IEC TS 62607-6-12:2024

Nanomanufacturing - Key Control Characteristics - Part 6-12: Graphene - Number of layers: Raman spectroscopy, optical reflection

IEC TS 62607-6-12:2024 establishes a standardized method to determine the key control characteristic
- number of layers
for films consisting of graphene by
- Raman spectroscopy and
- optical reflection.
Criteria for the determination of the number of layers are the G-peak integrated intensity and the optical contrast. Both methods enable to distinguish between graphene and multilayer graphene. However, neither method on its own nor the combination of the two enable a determination of the number of layers in all possible cases (especially regarding all possible stacking angles). But the comparison of the values deduced by each method allows to discriminate whether the determined number of layers is correct and can be specified or not.
- The method is applicable to exfoliated graphene and graphene grown on or transferred to a substrate with a small defect density, low surface contamination (e.g. transfer residue) and number of layers up to 5.
- The method is suitable for the following substrates:
a) glass (soda lime glass or similar with a refractive index between 1,45 and 1,55 at 532 nm);
b) oxidized silicon (SiO2 on silicon, with a SiO2 thickness of 90 nm ± 5 nm).
- The spatial resolution is in the order of 1 µm given by the spot size of the exciting laser.

General Information

• Status: Published
• Publication Date: 27-Jun-2024
• ICS: 07.120 - Nanotechnologies
• Technical Committee: TC 113 - Nanotechnology for electrotechnical products and systems
• Drafting Committee: WG 8 - TC 113/WG 8
• Current Stage: PPUB - Publication issued
• Start Date: 28-Jun-2024
• Completion Date: 17-Jul-2023

Overview

IEC TS 62607-6-12:2024 defines a standardized method for determining the number of layers in graphene films using Raman spectroscopy and optical reflection (optical contrast). Part of the IEC TS 62607 nanomanufacturing series on key control characteristics, this Technical Specification targets high‑quality graphene (exfoliated or grown/transferred) with low defect density and low surface contamination, for layer counts up to N ≤ 5. The procedure includes calibration, measurement, data analysis and reporting conventions to support consistent graphene characterization.

Key topics and requirements

• Measurement techniques: Combined use of Raman spectroscopy (G‑peak integrated intensity normalized to HOPG) and optical reflection (optical contrast relative to bare substrate).
• Decision criteria: Primary metrics are G‑peak integrated intensity and optical contrast. Both methods distinguish graphene (monolayer) from multilayer graphene, but neither alone - nor their combination - guarantees absolute layer counting for all stacking configurations (e.g., varying stacking angles).
• Scope limits: Applicable to films with up to 5 layers, deposited on:
  • Glass (soda‑lime or similar; refractive index 1.45–1.55 at 532 nm)
  • Oxidized silicon (SiO2 on Si, SiO2 thickness 90 nm ± 5 nm)
• Spatial resolution: Approximately 1 µm, set by the laser spot size.
• Calibration & procedure: Includes calibration of Raman spectrometers and optical reflection setups, use of Raman/reflection reference samples, a defined sampling plan and measurement accuracy statements.
• Reporting: Standardized test report content (sample ID, measurement conditions, specific measurement data, and interpretation) and decision tables for layer assignment.

Practical applications

• Quality control in nanomanufacturing and graphene production lines to verify monolayer vs few‑layer film status.
• Process validation for graphene device fabrication (electronics, sensors, transparent conductive films) where layer number affects electrical/optical properties.
• Metrology protocols in research labs and certification bodies performing repeatable graphene characterization using Raman and optical reflection.
• Integration into inspection workflows for transferred or grown graphene on industry‑relevant substrates (glass and SiO2/Si).

Who should use this standard

• Materials characterization and metrology laboratories
• Semiconductor and printed electronics manufacturers using graphene
• Quality assurance and process engineers in nanomanufacturing
• Researchers standardizing graphene layer-count measurements

Related standards

• Other parts of the IEC TS 62607 series (Nanomanufacturing – Key Control Characteristics) for complementary KCCs and measurement frameworks. For precise references, consult the IEC webstore.

