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GB/T 40071-2021: Nanotechnologies - Measurement of the number of layers of graphene-related two-dimensional (2D) materials - Optical contrast method
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Nanotechnologies - Measurement of the number of layers of graphene-related two-dimensional (2D) materials - Optical contrast method
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GB/T 40071-2021
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Basic data | Standard ID | GB/T 40071-2021 (GB/T40071-2021) | | Description (Translated English) | Nanotechnologies - Measurement of the number of layers of graphene-related two-dimensional (2D) materials - Optical contrast method | | Sector / Industry | National Standard (Recommended) | | Classification of Chinese Standard | A50 | | Word Count Estimation | 18,130 | | Issuing agency(ies) | State Administration for Market Regulation, China National Standardization Administration | GB/T 40071-2021: Nanotechnologies - Measurement of the number of layers of graphene-related two-dimensional (2D) materials - Optical contrast method
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(Nanotechnology Layer number measurement of graphene-related two-dimensional materials Optical contrast method)
ICS 17.180.30
CCSA50
National Standards of People's Republic of China
Nanotechnology graphene-related two-dimensional materials
Layer number measurement optical contrast method
Released on 2021-05-21
2021-12-01 implementation
State Administration of Market Supervision and Administration
Issued by the National Standardization Management Committee
Nanotechnology graphene-related two-dimensional materials
Layer number measurement optical contrast method
Warning---The personnel using this document should have practical experience in formal laboratory work. This document does not indicate all possible safety
problem. Some test procedures specified in this document may lead to dangerous situations, and the user is responsible for taking appropriate safety and health measures, and
Ensure compliance with the conditions stipulated by relevant national laws and regulations.
1 Scope
This document specifies the optical contrast method (including reflectance spectroscopy and optical image method) to measure the number of layers of graphene-related two-dimensional materials.
The contents of the equipment, sample preparation, measurement procedures, test reports, etc.
This document is applicable to the crystal quality prepared by mechanical peeling method or chemical vapor deposition method (CVD. chemical vapordeposition)
Measurement of the number of layers of graphene flakes and graphene films with a high volume, a lateral dimension of not less than 2μm, and a number of layers of not more than 5.Made by other methods
Graphene flakes and graphene films can be implemented with reference to this document.
2 Normative references
The contents of the following documents constitute the indispensable clauses of this document through normative references in the text. Among them, the dated reference documents, only
The version corresponding to this date is applicable to this document; for undated references, the latest version (including all amendments) is applicable to this document.
GB/T 30544.13 Nanotechnology terminology Part 13.Graphene and related two-dimensional materials
3 Terms and definitions
The following terms and definitions defined in GB/T 30544.13 apply to this document.
3.1
Graphene-related 2D material; GR2M
Carbon-based two-dimensional material with no more than 10 layers.
Note. Including graphene, double-layer graphene, few-layer graphene, graphene oxide, etc.
3.2
Grapheneflake grapheneflake
Graphene nanosheet graphenenanoplate; graphenenanoplatelet; GNP
Nanosheets composed of graphene layers.
Note. The common thickness is less than 3nm, and the lateral size range is about 100nm to 100μm.
[Source. GB/T 30544.13-2018, 3.1.2.11, with modification]
3.3
Graphenefilm
Nano flakes composed of graphene layers.
Note 1.The common thickness is less than 3nm.
Note 2.Compared with the graphene sheet (3.2), the graphene film (3.3) has a larger extension in length and width.
3.4
Numberoflayers
< Two-dimensional material> The number of layers constituting the two-dimensional material.
3.5
Opticalcontrastvalue
< Two-dimensional material> The relative difference between the reflected light intensity of the blank substrate area and the reflected light intensity of the area where the sample on the substrate is located, see the formula
3.7
Opticalcontrastmethod
< Two-dimensional material> A method to determine the number of layers (3.4) of nanosheets and nanosheets on a specific substrate using the optical contrast value (3.5).
4 Principle
4.1 Theoretical basis
As shown in Figure 1a), (from top to bottom) a multilayer film structure is formed by graphene flakes or graphene films, SiO2 layers, and Si layers. due to
The light absorption of the two-dimensional material itself and the influence of the interference effect of the multilayer film, there is a difference between Isample and Isubstrate, which can be calculated by formula (1)
To the optical contrast value C between the substrate and the sample. Both theoretical calculations and experimental results prove that the number of layers of graphene flakes or graphene films
At different times, C is also different, and there is a one-to-one correspondence between the number of layers and C. Therefore, C can be used to determine the graphene sheet or graphene film.
