Materials Horizons: From Nature to Nanomaterials

M. K. Jayaraj   Editor

Nanostructured Metal Oxides and DevicesOptical and Electrical Properties

Materials Horizons: From Natureto Nanomaterials

Series Editor

Vijay Kumar Thakur, School of Aerospace, Transport and Manufacturing,Cranfield University, Cranfield, UK

Materials are an indispensable part of human civilization since the inception of lifeon earth. With the passage of time, innumerable new materials have been exploredas well as developed and the search for new innovative materials continues briskly.Keeping in mind the immense perspectives of various classes of materials, thisseries aims at providing a comprehensive collection of works across the breadth ofmaterials research at cutting-edge interface of materials science with physics,chemistry, biology and engineering.

This series covers a galaxy of materials ranging from natural materials tonanomaterials. Some of the topics include but not limited to: biological materials,biomimetic materials, ceramics, composites, coatings, functional materials, glasses,inorganic materials, inorganic-organic hybrids, metals, membranes, magneticmaterials, manufacturing of materials, nanomaterials, organic materials andpigments to name a few. The series provides most timely and comprehensiveinformation on advanced synthesis, processing, characterization, manufacturing andapplications in a broad range of interdisciplinary fields in science, engineering andtechnology.

This series accepts both authored and edited works, including textbooks,monographs, reference works, and professional books. The books in this series willprovide a deep insight into the state-of-art ofMaterials Horizons and serve students,academic, government and industrial scientists involved in all aspects of materialsresearch.

More information about this series at http://www.springer.com/series/16122

M. K. JayarajEditor

Nanostructured Metal Oxidesand DevicesOptical and Electrical Properties

123

EditorM. K. JayarajDepartment of PhysicsCochin University of Science and TechnologyKochi, India

ISSN 2524-5384 ISSN 2524-5392 (electronic)Materials Horizons: From Nature to NanomaterialsISBN 978-981-15-3313-6 ISBN 978-981-15-3314-3 (eBook)https://doi.org/10.1007/978-981-15-3314-3

© Springer Nature Singapore Pte Ltd. 2020This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or partof the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations,recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmissionor information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilarmethodology now known or hereafter developed.The use of general descriptive names, registered names, trademarks, service marks, etc. in thispublication does not imply, even in the absence of a specific statement, that such names are exempt fromthe relevant protective laws and regulations and therefore free for general use.The publisher, the authors and the editors are safe to assume that the advice and information in thisbook are believed to be true and accurate at the date of publication. Neither the publisher nor theauthors or the editors give a warranty, expressed or implied, with respect to the material containedherein or for any errors or omissions that may have been made. The publisher remains neutral with regardto jurisdictional claims in published maps and institutional affiliations.

This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd.The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721,Singapore

To My Beloved Students……

Preface

The diverse range of optical, electrical and chemical properties exhibited by metaloxides makes them potential materials for fundamental research and technologicalapplications. The intriguing electronic structure of metal oxides has found theirapplications in different areas such as microelectronics, sensors, fuel cells, coatingsand catalysts.Wide band gap semiconducting oxides such as SnO2, ZnO and TiO2 arewidely being used as optical components, transparent conductors and gas sensors.Besides, millions of dollars’worth of metal oxides are employed in the chemical andpetrochemical industries as catalysts. Metal oxides are also under constant use ascatalysts for the removal of toxic gases for controlling environmental pollution.Manypotential applications are still being explored, and novel as well as facile synthesismethods are being developed. The advent of nanotechnology has triggered thedevelopment of nanostructures or nano-arrays with special properties when comparedto their bulk or single-particle counterparts. Nanostructured materials exhibit uniquephysical and chemical properties due to confinement effects at smaller sizes and a highdensity of corner or edge surface sites. The notable change in average particle size inturn alters the band gap of metal oxides which strongly influences their intrinsicelectrical conductivity and chemical reactivity. The less coordinated atoms atcorners/edges of metal oxide nanostructures or the presence of O vacancies createoccupied electronic states just above the valence band of the corresponding bulkmaterial, thereby enhancing the chemical activity of the nanostructures. In general,this book covers the fundamental science, synthesis, characterization, optoelectronicproperties and applications of metal oxide nanomaterials. The basic aspects of syn-thetic procedures and fabrication technologies are discussed, and the experimentaltechniques are explained. The current status of nanostructured oxide materials andrelated devices from a technological point of view is reviewed.

In this book, the two major aspects of metal oxide nanostructures, namely theiroptical and electrical properties, have been dealt with in detail. Each chapter iscontent-wise stand-alone though it shares a conceptual concurrence with the restof the chapters in terms of the optoelectronic properties of oxide nanomaterials. Thefirst five chapters help in understanding the optical characteristics of materials,especially metal oxides at nanoscale. A comprehensive idea on the luminescence

vii

observed in metal oxides and their wide-scale use in ACTFEL devices is included.The shift in research focus from sulphide-based phosphors to oxide-based lightemitters is briefly outlined. Various binary and ternary oxide-based phosphor systemmatrices are presented in detail. In the second chapter, different upconverted lumi-nescent nanomaterials along with the existing mechanisms of upconversion aresummarized. Reviews on the applications of upconverted materials in solar cell,bioimaging and security printing are also detailed in the discussions. The colloidssynthesized via liquid phase-pulsed laser ablation help in the growth of nanoparticleswithout any surfactants. The luminescent surfactant-free nanoparticles grown byLP-PLA technique can be used for bioimaging. The fabrication of symmetric andasymmetric quantum well structures based on ZnO with ZnMgO and CuGaO2 as thebarrier layer was realized by pulsed laser ablation technique. Moreover, the bookedifies another interesting phenomenon, surface-enhanced Raman scattering(SERS), exhibited by specially designed metal oxides nanostructures as substratesand their application as portable devices in the areas of sensing and bioimaging.

