IEC TS 62607-6-6:2021

Nanomanufacturing - Key control characteristics - Part 6-6: Graphene - Strain uniformity: Raman spectroscopy

IEC TS 62607-6-6:2021(E) establishes a standardized method to determine the structural key control characteristic
• strain uniformity
for single-layer graphene by
• Raman spectroscopy.
The width of the 2D-peak in the Raman spectrum is analysed to calculate the strain uniformity parameter which is a figure of merit to quantify the influence of nano-scale strain variations on the electronic properties of the layer. The classification will help manufacturers to classify their material quality to provide an upper limit of the electronic performance of the characterized graphene, to decide whether or not the graphene material quality is potentially suitable for various applications.

General Information

• Status: Published
• Publication Date: 13-Oct-2021
• ICS: 07.120 - Nanotechnologies
• Technical Committee: TC 113 - Nanotechnology for electrotechnical products and systems
• Drafting Committee: PT 62607-6-6 - TC 113/PT 62607-6-6
• Current Stage: PPUB - Publication issued
• Start Date: 14-Oct-2021
• Completion Date: 03-Nov-2021

Standards Content (Sample)

IEC TS 62607-6-6 ®
Edition 1.0 2021-10
TECHNICAL
SPECIFICATION
colour
inside
Nanomanufacturing – Key control characteristics –
Part 6-6: Graphene – Strain uniformity: Raman spectroscopy
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IEC TS 62607-6-6 ®
Edition 1.0 2021-10
TECHNICAL
SPECIFICATION
colour
inside
Nanomanufacturing – Key control characteristics –

Part 6-6: Graphene – Strain uniformity: Raman spectroscopy

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 07.120 ISBN 978-2-8322-1033-5

– 2 – IEC TS 62607-6-6:2021 © IEC 2021
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
3.1 General terms . 8
3.2 Key control characteristics . 8
3.3 Measurement related terms . 9
4 General introduction . 9
4.1 Measurement principle . 9
4.2 Sample preparation method . 10
4.3 Test equipment . 11
4.4 Calibration standards . 11
5 Measurement procedure . 12
5.1 Calibration of test equipment . 12
5.2 Description of the measurement procedure . 12
5.3 Measurement accuracy . 12
6 Data analysis/interpretation of results . 12
7 Sampling plan . 14
8 Test report . 14
Annex A (informative) Format of the test report . 15
Annex B (normative) Sampling plan . 17
B.1 General . 17
B.2 Sampling plan for circular substrates . 17
B.3 Sampling plan for square substrates . 18
B.4 Sampling plan for irregular substrates . 19
Annex C (informative) Recommendations for wavelengths depending on substrate . 20
Annex D (informative) Examples of Raman spectra of single-layer graphene on
different substrates . 21
−1
D.1 Example 1: FWHM(2D) = 16,6 cm – Graphene encapsulated in hexagonal
boron nitride . 21
−1
D.2 Example 2: FWHM(2D) = 22,3 cm – Graphene on SiO covered with hBN . 21
−1
D.3 Example 3: FWHM(2D) = 25,3 cm – Graphene on SiO . 22
−1
D.4 Example 4: FWHM(2D) = 34,8 cm – Graphene on SiO substrate covered
with hBN . 23
−1
D.5 Example 5: FWHM(2D) = 40,3 cm – Graphene on SiO covered with very
thin hBN . 23
Annex E (informative) Relation between observed Raman 2D linewidth and carrier
mobility . 25
Bibliography . 27

Figure 1 – Typical Raman spectra of an exfoliated graphene flake adopted from [6] . 10
Figure 2 – Schematic illustration of a confocal Raman setup . 11
Figure 3 – Example FWHM(2D) Raman map . 13
Figure 4 – Example FWHM(2D) histogram obtained from the Raman map in Figure 3 . 13

Figure B.1 – Sampling plan for circular substrates of diameter a . 17
Figure B.2 – Sampling plan for square substrates with edge length a . 18
Figure B.3 – Sampling plan for irregular substrates . 19
Figure D.1 – Spectrum of graphene encapsulated in hBN . 21
Figure D.2 – Spectrum of graphene on SiO covered with hBN . 22
Figure D.3 – Spectrum of graphene on SiO . 22
Figure D.4 – Spectrum of graphene on SiO covered with hBN . 23
Figure D.5 – Spectrum of graphene on SiO covered with hBN . 24
Figure E.1 – Relation of the inverse mobility and the average full width at half
maximum FWHM(2D) of the Raman 2D-peak . 26

Table A.1 – Sample identification . 15
Table A.2 – General material information . 15
Table A.3 – Test related information . 16
Table A.4 – Schematic of sample geometry/structure . 16
Table A.5 – Measured key control characteristic . 16
Table B.1 – Sampling plan for circular substrates . 18
Table B.2 – Sampling plan for square substrates . 18
Table C.1 – Laser wavelength recommendations . 20

