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新穎碳基奈米材料在場發射應用上的合成與改質

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(1)國 立 交 通 大 學 材料科學與工程學系 博士論文 新穎碳基奈米材料在場發射應用上的合成與改質. Fabrication and Modification of New Carbon Based Nanomaterials for Field Emission Devices. 研 究 生:蔡 佳 倫 指導教授:陳 家 富 博士. 中華民國 九十三 年 六 月.

(2) 新穎碳基奈米材料在場發射應用上的合成與改質. Fabrication and Modification of New Carbon Based Nanomaterials for Field Emission Devices. Student:Chia-Lun Tsai. 研 究 生:蔡佳倫. Advisor:Chia-Fu Chen. 指導教授:陳家富. 國 立 交 通 大 學 材料科學與工程學系 博 士 論 文. A Dissertation Submitted to Department of Material Science and Engineering College of Engineering National Chiao Tung University in partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Material Science and Engineering June 2004 Hsinchu, Taiwan. 中華民國 九十三 年 六 月.

(3) 新穎碳基奈米材料在場發射應用上的合成與改質 研究生:蔡佳倫. 指導教授:陳家富 博士 國立交通大學材料與工程學系 摘. 要. 場發射顯示器是一個由許多場發射源組成的高亮度平面顯示器。在未來的平 面顯示器中,場發射顯示器是一個令人值得期待的一個技術。由於深具潛力,奈 米碳基材料已被視為場發射源的最佳材料之一。因此本論文的研究主要著重在如 何提升奈米碳基材料的場發射電子特性。研究方向分為兩大類:第一則是材料改 質,藉此提升材料場發射之電子特性。第二則是合成新穎的奈米碳基材料,利用 其獨特的奈米效應來增加場發射電流。 在材料改質方面,主要是利用偏壓效應、P 型或 N 型之摻雜源與類鑽碳披覆 來提升傳統碳基材料的電子特性。實驗結果顯示,偏壓效應除了可提升材料的成 長速度,並可提供電場使材料在垂直基板方向成長。而在摻雜 N 型或 P 型的方 面,提供多餘的電子或電洞明顯使單位面積的場發射電流密度增加。 而在合成新穎奈米碳基材料上,除了利用上述方法提升奈米碳管的場發射特 性之外。我們也首先發表了新穎的奈米碳基材料:奈米石墨尖錐與奈米碳化鉻顆 粒。相對於奈米碳管的石墨空心結構,穿透式電子顯微鏡發現奈米石墨尖錐呈現 出石墨組成的實心結構與垂直基板的成長方向。此外,頂部的針狀結構亦提高了 電子激發效率與場發射特徵常數(β)。若先鍍上一層鉻的金屬薄膜,可發現金屬 鉻會被成長中的每根奈米石墨尖錐由下往上舉起,並逐漸碳化成一顆一顆的奈米 碳化鉻顆粒。而這些奈米級大小的碳化鉻在場發射量測中,藉其本身的量子尺寸 效應提供了較佳的表面電子傳輸,明顯地增加了場發射電流。這種自發性對位形 成的微小奈米顆粒將可以被應用在許多方面。此外,利用半導體技術我們成功製 造了一具有低孔徑 (4 微米) 的金屬/絕緣體/半導體 (MIS)的三極場發射元件。 元件中的閘極結構可輕易的激發電子跳出,除了增加場發射電流之外,也有效地 降低起始電壓。 i.

(4) Fabrication and Modification of New Carbon Based Nanomaterials for Field Emission Devices. Student: Chia-Lun Tsai. Advisor: Dr. Chia-Fu Chen. Institute of Materials Science and Engineering National Chiao Tung University Abstract Field emission display (FED) is a promising flat panel display in which the images are formed from large array of pixels, each addressed by controllable field emission sources. Recently, carbon based nanomaterials have attracted great interest owing to their potential application of field emission. This dissertation mainly aims at the improvement of carbon based nanomaterials on field emission characteristic. Research can be divided into two following categories. First is modifying materials’ property in order to enhance their field emission characteristic. Second is fabricating new carbon based nanomaterials to increase their field emission currents by using their unique properties. The bias effect; N or P-type dopants and diamond-like carbon cladding are used to improve field emission characteristics of materials. Experimental results indicate that bias effect would not only increase the growth rate but also lead to the well-aligned inclination. Doping additional electrons or holes into carbon material system results in the increase of field emission currents. In the fabrication of new material field, graphite nanotip and itself capped with Cr nano particles have been first reported in the world. Compared to the hollow structure of nanotubes, graphite nanotips display the solid body and well aligned growth direction. The needle-like shape causes the electrons easily induced and larger field enhancement (β). Pre-deposition of Cr thin film will form the nanocrystalline chromium carbides on the top of the individual graphite nanotips, providing higher surface conductivity for electrons transportation. This self-alignment could be used in many applications. Moreover, low threshold voltage and high current density characterization is successfully achieved by using gated structure device. ii.

