Nanotechnologies — Structural characterization of graphene — Part 1: Graphene from powders and dispersions

This document specifies the sequence of methods for characterizing the structural properties of graphene, bilayer graphene and graphene nanoplatelets from powders and liquid dispersions using a range of measurement techniques typically after the isolation of individual flakes on a substrate. The properties covered are the number of layers/thickness, the lateral flake size, the level of disorder, layer alignment and the specific surface area. Suggested measurement protocols, sample preparation routines and data analysis for the characterization of graphene from powders and dispersions are given.

Nanotechnologies — Caractérisation structurelle du graphène — Partie 1: Graphène issu de poudres et de dispersions

Le présent document spécifie la séquence des méthodes qui permettent de caractériser les propriétés structurelles du graphène, du graphène bicouche et des nanoplaquettes de graphène issus de poudres et de dispersions liquides, en utilisant un éventail de techniques de mesure, typiquement après l’isolation de flocons individuels sur un substrat. Les propriétés couvertes sont le nombre de couches/l’épaisseur, la taille latérale du flocon, le niveau de désordre, l’alignement des couches et la surface spécifique. Le présent document suggère également des protocoles de mesure, des modes opératoires pour la préparation des échantillons et des analyses de données pour la caractérisation du graphène issu de poudres et de dispersions.

General Information

Status
Published
Publication Date
11-Mar-2021
Current Stage
9092 - International Standard to be revised
Completion Date
09-Aug-2023
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TECHNICAL ISO/TS
SPECIFICATION 21356-1
First edition
2021-03
Nanotechnologies — Structural
characterization of graphene —
Part 1:
Graphene from powders and
dispersions
Nanotechnologies — Caractérisation structurelle du graphène —
Partie 1: Graphène issu de poudres et de dispersions
Reference number
ISO/TS 21356-1:2021(E)
©
ISO 2021

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ISO/TS 21356-1:2021(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved

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ISO/TS 21356-1:2021(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 3
5 Sequence of measurement methods . 3
6 Rapid test for graphitic material using Raman spectroscopy . 5
7 Preparing a liquid dispersion . 7
7.1 General . 7
7.2 Preparing a dispersion of the correct concentration . 7
7.2.1 Powder samples . 7
7.2.2 Samples already in a dispersion . 8
8 Determination of methods . 8
9 Structural characterization using optical microscopy, SEM, AFM and Raman spectroscopy 8
10 Structural characterization using TEM . 9
11 Surface area determination using the BET method .10
12 Graphene lateral size and number fraction calculation .10
Annex A (informative) Rapid test for graphitic material using Raman spectroscopy .11
Annex B (informative) Structural characterization protocol using SEM, AFM and Raman
spectroscopy .14
Annex C (informative) Structural characterization using TEM .29
Annex D (informative) Lateral size and number fraction calculation .36
Annex E (informative) Brunauer–Emmett–Teller method .43
Annex F (informative) Additional sample preparation protocols — Silicon dioxide on
silicon wafer preparation and cleaning .47
Bibliography .48
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ISO/TS 21356-1:2021(E)

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that
are members of ISO or IEC participate in the development of International Standards through
technical committees established by the respective organization to deal with particular fields of
technical activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other
international organizations, governmental and non-governmental, in liaison with ISO and IEC, also
take part in the work.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for
the different types of document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives or www .iec .ch/ members
_experts/ refdocs).
Attention is drawn to the possibility that some of the elements of this document may be the subject
of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent
rights. Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www .iso .org/ patents) or the IEC
list of patent declarations received (see patents.iec.ch).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso .org/
iso/ foreword .html. In the IEC, see www .iec .ch/ understanding -standards.
This document was prepared jointly by Technical Committee ISO/TC 229, Nanotechnologies, and
Technical Committee IEC/TC 113, Nanotechnology for electrotechnical products and systems.
A list of all parts in the ISO/IEC 21356 series can be found on the ISO and IEC websites.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html and www .iec .ch/ national
-committees.
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ISO/TS 21356-1:2021(E)

Introduction
Due to the many superlative properties of graphene and related 2D materials, there are many
application areas where these nanomaterials could be disruptive, areas such as flexible electronics,
nanocomposites, sensing, filtration membranes and energy storage.
There are barriers to commercialisation that are impeding the progress of products containing
graphene, which need to be overcome. One of these crucial barriers is answering the question “What
is my material?”. End-users of the raw materials containing graphene should be able to rely on the
advertised properties of the commercial graphene on the global market, instilling trust and allowing
worldwide trade. Reliable and repeatable measurement protocols are required to address this challenge.
This document provides a set of flow-charts for analysts to follow in order to determine the structural
properties of graphene from powders and liquid dispersions (suspensions). Initially, a quick check
should be undertaken to determine if graphene and/or graphitic material is present. If it is, then further
detailed analysis is required to determine if the samples contain a mixture of single-layer graphene,
bilayer graphene, few-layer graphene, graphene nanoplatelets and graphite particles. Depending on
the methods used, the samples are typically analysed after deposition on a substrate. The document
describes how to assess what measurements are required depending on the type of sample and includes
decision trees and flow diagrams to aid the user. This document describes a selected set of measurands
that are needed, namely:
a) the number of layers/thickness of the flakes;
b) the lateral dimensions of flakes;
c) layer alignment;
d) the level of disorder;
e) the estimated number fraction of graphene or few-layer graphene;
f) the specific surface area of the powder containing graphene.
The above physical properties of the material can change during its processing and lifetime, for example,
the samples can become more agglomerated, obtain different surface functionalities. The above
measurand list for the initial material defines their inherent characteristics that, along with the chosen
manufacturing processes, will determine the performance of real-world products. Generally, different
material properties can be important in different application areas, depending on the functional role of
the material.
The document provides methods for structural characterization of individual flakes of graphene,
bilayer graphene, graphene nanoplatelets and graphite particles isolated from powders and/or liquid
dispersions. It does not provide methods for determination of whether the powders and/or dispersions
are composed solely of these materials. No recommendation is provided as to when or how often to
measure samples, although it is not expected this would be for every batch of the same material. It is up
to the user to determine when, how often and which characterization routes described in this document
to take. As with all microscopical investigations, care is needed in drawing statistical conclusions
dependant on representative sampling.
A set of annexes provide example protocols on how to prepare and analyse the samples, sources of
uncertainty and how to analyse the data. The methods used are Raman spectroscopy, scanning electron
microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM) and the
BET (Brunauer–Emmett–Teller) method.
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TECHNICAL SPECIFICATION ISO/TS 21356-1:2021(E)
Nanotechnologies — Structural characterization of
graphene —
Part 1:
Graphene from powders and dispersions
1 Scope
This document specifies the sequence of methods for characterizing the structural properties of
graphene, bilayer graphene and graphene nanoplatelets from powders and liquid dispersions using a
range of measurement techniques typically after the isolation of individual flakes on a substrate. The
properties covered are the number of layers/thickness, the lateral flake size, the level of disorder, layer
alignment and the specific surface area. Suggested measurement protocols, sample preparation routines
and data analysis for the characterization of graphene from powders and dispersions are given.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO/TS 80004-1:2015, Nanotechnologies — Vocabulary — Part 1: Core terms
ISO/TS 80004-2:2015, Nanotechnologies — Vocabulary — Part 2: Nano-objects
ISO/TS 80004-6:2021, Nanotechnologies — Vocabulary — Part 6: Nano-object characterization
ISO/TS 80004-13:2017, Nanotechnologies — Vocabulary — Part 13: Graphene and related two-dimensional
(2D) materials
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/TS 80004-1:2015,
ISO/TS 80004-2:2015, ISO/TS 80004-6:2021, ISO/TS 80004-13:2017 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
graphene
graphene layer
single-layer graphene
monolayer graphene
single layer of carbon atoms with each atom bound to three neighbours in a honeycomb structure
Note 1 to entry: It is an important building block of many carbon nano-objects.
Note 2 to entry: As graphene is a single layer, it is also sometimes called monolayer graphene or single-layer
graphene and abbreviated as 1LG to distinguish it from bilayer graphene (2LG) (3.3) and few-layer graphene
(FLG) (3.4).
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ISO/TS 21356-1:2021(E)

