Luận văn fabrication of in2o3 nanowires for self heated gas sensor application

The response ot self-heated 80% wt SnOv/br-Os NW gas sensor versus time at difterent power of 300, 500 and 700 ,W RT a and the fimetion of response with Figure 3.10 Response and heating

IIANOI UNIVERSITY OF SCIENCE AND TECIINOLOGY

MASTER THESIS

Fabrication of InzO3 nanowires for self-

heated gas sensor application

NGUYEN THANII DUONG Duong.NT202353M(@sis.hust.edu.vn

Specialized: Materials science (Electronic materials)

Supervisor 1: Associate Professor Ph.D Nguyen Van Duy

Unit: International ‘Training Institute for Materials Science ([TIMS) Signature of supervisor

Supervisor 2: Ph.D.Phimg Thi Hong Vân

Unit: Hanoi University of Natural Resources & Environment Signature of supervisor

THANOI, 09/2022

DECLARATION

I hereby declare that this thesis represents my work which has been done after the registration for the degree of Master at the Intemational Training Institute of Materials Science — Ilanoi University of Science and Technology and has not been previously

included im a thesis or dissertation submilted to this or any other institution fora degree,

diploma or other qualifications

Hanoi, 224 Apnil, 2022 Nguyen Thanh Duong

ACKNOWLEDGEMENT

First of all, 1 am sincerely grateful to my thesis supervisor Assoc, Prof Nguyen Van Duy and Prof Nguyen Luc Lica - International ‘Iraining Institute of Materials Science, for allowing me this opportunity to be their student; all of their advices indication, and inspiration during the time T studied and canied ouL my Master thesis in ITIMS Tamm very proud fo have their whole guidaney, encouragement, and insight which

have always been invaluable

I would like to show my gratitude to all of teachers and staff not only in ITIMS but also in HUST to support me, I would like to send spectal thanks to Mr, Dang Ngoc Son and Mr Lai Van Duy - ITIMS tor sharing me the initial experiences and many usefil suggestions relevant to my work

Last but not the least, I would like to thank my family and my friends for their support

and encowagement

SUMMARY OF MASTER THESIS

In this work, we focused on the fabrication and testing of the H:S gas sensing

characteristic of the selt-heated Ins: nanowires sensor via a one-step CVD technique

and drop-casting on the IDE electrode The self-heated In-Q: NWs gas sensor was

measured at room temperature with different applied power toward H-S gas ‘This

performance was beller than the state-of-the-art tcroleater gas sensor The sensor is a potential canuidate for application related 10 H2S deleetion such as breath exhaled

analysis aud cnvironmental monitoring

#: Auysust, 2022 Master Student

Nguyen Thanh Duong

iii

L Foundation of the {hesis ) cnmsesenmmonenenneititnieiannemnsnnne

3 Research object and scope of the thesis 2

5 New contributions of the thesis - 3

1.3.1 InsOs mmafeTiali, smmosninineniminienmenmnesnnndd 1.3.2, InsOs nanowires I 2aS SEMSOT «sess sesssinnse sented

LA, Hazardous properties of H:$ 285 vaesscsesnomtnsnesintns nasntninssntntmnnnenned

CHAPTER 2 EXPERIMENTAL APPROACH

2.1 Synthesis of In:O nangwirvs is non re seo

2.1.1 Fanipment and chemical

2.2 Fabrication of InzO; nanowires

CHAPTER 3 RESULT AND DISCUSSION

3.1 Morphology of Indium Oxide (In.(:) synthesized by CVD method and In.Os

Ws based sensor fabricate by drop-casting 30 3.1.1 Effect of Sn proportion on the morphology of Indium Oxide (Ins)

International Training Institute for Malcrials Seicnes

NWs Parts per billion Parts per million

Ra

Ras

Sensitivity Scanning Electron Microscope Transition Fleetron Microscope Volatile Organic Compounds

vi

s for gas sensing application [1] 5

Figure 1.3 Sensing mechanism of metal oxide based gas scnsor [ ]

