臺灣博碩士論文加值系統

本研究利用一種簡單、無觸媒且單一步驟的熱氧化法，將球形微米鋅粉於大氣下製備出海膽狀鋅/氧化鋅的核殼結構，其熱氧化溫度為350至550 oC之間，並可利用生長溫度及時間控制氧化鋅奈米線的直徑及其徑長比，結果發現溫度550 oC有最佳的結構表現，於恆溫30小時，其奈米線的平均直徑、長度、徑長比及密度分別為17.7 nm、3.26 μm、184.01及13.02 nanowires/μm2。
經由儀器分析，進一步探討所合成出的海膽狀結構的成長機制及材料分析，發現其表面上的奈米線直徑、長度、徑長比及密度會隨著溫度及氧化時間的增加而增加，而成長出的材料主要是中空結構，氧化鋅奈米線均勻地呈現放射狀分布在球表面，球內層則為氧化鋅，但仍有殘餘未反應之金屬鋅，推測其所合成之材料為鋅/氧化鋅複合材料。
由前面材料合成及分析之結果，知其合成此海膽狀結構之方法，接著利用網印製程的方式製備，進一步分析不同比例於不同溫度下之成長結果，並進行表面的奈米線直徑、長度、徑長比、密度及覆蓋率面積分析，最後進行場發射性質分析，選用有機載體與鋅粉1:0.5的比例於450 oC下合成之結果，其起始電場及場增強因子分別為2.44 V/μm及5168.50，並將陽極使用綠色螢光粉(P22)應用於場發射光源，當施加電壓於5.0 kV時輝度為14150 cd/m2。

Urchin-like Zn/ ZnO structure are formed by a simple, catalyst-free and one-step thermal oxidation with zinc microspheres in an air atmosphere at temperature in the range of 350 – 550 oC. It was found that the diameter and aspect ratio can be controlled by temperature and dwell time. The optimal temperature of synthesis is suggested at 550 oC with a reaction time of 30 h. The average diameter, length, aspect ratio and population density of nanowires are 17.7 nm, 3.26 μm, 184.01 and 13.02 nanowires/μm2, respectively.
The study of formation mechanism and characterization of the material found that during the oxidation, the average diameter, length, aspect ratio and population density of the nanowires grown from surface increased with the increase of the temperature and oxidation time. The urchin-like structure consists of ZnO nanowires grown radially on the surface of sphere, a thick shell oxidation layer and a inner shell of Zn and a hollow core.
The urchin-like structure was used as emitters in the cathode for field emission application. The turn-on field and field enhancement factor are 2.44 V/μm and 5168.50, respectively. The luminance of 14150 cd/m2 was achieved at 5.0 kV.

誌謝 I
中文摘要 IV
表目錄 X
圖目錄 XII
第一章、緒論 1
1-1 鋅與氧化鋅材料介紹 1
1-2 場發射的介紹及應用 4
1-2-1 場發射介紹 4
1-2-2 場發射應用 6
1-2-2-1 場發射顯示器 6
1-2-2-2 場發射燈源發光 7
第二章、文獻回顧 9
2-1 氧化鋅奈米線材的發展與演進 9
2-1-1 氧化鋅的基本特性與結構 9
2-1-2 氧化鋅奈米線材的歷史 12
2-1-3 氧化鋅奈米線材之合成方法 17
2-1-3-1 化學氣相沉積法 (Chemical vapor deposited method) 17
2-1-3-2 熱分解法 (Thermal decomposition) 19
2-1-3-3 水熱法 (Hydrothermal method) 20
2-1-3-4 熱氧化法 (Thermal oxidation) 21
2-1-4 氧化鋅奈米線材之可能成長機制 23
2-1-5 利用熱氧化法合成氧化鋅奈米線之文獻整理 25
2-2 海膽狀氧化鋅介紹 30
2-2-1 熱蒸鍍法製備海膽狀氧化鋅 31
