IEC TS 62607-6-2:2023

Nanomanufacturing - Key control characteristics - Part 6-2: Graphene - Number of layers: atomic force microscopy, optical transmission, Raman spectroscopy

IEC TS 62607-6-2:2023 establishes a standardized method to determine the key control characteristic
- number of layers
for graphene flakes by a combination of
- atomic force microscopy,
- optical transmission, and
- Raman spectroscopy

General Information

• Status: Published
• Publication Date: 04-Apr-2023
• ICS: 07.120 - Nanotechnologies
• Technical Committee: TC 113 - Nanotechnology for electrotechnical products and systems
• Drafting Committee: PT 62607-6-2 - TC 113/PT 62607-6-2
• Current Stage: PPUB - Publication issued
• Start Date: 12-May-2023
• Completion Date: 05-Apr-2023

Standards Content (Sample)

IEC TS 62607-6-2
®

Edition 1.0 2023-04
TECHNICAL
SPECIFICATION

colour
inside


Nanomanufacturing – Key control characteristics –
Part 6-2: Graphene – Number of layers: atomic force microscopy,
optical transmission, Raman spectroscopy
IEC TS 62607-6-2:2023-04(en)

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IEC TS 62607-6-2

®


Edition 1.0 2023-04




TECHNICAL



SPECIFICATION








colour

inside










Nanomanufacturing – Key control characteristics –

Part 6-2: Graphene – Number of layers: atomic force microscopy,

optical transmission, Raman spectroscopy

























INTERNATIONAL

ELECTROTECHNICAL


COMMISSION





ICS 07.120 ISBN 978-2-8322-6749-3




  Warning! Make sure that you obtained this publication from an authorized distributor.


® Registered trademark of the International Electrotechnical Commission

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– 2 – IEC TS 62607-6-2:2023 © IEC 2023
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
3.1 General terms . 7
3.2 Terms related to measurements . 9
4 Method for preparation of graphene flake sample . 11
4.1 Micromechanical cleavage . 11
4.2 Sonication . 11
4.3 Ball milling . 11
4.4 Fluid dynamics . 11
5 Measurement of the number of graphene layers using combined method . 12
5.1 Basic concept of combined method . 12
5.2 General protocol . 12
5.2.1 Sample preparation . 12
5.2.2 AFM calibration . 12
5.2.3 Raman calibration . 12
5.2.4 Optical reflectance calibration . 12
5.3 Measurement procedure . 12
6 Data analysis and interpretation of results . 13
6.1 General protocol for data analysis . 13
6.2 Analysis of number of layers of graphene using Raman spectroscopy . 13
6.3 Analysis of number of layers of graphene using AFM topography . 13
6.4 Analysis of number of layers of graphene using reflectance (Rayleigh
scattering). 14
7 Report . 14
Annex A (informative) Summary of three simultaneous measurements and their
analysis . 15
A.1 Flowchart for determining the number of layers of graphene . 15
A.2 Summary table of analysis process . 16
Annex B (informative) Interpretation of the simultaneous measurement for Raman
scattering, AFM, and reflectance – case studies . 17
Annex C (informative) Description of the measurement apparatus . 20
C.1 General . 20
C.2 AFM system . 20
C.3 Spectroscopy system . 20
Annex D (informative) Measurement using currently available equipment . 21
D.1 Atomic force microscopy . 21
D.2 Optical transmittance and reflectance . 22
D.3 Raman scattering . 23
D.4 Reflection and optical contrast (Rayleigh scattering) . 23
Bibliography . 24

Figure 1 – Schematic of simultaneous measurement of AFM, Raman scattering, and
light reflectance . 13

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IEC TS 62607-6-2:2023 © IEC 2023 – 3 –
Figure A.1 – Flowchart for determining the number of layers of graphene . 15
Figure B.1 – Simultaneous measurement of Raman scattering, AFM, and reflectance
images to determine the number of graphene layers . 17
Figure B.2 – Confocal Raman spectrum, AFM line profile and reflectance intensity
profile of graphene flake extracted along red line in Figure B.1 . 18
Figure B.3 – Confocal Raman spectrum, AFM line profile and reflectance intensity
profile of graphene flake extracted along cyan line in Figure B.1 . 19
Figure B.4 – Confocal Raman spectrum, AFM line profile and reflectance intensity
profile of graphene flake extracted along black line in Figure B.1 . 19

Table A.1 – Summary table of analysis process . 16
Table D.1 – Summary of selected results for monolayer graphene thickness measured
by AFM with preparation method, AFM method, substrate, and whether monolayer
graphene was confirmed by Raman spectroscopy [7] . 22

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– 4 – IEC TS 62607-6-2:2023 © IEC 2023
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

NANOMANUFACTURING – KEY CONTROL CHARACTERISTICS –

Part 6-2: Graphene – Number of layers: atomic force microscopy,
optical transmission, Raman spectroscopy


FOREWORD
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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 62607-6-2 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
113/676/DTS 113/727/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.