Figure 2.5 Procadure of scli-heated InOs NWs based gas sensor 28 Figure 2.6, Gas sensitive measuring system at ITIMS (A), Diagram of the gas measuring

Figure 3.1 Menphotogy and snicrostructure of three eomposite simples at (A),(BY 0%: (C)CDY: 20 %, (ECE): 30 %; (G),CHD: 80 % mass ratio of Sn_ were observed by SEM

vũ

Figure 3.2 Distribution of TsO NWs onto silicon substrate with (A)10 ml (B)20 ml

Tigure 3.3 SEM nnage oŸTroO; nanowires dispersion em the eleelrode wi1h various ratio

Figure 3.4 (4D XRD pallern of 0%, 20%, 50 and 80% SnOwIn:03 NWs 34

Figure 3.5 EDX spect um of (A) Pưưe In:Os NW and (B),(C) SnO3/InzOy XW, 35

Tigure 3.6 The respdnse 0Í selÍ-heated TnsO; gas sensor versus time al different power

of 600, 800, 1200, 1200 pW (a) and the function of response with concentration H28

Figure 3.7 The response of sel heated 20% wi, SasiInOs NWs gas somisor versus lime

at different power af 300, 300 and 700 W (RT) (2) and the fimetion of response with concentration Hs§ gas ( Hi rrtereieireiririrrrerreoo.ÖB Figure 3.8 The response ot self-heated 50% wt 8nO›/InzQs NWS gas seIso versus time

at difterent power of 300, 500 and 700 wW (RT) (a) and the timetion of response with

Figure 3.9 The response ot self-heated 80% wt SnOv/br-Os NW gas sensor versus time

at difterent power of 300, 500 and 700 ,W (RT) (a) and the fimetion of response with

Figure 3.10 Response and heating power graph of four fabricated sensors 4L

Figure 3.11 The response of self-heated 80% wt SnOyIn-O: NWWs gas sensor versus

time at different tempcrature of 200°C, 250 °C, 300 °C and 350 °C and the function of

Figtwe 3.12 Rssponse characferistic of [nsO; ~ nanowires gas sensor toward 5 ppm 11:5

Figure 3.14 Response to HS of the 80% w1 SnO2/i2O; NWs sensor used sel Heating

effect (Orange Tine) and seisor using the external heater at 200 °C (Blue linc) 44 Figure 3.15 Stability of sensor A External healer B Sel healed made 45 Figure 3.16 Selectivity of ImaO; NWS gas sensor toward NIIs, Ethanol and Il:S gas

Figuue 3.17 IsO› malcrisl H›§ ga sensing mechaniste -4?

LIST OF TABLES Table 1.1 Summary of publication reporting quantitative information about self-heated

‘Table 1.2 Publications reported self- heating effects in gas sensor using metal oxide

Table 3.1: Comparison with previous study at ITIMS with same approach method 44

INTRODUCTION

1 Foundation of the thesis

Since the first device was invented by the Greeks to manage the level of water using a floater, similar to those that are used today in water boxes to keep a water container at a constant level, sensors have been used to gather signals trom the environment for more

than 2000 years Many other sensors and actuators, include gas sensors, a branch of the sensor family, have been developed after a thousand years of development It's critical

to monitor gases, hnmidity, and moisture in areas including agriculture, medicine, and

industrial provesses Gas sensors are frequently used to monitor enviromental pollution

amd delect low concentrations of hazardous, flammuble, or explosive gases In many different industries and applications, such as smart building and smart home systerns,

environmental monitoring, and food quality monitoring, the usage of chemical sensor

devices to detect and measure pases has become truly indispensable

Recently, the Fourth Industzial Revolution is dramatically changing the world with Internet of Things (JoT), cloud computing, 3D Graphic, Augmented Reality, Machine learning, sensor technology and Artificial intelligence Among them, ol’ brings in a lot of advantages in almost aspects of human life ol is the result of the fusion of the intemet, wireless technology, and micro mechatronics technology, all of which have great utility and are beneficial to human society Gas sensors and sensor nodes ave cascnliad parts of cutting-edge communication sysicias like the Internet of Things

