The document describes a study investigating the effect of substrate tilt angle and argon gas flow rate on the structural properties of zinc oxide nanowires synthesized using a hot tube thermal evaporation method. Zinc oxide nanowires were grown on silicon substrates under different tilt angles (0-30 degrees) and flow rates (1.1-5.0 sccm). The nanowires were characterized using field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. The results showed that higher tilt angles and flow rates produced nanowires with improved density, higher aspect ratio, and altered optical properties.

1. Zinc Oxide Nanowires Synthesized using a Hot
Tube Thermal Evaporation under Intermediate
Heating Period
Samsudi Sakrani, Peshawa Omer
Amin, Syahida Suhaimi
December 2012

2. Contents
• INTRODUCTION
• METHODOLOGY
• CHARACTERIZATION
• RESULTS AND DISCUSSION
• CONCLUSIONS
2

3. INTRODUCTION
Properties of Zinc Oxide
•Direct band gap semiconductor 3.37 eV.
•Large excitation binding energy 60 meV.
•Near UV emission and transparent
conductivity.
•Piezoelectric property resulting from its
non-centrosymetric structure.
•Biosafe and biocompatible.
3

4. Previous-Current Works
• Basically, previous works on ZnO NWs
covered randomly orientated samples
(Abdulgafour et al., Comedi et al.),
Synthesis (G¨uell et al.) and
characterization (Chenet et al., Pan et
al., Suh et al.).
• Current work investigates the effect
of tilt angle and flow rate on the
structural properties of ZnO
nanowires - Not reported before.
4

5. Crystal Structure of the ZnO
ZnO crystallizes in two main
forms, hexagonal wurtzite &
cubic zincblende
wurtzite
Wurtzite: Most stable at ambient conditions
and thus most common
Zincblende form can be stabilized by
zincblende growing ZnO on substrates with cubic
lattice structure
5

6. Vapor-Liquid-Solid growth mechanism
T liquid
960°C
Au + ZnO+ liquid
• Nucleation of Au catalyst liquid
Au + ZnO
• ZnO diffuses into Au (Au/Zn)
Au ZnO
• Eutectic is attained, melting
point of Au-Zn alloy ZnO
becomes lower, ∼650 °C ZnO
ZnO
• Precipitation at 960°C, i.e.
growth of vertical ZnO begin Au Au/Zn ZnO
with incoming vapour and
Substrate
increase its height. Wisker Au droplet Au/Zn- Supersaturation Nanorod
alloy
is formed (blue) and
formation precipitation
formation

7. METHODOLOGY
7

8. Characterization
8

9. Experimental Setup
TET
9

10. Thermal Evaporation Techniques
(TET)
10

11. Experiment
Source Preparation
2ZnO + C Zn + CO2,
ZnO + CO Zn + CO2,
ZnO + (1 – x)CO ZnOx + (1 – x)CO2, X<1
Growth Parameters
• Catalyst used: Au (gold) nanoparticles.
• Distance between source and substrate.
• Angle between substrate and horizontal axis.
• Flow rate.
• Growth time.
11

12. Samples & Variables
Sample Tilt Angle Distance, Flow rate Furnace Growth
source- (sccm) Temperatur time (hr)
(°) substrate e
(cm) (°)
S1 30 18 1.1 960 1.0
S2 30 18 3.0 960 1.0
S3 30 18 3.0 960 1.5
S4 0 18 3.0 960 1.5
S5 30 18 5.0 960 1.5
12

13. FESEM & EDAX: Tilt Angle, 30°
FESEM
images
001
7200
6400 Si
5600
001
4800
Counts 4000
3200
2400
Zn Au Au Au Au
1600 O
Zn Au Zn Zn
800
0
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
1.0 µm
1.0 µm
keV
(a) Detection position of EDX spectra, and (b) EDX spectra of ZnO
nanowires on Si at tilt angle 30° and growth time 90 min.
13