Number of layers.
Theoretically, the optical contrast method can be used under different incident light wavelengths. When the incident light is white light of continuous wavelength, the reflected light intensity
The size depends on the wavelength. Assuming that the reflected light intensity at the wavelength λ is I(λ), then according to formula (3), we can get
C(λ)=
Isubstrate(λ)-Isample(λ)
Isubstrateλ
Figure 1 Schematic diagram of the principle of optical contrast method
4.2 Measuring principle of common optical contrast method
4.2.1 Reflectance spectroscopy
Figure 1b) shows the theoretical calculation of graphene flakes or graphene films with different layers on a 300nm SiO2/Si substrate
The optical contrast spectrum C(λ), where the wavelength λ ranges from 400nm to 800nm, and the waves corresponding to the B, G, and R channels of the optical micrograph
The long range is marked with blue, green, and red areas respectively. It can be seen from Figure 1b).
a) The optical contrast spectrum C(λ) of graphene flakes or graphene films with different numbers of layers is different, and the number of layers is greater when the wavelength λ is the same.
More C(λ) is also greater;
b) The optical contrast spectrum C(λ) corresponding to different number of layers has one in the visible light wavelength range (about 435nm~720nm)
Peak (maximum value), record the peak value as Cp, and record the wavelength value corresponding to Cp as λp;
c) The difference between the optical contrast peak Cp corresponding to different layer numbers is the largest, and it is most suitable for judging the layer number of the sample. Therefore,
Use Cp to measure the number of layers of graphene flakes or graphene films.
4.2.2 Optical image method
As shown in Figure 1b), when the number of graphene sheets or graphene film layers is 1 to 5, although there are some differences in their respective λp, they are all at
In the G channel of the optical micrograph, therefore Isample(λp) and Isubstrate(λp) can also be replaced by the G channel values Gsample and Gsubstrate respectively.
And use formula (2) to obtain the G channel contrast value CG between the sample and the substrate. The theoretical value of the G channel contrast value is the optical contrast spectrum
The integrated average value within the corresponding wavelength range of the channel. It can be seen from Figure 1b) that when the number of layers of graphene flakes or graphene films is different, CG also
Different, the number of layers and CG have a one-to-one correspondence, so CG can also be used to measure the number of layers of graphene flakes or graphene films.
It should be noted that before applying the optical image method to measure the number of layers, first establish the "G channel contrast value" based on the sample with a known number of layers.
CG---layer number correspondence" table (as shown in Table 2). After the table is established, under the same test conditions, the optical image method can be used to quickly and
Accurately measure the number of layers.
5 Equipment
5.1 Microscopic spectrometer. used for reflection spectroscopy, including grating spectrometer and optical microscopy device, with reflection spectrum measurement function. its
Among them, the scanning range of the spectrometer is 400nm~800nm, and the spectral resolution is better than 2nm. Before measurement, the microscopic light should be measured according to the relevant technical specifications.
The spectrometer is calibrated and tested according to relevant test specifications.
5.2 Optical microscope. used for optical image method, equipped with white light source (such as halogen lamp or xenon lamp), 100 times objective lens (numerical aperture not less than
0.8), the observation method is bright field; including a digital camera, it can form a color image, and its pixels are better than 100,000.
6 Sample preparation
6.1 The substrate used in this document should be a Si substrate with a 300nm±5nm thick SiO2 layer (hereinafter referred to as 300nmSiO2/
Si substrate).
6.2 For the graphene flake samples mechanically peeled off on the 300nmSiO2/Si substrate, they can be used directly without further processing.
6.3 For the graphene film sample prepared by CVD, the sample needs to be transferred to a 300nm SiO2/Si substrate (for specific steps, please refer to the attached
Record A).
6.4 Observe the sample under the microscope, and there should be no obvious impurities in the test area.
7 Measurement steps
7.1 Measurement procedure of reflectance spectroscopy
7.1.1 Select measurement area
Observe the sample with an optical microscope to determine the measurement area of the sample. This area must contain both the blank substrate and the sample.
7.1.2 Collect reflection spectrum
7.1.2.1 Focus the measurement area to observe clear graphene flakes or film edges.
7.1.2.2 Measure the reflectance spectrum of the substrate, the wavelength scan range is 400nm~800nm, adjust the incident light intensity or integration time to make the wavelength
The signal light intensity at 570nm is more than 10 times the intensity of the background signal (that is, the signal in a dark environment).
