本文利用Nd-YAG 雷射融蝕金屬靶材，通入氧氣凝聚二氧化鈦(第一部分) 和二氧化鋯 (第二部分) 的奈米顆粒，經由解析穿透式電子顯微鏡，觀察這些凝聚物的相變化、形狀、顆粒大小分佈和合併生長的行為。

第一部份主要研究二氧化鈦凝聚物靠凡得瓦爾力聚簇的集體行為，雷射融蝕鈦靶的過程，所得凝聚物，還會受到後續輻射加熱，以致於形狀由原本奈米鏈狀聚簇，變成排列比較緊密的凝聚物，推測溫度約達到1000 K左右。在這麼高的溫度，二氧化鈦奈米顆粒的局部聚合，很容易藉由布朗運動達到低能量的磊晶關係，金紅石奈米顆粒不完美的聚合即為例證，而異相間也有不完美聚合的行為，例如a-PbO2態二氧化鈦和金紅石顆粒之間不完美的聚合。此外，利用雷射尚可合成二氧化鈦高密度結構以及經歷特殊的相變化途徑。

第二部份主要研究雷射融蝕鋯靶並與氧氣反應後，藉著高加熱/高冷卻速率合成高密度二氧化鋯正方晶相 (tetragonal) 和立方晶相 (cubic) 凝聚物。正方晶系無基材制約的ZrO2經由電子束照射下，產生變形雙晶和缺陷。此外尚探討高密度二氧化鋯正方晶相和立方晶相凝聚物，在特定大小及蒸鍍過程所受到殘留應力的因素下，並藉由電子束的照射下，所產生之缺陷或經由非平衡狀態下的相變化，以達到較低能量的狀態，依同素異構相之內能隨其單位晶胞體積而變化的趨勢而定。

This thesis is about the phase transformation, shape, size distribution and coalescence of TiO2 (part I) and ZrO2 (part II) nanopartilces produced by Nd-YAG laser ablation on metal targets under oxygen background gas, and characterized by analytical electron microscopy. The optimum laser ablation condition that satisfactory and routinely yield high-pressure phases of TiO2 (i.e. α-PbO2-type and fluorite-related structures) and ZrO2 with high residual stress were reported. Part I-1 focuses on physical coagulation, by Van der Waals force, of the TiO2 condensates at temperatures up to about 1000 K as a result of post-condensation radiant heating. In part I-2, imperfect oriented attachment of nanoparticles over specific surfaces is rationalized to cause accretion and defects for the rutile condensates. Brownian motion may proceed above a critical temperature for anchorage release at the interface of imperfect attached nanoparticles until an epitaxial relationship is reached. Part I-3 deals with further the Brownian-type rotation of the imperfectly impinged α-PbO2-type TiO2 and rutile nanocondensates until interfacial-energy cusp was reached. In part I-4 laser ablation condensation synthesis of dense TiO2 polymorphs and their phase transformations were documented. Part II-1 is about dense tetragonal (t)-ZrO2 and cubic (c-) nanocondensates which were synthesized under very rapid heating and cooling by pulsed Nd-YAG laser ablation with oxygen background gas. The t-ZrO2 nanoparticles were found to form deformation twins/faults and followed unique transformation path upon local electron dosage. Electron diffraction indicated that the dense c- and t- phase with specific size and residual stress were allowed to relax and/or kinetically phase change into lower-energy state as constrained by the intersections of the internal energy vs. cell volume plots calculated for the two polymorphs (Part II-2).

