(1) Mg1-xCux, where x is from 38 to 82, thin films which consist of the nanocrystalline MgCu2 and Mg-Cu amorphous phases are able to be fabricated by co-sputtering. In addition to liquid quenching, sputtering provides another possible path to fabricate amorphous alloys in the form of thin film.
(2) The composition variation is strongly related to the competition of the momentum and kinetic energy between Mg and Cu elements. Mg set at the RF gun provides a slower deposition rate but a compact structure, and Cu set at the DC gun provides the surface diffusion and the low-temperature continuous annealing near the localized region around the surface of the as-deposition films. Hence, Mg and Cu atom can mix each with other very well.
(3) Unbalanced competition of the momentum and kinetic energy between Mg and Cu elements would cause the irregular composition variation due to the “re-sputtering”.
Besides, the absence of the surface diffusion would occur at a low power, inducing the separated nano-grains of Mg and Cu. However, the high contact surface of the nanocrystalline phase would speed up the oxidation of the film in air.
(4) In multilayered films, the first formed phase in Mg-Cu multilayered thin film is always Mg2Cu, the most stable phase, due to a poor solubility between Mg and Cu, at any annealing temperatures.
67
(5) At the thick thickness of the individual layer, the thickness is unconcerned with the formation of Mg2Cu. As the thickness of the individual layer decreases, an increasing interface energy speeds up the solid-state reaction of Mg and Cu to induce the formation of Mg2Cu.
(6) For the Mg-Cu co-sputtering system, 100-100 (Mg23.5Cu76.5) exhibit a higher Young’s modulus than 100-150 (Mg17.7Cu82.3) and 100-50 (Mg40.4Cu59.6) due to the partial amorphous structure. Moreover, the pop-in effects with a smaller size occurs of the 100-100 sample in a higher frequency than of the 100-150 and 100-50 samples. The small pop-in effects in the 100-100 sample approximate match the width of amorphous matrix via the HRTEM observation.
(7) The Mg-Cu co-sputtered thin films with the nanocrystalline MgCu2 and amorphous Mg-Cu phases exhibit good nano-mechanical properties. The measured Young’s modulus of 100-150, 100-100, and 100-50 is about 90~100 GPa, very close to the Zr-, Pd-, Cu-based BMGs.
68
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73
Tables
Table 1-1 Functional properties and application fields of bulk amorphous and nanocrystalline alloys [6].
74
Table 2-1 The classification of amorphous alloy systems [7].
75
Table 2-2 The classification of amorphous alloy systems [7].
I ETM (or Ln) + Al + LTM
Zr-Al-Ni, Zr-Al-Cu, Zr-Al-Ni-Cu, Zr-Ti-Al-Ni-Cu, Zr-Nb-Al-Ni-Ln, Zr-Ga-Ni
Ln-Al-Ni, Ln-Al-Cu, Ln-Al-Ni-Cu, Ln-Ga-Ni, Ln-Ga-Nb-B
II LTM + ETM + Metalloid Fe-Zr-B, Fe-Hf-B, Fe-Zr-Hf-B, Fe-Co-Ln-B, Co-Zr-Nb-B
III LTM (Fe) + Al or Ga + Metalloid Fe- (Al, Ga)- Metalloid
IV
Mg + Ln + LTM Mg-Ln-Ni, Mg-Ln-Cu
TM (Zr ot Ti) + Be + LTM Zr-Ti-Be-Ni-Cu
V LTM + Metalloid Pd-Ni-P, Pd-Cu-Ni-P, Pt-Ni-P
76
Table 2-3 Prediction and observation of metallic glass formation by ion mixing in binary metal systems [40].
77
Table 2-4 Zone structures in thick evaporated and sputtered coating [51].
78
Table 2-5 Structure phase and ductility of Pd-TFMG made by different types of target at different Ar pressures [13].
79
Table 2-6 Tg, Tx and resistivity of Pd-TFMG made by arc-cast target at different Ar pressures [13].
80
Table 2-7 Properties of Pd-TFMG and bulk metallic glass [13].
81
Table 2-8 Electrical resistivity of the thin film metallic glasses and conventional electrical device materials [31].
82
Table 3-1 The details of the co-deposition conditions.