14. FESEM & EDAX: Tilt Angle, 0°
FESEM
images
002
3300
3000 Si
2700
002
2400
2100
Counts
1800
1500
1200
900 Zn Au Au Au Au
O Zn
600 Au Zn Zn
300
0
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
1.0 µm
1.0 µm keV
(a) Detection position of EDX spectra, and (b) EDX spectra of ZnO
nanowires on Si at tilt angle 0° and growth time 90 min.
14

15. Effect of Substrate Tilt’s Angle
Substrate Zn (Atom O (Atom Aspect
angle, θ %) %) Ratio
(°)
0 7.47 11.98 5.5
30 7.37 12.82 7.7
15

16. FESEM & EDAX: Flow Rate, 1.1 sccm
FESEM
images
005
15000
13500 Si
12000
10500
Counts
9000
7500
6000
Au Au
4500 Au
Zn Au Au Pt
3000 O Zn Pt
Pt Pt Pt Zn Zn
1500
0
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
keV
005 10 µm
10 µm
(a) Detection position of EDX spectra, and (b) EDX spectra of ZnO
nanowires on Si at flow rate 1.1 sccm and growth time 60 min.
16

17. FESEM & EDAX: Flow Rate, 3.0 sccm
FESEM
images
004
13500
Si
12000
10500
9000
Counts
7500
6000
4500 Au Au
Zn Au
Au Au Pt
3000 Pt
O Zn Pt Pt Pt Zn Zn
1500
0
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
keV
004 10 µm
10 µm
(a) Detection position of EDX spectra, and (b) EDX spectra of ZnO
nanowires on Si at flow rate 3 sccm and growth time 60 min.
17

18. FESEM & EDAX: Flow Rate, 5.0 sccm
FESEM
images
(a) Detection position of EDX spectra, and (b) EDX spectra of ZnO
nanowires on Si at flow rate 5 sccm and growth time 90 min.
18

19. Effect of Argon Flow Rate
Ar Flow Zn (Atom O (Atom Aspect
Rate %) %) Ratio
(sccm)
1.1 0.29 1.82 8.6
3.0 0.82 1.23 4.1
5.0 1.67 6.05 10.5
19

20. PL Measurement
Effect of Angle Between Substrate and Horizontal Axis on
the Optical Properties of ZnO Nanowires.
20

21. PL Measurement
Effect of Flow Rate on the Optical Properties of
ZnO Nanowires.
PL results of ZnO nanowires on Si PL results of ZnO nanowires on
(a) at flow rate 1.1 sccm, (b) at flow Si at growth time 90 mints and
rate 3 sccm and (c) at flow rate 5 flow rate 5 sccm
sccm.
21

22. CONCLUSION
• ZnO NWs have been successfully grown on Si
(100) substrate using a hot tube thermal
evaporation under the substrate tilt angle
30° and argon flow rate of 5 sccm.
• Improved densities and higher aspect ratio
were observed.
• Emission properties occurred at a peak
around 380 nm (Eg = 3.27 eV) over the
visible region, but could slightly shifted due
to different processes and contaminations.
22

23. Acknowledgement
•UTM for financial assistance under RU
grant (J130000.7126.01H38).
•Member of QuaSR group for the support.
•Everyone involved in assisting and
succeeding the research.
23