(5) Acknowledgment Many people have assisted me during this dissertation work. I’m very grateful to my graduate advisor Prof. C. F. Chen, whose inspiration and guidance benefited me significantly; without his support, this work could not have been finished. The author would like to acknowledge the financial support from the National Science Council of Taiwan. Thanks to Miss Jeng Mei-Li for providing access to the TEM. I would like to express my appreciation to my colleagues, especially the kindly discussion from Dr. Chien- Liang Lin. Many thanks to my family, my sister, sister-in-law; and my lovely nephew and niece. I feel particularly grateful to my brother Chia-Fong Tsai, who helped me and cared me greatly in my life. I really want to devote this dissertation to my parents, their endless love and spirit encouragement is my main motive power on research.. iii.

(6) TABLE OF CONTENTS Page ABSTRACT (CHINESE) .......................................................................................... i ABSTRACT (ENGLISH) ......................................................................................... ii ACKNOWLEDGEMENT....................................................................................... iii TABLE OF CONTENTS......................................................................................... iv LIST OF TABLES.................................................................................................. viii LIST OF FIGURES ................................................................................................. ix CHAPTER 1. INTRODUCTION ............................................................................ 1 1.1. Preface ............................................................................................... 1. 1.2. Why carbon-based materials?......................................................... 2. 1.3. Why nanosize requirement?.......................................................... 15. 1.4. Advantage of field emission display.............................................. 15. 1.5. Motivation ....................................................................................... 19. 1.6. Reference ......................................................................................... 21. CHAPTER 2. FUNDAMENTAL THEORY......................................................... 24 2.1. Field Emission from metals ........................................................... 24 2.1.1. Field emission from semiconductor .............................................. 26. 2.1.2. Fowler-Nordheim equation for gated FEA .................................. 28. 2.2. Bias enhances nucleation of diamond in microwave CVD ......... 30. 2.3. Reference ......................................................................................... 33. CHAPTER 3. EXPERIMENT METHOD............................................................ 35 3.1. Experimental details........................................................................35. 3.2. Bias assisted microwave plasma chemical vapor deposition system ...........................................................................................................35. 3.3. Deposition conditions of various carbon-based nanomaterials...38. 3.4. Characterization of carbon-based nanomaterials ........................38 3.4.1. Scanning electron microscopy (SEM)............................................38. 3.4.2. Micro-Raman spectroscopy ............................................................38. 3.4.3. Secondary ion mass spectrometry (SIMS) ....................................41. iv.

(7) 3.4.4. Measurement of field emission characterization ..........................41. 3.4.5. Transmission electron microscopy (TEM) ....................................42. 3.4.6. Electron energy loss spectroscopy(EELS).....................................42. 3.5. Reference ..........................................................................................46. CHAPTER 4. MODIFICATION OF SILICON NANO EMITTERS BY DIAMOND-CLAD PROCESS.......................................................47 4.1 Introduction........................................................................................................47 4.2 Experiment .........................................................................................................48 4.3 Results and discussion .......................................................................................49 4.4 Conclusion ..........................................................................................................60 4.5 Reference ...........................................................................................................61 CHAPTER 5. CHARACTERIZATION OF NANOSIZED DIAMOND-LIKE CARBON EMITTERS ARRAYS ..................................................63 5.1. Introduction .....................................................................................63. 5.2. Experiment.......................................................................................66 5.2.1. Deposition of silicon oxide by furnace and LPCVD system ........66. 5.2.2. Lithography .....................................................................................66. 5.2.3. Deposition of Ti and Pt films as gated layer using dual-gun evaporator........................................................................................66. 5.2.4. Remove photoresist by lift-off process...........................................67. 5.2.5. Removal of silicon oxide layer by metal etcher system ................67. 5.2.6. Diamond-like carbon emitters deposition condition. 5.3. Results and discussion.....................................................................70. 5.4. Conclusion........................................................................................85. 5.5. Reference..........................................................................................86. CHAPTER 6. BIAS AND REACTIVE GASES EFFECTS ON THE GROWTH OF CARBON NANOTUBES .........................................................89 6.1. Introduction .....................................................................................89. Part A. Bias effect on the growth of carbon nanotubes.............................90. 6.2A. Experiment.......................................................................................90. 6.3A. Results and discussion.....................................................................90. v.

