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Zinc Oxide Nanowires Prepared by Hot Tube Thermal Evaporation

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I presented at Regional Annual Fundamental Science Symposium 2012

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Zinc Oxide Nanowires Prepared by Hot Tube Thermal Evaporation

  1. 1. Zinc Oxide Nanowires Synthesized using a HotTube Thermal Evaporation under Intermediate Heating Period Samsudi Sakrani, Peshawa Omer Amin, Syahida Suhaimi December 2012
  2. 2. Contents• INTRODUCTION• METHODOLOGY• CHARACTERIZATION• RESULTS AND DISCUSSION• CONCLUSIONS 2
  3. 3. INTRODUCTIONProperties of Zinc Oxide•Direct band gap semiconductor 3.37 eV.•Large excitation binding energy 60 meV.•Near UV emission and transparentconductivity.•Piezoelectric property resulting from itsnon-centrosymetric structure.•Biosafe and biocompatible. 3
  4. 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. 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 byzincblende growing ZnO on substrates with cubic lattice structure 5
  6. 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. 7. METHODOLOGY 7
  8. 8. Characterization 8
  9. 9. Experimental SetupTET 9
  10. 10. Thermal Evaporation Techniques (TET) 10
  11. 11. ExperimentSource Preparation 2ZnO + C Zn + CO2, ZnO + CO Zn + CO2,  ZnO + (1 – x)CO ZnOx + (1 – x)CO2, X<1Growth Parameters• Catalyst used: Au (gold) nanoparticles.• Distance between source and substrate.• Angle between substrate and horizontal axis.• Flow rate.• Growth time. 11
  12. 12. Samples & VariablesSample 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. 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 ZnOnanowires on Si at tilt angle 30° and growth time 90 min. 13
  14. 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 ZnOnanowires on Si at tilt angle 0° and growth time 90 min. 14
  15. 15. Effect of Substrate Tilt’s AngleSubstrate Zn (Atom O (Atom Aspect angle, θ %) %) Ratio (°) 0 7.47 11.98 5.5 30 7.37 12.82 7.7 15
  16. 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 ZnOnanowires on Si at flow rate 1.1 sccm and growth time 60 min. 16
  17. 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 ZnOnanowires on Si at flow rate 3 sccm and growth time 60 min. 17
  18. 18. FESEM & EDAX: Flow Rate, 5.0 sccm FESEM images(a) Detection position of EDX spectra, and (b) EDX spectra of ZnOnanowires on Si at flow rate 5 sccm and growth time 90 min. 18
  19. 19. Effect of Argon Flow RateAr 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. 20. PL MeasurementEffect of Angle Between Substrate and Horizontal Axis onthe Optical Properties of ZnO Nanowires. 20
  21. 21. PL MeasurementEffect of Flow Rate on the Optical Properties ofZnO 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. 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. 23. Acknowledgement•UTM for financial assistance under RUgrant (J130000.7126.01H38).•Member of QuaSR group for the support.•Everyone involved in assisting andsucceeding the research. 23
  24. 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. 25. Thank you 25
  26. 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. 27. Au-Zn Phase Diagram 27
  28. 28. Contents• INTRODUCTION• METHODOLOGY• CHARACTERIZATION• RESULTS AND DISCUSSION• CONCLUSIONS 28
  29. 29. INTRODUCTIONProperties of Zinc Oxide•Direct band gap semiconductor 3.37 eV.•Large excitation binding energy 60 meV.•Near UV emission and transparentconductivity.•Piezoelectric property resulting from itsnon-centrosymetric structure.•Biosafe and biocompatible. 29
  30. 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. 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 byzincblende growing ZnO on substrates with cubic lattice structure 31
  32. 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. 33. METHODOLOGY 33
  34. 34. Characterization 34
  35. 35. Experimental SetupTET 35
  36. 36. Thermal Evaporation Techniques (TET) 36
  37. 37. ExperimentSource Preparation 2ZnO + C Zn + CO2, ZnO + CO Zn + CO2,  ZnO + (1 – x)CO ZnOx + (1 – x)CO2, X<1Growth Parameters• Catalyst used: Au (gold) nanoparticles.• Distance between source and substrate.• Angle between substrate and horizontal axis.• Flow rate.• Growth time. 37
  38. 38. Samples & VariablesSample 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. 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 ZnOnanowires on Si at tilt angle 30° and growth time 90 min. 39