24. References
• Abdulgafour, H. I., Hassan, Z., Al-Hardan, N. H. and Yam, F. K. Growth of highquality
zno nanowires without a catalyst. Physica B. 2010. 405: 42164218.
• Suh, D.-I., Byeon, C., Chisu, L. and Chang, L. Synthesis and optical characterization
of vertically grown zno nanowires in high crystallinity through vapor-liquid-solid growth
mechanism. Applied Surface Science. 2010. 257: 14541456.
• Pan Y., C. J., Tsao C. J., Kuo F. C., Chi C. H., Pong G. C., Chang B. J., Norton C. Y.,
Characterization of zno nanowires grown on si (100) with and without au catalyst.
Vacuum.
• Comedi, D., Tirado, M., Zapata, C., Heluani, S. P., Villafuerte, M., Mohseni, P. K. and
LaPierre, R. R. Randomly oriented zno nanowires grown on amorphous sio2 by
metal-catalyzed vapour deposition. Journal of Alloys and Compounds. 2010. 495:
439442.
• G¨uell, F., Osso, J. O., Go¨ni, A. R., Cornet, A. and Morante, J. R. Synthesis and
optical spectroscopy of zno nanowires. Superlattices and Microstructures. 2009. 45:
271–276.
• Wagner, R. S. and Ellis, W. C. Vapor-liquid-solid mechanism of single crystal growth.
Appl. Phys. Lett.. 1964. 89(4).
• Wang, N., Cai, Y. and Zhang, R. Growth of nanowires. Materials Science and
Engineering R. 2008. 60: 151.
24

25. Thank you
25

26. Note on Supersaturation
• Supersaturation refers to a solution that contains more of the
dissolved material than could be dissolved by the solvent under
normal circumstances. It can also refer to a vapor of a compound
that has a higher (partial) pressure than the vapor pressure of that
compound.
• In science, supersaturated is a solution that contains more
material dissolved in it than the liquid can absorb under normal
conditions. By heating the liquid, we can increase it absorption
capacity. The material to be dissolved is called solute while the
liquid in which the solute is being dissolved is called solvent.
Suppose water is your solvent while sugar is your solute. You
dissolve sugar in water slowly till a point comes that the water
does not dissolve anymore sugar in it and it starts to deposit at
the bottom of the container, called saturation point. To make the
solution supersaturated, now heat the solution, you will see that
the deposited sugar will also dissolve and water will absorb even
more sugar. This shows that when we heated the solution it
absorbed more solute than it did under normal conditions to form
a supersaturated solution.
26

27. Au-Zn Phase Diagram
27

28. Contents
• INTRODUCTION
• METHODOLOGY
• CHARACTERIZATION
• RESULTS AND DISCUSSION
• CONCLUSIONS
28

29. INTRODUCTION
Properties of Zinc Oxide
•Direct band gap semiconductor 3.37 eV.
•Large excitation binding energy 60 meV.
•Near UV emission and transparent
conductivity.
•Piezoelectric property resulting from its
non-centrosymetric structure.
•Biosafe and biocompatible.
29

30. Previous-Current Works
• Basically, previous works on ZnO NWs
covered randomly orientated samples
(Abdulgafour et al., Comedi et al.),
Synthesis (G¨uell et al.) and
characterization (Chenet et al., Pan et
al., Suh et al.).
• Current work investigates the effect
of tilt angle and flow rate on the
structural properties of ZnO
nanowires - Not reported before.
30

31. Crystal Structure of the ZnO
ZnO crystallizes in two main
forms, hexagonal wurtzite &
cubic zincblende
wurtzite
Wurtzite: Most stable at ambient conditions
and thus most common
Zincblende form can be stabilized by
zincblende growing ZnO on substrates with cubic
lattice structure
31

32. Vapor-Liquid-Solid growth mechanism
T liquid
960°C
Au + ZnO+ liquid
• Nucleation of Au catalyst liquid
Au + ZnO
• ZnO diffuses into Au (Au/Zn)
Au ZnO
• Eutectic is attained, melting
point of Au-Zn alloy
ZnO
becomes lower, ∼650 °C
ZnO
ZnO
• Precipitation at 960°C, i.e.
growth of vertical ZnO begin
with incoming vapour and Au Au/Zn ZnO
increase its height. Wisker Substrate
is formed (blue) Au droplet Au/Zn- Supersaturation
alloy and
Nanorod
formation
formation precipitation