The electrical properties of metal oxides are found to span from insulators andsemiconductors to metals and even superconductors. Nanostructured metal oxidesthat exhibit a high optical transmittance along with high electrical conductivity,referred to as transparent conductive oxides, have also gained immense attraction inthe field of solar cells, gas sensors, field emitters, light-emitting diodes (LED),photo-catalysts, piezoelectric nanogenerators and nano-optoelectronic devices. Thisbook compiles the reach of oxide materials in the form of nanoparticles, nanorods,nanowires, nanofibers, etc. for various device applications. A brief review explainsthe different growth techniques developed for fabricating one-dimensional ZnOnanostructures and their applications in conventional two terminal devices likediodes, LEDs, solar cells, etc., three terminal devices like transistors and otherdevices like energy generators and memory devices. The chemiresistive nature ofmetal oxides as efficient gas sensors, the interesting change in the magneticstructure of metal oxide thin films as dilute magnetic semiconductors for spintronicapplications and the role of epitaxial growth of dielectric thin films for microwaveapplications are the other major highlights of this book. The gas-sensing mecha-nism of oxide-based sensors including heterojunction sensors like p–n junction,Schottky junction, etc. is elaborated along with some interesting results of theethanol response characteristic of p-CuO/n-ZnO junction sensor. The book alsogives an insight into the correlation of various experimental results on ZnO-baseddilute magnetic semiconductors with supporting theories and ab-initio calculations.In addition to a generic overview on metal oxide-based thin-film transistors, thebook has also accommodated an exclusive detailed description of the calculation oftrap density states in the band gap of semiconductors using temperature-dependentmeasurements. In short, the book is addressed focussing active researchers andacademicians in the area of material science and semiconductor technology,especially nano-photonics and electronics.

Kochi, India M. K. Jayaraj

viii Preface

Acknowledgements

It is with great pleasure and pride that I acknowledge all those who contributed inrealizing this book on Nanostructured Metal Oxides and Devices—Optical andElectrical Properties.

I extend my sincere thanks to all my former students Dr. Aneesh P. M.,Dr. Krishnaprasad P. S., Dr. Minikrishna K., Dr. Reshmi R., Dr. Arun Aravind,Dr. Vikas L. S., Dr. Hasna K., Dr. Subha P. P., Dr. Shijeesh M. R., Dr. AnjanaRadhakrishnan, Mr. Kurias K. M. and Ms. Jasna M., who did their doctoralresearch under my guidance at Nanophotonic and Optoelectronic DevicesLaboratory, Department of Physics, Cochin University of Science and Technology.They have contributed their research results meticulously for each chapter of thisbook. I also take this opportunity to thank with due regards my students, Mr. ManuShaji, Ms. Anju K. S., Mr. Midhun P. S., Mr. Subin P. S., Ms. Priya M. J.,Ms. Anamika Ashok, Ms. Krishnapriya T. K. and Mr. Frenson P. Jose, for proofreading and correcting the manuscript.

My sincere thanks to Dr. Pillai Aswathy Mohan, Assistant Professor,St. Stephens College, Pathanapuram, for helping me in the compilation and sub-mission of this book to Springer.

I record my gratitude to the Cochin University of Science and Technology forthe sabbatical leave, which gave me enough opportunity to invest my time on thisbook.

I extend my warm regards and gratitude to my family, especially my wifeDr. Vanaja, and my children, Ms. Anooja and Ms. Anjala, for providing me all thepersonal and cordial support to make my academic life fruitful.

It was a pleasant experience to work with the Springer Editorial team whoenabled the timely publication of the book.

Prof. M. K. Jayaraj

ix

Contents

1 Oxide Luminescent Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1K. Mini Krishna and M. K. Jayaraj

2 Upconversion Nanophosphors: An Overview . . . . . . . . . . . . . . . . . 47Kurias K. Markose, R. Anjana and M. K. Jayaraj

3 Optical Properties of Metal, Semiconductor and CeramicNanostructures Grown by Liquid Phase-PulsedLaser Ablation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103P. M. Aneesh and M. K. Jayaraj

4 Optical Properties of Quantum Well Structures . . . . . . . . . . . . . . . 129P. M. Aneesh, R. Reshmi and M. K. Jayaraj

5 Metal Oxides-Based SERS Substrates . . . . . . . . . . . . . . . . . . . . . . . 155Kudilatt Hasna and M. K. Jayaraj

6 One-Dimensional ZnO Nanostructure: Growth & DeviceApplications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177L. S. Vikas, K. A. Vanaja and M. K. Jayaraj

7 Metal Oxide Semiconductor Gas Sensors . . . . . . . . . . . . . . . . . . . . 211Subha P. P, Pillai Aswathy Mohan and M. K. Jayaraj

8 Zno-Based Dilute Magnetic Semiconductors . . . . . . . . . . . . . . . . . . 233Arun Aravind and M. K. Jayaraj

9 Domain Matched Epitaxial Growth of Dielectric Thin Films . . . . . 271P. S. Krishnaprasad and M. K. Jayaraj

10 Metal-Oxide Transistors and Calculation of the Trap Densityof States in the Band Gap of Semiconductors . . . . . . . . . . . . . . . . . 303M. R. Shijeesh, M. Jasna and M. K. Jayaraj

xi

Editor and Contributors

About the Editor

Dr. M. K. Jayaraj is currently a Professor at the Department of Physics, CochinUniversity of Science and Technology (CUSAT), India. He earned his master’s andPh.D. from CUSAT, and completed his postdoctoral research at eminent institutionsin India, Italy, France, Japan, and the USA. He is the founder director of the Centreof Excellence in Advanced materials, CUSAT. He is also the mentor of ‘DelgadoCoating & Technology Solutions Private Limited’. Dr. Jayaraj is a pioneer in thefield of thin-film and nanocomposite devices, including sensors/detectors andenergy converters, and transparent conductors for photovoltaics. He has more than180 research publications, several edited books and book chapters, and patents tohis credit. In addition, he was honored with the MRSI Medal 2019, conferred by theMaterials Research Society of India.

