William Stratton Ph.D. Thesis - MINDS@UW Home

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C1 C2 & Objective Aperture Virtual aperture C3 Objective Lens Shift probe Sample 0.5 1/Å STEM TEM Diffraction Pattern Tilt beam 500 Å Real Real Image Image C1 C2 Sample Objective Lens Objective Aperture Projector Lens Figure 1.5: Schematic difference between STEM FEM and TEM FEM. STEM FEM with a STEM translates the probe to acquire multiple nanodiffraction patterns while TEM FEM with a TEM tilts the beam to obtain a real space image. TEM FEM with usually covers multiple more sample area in the V calculation compared to STEM FEM. Figure from 84 . 18
than the STEM FEM V 66,67,84 . This is seen in Figure 1.6. Furthermore, simulated FEM data has a similar absolute V as STEM FEM, which is still higher than TEM FEM. This difference is caused by the coherence of the imaging mode for each microscope. STEM experiments require a coherent electron beam for the acquisition of data. Likewise, all computer simulations are done with a simulated coherent electron beam 40,81,85 . Yet, TEM FEM experiments are done on a TEM with a small objective aperture size Q, and a large convergence angle. For our past experiments 40,86,87 with a LEO 912 EFTEM at 120 kV we use a 0.6 mrad objective aperture and a 4 mrad convergence angle. This configuration in a TEM creates a partially coherent imaging mode 83 . The partially coherent imaging mode will not be as sensitive to spatial fluctuations in the sample as a coherent beam. If the imaging mode is not fully coherent, not all of the MRO in the sample at or near a Bragg condition will generate coherent diffraction. This artificially decreases V(k) by some coherency factor, regardless of k. Since the difference is instrumental rather than structural, it explains why peak locations and relative heights are conserved between TEM FEM and STEM FEM while the absolute V is orders of magnitude different. To create a more coherent imaging mode in the TEM, one only needs to run at a lower convergence angle while keeping the objective aperture size small. This is not usually done, as it will drastically increase the time required to acquire a FEM series, which can be particularly detrimental by causing beam induced crystallization when working with beam sensitive materials. 19
Page 1 and 2: MEDIUM RANGE ORDER IN HIGH ALUMINUM
Page 3 and 4: To my wife Elisabeth i
Page 5 and 6: Abstract High Al-content metallic a
Page 7 and 8: Table of Contents List of Figures
Page 9 and 10: List of Figures Figure Page Figure
Page 11 and 12: Figure 2.8: V(Φ) at varying values
Page 13 and 14: electron beam exposure. The sharp f
Page 15 and 16: Figure 5.7: FEM data for Al88Y7Fe5
Page 17 and 18: Chapter 1. Introduction Amorphous m
Page 19 and 20: Material Type Tg ( o C) Reference P
Page 21 and 22: dH / dt (arb. units) time Figure 1.
Page 23 and 24: enough to avoid any nucleation onse
Page 25 and 26: nanocrystals are thermally stable u
Page 27 and 28: The structural difference between t
Page 29 and 30: Structures for various metallic gla
Page 31 and 32: ( , ) V k Q = ( r, , ) − ( r, , )
Page 33: of 1-3 nm is readily achievable in
Page 37 and 38: interesting behavior upon devitrifi
Page 39 and 40: Λ is a characteristic ordering len
Page 41 and 42: amorphous matrix crystal l R d R bi
Page 43 and 44: For a crystal oriented to a Bragg c
Page 45 and 46: number of crystals in a column will
Page 47 and 48: 3 d π 2 Rt max Zmax Φ = . (2.21)
Page 49 and 50: eciprocal lattice point 1 d hkl awa
Page 51 and 52: A hkl 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
Page 53 and 54: V(C hklΦ,d) 0.4 0.3 0.2 0.1 0.4 0.
Page 55 and 56: V(C 111 Φ) 0.12 0.10 0.08 0.06 0.0
Page 57 and 58: Φ = 6π d ( 72 − 6π + π ρ) m
Page 59 and 60: V(t) 0.16 0.14 0.12 0.10 0.08 0.06
Page 61 and 62: ⎛ 3 ⎛ 4 6tΩ⎞⎞ d = ⎜ Chkl
Page 63 and 64: Chapter 3. Experimental Set-up Prep
Page 65 and 66: A B 0.25 1/Å 0.25 1/Å Figure 3.1:
Page 67 and 68: 〈IBF〉, to the bright field inte
Page 69 and 70: Once the relative thickness is know
Page 71 and 72: Given that FEM is a quantitative el
Page 73 and 74: eam at a uniform intensity across t
Page 75 and 76: Low Filtering Limit ω l (Å -1 ) 0
Page 77 and 78: sample 101 . Much of the influence
Page 79 and 80: 3.07 Thickness Dependant Thinning A
Page 81 and 82: Residual XRD Intensity (arb. units)
Page 83 and 84: Intensity (arb. units) 0.30 Al 88 Y
Page 85 and 86:
3.08 Beam Induced Crystallization o
Page 87 and 88:
Fraction of Atoms 0 120 keV 100 200
Page 89 and 90:
V(k) x10 -3 10 8 6 4 2 Al 92 Sm 8 P
Page 91 and 92:
to produce an accurate FEM data set
Page 93 and 94:
Deformation Al 92Sm 8 sample: Rapid
Page 95 and 96:
intensity (arb. units) 3 4 {111} {2
Page 97 and 98:
Al2O3 Al hkl d (1/nm) hkl d (1/nm)
Page 99 and 100:
easons. First, the as-spun V(k) for
Page 101 and 102:
atoms locally organized into an FCC
Page 103 and 104:
in Figure 4.6. Still, this begs the
Page 105 and 106:
Φ 0.20 0.15 0.10 0.05 0.00 10 21 A
Page 107 and 108:
Chapter 5. Al88Y7Fe5 and Al88Y7Fe4C
Page 109 and 110:
diffracting condition through the m
Page 111 and 112:
increases the number of Al nanocrys
Page 113 and 114:
Fraction of nanocrystals x10 -3 Fra
Page 115 and 116:
Al 88 Y 7 Fe 5 Enthalpy (J/g) 0 -1
Page 117 and 118:
Al 88Y 7Fe 5 100 nm Al 88Y 7Fe 4Cu
Page 119 and 120:
5.04 Al88Y7Fe4Cu1 Discussion The de
Page 121 and 122:
FEM is sensitive to both critical a
Page 123 and 124:
devitrified structure has the possi
Page 125 and 126:
fraction between the as quenched ma
Page 127 and 128:
number, etc.) can give insight to t
Page 129 and 130:
24. Liquid Metals Website, http://w
Page 131 and 132:
66. Voyles, P. M., Gibson, J. M. &
Page 133:
105. Zuo, J. M. Electron detection
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