Vrije Universiteit Brussel

Mechanism of the Polarized Absorption of CVD-Prepared Carbon Nanofibers to TE Waves inthe Subterahertz BandCheng, Chen; Revilla, Reynier I.; Pourkazemi, Ali; Hauffman, Tom; Stiens, Johan

Published in:Journal of Physical Chemistry C

DOI:10.1021/acs.jpcc.0c07486

Publication date:2020

Document Version:Final published version

Link to publication

Citation for published version (APA):Cheng, C., Revilla, R. I., Pourkazemi, A., Hauffman, T., & Stiens, J. (2020). Mechanism of the PolarizedAbsorption of CVD-Prepared Carbon Nanofibers to TE Waves in the Subterahertz Band. Journal of PhysicalChemistry C, 124(45), 24957-24969. https://doi.org/10.1021/acs.jpcc.0c07486

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Download date: 09. Jun. 2022

1

Supporting Information

Mechanism of Polarized Absorption of CVD-prepared Carbon Nanofibers to TE-

waves in Sub-terahertz Band

Cheng Chen, Zhiyong Zhang, Reynier I. Revilla, Wu Zhao, Ali Pourkazemi, Tom

Hauffman, Junfeng Yan, Yao Peng, Johan Stiens

Keywords: Carbon nanofibers; Anisotropy; Chemical vapor deposition; Polarization

Table S1. The comparison of Vector Network Analyzer (VNA) and the Terahertz Time-

Domain spectroscopy (THz-TDS).

VNA THz-TDs

Source RF-harmonic generator Ultrashort pulsed laser

Communication

way

Waveguide indoor transmission;

outdoor antenna transmission (in our

study)

Necessary optical components

(steering mirrors, beam splitters,

delay stage, parabolic mirrors.)

Communication

environment

Free space or indoor Purge box

Type of

transmission media

Transverse electric (TE) mode wave Terahertz pulse laser

Test result S-parameter Amplitude and phase

Main Purpose for

materials

Characterization Identification

Test frequency

In sub-terahertz: W-band, F, D, G, Y,

J, 325-500 GHz, 500-750 GHz

0.1-4 THz (Maximum)

2

Table S2. The comparison of the CNFs prepared by CVD method and electrospinning

method.

morphology Diameter

Dispersion of

diameter

Length

surface

characteristic

CVD-prepared

CNFs

Intertwined 10-500 nm Inhomogeneous

Relatively

short

Polar

Electrospinning-

prepared CNFs

Regular shape 3-500 nm homogeneous

Continuous

long fibers

Non-polar

Table S3. The review of the THz characterization of 1D carbon nanostructure using

VNA (vector network analyzer), TDS (time domain spectroscopy), FDS (frequency

domain spectroscopy).

Frequency

CVD

prepared

CNFs

Electrospinnin

g prepared

CNFs

Other patterns of

CNFs (Polymer;

compounds etc.)

CNT

Microwave

Band

[15] (VNA, 2-18

GHz)

[8] (VNA, 2-18 Hz);

[13] (VNA, 2-18 GHz)

[14] (VNA, 2-18 GHz)

[16] (VNA, 8-12 GHz)

…

MMW band [4] (VNA, 200 MHz-8

GHz);

Sub-THz band

(W, F, D, Y, J,

325-500 GHz,

500-750 GHz,

750-1100 GHz

band)

[1] (FDS, 570-630

GHz);

[9] (VNA,570-630

GHz);

[10] (FDS,570-630

GHz);

>1.1 THz (TDS

test or FDS

test)

[6] (TDS, 0.2-1.2 THz)

[2] (FDS, 0-4 THz);

[3] (TDS, 0.3-2.5 THz);

[5] (TDS, 0.1-2 THz);

[7] (TDS, 0.08-2.5 THz);

[11] (TDS, 0.1-3 THz)

[12] (TDS, 0.1-4 THz) …

3

Reference

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4

Figure S1. (a) the scheme of the growth process of CNFs and the photo graphene of

the sample during each process; (b) SEM image of the Cu island layer; (c) SEM image

of dense CNFs.

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Figure S2. (a) AFM of Cu island layer; (b) AFM line scan of the Cu island layer.