2-2-2 水熱法製備海膽狀氧化鋅 32
2-2-3 製備海膽狀及類似形狀氧化鋅材料之文獻整理 33
2-3 場發射的演進與發展 38
2-4 場發射理論 41
2-4-1 場發射原理機制 41
2-4-2 Fowler-Nordheim方程式 42
2-4-3 場發射陰極材料 45
2-4-3-1 氧化鋅奈米線之場發射體 46
2-4-3-2 氧化鋅奈米線之場發射體文獻比較 48
2-5 研究目的及動機 51
第三章、實驗步驟與方法 52
3-1 實驗架構 52
3-2 實驗藥品與裝置 54
3-2-1 實驗藥品及耗材 54
3-2-2 實驗裝置 56
3-3 合成海膽狀氧化鋅材料 58
3-3-1 實驗步驟 58
3-3-2 材料性質檢測裝置 60
3-4 二極場發射發光元件之製備、組裝與量測 62
3-4-1 二極場發射陰極元件製備實驗步驟 62
3-4-2 二極場發射陽極元件製備實驗步驟 63
3-4-3 二極發光場發射光電性質量測 66
第四章、合成海膽狀氧化鋅之結果與討論 68
4-1 合成海膽狀氧化鋅 68
4-1-1 熱氧化反應升溫速率之評估 68
4-1-2 熱氧化反應溫度之評估 81
4-1-3 平均氧化速率與表面氧化層之關係探討 90
4-1-4 熱氧化法於不同升溫速率、溫度及恆溫時間下之表面分析 103
4-1-4-1 於550 oC下恆溫反應之表面型態 104
4-1-4-2 於450 oC下恆溫反應之表面型態 108
4-1-4-3 於350 oC下恆溫反應之表面型態 112
4-1-4-4 於250 oC下恆溫反應之表面型態 116
4-1-5 各升溫速率及溫度於不同恆溫時間下奈米線密度及長度分析 118
4-1-5-1 於550 oC下奈米線密度及長度與恆溫時間之變化 118
4-1-5-2 於450 oC下奈米線密度及長度與恆溫時間之變化 120
4-1-5-3 於350 oC下奈米線密度及長度與恆溫時間之變化 122
4-1-6 各升溫速率及溫度終端反應時間之奈米線徑長比較 124
4-1-7 實驗小結 126
4-2 海膽狀氧化鋅之材料分析 130
4-2-1 表面分析 130
4-2-1-1 X射線光電子能譜儀分析 (XPS) 130
4-2-1-2 穿透式電子顯微鏡分析 (TEM) 133
4-2-2 界面及內部結構分析 136
4-2-2-1 聚焦離子束顯微系統 (FIB) 136
4-2-2-2 X光能量散射光譜儀 (EDS - Mapping/ Line scan) 140
4-2-3 整體結構分析 144
4-2-3-1 拉曼光譜分析 (Raman spectrum) 144
4-2-3-2 紫外光分光光譜儀 (UV) 145
4-2-3-3 螢光光譜儀 (PL) 146
4-2-3-4 X射線繞射儀分析 (XRD) 147
4-2-4 實驗小結 155
4-3 海膽狀氧化鋅之可能成長機制推導 156
4-3-1 海膽狀氧化鋅合成結果小結 159
第五章、海膽狀鋅/氧化鋅應用之結果與討論 160
5-1 不同表面形態及覆蓋率之場發射陰極發射體探討 161
5-1-1 不同比例海膽狀鋅/氧化鋅之表面形態分析 162
5-1-1-1 於500 oC下恆溫48小時之表面形態分析 163
5-1-1-2 於450 oC下恆溫48小時之表面形態分析 166
5-1-1-3 於400 oC下恆溫48小時之表面形態分析 169
5-1-1-4 於350 oC下恆溫48小時之表面形態分析 172
5-1-1-5 不同溫度下恆溫48小時之表面形態分析結果比較 175
5-1-2 不同比例海膽狀鋅/氧化鋅之覆蓋率結果 179
5-1-2-1 於500 oC下恆溫48小時之覆蓋率結果 180
5-1-2-2 於450 oC下恆溫48小時之覆蓋率結果 182
5-1-2-3 於400 oC下恆溫48小時之覆蓋率結果 184
5-1-2-4 於350 oC下恆溫48小時之覆蓋率結果 186
5-1-2-5 不同溫度下恆溫48小時之覆蓋率結果比較 188
5-1-3 不同比例場發射陰極發射體之起始電場與場增強因子探討 189
5-1-3-1 於500 oC恆溫48小時不同鋅粉比例之起始電場與場增強因子 190
5-1-3-2 於450 oC恆溫48小時不同鋅粉比例之起始電場與場增強因子 192
5-1-3-3 於400 oC恆溫48小時不同鋅粉比例之起始電場與場增強因子 194
5-1-3-4 於350 oC恆溫48小時不同鋅粉比例之起始電場與場增強因子 196
5-1-3-5 不同鋅粉比例於不同溫度下之起始電場與場增強因子比較 198
5-1-4 實驗小結 200
5-2 二極場發射光源發光效果之探討 202
5-2-1 二極場發射光源發光結果 202
5-2-2 二極場發射光源之電壓及輝度分析 207
5-2-3 二極場發射光源之9點均勻度及效率分析 208
5-2-4 二極場發射光源穩定性之分析 210
5-2-4-1 二極場發射光源輝度穩定性之分析 211
5-2-4-2 二極場發射光源電流密度穩定性之分析 212
5-2-4-3 二極場發射光源穩定性之分析比較 213
5-2-5 實驗小結 214
5-3 海膽狀鋅/氧化鋅應用於場發射之光電性質評估及總結 215
第六章、總結與未來展望 218
6-1 總結 218
