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 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 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 i 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 .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 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 ii 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 iii 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 .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 twospotted 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 .9 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 Figure 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 iv 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 copper-covered, (b) 100 nm coppercovered water cabbage leave (c) 30 nm copper-covered, (d) 100 nm coppercovered 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 Figure 3.13 Temperatures of the samples over irradiation time MB0: Bauhinia leaf, MB30: 30 nm copper-coated bauhinia leaf, MB100: 100nm copper- v 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 .30 Figure 3.18 Maximum temperatures of the samples MB30: 30nm coppercoated Bauhinia purpurea leaf BC40: 40nm copper-coated Pistia stratiotes leaf .31 Figure 3.19 Mass change of water under the sun 32 vi LIST OF TABLES Table 1.1 The common chemical compounds in plant waxes Table 2.1 Sample manufacturing conditions 11 vii 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 UV: Ultraviolet viii 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 Figure 3.11 shows the calculated reflectance (R), transmittance (T) and absorption (A) spectra of flat copper thin films The absorption A is calculated following the relation A = – T – R, because there is no scattering in flat copper surface The calculation was done using the Finite-difference time domain with refractive index data of software The reflectance is more than 20% over the visible spectral range with cases of thickness which are calculated Although reflectance and transmittance vary with the thickness of copper, the absorption is almost independent with changing of thickness In the wavelength range from 380 nm to about 780 nm, the absorption is about 4% It explains the disappearance of the peak in range 500-600 nm in reflectivity and scattering spectrum of sputtered Bauhinia purpurea leaves The absorption is weak (< 4%) in range of wavelength over than 680 nm Meanwhile, the reflectivity and scattering intensity of sputtered leaves are much lower than both non-sputtering leaf and copper thin layer in this range of wavelength, indicating that the Pistia stratiotes leaf and Bauhinia purpurea leaf with copper coating has considerably low reflectivity because of not only the nature of copper layer but also the metallic surface structure With the incident light in the visible region, we predict that it has three phenomena in the surface of coated 23 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 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 twolayer copper with nanostructure pattern 24 Figure 3.12 Calculated reflectivity R, transmittance T and absorption efficiency A for the model with three layers 3.4 Efficient solar absorbers After assessing the sample's ability to absorb light, we conducted an investigation of energy conversion in the form of heat Figure 3.13 and Figure 3.14 show the process of changing the temperature of the samples under sunlight condition During the first 100 seconds, the temperature changes rapidly in all samples, then the temperature is maintained at a stable level at a later time In the bio-metamaterial sample, the observed temperature range is the largest and when the maximum temperature is reached the object samples have a temperature higher than the control samples over 10 ºC With purple bauhinia, the highest temperature measured about 54 ºC under luminous intensity condition about 0.0124 W/cm2 Meanwhile water cabbage, the highest temperature measures about 65 ºC under luminous intensity condition about 0.018 W/cm2 According to the chart, the temperature of the thin copper layer does not change much and when it reaches the maximum temperature, it only stops at about 29 ºC Control sample with 30 nm coating, the maximum temperature reached about 33 ºC Natural purple bauhinia 25 also had a larger range of temperature changes than the reference sample, the temperature recorded at the peak temperature of 43 ºC Meanwhile, purple bauhinia with 30 nm copper-covered thin layer had a maximum temperature near 55 ºC and the one with 100 nm copper-coated thin layer reached about 46 ºC This again demonstrates that the effect of the copper layer on the surface of the sample depends greatly on the thickness of the sputtering layer In compare with two research group [21] and [12], the maximum temperature of the biomaterial sample is about two times the maximum temperature of the two object samples in the previous study In addition, the metamaterial sample has a rapid heating capacity, which takes only 100 seconds to reach the maximum temperature while the two samples of the previous study object took about 1000s to reach the saturation threshold Thus, bio-metamaterials show the promising potential use in the solar steam-generation devices With good stability and heating ability, this