Note 3 to entry: Graphene has edges and can have defects and grain boundaries where the bonding is disrupted.
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.1]
3.2
graphite
allotropic form of the element carbon, consisting of graphene layers (3.1) stacked parallel to each other
in a three-dimensional, crystalline, long-range order
Note 1 to entry: Adapted from the definition in the IUPAC Compendium of Chemical Terminology.
Note 2 to entry: There are two primary allotropic forms with different stacking arrangements: hexagonal and
rhombohedral.
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.2]
3.3
bilayer graphene
2LG
two-dimensional material consisting of two well-defined stacked graphene layers (3.1)
Note 1 to entry: If the stacking registry is known, it can be specified separately, for example, as “Bernal stacked
bilayer graphene”.
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.6]
3.4
few-layer graphene
FLG
two-dimensional material consisting of three to ten well-defined stacked graphene layers (3.1)
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.10]
3.5
graphene nanoplate
graphene nanoplatelet
GNP
nanoplate consisting of graphene layers (3.1)
Note 1 to entry: GNPs typically have thickness of between 1 nm to 3 nm and lateral dimensions ranging from
approximately 100 nm to 100 μm.
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.11]
3.6
lateral size
flake size
<2D material> lateral dimensions of a 2D material flake
Note 1 to entry: If the flake is approximately circular then this is typically measured using an equivalent circular
diameter or if not via x, y measurements along and perpendicular to the longest side.
[SOURCE: ISO/TS 80004-13:2017, 3.4.1.15]
3.7
graphene oxide
GO
chemically modified graphene (3.1) prepared by oxidation and exfoliation of graphite (3.2), causing
extensive oxidative modification of the basal plane
Note 1 to entry: Graphene oxide is a single-layer material with a high oxygen content, typically characterized by
C/O atomic ratios of approximately 2,0 depending on the method of synthesis.
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ISO/TS 21356-1:2021(E)

[SOURCE: ISO/TS 80004-13:2017, 3.1.2.13]
3.8
reduced graphene oxide
rGO
reduced oxygen content form of graphene oxide (3.7)
Note 1 to entry: This can be produced by chemical, thermal, microwave, photo-chemical, photo-thermal or
microbial/bacterial methods or by exfoliating reduced graphite oxide.
Note 2 to entry: If graphene oxide was fully reduced, then graphene (3.1) would be the product. However, in
3 2
practice, some oxygen containing functional groups will remain and not all sp bonds will return back to sp
configuration. Different reducing agents will lead to different carbon to oxygen ratios and different chemical
compositions in reduced graphene oxide.
Note 3 to entry: It can take the form of several morphological variations such as platelets and worm-like
structures.
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.14]
4 Abbreviated terms
For the purposes of this document, the following abbreviated terms apply.
NOTE The final “M”, given as “microscopy”, can be taken equally as “microscope” depending on the context.
1LG single-layer graphene
2D two dimensional
2LG bilayer graphene
AFM atomic force microscopy
BET method Brunauer–Emmett–Teller method
CVD chemical vapour deposition
FLG few-layer graphene
FWHM full width at half maximum
GNP graphene nanoplate or graphene nanoplatelet
GO graphene oxide
NMP 1-methyl-2-pyrrolidinone also known as N-methylpyrrolidone
rGO reduced graphene oxide
SAED selected area electron diffraction
SEM scanning electron microscopy
TEM transmission electron microscopy
5 Sequence of measurement methods
This clause presents the sequence of measurement methods necessary to most efficiently characterize
graphene, bilayer graphene, few-layer graphene and graphene nanoplatelets from powders and liquid
dispersions (suspensions). In this document, graphene, bilayer graphene, few-layer graphene and
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ISO/TS 21356-1:2021(E)

graphene nanoplatelets are in the form of flakes of limited lateral dimensions. However, samples also
typically contain significant amounts of flakes having thicknesses that exceed ten layers, which are
flakes of graphite by definition.
After an initial examination by Raman spectroscopy, and assuming the sample is graphene or graphitic
in nature, a more detailed characterization should follow. Various characterization routes are then
possible, as shown in Figure 1. The characterization method or methods to be used will depend on the
time and equipment available and the measurands that the user requires.
NOTE 1 As the flakes are from a powder or liquid dispersion, they will typically require deposition onto a
substrate before analysis.
NOTE The numbers in brackets refer to the clauses where the item is detailed.
Figure 1 — Overview of the sequence and process of the measurement methods used to
determine the structural properties of graphene from a powder or liquid dispersion sample
Firstly, determine if the sample contains graphene and/or graphitic material, that is bilayer graphene,
FLG, GNPs or graphite by undertaking a rapid analysis using Raman spectroscopy, as detailed in
Clause 6 and Annex A. The sample needs to be in powder form deposited as a thin layer on a substrate,
therefore if a liquid dispersion has been supplied, the material will first need to be removed from the
solvent, as detailed in A.2.
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ISO/TS 21356-1:2021(E)

Decide which methods to use as outlined in Clause 8. Either use TEM or a combination of SEM, AFM
and Raman spectroscopy to determine the distribution of lateral flake sizes and the relationship with
flake thickness. For this stage, clearly separated flakes on a substrate are required. To prepare these
samples by deposition, a liquid dispersion is initially required, therefore, if the material was provided
as a powder, it requires dispersing in a suitable solvent, as described in Clause 7, before subsequent
deposition onto a suitable substrate with example procedures outlined in Annexes B and C.
If TEM is used (see Clause 10), prepare the sample on a TEM support grid as outlined in C.2, otherwise
prepare the sample on a silicon dioxide on silicon substrate, B.2. Then use optical microscopy as a
quick quality check to determine if the sample is too agglomerated and therefore cannot be accurately
measured. Optimize the sample preparation until an even deposition of the material across the
substrate occurs. Then undertake a combination of SEM, AFM and Raman spectroscopy measurements
(see Clause 9 and Annex B) or TEM (see Clause 10, Annex C). SEM, AFM and Raman spectroscopy should
be used in combination and not in individual isolation in order to determine the measurands listed in
Figure 1.
If required, use BET to determine the specific surface area of the powder (see Clause 11 and Annex E).
Once all the necessary measurements have been undertaken, calculate the median lateral flake size,
the range of flake sizes, the graphene 1LG number fraction and FLG number fraction, as discussed in
Clause 12 and Annex D. Here, number fraction is the fraction by number of graphene or FLG over the
total number of flakes, this can also be expressed as a percentage.
NOTE 2 It is assumed that the sample contains graphene/2LG/FLG/graphite. If the sample has different
chemistries, for example contains graphene oxide or functionalised graphene, this will not produce the same
Raman spectroscopy results as those described in this document. However, optical microscopy, SEM and AFM
characterization of lateral dimensions and thicknesses (but not number of layers) can still be applied to these
materials.
NOTE 3 There is currently no quantitative or standardised method for determining the specific surface area
of the graphitic material when the sample is in or from a liquid dispersion form.
6 Rapid test for graphitic material using Raman spectroscopy
Firstly, test the sample, in powder form deposited on a substrate using Raman spectroscopy to
determine whether the sample supplied contains graphene and/or graphitic material. This test can
also provide qualitative information on the structural properties of the material, including the level of
disorder and the dimensions of the flakes. If the sample is supplied in a liquid dispersion, then remove
the liquid from the dispersion and analyse the sample in powder form.
A thin layer of powder is required for this rapid Raman spectroscopy analysis step. If a powder has
been provided, this should be analysed with a significant amount of the sample secured on adhesive
tape (see A.2) such that only the flakes rather than the substrate are analysed.
A measurement protocol and sample preparation method are detailed in Annex A.
−1
To confirm the presence of graphitic material, a sharp (< 30 cm full width at half maximum
−1
(FWHM)) G-peak at approximately 1 580 cm and a 2D-peak (sometimes referred to as the G’ peak)
−1
at approximately 2 700 cm should be consistently observed in the Raman spectra as shown in the
graphene spectrum in Figure 2. If an intense symmetric Lorentzian peak shape is found for the 2D-peak
with close to or greater intensity than the G-peak, this suggests the sample could contain single-layer
graphene. However, restacked few-layer graphene flakes can also show a single Raman 2D-peak. If the
2D-peak is not symmetric, this suggests flakes of multiple layers are present. A prominent shoulder in
the 2D-peak is indicative of layered material, with a thickness of over ten graphene layers (i.e. graphite).
If the G- and 2D-peaks are not present, further characterization is not required, as the sample does not
contain graphene or graphite, however, a sufficient ratio of the Raman peak signal to background noise
(S/N) ratio should be established before this conclusion can be made, see Annex A for example details.
To improve the S/N ratio, longer acquisition times can be used, or averaging multiple scans with short
acquisition times can be used.
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ISO/TS 21356-1:2021(E)