Contributors

P. M. Aneesh Department of Physics, Central University of Kerala, Kasaragod,Kerala, India

R. Anjana Department of Physics, Cochin University of Science and Technology,Kochi, India

Arun Aravind Centre for Advanced Functional Materials, Department of Physics,Bishop Moore College, Mavelikkara, India

Kudilatt Hasna Government Arts and Science College, Calicut, India

M. Jasna Cochin University of Science and Technology, Kochi, India

M. K. Jayaraj Department of Physics, Cochin University of Science andTechnology, Kochi, India

xiii

P. S. Krishnaprasad Government Polytechnic College, Kothamangalam, India

Kurias K. Markose Department of Physics, Cochin University of Science andTechnology, Kochi, India

K. Mini Krishna Department of Physics, Vimala College, Thrissur, Kerala, India

Pillai Aswathy Mohan St. Stephen’s College, Pathanapuram, India

R. Reshmi Department of Physics, Union Christian College, Aluva, Kerala, India

M. R. Shijeesh Graphene & 2D Systems Laboratory, Department of Physics,Indian Institute of Technology Madras, Chennai, India

Subha P. P Department of Physics, Cochin University of Science andTechnology, Kochi, India

K. A. Vanaja Maharaja’s College, Ernakulam, India

L. S. Vikas Department of Physics, Govt. Arts College, Thiruvananthapuram,Kerala, India

xiv Editor and Contributors

Abbreviations

0D Zero dimensional1D One dimensional2DEG Two-dimensional electron gas3D Three dimensional4-MBA 4-Mercaptobenzoic acid4-Mpy 4-MercaptopyridineA ActivatorAA Amino hexanoic acidACPEL Alternating current powder electroluminescent displayACTFEL Alternating current thin-film electroluminescent displayAFM Atomic force microscopyAHE Anomalous Hall effectAl2O3 Aluminium oxideALD Atomic layer depositionALE Atomic layer epitaxyAOS Amorphous oxide semiconductorAPTE Addition de photon par transfertsd'energiesATO Antimony-doped tin oxideBMP Bound magnetic polaronBR Bloembergen–RowlandBST Barium strontium titanateBT Benzene thiolBZN Bismuth zinc niobateC2H4(NH2)2 EthylenediamineC2H6OS Dimethyl sulphoxideC6H12N4 HexamethylenetetramineCB Conduction bandCdO Cadmium oxideCE Chemical enhancement

xv

CF Crystal fieldCH3(CH2)11OSO3Na Sodium dodecyl sulphateCIE International commission on illuminationCL CathodoluminescenceCMR Colossal magnetoresistanceCR Cross-relaxationCRT Cathode ray tubec-Si Crystalline siliconCSU Cooperative sensitization upconversionCT Charge transferCTAB Cetyltrimethylammonium bromideCTS Charge transfer stateCuGaO2 Copper gallium oxideCVD Chemical vapour depositionDBR Distributed Bragg reflectorDCEL Direct current electroluminescent displayDME Domain matching epitaxyDMS Dilute magnetic semiconductorsDMSO Dimethyl sulphoxideDNA Deoxyribonucleic acidDOS Density of statesDRAM Dynamic random-access memoryDSSC Dye-sensitized solar cellE Excited stateEA Activation energyEBE Electron beam evaporationEBL Electron beam lithographyEDA EthylenediamineEDTA Ethylenediaminetetraacetic acidEG Ethylene glycolEL ElectroluminescenceEM ElectromagneticEMU Energy migration-mediated upconversionEQE External quantum efficiencyESA Excited state absorptionETU Energy transfer upconversionFC Field cooledFED Field emission displayFESEM Field emission scanning electron microscopyFET Field-effect transistorsFeTFT Ferroelectric thin-films transistorsFIB Focused ion beamFPD Flat panel displayFRET Förster resonance energy transfer or fluorescence resonance

energy transfer

xvi Abbreviations

FT-IR Fourier transform infrared spectroscopyFWHM Full width at half maximumG Ground stateGaN Gallium nitrideGMR Giant magnetoresistanceGSA Ground state absorptionHAp HydroxyapatiteHMTA HexamethylenetetramineHOMO Highest occupied orbitalHRTEM High-resolution transmission electron microscopyHRXRD High-resolution X-ray diffractionHVPE Halide vapour phase epitaxyIC Internal conversionICP-AES Inductively coupled plasma atomic emission spectroscopyID Drain currentIDC Interdigital capacitorIR InfraredISC Intersystem crossingITO Indium tin oxideIUPAC International Union of Pure and Applied ChemistryKPFM Kelvin probe microscopyLCD Liquid-crystal displayLDA Local-density approximationLED Light-emitting diodeLFM Lateral force microscopyLME Lattice matching epitaxyLP-PLA Liquid phase-pulsed laser ablationLSI Large-scale integrated circuitLUMO Lowest unoccupied molecular orbitalLVCL Low voltage cathodoluminescentMBE Molecular beam epitaxyMCD Magnetic circular dichroismMEMS Micro-electro-mechanical systemsMgO Magnesium oxideMIS Metal–insulator–semiconductorMISIM Metal–insulator–semiconductor–insulator–metalMOCVD Metal organic chemical vapour depositionMOS Metal oxide semiconductor gas sensorsMOSFET Metal oxide field-effect transistorMOVPE Metal organic vapour phase epitaxyMPMS Magnetic property measurement systemMQW Multiple quantum wellMRAM Magnetic random-access memoryMS Saturation magnetizationMTJs Magnetic tunnel junctions

Abbreviations xvii

NaOH Sodium hydroxideNd:YAG Neodymium-doped yttrium aluminium garnetNED Nano-emissive displayNEG Nippon Electric GlassNH4OH Ammonium hydroxideNIL Nano-imprint lithographyNIR Near infraredNMR Nuclear magnetic resonance spectroscopyNP Nano phosphorsNPs NanoparticlesOA Oleic acidODE 1-octadeceneOLED Organic light-emitting diodeOM OleylamineOTFT Organic thin-film transistorP3HT Poly(3-hexylthiophene-2,5-diyl)PA Photon avalanchePAA Polyacrylic acidPB Propagation breakdownPCE Photoconversion efficiencyPCVD Plasma chemical vapour depositionPDA Personal digital assistantPDP Plasma display panelPEDOT Poly3,4-ethylene dioxythiophenePEG Polyethylene glycolPEI PolyethyleniminePET Polyethylene terephthalatePICT Photoinduced charge transferPL PhotoluminescencePLD Pulsed laser depositionPMMA Polymethyl methacrylatePPC Parallel plate capacitorPTCDI-C8 N,n′-dioctyl-3,4,9,10-perylenedicarboximidePV PhotovoltaicPVA Polyvinyl alcoholPVP PolyvinylpyrrolidoneQC Quantum cascadeR6G Rhodamine-6gRE Rare earthRGB Red green blueRKKY Ruderman–Kittel–Kasuya–YosidaRSO Reciprocating sample optionRTA Rapid thermal annealingRTFM Room temperature ferromagnetism