Keywords: IEC TS 62607-6-12, graphene number of layers, Raman spectroscopy, optical reflection, G-peak integrated intensity, optical contrast, nanomanufacturing, graphene characterization, SiO2 on silicon, glass substrate.

Standards Content (Sample)

IEC TS 62607-6-12 ®
Edition 1.0 2024-06
TECHNICAL
SPECIFICATION
Nanomanufacturing – Key Control Characteristics –
Part 6-12: Graphene – Number of layers: Raman spectroscopy, optical reflection

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IEC TS 62607-6-12 ®
Edition 1.0 2024-06
TECHNICAL
SPECIFICATION
Nanomanufacturing – Key Control Characteristics –

Part 6-12: Graphene – Number of layers: Raman spectroscopy, optical reflection

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 07.120  ISBN 978-2-8322-9292-1

– 2 – IEC TS 62607-6-12:2024 © IEC 2024
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 8
3.1 General terms . 9
3.2 Graphene related terms . 9
3.3 Key control characteristics measured in accordance with this document . 11
3.4 Terms related to the measurement method described in this document . 12
4 General . 13
4.1 Measurement principle . 13
4.2 Sample preparation method . 14
4.3 Measurement environment . 14
4.4 Description of test equipment . 14
4.5 Calibration standards . 16
4.5.1 Raman reference sample . 16
4.5.2 Reflection reference sample . 16
5 Measurement procedure . 17
5.1 Calibration of test equipment . 17
5.1.1 Raman spectrometer . 17
5.1.2 Optical reflection setup . 17
5.2 Description of the measurement procedure . 17
5.3 Sampling plan . 17
5.4 Measurement accuracy . 17
6 Data analysis and interpretation of results . 18
6.1 Analysis of the Raman spectra . 18
6.2 Analysis of the reflectance measurement . 19
6.3 Interpretation of the combined measurement . 21
7 Test report . 22
7.1 General . 22
7.2 Sample identification . 22
7.3 Test conditions . 23
7.4 Measurement specific information . 23
7.5 Test results . 23
Annex A (informative) Format of the test report . 24
Annex B (informative) Sampling plan . 27
B.1 General . 27
B.2 Sampling plan depending on substrate geometry . 28
B.2.1 Circular substrates . 28
B.2.2 Rectangular substrates . 29
B.2.3 Irregular shaped substrates . 30
B.2.4 Coordinate system . 30
Bibliography . 32

Figure 1 – Raman spectra of HOPG (top), pristine graphene (middle) and defective
few-layer graphene (bottom) . 14

Figure 2 – Schematic illustration of the Raman and reflectance setup used for the
described graphene classification . 16
Figure 3 – Number of layers as a function of G-peak integrated intensity on glass (top)
and on 90 nm ± 5 nm SiO on Si (bottom) . 19
Figure 4 – Number of layers as a function of the optical contrast on glass (top) and on
90 nm ± 5 nm SiO on Si (bottom) . 20
Figure 5 – Decision criteria regarding the number of layers . 22
Figure B.1 – Schematic of sample plan for circular substrates . 28
Figure B.2 – Schematic of sample plan for square substrates . 29
Figure B.3 – Example sampling plan for irregular sample . 30
Figure B.4 – Coordinate system applied to the measurement results in the test report . 31

Table 1 – Number of layers decision table A, if the estimates of N and N agree . 21
G C
Table 2 – Number of layers decision table B, if the estimates are between numbers.
Exact number of layers cannot be specified but a range of N . 21
Table 3 – Number of layers decision table C, if the values of N are slightly lower than
G
N . . 21
C
Table A.1 – Product identification . 24
Table A.2 – General material description . 24
Table A.3 – Measurement related information . 24
Table A.4 – Measurement results . 25
Table A.5 – Colour map of KCC . 26
Table B.1 – Sampling plan for circular substrates . 28
Table B.2 – Sampling plan for square sample . 29