Contents
Preface Ⅰ
Abstract III
Contents V
List of Table IX
List of Figure X

Part I
Laser ablation condensation of TiO2 nanoparticles
I.1 Laser ablation condensation of TiO2 particles: Effects of laser energy, oxygen flow rate and phase transformation
1. Introduction 1
2. Experimental 2
3. Results 3
4. Discussion 5
4.1 Effect of radiant heating on phase identity
4.2 Effect of phase transformation on size and shape of titania condensates
5. Conclusions 8
Figures 11

I.2 Imperfect oriented attachment: accretion and defect generation of nanosize rutile condensates
1. Introduction 22
2. Experiment 22
3. Results and discussion 23
Figures 27
I.3 Lattice correspondence of a-PbO2-type TiO2 and rutile
1. Introduction 34
2. Experiment 34
3. Results and discussion 35
3.1 Identification of lattice correspondence and parameters
3.2 Stereographic projection of the crystallographic relationship
3.3 Energetics of interface coincidence site lattice
3.4 Martensitic transformation vs. coalescence mechanism
4. Conclusions 37
Figures 39

I.4 Laser ablation condensation and kinetic phase change of fluorite-type related TiO2
1. Introduction 44
2. Experimental 45
3. Results 46
4. Discussion 47
4.1 Stability of high pressure phase
4.2 Backtransformation specification of fluorite-type TiO2
4.3 Implications on photocatalysis
5. Conclusions 52
Figures 53

Part II
Laser ablation condensation of ZrO2 nanoparticles

II.1 Condensation and relaxation/transformation of dense t-ZrO2 nanoparticles
1. Introduction 80
2. Experimental 80
3. Results 81
4. Discussion 83
4.1 Residual stress and genesis of dense t-ZrO2 condensate
4.2 Stress-dependent relaxation of dense t-ZrO2
5. Conclusions 86
Figures 88

II.2 Laser ablation condensation of polymorphic ZrO2 nanoparticles: Effects of laser parameters, residual stress and kinetic phase change
1. Introduction 98
2. Experimental 99
3. Results 100
4. Discussion 102
4.1 Condensation of dioxides with fluorite-like rather than cotunnite-type structure
4.2 Residual stress of the c- and t-ZrO2 condensates
4.3 Energy - cell volume curves for bulk c- and t-ZrO2 at room and high temperature
4.4 Energy – cell volume curves for nanosized c- and t-ZrO2 at high temperature
4.5 Effect of residual stress on the relaxation/transformation of the nanocondensates
5. Conclusions 106
Figures 109

References 121

Appendix I On the crystallographic relationships, habit plane and coincidence site lattice for a-PbO2-type and baddeleyite-type TiO2 XIV
Appendix II Supplement figures about the condensation and relaxation/ transformation of dense t-ZrO2 nanoparticles and baddeleyite-type TiO2 XVII
Appendix III Photographs of the targets after laser ablation XX
Appendix IV EELS spectra of TiO2 XXV



























List of Tables
Table I-1.1. Average particle size of TiO2 condensate produced under specified laser ablation conditions. 10
Table I-3.1. Lattice misfit strain e for the exact/nearly coincided plane normals of a-PbO2-type TiO2 and rutile. 38
Table II-1.1. Observed and calculated d-spacings for t-ZrO2 condensed at a
representative laser power 4.4 x 107 Watt/cm2. 87
Table II-1.2. Cell parameters and residual stress of t-ZrO2 condensates prepared
under specified laser power density. 87
Table II-2.1. Laser ablation parameters and resultant phase assemblages of ZrO2. 108
Table II-2.2. Cell parameters and residual stress of c- and t-ZrO2 condensates
prepared under specified laser power density. 108


