xviii Abbreviations

S SensitizerSAED Selected area electron diffractionSAW Surface acoustic wavesSERS Surface-enhanced Raman scatteringSHB Self-healing breakdownSHG Second-harmonic generationSPM Scanning probe microscopySPR Surface plasmon resonanceSQ Shockley–QueisserSQUID Superconducting quantum interference deviceSQW Single quantum wellSTM Scanning tunnelling microscopySTPA Simultaneous two-photon absorptionTAMRA N,n,n′,n′-tetramethyl-6-carboxyrhodamineTC Curie temperatureTCNQ 7,7,8,8-tetracyanoquinodimethaneTCO Transparent conducting oxideTDEL Thick-film dielectric electroluminescenceTEM Transmission electron microscopeTFEL Thin-film electroluminescent displayTFT Thin-film transistorTM Transition metalTMOs Transition metal oxidesTMR Tunnel magnetoresistanceTOPO Tri-n-octylphosphine oxideTSO Transparent semiconducting oxideTTIP Titanium tetraisopropoxideUC UpconversionUCNPs Upconversion nano phosphorsUCQY Upconversion quantum yieldUV UltravioletV0 Vacancy of oxygenVB Valence bandVDS Drain-source voltageVFD Vacuum fluorescent displayVGS Gate-source voltageVLS Vapour liquid solidVLSI Very large-scale integrated circuitVOCs Volatile organic compoundsVPE Vapour phase epitaxyVT Threshold voltageXPS X-ray photoelectron spectroscopyZFC Zero field cooledZn(C5H7O2)2 Zinc acetylacetonate

Abbreviations xix

Zn(COOH)2 Zinc acetateZn(NO3)2 Zinc nitrateZni Zinc interstitialZnMgO Zinc magnesium oxideZnO Zinc oxideZnO:TM Transition metal-doped ZnOZnSO4 Zinc sulphateZTO Zinc tin oxideµB Bohr magneton

xx Abbreviations

List of Figures

Chapter 1

Fig. 1 Configuration coordinate diagram (left) and Jablonski diagram(right) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Fig. 2 Radiative recombination involving impurity levels: a conductionband–acceptor-state transition, b donor-state–valence bandtransition, c donor–acceptor recombination and d bound–excitonrecombination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Fig. 3 Sensitized luminescence: a emission reabsorption, b resonanceradiationless and c non-resonance radiationless. . . . . . . . . . . . . . . 8

Fig. 4 Schematic representation of display evolution. . . . . . . . . . . . . . . . 11Fig. 5 TFEL displays for use in industrial, medical, transportation,

military, public safety and other demanding applications(Courtesy Lumineq) (left) and transparent TFELdisplay (right) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Fig. 6 Comparison between the four types of EL displays . . . . . . . . . . . 13Fig. 7 Three general configurations of TFEL devices—

a MISIM-structured, b inverted MISIM and c dielectric/ceramicsubstrate-based . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Fig. 8 a Equivalent circuit of an ideal ACTFEL device and b idealI–V characteristics of the nonlinear resistorof the phosphor layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Fig. 9 Energy band diagram of ACTFEL device. . . . . . . . . . . . . . . . . . . 17Fig. 10 The typical device structure of a TFEL device. A pixel on

display is lit by applying a voltage to the row and columnelectrodes, thus causing the area of intersection to emit light . . . . 18

Fig. 11 Space charge-induced band bending of the phosphor layerin ACTFEL device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Fig. 12 Spinel structure of ZnGa2O4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Fig. 13 Ga3+-level splitting in an octahedral environment . . . . . . . . . . . . . 31

xxi

Fig. 14 Two different types of crystal structures in Y2O3 unit cell;C2 (vacancies along the face diagonal) and S6 (vacancies alongthe body diagonal) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Fig. 15 EL emission spectra of NEG/ITO/ATO/ZnGa2O4:Dy3+/BTO/Al

(Device A) and NEG/ITO/ATO/ZnO/ZnGa2O4:Dy3+/BTO/Al

(Device B) at a drive frequency 1.5 kHz for various appliedvoltages V (left) and luminance–voltage (L–V) curveof Devices A and B along with the L versus V−1/2 semilogplot (right) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Fig. 16 XRD patterns of the active ZnGa2O4:Mn2+ layer depositedat 600 °C on quartz substrates for a duration of (a) 45 min,(b) 60 min, (c) 90 min, (d) 120 min and (e) at 500 °C for 90 min(left-top) EL spectra of the ZnGa2O4:Mn2+ active ACTFELdevices fabricated with different phosphor layer thicknesses(right-top) and L–V curves of the devices fabricated (left-bottom)EL spectra of ZGO-4 device recorded for various appliedvoltages when excited at 1 kHz (right-bottom) . . . . . . . . . . . . . . . 38

Fig. 17 Chromaticity coordinate diagram indicating the CIEcoordinates of the fabricated ACTFEL devicesNEG/ITO/ATO/ZnO/ZnGa2O4:Dy

3+/BTO/Al (left)and NEG/ITO/ATO/ZnGa2O4:Mn2+/BTO/Al (right) . . . . . . . . . . . 39

Chapter 2

Fig. 1 Images of various a–c upconversion emissionsand d luminescence from perovskite material . . . . . . . . . . . . . . . . 48

Fig. 2 Anti-Stoke’s emission processes: a STPA, b SHG,and c UC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Fig. 3 Schematic diagram showing the applications of upconversionnanoparticles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Fig. 4 Excited-state absorption. G1, E1, and E2 represent the groundlevel, intermediate level, and the excited state, respectively . . . . . 51

