Summary of science materials doctoral thesis: Fabrication and investigation of characteristics of photonic microcavity 1D for optical sensors

The objectives of the thesis: Research and fabricate the one-dimensional (1D) – nanoporous silicon microcavity (1D-NPSMC) structures by using electrochemical etching method with the selectivity of wavelength in visible range from 200 nm to 800 nm. The 1D-NPSMC structures has high reflectivity, narrow linewidth of the pass-band and homogeneous pores ii) Design the photonic sensor device based on 1D-NPSMC structure which is capable of measuring in two modes: liquid phase (used for determination pesticides) and vapor phase (used for determination organic solvents) iii) Determinate the low concentrations of pesticides and organic solvents in aqueous medium.

AND TRAINING OF SCIENCE AND TECHNOLOGY

GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY



NGUYEN THUY VAN

FABRICATION AND INVESTIGATION OF

CHARACTERISTICS OF PHOTONIC MICROCAVITY 1D

FOR OPTICAL SENSORS

9

Materials and Devices, Institute of Materials Science, Vietnam Academy of Science and Technology

Supervisors:

1 Assocc Prof Dr Pham Van Hoi

2 Assocc Prof Dr Bui Huy

The thesis could be found at:

- National Library of Vietnam

- Library of Graduate University of Science and Technology

- Library of Institute of Science Materials

LIST OF PUBLICATIONS USED FOR THE THESIS

1 Huy Bui, Van Hoi Pham, Van Dai Pham, Thanh Binh Pham, Thi

Hong Cam Hoang, Thuy Chi Do and Thuy Van Nguyen,

Development of nano-porous silicon photonic sensors for pesticide monitoring, Digest Journal of Nanomaterials and

Biostructures, volume 13, No.1, January – March 2018

2 H Bui, V H Pham, V D Pham, T H C Hoang, T B Pham, T

C Do, Q M Ngo, and T Van Nguyen, “Determination of low

solvent concentration by nano-porous silicon photonic sensors using volatile organic compound method,” Environ Technol., pp

1–9, May 2018

3 Van Hoi Pham, Huy Bui, Thuy Van Nguyen, The Anh Nguyen,

Thanh Son Pham, Van Dai Pham, Thi Cham Tran, Thu Trang

Hoang and Quang Minh Ngo, “Progress in the research and

development of photonic structure devices”, Adv Nat Sci.:

Nanosci Nanotechnol 7, 015003, 17pp, 2016

4 Van Hoi Pham, Thuy Van Nguyen, The Anh Nguyen, Van Dai

Pham and Bui Huy, “Nano porous silicon microcavity sensor for

determination organic solvents and pesticide in water”, Adv Nat

Sci.: Nanosci Nanotechnol 5, 045003, 9pp, 2014

5 Bui Huy, Thuy Van Nguyen, The Anh Nguyen, Thanh Binh

Pham, Quoc Trung Dang, Thuy Chi Do, Quang Minh Ngo,

Roberto Coisson, and Pham Van Hoi, “A Vapor Sensor Based on

a Porous Silicon Microcavity for the Determination of Solvent Solution”, Jounal of the Optical Society of Korea, Vol 18, No 4,

pp 301-306, 2014

6 Van Hoi Pham, Huy Bui, Le Ha Hoang, Thuy Van Nguyen, The

Anh Nguyen, Thanh Son Pham, and Quang Minh Ngo,

“Nano-porous Silicon Microcavity Sensors for Determination of Organic Fuel Mixtures”, Jounal of the Optical Society of Korea, Vol 17,

No 5, pp 423-427, 2013

7 Nguyen Thuy Van, Pham Van Dai, Pham Thanh Binh, Tran Thi

Cham, Do Thuy Chi, Pham Van Hoi and Bui Huy, “A

micro-photonic sensor based on resonant porous silicon structures for

Photonics Spectroscopy & application, Ninh Binh city, Vietnam November 6 - 10, 2016, ISBN 978-604-913-578-1, pp 471-475,