‘Modern seusor requiremmeuts for loT include: (1) dependability, (2) energy consumplion; (3) cost; (4) communication ability; and (5) data security With that being said, alongside with the high requirement of energy saving, promote researches of low power consumption devices are critically important

In addition, the metal oxide-based gas sensor requires thermal energy to activate the interaction between the analytic gas molecule and the sensing material Self-heated gas sensors have recently been developed to reduce the device's power usage It has been proved that Joule self-heating effect is nearly ideal for operating NW gas sensors at

1

ullralow power consumption, without external heators, Tn this thesis, we present an optimal fabrication pracess of froO; multiple NWs as well as the sensing capability of the scl&heated networked In.0; NWs effectively prepared by drop-casting method with

HS pas, Finally, 1 identify the hmitations of these sensors and highlight the most promismg approaches to enable the use of these technologies in real-world applications

2, Aims of the thesis

+ To sue

sfillly fabricate sufcheated yas

sor based on InzO3 NWs using the

chemical vapor deposition inethod (CVD) and drop-casting inethod

- To investigate the microstructure of the synthesized IO: NWs as well as comparing

seliheated operating mode with using external heater sensor sensitivity toward H2S gas

3 Research object and scope of the thesis

‘To implement this study with the above objectives, the thesis focused on researching the

following key issues:

+ Fabrication InO3 NWs and InOs, SuO2 composite NWs

- Survey of gas sensing properties, analy

of

Twternalional Scientific Training on scientific research matenals University

Tachnology-Hanoi

§ New contributions of the thesis

By CVD and drop-casting method, the author has successfully synthesized Ins; nanowires as well ás 8uOz/InaO; temowires which being used lo fabricate set-heated gas scusor, At the same time, the results of the thesis also prove the polential application

of In:Os material in the gas scnsor, especially with low power consumption advantage

6 Structure of the thesis

To achieve the proposed goals, the thesis was divided into the fullawing sections

Chapter 1: Overview

In this chapter, we present an overview of gas sensor and self-heated gas sensor as well

as introducing the InoOs, Sn NWs material

Chapter 2: Experimental approach

In this chapter, we present the technological process of manufacturing In,O5 nanowire

by the CVD method and fabrication of self-heated gas sensor based om In; NWs sbucture Intreducing the method of surveying morphology of the malevial, gas- sensitive and electric propertics of sctf-heated gus scrisor uscd in the thesis

Chapter 3: Result and conclusion

Conclusions and recommendations

In this section, the author has presented the conclusions of the thesis, including the

outstanding results that the thesis has achieved, the scientitic conclusions about the research content as well as limitations and research directions for the next studies.

CHAPTER 1 OVERVIEW 1.1 Gas sensor

According to the mechanism of detection, gas sensors made from various sensing

materials may be divided into categories One class of sensing techniques uses variations

in electric characteristics, while others use optic, auditory, chromatographic, and

calorimetric gas sensors The primary physical properties of the sensing material, such

as conductivity, permittivity, and work function, vary when the gas sensor is exposed to

the environment, as illustrated in Figure 1.1

Figure 1.1 Detection methods of semiconductor gas sensing materials [1]

The transducer - a component of the gas sensor, transforms these physical properties

into electrical signal that are measurable as resistance, capacitance, and inductance Thus, interfaces play a crucial role in determining the sensitivity and durability of sensing devices in electrically transduced semiconductor gas sensors because gas molecules directly interact with the sensing material It is necessary to build the sensing material in a way that it has a sizable exposed surface for interacting with gas molecules,

adequate active sites for binding these molecules, and the capacity to efficiently translate

these binding events into detectable signals For simple processing, these materials must also have specific mechanical qualities

Figure 1.2 Different material classes for gas sensing application [1]

Research into various gas sensing materials has been extensive and intense for decades

From the very beginning with metal oxides to conducting polymers, to carbon nanotubes

and continued with their composites and more recently 2D materials, as shown in Figure 1.2 Among them, metal oxides, commonly referred to as semiconducting oxides, continue to be the most widely used sensing material Numerous studies have employed and described various oxide materials The most important quality indicators of gas

sensor performance are sensitivity, selectivity, response and recovery time, stability, and

working temperature [2] These parameters of gas sensors based on SMOxs can be significantly improved by reducing the particle size to nanoscale, doping (or

modification) of the sensing material, and enhancement of sensor design [3]