– 4 – IEC TS 62607-6-12:2024 © IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NANOMANUFACTURING –
KEY CONTROL CHARACTERISTICS –
Part 6-12: Graphene – Number of layers:
Raman spectroscopy, optical reflection

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC TS 62607-6-12 has been prepared by IEC technical committee 113: Nanotechnology for
electrotechnical products and systems. It is a Technical Specification.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
113/701/DTS 113/726/RVDTS
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Specification is English.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts in the IEC TS 62607 series, published under the general title
Nanomanufacturing – Key control characteristics, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates that it
contains colours which are considered to be useful for the correct understanding of its
contents. Users should therefore print this document using a colour printer.

– 6 – IEC TS 62607-6-12:2024 © IEC 2024
INTRODUCTION
Graphene, a single layer of carbon atoms arranged in a honeycomb lattice, has a high potential
for future nanotechnology applications due to the excellent conductivity, transparency and
flexibility of the material. Many physical properties of graphene and few-layer graphene depend
on the number of layers. For example, monolayer and some few-layer graphene admit a linear
dispersion relation of electronic bands and consequently show specific quantum hall effect and
conductivity. Optical transparency and chemical activity are also related to the number of layers
and their stacking angles.
Raman spectroscopy is a simple, fast and well-understood technique and has been proposed
as a key experimental technique to evaluate the number of layers. The interpretation of Raman
measurements however depends on many parameters such as laser wavelength, stacking
angles, doping, strain, heating from laser, focus, graphene quality or defect density, residues
and substrate. Raman spectroscopy can then not be used alone to determine the number of
layers. In this document for the number of layers (N), we combine Raman spectroscopy with
optical contrast on high quality graphene deposited on glass substrate and on SiO -on-silicon
substrate. The present procedure is restricted to N ≤ 5.
The analysis of the Raman spectra concentrates on two of the most dominating Raman peaks
-1 -1
) and the G-peak (1 580 cm ). High quality
for graphene: the D-peak (around 1 340 cm
graphene samples are characterized by a very low intensity of the D-peak. The number of layers
is determined by the measurement of the integrated intensity of the G-peak of the graphene
samples normalized to the integrated intensity of HOPG sample. The optical contrast of
graphene is measured relative to the bare substrate.
In the literature, mainly three criteria have been proposed to determine N.
1) 2D-peak based criteria: the dependencies of the full width at half maximum of the 2D-peak
(Γ ) and the ratio between 2D- and G-peaks integrated intensities (A /A ) as a function
2D 2D G
of N have been commonly used in the literature as metrics to distinguish monolayer
graphene (1LG) and few-layer graphene (FLG): 1LG has been proposed to have the lowest
Γ and highest A /A as compared to multilayer graphene (MLG). A systematic
2D 2D G
investigation evidences different and even opposite behaviours of these features with N [1] .
It has been analysed as the consequences of different stacking order between consecutive
graphene layers. In agreement with published reports on twisted bilayer graphene (2LG),
higher values of the A /A ratio and narrower 2D-peak widths than those measured on 1LG
2D G
can be measured on twisted FLG. In terms of control characteristics, these results confirm
that neither A /A nor Γ are valid criteria to identify 1LG or to count the number of layers
2D G 2D
in FLG. The sensitivity of these quantities to doping or strain also impacts their reliability.
As a consequence, criteria based on the 2D-peak have been ruled out.
___________
Numbers in square brackets refer to the Bibliography.