– 4 – IEC TS 62607-6-6:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_____________
NANOMANUFACTURING –
KEY CONTROL CHARACTERISTICS –
Part 6-6: Graphene –
Strain uniformity: 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 62607-6-6 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
113/579/DTS 113/605/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/standardsdev/publications.
A list of all parts of 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 62607-6-6:2021 © IEC 2021
INTRODUCTION
Graphene, a single layer of carbon atoms arranged in a honeycomb lattice, has a high potential
for future nanoelectronic applications thanks to the excellent conductivity and high flexibility of
the material. As there is a strong connection between nanoscale lattice deformations and carrier
mobility, the uniformity of strain and flatness of the graphene lattice is a key control
characteristic for the fabrication of high-quality graphene layers for electronic devices.
One of the most useful methods to evaluate the structural properties of graphene is Raman
spectroscopy (see, for example, [1] ). The method is simple, fast, non-destructive and well
understood so that the Raman spectrum can be used as a fingerprint for graphene especially if
the sample under evaluation consists of single-layer graphene not too far away from perfection.
Things become more complicated if the sample consists of more than one layer, perhaps with
different stacking angles and many lattice defects. As this document is intended to support the
fabrication of nearly defect-free high-quality single-layer graphene, the interpretation of the
Raman spectrum remains relatively simple.
As recently reported [2], nanometre-scale strain variations in graphene give rise to a pseudo-
vector disorder potential which allows the pseudo-spin in graphene to flip and thus enables
intra-valley backscattering. This scattering mechanism has been identified to be the responsible
mechanism for limiting the carrier mobility in high-quality graphene [2]. Interestingly these
nanometre-scale strain variations are directly connected to the experimentally observed
linewidth of the Raman 2D-peak [3], making this quantity a very interesting measure for
estimating the possibility of getting very high mobility graphene devices.
It is important to note that although graphene is a truly two-dimensional material, consisting
exclusively of surface atoms, it is embedded in our three-dimensional world. This has the
consequence that the properties of graphene are in all cases intrinsically influenced by its
intimate surrounding. Thus, substrates or contact gases (in the case of suspended graphene)
play a very crucial role when fabricating, transferring and characterizing graphene. Most
crucially, substrates, contact gases and moisture are actually becoming part of the graphene
system under investigation and there is no way (in practice) of eliminating their influence on the
two-dimensional graphene layer.

___________
Numbers in sqaure brackets refer to the Bibliography.

NANOMANUFACTURING –
KEY CONTROL CHARACTERISTICS –
Part 6-6: Graphene –
Strain uniformity: Raman spectroscopy

1 Scope
This part of IEC 62607 establishes a standardized method to determine the structural key
control characteristic
• strain uniformity
for single-layer graphene by
• Raman spectroscopy.
The width of the 2D-peak in the Raman spectrum is analysed to calculate the strain uniformity
parameter which is a figure of merit to quantify the influence of nano-scale strain variations on
the electronic properties of the layer. The classification will help manufacturers to classify their
material quality to provide an upper limit of the electronic performance of the characterized
graphene, to decide whether or not the graphene material quality is potentially suitable for
various applications.
• The uniformity of strain measured by this method is applicable for nearly defect free, high-
quality single-layer graphene, e.g. synthesized by chemical vapour deposition or graphene
integrated into 2D-material heterostructures.
• The method is used if the Raman spectrum shows a visible D-peak with an integrated
intensity ratio A(D)/A(G) < 0,1.
• Confocal Raman spectroscopy is used to consistently evaluate the graphene layer
according to strain variations on the nanoscale.
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.
IEC TS 62607-6-11, Nanomanufacturing – Key control characteristics – Part 6-11: Graphene
film – Defect density: Raman spectroscopy
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/
___________
Under preparation. Stage at the time of publication: IEC DTS 62607-6-11.

– 8 – IEC TS 62607-6-6:2021 © IEC 2021
• 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.
3.1.2
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]
3.1.3
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.
3.1.4
chemical vapour deposition
CVD
deposition of a solid material by chemical reaction of a gaseous precursor or mixture of
precursors, commonly initiated by heat on a substrate
[SOURCE: ISO/TS 80004-13:2017, 3.2.1.1]
3.2 Key control characteristics
3.2.1
strain uniformity
Γ
quality parameter describing the uniformity of the strain distribution in the graphene layer
Note 1 to entry: Γ is the 80 % value of the 2D-peak width distribution, FWHM(2D) .
80 80
Note 2 to entry: The strain uniformity is a figure of merit describing the quality of graphene layers in respect of the
uniformity of strain in the layer. Even if Γ can be calculated from basic physical principles, this is out of the scope
of this document.
Note 3 to entry: The lower the value of Γ , the higher is the strain uniformity in the graphene layer. Low values of
Γ are a necessary but not sufficient condition for high carrier mobility and high conductivity.
3.3 Measurement related terms
3.3.1
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.
3.3.2
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 approximately 50 cm /nm.
Note 2 to entry: The D-peak is most intense at defective graphene lattices and disappears for perfect monolayer
crystals. Therefore it is often called the disorder band.
3.3.3
D'-peak
−1
defect activated Raman peak in the spectrum of graphene located around 1 620 cm
originating from scattering away from the Brillouin zone centre
3.3.4
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.
3.3.5
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]
4 General introduction
4.1 Measurement principle
Raman spectroscopy is a very prominent tool for the investigation of carbon-based material
systems [1][4]. In particular, scanning confocal Raman spectroscopy [5] has various beneficial
features as a characterization tool for graphene and graphene-related materials such as a
particularly high spatial resolution of up to 0,5 µm. If operated with carefully chosen
parameters., it is generally a non-destructive method for investigating graphene, Other positive
aspects include it being rather fast, and the possibility to analyse graphene that is buried
underneath p
...