33. METHODOLOGY
33

34. Characterization
34

35. Experimental Setup
TET
35

36. Thermal Evaporation Techniques
(TET)
36

37. Experiment
Source Preparation
2ZnO + C Zn + CO2,
ZnO + CO Zn + CO2,
ZnO + (1 – x)CO ZnOx + (1 – x)CO2, X<1
Growth Parameters
• Catalyst used: Au (gold) nanoparticles.
• Distance between source and substrate.
• Angle between substrate and horizontal axis.
• Flow rate.
• Growth time.
37

38. Samples & Variables
Sample Tilt Angle Distance, Flow rate Furnace Growth
source- (sccm) Temperatur time (hr)
(°) substrate e
(cm) (°)
S1 30 18 1.1 960 1.0
S2 30 18 3.0 960 1.0
S3 30 18 3.0 960 1.5
S4 0 18 3.0 960 1.5
S5 30 18 5.0 960 1.5
38

39. FESEM & EDAX: Tilt Angle, 30°
FESEM
images
001
7200
6400 Si
5600
001
4800
Counts 4000
3200
2400
Zn Au Au Au Au
1600 O
Zn Au Zn Zn
800
0
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
1.0 µm
1.0 µm
keV
(a) Detection position of EDX spectra, and (b) EDX spectra of ZnO
nanowires on Si at tilt angle 30° and growth time 90 min.
39

40. FESEM & EDAX: Tilt Angle, 0°
FESEM
images
002
3300
3000 Si
2700
002
2400
2100
Counts
1800
1500
1200
900 Zn Au Au Au Au
O Zn
600 Au Zn Zn
300
0
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
1.0 µm
1.0 µm keV
(a) Detection position of EDX spectra, and (b) EDX spectra of ZnO
nanowires on Si at tilt angle 0° and growth time 90 min.
40

41. Effect of Substrate Tilt’s Angle
Substrate Zn (Atom O (Atom Aspect
angle, θ %) %) Ratio
(°)
0 7.47 11.98 5.5
30 7.37 12.82 7.7
41

42. FESEM & EDAX: Flow Rate, 1.1 sccm
FESEM
images
005
15000
13500 Si
12000
10500
Counts
9000
7500
6000
Au Au
4500 Au
Zn Au Au Pt
3000 O Zn Pt
Pt Pt Pt Zn Zn
1500
0
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
keV
005 10 µm
10 µm
(a) Detection position of EDX spectra, and (b) EDX spectra of ZnO
nanowires on Si at flow rate 1.1 sccm and growth time 60 min.
42

43. FESEM & EDAX: Flow Rate, 3.0 sccm
FESEM
images
004
13500
Si
12000
10500
9000
Counts
7500
6000
4500 Au Au
Zn Au
Au Au Pt
3000 Pt
O Zn Pt Pt Pt Zn Zn
1500
0
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
keV
004 10 µm
10 µm
(a) Detection position of EDX spectra, and (b) EDX spectra of ZnO
nanowires on Si at flow rate 3 sccm and growth time 60 min.
43

44. FESEM & EDAX: Flow Rate, 5.0
sccm
FESEM
images
(a) Detection position of EDX spectra, and (b) EDX spectra of ZnO
nanowires on Si at flow rate 5 sccm and growth time 90 min.
44

45. Effect of Argon Flow Rate
Ar Flow Zn (Atom O (Atom Aspect
Rate %) %) Ratio
(sccm)
1.1 0.29 1.82 8.6
3.0 0.82 1.23 4.1
5.0 1.67 6.05 10.5
45

46. PL Measurement
Effect of Angle Between Substrate and Horizontal Axis on
the Optical Properties of ZnO Nanowires.
46

47. PL Measurement
Effect of Flow Rate on the Optical Properties of
ZnO Nanowires.
PL results of ZnO nanowires on Si PL results of ZnO nanowires on
(a) at flow rate 1.1 sccm, (b) at flow Si at growth time 90 mints and
rate 3 sccm and (c) at flow rate 5 flow rate 5 sccm
sccm.
47

