Study of optical absorption of metamaterial based on nanostructures in nature

The surface of the metalens array is covered by nanotennas made of gallium nitride (GaN) which allow the tube to record bright field information. For electromagneti[r]

ººº VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY

DAO TRUNG DUC

STUDY OF OPTICAL ABSORPTION OF METAMATERIAL BASED ON

NANOSTRUCTURES IN NATURE

MASTER'S THESIS

VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

DAO TRUNG DUC

STUDY OF OPTICAL ABSORPTION OF METAMATERIAL BASED ON

NANOSTRUCTURES IN NATURE

MAJOR: NANO TECHNOLOGY CODE: PILOT

RESEARCH SUPERVISOR: Dr PHAM TIEN THANH

i

Acknowledgments

I am truly honored to submit my master thesis for the degree of Master at Nanotechnology Program, Vietnam Japan University This work has been carried out in the Nanotechnology program, Vietnam Japan University, Vietnam National University of Hanoi

I would like to express my sincere thạnks to my supervisor: Dr Pham Tien Thanh, lecturer, Vietnam Japan University (VJU), Vietnam National University (VNU) for accepting me as his student, for guidance, and his encouragement to complete this research

I would also like to thank all students and teachers of Nanotechnology, Vietnam Japan University, Vietnam National University of Hanoi for the pleasant and stimulating atmosphere during my research study

Hanoi, May 25, 2019 Student

ii

TABLE OF CONTENTS

Acknowledgments i

TABLE OF CONTENTS ii

LIST OF FIGURES iv

LIST OF ABBREVIATIONS viii

INTRODUCTION ix

CHAPTER LITERATURE REVIEW

1.1 Nanostructures in nature

1.2 Plant leaves surface

1.3 Metamaterials

CHAPTER METHOD AND MATERIAL

2.1 Fabrication of bio-metamaterial

2.1.1 Sputtering in the air at low pressure 10

2.1.2 Analysing surface structures (EDS, SEM, FT-IT, Spectrometer) 11

2.1.3 Checking of efficient solar absorption 12

2.2 Prediction the low reflectivity by Finite-difference time-domain (FDTD) 12

2.3 Solar steam-generation system 13

CHAPTER RESULTS AND DISCUSSION 15

3.1 Fabrication of absorbers based on some nanostructure in nature 15

iii

3.3 Prediction the low reflectivity by finite-difference time-domain 23

3.4 Efficient solar absorbers 25

CONCLUSION 33

FUTURE PLAN 34

iv

LIST OF FIGURES

Figure 1.1: Morpho rhetenor butterfly a) A picture of half of butterfly b) The surface on the wing c) An individual scale d) The reflection spectrum of the butterfly’s wing e) & f) Scanning electron micrograph (SEM) of a scale Scale bars (b, c) 50μm, d) 5μm, e) 2μm

Figure 1.2 Some common nanostructure on the surface of animal and plant a) Nanostructures on fruit fly eyes (Drosophila melanogaster) b) mold fibers with micrometer size with nanostructures on the cell surface c) Hook hair on two-spotted spider mite (Tetranychus urticae) d) & c) Structure on water fern (Azolla filiculoides) f) The structure on rose leaves (Rosa Chinensis)

Figure 2.1 Some equipment used in this research a) JSM-IT100 InTouchScope™ Scanning Electron Microscope b) JED-2300 Analysis Station Plus c) Syskey sputtering coater d) NanoMap-500LS Contact Surface Profilometer Figure 2.2 Process of conducting experiments 10 Figure 2.3 Experimental model for the record of reflection and scattering spectra with an MCPD-3000 spectrometer (Otsuka Electronics) using a halogen lamp 12

Figure 2.4 SEM images changes to black and white colours, then it uses to 3D structure in FDTD modelling 13

v

Figure 3.3 Scanning Electron Microscope (SEM) images show the surface of all the samples 18

Figure 3.4 40nm and 100nm copper-covered on water cabbage leaves 18 Figure 3.5 Copper-covered bauhinia leaves with different time sputtering 19 Figure 3.6 SEM images (a) 30 nm covered, (b) 100 nm covered water cabbage leave (c) 30 nm covered, (d) 100 nm copper-covered purple bauhinia leaves 19 Figure 3.7 Fourier-transform infrared (FT-IR) spectra (Z;\classes\spectroscopy\all spectra tables for web DOC) 20

Figure 3.8 Energy dispersion spectrometry (EDS) of the copper-covered leaf 22 Figure 3.9 Reflection spectra from the copper-covered bauhinia leaf and bare baubinia leaf without coating Scattering intensity spectra from the copper-covered purple bauhinia and purple baubinia leaf with no copper-coating 22

