Study of optical absorption of metamaterial based on nanostructures in nature

º VIETNAM NATIONAL UNIVERSITY, HANOIVIETNAM JAPAN UNIVERSITY DAO TRUNG DUC STUDY OF OPTICAL ABSORPTION OF METAMATERIAL BASED ON NANOSTRUCTURES IN NATURE MASTER'S THESIS Hanoi 2019... VIE

º 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 NANOSTRUCTURES IN NATURE

MAJOR: NANO TECHNOLOGY

CODE: PILOT

RESEARCH SUPERVISOR:

Dr PHAM TIEN THANH

Hanoi, 2019

I am truly honored to submit my master thesis for the degree of Master atNanotechnology Program, Vietnam Japan University This work has been carriedout in the Nanotechnology program, Vietnam Japan University, Vietnam NationalUniversity of Hanoi

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

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

Hanoi, May 25, 2019Student

Dao Trung Duc

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

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) 2μmm, d) 5μm, d) 5μm, e) 2μmm, e) 2μm, d) 5μm, e) 2μmm 2

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

Figure 2.1 Some equipment used in this research a) JSM-IT100InTouchScope™ Scanning Electron Microscope b) JED-2300 Analysis StationPlus c) Syskey sputtering coater d) NanoMap-500LS Contact Surface Profilometer9

Figure 2.2 Process of conducting experiments 10

Figure 2.3 Experimental model for the record of reflection and scatteringspectra with an MCPD-3000 spectrometer (Otsuka Electronics) using a halogenlamp 12

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

Figure 2.5 Solar steam-generation device 14

Figure 3.2 Photo images of (1) a rose periwinkle leaf (2) copper-coated roseperiwinkle 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 bauhinialeaf 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 19

(Z;\classes\spectroscopy\all spectra tables for web DOC) 20Figure 3.8 Energy dispersion spectrometry (EDS) of the copper-covered leaf

copper-covered water cabbage leaf with no copper-coating 23Figure 3.11 Calculated reflectivity R, transmittance T and absorptionefficiency 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 absorptionefficiency A for the model with three layers 25Figure 3.13 Temperatures of the samples over irradiation time MB0:

Bauhinia leaf, MB30: 30 nm coated bauhinia leaf, MB100: 100nm

copper-coated bauhinia leaf, Ct30: 30 nm copper-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

Figure 3.15 Temperatures of the samples over irradiation time BC0: watercabbage leaf, MB30: 30 nm copper-coated water cabbage leaf, MB100: 100nmcopper-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

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

Figure 3.18 Maximum temperatures of the samples MB30: 30nm

copper-coated Bauhinia purpurea leaf BC40: 40nm copper-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 6

Table 2.1 Sample manufacturing conditions 11

Metamaterials are artificial structures capable of interacting withelectromagnetic radiation in the desired fashion However, there are many livingcreatures featuring their own form of metamaterial structures with specificfunctionalities which change their colour without pigment or give hydrophobicity orbust up bacteria People who are a lack of melanin, the pigment appearing in peoplewith brown eyes, have blue eyes like an example Without melanin, the blue irisstems from the structure of eyeball tissue itself not because of a different type ofpigment In other words, the iris is capable of displaying a natural form ofmetamaterial 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 themoth’s eye can absorb more light [20] A research group at Jacobs UniversityBremen published a paper in the IOP science that designed better thin film solarcells based on nanostructured nipple arrays of the moth-eye The coating thatimitates the moth-eye array allows for an increase of the short circuit current andconversion efficiency of more than 40% [5] For a material to be regarded as ametamaterial, it must operate on a microscopic-scale and cannot be detected by thenaked 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 nanorodsstructures The recent researches involved the fabrication of bio-metamaterials on alotus leaf and taro leaf and scrutinizing its property using the sputtering method.The results showed the surface reflectively below 0.01 over the entire visiblespectral range with the 10-nm thick gold-thin film on a lotus leaf and 30-nm thickgold-thin film on taro leaf Therefore, they can be applied to blackbody or lightabsorber