7.1.2.3 Under the same observation conditions, sequentially collect the reflectance spectrum Isubstrate (λ) and Isample (λ) of the substrate and the sample. Among them, substrate, sample
The area where the product is located randomly selects 5 locations to collect, and get I i()substrateλ(), I i()sampleλ(), where i=1~5.
7.1.3 Obtain the optical contrast spectrum
According to formula (3), from the reflection spectrum of the substrate and the sample I i()substrateλ(), I i()sampleλ(), the optical contrast spectrum C i() (λ) is obtained, where i=
1~5.
7.1.4 Obtain the peak of optical contrast spectrum
Take the arithmetic average of the peaks of 5 optical contrast spectra C i() (λ), see formula (4), and calculate the optical contrast peaks of the sample
Value Cp (reserved to 2 decimal places).
Cp=
·∑
i=1
C i()p (4)
Where.
C i()p ---C i() (λ) peak value, where i=1~5.
Note that the deviation of a single measurement value from the arithmetic mean value should not be greater than 10%, otherwise the measurement will be performed again. At the same time, if the wavelength corresponding to Cp
If the value λp >600nm, this method should not be used to measure the number of layers.
7.1.5 Determine the number of sample layers
According to Table 1, the number of sample layers is obtained from the peak value Cp of the optical contrast spectrum.
7.1.6 Test example
See Appendix B for the test sample.
7.2 Optical image method measurement steps
7.2.1 Select samples with known number of layers to create a table of "G channel contrast value CG---layer number correspondence"
7.2.1.1 Select 3 samples prepared by mechanical peeling method with a known number of layers n (where n = 1, 2, 3, 4, 5, 6). Sample preparation process parameters
According to Chapter 6.For n=1,2,3,4,5,6, repeat steps 7.2.1.4~7.2.1.7 respectively.
7.2.1.2 Place a standard white board under the 100x objective lens, and perform white balance calibration after focusing.
7.2.1.3 Select a blank substrate area without sample coverage, and adjust the gamma value of the digital camera image processing software to make
The color of the picture is basically the same as the color seen by the microscope eyepiece (the difference in gamma value will lead to the difference in the contrast value of the G channel, the adjustment is complete
Don’t change it later), and then adjust the brightness to make the image grayscale value 125~135.
7.2.1.4 Select the measurement area according to 7.1.1.
7.2.1.5 The steps for taking optical pictures are as follows.
a) Ensure that the sample to be tested is in the center of the observation window, and focus the measurement area to observe a clear graphene flake or
Film edge. Take an optical micrograph of the sample.
b) Under the same observation and shooting conditions (including gamma value, light intensity, integration time, focus, pixels, etc.), in three different samples
Take 3 optical micrographs on the blank substrate area covered by the product.
7.2.1.6 The steps to obtain the G channel contrast value image are as follows.
a) Extract the G channel value of each pixel of 3 substrate optical micrographs and sample optical micrographs.
b) For the substrate, the G channel value of each pixel is averaged from the G channel values at the same position in 3 optical micrographs of the substrate
Value.
c) For each corresponding pixel, calculate its G channel contrast value according to formula (2) to obtain the G channel contrast value image.
7.2.1.7 The steps to obtain the typical G channel contrast value of a sample with a known number of layers are as follows.
a) In the G channel contrast value image obtained in 7.2.1.6c), randomly select 5 positions in the sample area to obtain 5 G
Channel contrast value, find its arithmetic average (the deviation between a single measurement value and the average value should not be greater than 10%), this value is the
The G channel contrast value of the sample with a known number of layers. For the 3 samples with the same number of layers, the G channel contrast values are respectively recorded as
C 1()G (n), C 2()G n(), C 3()G (n).
b) Calculate the arithmetic average of C 1()G (n), C 2()G n(), C 3()G (n), and get An. An is the G channel of the sample with the number of layers n
The typical value of the contrast value CG (retained to 2 decimal places). Note that the deviation of a single measurement value from the arithmetic mean value should not be large
Less than 10%, otherwise re-determination.
7.2.1.8 Use A1, A2, and A6 to establish the "G channel contrast value CG---layer number correspondence" table (see Table 2).
7.2.2 Determine the number of layers of unknown samples
7.2.2.1 Ensure that the observation conditions and shooting conditions of the optical microscope are the same as those in 7.2.1.