Fig. 5 Energy transfer upconversion (ETU). G1, E1, and E2 representthe ground level, intermediate level, and the excited state,respectively. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Fig. 6 Energy-level diagram of Er3+/Yb3+ co-doped system . . . . . . . . . . 53Fig. 7 Cooperative sensitization upconversion. . . . . . . . . . . . . . . . . . . . . 54Fig. 8 a, b Double log plots of CSU emission of Tb-doped NaYbF4

as a function of excitation power. c The schematic diagramof the CSU mechanism in NaYbF4:Tb phosphor. Reprintedwith permission from [38] Copyright © 2016, AmericanChemical Society . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Fig. 9 Schematic of cross-relaxation energy transfer between Tm3+ . . . . 56Fig. 10 Photon avalanche upconversion . . . . . . . . . . . . . . . . . . . . . . . . . . 57

xxii List of Figures

Fig. 11 EMU upconversion mechanism observed in core–shell structures(core–shell regions are shown in different colors. The “nx”indicates random hopping through many type-3 ions).Adapted with permission from [43], Copyright @ 2011,Springer Nature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Fig. 12 Different interactions reasonable for the loss of degenerationof lanthanide 4f free ion (HC–Coulombic, HSO–spin–orbit,and HCF–crystal field interactions) . . . . . . . . . . . . . . . . . . . . . . . . 61

Fig. 13 Dieke diagram: partial energy diagrams for the lanthanideions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Fig. 14 Typical host lattice with activator alone and activatorand sensitizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Fig. 15 UC luminescence spectra of Yb3+/Er3+ co-doped a YF3, b YOFand c Y2O3 under 980 nm laser illumination and d the intensityratio of red and green bands are shown at a laser power of 16.6mW. Reprinted with permission from [15] Copyright © 2018,Elsevier) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Fig. 16 Schematic diagram shows the energy transfer in Yb/Er co-dopedsystem under 980 nm excitation. Reprinted with permission from[15] Copyright @ 2018, Elsevier . . . . . . . . . . . . . . . . . . . . . . . . . 66

Fig. 17 Dependence of upconversion emission on sensitizerconcentration. a Upconversion luminescence spectrum obtainedfrom 2% Er3+, x% Yb3+: YF3, b variation of red/green intensityratio on Yb3+ concentration, and c CIE color coordinate diagramshowing the variation of emission color with Yb3+ concentration,photographs of emission from 2% Er3+, x% Yb3+:YF3for x = d 0, e 2, f 6, g 10, h 20 . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Fig. 18 Schematic energy-level diagram and energy transfer mechanismof Er, Yb, Mo co-doped system © IOP Publishing. Reproducedwith permission [58]. All rights reserved . . . . . . . . . . . . . . . . . . . 69

Fig. 19 a UC emission intensity dependence on excitation power(980 nm) in a Yb/Er co-doped Y2O3 phosphor and b log–log plotof intensities of the 650 nm (green) and 520 nm (red) emissionbands versus excitation power (980 nm). . . . . . . . . . . . . . . . . . . . 71

Fig. 20 SEM images of Yb3+/Er3+ co-doped a YF3, b YOF, and c Y2O3

UCNPs synthesized by co-precipitation method followedby annealing process (scale: 300 nm, inset is the magnifiedview). Reprinted with permission from [15] copyright @ 2018,Elsevier. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Fig. 21 Solar spectral loss due to various mechanismsin the solar cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Fig. 22 Schematic diagram showing how the upconversion layerworks in solar cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

List of Figures xxiii

Fig. 23 Semiconductor bandgap and efficiency comparisonsof different solar cell absorbers . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Fig. 24 J-V characteristics of a-Si:H solar cell with a YF3 UC phosphor,b YOF UC phosphor, and c Y2O3 UC phosphor with 980 nm IRillumination. d J-V characteristics of a-Si:H solar cell with thethree Yb3+/Er3+ doped phosphors, undoped host material underAM 1.5 M illumination along with 980 nm NIR radiation.Reprinted with permission from [15] copyright @ 2018,Elsevier. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

Fig. 25 A typical schematic configuration of a DSSC equippedwith upconverters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Fig. 26 Surface modification of amine-functionalized upconversionnanoparticles using different biomolecules. Reagents:succinimidyl iodoacetate (SIA), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC),succinimidyl ester (NHS), and N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP) [134] . . . . . . . . . . . . . . . . . . 86

Fig. 27 a In vitro cell imaging and b in vivo imaging of mouse usingUCNPs where red color indicates emission from UCNPs.Reprinted (adapted) with permission from [137]Copyright @ 2008, American Chemical Society. . . . . . . . . . . . . . 87

Fig. 28 Schematic diagram of showing multifunctionality of porousUCNP in the diseased cell [142]. . . . . . . . . . . . . . . . . . . . . . . . . . 88

Fig. 29 Analyte detection using FRET-based energy transfer . . . . . . . . . . 89Fig. 30 Photographs of different step involving in the printing of UC

security ink QR code and the printed QR code prototype.Reprinted with permission from [154] Copyright © IOPPublishing, 2012. All rights reserved . . . . . . . . . . . . . . . . . . . . . . 91

Chapter 3

Fig. 1 Experimental setup for the LP-PLA technique . . . . . . . . . . . . . . . 105Fig. 2 The UV-Vis absorption spectra of silver and gold nanoparticles

grown by LP-PLA technique at a laser fluenceof 1.2 J/cm2 for 1 h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

Fig. 3 UV-Vis absorption spectra of colloidal Au nanoparticlesprepared at different laser fluences . . . . . . . . . . . . . . . . . . . . . . . . 110

Fig. 4 UV-Vis absorption spectra of silver nanoparticles preparedat different laser fluences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

Fig. 5 a and d TEM, b and e size histograms, inset of b and e HRTEM,c and f SAED patterns of Au nanoparticles preparedat 1.2 (top row) and 3.8 J/cm2 (bottom row) . . . . . . . . . . . . . . . . 111

xxiv List of Figures

Fig. 6 HRTEM of Ag nanoparticles grown at a laser fluenceof a 1.2 J/cm2 and c 3.8 J/cm2. b and d represent the SAEDpattern of Ag nanoparticles (inset shows the parallel linesof atoms) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

Fig. 7 UV-Vis absorption spectra of Au nanoparticles grown at variousduration of ablation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

Fig. 8 UV-Vis absorption spectra of silver nanoparticles grownat a laser fluence of 1.2 J/cm2 for different durationsof ablation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

Fig. 9 Variation of size of the LP-PLA grown ZnO NPs with laserfluence [83]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