Figure 3.10 Reflection spectra from the copper-covered water cabbage leaf and bare water cabbage leaf without coating Scattering intensity spectra from the copper-covered water cabbage leaf with no copper-coating 23

Figure 3.11 Calculated reflectivity R, transmittance T and absorption efficiency A for (a) a flat 30-nm thick gold thin film using FDTD method, (b) The model of two-layer copper with nanostructure pattern 24

Figure 3.12 Calculated reflectivity R, transmittance T and absorption efficiency A for the model with three layers 25

copper-vi

coated bauhinia leaf, Ct30: 30 nm copper-coated rose periwinkle leaf, Cu100: 100nm thin-film of copper 27

Figure 3.14 Maximum temperatures of the samples MB0: natural Bauhinia purpurea leaf MB30: 30nm copper-coated Bauhinia purpurea leaf MB100: 100nm copper-coated Bauhinia purpurea leaf Control: 30nm copper-coated Catharanthus roseus leaf Cu100: 100 nm Copper thin-layer on glass’s surface 28

Figure 3.15 Temperatures of the samples over irradiation time BC0: water cabbage leaf, MB30: 30 nm copper-coated water cabbage leaf, MB100: 100nm copper-coated water cabbage leaf, Ct30: 30 nm copper-coated rose periwinkle leaf, Cu100: 100nm thin-film of copper 29

Figure 3.16 Maximum temperatures of the samples BC0: natural Pistia stratiotes leaf BC30: 30nm copper-coated Pistia stratiotes leaf BC110: 100nm copper-coated Pistia stratiotes leaf Control: 40nm copper-coated Catharanthus roseus leaf Cu100: 100 nm Copper thin-layer on glass’s surface 30

vii

LIST OF TABLES

viii

LIST OF ABBREVIATIONS

3D: Three-dimensional

EDS: Energy Dispersive X-Ray Spectroscopy FDTD: Finite-difference time-domain

FT-IR: Fourier-transform infrared spectroscopy SEM: Scanning electron microscope

ix

INTRODUCTION

Metamaterials are artificial structures capable of interacting with electromagnetic radiation in the desired fashion However, there are many living creatures featuring their own form of metamaterial structures with specific functionalities which change their colour without pigment or give hydrophobicity or bust up bacteria People who are a lack of melanin, the pigment appearing in people with brown eyes, have blue eyes like an example Without melanin, the blue iris stems from the structure of eyeball tissue itself not because of a different type of pigment In other words, the iris is capable of displaying a natural form of metamaterial that reflects blue but selectively absorbs other colours The compound eyes of month (Cameraria ohridella) contain thousands of nanostructures on its surface that allow them see much better than humans in dim and dark conditions These patterns reveal almost perfect broadband anti-reflection properties so the moth’s eye can absorb more light [20] A research group at Jacobs University Bremen published a paper in the IOP science that designed better thin film solar cells based on nanostructured nipple arrays of the moth-eye The coating that imitates the moth-eye array allows for an increase of the short circuit current and conversion efficiency of more than 40% [5] For a material to be regarded as a metamaterial, it must operate on a microscopic-scale and cannot be detected by the naked human eyes

x

Water cabbage (Pistia stratiotes) belongs to a genus of aquatic plant in the arum family, Araceae, and Bauhinia purpurea is a member of the family Fabaceae with a common name, purple bauhinia The surface of a water cabbage leaf and a purple bauhinia leaf is also highly water-repellent, although the surface nanostructure two both of leaves completely differs from that of lotus leaves We coated the surface of a water cabbage and purple bauhinia and found that copper-coated surface of the leaves is almost back The copper-copper-coated water cabbage leaf surface and purple bauhinia leaf surface have reflectivity below 2.5% over the visible spectral range

Thus, our research team has carried out this research, named “Study of optical absorption of metamaterial based on nanostructure in nature” Although there are a thousand of reports and public related to metamaterial, research on natural structure-based metamaterials is still quite new The study consists of three main purposes:

1

CHAPTER 1.LITERATURE REVIEW

1.1 Nanostructures in nature

Life-forms own numerous magnificent structures in order to serve their life activities such as hooks in fore- and hindwings in sawfly or suctions cups on tentacles of Octopus However, not only did a selection of macrostructures evolve but also selected structures at even smaller scale too, producing a ton of nanostructure on living things’ organs with a size range about nm to 100 nm in at least one dimension

