0 20 40 60 80 100 120 140 160 180 20025

30

35

40

45

50

55

60

65

70

75

80

Cyr

NMP

T %

Rs (kohms)

8ml

12ml14ml

16ml

18ml 6ml

7ml

8ml

9ml

Characteristics of spray-coated samples made with the graphene dispersions

0 5 10 15 20 25 300

1

2

3

4

5

6

7

8

9

10

11

12

%

thickness (nm)

NMP US+SM

Cyr US+SM

Thickness histogram by AFM Raman analysis

0.0 0.1 0.2 0.3 0.4 0.50.0

0.1

0.2

0.3

0.4

I(2D

1)

/ I(

G)

I(2D2) / I(G)

Cyr

NMP

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

ContactsMiguel.Monteiro@inl.intAndrea.Capasso@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

1200 1300 1400 1500 1600 1700 2600 2800 3000 3200 3400

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

0.0 0.5 1.0 1.5 2.00

1

2

3

4

5

sh

ee

t re

sis

tance

(K)

volume of PEDOT (mL)

graphene inks

PEDOT

Electrical characteristics of test electrodes

0.3

6 KΩ

/

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.