48. CONCLUSION
• ZnO NWs have been successfully grown on Si
(100) substrate using a hot tube thermal
evaporation under the substrate tilt angle
30° and argon flow rate of 5 sccm.
• Improved densities and higher aspect ratio
were observed.
• Emission properties occurred at a peak
around 380 nm (Eg = 3.27 eV) over the
visible region, but could slightly shifted due
to different processes and contaminations.
48

49. Acknowledgement
•UTM for financial assistance under RU
grant (J130000.7126.01H38).
•Member of QuaSR group for the support.
•Everyone involved in assisting and
succeeding the research.
49

50. References
• Abdulgafour, H. I., Hassan, Z., Al-Hardan, N. H. and Yam, F. K. Growth of highquality
zno nanowires without a catalyst. Physica B. 2010. 405: 42164218.
• Suh, D.-I., Byeon, C., Chisu, L. and Chang, L. Synthesis and optical characterization
of vertically grown zno nanowires in high crystallinity through vapor-liquid-solid growth
mechanism. Applied Surface Science. 2010. 257: 14541456.
• Pan Y., C. J., Tsao C. J., Kuo F. C., Chi C. H., Pong G. C., Chang B. J., Norton C. Y.,
Characterization of zno nanowires grown on si (100) with and without au catalyst.
Vacuum.
• Comedi, D., Tirado, M., Zapata, C., Heluani, S. P., Villafuerte, M., Mohseni, P. K. and
LaPierre, R. R. Randomly oriented zno nanowires grown on amorphous sio2 by
metal-catalyzed vapour deposition. Journal of Alloys and Compounds. 2010. 495:
439442.
• G¨uell, F., Osso, J. O., Go¨ni, A. R., Cornet, A. and Morante, J. R. Synthesis and
optical spectroscopy of zno nanowires. Superlattices and Microstructures. 2009. 45:
271–276.
• Wagner, R. S. and Ellis, W. C. Vapor-liquid-solid mechanism of single crystal growth.
Appl. Phys. Lett.. 1964. 89(4).
• Wang, N., Cai, Y. and Zhang, R. Growth of nanowires. Materials Science and
Engineering R. 2008. 60: 151.
50

51. Thank you
51

52. Note on Supersaturation
• Supersaturation refers to a solution that contains more of the
dissolved material than could be dissolved by the solvent under
normal circumstances. It can also refer to a vapor of a compound
that has a higher (partial) pressure than the vapor pressure of that
compound.
• In science, supersaturated is a solution that contains more
material dissolved in it than the liquid can absorb under normal
conditions. By heating the liquid, we can increase it absorption
capacity. The material to be dissolved is called solute while the
liquid in which the solute is being dissolved is called solvent.
Suppose water is your solvent while sugar is your solute. You
dissolve sugar in water slowly till a point comes that the water
does not dissolve anymore sugar in it and it starts to deposit at
the bottom of the container, called saturation point. To make the
solution supersaturated, now heat the solution, you will see that
the deposited sugar will also dissolve and water will absorb even
more sugar. This shows that when we heated the solution it
absorbed more solute than it did under normal conditions to form
a supersaturated solution.
52

53. Au-Zn Phase Diagram
53

54. Contents
• INTRODUCTION
• METHODOLOGY
• CHARACTERIZATION
• RESULTS AND DISCUSSION
• CONCLUSIONS
54

55. INTRODUCTION
Properties of Zinc Oxide
•Direct band gap semiconductor 3.37 eV.
•Large excitation binding energy 60 meV.
•Near UV emission and transparent
conductivity.
•Piezoelectric property resulting from its
non-centrosymetric structure.
•Biosafe and biocompatible.
55

56. Previous-Current Works
• Basically, previous works on ZnO NWs
covered randomly orientated samples
(Abdulgafour et al., Comedi et al.),
Synthesis (G¨uell et al.) and
characterization (Chenet et al., Pan et
al., Suh et al.).
• Current work investigates the effect
of tilt angle and flow rate on the
structural properties of ZnO
nanowires - Not reported before.
56