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IEC TS 62607-6-2:2023 © IEC 2023 – 5 –
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 http://www.iec.ch/standardsdev/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.

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– 6 – IEC TS 62607-6-2:2023 © IEC 2023
INTRODUCTION
Graphene has attracted significant interest as a next-generation electronic material due to its
good conductivity and mobility. It has been regarded as more advantageous than carbon
nanotube (CNT) because of its isotropic and homogeneous electronic properties. For these
reasons and many more, a Nobel prize in physics was awarded to A. Geim and C. Novoselov
in 2010 for their efforts in discovering graphene when they isolated a single layer of graphene
using clear adhesive tape.
Graphene has been widely studied by researchers from academic institutions, research
1
institutes, and industries due to its unique and interesting properties such as conductivity [1] ,
mechanical strength and flexibility [2], which are better than other metals or semiconductors.
These properties are influenced by the number of layers of graphene and disappear as the
number of layers increases. Graphene also shows an unusual reduction in optical transparency
even considering a single atomic layer [3]. Therefore, graphene applications need to investigate
the precise number of layers of graphene.
Many companies are now providing graphene samples to industries and research communities.
These are prepared (or manufactured) by various methods such as CVD or mechanical
exfoliation. Defining and evaluating the number of layers of this fabricated graphene is critical
both from research and industrial points of view. Unfortunately, there are no commonly accepted
standards for this purpose, hindering the reliable production and expansion of graphene
applications.
The number of layers of graphene is usually observed by atomic force microscopy (AFM), light
transmittance, Raman spectroscopy, transmission electron microscopy (TEM), and ellipsometry.
Every analytical method has its own limitations in terms of precisely measuring the number of
graphene layers and can also cause ambiguity for providing reliable information. For these
reasons, developing an easy, fast, and reliable method for counting the number of graphene
layers is needed.
This document describes a combined method to evaluate accurate number of layers of
graphene, which includes measurement method.
Description of combined method and case studies illustrating the application of the standard
are provided in Annex A and Annex B, respectively.

___________
1
 Numbers in square brackets refer to the Bibliography.

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IEC TS 62607-6-2:2023 © IEC 2023 – 7 –
NANOMANUFACTURING – KEY CONTROL CHARACTERISTICS –

Part 6-2: Graphene – Number of layers: atomic force microscopy,
optical transmission, Raman spectroscopy



1 Scope
This part of IEC TS 62607 establishes a standardized method to determine the key control
characteristic
– number of layers
for graphene flakes by a combination of
– atomic force microscopy,
– optical transmission, and
– Raman spectroscopy
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 terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1 General terms
3.1.1
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 [4], 3.1.2.1]
3.1.2
graphene oxide
GO
chemically modified graphene prepared by oxidation and exfoliation of graphite, causing
extensive oxidative modification of the basal plane

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– 8 – IEC TS 62607-6-2:2023 © IEC 2023
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]
3.1.3
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]
3.1.4
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]
3.1.5
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]
3.1.6
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 allotropic forms with different stacking arrangements: hexagonal and rhombohedral.
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.2]
3.1.7
highly oriented pyrolytic graphite
HOPG
highly pure and ordered form of synthetic graphite
Note 1 to entry: Material often used as reference material for calibration of measurement equipment.

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IEC TS 62607-6-2:2023 © IEC 2023 – 9 –
3.1.8
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, 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.
[SOURCE: ISO/TS 80004-13:2017, 3.1.1.1]
3.1.9
chemical vapour deposition
CVD
deposition of a solid material onto a substrate by chemical reaction of a gaseous precursor or
mixture of precursors, commonly initiated by heat
[SOURCE: ISO/TS 80004‑8:2020 [5], 8.2.4]
3.2 Terms related to measurements
3.2.1
atomic force microscopy
AFM
method for imaging surfaces by mechanically scanning their surface contours, in which the
deflection of a sharp tip sensing the surface forces, mounted on a compliant cantilever, is
monitored
Note 1 to entry: AFM can provide a quantitative height image of both insulating and conducting surfaces.
Note 2 to entry: Some AFM instruments move the sample in the x-, y- and z-directions while keeping the tip position
constant, and others move the tip while keeping the sample position constant.
Note 3 to entry: AFM can be conducted in a vacuum, a liquid, a controlled atmosphere or air. Atomic resolution may
be attainable with suitable samples, with sharp tips, and by using an appropriate imaging mode.
Note 4 to entry: Many types of force can be measured, such as the normal forces or the lateral, friction or shear
force. When the latter is measured, the technique is referred to as lateral, frictional or shear force microscopy. This
generic term encompasses all of these types of force microscopy.
Note 5 to entry: AFMs can be used to measure surface normal forces at individual points in the pixel array used for
imaging.
[SOURCE: ISO 18115-2:2021 [6], 3.1.2, modified – Note 6 to entry has been deleted.]
3.2.2
offset height
difference between the height of monolayer graphene on the substrate using AFM and the actual
height of monolayer graphene
Note 1 to entry: The offset height can be affected by the type of substrate, AFM mode, and environment.
Note 2 to entry: Large thickness variation of monolayer graphene (0,4 nm to 1,7 nm) due to the offset height has
been reported [7].