6-2 未來展望 220
參考文獻 221
附錄 228
附錄A 於450 oC下不同升溫速率之結果 228
A-1 升溫速率1 oC/min 228
A-2 升溫速率15 oC/min 231
附錄B 升溫速率5 oC/min於不同溫度之XRD結果 234
B-1 升溫速率5 oC/min於不同溫度反應0小時之XRD圖 234
B-2 升溫速率5 oC/min於不同溫度反應24小時之XRD圖 238
附錄C 比例0.5於450 oC恆溫24小時之場發射元件發光結果 242
C-1 發光結果及電流值變化 242
C-2 電壓及輝度分析 245
C-3 9點均勻度及效率分析 247

[1]Lin CC, Lin WH, Hsiao CY, Lin KM, Li YY. Synthesis of one-dimensional ZnO nanostructures and their field emission properties. J Phys D-Appl Phys. 2008;41(4):045301.
[2]Khan A, Abbasi MA, Hussain M, Ibupoto ZH, Wissting J, Nur O, et al. Piezoelectric nanogenerator based on zinc oxide nanorods grown on textile cotton fabric. Appl Phys Lett. 2012;101(19):193506.
[3]Nunez CG, Pau JL, Ruiz E, Marin AG, Garcia BJ, Piqueras J, et al. Enhanced fabrication process of zinc oxide nanowires for optoelectronics. Thin Solid Films. 2014;555:42-7.
[4]Choopun S, Tubtimtae A, Santhaveesuk T, Nilphai S, Wongrat E, Hongsith N. Zinc oxide nanostructures for applications as ethanol sensors and dye-sensitized solar cells. Appl Surf Sci. 2009;256(4):998-1002.
[5]Mo XM, Fang GJ, Long H, Li SZ, Huang HH, Wang HN, et al. Near-ultraviolet light-emitting diodes realized from n-ZnO nanorod/p-GaN direct-bonding heterostructures. J Lumines. 2013;137:116-20.
[6]Liu G, Wang LY, Chen GM, Hua SC, Ge CQ, Zhang H, et al. Enhanced electromagnetic absorption properties of carbon nanotubes and zinc oxide whisker microwave absorber. J Alloy Compd. 2012;514:183-8.
[7]Hassan NK, Hashim MR. Flake-like ZnO nanostructures density for improved absorption using electrochemical deposition in UV detection. J Alloy Compd. 2013;577:491-7.
[8]Lin CC, Lin WH, Li YY. Synthesis of ZnO Nanowires and Their Applications as an Ultraviolet Photodetector. J Nanosci Nanotechnol. 2009;9(5):2813-9.
[9]Li XW, Sun P, Yang TL, Zhao J, Wang ZY, Wang WN, et al. Template-free microwave-assisted synthesis of ZnO hollow microspheres and their application in gas sensing. Crystengcomm. 2013;15(15):2949-55.
[10]Li CF, Hsu CY, Li YY. NH3 sensing properties of ZnO thin films prepared via sol - gel method. J Alloy Compd. 2014;606:27-31.
[11]Mosquera E, Bernal J, Zarate RA, Mendoza F, Katiyar RS, Morell G. Growth and electron field-emission of single-crystalline ZnO nanowires. Mater Lett. 2013;93:326-9.