The male blue morpho (Morpho rhetenor) boasts breath-taking blue wings Figure 1.1 illustrated images for the blue morpho’s wing and nanostructure on the surface of the scale [11] Multilayer nanoscale patterns found on every scale which is the secret to creating iridescent blue wings It absorbs selective light in the visible region and reflects almost completely blue, so male blue morpho’s wings have a single blue colour This optical behaviour is caused by physical structures not for pigments so its product of this method is known as physical colours This phenomenon is formed by random scattering or interference and is quite popular in insect groups such as adult Lepidoptera, Odonata or Coleoptera

2

the surface of animals Thus, we want to rely on these special surface structures to create new materials with features that can be applied to everyday life As characteristics of a tropical country, Vietnam with a high level of biodiversity is an advantage to discover new surface structures in nature In this study, our team focused on plant objects with leaf surfaces with the appearance of nanostructures

3

4

1.2 Plant leaves surface

5

plant surface Such results of studies displayed wax films consisted of various monomolecular layers with thicknesses up to a few hundred nanometers According to the thickness of wax films, it is classified into two groups: first is called three-dimensional (2-D) thin wax films with the size range up to 0.5μm and second is three-dimensional (3-D) waxes with size range about 0.5-1μm [2]

6

Table 1.1 The common chemical compounds in plant waxes [2] Aliphatic compounds

Frequently existing in waxes, but mostly as minor compounds Chain length

Alkanes CH3-(CH2)n-CH3 Odd C19 – C37

Primary alcohols CH3-(CH2)n-CH2-OH Even C12 – C36

Esters CH3-(CH2)n-CO-O-(CH2)m-CH3 Even C30 – C60

Fatty acids CH3-(CH2)n-COOH Even C12 – C36

Aldehydes CH3-(CH2)n-CHO Even C14 – C34

Rarely existing in waxes, but if present, than major wax compounds

Ketones CH3-(CH2)n-CO-(CH2)m-CH3 Odd C25 – C33

β-Diketones CH3-(CH2)n-CO-CH2-CO-(CH2)m-CH3 Odd C27 – C35

Secondary alcohols CH3-(CH2)n-COH-(CH2)m-CH3 Odd C21 – C33

Cyclic compounds

Flavonoids e.g Quercetin Triterpene e.g β-Amyrin

1.3 Metamaterials

7

Nevertheless, when interacting with the components of electromagnetic waves, it generates a completely extraordinary property Because of this special property, metamaterial has the potential to be applied in many areas such as medical devices, remote aerospace applications, solar batteries, high-frequency information transmission, blackbody or absorber [4], [3], [15], [10] Recently, lenses allow both the light intensity and the direction of the incoming light to be developed by metamaterials [13] This allows the user to re-focus the image and then refactoring the depth of field information The surface of the metalens array is covered by nanotennas made of gallium nitride (GaN) which allow the tube to record bright field information

For electromagnetic waves to be able to interact or penetrate the homogeneous structure of metamaterials in an efficient and accurate way, the structures on the surface of the metamaterial must be much smaller than the size scale of the wavelength Electromagnetic absorbing materials can be divided into two main types: resonant absorbers and broadband absorbers [16] While the resonant absorber is based on an interaction with a specific appropriate frequency, the broadband absorber is usually a frequency-independence material and therefore absorbs radiation with a wide absorption spectrum than the other one Metamaterials are designed based on the determination of magnetism permeability and electric permittivity so they can interact directly with the two components, electric and magnetic of light [19]

8

9

CHAPTER 2. METHOD AND MATERIAL

2.1. Fabrication of bio-metamaterial

10

Figure 2.2 Process of conducting experiments

2.1.1 Sputtering in the air at low pressure

11

Table 2.1 Sample manufacturing conditions

The conditions during sputtering operation

Temperature 20 ºC – 25 ºC

Power 100V

Pressure before sputtering 10-6 torr Pressure during sputtering 10-3 torr

2.1.2 Analysing surface structures (EDS, SEM, FT-IT, Spectrometer)

12

Figure 2.3 Experimental model for the record of reflection and scattering spectra with an MCPD-3000 spectrometer (Otsuka Electronics) using a halogen lamp

2.1.3 Checking of efficient solar absorption

All the object samples are placed on a thermal insulator that made of polystyrene foam The temperature is determined by FLIR C2 thermal camera The sun is used as the light source of the experiment Benetech GM1010 device is used to measure light intensity

2.2. Prediction the low reflectivity by Finite-difference time-domain (FDTD)

13

There are simulation models to predict the absorption capacity of the bio-metamaterials and the 30 nm copper thin layer:

 30 nm copper thin layer

 Nanostructure pattern with 30 nm copper thin layer with the height is 500 nm

 layers: the bottom is 30 nm copper thin layer, the center is nanostructure pattern with the height is 500 nm, and the top is 30 nm copper thin layer

Nanostructures pattern used in the model is constructed from the actual structure contained in SEM images SEM images are transferred to black and white images then used to create 3D nanostructure models in FDTD software with the same length and width compared to the original image

Figure 2.4 SEM images changes to black and white colours, then it uses to 3D structure in FDTD modelling

2.3. Solar steam-generation system

14

15

CHAPTER 3.RESULTS AND DISCUSSION

3.1 Fabrication of absorbers based on some nanostructure in nature

Figure 3.1 (a) Bauhinia purpurea, (b) Pistia stratiotes

Based on the ability of water resistance, two kinds of leave, Bauhinia purpurea and Pistia stratiotes, were selected for the experiment Water cabbage (Pistia stratiotes) belongs to a genus of aquatic plant in the arum family, Araceae, and Bauhinia purpurea is a member of the family Fabaceae with a common name, purple bauhinia Their photographic images are shown in Figure 3.1 (a, b) The surface of a water cabbage leaf and a purple bauhinia leaf is also highly water-repellent, although the surface nanostructure two both of leaves completely differs from that of lotus leaves

Figure 3.2 shows the photographic images of copper-coated leaves There are four samples, including of Bauhinia purpurea, Pistia stratiotes and two controls which have really low water resistance: Catharanthus roseus and Rosa Chinensis

16

Figure 3.3 displays the structures on surface of four samples The surface of rose periwinkle leaf has no micro- and nanoscale patterns and the surface of the rose leaf have microstructure patterns However, purple bauhinia shows plate-like nanostructures with the thickness about 100 nm while water cabbage shows root-hair-like nanostructures with the thickness about 80 nm The estimated height of each wax is about μm This structure is quite similar to the nanostructure in taro leaves which was studied It suggests that the mechanism of colour of Bauhinia purpurea leaves can be similar to taro leaves In the case of Pistia stratiotes leaves, the leaf surface has many roots in micro scale which include hair-like nanostructure having predicted length is 80nm Both structures in Bauhinia purpurea leaves and

Pistia stratiotes leaves have random orientation and dense distribution

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18

Figure 3.3 Scanning Electron Microscope (SEM) images show the surface of all the samples

19

Figure 3.5 Copper-covered bauhinia leaves with different time sputtering

20

Figure 3.7 Fourier-transform infrared (FT-IR) spectra (Z;\classes\spectroscopy\all spectra tables for web DOC.)

3.2 Analysing the surface structures

The results of the analysis of the surface composition of natural leaves indicate the appearance of hydrophobic organic groups Figure 3.7 shows the peaks of Fourier-transform infrared spectra at 2920 and 2850 cm-1, 1398 and 1318 cm-1 that display the carbon chain The peaks at 1735 cm-1 and 1075 cm-1 confirmed the existence of the ester group However, after covering copper thin-layer on the surface of leaves, the spectra did not show new peaks especially the signals related to copper while the EDS method determines the presence component of copper layer on the surface of the sample

Figure 3.9 and Figure 3.10 display reflection spectra of the copper-covered purple bauhinia leaf and natural purple bauhinia leaf Visible spectrum with the

4000 3500 3000 2500 2000 1500 1000 500 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 Abs (J cm -2 )

Wavenumber (cm-1)

Bauhinia purpurea Pistia stratiotes

Copper-covered Bauhinia 30nm Copper-covered Pistia 30nm (C-H)

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wavelengths from 380 nm to 760 nm, the natural leaf has two wide peaks at 540 nm and longer than 680 nm The reason is that some pigments such as Chlorophyll a, b and β-Carotene in chloroplast can absorb most of the visible wavelengths in order to use for photosynthesis reaction but except for the wavelengths in the green and far-red Meanwhile, a copper-covered leaf absorbs the visible light completely and reflectivity below 2% Thus, all object samples have low reflectance over the range of 380 to 760 nm and are black It means that the optical properties of coated leaves are decided not by the material of leaves The coated Bauhinia purpurea leaves, which correspond to copper coating 30 nm thick, have the lowest reflectance and the lowest scattering efficiency compare with the other samples of this type of leaf In the case of Pistia stratiotes leaves, the lowest reflectance and the lowest scattering efficiency are achieved with 40 nm thickness of the copper coating The reflectance spectrum of 30 nm of copper coating and the scattering efficiency spectrum of 30 nm and 40 nm of copper coating show some similar peaks as in uncoated leaves This is a storage problem with Pistia stratiotes samples Few days after fabrication, the black color of Pistia stratiotes gradually disappears However, the lower reflectance and scattering efficiency of Pistia stratiotes in comparing with