Fig. 10 a TEM image of ZnO NPs; b histogram representing sizedistribution; c SAED patterns matching hexagonal ZnO NPsprepared by LP-PLA technique with a fluence of 25 mJ/pulsein water. d HRTEM image for a single ZnO nanoparticleshowing (002) crystalline plane and inset shows the stackingin hexagonal close-packed mode [66] . . . . . . . . . . . . . . . . . . . . . . 116

Fig. 11 TEM image of zinc oxide NPs grown by LP-PLA in watera oxygen atmosphere; b with nitrogen atmosphereand c without any gases [83] . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

Fig. 12 a PL emission spectra of ZnO NPs grown without (curve I)and with (curve II) oxygen atmosphere at an excitationwavelength of 345 nm. c The photograph of synthesizedtransparent ZnO NPs and d its yellow PL emission under UVexcitation. b The bluish-violet PL from the NPs grown in oxygenatmosphere [66] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

Fig. 13 a HRTEM image and b SAED pattern of ZnO NPs synthesizedin acid media by LP-PLA method [83]. . . . . . . . . . . . . . . . . . . . . 118

Fig. 14 a HRTEM image and b SAED pattern of ZnO NPs synthesizedin basic media by LP-PLA method. . . . . . . . . . . . . . . . . . . . . . . . 119

Fig. 15 HRTEM image (left) and SAED pattern (right) of Eu:HApnanoparticles grown by LP-PLA technique. . . . . . . . . . . . . . . . . . 121

Fig. 16 PL emission spectra of Eu-doped HAp nanoparticles grownat different laser fluences. Inset shows the variationof PL intensity with laser fluence . . . . . . . . . . . . . . . . . . . . . . . . . 122

Fig. 17 PL spectra of Eu-doped HAp nanoparticles grown for differentduration of ablation. Inset shows variation of PL intensitywith duration of ablation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

Fig. 18 TEM images of Eu-doped HAp nanoparticles grown at differentduration of ablation. a 2 h and b 4 h . . . . . . . . . . . . . . . . . . . . . . 123

Fig. 19 Luminescence excitation (left) and emission (right) spectra undervisible excitation of Eu-doped HAp nanoparticles . . . . . . . . . . . . 123

List of Figures xxv

Chapter 4

Fig. 1 Band diagram of type I quantum well structures formedby n-type semiconductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

Fig. 2 Band diagram of n-type semiconductors forming type IIquantum well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

Fig. 3 Schematic illustration of quantum well structures and densityof states . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

Fig. 4 Variation of band gap at room temperature of AxZn(1−x)O alloyand its lattice parameters [21] . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

Fig. 5 Band gap energies of ZnO and 5 at.% Mg and Cd-doped ZnOthin films grown by PLD [22] . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

Fig. 6 Transmission spectra of Zn0.8Mg0.2O, Zn0.9Mg0.1O and ZnOfilms grown on quartz substrate by PLD. . . . . . . . . . . . . . . . . . . . 137

Fig. 7 Transmission spectra of ZnO and 5% Mg and Cd-doped ZnOfilms grown by PLD [22] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

Fig. 8 Band diagram of the ZnMgO/ZnO/ZnMgO symmetric MQWsystems grown by PLD [38] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

Fig. 9 Room-temperature PL emission (kex = 266 nm)of ZnMgO/ZnO/ZnMgO symmetric MQW grown with thirdharmonic of Nd:YAG laser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

Fig. 10 Low-temperature PL (a 77–160 K and b 180–280 K)of symmetric ZnMgO/ZnO/ZnMgO MQW at an excitationof kex = 266 nm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

Fig. 11 Room-temperature PL emission of ZnMgO/ZnO/ZnMgOsymmetric MQW grown with fourth harmonic of Nd:YAG laser(kex = 266 nm) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142

Fig. 12 Low-temperature PL emission of symmetricZnMgO/ZnO/ZnMgO MQW grown by PLD [53]. . . . . . . . . . . . . 143

Fig. 13 Variation of PL integral intensity with temperatureof the ZnMgO/ZnO/ZnMgO symmetric MQW grownby PLD [53] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

Fig. 14 Variation of FWHM and PL peak positionof ZnMgO/ZnO/ZnMgO symmetric MQWwith temperature [53] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

Fig. 15 Room-temperature PL emission spectraof ZnMgO/ZnO/ZnMgO symmetric MQWs for ZnOconfinement layer thickness 2 and 6 nm [53] . . . . . . . . . . . . . . . . 144

Fig. 16 Sample cross sections and band diagram of the asymmetricMQW CuGaO2/ZnO/ZnMgO structure grown by PLD [53] . . . . . 146

Fig. 17 Cross-sectional TEM image of the asymmetric MQWCuGaO2/ZnO/ZnMgO structures grown by pulsed laserdeposition [53] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

xxvi List of Figures

Fig. 18 Low-temperature PL of asymmetric CuGaO2/ZnO/ZnMgOMQW grown by PLD [53] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

Fig. 19 Temperature-dependent PL integral intensity of CuGaO2/ZnO/ZnMgO asymmetric MQW grown by PLD [53] . . . . . . . . . . 148

Fig. 20 Variation of FWHM and PL peak position of CuGaO2/ZnO/ZnMgO asymmetric MQW with temperature [53] . . . . . . . . 148

Fig. 21 Room-temperature PL emission from asymmetric MQWCuGaO2/ZnO/ZnMgO with ZnO confinement layer thicknessof 2 and 6 nm [53] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

Fig. 22 Normalized room-temperature PL spectra of ZnO film,CuGaO2/ZnO/ZnMgO asymmetric and ZnMgO/ZnO/ZnMgOsymmetric MQW structures [53]. . . . . . . . . . . . . . . . . . . . . . . . . . 150

Chapter 5

Fig. 1 Field enhancement in metal nanostructures (red colour representregion of enhanced electric field) . . . . . . . . . . . . . . . . . . . . . . . . . 157

Fig. 2 FESEM images of silicon master with triangular pits with edgelength 200 nm a top view, b large area view, c depth view andd its replica in PMMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

Fig. 3 SERS spectra of 103 M BT on nanotriangular pillar arraysof edge length 200 nm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