Materials Mg Cu
Power RF power
100 and 50 W
DC power
150, 100, 50, 25, and 15 W
Pre-sputtering time 1 min
Working pressure 3×10-3 torr
Argon flow rate 30 sccm
83
Table 3-2 The details of multilayer sputtering conditions.
Material Mg individual layer Cu individual layer
Power RF 100 W DC 150 W
Pre-sputtering time 1 min 1 min
Working pressure 3×10-3 torr
Argon flow rate 30 sccm
Deposition rate 10 nm/min 40 nm/min
84
Table 3-3 The information of the Mg-Cu multilayered films.
Sample Thickness of individual layers (nm) Thickness ratio Calculated atomic ratio
20T32 Mg 150 Cu 50 Mg 3 Cu 1 Mg 3 Cu 2
40N32 Mg 15 Cu 5 Mg 3 Cu 1 Mg 3 Cu 2
20T14 Mg 100 Cu 200 Mg 1 Cu 2 Mg 1 Cu 4
40N14 Mg 10 Cu 20 Mg 1 Cu 2 Mg 1 Cu 4
85
Table 3-4 The information of the Mg-Cu co-sputtered films
Sample Deposition condition
100 series
100-150 Mg RF 100 W Cu DC 150 W
100-100 Mg RF 100 W Cu DC 100 W
100-50 Mg RF 100 W Cu DC 50 W
100-25 Mg RF 100 W Cu DC 25 W
100-15 Mg RF 100 W Cu DC 15 W
50 series
50-150 Mg RF 50 W Cu DC150 W
50-100 Mg RF 50 W Cu DC 50 W
50-50 Mg RF 50 W Cu DC 50 W
50-25 Mg RF 50 W Cu DC 25 W
86
Table 4-1 The composition of the Mg-Cu co-sputtered films
specimen Composition (at%)
100 series
100-150 Mg 17.7 Cu 82.3 O 0 100-100 Mg 23.5 Cu 76.5 O 0 100-50 Mg 40.4 Cu 59.6 O 0 100-25 Mg 61.9 Cu 38.1 O 0 100-15 Mg 39.9 Cu 43.5 O 16.6
50 series
50-150 Mg 0 Cu 100 O 0 50-100 Mg 0 Cu 100 O 0 50-50 Mg 10.1 Cu 89.9 O 0 50-25 Mg 15.6 Cu 63.9 O 20.5
87
Table 4-2 Structural and compositional comparison between Mg-Cu co-sputtered and multilayered thin films
Type Specimen composition Situation Structure Oxidation
Co-sputtered 50 series
Cu-rich
50-150 Pure Cu As-deposited Nanocrystalline Cu No 50-100 Pure Cu As-deposited Nanocrystalline Cu No 50-50 Mg10.1Cu89.9 As-deposited Nanocrystalline Mg and Cu No 50-25 Mg15.6Cu63.9O20.5 As-deposited Nanocrystalline Mg and Cu Yes
100 series
Cu-rich
100-150 Mg17.7Cu82.3
As-deposited Amorphous with Nanocrystalline MgCu2 No
Annealing Nanocrystalline MgCu2 No 100-100 Mg23.5Cu76.5
As-deposited Amorphous with Nanocrystalline MgCu2 No
Annealing Nanocrystalline MgCu2 No 100-50 Mg40.4Cu59.6
As-deposited Amorphous with Nanocrystalline MgCu2 No
Annealing Nanocrystalline MgCu2 No Mg-rich 100-25 Mg61.9Cu38.1
As-deposited Nanocrystalline Mg2Cu with amorphous No
Annealing Nanocrystalline Mg2Cu No Mg-rich 100-15 Mg39.9Cu43.5O16.6 As-deposited Nanocrystalline Mg2Cu Yes
Multilayered
Cu-rich 20T14 & 40N14 As-deposited Nanocrystalline Mg and Cu No
Annealing Nanocrystalline Mg2Cu No Mg-rich 20T32 & 40N32 As-deposited Nanocrystalline Mg and Cu No
Annealing Nanocrystalline Mg2Cu No
88
Table 5-1 Comparison between thermal properties of Mg-based binary and ternary amorphous alloys.