material sample can be selected as a cheap and environmentally friendly material In addition, with a higher heating capacity than the control sample and a thin copper layer, the metamaterial sample exhibited the property of interacting with light waves at least in the visible region After that, they transformed that energy in the form of heat Therefore, we can use bio-metamaterial in many other applications 26 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 thinfilm of copper In the case with water cabbage, due to adapting to underwater life, their leaves contain air chambers This helps the natural leaves to be able to regulate its own temperature The temperature of the natural water cabbage sample recorded at a stable time is 32 ºC Meanwhile, the temperature of the object sample sputtered with a copper layer of 40 nm thickness was recorded as 65 ºC and higher than the temperature of natural samples by 30 ºC In addition, we also conducted experiments to compare the temperature of two object samples under the same conditions Figure 3.17 and Figure 3.18 shows the process of changing the 27 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 coppercovered 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 60 Temperature (oC) 55 50 45 40 35 30 MB0 MB30 MB100 Control Cu100 25 20 15 100 200 300 400 500 600 700 800 900 1000 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 Catharanthus roseus leaf Cu100: 100 nm Copper thin-layer on glass’s surface 28 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 biometamaterials in a system that evaporates water based on sunlight energy Figure 3.15 Temperatures of the samples over irradiation time BC0: water cabbage leaf, MB30: 30 nm copper-coated water cabbage leaf, MB100: 100 nm copper-coated water cabbage leaf, Ct30: 30 nm copper-coated rose periwinkle leaf, Cu100: 100 nm thin-film of copper 29 70 65 Temperature (oC) 60 55 50 45 40 35 30 Cu100 BC40 BC100 BC0 Control 25 20 15 100 200 300 400 500 600 700 800 900 1000 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 coppercoated Pistia stratiotes leaf Control: 40 nm copper-coated Catharanthus roseus leaf Cu100: 100 nm Copper thin-layer on glass’s surface Figure 3.17 Temperatures of the samples over irradiation time MB30: 30 nm copper-coated purple bauhinia leaf, BC40: 40 nm copper-coated water cabbage leaf 30 70 65 Temperature (oC) 60 55 50 45 40 35 30 MB30 BC40 White Foam 25 20 15 100 200 300 400 500 600 700 800 900 1000 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 Figure 3.19 shows the process of dehydration of the evaporating system during the investigation in one hour under the luminous intensity is 0.1 kW/m2 After a one-hour investigation, the amount of water lost in the sample using the metamaterial-based evaporation system is more than the control sample Specifically, the control sample lost 0.8 kg m-2 h-1 while the object sample lost 1.5 kg m-2 h-1 The efficiency of solar steam-generation system compared to the free evaporation rate of water is more than 75% in the same condition The results between use of purple bauhinia with 30 nm copper-coated and water cabbage with 40 nm copper-coated are near the same In compare with solar steam-generation devices based on the carbonized mushroom, our object sample and carbonized mushroom in one hour lose the same amount of water, about 1.5 kg m-2 h-1 [21] 31 However, in this experiment, the authors used normal solar illumination with luminous intensity 1kW m-2, more than 10 times in our conditions 0.0 MB30 BC40 Control Mass change (kg/m2) -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -1.4 -1.6 500 1000 1500 2000 2500 Time (s) Figure 3.19 Mass change of water under the sun 32 3000 3500 4000 CONCLUSION Our research team found two suitable objects: Bauhinia purpurea and Pistia stratiotes for the aim of metamaterial fabrication The nanostructures of these two leaf sheets are periodic The thickness of the nanostructure layer on these two types of leaves is predicted from 80-100 nm We also showed the ability to absorb light well when leaf samples are coated with copper metal with a thickness of 20-80 nm Absorption capacity predicts about 90% of light entering the structure A purple bauhinia leaf with about 30 nm copper layer has the best ability to absorb light while a water cabbage leaf needs about 40 nm of a copper-coated layer to achieve the best light absorption After sputtering a copper layer, two object leaves are capable of converting light energy into heat and are potential in the solar steamgeneration system 33 FUTURE PLAN Our research team will optimize the solar steam-generation device based on bio-metamaterials to improve system performance In addition, our research team would like to fabricate the imitation of the models based on the nanostructure in Bauhinia purpurea and Pistia stratiotes leaves’ surface in order to create a material with the same properties but more stable than natural object leaf samples 34 REFERENCES [1] Bandara, C D., Singh, S., Afara, I O., Wolff, A., Tesfamichael, T., Ostrikov, K., & 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(Rosa Chinensis) After preparation of the sample, the sample is put into the chamber of a sputtering coater in order to vacuum 10 Table 2.1 Sample manufacturing conditions The conditions during sputtering