SIST-TS CEN ISO/TS 21356-1:2022
(Main)Nanotechnologies - Structural characterization of graphene - Part 1: Graphene from powders and dispersions (ISO/TS 21356-1:2021)
Nanotechnologies - Structural characterization of graphene - Part 1: Graphene from powders and dispersions (ISO/TS 21356-1:2021)
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.
Nanotechnologien - Strukturelle Charakterisierung von Graphen - Teil 1: Graphen aus Pulvern und Dispersionen (ISO/TS 21356-1:2021)
Dieses Dokument legt die Abfolge von Verfahren zur Charakterisierung der strukturellen Eigenschaften von Graphen, Zweischicht-Graphen und Graphen-Nanotäfelchen aus Pulvern und flüssigen Dispersionen mittels einer Reihe von Messverfahren, üblicherweise nach der Isolierung einzelner Flocken auf einem Substrat, fest. Zu den erfassten Eigenschaften gehören die Anzahl an Schichten/Dicke, die laterale Flockengröße, der Grad der Unordnung, die Schichtenanordnung und die spezifische Oberfläche. Es werden Vorschläge für Messprotokolle, Probenaufbereitungsabläufe und die Datenanalyse für die Charakterisierung von Graphen aus Pulvern und Dispersionen dargelegt.
Nanotechnologies - Caractérisation structurelle du graphène - Partie 1: Graphène issu de poudres et de dispersions (ISO/TS 21356-1:2021)
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.
Nanotehnologije - Strukturne značilnosti grafena - 1. del: Grafen iz prahu in disperzije (ISO/TS 21356-1:2021)
Ta dokument določa zaporedje metod za karakterizacijo strukturnih lastnosti grafena, dvoslojnega grafena ter grafenskih nanoploščic iz prahu in tekoče disperzije z uporabo različnih merilnih tehnik, običajno po izolaciji posameznih kosmov na podlagi. Zajete lastnosti so število slojev/debelina, velikost lateralnih kosmov, stopnja motnje, poravnava slojev in določena površina. Podani so predlogi za protokole merjenja, postopki priprave vzorcev in analizo podatkov za karakterizacijo grafena iz prahu in disperzije.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST-TS CEN ISO/TS 21356-1:2022
01-maj-2022
Nanotehnologije - Strukturne značilnosti grafena - 1. del: Grafen iz prahu in
disperzije (ISO/TS 21356-1:2021)
Nanotechnologies - Structural characterization of graphene - Part 1: Graphene from
powders and dispersions (ISO/TS 21356-1:2021)
Nanotechnologien - Strukturelle Charakterisierung von Graphen - Teil 1: Graphen aus
Pulvern und Dispersionen (ISO/TS 21356-1:2021)
Nanotechnologies - Caractérisation structurelle du graphène - Partie 1: Graphène issu
de poudres et de dispersions (ISO/TS 21356-1:2021)
Ta slovenski standard je istoveten z: CEN ISO/TS 21356-1:2022
ICS:
07.120 Nanotehnologije Nanotechnologies
SIST-TS CEN ISO/TS 21356-1:2022 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST-TS CEN ISO/TS 21356-1:2022
CEN ISO/TS 21356-1
TECHNICAL SPECIFICATION
SPÉCIFICATION TECHNIQUE
March 2022
TECHNISCHE SPEZIFIKATION
ICS 07.120
English Version
Nanotechnologies - Structural characterization of
graphene - Part 1: Graphene from powders and
dispersions (ISO/TS 21356-1:2021)
Nanotechnologies - Caractérisation structurelle du Nanotechnologien - Strukturelle Charakterisierung von
graphène - Partie 1: Graphène issu de poudres et de Graphen - Teil 1: Graphen aus Pulvern und
dispersions (ISO/TS 21356-1:2021) Dispersionen (ISO/TS 21356-1:2021)
This Technical Specification (CEN/TS) was approved by CEN on 13 March 2022 for provisional application.
The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to
submit their comments, particularly on the question whether the CEN/TS can be converted into a European Standard.
CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS
available promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in
parallel to the CEN/TS) until the final decision about the possible conversion of the CEN/TS into an EN is reached.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN ISO/TS 21356-1:2022 E
worldwide for CEN national Members.
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CEN ISO/TS 21356-1:2022 (E)
Contents Page
European foreword . 3
2
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CEN ISO/TS 21356-1:2022 (E)
European foreword
The text of ISO/TS 21356-1:2021 has been prepared by Technical Committee ISO/TC 229
"Nanotechnologies” of the International Organization for Standardization (ISO) and has been taken over
as CEN ISO/TS 21356-1:2022 by Technical Committee CEN/TC 352 “Nanotechnologies” the secretariat
of which is held by AFNOR.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to announce this Technical Specification: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO/TS 21356-1:2021 has been approved by CEN as CEN ISO/TS 21356-1:2022 without any
modification.
3
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SIST-TS CEN ISO/TS 21356-1:2022
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
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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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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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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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SIST-TS CEN ISO/TS 21356-1:2022
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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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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[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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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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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
...
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