Alloys Sample type Structure Tg (K) Tx (K) ΔTx (K) Mg65Cu25Gd10 [76] Bulk Fully amorphous 408 478 60
Mg65Cu25Y10 [76] Bulk Fully amorphous 413 473 70 Mg23.5Cu76.5 Thin film Partial amorphous 425 460 35 Mg17.7Cu82.3 Thin film Partial amorphous 428 460 32
89
Table 5-2 Comparison between Values of Young’s modulus and hardness from published nanoindentation works and this study.
Meterials Sample Type Young’s modulus (GPa) Hardness (GPa)
Zr41.25Ti13.75Cu12.5Ni10Be22.5 [77] Bulk 96 7.3
Zr60Cu20Pd10Al10 [78] Bulk 87 5.7
Pd40Ni40P20 [78] Bulk 108 5.5
Mg65Ni20Nd15 [78] Bulk 57 3.4
Mg60Cu30Y10 [79] Bulk 51.5 3.3
Cu60Zr22Ti18 [80] Bulk 104.7 6.6
Pure Mg Bulk 45* x
Pure Cu Thin film 104 [81] x
Al-SiC multilayer [82] Thin film 71 2.4
100-150 (Mg17.7Cu82.3) Thin film 100.1 3.6
100-100 (Mg23.5Cu76.5) Thin film 118 4.6
100-50 (Mg40.4Cu59.6) Thin film 96.8 4.3
* The normal Young’s modulus value of the Mg bulk.
90
Figures
Figure 1-1 A scheme of long-range-ordered structure [1].
Figure 1-2 A scheme of short-range-ordered structure [1].
91
Figure 1-3 The frame for the upscale models of the Vertu mobile phone is made of liquid-metal alloy because of its high strength, hardness, and scratch resistance[3].
92
Figure 1-4 (a) A sketch of conical spring microactuator, and (b) a fundamental structure of micro-switch made by metallic glass thin films [5].
93
Figure 1-5 FIB nanomold on completely glassy Zr-Al-Cu-Ni thin films [4].
94
Figure 1-6 Schematic representation of the solid-state reaction at the interface of (a) Fe0.67Hf0.33 and (b) Fe0.50Hf0.50 films, showing the hypothetical iron profiles, considering a planar growth for every reacted layer [14].
95
Figure 2-1 A schematic diagram of the splat quenching methods[43].
Figure 2-2 A schematic diagram of the two roller quenching method[43].
96
Figure 2-3 A schematic diagram of the chill block melt spinning [43].
Figure 2-4 A schematic diagram of the planar flow casting process [43].
97
Figure 2-5 Characteristics of metallic glasses [11].
Figure 2-6 New approach for understanding GFA of amorphous materials [49].
98
Figure 2-7 Events that occur on a surface being bombarded with energetic atomic-sized particles [51].
Figure 2-8 A schematic illustration of a DC diode Sputtering System [53].
99
Figure 2-9 A schematic illustration of the RF diode sputtering deposition [53].
Figure 2-10 A schematic illusion of a planar magnetron sputtering system [53].
100
Figure 2-11 The side view of the magnetic field configuration for circular planar magnetron cathode [50].
Figure 2-12 The top view of the magnetic field configuration for a circular planar magnetron cathode [50].
101
Figure 2-13 Basic modes of thin-film growth [54].
Figure 2-14 Coarsing of islands due to (a) Ostwald ripening, (b) sintering, and (c) cluster migration [54].
102
Figure 2-15 A schematic representation showing the superposition of physical process which establishes structural zones [51].
103
Figure 2-16 Structure zone model of sputtering deposited materials [51].
104
Figure 2-17 Plane-view TEM micrographs and diffraction pattern of the films in (a) as-deposited and annealed conditions at (b) 650, (c) 750, (d) 800, and (e) 850 K. The circled regions indicate the location for obtaining the diffraction patterns [12].
105
Figure 2-18 The heat-flow rate as a function of temperature for a sputtered, multilayered thin film of the average stoichiometry Ni68Zr32 [27].
Figure 2-19 X-ray diffraction profile for the Ni-Zr thin film: (a) as deposited, (b) after DSC scan to 670 K and quench to room temperature, (c) after a DSC scan to 870 K [27].