[12]Lin CC, Lin WH, Li YY. Field emission properties of ZnO nanowires synthesized by thermal decomposition process. J Phys D-Appl Phys. 2008;41(22):225411.
[13]Sun K, Jing Y, Li C, Zhang XF, Aguinaldo R, Kargar A, et al. 3D branched nanowire heterojunction photoelectrodes for high-efficiency solar water splitting and H-2 generation. Nanoscale. 2012;4(5):1515-21.
[14]Drexler KE. Engines of Creation: The Coming Era of Nanotechnology. Doubleday. 1986.
[15]羅吉宗, 戴明鳳, 林鴻明, 鄭振宗, 蘇程裕. 奈米科技導論. 2008.
[16]Vakurov A, Mokry G, Drummond-Brydson R, Wallace R, Svendsen C, Nelson A. ZnO nanoparticle interactions with phospholipid monolayers. J Colloid Interface Sci. 2013;404:161-8.
[17]Khanlary MR, Vahedi V, Reyhani A. Synthesis and Characterization of ZnO Nanowires by Thermal Oxidation of Zn Thin Films at Various Temperatures. Molecules. 2012;17(5):5021-9.
[18]Ong WL, Natarajan S, Kloostra B, Ho GW. Metal nanoparticle-loaded hierarchically assembled ZnO nanoflakes for enhanced photocatalytic performance. Nanoscale. 2013;5(12):5568-75.
[19]Lee GH. Synthesis and cathodoluminescence of ZnO tetrapods prepared by a simple oxidation of Zn powder in air atmosphere. Ceram Int. 2011;37(1):189-93.
[20]Zhou M, Lv W, Liu CL, Liu DM, Wang YP. Flower-like and hollow sphere-like ZnO assisted by microorganisms and their UV absorption and photo catalytic performance. J Mater Sci-Mater Electron. 2013;24(1):36-43.
[21]Pawar RC, Kim HS, Lee CS. Improved field emission and photocatalysis properties of cacti-like zinc oxide nanostructures. Scr Mater. 2013;68(2):142-5.
[22]楊素華, 藍慶忠. 奈米碳管場發射顯示器. 科學發展期刊. 2004;382:68-71.
[23]黃宣宜. 場發射顯示器技術現況與發展. 光連雙月刊. 2002;39:57-64.
[24]蔡宗岩. 以奈米碳管、碳纖維製備場發射陰極材料並探討電極幾何形狀對場發射特性之影響. 國立清華大學材料科學工程學系. 2002.
[25]孫紫茹. 以化學複合鍍法製備奈米碳材/Ni-P 場發射陰極研究. 國防大學理工學院化學及材料工程系. 2012.
[26]大同股份有限公司. http://wwwtatungcomtw/b5/.
[27]Wikipedia. http://zhwikipediaorg/wiki/ZnO.
[28]鄭天佑. 氧化物半導體之光學特性研究. 國立中山大學光電工程研究所. 2006.
[29]陳怡如. 大氣熱裂解法成長氧化鋅奈米結構在紫外光感測與光觸媒特性之研究. 逢甲大學材料科學與工程學系. 2010.
[30]Pearton SJ, Norton DP, Ip K, Heo YW, Steiner T. Recent progress in processing and properties of ZnO. Prog Mater Sci. 2005;50(3):293-340.
[31]Brusse J, Sampson M. Zinc whiskers: Hidden cause of equipment failure. IEEE IT Professional Magazine. 2004;6:43-7.
[32]Sears GW. A mechanism of whisker growth. Acta Metallurgica. 1955;3(4):367-9.
[33]Coleman RV, Sears GW. Elasticity of zinc whiskers. Acta Metallurgica. 1956;4(2):214-5.
[34]Brenner SS, Sears GW. Mechanism of whisker growth. 3. Nature of growth sites. Acta Metallurgica. 1956;4(3):268-70.
[35]Coleman RV, Sears GW. Growth of zinc whiskers. Acta Metallurgica. 1957;5(3):131-6.
[36]Wagner RS, Ellis WC. Vapor-liquid-solid mechanism of crystal growth and its application to silicon. Transactions of the Metallurgical Society of Aime. 1965;233(6):1053-&.
[37]Yang PD, Yan HQ, Mao S, Russo R, Johnson J, Saykally R, et al. Controlled growth of ZnO nanowires and their optical properties. Adv Funct Mater. 2002;12(5):323-31.