22

Figure 3.8 Energy dispersion spectrometry (EDS) of the copper-covered leaf

23

Figure 3.10 Reflection spectra from the copper-covered water cabbage leaf and bare water cabbage leaf without coating Scattering intensity spectra from the copper-covered water cabbage leaf with no copper-coating

3.3 Prediction the low reflectivity by finite-difference time-domain

24

leaves One is the light absorption by copper The other is the interference due to the reflection inside the nanostructure of leaves The last is localized surface plasmon resonance which causes greater absorption at the plate edges Figure 3.12 show calculation of nanostructured simulation model with 500 nm height with 30nm thick copper coating capable of absorbing light in high visible light Through the model, we realized that the copper coating layer changed the reflection and transmittance that did not show in the model of a copper thin layer or natural leaves

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Figure 3.12 Calculated reflectivity R, transmittance T and absorption efficiency A for the model with three layers

3.4 Efficient solar absorbers

26

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Figure 3.13 Temperatures of the samples over irradiation time MB0: Bauhinia leaf, MB30: 30 nm copper-coated bauhinia leaf, MB100: 100 nm copper-coated bauhinia leaf, Ct30: 30 nm copper-coated rose periwinkle leaf, Cu100: 100 nm thin-film of copper

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temperature of two object samples under the condition of luminous intensity is 0.014 – 0.015 W/cm2 The temperature of the water cabbage with 40 nm copper-covered thin layer sample is about 62 ºC higher than the purple bauhinia sample with the temperature about 52 ºC under the same conditions Maybe due to the density of the wax on the water cabbage leaves’ surface combined with microstructures that increase the surface area, the copper-coated water cabbage is possible to absorb higher than copper-coated purple bauhinia on the same area Thus, the temperature on 40 nm copper-coated water cabbage is higher than the temperature on 30 nm copper-coated purple bauhinia

0 100 200 300 400 500 600 700 800 900 1000 15 20 25 30 35 40 45 50 55 60 MB0 MB30 MB100 Control Cu100 Temperat ure ( o C) Time (s)

Figure 3.14 Maximum temperatures of the samples MB0: natural Bauhinia purpurea leaf MB30: 30 nm copper-coated Bauhinia purpurea leaf MB100: 100 nm copper-coated Bauhinia purpurea leaf Control: 30 nm copper-coated

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Through three experiments investigating the temperature change of samples under sunlight conditions, we can evaluate the ability to convert light energy into thermal form of bio-metamaterials The temperature of bio-metamaterial always is higher than the temperature of natural leaves at least 10 ºC Therefore, they can be used as a sunlight absorbing material In the next experiment, I will use this bio-metamaterials in a system that evaporates water based on sunlight energy

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0 100 200 300 400 500 600 700 800 900 1000 15 20 25 30 35 40 45 50 55 60 65 70 Cu100 BC40 BC100 BC0 Control Temperat ure ( o C) Time (s)

Figure 3.16 Maximum temperatures of the samples BC0: natural Pistia stratiotes

leaf BC30: 30 nm copper-coated Pistia stratiotes leaf BC110: 100 nm copper-coated Pistia stratiotes leaf Control: 40 nm copper-coated Catharanthus roseus

leaf Cu100: 100 nm Copper thin-layer on glass’s surface

31

0 100 200 300 400 500 600 700 800 900 1000 15 20 25 30 35 40 45 50 55 60 65 70 MB30 BC40 White Foam Temperat ure ( o C) Time (s)

Figure 3.18 Maximum temperatures of the samples MB30: 30 nm copper-coated

Bauhinia purpurea leaf BC40: 40 nm copper-coated Pistia stratiotes leaf

32

However, in this experiment, the authors used normal solar illumination with luminous intensity 1kW m-2, more than 10 times in our conditions

0 500 1000 1500 2000 2500 3000 3500 4000 -1.6

-1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0

Mass

change (

kg/m

2 )

Time (s)

MB30 BC40 Control

33 CONCLUSION

34 FUTURE PLAN

1 Our research team will optimize the solar steam-generation device based on bio-metamaterials to improve system performance

2 In addition, our research team would like to fabricate the imitation of the models based on the nanostructure in Bauhinia purpurea and Pistia stratiotes

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