106
Figure 2-20 Cross-section bright-field TEM micrograph of a Ni/Zr bilayer annealed at 300oC for 60 min. Void may be seen at the Ni/NiZr interface as at V [39].
SiO2 substrate Voids
107
Figure 2-21 Cross-section bright-field TEM micrographs of Ni/Zr bilayer annealed at 300oC for (a) 240 min and (b) 720 min. The growth of the voids can be noted [39].
Voids
Voids
108
Figure 2-22 Correlations exist between vapor phase growth conditions and many of properties of the resultant thin film [53].
Figure 2-23 The DSC curve of Pd-TFMG [13].
109
Figure 2-24 TTT diagram for the onset of crystallization of Pd-TFMG [13].
Figure 2-25 SEM image of a Pd-thin-film metallic glass free-standing microbeam with a notch fabricated by FIB [33].
110
Figure 2-26 Variation of notch fracture toughness (KC) of Pd-based thin-film metallic glass as a function of annealing time in the supercooled liquid region at 640 K close to Tg = 637 K [33].
Figure 2-27 SEM micrographs of the fracture behaviors ahead of the notch tips in Pd-based TFMG (a) as-deposited, an overview of the fractured sample, (b) as-deposited, a high magnification observation of the fracture surface, (c) annealed for 90 s and (d) annealed for 480 s [33].
111
Figure 2-28 The SEM image of the deformation morphologies around the indents in the Au/Cu multilayers with individual layer thicknesses [32].
Figure 2-29 The pileup height (hpu) and the hardness (H) as a function of λ. Hardness (H) was measured at the 200 nm indentation depth [32].
112
Figure 2-30 FIB cross-sectional views of the indents in the Au/Cu multilayers with individual layer thickneses (λ) of (a) λ = 250 nm, (b) λ = 100 nm, (c) λ = 50 nm, (d) λ = 25 nm. The bright and dark layers correspond to Au and Cu layers, respecrively. Inhomogeneous shear banding becomes prevalent with the decrease in λ [32].
Figure 2-31 Electrical resistivity ρ as a function of annealing time Ta in the Pd76Cu6Si18
thin film metallic glasses annealed at various temperatures [31].
Ta
113
Figure 2-32 Magnetic force microscopy images of films in the as-deposited and annealed conditions [61].
114
Figure 3-1 Mg-Cu binary phase diagram.
115
Figure 3-2 Flow chart of the experimental procedures.
116
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70
300 320 340 360 380 400 420 440
Temperature (K)
Time (min)
Co-sputtered thin films at 423 K
20 K/min
60 K/min
Isothermal
Figure 3-3 Temperature profile of the isothermal heat-treatment at 423 K of the co-sputtered thin films.
117
0 5 10 15 20 25 30 35
300 320 340 360 380 400 420
Temperaure (K)
Time (min)
multilayered thin films at 413 K
20 K/min
60 K/min
Isothermal
Figure 3-4 Temperature profile of the isothermal heat-treatment at 413 K of the multilayered 20T32 and 40N32 films.
118
0 5 10 15 20 25 30
300 310 320 330 340 350 360 370
Temperature (K)
Time (min)
Multilayered thin films at 363 K
60 K/min
Isothermal
Figure 3-5 Temperature profile of the isothermal heat-treatment at 363 K of the multilayered 20T14 and 40N14.
119
Figure 3-6 Schematic illustrations of (a) Top-view and (b) Side-view of preparation of XTEM-specimen by focus ion beam (FIB).
Trapezoid shape
120
(a) (b)
Figure 3-7 Cross-section images of 20T32 and annealed 20T32 specimens during XTEM preparation via FIB technique.
121
20 25 30 35 40 45 50 55 60
In te ns it y
2 theta
100-150 (Mg17.7Cu82.3)100-100 (Mg23.5Cu76.5)
100-50 (Mg40.4Cu59.6) 100-25 (Mg61.9Cu38.1) 100-15 (Mg39.9Cu43.5O16.6)
Figure 4-1 XRD patterns of the 100 series.
122
20 25 30 35 40 45 50 55 60
Intenrisy
2 theta 50-150 (Cu)
50-100 (Cu)
50-50 (Mg10.1Cu89.9) 50-25 (Mg15.6Cu63.9O20.5)
Cu (111) Cu (002)
Mg
Figure 4-2 XRD patterns of the 50 series.