Fig. 4 Schematic of decoration of Ag on TiO2 nanorods . . . . . . . . . . . . 162Fig. 5 FESEM image of TiO2 nanorods synthesized via solvothermal

method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162Fig. 6 TEM image of TiO2 nanorods decorated with silver

nanoparticles for a decoration cycle of a one, b sixand c seven. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

Fig. 7 SERS activity of Ag-TiO2 using 10−5 M R6G molecules. . . . . . . 163Fig. 8 Schematic of recycling nature of Ag-TiO2-based SERS

substrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164Fig. 9 Raman signal from Ag-TiO2-based substrate after

photodegradation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165Fig. 10 SERS spectra of 10−5 M R6G molecule from as-prepared

substrate and recycled substrate . . . . . . . . . . . . . . . . . . . . . . . . . . 165Fig. 11 Possible charge transfer during PICT . . . . . . . . . . . . . . . . . . . . . . 168Fig. 12 a XRD spectra of TiO2 nanoparticles and b FESEM image

of TiO2 nanoparticles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169Fig. 13 Model for adsorption of 4-MBA molecules onto TiO2

nanoparticles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169Fig. 14 Normal Raman spectra of bulk 4-MBA and SERS spectra

of 10−3 M 4-MBA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170Fig. 15 Photoluminescence spectra from TiO2 nanoparticles

under 517 nm excitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

List of Figures xxvii

Fig. 16 SERS activity of TiO2 nanoparticles for different annealingtemperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

Fig. 17 Model for PICT mechanism in TiO2-4-MBA complex . . . . . . . . . 171

Chapter 6

Fig. 1 a The total number of publications based on various oxidematerials in the past 28 years. b The rising trend in a numberof publications of ZnO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178

Fig. 2 Comparison of electron transport in a 0D nanostructuresand b 1D nanostructures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179

Fig. 3 a Band diagram and b V–I characteristics of p-CuO/n-ZnOheterojunction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185

Fig. 4 Capacitance–voltage characteristics of the p-CuO/n-ZnOnanorod heterojunction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187

Fig. 5 a Photoluminescence emission from GaN:Mg substrate,ZnO/GaN heterojunction, before (Zn) and after(GZnA)annealing. b Electroluminescence from as-prepared (GZn)and annealed (GZnA) devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . 191

Fig. 6 Schematic diagram of the arrangement for measuringthe response of the detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192

Fig. 7 Photoresponse of a typical detector. . . . . . . . . . . . . . . . . . . . . . . . 192Fig. 8 Well-ordered hexagonal facets of ZnO nanorods grown

by hydrothermal synthesis over Mg:GaN substrate (a).The high-resolution reciprocal space map of (0002) peakof ZnO nanorods over GaN substrate (b) . . . . . . . . . . . . . . . . . . . 195

Fig. 9 a UV response of ZnO/GaN heterojunction for UV light pulsesof 325 nm He-Cd laser light and b the photoresponseof the device for various wavelengths. . . . . . . . . . . . . . . . . . . . . . 195

Fig. 10 Schematic diagram of top gate staggered structure (a) andbottom gate (inverted) staggered structure (b) of nanorod-basedtransistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

Fig. 11 The FESEM image shows the implementation of a single ZnOnanorod-based top gate transistor. Inset shows the top viewof the same nanorod after connecting S and D . . . . . . . . . . . . . . . 200

Chapter 7

Fig. 1 Studies on n- and p-type oxide semiconductor gassensors [15] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213

Fig. 2 Schematic depicting the potential barrier developedat the intergranular contact of two oxide particles. . . . . . . . . . . . . 214

Fig. 3 Factors determining the response of metal oxidesemiconductor gas sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215

xxviii List of Figures

Fig. 4 Schematic representation of grain size effects . . . . . . . . . . . . . . . . 215Fig. 5 Schematic representation of a compact sensing layer . . . . . . . . . . 216Fig. 6 Schematic representation of a porous sensing layer . . . . . . . . . . . 217Fig. 7 The typical response curve of a chemiresistive gas sensor . . . . . . 218Fig. 8 Schematic for heterostructures . . . . . . . . . . . . . . . . . . . . . . . . . . . 222Fig. 9 Schematic diagram showing the possible band structures

at Schottky junction a before and b after thermal equilibrium . . . 223Fig. 10 Schematic diagram showing the possible band structures

at p–n junction a before and b after thermal equilibrium . . . . . . . 224Fig. 11 Schematic of the p-CuO/n-ZnO heterojunction sensor device . . . . 225Fig. 12 Room-temperature response characteristics of ZnO and

ZnO/CuO heterojunction sensors to different concentrationsof ethanol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226

Fig. 13 Variation of a response time and b recovery time of ZnOand ZnO/CuO sensors with concentration of ethanol . . . . . . . . . . 226

Fig. 14 Energy band diagram of a ZnO and CuO and b ZnO/CuOheterojunction device at thermal equilibrium . . . . . . . . . . . . . . . . 228

Chapter 8

Fig. 1 Predicted Curie temperature for semiconductors [5, 9] . . . . . . . . . 235Fig. 2 Schematic representation of four virtual transitions

of the superexchange ion–ion interactions [20] . . . . . . . . . . . . . . . 237Fig. 3 Schematic representation of magnetic polarons with magnetic

cation concentration x = 0. Cation sites are representedby small circles [23] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238

Fig. 4 Spin FET—single transistor non-volatile memory [6, 16, 57] . . . . 243Fig. 5 Schematic representation of a (Zn,Co)O/ZnO/(Zn,Co)O

junction [6, 16] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244Fig. 6 Schematic of ZnO-based transparent photomagnet [57] . . . . . . . . 244Fig. 7 Experimental prediction of ferromagnetism in various

semiconductors [5] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245Fig. 8 Plots of magnetic moment per transition-metal cation (5 at.%)

doped in ZnO thin films [6] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248Fig. 9 Pie chart of ZnO-based DMS with different TM dopants

[6, 41–44] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253Fig. 10 Transmission spectra of Zn1-xTMxO films for x = 0.05. . . . . . . . . 255Fig. 11 Room-temperature Raman spectra of Zn0:95TM0:05O films