(8) Part B. Reactive gas effect on the growth of carbon nanotubes.............104. 6.2B. Experiment.....................................................................................104. 6.3B. Results and discussion...................................................................104. 6.4. Conclusion...................................................................................... 118. 6.5. Reference ........................................................................................ 119. CHAPTER 7. CHARACTERIZATION OF BORON-DOPED CARBON NANOTUBE ARRAYS .................................................................121 7.1. Introduction ...................................................................................121. 7.2. Experiment.....................................................................................121. 7.3. Results and discussion...................................................................123. 7.4. Conclusion ......................................................................................143. 7.5. Reference ........................................................................................145. CHAPTER 8. FIELD EMISSION FROM WELL-ALIGNED CARRBON NANOTIPS ....................................................................................147 8.1. Introduction ...................................................................................147. Part A. Field emission of well-aligned carbon nanotips in diode structure. .........................................................................................................148. 8.2A. Experiment.....................................................................................148. 8.3A. Results and discussion...................................................................148. Part B. Field emission of well-aligned carbon nanotips in gated structure. .........................................................................................................158. 8.2B. Experiment.....................................................................................158. 8.3B. Results and discussion...................................................................158. 8.4. Conclusion......................................................................................166. 8.5. Reference ........................................................................................167. CHAPTER 9. SELF-EMBEDDED OF NANOCRYSTALLINE CHROMIUM CARBIDES ON WELL-ALIGNED CARBON NANOTIPS ....169 9.1. Introduction ...................................................................................169. 9.2. Experiment.....................................................................................170. 9.3. Results and discussion...................................................................171. 9.4. Conclusion ......................................................................................182. vi.

(9) 9.5. Reference ........................................................................................183. CHAPTER 10. CONCLUSION ..........................................................................184 LIST OF PUBLICATIONS ...................................................................................187 RESUME ................................................................................................................190. vii.

(10) LIST OF TABLES Page 5.1. Conditions of deposited Ti and Pt layers ........................................................ 67. 5.2. Deposition conditions of undoped, boron and phosphours-doped DLC emitters, respectively ..................................................................................................... 69. 6.1. Summaries of the comparison of CNTs grown with CH4/H2 and CH4/CO2 mixtures..........................................................................................................113. 6.2. Deposition conditions of low temperature growth of carbon nanofibers ......115. 7.1. Deposition conditions undoped and boron-doped carbon nanotubes ........... 122. 8.1. Deposition conditions of carbon nanotips..................................................... 158. viii.