If functionalised graphene or graphene oxide is present, Raman spectroscopy will show the D-
and G-peaks, but not necessarily a 2D-peak, and the D- and G-peaks will have much larger FWHM
−1
values (> 30 cm ) than expected for graphene. Here, additional chemical characterization should be
undertaken to determine the oxygen content and any other components, which if found to be high
means that the material is out of the scope of this document.
Key
−1
X Raman shift, cm
Y normalized intensity, arbitrary units
1 graphene
Figure 2 — Example Raman spectra of highly oriented pyrolytic graphite (HOPG), graphene,
reduced graphene oxide with lower oxygen content [rGO(L)], reduced graphene oxide with
higher oxygen content [rGO(H)] and graphene oxide (GO)
This step should not be confused with the processes used later for measurement of individual flakes
with AFM and Raman spectroscopy (detailed in Clause 9 and Annex B) after further sample preparation.
NOTE 1 Adhesive tape is specified to stop the powder moving for both health and safety reasons and to stop
possible electrostatic attraction and contamination of the lens.
NOTE 2 Chemical characterization of graphene including thermogravimetric analysis (TGA) and X-ray
photoelectron spectroscopy (XPS) will be detailed in a further ISO document in development at the time of
publication of this document.
NOTE 3 Other methods such as X-ray diffraction (XRD) can be used to determine the presence of graphitic
material. Raman spectroscopy is used here as a rapid confirmation step, as Raman spectroscopy is also required
for the detailed analysis of individual flakes (see Clause 9).
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ISO/TS 21356-1:2021(E)

7 Preparing a liquid dispersion
7.1 General
For further, more detailed characterization of the sample, the flakes should be prepared such that they
are isolated on a substrate. This allows the next characterization steps, as shown in Figure 1, to be
performed either using a combination of SEM, AFM and Raman spectroscopy with the sample on a
silicon dioxide on silicon substrate, or TEM with the sample on a TEM grid. For the preparation of the
flakes on a substrate, initially a liquid dispersion is required, therefore, if the material is provided as a
powder, it requires dispersing in a suitable solvent.
7.2 Preparing a dispersion of the correct concentration
7.2.1 Powder samples
Disperse the powder in a solvent such that a concentration of approximately 0,1 mg/ml is achieved. The
suitability of the solvent should be determined through the observation of how quick and how much, if
any, sedimentation of the material occurs. There are a number of different solvents that can be used.
Use the solvent that will disperse the powder and allow flakes to be characterized with the minimum of
unwanted residue on the surface. The order of preference of three solvents is given in Figure 3.
NOTE An order of preference of the solvent to be used is outlined.
Figure 3 — Flowchart for the creation of a dispersion
Firstly, try to disperse the powder with deionised water. Place the liquid and powder in a glass vial
or bottle and agitate. Sonicate the dispersion for up to a maximum of 10 min in a table-top ultrasonic
bath at 30 kHz to 40 kHz. Longer sonication times can cause changes to the structural properties,
including basal-plane scission (reducing the lateral size) and further exfoliation (reducing thickness/
layer number). Observe the dispersion over a period of several minutes. If a significant amount of
sedimentation occurs and occurs quickly then repeat the procedure using a different solvent.
If deionised water does not disperse the material, isopropanol should be used as the solvent using the
same method. If this does not work, then N-methylpyrrolidone (NMP) should be used as the solvent as
graphene disperses well in this. However, due to the high boiling point of NMP (203 °C), this can affect
the characterization results in the form of solvent residue.
The deposition of the material onto a substrate is detailed in Clauses 9 and 10 and in particular in
Annexes B and C.
Typically, graphene flakes will stay dispersed in deionised water only if a stabilizing agent, such as a
surfactant, is present as part of the manufacturing process. However, it should be noted that significant
use of surfactants can influence both the sample condition and the later measurement of the materials,
see examples in B.2.
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ISO/TS 21356-1:2021(E)

Using a significant amount of ultrasonication to disperse the material can induce flake scission
and therefore affect the structural characterization results obtained for a sample. The amplitude
(
...

SPÉCIFICATION ISO/TS
TECHNIQUE 21356-1
Première édition
2021-03
Nanotechnologies — Caractérisation
structurelle du graphène —
Partie 1:
Graphène issu de poudres et de
dispersions
Nanotechnologies — Structural characterization of graphene —
Part 1: Graphene from powders and dispersions
Numéro de référence
ISO/TS 21356-1:2021(F)
©
ISO 2021

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ISO/TS 21356-1:2021(F)

DOCUMENT PROTÉGÉ PAR COPYRIGHT
© ISO 2021
Tous droits réservés. Sauf prescription différente ou nécessité dans le contexte de sa mise en œuvre, aucune partie de cette
publication ne peut être reproduite ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique,
y compris la photocopie, ou la diffusion sur l’internet ou sur un intranet, sans autorisation écrite préalable. Une autorisation peut
être demandée à l’ISO à l’adresse ci-après ou au comité membre de l’ISO dans le pays du demandeur.
ISO copyright office
Case postale 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Genève
Tél.: +41 22 749 01 11
E-mail: copyright@iso.org
Web: www.iso.org
Publié en Suisse
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ISO/TS 21356-1:2021(F)

Sommaire Page
Avant-propos .iv
Introduction .v
1 Domaine d’application . 1
2 Références normatives . 1
3 Termes et définitions . 1
4 Termes abrégés . 3
5 Séquence des méthodes de mesure . 4
6 Contrôle rapide du matériau graphitique par spectroscopie Raman .6
7 Préparation d’une dispersion liquide . 8
7.1 Généralités . 8
7.2 Préparation d’une dispersion à la concentration exacte. 8
7.2.1 Échantillons en poudre . 8
7.2.2 Échantillons déjà sous forme de dispersion . 9
8 Détermination des méthodes . 9
9 Caractérisation structurelle par microscopie optique, MEB, AFM et spectroscopie Raman .9
10 Caractérisation structurelle par MET .10
11 Détermination de la surface par la méthode BET .11
12 Calcul de la taille latérale des flocons de graphène et de leurs proportions en nombre .11
Annexe A (informative) Contrôle rapide du matériau graphitique par spectroscopie Raman .12
Annexe B (informative) Protocole de caractérisation structurelle par MEB, AFM et
spectroscopie Raman .15
Annexe C (informative) Caractérisation structurelle par MET .30
Annexe D (informative) Calcul de la taille latérale et de la proportion en nombre .37
Annexe E (informative) Méthode Brunauer-Emmett-Teller .44
Annexe F (informative) Protocoles supplémentaires de préparation d’échantillons —
Préparation du substrat de silicium couvert de dioxyde de silicium et nettoyage.48
Bibliographie .49
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ISO/TS 21356-1:2021(F)