List of Figures
Part I-1
Fig. I-1.1 Schematic drawing showing the phase assemblages of titania condensates obtained at specified oxygen flow rate and laser energy input. ………………………………………………………………..... 11
Fig. I-1.2 (a) Selected area electron diffraction pattern of randomly oriented rutile and anatase particles. (b) Line profile along the trace in (a). (c) Energy-dispersive x-ray analysis of (a). …………………………….. 12
Fig. I-1.3 TEM bright-field images (a) and (b) taken at 25,000x and 100,000x.. 13
Fig. I-1.4 TEM bright-field images (a) and (b) taken at 25,000x and 100,000x.. 14
Fig. I-1.5 Histogram with curve fitting showing the size distribution………….. 15
Fig. I-1.6 (a) Lattice image of (011)-faceted anatase nanoparticles necking. (b) Two dimensional Fourier transform. (c) reconstructed image……….. 16
Fig. I-1.7 (a) Lattice image of anatase nanoparticle with well-developed (101), (110) and (112) faces. (b) Two dimensional Fourier transform. (c) reconstructed image………………………………………………….. 17
Fig. I-1.8 (a) Lattice image of multiple anatase nanoparticles coalescence over (011) (b) Two dimensional Fourier transform. (c) reconstructed image…………………………………………………………………. 18
Fig. I-1.9 (a) Lattice image of anatase nanoparticle with well-developed {101} and (112) faces (b) Two dimensional Fourier transform. (c) reconstructed image………………………………………………….. 19
Fig. I-1.10 The dense TiO2 formed particulates and nanoparticles………………. 20

Part I-2
Fig. I-2.1 (a) Lattice image of a typical rutile nanoparticle (b) Two dimensional Fourier transform. (c) Reconstructed image………………………….. 27
Fig. I-2.2 (a) Lattice image of two rutile nanoparticles coalesced over ( 10) face (b) Two dimensional Fourier transform. (c) Reconstructed image………………………………………………………………….. 28
Fig. I-2.3 (a) Lattice image of two rutile nanoparticles coalesced over (10 ) to form fault (b) Two dimensional Fourier transform. (c) reconstructed image………………………………………………………………….. 29
Fig. I-2.4 (a) Lattice image of two rutile nanoparticles coalesced over (011) to form twin (b) Two dimensional Fourier transform. (c) reconstructed image………………………………………………………………….. 30
Fig. I-2.5 The projection of rutile lattice (a) (110) projection (b) (011) projection……………………………………………………………… 32
Fig. I-2.6 Schematic drawing for the rutile crystals coalesced over (011)…….… 33

Part I-3
Fig. I-3.1 TEM lattice image of a-PbO2-type TiO2 partially transformed as rutile structure………………………………………..………………. 39
Fig. I-3.2 Stereographic projection of the plane normals and zone axis of rutile and epitaxial a-PbO2-type TiO2 (a) relationship A (b) relationship B……………………………………………………………………… 40
Fig. I-3.3 Projection of specific TiO2 surfaces: (a) rutile (011), (b) a-PbO2-type TiO2 (001), (c) a-PbO2-type TiO2 (100)……………………………... 41
Fig. I-3.4 Top view of (a) (001)a//(011)rut and (b) (100)a//(011)rut interface for the relationship A and B in terms of unrelaxed oxygen positions of rutile and a-PbO2-type TiO2…………………………………………. 42
Fig. I-3.5 Schematic drawing of atom positions and crystallographic axes b and c for rutile and a-PbO2-type TiO2 with relationship A………….. 43