Sensitivity indicates a change in the physical and/or chemical properties of the sensitive material in the presence of gas It is determined as the ratio of sensor's resistance in the atmosphere of the target gas to its resistance in the air if the target gas is an oxidizing

one

gu Be

Rair

and in the ease of the reductive gas as the ratio of the device's resistance in the air to its

Tesistance in the target gas almosphere

The analytical signal can also be defined as the absolute difference between the

Tesistanice of the sensing chament under the referee medium (air) and under the target

gas fo the resistance under the air where Rags is the resistance of the sensor clenent in

the atmosphere of the target gas, Olim; Rax is the resistance of the sensor clement in the

air, Ohm

Selectivity: the capacity of the semiconductor layer to differentiate belwcen a mix of

jargel gases or a single gas in the gas mixlure is known as selectivity To increase the

selectivity of gas scnsors, surface modification or bulk doping with various catalytic

additives is used for better adsorption of the target components |4],[5],|6] Previous

literature demonstrate that sensing materials based on SnO and TiC nanostructures

yield high selectivity sensors through either their surface modification with XM loading

or bulk doping with redox capable elements thus facilitating the selective gas detection

in mixed gas environments ‘I‘hese studies indicate that the improvement of sensing

performance in such cases is due to the creation of new active centers on the MO

surface om changing the electronic structure of material [3]

Stability or reproducibility is the ability of the gas sensors to provide repeatability of ingasurenent tesudts for the prolonged usage, The preheat treatment at temperatures

above the sensor operating temperatures improves the stability of the sensitive layers

Response fime dcormnines the poriod during which the parameter valuc chimes by a corlain percentage of ils initial value at the corlain gas com

iration

After considering gas sensing properties of metal oxides, it is necessary to reveal the

sing mechanism of molal oxide gas sensor There is ongoing debate on the precise

at adsorbed molecules and band bending induced by these charged molecules are

responsible for a change in conductivity The negative charge trapped in these oxygen

species causes an upward band bending and thus a reduced conductivity compared to

the flat band situation [7]

Figure 1.3 Sensing mechanism of metal oxide based gas sensor [1]

As shown in Figure 1,3, when O: molecules are adsorbed on the surface of metal oxides, they would extract electrons from the conduction band E, and trap the electrons at the

surface in the form of ions This will lead a band bending and an electron-depleted region The electron-depleted region is so called space-charge layer, of which thickness

is the length of band bending region Reaction of these oxygen species with reducing gases or a competitive adsorption and replacement of the adsorbed oxygen by other

molecules decreases and can reverse the band bending, resulting in an increased

conductivity The oxygen species, i.e O”, is the dominant at the operating temperature

of 300—-450°C which is the work temperature for most metal oxide gas sensors [5]

Adsorption phenomena, more specifically, the thermodynamics of gas adsorption on the surface of semiconductor materials, which are connected to temperature, play a key role

in the detection of a particular gas The temperature at which the equilibrium between

the adsorption and desorption rates is attained yields for a particular sensor the

maximum response for a given gas In addition, the activation energy of the reaction

7

taking place during the detection is reached at an optimum temperature, then the

optimization of the sensor working temperature by the detection of a target gas is usually

used to enhance the selectivity In general, the response and recovery times of a sensor

depend also on the temperature because the kinetic reactions between semiconductors

and gases are temperature dependent Then, at the low temperature, sensors have a long

response and recovery times because the kinetic reaction rate is low Therefore, conductometric gas sensors based on semiconductor especially metal oxide materials are a paradigmatic example of the need for temperature control and the challenges related to achieving it in a power efficient manner [2]

Several methods have been tested to reduce operating temperature as well as power consumption of metal oxide-based gas sensor, such as: surface coating sensor metal oxide layer with catalyst [16] or use of micro-heater as a component of the sensor Sung

Hoon Choa and his group has fabricated a micro-heater using a novel design of a poly-