(11) LIST OF FIGURES Page 1.1. (a) orientational correlations and intermolecular interactions of C60 and C70. (b) spherical-like carbon onions [9]........................................................................ 7. 1.2. (a) TEM images as the indicated magnification of Ni catalyzed nanofibers [10]; (b) SEM image of as-grown MWNT and (c) HRTEM image of individual MWNT. Inset-figure shows the (002) diffraction spots [11] ............................ 8. 1.3. Optimized structures for a T carbon nanotube junction obtained using a GTBMD simulation [22] .................................................................................. 9. 1.4. (a) CNTs grown on Si substrate, there are Y and H-junction CNTs and 3D CNT webs. (b) H-junction or multiple Y-junction CNTs on the substrate [23] ....... 10. 1.5. (a) TEM images of hollow rectangular parallelepiped graphitic cages and (b) breakage of graphitic layers can be seen at corners A-D [24] .........................11. 1.6. (a) SEM image of SWNT rings and (b) TEM image of a section of the ring and (c) Histogram showing distribution of ring radii [25] .................................... 12. 1.7. (a) TEM images (with scale bar=200 nm) of the carbon nanocones and (b) Five different types of cones in a-e (with scale bar = 200 nm). Magnified image of a cone tip is shown in f (with scale bar=5 nm) [26] .......................................... 13. 1.8. (a) TEM images of uniformly shaped spherical particles (b) image of a particle, showing aggregation of tube-like structures; and (c) Conical horn-like tips can be seen at the end of the tube-like structure [27] ............................................ 14. 1.9. Schematic cross section of a Field Emission Display..................................... 18. 2.1 2.2. Diagram of potential energy of electrons at the surface of metal ................... 24 Diagram of potential energy of electrons at the surface of an n-type semiconductor with field penetration into semiconductor interior ................. 27. 2.3 3.1. Schematic diagram of a cell of a microfabricated gated FEA ........................ 28 Schematic diagram of the bias assisted microwave plasma CVD system ...... 37. 3.2. Raman spectrum of the CVD diamond film grown on a Fused quartz substrate. Insert: optical micrograph displaying the morphology................................... 40. 3.3. The scheme of the instrument of the I-V measurement .................................. 44. 3.4. (a) EELS spectra of graphite, diamond, amorphous (hydrogenated) carbon, in the 280-296 eV region; (b) the EELS spectrum for an ion-grown carbon filament in the 0-40 eV range ......................................................................... 45. 4.1. (a) High and (b) low magnification of SEM photographs of Si nanotips....... 50 ix.

(12) 4.2. TEM of (a) Si tips and (b) high-resolution images of individual Si tip.......... 51. 4.3. (a) High and (b) low magnification of SEM photographs of DLC-clad Si nanotips ........................................................................................................... 52. 4.4. AES profile of DLC-clad Si tips..................................................................... 54. 4.5. AES surface survey of DLC-clad Si tips ........................................................ 55. 4.6. Raman spectrum of DLC-clad Si nanotips ..................................................... 57. 4.7. Electric field (E) versus current density (J) of Si and DLC-clad Si tips,. 5.1. respectively ..................................................................................................... 60 Fabricated procedure of diamond-like carbon emitters on the FEAS with gated diode pattern.................................................................................................... 65. 5.2. SEM photographs of MIS diode structure with 50 x 50 circles...................... 68. 5.3. SEM photographs of undoped diamond-like carbon emitters -grown under condition C...................................................................................................... 71. 5.4. SEM photographs of undoped diamond-like carbon emitters with various methane concentrations (a) sample A, (b) sample B and (c) sample C, respectively ..................................................................................................... 72. 5.5. The SEM photograph of phosphorus-doped diamond-like carbon emitters with various doping concentration (a) 2sccm, (b) 1sccm and (c) 0.5sccm, respectively ..................................................................................................... 74. 5.6. The SEM photograph of boron-doped diamond-like carbon emitters with various doping concentration (a) 2sccm, (b) 1sccm and (c) 0.5sccm, respectively ..................................................................................................... 75. 5.7. The Raman spectrum of samples A, B, C grown at different methane concentration................................................................................................... 77. 5.8. The Raman spectrum of samples D, E, F grown at different phosphorus concentration................................................................................................... 78. 5.9. The Raman spectrum of samples G, H, I grown at different boron concentration. ......................................................................................................................... 79 5.10 A SIMS depth profile of phosphorus (note: only qualitative analysis)........... 80 5.11 A SIMS depth profile of boron (note: only qualitative analysis).................... 81 5.12 The Je-V curve of undoped; phosphorus-doped and boron-doped diamond emitters and an insert of Fowler-Nordheim plot............................................. 83 6.1. SEM photographs of CNTs grown with CH4/H2under (a) –120V; (b) -80V and (c) 0V, respectively ......................................................................................... 92. 6.2. SEM photographs of CNTs grown under (a) +40V; (b) +80V and (c) +120V, x.