Part I-4
Fig. I-4.1 The titanium NCA produced by Lotis laser (1064 nm) ablation at 0.5 J/pulse and oxygen flow rate of 20 L/min……………………………. 54
Fig. I-4.2 The titanium NCA produced by Lotis laser (1064 nm) ablation at 0.5 J/pulse flow rate of 25 L/min………………………………………… 55
Fig. I-4.3 TEM bright-field image of a spherical anatase particle about 150 nm 57
Fig. I-4.4 TEM bright-field image of a spherical anatase particle about 80 nm 58
Fig. I-4.5 TEM bright-field image of spherical anatase particle about 100 nm 59
Fig. I-4.6 Lattice image of rutile nanoparticle about 20 nm…………………… 60
Fig. I-4.7 Lattice image of anatase nanoparticle with well-developed (001) surface………………………………………………………………… 61
Fig. I-4.8 Lattice image of two anatase nanoparticle coalesced over (001) face.. 62
Fig. I-4.9 Lattice image of two anatase nanoparticles coalesced over a specific (1 2) surface to form twinned bicrystals…………………………….. 64
Fig. I-4.10 Lattice image of two α-PbO2 nanoparticles coalesced over arbitrary contact to form a single crystal……………………………………….. 65
Fig. I-4.11 Lattice image of a fluorite-type TiO2 nanoparticle which was partially transformed to three variants of anatase……………………. 66
Fig. I-4.12 Lattice image of the fluorite type TiO2 nanoparticle that partially transformed to anatase twin variants…………………………………. 69
Fig. I-4.13 Lattice image of partially transformed fluorite type TiO2 in Fig. I-4.11 fousing on defects and the crystallographic relationship between fluorite- type and anatase structure…………………………. 71
Fig. I-4.14 Lattice image of baddeleyite-type nanoparticle partially transformed to α-PbO2 type TiO2…………………………………………………... 73
Fig. I-4.15 Lattice image of the baddeleyite nanoparticle in Fig I-4.14 focusing on its crystallographic relationship with the α-PbO2 type descendant.. 75
Fig. I-4.16 The energy difference, relative to rutile with respect to pressure for the TiO2 polymorphs…………………………………………………. 76
Fig. I-4.17 Stereographic projection of the plane normals and zone axes of the parent fluorite-type TiO2 and three anatase variants…………………. 77
Fig. I-4.18 Projection of specific TiO2 surfaces: (a) fluorite-type TiO2 (100) (b) anatase (010)…………………………………………………………. 78
Fig. I-4.19 Top view of (001)a//(100)f interface for anatase variant 1 and fluorite-type TiO2…………………………………………………….. 79


Part II-1
Fig. II-1.1 (a) TEM bright field image and (b) corresponding SAED pattern of randomly oriented ZrO2 condensates assembled as NCA…………... 88
Fig. II-1.2 Lattice image of {111}-faceted t-ZrO2 condensates of electron irradiation induce transformation……………………………………. 90
Fig. II-1.3 Lattice image of coalesced t-ZrO2 condensates of electron irradiation induce deformation…………………………………………………... 92
Fig. II-1.4 Lattice image of coalesced t-ZrO2 condensates of electron irradiation and induce deformation……………………………………………… 94
Fig. II-1.5 (a) T-P phase boundaries (dotted lines) of bulk ZrO2 (b) Hypothetical size-dependent internal energy versus volume curve for c- and t-ZrO2……………………………………………………... 96


Part II-2
Fig. II-2.1 TEM bright field image of the t+m ZrO2 condensates assembled as NCA…………………………………………………………………. 109
Fig. II-2.2 Lattice image of a representative t-ZrO2 nanoparticle showing well-developed {111}, {110}, (001) faces and ( 12) facet…………. 111
Fig. II-2.3 Lattice image of m-ZrO2 nanoparticle about 20nm…………………. 112
Fig. II-2.4 TEM bright field image of the c+t ZrO2 condensates assembled as NCA or close-packed manner……………………………………….. 113
Fig. II-2.5 Lattice image of a cubo-octahedral c-ZrO2 nanoparticle……………. 115
Fig. II-2.6 Lattice image showing two c-ZrO2 nanoparticles were coalesced over exact (11 ) face into a single crystal…………………………... 116
Fig. II-2.7 Lattice image of three t-ZrO2 nanoparticles coalesced over ~(1 1) vicinal surface into a single crystal………………………………….. 117
Fig. II-2.8 Internal energy vs. cell volume curves for the bulk c- and t- ZrO2…………………………………………………………………. 118
Fig. II-2.9 Internal energy vs. cell volume curves for nanocrystalline c- and t- zirconia……………………………………………………………… 119
Fig. II-2.10 T-P phase diagram of bulk ZrO2 showing the predicted c/t phase boundary…………………………………………………………….. 120

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