Si in order to improve the uniformity of heat dissipation on the heating plate

Temperature uniformity of the micro-heater is achieved by compensating for the variation in power consumption around the perimeter of the heater

Toantmnum Tempersture of standard miero-nener ige temperature of standard micro-heater

ae aximons temperature of power compensated micro-heater

—>— average temperature of power compensated micro-heater

With the power compensated design, the uniform heating area is increased by 2.5 times and the average temperature goes up by 40 °C Power consumption and sensor temperature characteristic using fabricated micro heater is shown as Figure 1.4

Figure 1.5 Sang Clung Gwiy, Jae-Min Young group’s micro heater [9|

As shown in Figure 1.5, this micro heater consumes a power of 250 mW to heat up the

system to temperature of 400°C Sang Chung Gwiy and his co-author reported a micro

heater on polycrystalline 3C-SiC suspended membranes, The heater was designed for

an operating temperature up to about 800 °C and can be operated at about 500 °C with

a power of 312 mW The thermal coefficient of the resistance (TCR) of fabricated Pt

RTD’s is 3174.64 ppmv/*C In commercial field, as shown in Figure 1.6, a MEMS

microheater with lower power consumption which is 120 mW at the temperature of

500°C.

Figure 1.6 KMHP 100 commercial micro heater

Although researches in micro heater of gas sensor have gained a lot of achievement, its fabrication processes are still remains complex and requiring expensive equipment

1.2 Self-heated gas sensor

1.2.1 Self-heating effect

It has been understood that the electrical energy lost bya resistive component causes

the component's temperature to rise Even when just small amounts of electrical power

are used, the self-heating effect is pushed to such a small scale that the temperature

increase is remarkable A definition of the Efficient Self-Heating coefficient (ESH) has

been proposed:

AT

ESH = Pp

where AT is the temperature increase experimented by the device when it is subject to

electrical power dissipation P Different materials and device configurations lead to a

broad range of ESH values as shown in Table 1.1

Table 1.1 Stanmary af publication reporting quantitative information about self-

heated devices based on nanomaterial

wired Graphene Patterned, Single stip 2500 1 Graphlay< 7 1m

1.1.2, Research on nanowire based self-heated gas sensor

Due to their high surface-to-volume ratio, one-dimensional (1D) nanostructures, such as nanowires, nanorods, nanotubes, and nanofibers, have attracted considerable interest for

a wide range of applications, including catalysis, electronic devices, optoelectronic devices, storage devices, and gas sensors, Nanowires (NWs) and N\W-based heterostructures thanks to their peculiar properes such as high crystallinity, flexibility conductivity, and oplicel activity are key components of future sensing devices When electrically driven, rescarch using 1D nanowire has revealed an exta and unexpected benefit Even with the minimal elcetrical power expended during the eleetrival probing, they can nonetheless attain relatively high temperatures when put through clcetrieal tests (such as alectrical resistance measures, The self-heating effect makes it possible to

1

reduce the power consumption of nanoscale devices down to the microwatt regime Technically, the self-heating effect is just the consequence of the Joule dissipation of

power at a very small scale Simple figures about the power dissipated per unit volume

(ie the power density) can help to dramatic decrease the power consumption when it comes to large device scale As a matter of fact, one nanowire in self-heating operation can easily reach larger power densities than a conventional external heater

A decade of research on self-heated devices has shown that nanowire-like structures

have such a huge potential for efficient heating in miniaturized devices, which could be

of application in several fields of sensing and actuation Table 1.2 summarizes some of

the works reporting self- heating effects in electronic devices The community mostly

used two bottom-up approaches: either transferring a fully grown nanowire to a chip, placing it ina certain position, orienting it, and connecting it; or alternatively, attempting

the direct growth of the nanowire in the nght position in the final chip

Table 1.2 Publications reported self- heating effects in gas sensor using metal oxide

doped In:O; nanofibers

with gold coating for

20s reach the best

However, it is evident that the self-heating effect in nanowire-based devices can damage

or destroy them, similarly to well-known equivalent effects in other microelectronic components (Figure 1.7 (a-b)) The self-heated sensors operated with a Joule-heating effect can lead to thermal destruction of the networked NWs upon supplying heating

power Therefore, the heating power threshold should determine for long term stability

of the sensors

Figure 1.7 Single SnO: NW contacted with electron beam assisted platiman deposition in a