[38]Li Y, Meng GW, Zhang LD, Phillipp F. Ordered semiconductor ZnO nanowire arrays and their photoluminescence properties. Appl Phys Lett. 2000;76(15):2011-3.
[39]Gomez JL, Tigli O. Zinc oxide nanostructures: from growth to application. J Mater Sci. 2013;48(2):612-24.
[40]Kar S, Pal BN, Chaudhuri S, Chakravorty D. One-dimensional ZnO nanostructure arrays: Synthesis and characterization. J Phys Chem B. 2006;110(10):4605-11.
[41]Wan H, Ruda HE. A study of the growth mechanism of CVD-grown ZnO nanowires. J Mater Sci-Mater Electron. 2010;21(10):1014-9.
[42]Chen RQ, Zou CW, Yan XD, Alyamani A, Gao W. Growth mechanism of ZnO nanostructures in wet-oxidation process. Thin Solid Films. 2011;519(6):1837-44.
[43]Zhang GH, Wei L, Chen YX, Mei LM, Jiao J. Field emission property of ZnO nanoneedle arrays with different morphology. Mater Lett. 2013;96:131-4.
[44]Lin CC, Li YY. Synthesis of ZnO nanowires by thermal decomposition of zinc acetate dihydrate. Mater Chem Phys. 2009;113(1):334-7.
[45]Podrezova LV, Porro S, Cauda V, Fontana M, Cicero G. Comparison between ZnO nanowires grown by chemical vapor deposition and hydrothermal synthesis. Appl Phys A-Mater Sci Process. 2013;113(3):623-32.
[46]Ibrahim NB, Al-Shomar SM, Ahmad SH. Effect of aging time on the optical, structural and photoluminescence properties of nanocrystalline ZnO films prepared by a sol-gel method. Appl Surf Sci. 2013;283:599-602.
[47]Zhao CX, Li YF, Zhou J, Li LY, Deng SZ, Xu NS, et al. Large-Scale Synthesis of Bicrystalline ZnO Nanowire Arrays by Thermal Oxidation of Zinc Film: Growth Mechanism and High-Performance Field Emission. Cryst Growth Des. 2013;13(7):2897-905.
[48]Wen XG, Fang YP, Pang Q, Yang CL, Wang JN, Ge WK, et al. ZnO nanobelt arrays grown directly from and on zinc substrates: Synthesis, characterization, and applications. J Phys Chem B. 2005;109(32):15303-8.
[49]Sekar A, Kim SH, Umar A, Hahn YB. Catalyst-free synthesis of ZnO nanowires on Si by oxidation of Zn powders. J Cryst Growth. 2005;277(1-4):471-8.
[50]Kirkham M, Wang ZL, Snyder RL. In situ growth kinetics of ZnO nanobelts. Nanotechnology. 2008;19(44):445708.
[51]Yu W, Pan CX. Low temperature thermal oxidation synthesis of ZnO nanoneedles and the growth mechanism. Mater Chem Phys. 2009;115(1):74-9.
[52]Ren S, Bai YF, Chen J, Deng SZ, Xu NS, Wu QB, et al. Catalyst-free synthesis of ZnO nanowire arrays on zinc substrate by low temperature thermal oxidation. Mater Lett. 2007;61(3):666-70.
[53]Kim TW, Kawazoe T, Yamazaki S, Ohtsu M, Sekiguchi T. Low-temperature orientation-selective growth and ultraviolet emission of single-crystal ZnO nanowires. Appl Phys Lett. 2004;84(17):3358-60.
[54]Barreca D, Bekermann D, Comini E, Devi A, Fischer RA, Gasparotto A, et al. Urchin-like ZnO nanorod arrays for gas sensing applications. Crystengcomm. 2010;12(11):3419-21.
[55]Cheng CW, Zhang HF, Ren WN, Dong WJ, Sun Y. Three dimensional urchin-like ordered hollow TiO2/ZnO nanorods structure as efficient photoelectrochemical anode. Nano Energy. 2013;2(5):779-86.
[56]Zhu YQ, Chen YQ, Zhang XH, Chen Q, Shao Y. Urchin-like ZnO nanostructures: Synthesis, characterization and optical properties. Mater Lett. 2009;63(15):1242-4.
[57]Jiang H, Hu JQ, Gu F, Li CZ. Stable field emission performance from urchin-like ZnO nanostructures. Nanotechnology. 2009;20(5):055706.
