Semiconducting Metal Oxides for Gas Sensing

253 Pages·2019·11.668 MB·English

by  Yonghui Deng

Yonghui Deng
Semiconducting
Metal Oxides for
Gas Sensing
Semiconducting Metal Oxides for Gas Sensing
Yonghui Deng
Semiconducting Metal
Oxides for Gas Sensing
123
Yonghui Deng
Department ofChemistry
FudanUniversity
Shanghai, China
ISBN978-981-13-5852-4 ISBN978-981-13-5853-1 (eBook)
https://doi.org/10.1007/978-981-13-5853-1
LibraryofCongressControlNumber:2018965897
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This book is dedicated
To my wife, Ming and my son Tao. It is
because of your love and patience that
support my academic pursuit along with
enjoying happy life with you.
To my parents for giving me lasting love and
education that make me to be brave,
industrial, sympathetic and to be able to love
and understand…
To my brothers for giving me endless support
and sharing much more responsibility in
taking good care of our parents
Foreword
The past decades have witnessed the fast advance in science, technology, and
engineering of small, smart, and highly sensitive semiconducting metal oxides
(SMOs) gas sensors, which have found a broad range of applications including
detection of toxic and combustible gases, breath analysis in medical diagnosis,
food safety monitoring, and other industrial areas. Rapid developments in high-
performance SMO gas sensor require semiconducting metal oxide nanomaterials
with precise control of composition, morphology, surface-to-volume ratio, and
electrical properties. From the viewpoint of chemical synthesis and material
applications, how to achieve a good control over the composition, micro- or
nano-structures, and interface properties and how to understand the relationships
ofthese factorsandgassensingperformance ofSMOsarekey tothedevelopment
of modern intelligent gas sensors.
Inthisbook,theauthorsummarizesthecharacteristicsofSMOgassensors,with
an emphasis on basic properties, their principles of gas sensors, the progress that
hasbeenongoinginrefiningtheiroperationandthetrendsdefiningwhereprogress
is likely to take us in the future.
In particular, the book highlights the state-of-the-art progress in SMO gas sen-
sors based on different semiconducting metal oxides, strategies to improve the
performance,andvariousapplicationfields.Moreover,itpresentsanoutlookonthe
futuredevelopmentofSMOgassensors,includingmaterialdesignandgassensing
mechanism,nanodeviceandstructuredesign,andthedevelopment ofapplications.
This book also offers broad examples of recent developments in semiconducting
metal oxide gas sensors and an excellent introduction to applied physics, material
science, nano-electronics, and their various applications.
Shanghai, China Dongyuan Zhao
November 2018
vii
Preface
WiththedevelopmentofInternetofthings(IoT),gassensorsareshowingattractive
prospects in a wide range of application fields covering industrial processes,
environmentalmonitoring,andmedicaldiagnosis,etc.Amongvarioustypesofgas
sensors, the semiconducting metal oxides (SMOs) based ones have gained partic-
ularattentionduetotheirgoodsensitivityandlowcost,whicharehighlydesiredin
both technological and market demands. The current research about SMO-based
gas sensors focuses on the development of high-quality sensing materials and
design of optimal sensing devices to further improve the sensing performance to
meet the even increasing standard in practical applications.
This book focuses on semiconducting metal oxides as gas sensing materials,
especiallytherecentadvancesinnano-sizedSMOmaterialswithhighsurfacearea,
tunable morphology, and chemically micro-/nanostructure and crystal facet effect.
Various factors that have influence on the sensing performances of SMOs sensors,
such as chemical composition, nanostructure, and morphology, and surface prop-
erties of a SMO materials, are thoroughly discussed and analyzed in this book,
alongwiththein-depthelucidationonthegassensingmechanism.Theapplications
of gas sensors and some new interdisciplinary techniques, such as electronic-nose
(e-nose)devicesconsistingofmultisensorarrays,arealsohighlightedinthisbook.
This book offers researchers in the field of metal oxide nanomaterials and gas
sensor with relevantfrontier theories and concepts.Engineersworking onresearch
and development about semiconductor gas sensor can obtain new ideas in sensor
design and fabrication. And also, this book can serve as a valuable guidance for
newresearchersingassensingarea,providingthemwiththebasicsofmetaloxide
nanomaterials and the principle of gas sensors.
Thanks to many people in my research group who have helped with this book,
including Xinran Zhou, Yongheng Zhu, Junhao Ma, Yidong Zou and Yuan Ren.
Particularly, Xinran Zhou and Yongheng Zhu contributed a lot for their consci-
entious assistance in organizing and proofreading with the book. Thanks to Dr.
Mengchu Huang for his valuable suggestions on writing this book. Thanks to my
ix
x Preface
colleagues throughout the gas sensing community, who have guided me in this
field. Thanks to my collaborators, including Prof. Jiaqiang Xu, Prof. Xinxin Li,
Prof. Pengcheng Xu, Xiaowei Cheng and Prof. Wei Luo for their kind assistance,
support, and inspiration.