123
20 25 30 35 40 45 50 55
Intensity
2 theta 20T32
40N32
Mg (0002) Cu (002)
Cu (111)
Figure 4-3 XRD patterns of the as-deposited 20T32 and 40N32.
124
20 25 30 35 40 45 50 55
Cu (111) Cu (002)
Mg (0002)
Intensity
2 theta 20T14
40N14
Figure 4-4 XRD patterns of the as-deposited 20T14 and 40N14.
125
20 25 30 35 40 45 50 55 60
Intensity
2 theta Mg
Cu
Mg (0002) Cu (111) Cu (002)
Figure 4-5 XRD patterns of the pure Mg and Cu metallic films.
126
Figure 4-6 TEM plane-view bright-field image of 100-150.
127
Figure 4-7 Selected area diffraction pattern of 100-150.
MgCu2 (113)
MgCu2 (222) MgCu2 (224) MgCu2 (440) MgCu2 (226)
MgCu2 (660) Cu (113) MgCu2 (220)
Cu (002)
128
Figure 4-8 TEM plane-view low-magnitude bright-field image of 100-100.
129
Figure 4-9 TEM plane-view low-magnitude dark-field image of 100-100.
130
Figure 4-10 TEM plane-view high-magnitude bright-field image of 100-100. In the circle, the typical form indirectly postulated the Mg-Cu amorphous phases in nature.
131
Figure 4-11 Selected area diffraction pattern of 100-100.
MgCu2 (220) MgCu2 (113)
MgCu2 (222) Cu (002)
MgCu2 (224) MgCu2 (440)
Cu (113) MgCu2 (226)
MgCu2 (660)
132
Figure 4-12 High-resolution TEM image of 100-100 with Mg-Cu amorphous/MgCu2 {110}
crystalline structure. The marked region is the Mg-Cu amorphous phase.
133
Figure 4-13 High-resolution TEM image of the 100-100 specimen. MgCu2 particles in the {110} are around the Mg-Cu amorphous matrix in the marked region.
134
Figure 4-14 High-resolution TEM image of the structure of Mg-Cu amorphous/MgCu2 in the {110} plane in the 100-100 specimen.
135
360 380 400 420 440 460 480 500 520
Heat flow
Temperature (K)
100-150 (Mg17.7Cu82.3)
exothermic heating rate = 5 K/min
Tg Tx
Figure 4-15 Modified non-isothermal DSC curve of 100-150.
410 420 430 440 450 460
Tg
136
20 25 30 35 40 45 50 55 60
4 hr at 433 K
Intensity
2 theta
100-150 (Mg17.7Cu82.3) annealed at 423 K
as-deposited
1 hr 2 hr
3 hr
MgCu2 (311) (222) MgCu2 (111)
Si
Figure 4-16 The structural transformation of 100-150 at 423 K.
137
20 25 30 35 40 45 50 55 60
1 hr 2 hr 3 hr
Intensity
2 theta
100-100 (Mg23.5Cu76.5) annealed at 423 K
as-deposited
4 hr at 433 K
MgCu2 (311) (222) MgCu2 (110)
Figure 4-17 The structural transformation of 100-100 at 423 K.
138
20 25 30 35 40 45 50 55 60
Intensity
2 theta
100-50 (Mg40.4Cu59.6) annealed at 423 K
as-deposited
1 hr
2 hr
3 hr
Figure 4-18 The structural transformation of 100-50 at 423 K.
139
20 25 30 35 40 45 50 55 60
Intenristy
2 theta
100-25 (Mg61.9Cu38.1) annealed at 423 K
as-deposited
1 hr
2 hr
3 hr Mg2Cu (080) Mg2Cu (331)
Mg2Cu (440)
Mg2Cu (131) Si
Figure 4-19 The structural transformation of 100-25 at 423 K.
140
20 25 30 35 40 45 50 55
Mg 2Cu (440) Mg 2Cu (080)
Mg 2Cu (111)
20T32 annealed at 413 K
Intensity
2 theta as-deposited
30 min
60 min
90 min 120 min at 473 K
Mg 2Cu (040) Mg (0002) Cu (111) Cu (002)
Figure 4-20 The structural transformation of 20T32 at 413 K.