2017

8 Phạm Văn Hội, Bùi Huy, Nguyễn Thúy Vân, Nguyễn Thế Anh,

“Thiết bị cảm biến quang tử và phương pháp để đo nồng độ dung

môi hữu cơ và chất bảo vệ thực vật trong môi trường nước” sáng

chế số: 16527, cấp theo quyết định số: 5424/QĐ-SHTT, ngày 24.01.2017

LIST OF PUBLICATIONS RELATED TO THE THESIS

1 Pham Van Dai, Nguyen Thuy Van, Pham Thanh Binh, Bui Ngoc

Lien, Phung Thi Ha, Do Thuy Chi, Pham Van Hoi and Bui Huy,

“Vapor sensor based on porous silicon microcavity for

determination of methanol content in alcohol”, Proc of Advances

in optics Photonics Spectroscopy & application, Ninh Binh city, Vietnam November 6 - 10, 2016, ISBN 978-604-913-578-1, pp 404-408, 2017

2 Nguyen Thuy Van, Nguyen The Anh, Pham Van Hai, Nguyen

Hai Binh, Tran Dai Lam, Bui Huy and Pham Van Hoi, “Optical

sensors for pesticides determaination in water using nano scale porous silicon microcavity ”, Proc of Advances in Optics,

Photonics, Spectrscopy & Applications VIII, ISSN 1859-4271, pp.603-608,2015

3 Thuy Van Nguyen, Huy Bui, The Anh Nguyen, Hai Binh

Nguyen, Dai Lam Tran, Roberto Coisson and Van Hoi Pham,

“An improved nano porous silicon microcavity sensor for monitoring atrazine in water”, Proc of The 7th International

Workshop on Advanced Materials Science and Nanotechnology (IWAMSN2014)- November 02-06, 2014- Ha Long City, Vietnam, ISBN: 978-604-913-301-5, pp.173-179, 2015

INTRODUCTION

1 The urgency of the thesis

In recent years, photonic sensors have generated an increasing interest because of their already well-known advantages, as immunity

to electromagnetic interferences, high sensitivity, no impact noise and working in harsh environment Photonic sensors are generally classified according to the physical principle including endogenous sensors and exogenous sensors Exogenous sensors often use the physical principle that light is altered in intensity of spread; reflex; scattering; refraction; or wavelength conversion due to interaction with the external environment These sensors are relative easiness of fabrication, but the processing of light signals varies due to the complexity of the external environment requiring high sensitivity The endogenous photonic sensor uses the physical principle that the optical properties of sensor structure is changed when interacting with the environment Therefore, they have very high sensitivity, easiness of signal processing and compact device size However, the disadvantage of endogenous photonic sensor is the ability to reuses and selectivity Endogenous photonic sensors are being promoted in research because of their extremely high sensitivity which can be combined with many specializations in chemistry and biology At present, the sensitivity and selectivity of endogenous photonic sensors can be enhanced and have had some very good results

In general, scientists and technologists have proposed the standard approach of quantitative analysis of components with extremely small concentrations by using gas chromatography or liquid chromatography (GC / MS, LC / MS or HPLC / MS-MS) [1]-[4],

liquid chromatography combined with UV-Vis [5] These methods have played a key role in the analysis of residues of low organic dissolved organic substances in the process of controlling or controlling the environment However, these methods suffer some drawbacks since thay require professional laboratories with specialized personel and expensive equipment

In the field of electrochemical sensors [6-7], the enzyme-linked immunosorbent assay (ELISA) has been developed for determination

of residues of organic matter based on the principle of antigen - antibody The ELISA technique has high sensitivity, easiness of manipulation and rapid analysis time, so there are many models of sensor devices using the ELISA principle The disadvantage of the ELISA approach is the low accuracy in harsh environment, inflexible due to the dependence on the chemicals of the manufacturer Thus, finding new analytical methods is more convenient than the goal of many sensing laboratories in the world