‘four probes configuration before (a) cand after (b) a few hours of operating in self-heating

mode

It was demonstrated that the self-heating effect could be controlled, not only with costly lab-class equipment but also with inexpensive commercial electronic components, paving the way to use nanowire-devices in consumer electronic products In that work, sel

heating was controlled and minimized in constant current operation

In any case, special care must be taken during device manipulation, connection, and

start-up stages to avoid static discharge effects and power peaks

1,3 In;O; materials in gas sensor

1.3.1, ImOs materials

Indium (IIT) oxide is one of the important metal oxides in the TCO group (Transparent

conducting oxides) including: G ~ ImeO: - §nO›, In:O; nanomaterials is an essential

and interesting nanomaterial for a number of applications, including solar cells,

photocatalysts, organic light emitting diodes, architectural glasses, panel displays

19

Number of studies on the synthesis of different structured In:O; like nanotubes,

nanowires [26], nanobelts, nanofibers, have been reported for wide applications In recent years, together with materials such as SnO», ZnO, In:O; material has received great attention in the manufacture of toxic gas sensors, biosensors[27], along with a

number of projects Some recent studies related to In:O3 nanostructured materials increase rapidly [28] In this session, we are given some overviews of the properties of

In.Os materials

Figure 1.8: In:O; crystalline structure

InzOs is wide band gap transparent n-type semiconductor (Eg ~ 3.6 eV) The crystal

structure and lattice parameters of InsO; crystal structure were studied by X-ray

diffraction method, the energy band structure of InsO; was studied by X-ray emission and absorption spectroscopy InOs crystal has a body-centered cubic structure - BCC

(body centered cubic), with lattice constant a= 10.118 A, InsO; unit cell has 80 atoms

in which 48 O anions are at the vertices, 8 In cations are at positions b-site, 24 cations

In at d-site, 16 O-anion vacancies (the b-site is the position where the two oxygen vacancies lie on the diagonal face of the lattice, and the d-site is the position where 2 oxygen vacancies lie on the block diagonal of the lattice cell) [29]

.2 ImOs nanowires in gas vensor

InzO3 NWs has been used for gas sensor fabrication towards various reducing and

such as ellanol [25][26], 138 [30], 1s [31], NOs[32] Well known to

oxidizing gz

improve the response and rceavery times of TO) mmostrustures scnsors, their

nanostructures size must be reduced or doping with convenient metal nanoparticles [35]

In addition, it is possible to obtain a matenal with a high sensitivity to gas sensing by controlling the morphology and structure of the material These materials should exhibit

a large surface to volume ratios There are many parameters of materials for gas sensor applications, for example, adsorption ability, catalytic activity, sensitivity,

thermodynamic stability, etc Many different metal oxide materials appear favorable in some of these properties, but very few of them are suitable to all requirements Mor this

situation, more recent works focus om composite materiafs, such as SnO2-7.nO [33]

Fe:03-2nO [34], ZnO-CuO [35] ete

There me several terwaics, quatemary, and complex metal oxides in addition to binary oxides that arc of interest for the aforementioned purposes, Much rescarch has also been done on the interaction between metal oxides and other substainces, such as orgame and carbon nanotubes, Here, we mostly use composite metal oxides as examples to ilustiate how chemical composition may have an impact The composite ZnO-SnO+ sensors exhibited significantly higher response than sensors constructed solely from tin dioxide

or zine oxide when tested under identical experimental conditions [36] Sensors based

on the two components mixed together are more sensitive than the individual

components alone suggesting 2

to butanal by tin dioxide, but that tin dioxide as relatively inefiective in the catalytic breakdown of butanal On the other hand, zine oxide catalysis the breakdown of butanal extremely effectively A combination of the two materials would effectively dehydrogenate bulanol aud then subsequently calalyze the breakdown of bulanal The