Avant-propos
L’ISO (Organisation internationale de normalisation) est une fédération mondiale d’organismes
nationaux de normalisation (comités membres de l’ISO). L’élaboration des Normes internationales est
en général confiée aux comités techniques de l’ISO. Chaque comité membre intéressé par une étude
a le droit de faire partie du comité technique créé à cet effet. Les organisations internationales,
gouvernementales et non gouvernementales, en liaison avec l’ISO participent également aux travaux.
L’ISO collabore étroitement avec la Commission électrotechnique internationale (IEC) en ce qui
concerne la normalisation électrotechnique.
Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont
décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier de prendre note des différents
critères d’approbation requis pour les différents types de documents ISO. Le présent document a été
rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2 (voir www
.iso .org/ directives).
L’attention est attirée sur le fait que certains des éléments du présent document peuvent faire l’objet de
droits de propriété intellectuelle ou de droits analogues. L’ISO ne saurait être tenue pour responsable
de ne pas avoir identifié de tels droits de propriété et averti de leur existence. Les détails concernant
les références aux droits de propriété intellectuelle ou autres droits analogues identifiés lors de
l’élaboration du document sont indiqués dans l’Introduction et/ou dans la liste des déclarations de
brevets reçues par l’ISO (voir www .iso .org/ brevets).
Les appellations commerciales éventuellement mentionnées dans le présent document sont données
pour information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer un
engagement.
Pour une explication de la nature volontaire des normes, la signification des termes et expressions
spécifiques de l’ISO liés à l’évaluation de la conformité, ou pour toute information au sujet de l’adhésion
de l’ISO aux principes de l’Organisation mondiale du commerce (OMC) concernant les obstacles
techniques au commerce (OTC), voir le lien suivant: www .iso .org/ iso/ fr/ avant-propos.
Le présent document a été préparé conjointement par le comité technique ISO/TC 229,
Nanotechnologies et le comité technique IEC/TC 113, Nanotechnologies relatives aux appareils et systèmes
électrotechnologiques. Le projet a été soumis au vote des organismes nationaux de l’ISO et de l’IEC.
Une liste de toutes les parties de la série ISO 21356 se trouve sur le site web de l’ISO.
Il convient que l’utilisateur adresse tout retour d’information ou toute question concernant le présent
document à l’organisme national de normalisation de son pays. Une liste exhaustive desdits organismes
se trouve à l’adresse www .iso .org/ fr/ members .html.
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ISO/TS 21356-1:2021(F)

Introduction
Du fait des nombreuses propriétés exceptionnelles du graphène et des matériaux bidimensionnels
(2D) apparentés, ces nanomatériaux pourraient créer des ruptures dans de nombreux domaines
d’application, tels que l’électronique flexible, les nanocomposites, la détection, les membranes filtrantes
et le stockage de l’énergie.
Il existe des obstacles à la commercialisation qui entravent les progrès des produits contenant du
graphène et qu’il est indispensable de surmonter. L’un de ces obstacles cruciaux est d’être capable de
répondre à la question «De quoi se compose le matériau ?». Il convient que les utilisateurs finaux des
matières premières contenant du graphène puissent se fier aux propriétés annoncées pour le graphène
commercialisé sur le marché international, de manière à instaurer la confiance et permettre des
échanges à l’échelle mondiale. Des protocoles de mesure fiables et répétables sont requis pour relever
ce défi.
Le présent document fournit aux analystes un ensemble de logigrammes à suivre afin de déterminer
les propriétés structurelles du graphène issu de poudres et de dispersions liquides (suspensions). Au
départ, il convient d’effectuer un contrôle rapide pour établir la présence de graphène et de matériau
graphitique. Si cette présence est confirmée, une analyse plus minutieuse doit être réalisée pour
déterminer si les échantillons contiennent un mélange de graphène monocouche, de graphène bicouche,
de graphène à quelques couches, de nanoplaquettes de graphène et de particules de graphite. Selon
les méthodes employées, les échantillons sont typiquement analysés après dépôt sur un substrat. Le
présent document décrit le mode opératoire qui permet d’évaluer les mesurages requis en fonction du
type d’échantillon et fournit des arbres décisionnels et des logigrammes destinés à aider l’utilisateur. Le
présent document décrit un ensemble sélectionné de mesurandes qui sont nécessaires, à savoir:
a) le nombre de couches/l’épaisseur des flocons;
b) les dimensions latérales des flocons;
c) l’alignement des couches;
d) le niveau de désordre;
e) la proportion estimée de graphène ou de graphène à quelques couches;
f) la surface spécifique de la poudre contenant du graphène.
Les propriétés physiques ci-dessus peuvent varier au cours du traitement du matériau et de sa durée
de vie, l’état d’agglomération des échantillons pouvant par exemple s’accentuer ou des fonctionnalités
de surface différentes apparaître. La liste ci‑dessus des mesurandes du matériau initial définit ses
caractéristiques inhérentes qui, en association avec les processus de fabrication choisis, détermineront
les performances des produits réels. En général, les propriétés d’un matériau qui peuvent s’avérer
importantes diffèrent d’un domaine d’application à un autre, selon le rôle fonctionnel de ce matériau.
Le présent document décrit des méthodes de caractérisation structurelle de flocons individuels de
graphène, de graphène bicouche, de nanoplaquettes de graphène et de particules de graphite isolés à
partir de poudres et/ou de dispersions liquides. Il ne fournit aucune méthode permettant de déterminer
si les poudres et/ou les dispersions sont ou non uniquement composées de ces matériaux. Aucune
recommandation n’est donnée quant à l’instant ou à la fréquence auxquels des échantillons doivent
être mesurés, bien qu’il ne soit pas prévu de le faire pour chaque lot du même matériau. Il revient à
l’utilisateur de déterminer les approches à adopter pour la caractérisation, parmi celles décrites dans
le présent document, ainsi que les instants opportuns et les fréquences pour le faire. Comme pour tous
les examens microscopiques, une attention particulière est requise au moment de tirer des conclusions
statistiques en fonction de la représentativité de l’échantillonnage.
Un ensemble d’annexes donne des exemples de protocoles pour la préparation et l’analyse des
échantillons, ainsi que des exemples de sources d’incertitude et de mode opératoire pour l’analyse des
données. Les méthodes employées sont la spectroscopie Raman, la microscopie électronique à balayage
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ISO/TS 21356-1:2021(F)

(MEB), la microscopie à force atomique (AFM), la microscopie électronique à transmission (MET) et la
méthode BET (Brunauer–Emmett–Teller).
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SPÉCIFICATION TECHNIQUE ISO/TS 21356-1:2021(F)
Nanotechnologies — Caractérisation structurelle du
graphène —
Partie 1:
Graphène issu de poudres et de dispersions
1 Domaine d’application
Le présent document spécifie la séquence des méthodes qui permettent de caractériser les propriétés
structurelles du graphène, du graphène bicouche et des nanoplaquettes de graphène issus de poudres et
de dispersions liquides, en utilisant un éventail de techniques de mesure, typiquement après l’isolation
de flocons individuels sur un substrat. Les propriétés couvertes sont le nombre de couches/l’épaisseur,
la taille latérale du flocon, le niveau de désordre, l’alignement des couches et la surface spécifique.
Le présent document suggère également des protocoles de mesure, des modes opératoires pour la
préparation des échantillons et des analyses de données pour la caractérisation du graphène issu de
poudres et de dispersions.
2 Références normatives
Les documents suivants sont cités dans le texte de sorte qu’ils constituent, pour tout ou partie de leur
contenu, des exigences du présent document. Pour les références datées, seule l’édition citée s’applique.
Pour les références non datées, la dernière édition du document de référence s’applique (y compris les
éventuels amendements).
ISO/TS 80004-1:2015, Nanotechnologies — Vocabulaire — Partie 1: Termes "coeur"
ISO/TS 80004-2:2015, Nanotechnologies — Vocabulaire — Partie 2: Nano-objets
ISO/TS 80004-6:2013, Nanotechnologies — Vocabulaire — Partie 6: Caractérisation des nano-objets
ISO/TS 80004-13:2017, Nanotechnologies — Vocabulaire — Partie 13: Graphène et autres matériaux
bidimensionnels
3 Termes et définitions
Pour les besoins du présent document, les termes et définitions de l’ISO/TS 80004‑1:2015,
l’ISO/TS 80004-2:2015, l’ISO/TS 80004-6:2013 et l’ISO/TS 80004-13:2017 ainsi que les suivants
s’appliquent.
L’ISO et l’IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en
normalisation, consultables aux adresses suivantes:
— ISO Online browsing platform: disponible à l’adresse https:// www .iso .org/ obp;
— IEC Electropedia: disponible à l’adresse https:// www .electropedia .org/ .
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ISO/TS 21356-1:2021(F)