Figure S3. EDS spectrum and surface atomic percentage of CNFs sample. (b) Mapping

6

image.

Figure S4. (a) A millimeter-wave VNA (8 Hz-70 GHz, AB Millimeter Corp, Paris,

France) with a set of W-band near-field test components; (b) a PNA equipment

(Keysight Corp, N5247B, PNA-X Microwave Network Analyzer, USA) and a set of

extension modules.

7

Figure S5. Corresponding to the Fig. 3b. (a) (b) The S11 and S21 curves of W-band

test; (c) (d) Another S11 and S21 curves of W-band test.

Figure S6. The calibrated S11 and S21 curves of polycarbonate sheet holder for: (a) W-

band; (b) 500-750 GHz band.

8

Figure S7. (a) (b) The S11 and S21 curves of 500-750 GHz band test; (c) (d) Another

S11 and S21 curves of 500-750 GHz band test.

Figure S8. (a) (b) Full absorption curve of W-band test and 500-750 GHz test of CNFs

sample; (c) The comparison.

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Feasibility analysis and simulation method of CNFs model

1. The relationship between the beam size and model size

In this section, a Teflon cube model was used to prove the S11 and S21 parameters

of CNFs model is not correct and also cannot be used for comparison. Firstly, two

simulation with different unit was designed, as shown in Table S4.

Table S4. The size of Teflon in the axis is: 3*3*2 (X: -1.5 to 1.5; Y: -1.5 to 1.5; Z: 0

to 2)

Name Background Boundary

condition

Size State

Experiment 1 PEC Electric=0 μm Beam size>sample size

Experiment 2 PEC Electric=0 cm Correction

As shown in Figure S9a, a Teflon cube with the size of 3*3*2 was built as the

model. The Figure S9b shows the direction of irradiation of transvers electric waves

(TE-mode) wave from the surface of port 1 to the back side of port 2. In the simulation

of Experiment 1, the unit of the model size was set to μm, which is as same as the unit

of CNFs model. The wavelength range of 500-750 GHz band waves is 0.4-0.6 mm.

Therefore, in the near field test of free-space, the irradiation area from the waveguide

port should be in micro-meter level. According to the diffraction behavior of

electromagnetic waves, the area of Teflon model with the size unit of μm is almost

impossible to block out the TE-mode waves. And since the boundary conditions of the

model are set as perfect conductor conditions (PEC), the calculation result of S-

parameters should be incorrect.

10

Figure S9. (a)-(b) the Teflon model with the waveguide port; (c)-(d) The comparison

of S11 and S21 curves of experiment 1 and 2; (e) The Y-axis is used as the symmetry

axis to simplify the calculation of the model; (f) The X-axis and Y-axis are used as the

symmetry axis to simplify the calculation of the model.

As shown in Figure S9c and S9d, the value of S11 and S21 curves (black line) of

Experiment 1 is not calculated incorrect. In the simulation experiment, the magnitude

of reflection curve and transmission curve should be coupled to each other according

to the conservation of energy, such as the S11 and S21 curves of Experiment 2. In the

simulation of experiment 2, the unit size of Teflon model was set to centimeter. On the

11

one hand, Teflon as an organic polymer insulator, so that THz waves can be easily

penetrated, the S21 curve in Figure S9d can prove this point. Also, as can be seen from

the waveform of the S11 and S21 curves of Experiment 2, the magnitude of the

reflection and transmission can be well coupled.

Conclusion 1: In the above simulation environment, the model size should be greater

than or equal to the corresponding waveguide size. For example, according to the

waveguide standard, the inner diameter of the waveguide size in the 500-750 GHz

frequency band is 0.381*0.191 mm. The model size in Experiment 2 can completely

cover the beam size.

2. The modeling process of CNFs.

The details of 1x1 CNFs model in the Figure 12c of the manuscript is shown in

below:

Table S5. The physical parameters of CNFs model in CST Microwave Studio.