2) G-peak area based criterion: A more robust parameter to count the number of graphene
layers is the G-peak area or integrated intensity (A ). Since it relies on Raman intensity
G
measurement, it is important to define a reference for intensity normalization. HOPG has
been chosen as a reference since it is a well-defined, easy to purchase material. A has the
G
advantage to enable to distinguish between 1LG and FLG in all cases, if the signal-to-noise
ratio is high enough. However, regarding the number of layers counting, two limitations
related to the relative orientation and stacking of the graphene layers exist: First, an
intensity enhancement can occur due to changes in the joint density of states, for given
relative orientations of the layers [2]. Second, a significant G-peak intensity decrease (down
to 70 % of the one of equivalent Bernal stacked structures) can occur for some relative
orientations [3], [4], [5]. As an example, for 2LG and a laser wavelength of 532 nm, the
optical resonance increases A for twist angles in the range 10° to 16° and A is found
G G
lower than in Bernal 2LG for twist angles in the range 16° to 23°. These two limitations
circumvent the use of A alone as metrics for counting the number of layers.
G
3) Optical contrast based criterion: The optical contrast in the visible, defined as the ratio
between the laser signal reflected by the sample and the laser signal reflected by the bare
substrate minus one, has also been proposed as a tool for counting graphene layers.
Indeed, the optical properties of MLG are, in most of the cases, directly related to the
number of layers. However, the optical contrast is also changing near optical resonances.
In this case, this criterion also leads to a wrong determination of the number of layers.
In summary, the last two methods enable to distinguish between graphene and multilayer
graphene. However, neither method on its own nor the combination of the two enable a
determination of the number of layers in all possible cases (especially regarding all possible
stacking angles). But the comparison of the values deduced by each method allows to
discriminate if the determined number of layers is correct and can be specified or not. For N >>
5, the variation of the measured parameters with N becomes too small as compared to the
possible deviations from the reference values (obtained on Bernal stacked layers). An upper
limit of five layers has been fixed for this document to avoid such problems.
Moreover, both A and optical contrast are strongly dependent on the nature of the substrate
G
and on the laser wavelength used. Therefore, it is important that each substrate is specifically
studied and a large set of experimental data is a prerequisite to validate theoretical predictions.
In conclusion, a standard method is proposed for the specification of the number of layers based
on the combination of Raman spectroscopy (normalized G-peak area) and optical reflection
(optical contrast) [3]. Both methods enable the user to distinguish unambiguously between
single-layer graphene and multilayer graphene. However, neither method on its own nor the
combination of the two enable a determination of the number of layers for all possible stacking
orientations. But importantly, since the two methods always significantly disagree when they
fail, the comparison of the values deduced by each method allows to discriminate if the
determined number of layers is correct and can be specified or not.

– 8 – IEC TS 62607-6-12:2024 © IEC 2024
NANOMANUFACTURING –
KEY CONTROL CHARACTERISTICS –
Part 6-12: Graphene – Number of layers:
Raman spectroscopy, optical reflection

1 Scope
This part of IEC TS 62607 establishes a standardized method to determine the key control
characteristic
– number of layers
for films consisting of graphene by
– Raman spectroscopy and
– optical reflection.
Criteria for the determination of the number of layers are the G-peak integrated intensity and
the optical contrast. Both methods enable to distinguish between graphene and multilayer
graphene. However, neither method on its own nor the combination of the two enable a
determination of the number of layers in all possible cases (especially regarding all possible
stacking angles). But the comparison of the values deduced by each method allows to
discriminate whether the determined number of layers is correct and can be specified or not.
– The method is applicable to exfoliated graphene and graphene grown on or transferred to a
substrate with a small defect density, low surface contamination (e.g. transfer residue) and
number of layers up to 5.
– The method is suitable for the following substrates:
a) glass (soda lime glass or similar with a refractive index between 1,45 and 1,55 at
532 nm);
b) oxidized silicon (SiO2 on silicon, with a SiO2 thickness of 90 nm ± 5 nm).
NOTE 90 nm and 300 nm are the most used SiO thicknesses for graphene substrates. Due to the current
state of the art, the method can securely be used for 90 nm ± 5 nm thick SiO layers and a laser wavelength
of 532 nm, but cannot be fulfilled for 300 nm ± 15 nm SiO layers even by changing the laser wavelength.
It is possible that future editions of IEC TS 62607-6-12 will include thick layers and other substrates also.
– The spatial resolution is in the order of 1 µm given by the spot size of the exciting laser.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp

3.1 General terms
3.1.1
key control characteristic
KCC
key performance indicator
material property or intermediate product characteristic which can affect safety or compliance
with regulations, fit, function, performance, quality, reliability or subsequent processing of the
final product
Note 1 to entry: The measurement of a key control characteristic is described in a standardized measurement
procedure with known accuracy and precision.
Note 2 to entry: It is possible to define more than one measurement method for a key control characteristic if the
correlation of the results is well-defined and known.
Note 3 to entry: In ISO TC 16949 the term “special characteristic” is used for a KCC. The term key control
characteristic is preferred since it signals directly the relevance of the parameter for the quality of the final product.
[SOURCE: IEC TS 62565-1, 3.1]
3.2 Graphene related terms
3.2.1
two-dimensional material
2D material
material, consisting of one or several layers with the atoms in each layer strongly bonded to
neighbouring atoms in the same layer, which has one dimension, its thickness, in the nanoscale
or smaller, and the other two dimensions generally at larger scales
Note 1 to entry: The number of layers when a two-dimensional material becomes a bulk material varies depending
on both the material being measured and its properties. In the case of graphene layers, it is a two-dimensional
material up to ten layers thick for electrical measurements [1], beyond which the electrical properties of the material
are not distinct from those for the bulk (also known as graphite).
Note 2 to entry: Interlayer bonding is distinct from and weaker than intralayer bonding.
Note 3 to entry: Each layer may contain more than one element.
Note 4 to entry: This includes bilayer graphene, trilayer graphene and few-layer graphene.
[SOURCE: ISO/TS 80004-3:2016, 3.1.1]
3.2.2
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-layer graphene (FLG).
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]

– 10 – IEC TS 62607-6-12:2024 © IEC 2024
3.2.3
graphene-based material
GBM
graphene material
grouping of carbon-based 2D materials that include one or more of graphene, bilayer graphene,
few-layer graphene, graphene nanoplate and functionalized variations thereof as well as
graphene oxide and reduced graphene oxide
Note 1 to entry: "Graphene material" is a short name for graphene-based material.
3.2.4
bilayer graphene
2LG
two-dimensional material, either as free-standing films, on a substrate or flakes 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 80004-13:2016, 3.2.6]
3.2.5
trilayer graphene
3LG
two-dimensional material, either as free-standing films, bonded to a substrate or flakes
consisting of three well-defined stacked graphene layers
Note 1 to entry: If the stacking registry is known it can be specified separately, for example, as "twisted trilayer
graphene".
[SOURCE: ISO/TS 80004-3:2016, 3.2.9]
3.2.6
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]
3.2.7
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]
3.2.8
highly oriented pyrolytic graphite
HOPG
highly pure and ordered form of synthetic graphite
Note 1 to entry: HOPG is often used as reference material for calibration of measurement equipment.