3.1
graphène
couche de graphène
graphène à couche unique
graphène monocouche
monocouche d’atomes de carbone où chaque atome est lié à trois voisins, dans une structure en nid
d’abeilles
Note 1 à l'article: C’est un élément de base important pour beaucoup de nano-objets carbonés.
Note 2 à l'article: Lorsque le graphène possède une couche unique, il est parfois appelé graphène monocouche
ou bien graphène à couche unique et il est abrégé en 1LG pour le distinguer du graphène bicouche (2LG) et du
graphène à quelques couches (FLG).
Note 3 à l'article: Le graphène possède des bords latéraux et peut avoir des défauts et des joints de grains à
l’endroit où la liaison est perturbée.
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.1]
3.2
graphite
forme allotropique du carbone élémentaire, constituée de couches de graphène empilées parallèlement
les unes aux autres dans un ordre tridimensionnel cristallin à longue portée
Note 1 à l'article: Adaptée de la définition donnée dans l’IUPAC Compendium of Chemical Terminology.
Note 2 à l'article: Il existe deux formes allotropiques avec des empilements différents: hexagonale et
rhomboédrique.
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.2]
3.3
graphène bicouche
2LG
matériau bidimensionnel constitué de deux couches de graphène empilées et bien définies
Note 1 à l'article: Si le mode d’empilement est connu, il peut être spécifié séparément, par exemple comme
«graphène bicouche en empilement Bernal».
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.6]
3.4
graphène à quelques couches
FLG
matériau bidimensionnel constitué de trois à dix couches de graphène empilées et bien définies
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.10]
3.5
nanoplaque de graphène
nanoplaquette de graphène
GNP
nanoplaque constituée de couches de graphène
Note 1 à l'article: Elles possèdent typiquement une épaisseur comprise entre 1 nm et 3 nm et des dimensions
latérales comprises entre 100 nm et 100 µm.
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.11]
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ISO/TS 21356-1:2021(F)

3.6
taille latérale
taille du flocon
dimensions latérales du flocon d’un matériau bidimensionnel
Note 1 à l'article: Si le flocon est environ circulaire, il est alors typiquement mesuré à l’aide d’un diamètre
équivalent circulaire ou bien par les mesures x et y le long du côté le plus long et du côté perpendiculaire à celui-ci.
[SOURCE: ISO/TS 80004-13:2017, 3.4.1.15]
3.7
oxyde de graphène
GO
graphène modifié chimiquement et préparé par une oxydation et une exfoliation du graphite, engendrant
une modification oxydante étendue du plan de base
Note 1 à l'article: L’oxyde de graphène est un matériau monocouche ayant une forte teneur en oxygène,
typiquement caractérisé par un rapport atomique C/O d’environ 2,0 en fonction de la méthode de synthèse.
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.13]
3.8
oxyde de graphène réduit
rGO
forme d’oxyde de graphène ayant une teneur en oxygène réduite
Note 1 à l'article: Il peut être produit par des méthodes chimiques, thermiques, photochimiques, photothermiques,
microbiennes/bactériennes, par micro-ondes, ou bien encore par une exfoliation d’oxyde de graphite réduit.
Note 2 à l'article: Si l’oxyde de graphène était entièrement réduit, le produit serait le graphène. Cependant,
3
dans la pratique, certains groupes fonctionnels contenant de l’oxygène subsisteront et toutes les liaisons sp
2
ne retourneront pas à une configuration sp . Des réducteurs différents donneront lieu à des rapports carbone/
oxygène différents et à des compositions chimiques différentes dans l’oxyde de graphène réduit.
Note 3 à l'article: Il peut prendre la forme de plusieurs variations morphologiques, telles que des plaquettes et
des structures vermiculaires.
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.14]
4 Termes abrégés
Pour les besoins du présent document, les abréviations suivantes s’appliquent.
NOTE Selon le contexte, le «M» final ou initial peut aussi bien sous‑entendre «microscopie» que «microscope».
1LG graphène à couche unique/monocouche
2D bidimensionnel
2LG graphène bicouche
AFM microscopie à force atomique
méthode BET méthode Brunauer-Emmett-Teller
CVD dépôt chimique en phase vapeur
FLG graphène à quelques couches
FWHM largeur à mi-hauteur
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ISO/TS 21356-1:2021(F)

GNP nanoplaque de graphène
GO oxyde de graphène
NMP N-méthylpyrrolidone
rGO oxyde de graphène réduit
SAED diffraction électronique à aire sélectionnée
MEB microscopie électronique à balayage
MET microscopie électronique à transmission
5 Séquence des méthodes de mesure
Le présent article présente la séquence des méthodes de mesure nécessaire pour caractériser le plus
efficacement le graphène, le graphène bicouche, le graphène à quelques couches et les nanoplaquettes
de graphène issus de poudres et de dispersions liquides (suspensions). Dans le présent document, le
graphène, le graphène bicouche, le graphène à quelques couches et les nanoplaquettes de graphène
se présentent sous forme de flocons aux dimensions latérales limitées. Cependant, les échantillons,
typiquement, contiennent aussi d’importantes quantités de flocons dont l’épaisseur est supérieure à
10 couches, qui sont des flocons de graphite par définition.
Après un examen initial par spectroscopie Raman et en supposant que l’échantillon est constitué de
graphène ou qu’il a une nature graphitique, il convient d’effectuer une caractérisation plus détaillée.
Différentes approches sont alors possibles pour cette caractérisation, comme le montre la Figure 1. La
ou les méthodes de caractérisation à utiliser dépendront du temps et du matériel disponibles, ainsi que
des mesurandes que l’utilisateur exige.
NOTE 1 Comme les flocons sont issus d’une poudre ou d’une suspension liquide, ils nécessiteront généralement
d’être déposés sur un substrat avant analyse.
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ISO/TS 21356-1:2021(F)

NOTE Les numéros entre parenthèses font référence aux articles où l’élément est détaillé.
Figure 1 — Vue d’ensemble de la séquence et des modalités des méthodes de mesure utilisées
pour déterminer les propriétés structurelles du graphène issu d’un échantillon de poudre ou de
dispersion liquide
Déterminer tout d’abord si l’échantillon contient du graphène et/ou un matériau graphitique,
c’est-à-dire du graphène bicouche, du graphène à quelques couches, des nanoplaquettes de graphène ou
du graphite, en effectuant une analyse rapide par spectroscopie Raman, telle que détaillée à l’Article 6
et à l’Annexe A. L’échantillon doit nécessairement se présenter sous forme de poudre déposée en couche
fine sur un substrat. Par conséquent, si une dispersion liquide a été fournie, il est d’abord nécessaire
d’extraire le matériau du solvant, tel que décrit en A.2.
Choisir ensuite les méthodes à appliquer, sur la base des indications de l’Article 8. Utiliser la MET ou
une combinaison de MEB, d’AFM et de spectroscopie Raman pour déterminer la distribution des tailles
latérales des flocons et la relation avec leur épaisseur. Cette étape nécessite des flocons clairement
séparés sur un substrat. Pour la préparation de ces échantillons par dépôt, une dispersion liquide
est initialement requise. Par conséquent, si le matériau a été fourni sous forme de poudre, il doit être
dispersé dans un solvant adapté, tel que décrit à l’Article 7, avant d’être déposé ultérieurement sur un
substrat adapté en appliquant les exemples de mode opératoire des Annexes B et C.
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ISO/TS 21356-1:2021(F)