Name Materials Type Epsilon Mu Size (μm)

Air Air Normal 1.00059 1.0 1*1*2.5

CNFs Graphite Normal 12 1 Diagram: 0.1; Hight: 2

Cu Cu 217LX Normal 2.2 1 1*1*0.5

Table S6. Each rotation angle (°) of 1x1 unit model in 3x3 CNFs model (Corresponding

to the Figure 12f in manuscript)

0 35 78

69 43 25

58 86 29

12

Table S7. Each rotation angle (°) of 3x3 model in 18x18 CNFs model (Corresponding

to the Figure 12i in manuscript)

0 30 27 16 78 64

37 7 74 11 37 17

76 65 58 54 65 42

38 56 50 63 60 35

40 62 14 5 47 70

82 36 44 56 6 82

Figure S10. The direction of Ex and Hy of 18x18 CNFs model which corresponding to

the Figure 12h.

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Figure S11. The 2D results of X component (XOZ-plane), Y component (YOZ-plane),

Z component (XOY-plane) of simulation result for the CNFs model.

14

Figure S12. (a) and (b) are the SEM images of CNFs with different diameter prepared

by CVD method; (c) and (d) are the corresponding AFM images.

The diameter of CNFs was decided by the size of Cu island on the Cu/Substrate

which was regulated by the change of the sputtering process. Also, the CVD process

parameter such as the flow ratio of hydrocarbon mixture gas, the cooling rate will affect

the growth morphology of CNFs. Through systematic experiments, we found that there

was no linear relationship between the diameter of CNFs and the effect of anisotropic

absorption in the terahertz band.

15

Table S8. Information on instruments and consumables.

Items Type

Polished Si substrate Crystal orientation: (111); Size: 10mm*15mm.

Cu target

Purity: 99.99%; Size: 60mm (Diameter)*5 mm

(Thickness).

Sputtering gas: Ar Purity: 99.999%.

Impurity cleaning solution for substrate H2SO4 (purity:98%):H2O2 (30%) = 7:3.

Grease cleaning solution for substrate Acetone; Ethanol; Deionized water.

Supersonic cleaner

ED12-100-U; Ever Young Enterprises

Development Co., LTD.

Multifunctional magnetron sputtering coating

equipment

MSP-3200C; Beijing Chuangshiweina

Technology Co., LTD.

Vacuum/atmosphere sliding tube-type

furnace (CVD system)

SK-G08123K-HD; Tianjin Zhonghuan

Experimental Electric Furnace Co. LTD.

Table S9. Sputtering Parameters

Items Parameters

Distance from the target to the substrate 8 cm

Initial background pressure <3*10-4 Pa

Substrate temperature (TS) 450 ℃

Radio frequency-power 150 W

Argon flow 20 SCCM

Sputtering pressure 1 Pa

Pre-sputtering time 30 min

Sputtering time 120 min

Substrate rotation speed 1 rpm

Note: 1) For the parameter of the distance from the target to the substrate, this parameter

may be different for sputtering instruments provided by different manufacturers. We

16

also found that when this parameter is different, the samples can be made inconsistent

despite using the same process. Also, the stability of the process may be affected by the

angle between the axis of the target and the substrate platform.

2) The purpose of the pre-sputtering process is to remove the oxide layer and the

impurity atoms adsorbed on the surface of the Cu target. There is an adjustable baffle

about 1 cm from the target. When the substrate temperature, pressure, and argon flow

stabilized to the required parameters, the RF power was turned on to ionize the argon

and cause glow discharge. At this point, sputtering only occurred between the target and

the baffle. After 30 minutes, the surface of the target was cleaned up, and impurities

and other atoms attached to the baffle surface. Then, the baffle is opened so that the

sputtered particles can reach the substrate directly.

17

Table S10. CVD process Parameters

Items Parameters

Length of the flat-temperature zone of the CVD

system

600 mm

Pipe diameter 80 mm

Heating rate

8 ℃/min (20-800℃)

2℃/min (800-1000℃)

Protection gas during the heating process Ar; 600 SCCM

The flow rate of the hydrocarbon mixture gas CH4:H2=10:100 SCCM

Transportation gas flow Ar; 1000℃

Substrate temperature 1000 ℃

Deposition time 600 s

Cooling rate

42℃/min (1000℃-600℃)

25℃/min (600-20℃)

Cooling method The external air cooling

Note: The growth and crystalline of CNFs are influenced by the flow of carbon source

gas, the transport speed of gas mixture (decided by Ar flow), substrate temperature,

deposition time and cooling rate (affecting the crystallization of CNFs).