(13) respectively ..................................................................................................... 93 6.3. Diameter of CNTs grown with CH4/H2 as a function of applied biases ......... 94. 6.4. Schematic of the models of (a) negative and (b) positive bias effects............ 97. 6.5. TEM images of CNTs grown with CH4/H2 under (a) positive and (b) negative biases .............................................................................................................. 98. 6.6. (a) Raman spectra of CNTs grown with CH4/H2 under various biases and (b) the ID/IG ratio as a function of applied biases ..................................................... 100. 6.7. The I-V curve and an insert of F-N plot of CNTs grown with CH4/H2 under (a) +120 V, (b) 0 V and (c) –120 V, respectively................................................ 103. 6.8. SEM photographs of CNTs grown with CH4/CO2under (a) 0V; (b) -40V and (c) -150V, respectively ....................................................................................... 106. 6.9. SEM photographs of CNTs grown with CH4/CO2under (a) +40V; (b) +150V and (c) 0V, respectively ................................................................................ 107. 6.10 Diameter of CNTs grown with CH4/CO2 as a function of applied biases..... 108 6.11 TEM images of CNTs grown with CH4/CO2 under (a) positive and (b) negative biases ............................................................................................................ 109 6.12 EDX spectrum of CNTs grown with Pd catalyst ...........................................110 6.13 The I-V curve of CNTs grown with CH4/H2 and CH4/CO2, respectively......112 6.14 (a) top view, (b) low magnification and (c) high magnification SEM photographs of carbon nanofibers grown with CH4/CO2 under applied –100 V on catalyst-free soda-lime glass .....................................................................116 6.15 SEM photographs of carbon nanofibers grown with CH4/CO2 under various applied biases on catalyst-free soda-lime glass (a) 0 V, (b) –50 V and (c) –130, respectively ....................................................................................................117 7.1. SEM photographs of undoped CNT film (a) cross-section view, (b) low magnification and (c) high magnification view ............................................ 125. 7.2. SEM photographs of undoped-CNT films grown on the backside of substrate . ....................................................................................................................... 126. 7.3. SEM photographs of coiled carbon nanotubes ............................................. 128. 7.4. SEM photographs of (a) undoped and (b) boron-doped CNTs arrays .......... 129. 7.5. TEM images of undoped CNTs .................................................................... 131. 7.6. TEM images of boron-doped CNT with various boron concentration at (a) 1 sccm and (b) 2 sccm ..................................................................................... 132. 7.7. Raman spectrum of undoped and various concentrations of boron-doped CNTs. xi.

(14) ....................................................................................................................... 135 7.8. ID/IG ratio of undoped and various concentrations of Boron-doped CNTs... 136. 7.9. A SIMS depth profile of boron ..................................................................... 137. 7.10 Current density (J)- electric field (E) curve of undoped CNTs films, undoped and boron-doped CNTs arrays ...................................................................... 139 7.11 F-N plot of (a) undoped and (b) boron-doped CNTs arrays ......................... 140 7.12 Electrical resistivities of carbon nanotubes film with various -boron concentration under room temperature ......................................................... 142 8.1. SEM photographs of carbon nanotips grown on Pt under (a)–80V and (b)–150V ....................................................................................................................... 150. 8.2. SEM photographs of carbon nanotips grown under –120V on (a) Pt and (b) Si ....................................................................................................................... 151. 8.3. TEM images and diffraction pattern of (a) the end section and (b) lateral section of an individual tip ........................................................................................ 153. 8.4 Raman spectra of carbon nanotips grown under various biases and substrates.... ......................................................................................................................... 154 8.5 The current density versus electric field and F-N plot of carbon nanotips grown under –120V on (a) Pt and (b) Si .................................................................... 157 8.6 SEM photographs of nanotips grown under (a) -100V, (b) -130V and (c) -150V...160 8.7 TEM images and Fourier filtering transformation (FFT) of (a) the end section and (b) lateral section of an individual tip...................................................... 163 8.8 Raman spectra of nanotips growing under different applied biases ............... 164 8.9 The emission current versus the gate voltage of nanotips on a gated device structure........................................................................................................... 165 9.1 SEM photographs of (a) cross-section view; (b) top view and (c) high magnification images of CNTWNCCs ........................................................... 175 9.2 TEM images of (a) cross-section view; (b) individual of CNTWNCCs and (c) the lateral section of carbon nanotip..................................................................... 176 9.3 (a) TEM images; and (b) diffraction pattern (DP) (c) EDX spectrum of nanocrystalline chromium carbide, respectively ............................................ 177 9.4 (a) EDX and (b) EELS spectrum of nanocrystalline chromium carbide, respectively ..................................................................................................... 178 9.5 (a) The current density (J) versus electric field (E) and (b) F-N plot of CNTWNCCs .................................................................................................. 181. xii.

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