(TM = Mn/Co/Ni/Cu) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255Fig. 12 Room-temperature M-H curve of a Zn0:97Ni0:03O,

b Zn0:95Co0:05O, and c Zn0:97Cu0:03O films . . . . . . . . . . . . . . . . . 256Fig. 13 SEM images of pristine ZnO and ZnO:TM nanostructures

synthesized at 150 °C for 6 h a pristine ZnO and ZnO dopedwith 0.05 M, b Cu(CH3COO)2, c Mn(CH3COO)2, d Ni(CH3COO)2 in the precursor solution . . . . . . . . . . . . . . . . . . . . . . 258

List of Figures xxix

Fig. 14 Room-temperature PL spectra (kexc= 325 nm) of ZnO:TMnanostructures synthesized at 150 °C for 3 h with 0.05 M TMconcentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

Fig. 15 Raman spectra of ZnO:TM nanostructures synthesized at 150 °Cfor 3 h with 0.05 M TM concentration . . . . . . . . . . . . . . . . . . . . . 259

Fig. 16 Room-temperature M-H loop of ZnO:TM nanostructureswith various concentrations of TM doping . . . . . . . . . . . . . . . . . . 260

Chapter 9

Fig. 1 Hysteresis loop in ferroelectric and paraelectric phases. . . . . . . . . 272Fig. 2 Schematic illustration of domain matched epitaxial growth . . . . . 281Fig. 3 a JCPDS data of Ba0.5Sr0.5TiO3, b the XRD x-2h scan

of the BST film deposited directly on to Al2O3 substrateand (c–f) the XRD x-2h scan of the BST films with a ZnO bufferlayer deposited at various oxygen partial pressures, c 3 � 10−4

mbar, d 5 � 10−4 mbar, e 7 � 10−4 mbar and f 10 � 10−4

mbar. In all the cases, BST was deposited at an optimizedoxygen partial pressure of 0.01 mbar and substrate temperatureof 700 °C. Reprinted from Krishnaprasad et al. [16],with the permission of AIP Publishing . . . . . . . . . . . . . . . . . . . . . 287

Fig. 4 a Schematic representation of atoms in the base plane of ZnOand Al2O3 [29] and b schematic diagram of the observedepitaxial relationship between BST and ZnO. Reprinted fromKrishnaprasad et al. [16], with the permission of AIPPublishing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287

Fig. 5 X-ray diffraction U-scan for a Al2O3 ð11�23Þ, b ZnO ð11�20Þbuffer layer, c BST(111) thin film and d (111) pole figure of BSTthin films deposited on ZnO buffer. Reprinted fromKrishnaprasad et al. [16], with the permission of AIPPublishing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288

Fig. 6 Reciprocal space mapping of (111) planes of BST thin film witha ZnO buffer layer on Al2O3 substrate. Reprinted fromKrishnaprasad et al. [16], with the permission of AIPPublishing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289

Fig. 7 a HRTEM image of BST-ZnO-Al2O3 film cross section.b Fourier-filtered HRTEM image of the black box area markedin figure (a) showing alignment of BST (111) orientation withd-spacing of 2.29Å. c Schematic representation of BST along(111) direction of the selected area in figure (b). Reprinted fromKrishnaprasad et al. [16], with the permission of AIPPublishing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290

xxx List of Figures

Fig. 8 a Domain matching epitaxy in the BST/ZnO system,Fourier-filtered image of matching of BST ð1�10Þ and ZnO ð�100Þplanes for 9/8 and 10/9 domains across the BST-ZnO interface,b schematic representation of 9/8 domain matching in theBST-ZnO interface and c corresponding electron diffractionpattern showing the alignment of planes in BST and ZnO.Reprinted from Krishnaprasad et al. [16], with the permissionof AIP Publishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291

Fig. 9 Domain matching epitaxy in the BZN/ZnO system, a HRTEMimage of BZN-ZnO–Al2O3 film cross section. b Fourier-filteredimage of the selected area in (a) showing domain matching ofBZN ð2�20Þ and ZnO ð�100Þ planes for 7/8 and 6/7 domainsacross the BZN-ZnO interface . . . . . . . . . . . . . . . . . . . . . . . . . . . 292

Fig. 10 Capacitance-voltage measurements for the fabricated IDC overBST films with ZnO buffer layer. The ZnO buffer layers weredeposited at various oxygen partial pressures, a 5 � 10−4 mbar,b 7 � 10−4 mbar, and c 10 � 10−4 mbar and BST thin filmswere deposited at optimized conditions. Schematicrepresentation of the IDC structure patterned over the BST thinfilm is shown in the inset. Reprinted from Krishnaprasad et al.[16], with the permission of AIP Publishing. . . . . . . . . . . . . . . . . 292

Fig. 11 Variation of capacitance and dielectric loss of the epitaxial BSTthin film as a function of the frequency. Reprinted fromKrishnaprasad et al. [16], with the permission of AIPPublishing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293

Chapter 10

Fig. 1 Schematic diagram of the different types of solution processand types of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305

Fig. 2 Schematic diagram of the different device structure of TFT:a bottom-gate staggered TFT, b bottom-gate coplanar TFT,c top-gate staggered TFT, d top-gate coplanar TFT . . . . . . . . . . . 306

Fig. 3 Schematic representation of density of localized statesin the band gap. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

Fig. 4 Schematic structure of n-type thin-film transistor . . . . . . . . . . . . . 309Fig. 5 Extraction of n-type TFT parameters from the transfer

characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310Fig. 6 Schematic representation of the basic operation behind

the n-type TFT by plotting density of statesof the electronic sates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311

Fig. 7 Transfer characteristics measured at different temperaturesduring heating of ZTO TFT. Inset figure shows the Arrheniusplot of the drain current versus 1000/T for different gatevoltages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313

List of Figures xxxi

Fig. 8 Dependence of EA with the gate voltage of ZTO TFT . . . . . . . . . 314Fig. 9 Density of states in the band gap of ZTO channel calculated from

the derivative of the activation energy of ZTO TFT . . . . . . . . . . . 314Fig. 10 a Transfer characteristics of OTFTs measured at different

temperatures during heating. b EA variation with the gatevoltage. c Calculated density of states in the gapof PTCDI-C8 [34] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316

xxxii List of Figures