3.2.9
Bernal stacking
AB stacking
stacking of 2D material layers on top of another in such a way that the neighbouring layers only
have half of their atoms positioned equivalently in the out of plane direction with every third
layer located in the same position in the out of plane axis
Note 1 to entry: The second layer is horizontally displaced with respect to the first layer by half the lattice constant.
[SOURCE: ISO/TS 80004-13:2017, 3.4.1.10]
3.2.10
rhombohedral stacking
ABC stacking
stacking of 2D material layers consisting of three repeating layers where the second layer is
displaced in plane with respect to the first layer by half a lattice constant, and the third layer is
horizontally displaced in the same direction, thus every fourth layer is located in the same
position in the vertical axis
Note 1 to entry: The three layer system may repeat. The layers are stacked on top of one another in the vertical
axis in such a way that the neighbouring layers only have half of their atoms positioned equivalently.
[SOURCE: ISO/TS 80004-13:2017, 3.4.1.11]
3.2.11
turbostratic stacking
stacking of layers of 2D materials that cannot be described as Bernal or rhombohedral stacking,
instead having a relative stacking angle between the layers and which does not allow to develop
atomic plane families other than that parallel to the basal plane, because the stacked layers
exhibit a relative and random rotational angle or commensurate rotation between the layers
Note 1 to entry: Correspondingly, the only diffraction peaks with three Miller indices seen in XRD patterns are 001
peaks (002, 004, etc.), the others are 2-indices only (typically 10 and 11).
[SOURCE: ISO/TS 80004-13:2017, 3.4.1.13]
3.2.12
stacking angle
angle measured in the horizontal plane between the orientations of two layers of 2D material
that are stacked vertically on top of one another
[SOURCE: ISO/TS 80004-13:2017, 3.4.1.12]
3.2.13
defect
local deviation from regularity in the crystal lattice of a 2D material
[SOURCE: ISO/TS 80004-13:2017, 3.4.1.1]
3.3 Key control characteristics measured in accordance with this document
3.3.1
number of layers
N
number of graphene layers stacking on top of one another
Note 1 to entry: As a reasonable estimation for the thickness of the graphene layer, the “number of layers” can be
multiplied by 0,355 nm.
Note 2 to entry: The measurement of the number of layers and the estimation of the film thickness is hampered due
to potential variations of the stacking angle between the layers.