Endothelial photonic sensors based on the principle of changing the refractive index of the sensor environment due to the interaction with environment are being extensively studied for the development of sensors in the world Principles of transmission, interference, scattering and refraction of light is studied and applied radically in the photonic sensor based on changing the refractive index of the environment The most recent publish reported that the optical fiber Bragg grating is capable of detecting the refractive index change to as low as 7.2x10-6 in liquid environment [8] which allows the determination of solution at low concentration Endothelial photonic sensors based on the 1D – nanoporous silicon microcavity (1D-NPSMC) have high sensitivity, low cost and ability to analyse

substances quickly and easily [9] In recent years, scientists have promoted research on endogenous photonic sensors for determining concentrations of solvents, biological antibodies [10], cadavers petroleum contamination norms and petroleum products [11], determination of pesticide residues in water and sludge (recorded pesticide concentration at 1 ppm) [12], determination of concentration DNA level (0.1 mol / mm2 DNA concentration) [13], chemical sensor [14] Current trends in the development of endogenous photonic sensors in the world are enhancing the sensitivity of the sensor (down to ppm), the selectivity of close-optical properties and portable sensor devices

In addition, the nano porous silicon with different porosity have different refractive indexes, so that the multilayer porous silicon can easily form an optical resonance cavity with cost low, durable in the environment for application in photonic sensor technology The research results show that photonic sensors based on resonant cavity have the ability to measure the concentration of solvents and pesticides in the aqueous medium at extremely low concentrations

So that PSMC devices show promise for a simple and portable instruments for measuring the level of water pollution caused by organic solvents from industrial production or agricultural protective substances Based on the large surface area of the porous silicon, the porous silicon material has become the ideal material for liquid and vapor phase sensors The principle of pSi-sensors is a determination

of the optical spectral shift caused by refractive index change of the porous silicon layers in the device due to the interaction with liquid and/or gas The advantages of photonic sensors are highly sensitivity,

so that they are suitable for determination of organic solvents or

pesticides at low concentrations Therefore, “Fabrication and investigation of characteristics of photonic microcavity 1D for optical sensors” has been selected as a research topic of the thesis

2 The objectives of the thesis

i) Research and fabricate the one-dimensional (1D) – nanoporous

silicon microcavity (1D-NPSMC) structures by using electrochemical etching method with the selectivity of wavelength in visible range from 200 nm to 800 nm The 1D-NPSMC structures has high reflectivity, narrow linewidth of the pass-band and homogeneous

pores ii) Design the photonic sensor device based on 1D-NPSMC

structure which is capable of measuring in two modes: liquid phase (used for determination pesticides) and vapor phase (used for determination organic solvents) iii) Determinate the low concentrations of pesticides and organic solvents in aqueous medium

3 The main contents of the thesis

i) Research and fabricate 1D-NPSMC structures based on porous

silicon ii) Calculate and simulate optical characteristics of NPSMC structures by using Transfer Matrix Method (TMM) iii)

1D-Design the photonic sensor device based on 1D-NPSMC structure which is capable of measuring in two modes: liquid phase (used for determination pesticides) and vapor phase (used for determination

organic solvents) iv) Determinate the low concentrations of

pesticides and organic solvents in aqueous medium

4 Thesis structure: This thesis consists of 148 pages: introduction,

five chapters in content, conclusion The main results were published

on 06 articles was published on international journal, 01 presentation

at an international workshop and 01 patent

Chapter 1: OVERVIEW ABOUT PHOTONIC MICROCAVITY

1D AND POROUS SILICON:

In this chapter, we introduce photonic crystals from the concept to the structure of all 1D, 2D and 3D photonic crystals Particularly, this chapter details the structure of the 1D photonic resonator and the formation of silicon by electrochemical etching method The advantages of silicon and its application in the field of sensing are detailed in this chapter

simulation result based on the Kronig-Penny model, and the structure parameters defined from the simulated reflection spectra laid the foundation for the following fabrication work Parameters affecting the sensitivity of the optical sensor based on the 1D microcavity structure on the silicon wafer are also detailed

Chapter 3:

FABRICATION OF THE 1D – MICROCAVITY BASED ON

POROUS SILICON 3.1 Principle, process of fabrication of the 1D microcavity based

on porous silicon

3.1.1 Fabricating principles

This part introduces the principle of fabricating 1D microcavity based

on porous silicon by using electrochemical etching method

3.1.2 Process of fabricating 1D microcavity structure

This section details the steps of fabrication of 1D microcavity structure

3.2 Design and fabrication of 1D microcavity structure

The microcavity structure

consists of two parallel

reflectors separated by a

spacer layer Usually the

reflectors used are λ/4 DBR

with optical thickness of the

layers λ/4 The optical

thickness of the spacer layer

can be either λ or λ/2

microcavities are formed

Figure 3.5 (a) Schematic illustration of microcavity

structure represented by a half-wave optical thickness defect layer between two Bragg mirrors The Bragg mirrors consist of alternating layers of high and low refractive index quarter-wave optical thickness layers (b) Reflectance spectrum of microcavity The defect layer introduces a narrow resonance in the middle of the high reflectance stopband.

by first etching a top Bragg mirror with alternating quarter wavelength optical thickness layers of low and high porosities (high and low refractivve indices, respectively), then etching a half wavelength optical thickness defect layer with the same refractive index as the high porosity mirror layers, and finally etching a bottom Bragg mirror with the same conditions as the top mirror Detailed electrochemical etching conditions are provided in Table 3.1

The characteristics of the microcavitity structures were determined

by field-emission scanning electron microscopy (FE-SEM; S-4800) and the reflectance spectra of samples were studies by a UV-VIS-NIR spectrophotometer (Varian Cary-5000) and USB 4000 spectrophotometer

3.3 Some methods of studying the structure and optical properties of porous silicon materials

The optical properties and quality of the 1D photonic resonator structure depend greatly on the size of the porous holes, the thickness

of the layers Therefore, the identification of these factors is of particular importance in understanding the relationship between the structure and optical characteristics of microcavites made of silicon

In this section, we present some of the methods used in this thesis to observe the morphology, size, structure and optical characteristics of 1D microvities such as scanning electron microscopy SEM, Metricon Prism 2010 Model, Varian Carry 5000 Spectrum Analyzer, USB

4000

3.4 The 1D microcavity structures

Table 3.3 Parameters of fabrication of 1D-PCs structure in

visible range with 12 periods

Sample Layers Periods Current Density

structure in visible range

are provided in Table 3.4 The

porous silicon microcavities

used in this thesis typically

consist of 4.5/5 period upper/lower Bragg mirrors Each period consists of one low porosity and one high porosity layer Therefore, a half period means that there is an additional low porosity layer formed Increasing the naumber of mirror periods enables higher Q-factor microcavities

Figure 3.18 FE-SEM images of the 1D-PC in the visible range with 12

periods

Hình 3.19 The reflection spectra of 1D-PC

structure in visible range at 608 nm centre

wavelength

Bảng 3.4 Electrochemical etching conditions for a porous

silicon microcavity at 650 nm resonant wavelength

Descriptionả Period Current density

(mA/cm 2 )

Etching time (s)

cross-section and

plan-view images of the

Figure 3.20 (a) Cross-section and (b) SEM plan-view

images of a porous silicon microcavity design in the

(HL) 4.5 LL(HL) 5

Figure 3.23 04 samples of microcavity

structure in the visible range

Figure 3.23 The reflection spectrum of

1D microcavity structure at 654 nm

resonant wavelength

high and low refractive index layers, respectively, 4.5 and 5.0 mean four and half and five pairs of HL, because this gives a good reflectivity spectrum, possibly controlling the porosity of layers, and easily repeatable electrochemical etching method Figure 3.23 presents images of 4 microcavity structure samples in the visible range

3.5 Design of photonic sensor device based on 1D-porous silicon microcavity

Figure 3.34 is a block diagram of a photonic sensor device used in a thesis including a liquid method (application of non-volatile analytical substance) and vapor organic compounds (application for volatile compounds)

Hình 3.23 Phổ phản xạ của cấu trúc vi cộng

hưởng quang tử 1D sau khi chia cho cường độ

phản xạ của mẫu nền

Figure 3.26 The schematic of photonic sensor device

Figure 3.27 Schematic of the pesticide concentration

measurement by liquid-drop method using the porous

silicon microcavity sensor

Figure 3.28 Schematic of the concentration measurement for VOC using a sensor based on the porous silicon microcavity