CHEMICAL VAPOR DEPOSITION OF THIN FILM MATERIALS FOR ...

More documents

Recommendations

Info

2.2 Spinel ferrite: Nickel Ferrite and Lithium Ferrite 2.2.1 Physical Properties and Potential Applications Nickel ferrite (NiFe2O4) and lithium ferrite (LiFe5O8) belong to the family of ferrimagnetic ferrites, which possess both high permeability and resistivity.[73] In terms of crystal structure, NiFe2O4 and LiFe5O8 are both spinel structure. In a spinel (AB2O4) structure, the unit cell consists of eight formula units and the 8 A 2+ and 16 B 3+ cations are distributed in the interstices of the 32 close packed oxygen anions (Fig.15). If all of the 8 A 2+ occupy tetrahedral sites and all of the 16 B 3+ occupy octahedral sites then the structure is called normal spinel; If all of the 8 A 2+ and 8 B 3+ occupy octahedral sites and 8 B 3+ occupy tetrahedral sites, the structure is called inverse spinel. Fig. 15. Representation of a spinel structure. Adapted from ref. [73]. Usually, NiFe2O4 and LiFe5O8 both exist in inverse spinel structure at room temperature and their formulas can be written as Fe 3+ [Ni 2+ Fe 3+ ]O4 and Fe 3+ [Li + 0.5Fe 3+ 1.5]O4 respectively. According to the Néel model, the ferrimagnetism of these ferrite materials comes from a mechanism of superexchange, in which different magnetic cation occupied sublattices are antialigned with each other in the presence of an external magnetic field and thus imbalance in the number of antialigned sublattices results in net magnetism. 39
In spite of the same spinel structure, nickel ferrite and lithium ferrite have their own crystal parameters and physical properties due to different elements present in the materials. Nickel ferrite has a lattice constant of 8.340 Å, saturation magnetization of ~3200 G (room temperature) and Néel temperature of 585 ˚C. The effect of cation distribution and addition of different divalent cations (Zn 2+ , Cu 2+ , Mn 2+ ) on its magnetic properties have been widely investigated in the past.[74,75] This material is microwave lossy due to the orbital state of Ni 2+ , a relaxing ion. Lithium ferrite exists in two states: ordered and disordered state. In the ordered phase, the lithium and ferric ions are ordered in a 1:3 molar ratio in the octahedral sites of the cubic structure. The disordered phase of lithium ferrite has a disordered face centered cubic structure where the lithium and ferric ions are randomly located in the octahedral interstices. The disordered phase is produced with quenching from high temperatures as it is formed and prevalent in the temperature range of 750~1000 ˚C. This is due to the relative diffusion rates of the ions in the cubic lattice. Slow cooling allows redistribution and ordering of the ions in the cubic lattice and provides the condition for reversion to ordered phase. The lattice parameters for the ordered and disordered phase are 8.337 Å and 8.333 Å, respectively. Lithium ferrite has a saturation magnetization of 3750G (room temperature) and Néel temperature of ~620 ˚C, which are both higher than that of nickel ferrite. A unique feature of lithium ferrite among those spinel ferrites is its low microwave loss, which is indicated by its extremely narrow FMR line width of less than 10 G at room temperature, as showed in Fig.16. It's much lower than the value of nickel ferrite (40~80G) and comparable to that of yttrium iron garnet (Y3Fe5O8). This is because only S state Fe 3+ ions present in this material. Another advantage of lithium ferrite is its low cost compared to YIG. However, its practical application is still limited by the challenges of high quality material preparation, especially for thin films. Also, for microwave applications, both 40
Page 1 and 2:
CHEMICAL VAPOR DEPOSITION OF THIN F
Page 3 and 4:
ABSTRACT Chemical vapor deposition
Page 5 and 6:
DEDICATION This dissertation is ded