  40. 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 ZnOnanowires on Si at tilt angle 0° and growth time 90 min. 40
  41. 41. Effect of Substrate Tilt’s AngleSubstrate Zn (Atom O (Atom Aspect angle, θ %) %) Ratio (°) 0 7.47 11.98 5.5 30 7.37 12.82 7.7 41
  42. 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 ZnOnanowires on Si at flow rate 1.1 sccm and growth time 60 min. 42
  43. 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 ZnOnanowires on Si at flow rate 3 sccm and growth time 60 min. 43
  44. 44. FESEM & EDAX: Flow Rate, 5.0 sccm FESEM images(a) Detection position of EDX spectra, and (b) EDX spectra of ZnOnanowires on Si at flow rate 5 sccm and growth time 90 min. 44
  45. 45. Effect of Argon Flow RateAr 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. 46. PL MeasurementEffect of Angle Between Substrate and Horizontal Axis onthe Optical Properties of ZnO Nanowires. 46
  47. 47. PL MeasurementEffect of Flow Rate on the Optical Properties ofZnO 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. 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. 49. Acknowledgement•UTM for financial assistance under RUgrant (J130000.7126.01H38).•Member of QuaSR group for the support.•Everyone involved in assisting andsucceeding the research. 49
  50. 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. 51. Thank you 51
  52. 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. 53. Au-Zn Phase Diagram 53
  54. 54. Contents• INTRODUCTION• METHODOLOGY• CHARACTERIZATION• RESULTS AND DISCUSSION• CONCLUSIONS 54
  55. 55. INTRODUCTIONProperties of Zinc Oxide•Direct band gap semiconductor 3.37 eV.•Large excitation binding energy 60 meV.•Near UV emission and transparentconductivity.•Piezoelectric property resulting from itsnon-centrosymetric structure.•Biosafe and biocompatible. 55
  56. 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. 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 byzincblende growing ZnO on substrates with cubic lattice structure 57
  58. 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. 59. METHODOLOGY 59
  60. 60. Characterization 60
  61. 61. Experimental SetupTET 61
  62. 62. Thermal Evaporation Techniques (TET) 62
  63. 63. ExperimentSource Preparation 2ZnO + C Zn + CO2, ZnO + CO Zn + CO2,  ZnO + (1 – x)CO ZnOx + (1 – x)CO2, X<1Growth Parameters• Catalyst used: Au (gold) nanoparticles.• Distance between source and substrate.• Angle between substrate and horizontal axis.• Flow rate.• Growth time. 63
  64. 64. Samples & VariablesSample 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. 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 ZnOnanowires on Si at tilt angle 30° and growth time 90 min. 65
  66. 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 ZnOnanowires on Si at tilt angle 0° and growth time 90 min. 66
  67. 67. Effect of Substrate Tilt’s AngleSubstrate Zn (Atom O (Atom Aspect angle, θ %) %) Ratio (°) 0 7.47 11.98 5.5 30 7.37 12.82 7.7 67
  68. 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 ZnOnanowires on Si at flow rate 1.1 sccm and growth time 60 min. 68
  69. 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 ZnOnanowires on Si at flow rate 3 sccm and growth time 60 min. 69
  70. 70. FESEM & EDAX: Flow Rate, 5.0 sccm FESEM images(a) Detection position of EDX spectra, and (b) EDX spectra of ZnOnanowires on Si at flow rate 5 sccm and growth time 90 min. 70
  71. 71. Effect of Argon Flow RateAr 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. 72. PL MeasurementEffect of Angle Between Substrate and Horizontal Axis onthe Optical Properties of ZnO Nanowires. 72
  73. 73. PL MeasurementEffect of Flow Rate on the Optical Properties ofZnO 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. 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. 75. Acknowledgement•UTM for financial assistance under RUgrant (J130000.7126.01H38).•Member of QuaSR group for the support.•Everyone involved in assisting andsucceeding the research. 75
  76. 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.• 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. 76
  77. 77. Thank you 77
  78. 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. 78
  79. 79. Au-Zn Phase Diagram 79

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