7.2.2.2 Select the measurement area in accordance with 7.2.1.4.
7.2.2.3 Take optical pictures in accordance with 7.2.1.5.
7.2.2.4 Obtain the G channel contrast value image according to 7.2.1.6.
7.2.2.5 Obtain the G channel contrast value of the unknown sample.
Randomly select 5 locations in the sample area to be tested in the G channel contrast value image to obtain 5 G channel contrast values respectively
C i()G, where i=1~5.According to the following formula (5), the arithmetic mean CG (retained to 2 decimal places) is obtained. Single measurement value and calculation
The deviation of the operative mean should not be greater than 10%, otherwise the measurement should be repeated.
CG=
·∑
i=1
C i()G (5)
7.2.2.6 Refer to Table 2, and get the number of layers of the sample to be tested according to the reference range where the CG is located.
7.2.3 Test sample
See Appendix C for test examples.
8 Test report
The test report should include the following information.
---Test date;
---Test number;
---Measurer;
---Sample source and information;
---Measurement method;
---The type, brand and model of the test instrument;
---If the layer number is measured based on the optical image method, the table of "G channel contrast value CG---layer number correspondence" should be attached;
---Test Results;
---If necessary, error analysis.
Appendix A
(Informative)
Sample transfer operation example --- CVD-grown copper-based graphene film sample transfer operation steps
A.1 Spin-coat a drop of polymethylmethacrylate (PMMA) at a speed of 3000r/min to
CVD-grown copper-based graphene film sample (i.e. GR2M/Cu/GR2M multilayer film) surface to form PMMA/GR2M/Cu/GR2M
Multi-layer film structure, where PMMA is the transfer support layer, and GR2M refers to single-layer, double-layer, or few-layer graphene.
A.2 Use 0.5mol/L ammonium persulfate [(NH4)2S2O8] solution to slightly corrode the Cu substrate of the sample, and use ultrapure water repeatedly
Clean. During this process, the PMMA/GR2M/Cu/GR2M multilayer film structure will float on the surface of the (NH4)2S2O8 solution.
The GR2M layer will be dissolved, and the PMMA/GR2M layer on the top will remain unreacted, so that the GR2M on the bottom of the Cu can be removed.
To PMMA/GR2M/Cu structure. The specific corrosion and cleaning steps are.
a) Float in (NH4)2S2O8 solution for 3 minutes, and then float in ultrapure water for 5 minutes;
b) Repeat step a) 3~5 times.
A.3 Completely etch away the Cu layer with (NH4)2S2O8 solution to obtain PMMA/GR2M multilayer film structure. The processing time of this step is taken as
It depends on the thickness of Cu and the concentration of (NH4)2S2O8, for example, the corrosion of 25μm thick Cu in 0.5mol/L (NH4)2S2O8 solution
The eclipse time is about 2h.
A.4 Float in ultrapure water for 30 minutes (this step can be operated multiple times). Each ultrapure water bath should be prepared in a separate container.
A.5 Pick up the PMMA/GR2M sample floating on the surface of ultrapure water with a 300nmSiO2/Si substrate. Put it on a hot plate at 80°C
10min to remove water, and then placed on a hot plate at 180℃ for 15min to relax the PMMA film.
A.6 Soak PMMA/GR2M/300nmSiO2/Si in acetone and let it stand for 10h to dissolve the PMMA layer. After GR2M/
Put 300nmSiO2/Si into absolute ethanol and soak in ultrapure water for 10 minutes each. After taking it out, blow dry with high-purity nitrogen to get clean
The GR2M/300nmSiO2/Si sample.
A.7 If the surface of the sample is not clean after the above steps, the time and frequency of corrosion or ultrapure water cleaning can be appropriately extended, or use 50℃
Acetone dissolves the PMMA layer. The following steps can be used as a reference.
a) Increase or decrease the concentration of (NH4)2S2O8 solution to increase or decrease the corrosion rate. Low corrosion rate helps keep the sample in
Integrity during corrosion.
b) Choose other corrosive solutions, such as FeCl3 solution.
c) Choose other organic substances as the transfer support layer, such as polydimethylsiloxane (PDMS for short) and so on.
d) Treat the backside of PMMA/GR2M/Cu/GR2M multilayer film structure with oxygen (O2) plasma, the etching time is
3min~5min, the GR2M on the bottom of Cu is corroded, and then proceed to A.2 and subsequent steps. This method can be appropriate
Reduce the number of (NH4)2S2O8 solution corrosion and ultrapure water cleaning in step A.2.
A.8 An example of an optical picture taken after the transfer of a CVD-grown copper-based graphene film is shown in Figure A.1.
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