En cas d’utilisation de la MET (voir l’Article 10), préparer l’échantillon sur une grille de support de
MET suivant la description de C.2. Sinon, préparer l’échantillon sur un substrat de silicium couvert de
dioxyde de silicium (B.2). Effectuer ensuite un rapide contrôle de la qualité par microscopie optique.
Si l’échantillon est trop aggloméré, il ne peut pas être mesuré avec exactitude. Optimiser alors la
préparation de l’échantillon jusqu’à ce que le matériau se dépose sur le substrat de façon uniforme.
Réaliser ensuite une combinaison de mesurages par MEB, AFM et spectroscopie Raman (voir l’Article 9
et l’Annexe B) ou un mesurage par MET (voir l’Article 10 et l’Annexe C). Il convient d’utiliser la MEB, l’AFM
et la spectroscopie Raman de façon combinée, et non indépendamment, afin de pouvoir déterminer les
mesurandes indiqués sur la Figure 1.
Si cela est requis, utiliser la méthode BET pour déterminer la surface spécifique de la poudre (voir
l’Article 11 et l’Annexe E).
Une fois que tous les mesurages nécessaires ont été effectués, calculer la taille latérale médiane des
flocons, l’intervalle de leurs tailles et la proportion de graphène monocouche et la proportion de FLG,
tel que décrit à l’Article 12 et l’Annexe D. Ici, la proportion désigne la proportion en nombre de flocons
de graphène monocouche ou de flocons de FLG sur le nombre total de flocons et elle peut également
être exprimée en pourcentage.
NOTE 2 Par hypothèse, l’échantillon contient du graphène monocouche/2LG/FLG/graphite. Si l’échantillon
présente différentes formes chimiques (en contenant, par exemple, de l’oxyde de graphène ou du graphène
fonctionnalisé), les résultats obtenus par spectroscopie Raman seront différents de ceux décrits dans le présent
document. Cependant, la caractérisation par microscopie optique, MEB et AFM des dimensions latérales et des
épaisseurs (mais pas du nombre de couches) peut toujours être appliquée à ce type de matériaux.
NOTE 3 Il n’existe actuellement aucune méthode normalisée ou quantitative pour déterminer la surface
spécifique du matériau graphitique lorsque l’échantillon se présente sous forme de dispersion liquide ou provient
d’une dispersion de ce type.
6 Contrôle rapide du matériau graphitique par spectroscopie Raman
Contrôler tout d’abord l’échantillon, qui se présente sous forme de poudre déposée sur un substrat, par
spectroscopie Raman afin de déterminer si l’échantillon fourni contient du graphène et du matériau
graphitique. Ce contrôle peut également fournir des informations qualitatives sur les propriétés
structurelles du matériau, y compris le niveau de désordre et les dimensions des flocons. Si l’échantillon
est fourni dans une dispersion liquide, extraire alors le liquide de la dispersion et analyser l’échantillon
sous forme de poudre.
Une fine couche de poudre est requise pour cette étape d’analyse rapide par spectroscopie Raman. Si
une poudre a été fournie, il convient de l’analyser en fixant une quantité significative de l’échantillon
sur un ruban adhésif (voir A.2) afin d’analyser uniquement les flocons plutôt que le substrat.
Un protocole de mesure et une méthode de préparation de l’échantillon sont détaillés à l’Annexe A.
Pour confirmer la présence de matériau graphitique, il convient d’observer de manière concordante
−1 −1
un pic G effilé (largeur à mi‑hauteur (FWHM) < 30 cm ) à 1 580 cm environ et un pic 2D (parfois
−1
appelé pic G’) à 2 700 cm environ dans les spectres Raman, comme le montre le spectre du graphène
de la Figure 2. Si le pic 2D prend la forme symétrique d’un pic de Lorentz avec une intensité proche
ou supérieure à celle du pic G, cela laisse à penser que l’échantillon pourrait contenir du graphène
monocouche. Cependant, les flocons de graphène à quelques couches réempilées peuvent également
produire un pic 2D de Raman unique. Si le pic 2D n’est pas symétrique, cela suggère la présence de
flocons à couches multiples. Un épaulement net dans le pic 2D est indicatif d’un matériau à plusieurs
couches, avec une épaisseur de plus de 10 couches de graphène (c’est-à-dire du graphite). Si les pics G
et 2D sont absents, aucune caractérisation supplémentaire n’est requise car l’échantillon ne contient
pas de graphène ou de graphite. Il convient toutefois d’établir que le signal des pics de Raman par
rapport au bruit de fond (rapport signal/bruit S/B) est suffisant avant de parvenir à cette conclusion
(voir l’Annexe A pour obtenir des détails). Pour améliorer le rapport S/B, il est possible d’augmenter les
temps d’acquisition ou de faire la moyenne de multiples balayages avec des temps d’acquisition courts.
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ISO/TS 21356-1:2021(F)

En cas de présence de graphène fonctionnalisé ou d’oxyde de graphène, la spectroscopie Raman fera
apparaître les pics D et G, mais pas nécessairement un pic 2D, et les pics D et G auront des valeurs
−1
de FWHM nettement plus élevées (> 30 cm ) que celles attendues pour le graphène. Il convient de
procéder ici à une caractérisation chimique supplémentaire afin de déterminer la teneur en oxygène et
tout autre composant qui, s’il s’avérait en teneur élevée, impliquerait que le matériau n’entre pas dans le
domaine d’application du présent document.
Légende
−1
X décalage de Raman (cm )
Y intensité normalisée (unités arbitraires)
1 graphène
Figure 2 — Exemples de spectres Raman de poudres de graphite pyrolytique fortement orienté
(HOPG), de graphène, d’oxyde de graphène réduit à teneur réduite en oxygène (rGO(L), d’oxyde
de graphène à teneur accrue en oxygène (rGO(H)) et d’oxyde de graphène (GO)
Il convient de ne pas confondre cette étape avec les procédures qui seront utilisées par la suite pour
le mesurage des flocons individuels par AFM et par spectroscopie Raman (voir détails à l’Article 9 et à
l’Annexe B) après une préparation plus poussée des échantillons.
NOTE 1 Un ruban adhésif est spécifié pour des raisons de santé et de sécurité afin d’éviter tout mouvement
de la poudre, ainsi que pour empêcher toute éventuelle attraction électrostatique et toute contamination de la
lentille.
NOTE 2 La caractérisation chimique du graphène incluant l’analyse thermogravimétrique (TGA), et la
spectroscopie de photoélectrons X (XPS) sont détaillées dans un autre document ISO en cours d'élaboration au
moment de la publication de ce document.
NOTE 3 D’autres méthodes telles que la diffraction des rayons X (XRD) peuvent être util
...

TECHNICAL ISO/TS
SPECIFICATION 21356-1
First edition
Nanotechnologies — Structural
characterization of graphene —
Part 1:
Graphene from powders and
dispersions
Nanotechnologies — Caractérisation structurelle du graphène —
Partie 1: Graphène issu de poudres et de dispersions
Member bodies are requested to consult relevant national interests in IEC/TC
113 before casting their ballot to the e-Balloting application.
PROOF/ÉPREUVE
Reference number
ISO/TS 21356-1:2021(E)
©
ISO 2021

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ISO/TS 21356-1:2021(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
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ii PROOF/ÉPREUVE © ISO 2021 – All rights reserved

