Study of optical absorption of metamaterial based on nanostructures in nature

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 Hanoi 2019

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

Hanoi 2019

VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

DAO TRUNG DUC

STUDY OF OPTICAL ABSORPTION OF METAMATERIAL BASED ON

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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

Dao Trung Duc

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TABLE OF CONTENTS

Acknowledgments i

TABLE OF CONTENTS ii

LIST OF FIGURES iv

LIST OF ABBREVIATIONS viii

INTRODUCTION ix

CHAPTER 1 LITERATURE REVIEW 1

1.1 Nanostructures in nature 1

1.2 Plant leaves surface 4

1.3 Metamaterials 6

CHAPTER 2 METHOD AND MATERIAL 9

2.1 Fabrication of bio-metamaterial 9

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 3 RESULTS AND DISCUSSION 15

3.1 Fabrication of absorbers based on some nanostructure in nature 15

3.2 Analysing the surface of bio-metamaterials 20

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

3.4 Efficient solar absorbers 25

CONCLUSION 33

FUTURE PLAN 34

REFERENCES 35

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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 2Figure 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) 3

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 9Figure 2.2 Process of conducting experiments 10Figure 2.3 Experimental model for the record of reflection and scattering spectra with an MCPD-3000 spectrometer (Otsuka Electronics) using a halogen lamp 12Figure 2.4 SEM images changes to black and white colours, then it uses to 3D structure in FDTD modelling 13Figure 2.5 Solar steam-generation device 14

Figure 3.1 (a) Bauhinia purpurea, (b) Pistia stratiotes 15

Figure 3.2 Photo images of (1) a rose periwinkle leaf (2) copper-coated rose periwinkle leaf, (3) a rose leaf (4) copper-coated rose leaf, (5) a water cabbage leaf (6) copper-coated water cabbage leaf (7) a bauhinia leaf (8) copper-coated bauhinia leaf 17

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Figure 3.3 Scanning Electron Microscope (SEM) images show the surface of all the samples 18Figure 3.4 40nm and 100nm copper-covered on water cabbage leaves 18Figure 3.5 Copper-covered bauhinia leaves with different time sputtering 19Figure 3.6 SEM images (a) 30 nm copper-covered, (b) 100 nm copper-covered water cabbage leave (c) 30 nm copper-covered, (d) 100 nm copper-covered purple bauhinia leaves 19Figure 3.7 Fourier-transform infrared (FT-IR) spectra (Z;\classes\spectroscopy\all spectra tables for web DOC) 20Figure 3.8 Energy dispersion spectrometry (EDS) of the copper-covered leaf 22Figure 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 22Figure 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 23Figure 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 24Figure 3.12 Calculated reflectivity R, transmittance T and absorption efficiency A for the model with three layers 25Figure 3.13 Temperatures of the samples over irradiation time MB0: Bauhinia leaf, MB30: 30 nm copper-coated bauhinia leaf, MB100: 100nm copper-

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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

Figure 3.17 Temperatures of the samples over irradiation time MB30: 30 nm copper-coated purple bauhinia leaf, BC40: 40nm copper-coated water cabbage leaf 30Figure 3.18 Maximum temperatures of the samples MB30: 30nm copper-

coated Bauhinia purpurea leaf BC40: 40nm copper-coated Pistia stratiotes leaf 31

Figure 3.19 Mass change of water under the sun 32

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LIST OF TABLES

Table 1.1 The common chemical compounds in plant waxes 6Table 2.1 Sample manufacturing conditions 11

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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

The surface of the lotus leaf (Nelumbo nucifera) is an ability to be highly

water-repellent due to the combination of the microscale mounds and the nanorods structures The recent researches involved the fabrication of bio-metamaterials on a lotus leaf and taro leaf and scrutinizing its property using the sputtering method The results showed the surface reflectively below 0.01 over the entire visible spectral range with the 10-nm thick gold-thin film on a lotus leaf and 30-nm thick gold-thin film on taro leaf Therefore, they can be applied to blackbody or light absorber

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:

All the works and experiments were done in Nanotechnology Laboratory, VNU – Vietnam Japan University

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

The structure on surface of dragonfly’s wings is another example in the nanoscale pattern in nature [18] Recent studies showed the bactericidal ability of nanostructures on dragonfly wings Instead of killing bacteria with antibacterial compounds or growth inhibitors such as antibiotics, they kill bacteria by physical mechanisms [1] Nanostructures have the ability to penetrate the cell wall when bacteria try to move on this surface Therefore, this structure limits the number of bacteria and prevents them from forming biofilm on the wing surface of dragonflies These structures inspired the antibacterial materials to be born with the surface covered with nanostructures similar to those on dragonfly wings With the exception of dragonflies, similar structures are also common in both animals and plants From the examples above we can imagine the diversity of nanostructures on

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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

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

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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)