57. Crystal Structure of the ZnO
ZnO crystallizes in two main
forms, hexagonal wurtzite &
cubic zincblende
wurtzite
Wurtzite: Most stable at ambient conditions
and thus most common
Zincblende form can be stabilized by
zincblende growing ZnO on substrates with cubic
lattice structure
57

58. Vapor-Liquid-Solid growth mechanism
T liquid
960°C
Au + ZnO+ liquid
• Nucleation of Au catalyst liquid
Au + ZnO
• ZnO diffuses into Au (Au/Zn)
Au ZnO
• Eutectic is attained, melting
point of Au-Zn alloy
ZnO
becomes lower, ∼650 °C
ZnO
ZnO
• Precipitation at 960°C, i.e.
growth of vertical ZnO begin
with incoming vapour and Au Au/Zn ZnO
increase its height. Wisker Substrate
is formed (blue) Au droplet Au/Zn- Supersaturation
alloy and
Nanorod
formation
formation precipitation

59. METHODOLOGY
59

60. Characterization
60

61. Experimental Setup
TET
61

62. Thermal Evaporation Techniques
(TET)
62

63. Experiment
Source Preparation
2ZnO + C Zn + CO2,
ZnO + CO Zn + CO2,
ZnO + (1 – x)CO ZnOx + (1 – x)CO2, X<1
Growth Parameters
• Catalyst used: Au (gold) nanoparticles.
• Distance between source and substrate.
• Angle between substrate and horizontal axis.
• Flow rate.
• Growth time.
63

64. Samples & Variables
Sample Tilt Angle Distance, Flow rate Furnace Growth
source- (sccm) Temperatur time (hr)
(°) substrate e
(cm) (°)
S1 30 18 1.1 960 1.0
S2 30 18 3.0 960 1.0
S3 30 18 3.0 960 1.5
S4 0 18 3.0 960 1.5
S5 30 18 5.0 960 1.5
64

65. FESEM & EDAX: Tilt Angle, 30°
FESEM
images
001
7200
6400 Si
5600
001
4800
Counts 4000
3200
2400
Zn Au Au Au Au
1600 O
Zn Au Zn Zn
800
0
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
1.0 µm
1.0 µm
keV
(a) Detection position of EDX spectra, and (b) EDX spectra of ZnO
nanowires on Si at tilt angle 30° and growth time 90 min.
65

66. FESEM & EDAX: Tilt Angle, 0°
FESEM
images
002
3300
3000 Si
2700
002
2400
2100
Counts
1800
1500
1200
900 Zn Au Au Au Au
O Zn
600 Au Zn Zn
300
0
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
1.0 µm
1.0 µm keV
(a) Detection position of EDX spectra, and (b) EDX spectra of ZnO
nanowires on Si at tilt angle 0° and growth time 90 min.
66

67. Effect of Substrate Tilt’s Angle
Substrate Zn (Atom O (Atom Aspect
angle, θ %) %) Ratio
(°)
0 7.47 11.98 5.5
30 7.37 12.82 7.7
67

68. FESEM & EDAX: Flow Rate, 1.1 sccm
FESEM
images
005
15000
13500 Si
12000
10500
Counts
9000
7500
6000
Au Au
4500 Au
Zn Au Au Pt
3000 O Zn Pt
Pt Pt Pt Zn Zn
1500
0
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
keV
005 10 µm
10 µm
(a) Detection position of EDX spectra, and (b) EDX spectra of ZnO
nanowires on Si at flow rate 1.1 sccm and growth time 60 min.
68