141
20 25 30 35 40 45 50 55
40N32 annealed at 413 K
Intensity
2 theta as-deposited
30 min
60 min
90 min at 473 K
Mg (0002) Cu (111)
Mg 2Cu (080) Mg 2Cu (040)
Figure 4-21 The structural transformation of 40N32 at 413 K.
142
20 25 30 35 40 45 50 55
Intensity
2 theta 20T14 annealed at 363 K
as-deposited
30 min
60 min
Mg 2Cu (040) Mg (0002) Cu (111) Cu (002)
Figure 4-22 The structural transformation of 20T14 at 363 K.
143
20 25 30 35 40 45 50 55
Intensity
2 theta 40N14 annealed at 363 K
as-deposited
30 min
60 min
90 min
Mg (0002) Cu (111)
Mg 2Cu (040) Mg 2Cu (080)
Figure 4-23 The structural transformation of 40N14 at 363 K.
144
Figure 4-24 (a) TEM bright-field image of the as-deposited 20T32 film with nominally Mg 150-nm-thick and Cu 50-nm-thick individual layers. (b) TEM bright-field image of the 20T32 film annealed at 413 K for 2 hours.
(a) (b)
Mg Cu
Mg Cu Mg2Cu
145
50 100 150 200 250 300 350 4002
3 4 5 6 7 8
Hardness (GPa)
Displacement (nm) Strain rate = 5x10-3 s-1
60 80 100 120 140 160 180
Young's modulus (GPa)
100-150 (Mg17.7Cu82.3) 100-100 (Mg23.5Cu76.5) 100-50 (Mg40.4Cu59.6) Film thickness = 4000 nm
Indentation depth = 400 nm
Figure 4-25 Modulus-displacement and hardness-displacement curves of 100-150, 100-100, and 100-50 at the strain rate of 5×10-3 s-1.
146
50 100 150
70 80 90 100 110 120
2 3 4 5 6
Young's modulus (GPa)
Cu power (W)
100-150 Mg17.7Cu82.3 100-100
Mg23.5Cu76.5 100-50
Mg40.4Cu59.6
Hardness (GPa)
Figure 4-26 The compositional variation of Young’s modulus and hardness from the unloading regions compared among 100-150, 100-100, and 100-50.
147
0 50 100 150 200 250 300 350 400 450
-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Load (mN)
Displacement (nm) 100-150 (Mg17.7Cu82.3)
Strain rate = 5x10-3 s-1
Figure 4-27 Load-displacement curve of 100-150.
148
0 50 100 150 200 250 300 350 400
-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Load (mN)
Displacement (nm) 100-100 (Mg23.5Cu76.5)
Strain rate = 5x10-3 s-1
Figure 4-28 Load-displacement curve of 100-100.
149
0 50 100 150 200 250 300 350 400
-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Load (mN)
Displacement (nm) 100-50 (Mg40.4Cu59.6)
Strain rate = 5x10-3 s-1
Figure 4-29 Load-displacement curve of 100-50.
150
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 35
40 45 50 55 60 65 70 75 80 85 90 95 100
Cu percent (at%)
Cu Power (W)
50 series 100 series
expected values for the 100 series Ar pressure = 3x10-3 torr
Figure 5-1 Cu content as a function with Cu power in the Mg-Cu co-sputtered films, where the 100 series means the Mg power is RF 100 W, and the 50 series means the Mg power is RF 50 W.
151
Figure 5-2 Probability of collision in Xe, Kr, Ar, and Ne [52].
I
II
III
152
Figure 5-3 The structural transformation of Mg79Cu21 amorphous alloy annealed at 363 K [72].
153
Figure 5-4 A transmission electron micrograph showing the lamellar structure in the eutectic Cu-MgCu2 alloy, where white regions represent Cu crystalline phases, and black regions represent MgCu2 crystalline phases [73].
154
Figure 5-5 The indentation depth increasing from one step to the next is the sum of the elastic (Δhe) and the slow (Δhslow) and fast (Δhfast) plastic deformations, which can be determined by the slopes of the smoothed average curve, the corrected unloading curve and the slow regime [74].