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ISO/TS 21356-1:2021(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 3
5 Sequence of measurement methods . 3
6 Rapid test for graphitic material using Raman spectroscopy . 5
7 Preparing a liquid dispersion . 6
7.1 General . 6
7.2 Preparing a dispersion of the correct concentration . 7
7.2.1 Powder samples . 7
7.2.2 Samples already in a dispersion . 8
8 Determination of methods . 8
9 Structural characterization using optical microscopy, SEM, AFM and Raman spectroscopy 8
10 Structural characterization using TEM . 9
11 Surface area determination using the BET method .10
12 Graphene lateral size and number fraction calculation .10
Annex A (informative) Rapid test for graphitic material using Raman spectroscopy .11
Annex B (informative) Structural characterization protocol using SEM, AFM and Raman
spectroscopy .14
Annex C (informative) Structural characterization using TEM .29
Annex D (informative) Lateral size and number fraction calculation .36
Annex E (informative) Brunauer–Emmett–Teller method .43
Annex F (informative) Additional sample preparation protocols — Silicon dioxide on
silicon wafer preparation and cleaning .47
Bibliography .48
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Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO’s adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared jointly by Technical Committee ISO/TC 229, Nanotechnologies, and
Technical Committee IEC/TC 113, Nanotechnology for electrotechnical products and systems. The draft
was circulated for voting to the national bodies of both ISO and IEC.
A list of all parts in the ISO 21356 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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Introduction
Due to the many superlative properties of graphene and related 2D materials, there are many
application areas where these nanomaterials could be disruptive, areas such as flexible electronics,
nanocomposites, sensing, filtration membranes and energy storage.
There are barriers to commercialisation that are impeding the progress of products containing
graphene, which need to be overcome. One of these crucial barriers is answering the question “What
is my material?”. End-users of the raw materials containing graphene should be able to rely on the
advertised properties of the commercial graphene on the global market, instilling trust and allowing
worldwide trade. Reliable and repeatable measurement protocols are required to address this challenge.
This document provides a set of flow-charts for analysts to follow in order to determine the structural
properties of graphene from powders and liquid dispersions (suspensions). Initially, a quick check
should be undertaken to determine if graphene and graphitic material is present. If it is, then further
detailed analysis is required to determine if the samples contain a mixture of single-layer graphene,
bilayer graphene, few-layer graphene, graphene nanoplatelets and graphite particles. Depending on
the methods used, the samples are typically analysed after deposition on a substrate. The document
describes how to assess what measurements are required depending on the type of sample and includes
decision trees and flow diagrams to aid the user. This document describes a selected set of measurands
that are needed, namely:
a) the number of layers/thickness of the flakes;
b) the lateral dimensions of flakes;
c) layer alignment;
d) the level of disorder;
e) the estimated number fraction of graphene or few-layer graphene;
f) the specific surface area of the powder containing graphene.
The above physical properties of the material can change during its processing and lifetime, e.g.
the samples can become more agglomerated, obtain different surface functionalities. The above
measurand list for the initial material defines their inherent characteristics that, along with the chosen
manufacturing processes, will determine the performance of real-world products. Generally, different
material properties can be important in different application areas, depending on the functional role of
the material.
The document provides methods for structural characterization of individual flakes of graphene,
bilayer graphene, graphene nanoplatelets and graphite particles isolated from powders and/or liquid
dispersions. It does not provide methods for determination of whether the powders and/or dispersions
are composed solely of these materials. No recommendation is provided as to when or how often to
measure samples, although it is not expected this would be for every batch of the same material. It is up
to the user to determine when, how often and which characterization routes described in this document
to take. As with all microscopical investigations, care is needed in drawing statistical conclusions
dependant on representative sampling.
A set of annexes provide example protocols on how to prepare and analyse the samples, sources of
uncertainty and how to analyse the data. The methods used are Raman spectroscopy, scanning electron
microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM) and the
BET (Brunauer–Emmett–Teller) method.
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TECHNICAL SPECIFICATION ISO/TS 21356-1:2021(E)
Nanotechnologies — Structural characterization of
graphene —
Part 1:
Graphene from powders and dispersions
1 Scope
This document specifies the sequence of methods for characterizing the structural properties of
graphene, bilayer graphene and graphene nanoplatelets from powders and liquid dispersions using a
range of measurement techniques typically after the isolation of individual flakes on a substrate. The
properties covered are the number of layers/thickness, lateral flake size, the level of disorder, layer
alignment and specific surface area. Suggested measurement protocols, sample preparation routines
and data analysis for the characterization of graphene from powders and dispersions are given.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO/TS 80004-1:2015, Nanotechnologies — Vocabulary — Part 1: Core terms
ISO/TS 80004-2:2015, Nanotechnologies — Vocabulary — Part 2: Nano-objects
ISO/TS 80004-6:2013, Nanotechnologies — Vocabulary — Part 6: Nano-object characterization
ISO/TS 80004-13:2017, Nanotechnologies — Vocabulary — Part 13: Graphene and related two-dimensional
(2D) materials
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/TS 80004-1:2015,
ISO/TS 80004-2:2015, ISO/TS 80004-6:2013, ISO/TS 80004-13:2017 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
graphene
graphene layer
single-layer graphene
monolayer graphene
single layer of carbon atoms with each atom bound to three neighbours in a honeycomb structure
Note 1 to entry: It is an important building block of many carbon nano-objects.
Note 2 to entry: As graphene is a single layer, it is also sometimes called monolayer graphene or single-layer
graphene and abbreviated as 1LG to distinguish it from bilayer graphene (2LG) and few-layered graphene (FLG).
Note 3 to entry: Graphene has edges and can have defects and grain boundaries where the bonding is disrupted.
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[SOURCE: ISO/TS 80004-13:2017, 3.1.2.1]
3.2
graphite
allotropic form of the element carbon, consisting of graphene layers stacked parallel to each other in a
three-dimensional, crystalline, long-range order
Note 1 to entry: Adapted from the definition in the IUPAC Compendium of Chemical Terminology.
Note 2 to entry: There are two primary allotropic forms with different stacking arrangements: hexagonal and
rhombohedral.
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.2]
3.3
bilayer graphene
2LG
two-dimensional material consisting of two well-defined stacked graphene layers
Note 1 to entry: If the stacking registry is known, it can be specified separately, for example, as “Bernal stacked
bilayer graphene”.
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.6]
3.4
few-layer graphene
FLG
two-dimensional material consisting of three to ten well-defined stacked graphene layers
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.10]
3.5
graphene nanoplate
graphene nanoplatelet
GNP
nanoplate consisting of graphene layers
Note 1 to entry: GNPs typically have thickness of between 1 nm to 3 nm and lateral dimensions ranging from
approximately 100 nm to 100 μm.
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.11]
3.6
lateral size
flake size
<2D material> lateral dimensions of a 2D material flake
Note 1 to entry: If the flake is approximately circular then this is typically measured using an equivalent circular
diameter or if not via x, y measurements along and perpendicular to the longest side.
[SOURCE: ISO/TS 80004-13:2017, 3.4.1.15]
3.7
graphene oxide
GO
chemically modified graphene prepared by oxidation and exfoliation of graphite, causing extensive
oxidative modification of the basal plane
Note 1 to entry: Graphene oxide is a single-layer material with a high oxygen content, typically characterized by
C/O atomic ratios of approximately 2,0 depending on the method of synthesis.
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.13]
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3.8
reduced graphene oxide
rGO
reduced oxygen content form of graphene oxide
Note 1 to entry: This can be produced by chemical, thermal, microwave, photo-chemical, photo-thermal or
microbial/bacterial methods or by exfoliating reduced graphite oxide.
Note 2 to entry: If graphene oxide was fully reduced, then graphene would be the product. However, in practice,
3 2
some oxygen containing functional groups will remain and not all sp bonds will return back to sp configuration.
Different reducing agents will lead to different carbon to oxygen ratios and different chemical compositions in
reduced graphene oxide.
Note 3 to entry: It can take the form of several morphological variations such as platelets and worm-like
structures.
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.14]
4 Abbreviated terms
For the purposes of this document, the following abbreviated terms apply.
NOTE The final “M”, given as “microscopy”, may be taken equally as “microscope” depending on the context.
1LG single layer graphene
2D two dimensional
2LG bilayer graphene
AFM atomic force microscopy
BET method Brunauer–Emmett–Teller method
CVD chemical vapour deposition
FLG few-layer graphene
FWHM full width at half maximum
NMP N-methylpyrrolidone
SAED selected area electron diffraction
SEM scanning electron microscopy
TEM transmission electron microscopy
5 Sequence of measurement methods
This clause presents the sequence of measurement methods necessary to most efficiently characterize
graphene, bilayer graphene, few-layer graphene and graphene nanoplatelets from powders and liquid
dispersions (suspensions). In this document, graphene, bilayer graphene, few-layer graphene and