– 12 – IEC TS 62607-6-12:2024 © IEC 2024
3.4 Terms related to the measurement method described in this document
3.4.1
2D-peak
second order Raman peak related to a two-phonon process located at approximately twice the
frequency of the D-peak
Note 1 to entry: As well as the D-peak the 2D-peak is also dispersive with wavelength. The position of the 2D-peak
changes strongly with laser energy.
Note 2 to entry: The 2D-peak is always present in the Raman spectrum of graphene and does not need defects to
be activated.
3.4.2
D-peak
defect activated Raman peak related to lattice breathing modes in six-carbon rings away from
the centre of the Brillouin zone
-1 -1
Note 1 to entry: The D-peak is located between 1 270 cm and 1 450 cm depending on the wavelength of the
-1
excitation laser. The dispersion with wavelength is around 50 cm /eV.
Note 2 to entry: The D-peak is most intense at defective graphene lattices and disappears for perfect monolayer
crystals.
3.4.3
D-peak integrated intensity
A
D
-1 -1
integral over the intensity of the D-peak in the range between 1 250 cm and 1 400 cm using
on a Lorentzian fit function
Note 1 to entry: Only the data with a coefficient of determination (R ) greater than 0,99 are considered.
3.4.4
doping
addition of a quantity of different material to the host material with a view to modifying properties
[SOURCE: ISO/TS 80004-13:2017, 3.4.2.3]
3.4.5
G-peak
-1
Raman peak related to in-plane motion of the carbon atoms located near 1 580 cm originating
from scattering at the centre of the Brillouin zone
Note 1 to entry: The G-peak can be observed in pristine graphene and does not need lattice defects to occur.
3.4.6
G-peak integrated intensity
A
G
-1 -1
integral over the intensity of the G-peak in the range between 1 400 cm and 1 700 cm using
one or two Lorentzian fit functions
Note 1 to entry: Only the data with a coefficient of determination (R ) greater than 0,99 are considered. In some
cases, a sum of two Lorentzian functions can be necessary to reach such values (the G-peak integrated intensity
being then the sum of the integrals of the two Lorentzians). The integrated intensity of the G-peak, A , in counts per
G
second per watt is the Lorentzian integrated intensity normalized versus the laser power and acquisition time of the
spectrum.
3.4.7
optical contrast
C
ratio between the laser signal reflected by the sample and the laser signal reflected by the bare
substrate minus 1
R
C − 1
Note 1 to entry: , where C is the optical contrast, R is the laser signal reflected by the sample and R is
R
the laser signal reflected by the bare substrate.
3.4.8
Raman spectroscopy
spectroscopy in which the radiation emitted from a sample illuminated with monochromatic
radiation is characterized by an energy loss or gain arising from rotational, vibrational or phonon
excitations
[SOURCE: ISO/TS 80004-13:2017, 3.3.1.6]
3.4.9
surface contamination
material, generally unwanted, on the sample surface which either is not characteristic of that
sample and any process investigated or has arisen from exposure of the sample to particular
environments other than those relevant for the original surface or the process to be studied
Note 1 to entry: Common surface contaminants are hydrocarbons and water. Local reactions with these and the
environment can lead to a wide range of oxidation and other products.
[SOURCE: ISO 18115-1:2013, 4.459]
3.4.10
transfer residue
surface contamination that is left after the transfer of a 2D material from one substrate to
another
Note 1 to entry: An example is the unwanted surface contamination that is left due to sacrificial polymer used to
transfer graphene grown by CVD on a metal catalyst to a different substrate.
[SOURCE: ISO/TS 80004-13:2017, 3.4.2.2]
4 General
4.1 Measurement principle
The measurement method described in this document takes advantage of the change of Raman
spectra and optical reflection of graphene with increasing numbers of layers. Nevertheless, the
relation between measurements and the number of layers is not simple and straightforward as
there are multiple ways for the stacking arrangement of the layers and interaction with the
substrate can lead to misinterpretation of the results. Fortunately, this problem can be solved
by a simultaneous measurement of optical reflection and Raman spectroscopy under the
assumption that the number of layers is not larger than five. To perform the simultaneous
measurement with a regular Raman spectrometer, the only required modification in the Raman
setup is to implement a way to measure the reflected light of the excitation laser.
-1
The analysis of the Raman spectra concentrates on the G-peak (1 580 cm ) for graphene. The
method is limited to high quality graphene. In the content of this document, “high quality” is
related to a low intensity of the D-peak, [A /A ] < 0,1 measured with an excitation wavelength
D G
11 2
of 532 nm, corresponding to a defect density below 10 per cm , low enough to prevent the
Raman and optical reflection measurements to be affected by defects. The quantity that should
be extracted is the G-peak integrated intensity of the sample normalized to a HOPG reference
sample. Typical Raman spectra for graphite (HOPG), high quality graphene and defective
graphene are shown in Figure 1.
Analysis of the optical contrast is performed from reflectance measurements on both the bare
substrate and the substrate with the graphene sample.
=
– 14 – IEC TS 62607-6-12:2024 © IEC 2024

Figure 1 – Raman spectra of HOPG (top), pristine graphene (middle)
and defective few-layer graphene (bottom)
The main peaks are labelled.
4.2 Sample preparation method
The sample should be measured as it is delivered by the supplier. No special sample
preparation is required. Any treatment of the sample can change the structural quality and
morphology.
It should be ensured that the Raman peaks of graphene and few-layer graphene, the D-peak
-1 -1
(around 1 340 cm ) and the G-peak (around 1 580 cm ) are not masked by Raman modes
originating from the substrate material. The exact same bare substrate shall be used as a
reflectance reference.
As an initial test, the sample shall fulfil the quality requirement in terms of defects: [A /A ] < 0,1.
D G
Otherwise, this document is not applicable.
4.3 Measurement environment
The measurements shall be performed at room temperature.
4.4 Description of test equipment
The tests are performed by using a Raman set-up consisting of an optical microscope, laser
light source, Raman filters and a spectrometer. The setup is optimized to measure the low level
of Raman scattered light from a well stabilized laser; in other words, with a long-term power
stability better than 2 %. Due to the low level of Raman scattered light, the system shall be able
to accumulate individual Raman spectra with a high measurement rate to achieve results with
a high signal-to-noise ratio in a reasonable time (few seconds). The sample shall be mounted
on a high precision translation stage allowing Raman mappings of the sample to be performed
with an XY-spatial resolution below 1 µm.
The laser wavelength is 532 nm.
Additional equipment is also needed to measure the laser light power reflected from the samples
(Photodiode B in Figure 2). It can be a commercial photodiode power sensor or merely a
photodiode from which the photocurrent at zero bias is measured. With such devices, the