Shanghai, China Yonghui Deng
November 2018
Contents
1 Understanding Semiconducting Metal Oxide Gas Sensors . . . . . . . . 1
1.1 Development of Semiconducting Metal Oxide Gas Sensors. . . . . . 1
1.1.1 Kinds of Metal Oxides Used in Gas Sensors. . . . . . . . . . . 3
1.1.2 Ways to Enhance Properties of Metal Oxide
Semiconductors Gas Sensors . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Application of Semiconducting Metal Oxide Gas Sensors. . . . . . . 4
1.2.1 Use of Semiconductor Metal Oxide (SMO)
Sensors in Outdoor Air Quality Assessment . . . . . . . . . . . 5
1.2.2 Use of Semiconductor Metal Oxide (SMO)
Sensors in Indoor Air Quality Assessment. . . . . . . . . . . . . 5
1.2.3 Use of Semiconductor Metal Oxide (SMO)
Sensors in Disease Diagnosis . . . . . . . . . . . . . . . . . . . . . . 6
1.2.4 Use of Semiconductor Metal Oxide (SMO)
Sensors in Food Safety . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3 Physicochemical Properties of Semiconducting Metal Oxides . . . . 7
1.3.1 Definition of Semiconducting Metal Oxides . . . . . . . . . . . 8
1.3.2 Potential Performances. . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3.3 Physical Fundamental of Semiconducting
Metal Oxides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2 Sensing Mechanism and Evaluation Criteria of Semiconducting
Metal Oxides Gas Sensors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.1 Pure Metal Oxides Semiconductors . . . . . . . . . . . . . . . . . . . . . . . 24
2.1.1 N-Type Metal Oxides . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.1.2 P-Type Metal Oxides. . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.2 Metal Oxide Heterojunctions. . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.2.1 N–N Heterojunctions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.2.2 P–P Heterojunctions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.2.3 P–N Heterojunctions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
xi
xii Contents
2.3 Doped Metal Oxides Semiconductors . . . . . . . . . . . . . . . . . . . . . 36
2.4 Noble Metal Sensitized Metal Oxides . . . . . . . . . . . . . . . . . . . . . 38
2.5 The Effect of the Crystallite Size. . . . . . . . . . . . . . . . . . . . . . . . . 42
2.6 Gas Sensor Evaluation Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . 43
2.6.1 Sensitivity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
2.6.2 Operating Temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . 45
2.6.3 Selectivity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
2.6.4 Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
2.6.5 Response–Recovery Time . . . . . . . . . . . . . . . . . . . . . . . . 49
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3 Semiconducting Metal Oxides: Morphology and Sensing
Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.1 The Effect of Morphology and Structure on Gas Sensing . . . . . . . 53
3.1.1 Grain Size. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.1.2 Grain Phase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
3.1.3 Surface Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.1.4 Grain Networks, Porosity and the Area
of Inter-grain Contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
3.1.5 Agglomeration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3.2 Synthesis Approaches to Metal Oxide Sensing Materials. . . . . . . . 60
3.2.1 Sol–gel Synthesis of Metal Oxides . . . . . . . . . . . . . . . . . . 60
3.2.2 Hydro- and Solvothermal Synthesis . . . . . . . . . . . . . . . . . 61
3.2.3 Self-assembly Methods . . . . . . . . . . . . . . . . . . . . . . . . . . 65
3.2.4 Chemical Vapor Deposition (CVD) . . . . . . . . . . . . . . . . . 69
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
4 Semiconducting Metal Oxides: Composition and Sensing
Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
4.1 Binary Oxides Heterojunctions . . . . . . . . . . . . . . . . . . . . . . . . . . 78
4.1.1 P–N Heterojunctions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
4.1.2 N–N Heterojunctions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
4.1.3 P–P Heterojunctions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
4.2 Noble Metal Modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
4.3 Doping with Heteroatom. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4.3.1 Doping with Nonmetallic Elements. . . . . . . . . . . . . . . . . . 92
4.3.2 Doping with Metallic Elements . . . . . . . . . . . . . . . . . . . . 94
4.3.3 Doping with Rare Earth Elements. . . . . . . . . . . . . . . . . . . 96
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
5 Semiconducting Metal Oxides: Microstructure and Sensing
Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
5.1 Potential Features of Semiconducting Metal Oxides . . . . . . . . . . . 105
5.2 Structure Type and Typical Architectures. . . . . . . . . . . . . . . . . . . 106
5.3 Grain Size and Porous Structure . . . . . . . . . . . . . . . . . . . . . . . . . 114
5.4 Surface Area and Heterogeneous Interface . . . . . . . . . . . . . . . . . . 119
5.5 Crystal Structure and Internal Defects . . . . . . . . . . . . . . . . . . . . . 122
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129