graphene nanoplatelets are in the form of flakes of limited lateral dimensions. However, samples also
typically contain significant amounts of flakes having thicknesses that exceed 10 layers, which are
flakes of graphite by definition.
After an initial examination by Raman spectroscopy, and assuming the sample is graphene or graphitic
in nature, a more detailed characterization should follow. Various characterization routes are then
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possible, as shown in Figure 1. The characterization method or methods to be used will depend on the
time and equipment available and the measurands that the user requires.
NOTE 1 As the flakes are from a powder or liquid dispersion, they will typically require deposition onto a
substrate before analysis.
NOTE The numbers in brackets refer to the clauses where the item is detailed.
Figure 1 — Overview of the sequence and process of the measurement methods used to
determine the structural properties of graphene from a powder or liquid dispersion sample
Firstly, determine if the sample contains graphene and/or graphitic material, that is bilayer graphene,
FLG, GNPs or graphite by undertaking a rapid analysis using Raman spectroscopy, as detailed in
Clause 6 and Annex A. The sample needs to be in powder form deposited as a thin layer on a substrate,
therefore if a liquid dispersion has been supplied, the material will first need to be removed from the
solvent, as detailed in A.2.
Decide which methods to use as outlined in Clause 8. Either use TEM or a combination of SEM, AFM
and Raman spectroscopy to determine the distribution of lateral flake sizes and the relationship with
flake thickness. For this stage, clearly separated flakes on a substrate are required. To prepare these
samples by deposition a liquid dispersion is initially required, therefore if the material was provided
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as a powder, it requires dispersing in a suitable solvent, as described in Clause 7, before subsequent
deposition onto a suitable substrate with example procedures outlined in Annexes B and C.
If TEM is used (see Clause 10), prepare the sample on a TEM support grid as outlined in C.2, otherwise
prepare the sample on a silicon dioxide on silicon substrate, B.2. Then use optical microscopy as a
quick quality check to determine if the sample is too agglomerated and therefore cannot be accurately
measured. Optimize the sample preparation until an even deposition of the material across the
substrate occurs. Then undertake a combination of SEM, AFM and Raman spectroscopy measurements
(see Clause 9 and Annex B) or TEM (see Clause 10, Annex C). SEM, AFM and Raman spectroscopy should
be used in combination and not in individual isolation in order to determine the measurands listed in
Figure 1.
If required, use BET to determine the specific surface area of the powder (see Clause 11 and Annex E).
Once all the necessary measurements have been undertaken, calculate the median lateral flake size,
the range of flake sizes, the graphene 1LG number fraction and FLG number fraction, as discussed in
Clause 12 and Annex D. Here, number fraction is the fraction by number of graphene or FLG over the
total number of flakes, this can also be expressed as a percentage.
NOTE 2 It is assumed that the sample contains graphene/2LG/FLG/graphite. If the sample has different
chemistries, for example contains graphene oxide or functionalised graphene, this will not produce the same
Raman spectroscopy results as those described in this document. However, optical microscopy, SEM and AFM
characterization of lateral dimensions and thicknesses (but not number of layers) can still be applied to these
materials.
NOTE 3 There is currently no quantitative or standardised method for determining the specific surface area
of the graphitic material when the sample is in or from a liquid dispersion form.
6 Rapid test for graphitic material using Raman spectroscopy
Firstly, test the sample, in powder form deposited on a substrate using Raman spectroscopy to
determine if the sample supplied contains graphene and graphitic material. This test can also provide
qualitative information on the structural properties of the material, including the level of disorder and
the dimensions of the flakes. If the sample is supplied in a liquid dispersion, then remove the liquid from
the dispersion and analyse the sample in powder form.
A thin layer of powder is required for this rapid Raman spectroscopy analysis step. If a powder has
been provided, this should be analysed with a significant amount of the sample secured on adhesive
tape (see A.2) such that only the flakes rather than the substrate are analysed.
A measurement protocol and sample preparation method are detailed in Annex A.
−1
To confirm the presence of graphitic material, a sharp (<3 0 cm full width at half maximum (FWHM))
−1
G-peak at approximately 1 580 cm and a 2D-peak (sometimes referred to G’ peak) at approximately
−1
2 700 cm should be consistently observed in the Raman spectra as shown in the graphene spectrum
in Figure 2. If an intense symmetric Lorentzian peak shape is found for the 2D-peak with close to or
greater intensity than the G-peak, this suggests the sample could contain single layer graphene.
However, restacked few-layer graphene flakes can also show a single Raman 2D-peak. If the 2D-peak is
not symmetric this suggests flakes of multiple layers are present. A prominent shoulder in the 2D-peak
is indicative of layered material, with a thickness of over 10 graphene layers (i.e. graphite). If the G-
and 2D-peaks are not present, further characterization is not required, as the sample does not contain
graphene or graphite, however, a sufficient ratio of the Raman peak signal to background noise (S/N)
ratio should be established before this conclusion can be made, see Annex A for example details. To
improve the S/N ratio, longer acquisition times can be used, or averaging multiple scans with short
acquisition times can be used.
If functionalised graphene or graphene oxide is present, Raman spectroscopy will show the D-
and G-peaks, but not necessarily a 2D-peak, and the D- and G-peaks will have much larger FWHM
−1
values (> 30 cm ) than expected for graphene. Here, additional chemical characterization should be
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undertaken to determine the oxygen content and any other components, which if found to be high
means that the material is out of the scope of this document.
Key
−1
X raman shift, cm
Y normalized intensity, arbitrary units
1 graphene
Figure 2 — Example Raman spectra of powders of highly oriented pyrolytic graphite (HOPG),
graphene, reduced graphene oxide with lower oxygen content(rGO(L), reduced graphene oxide
with higher oxygen content (rGO(H)) and graphene oxide (GO)
This step should not be confused with the processes used later for measurement of individual flakes
with AFM and Raman spectroscopy (detailed in Clause 9 and Annex B) after further sample preparation.
NOTE 1 Adhesive tape is specified to stop the powder moving for both health and safety reasons and to stop
possible electrostatic attraction and contamination of the lens.
NOTE 2 Chemical characterization of graphene including thermogravimetric analysis (TGA) and X-ray
photoelectron spectroscopy (XPS) are detailed in ISO/PWI 23359.
NOTE 3 Other methods such as X-ray diffraction (XRD) can be used to determine the presence of graphitic
material. Raman spectroscopy is used here as a rapid confirmation step, as Raman spectroscopy is also required
for the detailed analysis of individual flakes (see Clause 9).
7 Preparing a liquid dispersion
7.1 General
For further, more detailed, characterization of the sample, the flakes should be prepared such that
they are isolated on a substrate. This allows the next characterization steps, as shown in Figure 1, to
be performed either using a combination of SEM, AFM and Raman spectroscopy with the sample on a
silicon dioxide on silicon substrate, or TEM with the sample on a TEM grid. For the preparation of the
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flakes on a substrate, initially a liquid dispersion is required, therefore if the material is provided as a
powder, it requires dispersing in a suitable solvent.
7.2 Preparing a dispersion of the correct concentration
7.2.1 Powder samples
Disperse the powder in a solvent such that a concentration of approximately 0,1 mg/ml is achieved. The
suitability of the solvent should be determined through the observation of how quick and how much, if
any, sedimentation of the material occurs. There are a number of different solvents that can be used.
Use the solvent that will disperse the powder and allow flakes to be characterized with the minimum of
unwanted residue on the surface. The order of preference of three solvents is given in Figure 3.
NOTE An order of preference of the solvent to be used is outlined.
Figure 3 — Flowchart for the creation of a dispersion
Firstly, try to disperse the powder with deionised water. Place the liquid and powder in a glass vial
or bottle and agitate. Sonicate the dispersion for up to a maximum of 10 min in a table-top ultrasonic
bath at 30 kHz to 40 kHz. Longer sonication times can cause changes to the structural properties,
including basal-plane scission (reducing the lateral size) and further exfoliation (reducing thickness/
layer number). Observe the dispersion over a period of several minutes. If a significant amount of
sedimentation occurs and occurs quickly then repeat the procedure using a different solvent.
If deionised water does not disperse the material, isopropanol should be used as the solvent using the
same method. If this does not work, then N-methylpyrrolidone (NMP) should be used as the solvent as
graphene disperses well in this. However, due to the high boiling point of NMP (203 °C), this can affect
the characterization results in the form of solvent residue.
The deposition of the material onto a substrate is detailed in Clauses 9 and 10 and in particular in
Annexes B and C.
Typically graphene flakes will stay dispersed in deionised water only if a stabilizing agent, such as a
surfactant, is present as part of the manufacturing process. However, it should be noted that significant
use of surfactants can influence both the sample condition and the later measurement of the materials,
see examples in B.2.
Using a significant amount of ultrasonication to disperse the material can induce flake scission and
therefore affect the structural characterization results obtained for a sample. The amplitude (commonly
expressed as power) and duration of ultrasonication should therefore be kept to the minimum required
to disperse the flakes. A comparison of flake size measurement as a function of the amplitude and
duration of ultrasonication can be undertaken to
...

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