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3.2.3
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]
3.2.4
G-peak
−1
Raman peak related to the 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 graphite materials including pristine graphene and does not need
lattice defects to occur.
3.2.5
D-peak
defect activated Raman peak related to lattice breathing modes in six-carbon rings away from
the centre of the Brillouin zone
−1
Note 1 to entry: The D-peak is located at approximately 1 350 cm depending on the wavelength of the excitation
−1
laser. The dispersion with wavelength is ~50 cm /nm.
Note 2 to entry: The D-peak is most intense at defective graphene lattices and disappears for perfect monolayer
crystals. It is often called the disorder (defect) band.
3.2.6
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.
3.2.7
Raman shift
wavenumber shift that has units of inverse length caused by Raman scattering effect, as this
value is directly related to energy
Note 1 to entry: The Raman shift indicates the vibration frequency of a molecule.
3.2.8
Raman intensity
intensity where the Raman scattered light from the sample enters the detector and is perceived
Note 1 to entry: Raman intensity is directly proportional to the fourth power of the excitation frequency. So, the
choice of the incident laser beam plays an essential role in the resulting intensities of the observed Raman signals.
Note 2 to entry: The measurements of the Raman intensities are used to determine quantitatively the amount,
distribution and degree of crystallization of different phases in a material.
3.2.9
full width at half maximum
FWHM
range of a variable over which a given characteristic is greater than 50 % of its maximum value
Note 1 to entry: FWHM can be applied to characteristics such as radiation patterns, spectral linewidths, etc. and
the variable can be wavelength, spatial or angular properties, etc., as appropriate.

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IEC TS 62607-6-2:2023 © IEC 2023 – 11 –
3.2.10
optical transmittance
ratio of the radiant flux transmitted through and emerging from a body to the total flux incident
on it
−2
Note 1 to entry: The transmittance (T) for two-dimensional Dirac fermions like graphene is given by T = (1 + 0,5πα)
where α is the fine structure constant, α = 1/137. Accordingly, the T of monolayer graphene is about 2,3 %.
3.2.11
optical contrast
CTRS
spectra difference between substrate and graphene sheet
Note 1 to entry: Optical contrast is given by CTRS = (R(λ) − R(λ))/R (λ), where R (λ) is the reflection spectrum from
0 0 0
the substrate and R(λ) is the reflection spectrum from graphene sheet.
4 Method for preparation of graphene flake sample
4.1 Micromechanical cleavage
The concept of this method is the cleavage of graphene layers from the bulk HOPG surface.
The exfoliation mechanics of this method are that clear adhesive tape is applied to top of the
HOPG surface and thus exerts a normal force. If this exfoliation process repeats numerous
times, the graphitic layer becomes thinner and thinner and finally it can be expected there will
be monolayer graphene.
4.2 Sonication
Sonication-assisted liquid-phase exfoliation of graphite is considered one of the methods for
large-scale production of graphene. Due to the sonication-induced cavitation, however, the
graphene prepared by this method has many more defects than that prepared by other methods.
4.3 Ball milling
Ball milling is a method to laterally exfoliate graphite into graphene flakes by generating shear
force. There are two ways to induce exfoliation and fragmentation effects in most ball milling
devices. The most important thing is shear force, which is thought to be an excellent mechanical
route for exfoliation. This method is very desirable to obtain large graphene flakes. The second
is a collision or vertical impact applied by the ball in a rolling motion. This method can break
large pieces into smaller pieces and sometimes even destroy crystal structures in an amorphous
or non-equilibrium state. Therefore, in order to obtain high-quality, large-sized graphene, the
secondary effect shall be minimized.
4.4 Fluid dynamics
Graphene flakes can move with the liquid and be exfoliated repeatedly with this method. The
feature of fluid dynamics is intrinsically different from that of sonication and ball milling, making
it a potentially efficient technique for the scalable production of graphene.

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