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 apurple bauhinia leaf is also highly water-repellent, although the surfacenanostructure two both of leaves completely differs from that of lotus leaves Wecoated the surface of a water cabbage and purple bauhinia and found that copper-coated surface of the leaves is almost back The copper-coated water cabbage leafsurface and purple bauhinia leaf surface have reflectivity below 2.5% over thevisible spectral range

Thus, our research team has carried out this research, named “Study of opticalabsorption of metamaterial based on nanostructure in nature” Although there are athousand 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

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CHAPTER 1 LITERATURE REVIEW

1.1 Nanostructures in nature

Life-forms own numerous magnificent structures in order to serve their lifeactivities such as hooks in fore- and hindwings in sawfly or suctions cups ontentacles of Octopus However, not only did a selection of macrostructures evolvebut also selected structures at even smaller scale too, producing a ton ofnanostructure on living things’ organs with a size range about 1 nm to 100 nm in atleast 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 thesurface 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 visibleregion and reflects almost completely blue, so male blue morpho’s wings have asingle blue colour This optical behaviour is caused by physical structures not forpigments so its product of this method is known as physical colours Thisphenomenon is formed by random scattering or interference and is quite popular ininsect groups such as adult Lepidoptera, Odonata or Coleoptera

The structure on surface of dragonfly’s wings is another example in thenanoscale pattern in nature [18] Recent studies showed the bactericidal ability ofnanostructures on dragonfly wings Instead of killing bacteria with antibacterialcompounds or growth inhibitors such as antibiotics, they kill bacteria by physicalmechanisms [1] Nanostructures have the ability to penetrate the cell wall whenbacteria try to move on this surface Therefore, this structure limits the number ofbacteria and prevents them from forming biofilm on the wing surface of dragonflies.These structures inspired the antibacterial materials to be born with the surfacecovered with nanostructures similar to those on dragonfly wings With the exception

of dragonflies, similar structures are also common in both animals and plants Fromthe examples above we can imagine the diversity of nanostructures on

the surface of animals Thus, we want to rely on these special surface structures tocreate new materials with features that can be applied to everyday life Ascharacteristics of a tropical country, Vietnam with a high level of biodiversity is anadvantage 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 thebutterfly’s wing e) & f) Scanning electron micrograph (SEM) of a scale Scale bars(b, c) 50μm, d) 5μm, e) 2μmm, d) 5μm, d) 5μm, e) 2μmm, e) 2μm, d) 5μm, e) 2μmm

2

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)

1.2 Plant leaves surface

The surfaces of leaves display a number of functional interfaces between theplants and their environment, both biotic and non-biotic things Plant leaf surfaceshave evolved to adapt thousands of different living conditions leading to thediversity of their surfaces Many surfaces present a large variety of features such assuper-hydrophobicity, self-cleaning, super-hydrophilicity and reduction of adhesionand 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, andhave resulted in the concept of the “Lotus effect” Scanning electron microscopy(SEM) images allowed to be seen microstructure and nanostructure in of lotusleaves’ epidermis layer which is an outermost complex tissue with protecting andgas exchanging function Covered on structures are cutin, a hydrophobic compositematerial consisting of nonacosane-10-ol and nonacosanediol in lotus, which areresponsible 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 UVradiation index, the greater the potential for harm to the cells and deoxyribonucleicacid (DNA) To survive in the alpine zone, this plant develops a thousand of whitetiny 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 fromburning in the sun and also reflect all visible light Therefore, hierarchical structuresplay an important role in wetting behaviour, light reflection, and absorption of plantsurfaces 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 somicroscopic techniques are really useful to investigation of this epicuticular waxes.However, on a small group of the wax film has some special few molecular layersbringing about hardly visible in the SEM Thus, in some cases, atomic forcemicroscopy (AFM) can be useful to investigate this wax film formation on a living

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plant surface Such results of studies displayed wax films consisted of variousmonomolecular 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 dimensional (2-D) thin wax films with the size range up to 0.5μm, d) 5μm, e) 2μmm and second isthree-dimensional (3-D) waxes with size range about 0.5-1μm, d) 5μm, e) 2μmm [2]