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1.2 Plant leaves surface

The surfaces of leaves display a number of functional interfaces between the plants and their environment, both biotic and non-biotic things Plant leaf surfaces have evolved to adapt thousands of different living conditions leading to the diversity of their surfaces Many surfaces present a large variety of features such as super-hydrophobicity, self-cleaning, super-hydrophilicity and reduction of adhesion and light reflection, and absorption of harmful ultraviolet (UV) radiation, based on

the existence of three-dimensional waxes For example, lotus (Nelumbo nucifera)

leaves are known as an icon for a self-cleaning and superhydrophobic surfaces, and have resulted in the concept of the “Lotus effect” Scanning electron microscopy (SEM) images allowed to be seen microstructure and nanostructure in of lotus leaves’ epidermis layer which is an outermost complex tissue with protecting and gas exchanging function Covered on structures are cutin, a hydrophobic composite material consisting of nonacosane-10-ol and nonacosanediol in lotus, which are responsible for the superhydrophobic and self-cleaning ability of leaves Edelweiss

or Leontopodium nivale inhabits at high altitudes of about 3000m and is the symbol

of the Alps where UV radiation index reaches high-risk level The higher the UV radiation index, the greater the potential for harm to the cells and deoxyribonucleic acid (DNA) To survive in the alpine zone, this plant develops a thousand of white tiny hairs with nanoscale patterns around 100-200 nm in size to cover its flowers These structures are capable of absorbing the UV light, protecting the flower from burning in the sun and also reflect all visible light Therefore, hierarchical structures play an important role in wetting behaviour, light reflection, and absorption of plant surfaces Three-dimensional wax crystals on the cuticle such as platelets, filaments, rods, crusts, and tubules often occur in the size range from 100 nm to 1000 nm so microscopic techniques are really useful to investigation of this epicuticular waxes However, on a small group of the wax film has some special few molecular layers bringing about hardly visible in the SEM Thus, in some cases, atomic force microscopy (AFM) can be useful to investigate this wax film formation on a living

three-Inhabitation, plants are host to infection by a lot of pathogenic vectors that could do damage to organs or even kill the plant Therefore, all plant organs are covered with layers of hydrophobic compound that diminish dehydration and hinder the pathway of pathogenic microorganisms Several types of research have shown that the chemical compounds of plant waxes belonged to alkanes, alcohols, esters and aldehydes groups Other compounds are determined as ketones, β-Diketones, flavonoids, and triterpene The length of the hydrocarbons chain in all compounds is around 20 to 40 atoms, in some case with esters about 60 atoms These compounds are arranged in crystal form which plays a role as a water-repellent coat Previous studies on hydrophobic surfaces on leaves showed that water-resistant surfaces frequently appear with micrometer or nanometer-sized structures [8] Thus, we can choose samples through the water resistance of the surface

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

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

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

Metamaterials are a group of artificial materials capable of interacting with electromagnetic waves in the desired way On the surface of metamaterial is often made a structure layer with a smaller size than the wavelength being considered Therefore, with this group of materials, scientists pay more attention to their surface structure which is capable of interacting with electrical and magnetic components of light rather than their chemical composition [9] Basically, each artificial structure has the basic properties of natural atoms that act as in common materials

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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]

One of the most contributing applications of metamaterials is solar cells It is capable of helping the surface increase the ability to absorb light in solar panels by trapping light from all corners without a concentrator or monitoring system [17] Besides the technology of using solar in the solar steam-generation device is also a promising direction Therefore, the team focused on making the surface of the material capable of absorbing the energy of light and then converting that energy into thermal energy [7] Some researchers chose simple natural or artificial structures used as light-absorbing materials are being developed as environmentally

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friendly solutions, [12] For example, the use of mushrooms after carbonization to increase the evaporation efficiency by 3 times in the artificial sunlight conditions of the authors from China [21] Recently, studies of sputtering of metals such as gold

on natural surfaces such as taro leaves or lotus leaf have created super-materials with good absorption of visible light [6] Therefore, our team focused on finding and developing metamaterials that use nanostructures in nature to apply them to solar steam-generation technology

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CHAPTER 2 METHOD AND MATERIAL

2.1 Fabrication of bio-metamaterial

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

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Figure 2.2 Process of conducting experiments

2.1.1 Sputtering in the air at low pressure

The samples were prepared by the following procedure: (i) The young developed leave of both water cabbage and purple bauhinia were collected in wild

at Hanoi (ii) After treating samples with deionized water (DIW), it was nipped off and fixed on a glass slide (iii) A thin copper film was deposited on the leaves The copper coating was carried out using sputtering in the air at low pressure For control, we prepared the samples of copper-sputtered leaves of rosy periwinkle

(Catharanthus roseus) and (Rosa Chinensis) After preparation of the sample, the

sample is put into the chamber of a sputtering coater in order to vacuum

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

The optical consideration was performed by a similar system which shows in Figure 2.3 The reflection spectra were recorded with MCPD – 3000 spectrometer (Otsuka Electronics) using a halogen lamp as a light source For the measurements

of reflectance, the light was conveyed to the samples with Y-type optical fiber and the reflected light was collected by it The angle of incident light is 0o The commercial aluminum sample film is used as a reflectivity reference For the measurements of scattering, the light from light source was conveyed by an optical fiber to the sample with angle equal 0o The back-scattered light was collected by another optical fiber and transferred to the spectrometer An SRS-99 diffused reflectance standard (Labsphere) was used as reflectance reference The scattering angle was approximately 60o with respect to the surface normal SEM pictures were performed and analysed with a JSM-IT100 InTouchScope™ combined with JED-

2300 Analysis Station Plus

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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)

The finite-difference time-domain (FDTD) method is arguably the simplest, both conceptually and in terms of implementation, of the full-wave techniques used

to solve problems in electromagnetics The FDTD method can solve complicated problems, but it is generally computationally expensive Solutions may require a large amount of memory and computation time The FDTD method loosely fits into the category of “resonance region” techniques, i.e., ones in which the characteristic dimensions of the domain of interest are somewhere on the order of a wavelength in size If an object is very small compared to a wavelength, quasi-static approximations generally provide more efficient solutions Alternatively, if the wavelength is exceedingly small compared to the physical features of interest, ray-based methods or other techniques may provide a much more efficient way to solve the problem [14]