reflected laser light power shall be measured on the same locations on the graphene samples
as the Raman spectra since the measured quantities (integrated intensity of the G-peak and
optical contrast) shall be compared. The reflected laser light power can be measured before or
after the acquisition of each Raman spectrum by intercepting the reflected laser beam with
photodiode while keeping the laser at the same location on the sample. It is however preferable
to perform both measurements simultaneously. This can be achieved either by measuring the
power of the laser beam reflected from the Raman (edge or notch) filter or by using a beam-
sampler to pick-up a small amount (typically 10 %) of the signal reflected from the sample and
direct it to the photodiode sensor. It should be ensured that at least a few percent of the light
reflected from the sample is impinging on the photodiode. The optical power range, sensitivity
and resolution of the photodiode should be chosen accordingly. For graphene on glass or on
-on-silicon substrates and within the experimental configuration specified here, the
90 nm SiO
optical power range received by the photodiode varies typically from 100 nW to 1 mW and the
resolution needed is around 1 nW.
The laser power impinging on the sample should be checked (Photodiode A in Figure 2) to be
stable during the measurements or, better, it should be measured during each measurement.
A state-of-the-art scanning Raman spectroscopy tool with a minimal XY scan range of
10 µm × 10 µm is required. XY scan steps of 1 µm will be typically used for the Raman mapping.
A laser with around or lower than 1 mW power on the sample and a wavelength of 532 nm is
used for excitation. With a good combination of laser beam diameter and divergence,
microscope objective and confocal hole dimension, the spatial resolution on sample can achieve
400 nm to 500 nm (close to a diffraction limited system). Here, a confocal system is not required
but can be used, the microscope objective should be a 100× with a numerical aperture of 0,85
to 0,95.
For signal detection a spectrometer with a charge-coupled device (CCD) array detector and a
suitable grating should be used to ensure best instrumental parameters compromise for
graphene application: sufficient spectral resolution and full fingerprint spectral range on the
detector without moving the grating. A typical Raman setup is illustrated in Figure 2.

– 16 – IEC TS 62607-6-12:2024 © IEC 2024

Photodiode A measures the laser power.
Photodiode B measures the power of the laser beam reflected from the Raman (edge or notch) filter.
Figure 2 – Schematic illustration of the Raman and reflectance
setup used for the described graphene classification
4.5 Calibration standards
4.5.1 Raman reference sample
The reference sample is HOPG grade ZYA or single crystal graphite. The Raman spectrum is
-1
plotted as the Raman intensity as a function of the Raman shift (cm ). The Raman spectrum
should show no observable D-peak. The laser power should be recorded during the
measurement and used for intensity normalization. The extracted quantity is the G-peak
integrated intensity normalized versus laser power and effective acquisition time. The Raman
spectrum of the reference should be acquired in the same experimental configuration and
conditions as the one used for the test sample (laser wavelength, optimized focus conditions,
microscope objective, and spectrometer and detector configurations (grating, spectral range,
slits, gain)).
4.5.2 Reflection reference sample
measurement, a bare and clean substrate should be used which is the
As reference for the R
same as the one supporting the graphene to be characterized. Alternatively, a bare a
...