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

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

Aliphatic compounds

Chain lengthFrequently existing in waxes, but mostly as minor compounds

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

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

1.3 Metamaterials

Metamaterials are a group of artificial materials capable of interacting withelectromagnetic waves in the desired way On the surface of metamaterial is oftenmade a structure layer with a smaller size than the wavelength being considered.Therefore, with this group of materials, scientists pay more attention to their surfacestructure which is capable of interacting with electrical and magnetic components oflight rather than their chemical composition [9] Basically, each artificial structurehas 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, itgenerates 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 informationtransmission, blackbody or absorber [4], [3], [15], [10] Recently, lenses allow boththe light intensity and the direction of the incoming light to be developed bymetamaterials [13] This allows the user to re-focus the image and then refactoringthe depth of field information The surface of the metalens array is covered bynanotennas made of gallium nitride (GaN) which allow the tube to record brightfield information.

For electromagnetic waves to be able to interact or penetrate the homogeneousstructure of metamaterials in an efficient and accurate way, the structures on thesurface of the metamaterial must be much smaller than the size scale of thewavelength Electromagnetic absorbing materials can be divided into two maintypes: resonant absorbers and broadband absorbers [16] While the resonantabsorber is based on an interaction with a specific appropriate frequency, thebroadband absorber is usually a frequency-independence material and thereforeabsorbs radiation with a wide absorption spectrum than the other one Metamaterialsare designed based on the determination of magnetism permeability and electricpermittivity so they can interact directly with the two components, electric andmagnetic of light [19]

One of the most contributing applications of metamaterials is solar cells It iscapable of helping the surface increase the ability to absorb light in solar panels bytrapping 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 apromising direction Therefore, the team focused on making the surface of thematerial capable of absorbing the energy of light and then converting that energyinto thermal energy [7] Some researchers chose simple natural or artificialstructures 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 toincrease the evaporation efficiency by 3 times in the artificial sunlight conditions ofthe 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-materialswith good absorption of visible light [6] Therefore, our team focused on findingand developing metamaterials that use nanostructures in nature to apply them tosolar steam-generation technology

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) Syskeysputtering 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 youngdeveloped 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 offand fixed on a glass slide (iii) A thin copper film was deposited on the leaves Thecopper coating was carried out using sputtering in the air at low pressure Forcontrol, 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

Table 2.1 Sample manufacturing conditions The conditions during sputtering operation

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

The optical consideration was performed by a similar system which shows inFigure 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 andthe reflected light was collected by it The angle of incident light is 0o Thecommercial aluminum sample film is used as a reflectivity reference For themeasurements of scattering, the light from light source was conveyed by an opticalfiber to the sample with angle equal 0o The back-scattered light was collected byanother optical fiber and transferred to the spectrometer An SRS-99 diffusedreflectance standard (Labsphere) was used as reflectance reference The scatteringangle was approximately 60o with respect to the surface normal SEM pictures wereperformed 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 ofpolystyrene foam The temperature is determined by FLIR C2 thermal camera Thesun 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 complicatedproblems, but it is generally computationally expensive Solutions may require alarge amount of memory and computation time The FDTD method loosely fits intothe category of “resonance region” techniques, i.e., ones in which the characteristicdimensions of the domain of interest are somewhere on the order of a wavelength insize If an object is very small compared to a wavelength, quasi-staticapproximations generally provide more efficient solutions Alternatively, if thewavelength is exceedingly small compared to the physical features of interest, ray-based methods or other techniques may provide a much more efficient way to solvethe problem [14]

There are 3 simulation models to predict the absorption capacity of the metamaterials and the 30 nm copper thin layer:

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

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

50 ml beaker used in the experiment marked with lines to indicate 10, 20, 30,

40 and 50ml of volume Cotton pad-wrapped polystyrene foams had a thicknessaround 1.5 cm which covered fully the brim of the beaker Bio-metamaterials arefixed between two layers of cotton that play a role as a capillary path Beakers areplaced on an insulating foam that made of polystyrene

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