Page 7 and 8: φ In-plane tilt angle of X-ray dif
Page 9 and 10: ACKNOWLEDGMENTS It is my pleasure t
Page 11 and 12: CONTENTS ABSTRACT .................
Page 13 and 14: 3.2.1 Introduction ................
Page 15 and 16: LIST OF TABLES Table 1. Hafnium ami
Page 17 and 18: indicated by the complex FMR curve.
Page 19 and 20: Fig. 49. Ferromagnetic resonance cu
Page 21 and 22: growth rate, good step coverage and
Page 23 and 24: growth of thin film oxides due to t
Page 25 and 26: one can uniformly deliver precursor
Page 27 and 28: for the next reaction step as shown
Page 29 and 30: Fig. 3. Schematic of a typical dire
Page 31 and 32: is predominantly dependent on syste
Page 33 and 34: J r J A -D n b-n 0 δ n or for the
Page 35 and 36: surface passivation with certain in
Page 37 and 38: ay spectroscopy (EDS), Wavelength d
Page 39 and 40: incidence angle is larger than cert
Page 41 and 42: epresenting those characteristic ph
Page 43 and 44: 1.2.3.3 X-ray Diffraction (XRD) X-r
Page 45 and 46: exhibit diffraction peaks in the no
Page 47 and 48: (nanometers to tens of nanometers),
Page 49 and 50: strongest absorption of microwave s
Page 51 and 52: pinch-off to indicate the lack of a
Page 53 and 54: coupling is from unbound ferrite-fe
Page 55 and 56: diffusion barrier material in micro
Page 57: Fig. 14. A cross sectional scanning
Page 61 and 62: ferrites has been investigated exte
Page 63 and 64: systems is showed in Fig.18.[83] As
Page 65 and 66: precursor vaporization process, e.g
Page 67 and 68: CHAPTER 3. PLASMA ENHANCED ATOMIC L
Page 69 and 70: the initial surface chemistry for t
Page 71 and 72: delay time of 2 seconds between spe
Page 73 and 74: Kcal/mol respectively. The stronger
Page 75 and 76: negative slope) behavior in the pum
Page 77 and 78: the existence of both physisorbed a
Page 79 and 80: decomposition products (Hf-H) and g
Page 81 and 82: dried by ultra high purity N2 gas.
Page 83 and 84: pressure for XPS analysis is around
Page 85 and 86: Hf and N elements, incorporation of
Page 87 and 88: [150,151] This is a unique feature
Page 89 and 90: software. The thickness results are
Page 91 and 92: CHAPTER 4. DIRECT LIQUID INJECTION
Page 93 and 94: film growth region. The properties
Page 95 and 96: solution was accurately controlled
Page 97 and 98: size). For the rocking curve analys
Page 99 and 100: oxygen does not participate in the
Page 101 and 102: ecause vapor velocity cannot be cha
Page 103 and 104: Fig. 40. Cross-sectional view by fi
Page 105 and 106: the MgAl2O4 substrate confirms cube
Page 107 and 108: pattern. Fig.44(b) has diffraction
Page 109 and 110:
We have used an AGM (Alternating Gr
Page 111 and 112:
as derived equations for different
Page 113 and 114:
deposited at 600˚C is the lowest.
Page 115 and 116:
wave states degenerate with the FMR
Page 117 and 118:
Fig. 53. ϕ-scan of nickel ferrite
Page 119 and 120:
Surface roughness characterized by
Page 121 and 122:
Fig. 56. X-ray diffraction θ-2θ c
Page 123 and 124:
4.4 Conclusion In summary, we have
Page 125 and 126:
CHAPTER 5. DIRECT LIQUID INJECTION
Page 127 and 128:
eaction zone of the tube furnace is
Page 129 and 130:
Fig. 58. X-ray diffraction characte
Page 131 and 132:
interface. This phenomenon probably
Page 133 and 134:
6.1 Conclusion CHAPTER 6. CONCLUSIO
Page 135 and 136:
the temperature range of 600˚C to
Page 137 and 138:
such as PMN-PT and PZN-PT. CVD proc
Page 139 and 140:
[18]. L. S.-J. Peng, X. X. Xi, B. H
Page 141 and 142:
[54]. B. O. Johansson, J. -E. Sundg
Page 143 and 144:
[96]. J. D. Adam, S. V. Krishnaswam
Page 145 and 146:
[136]. J. Zhao, V. Fuflyigin, F. Wa
Page 147 and 148:
APPENDIX A: LabVIEW PROGRAM FOR PEA
Page 149 and 150:
APPENDIX B: TDMAH MOLECULAR STRUCTU
Page 151 and 152:
H 18 B19 2 A18 1 D17 H 18 B20 2 A19
show all

CHEMICAL VAPOR DEPOSITION OF THIN FILM MATERIALS FOR ...

Create successful ePaper yourself

Delete template?

Save as template?