69. FESEM & EDAX: Flow Rate, 3.0 sccm
FESEM
images
004
13500
Si
12000
10500
9000
Counts
7500
6000
4500 Au Au
Zn Au
Au Au Pt
3000 Pt
O Zn Pt Pt Pt Zn Zn
1500
0
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
keV
004 10 µm
10 µm
(a) Detection position of EDX spectra, and (b) EDX spectra of ZnO
nanowires on Si at flow rate 3 sccm and growth time 60 min.
69

70. FESEM & EDAX: Flow Rate, 5.0
sccm
FESEM
images
(a) Detection position of EDX spectra, and (b) EDX spectra of ZnO
nanowires on Si at flow rate 5 sccm and growth time 90 min.
70

71. Effect of Argon Flow Rate
Ar Flow Zn (Atom O (Atom Aspect
Rate %) %) Ratio
(sccm)
1.1 0.29 1.82 8.6
3.0 0.82 1.23 4.1
5.0 1.67 6.05 10.5
71

72. PL Measurement
Effect of Angle Between Substrate and Horizontal Axis on
the Optical Properties of ZnO Nanowires.
72

73. PL Measurement
Effect of Flow Rate on the Optical Properties of
ZnO Nanowires.
PL results of ZnO nanowires on Si PL results of ZnO nanowires on
(a) at flow rate 1.1 sccm, (b) at flow Si at growth time 90 mints and
rate 3 sccm and (c) at flow rate 5 flow rate 5 sccm
sccm.
73

74. CONCLUSION
• ZnO NWs have been successfully grown on Si
(100) substrate using a hot tube thermal
evaporation under the substrate tilt angle
30° and argon flow rate of 5 sccm.
• Improved densities and higher aspect ratio
were observed.
• Emission properties occurred at a peak
around 380 nm (Eg = 3.27 eV) over the
visible region, but could slightly shifted due
to different processes and contaminations.
74

75. Acknowledgement
•UTM for financial assistance under RU
grant (J130000.7126.01H38).
•Member of QuaSR group for the support.
•Everyone involved in assisting and
succeeding the research.
75

76. References
• Abdulgafour, H. I., Hassan, Z., Al-Hardan, N. H. and Yam, F. K. Growth of highquality
zno nanowires without a catalyst. Physica B. 2010. 405: 42164218.
• Suh, D.-I., Byeon, C., Chisu, L. and Chang, L. Synthesis and optical characterization
of vertically grown zno nanowires in high crystallinity through vapor-liquid-solid growth
mechanism. Applied Surface Science. 2010. 257: 14541456.
• Pan Y., C. J., Tsao C. J., Kuo F. C., Chi C. H., Pong G. C., Chang B. J., Norton C. Y.,
Characterization of zno nanowires grown on si (100) with and without au catalyst.
Vacuum.
• Comedi, D., Tirado, M., Zapata, C., Heluani, S. P., Villafuerte, M., Mohseni, P. K. and
LaPierre, R. R. Randomly oriented zno nanowires grown on amorphous sio2 by
metal-catalyzed vapour deposition. Journal of Alloys and Compounds. 2010. 495:
439442.
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77. Thank you
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78. Note on Supersaturation
• Supersaturation refers to a solution that contains more of the
dissolved material than could be dissolved by the solvent under
normal circumstances. It can also refer to a vapor of a compound
that has a higher (partial) pressure than the vapor pressure of that
compound.
• In science, supersaturated is a solution that contains more
material dissolved in it than the liquid can absorb under normal
conditions. By heating the liquid, we can increase it absorption
capacity. The material to be dissolved is called solute while the
liquid in which the solute is being dissolved is called solvent.
Suppose water is your solvent while sugar is your solute. You
dissolve sugar in water slowly till a point comes that the water
does not dissolve anymore sugar in it and it starts to deposit at
the bottom of the container, called saturation point. To make the
solution supersaturated, now heat the solution, you will see that
the deposited sugar will also dissolve and water will absorb even
more sugar. This shows that when we heated the solution it
absorbed more solute than it did under normal conditions to form
a supersaturated solution.
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79. Au-Zn Phase Diagram
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