray coating Blade coating
LPE via ultrasonication and shear mixing
Methods
200 µm
Raw material: natural graphite
Ultrasonication (US)Shear mixing (SM)
The sensor showed high signal-to-noise ratio and featured multi touchdetection.
• We exploited different processes and solvents (NMP and cyrene) to obtain highyield and tune the size and thickness of the graphene flakes.
SM+US
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Inte
nsity (
a.u
.)
Raman shift (cm-1)
DMF
Graphite
Cyrene
NaC
NMP
FLG CVD
Raman spectra of flakes in different solvents AFM image of flakes TEM image of flakes
Working principle Graphene touch sensor Sensor attenuation map
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sis
tance
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volume of PEDOT (mL)
graphene inks
PEDOT
Electrical characteristics of test electrodes
0.3
6 KΩ
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Transparent conductive electrodes on flexible PET subtracts
T%: 70-92%
SM+US
Graphene on flexiblepolypropylene film
SEM image of the graphene film
We deposited a highly conductiveelectrode on flexible polypropylene byblade coating the graphene-based paste.The device serves for electromagneticinterference shielding.
Our paste demonstrated:• High adhesion to the substrate• Possibility to use in screen-printing
10 Ω/
By using the two LPE processes we produced highly concentrated graphenedispersions that were further optimized to prepare:• Highly conductive paste - The viscosity was adjusted with binders, such as
CMC sodium salt.• Conductive ink - PEDOT:PSS was added as a stabilizer agent, overall
improving uniformity, adhesion and electrical conductivity of the sprayedfilms.