[58]Umar A, Kim SH, Hahn YB. Sea-urchin-like ZnO nanostructures on Si by oxidation of Zn metal powders: Structural and optical properties. Superlattices Microstruct. 2006;39(1-4):145-52.
[59]Shen GZ, Bando Y, Lee CJ. Synthesis and evolution of novel hollow ZnO urchins by a simple thermal evaporation process. J Phys Chem B. 2005;109(21):10578-83.
[60]Gu ZJ, Paranthaman MP, Xu J, Pan ZW. Aligned ZnO Nanorod Arrays Grown Directly on Zinc Foils and Zinc Spheres by a Low-Temperature Oxidization Method. ACS Nano. 2009;3(2):273-8.
[61]Jia XH, Fan HQ. Room temperature solid-state synthesis and ethanol sensing properties of sea-urchin-like ZnO nanostructures. Mater Lett. 2010;64(14):1574-6.
[62]Fowler RH, Nordheim L. Electron emission in intense electric fields. Proc R soc Lond Ser A-Contain Pap Math Phys Character. 1928;119(781):173-81.
[63]Spindt CA, Brodie I, Humphrey L, Westerberg ER. Physical-properties of thin-film field-emission cathodes with molybdenum cones. J Appl Phys. 1976;47(12):5248-63.
[64]Paul R, Bhar R, Pal AK. Field emission properties of composite nano-Au/DLC films prepared by CVD technique. Mater Res Bull. 2010;45(5):576-83.
[65]Mo CB, Hwang JW, Cha SI, Hong SH. Multi-walled carbon nanotube/Co composite field emitters fabricated by in situ spray coating. Carbon. 2009;47(5):1276-81.
[66]Lisunova M, Lisunova Y, Lee S, Kim J, Joo K, Kim Y, et al. Field emission properties of screen-printed activated carbons. Carbon. 2009;47(4):1119-25.
[67]Fang YG, Wong KM, Lei Y. Synthesis and field emission properties of different ZnO nanostructure arrays. Nanoscale Res Lett. 2012;7.
[68]Nilsson L, Groening O, Emmenegger C, Kuettel O, Schaller E, Schlapbach L, et al. Scanning field emission from patterned carbon nanotube films. Appl Phys Lett. 2000;76(15):2071-3.
[69]Qian X, Liu H, Guo Y, Song Y, Li Y. Effect of aspect ratio on field emission properties of ZnO nanorod arrays. Nanoscale Res Lett. 2008;3(8):303-7.
[70]蔡增光, 潘扶民. 降低平面顯示器之工作電壓的新製程. 奈米通訊. 1999;6(2):11-6.
[71]Shi MM, Pan XW, Qiu WM, Zheng DX, Xu MS, Chen HZ. Si/ZnO core-shell nanowire arrays for photoelectrochemical water splitting. Int J Hydrog Energy. 2011;36(23):15153-9.
[72]Jiang ZX, Xue SL, Wu SX, Zou RJ, Zhang ZY, Jang M. Synthesis of unique SnO2/ZnO core-shell nanorods and nanoflowers and their field emission properties. Mater Lett. 2013;105:239-41.
[73]Fang YL, Li ZY, Xu S, Han DD, Lu DY. Optical properties and photocatalytic activities of spherical ZnO and flower-like ZnO structures synthesized by facile hydrothermal method. J Alloy Compd. 2013;575:359-63.
[74]Yi F, Huang YH, Zhang Z, Zhang Q, Zhang Y. Photoluminescence and highly selective photoresponse of ZnO nanorod arrays. Opt Mater. 2013;35(8):1532-7.
[75]Zhang Y, Deng SZ, Xu NS, Chen J. Fully sealed carbon nanotube flat-panel light source and its application as thin film transistor-liquid-crystal display backlight. J Vac Sci Technol B. 2008;26(3):1033-7.
[76]Kim YC, Yoo EH. Printed carbon nanotube field emitters for backlight applications. Jpn J Appl Phys Part 2 - Lett Express Lett. 2005;44(12-15):L454-L6.
[77]Hsu LC, Yu HC, Chang TH, Li YY. Formation of Three-Dimensional Urchin-like alpha-Fe2O3 Structure and Its Field-Emission Application. ACS Appl Mater Interfaces. 2011;3(8):3084-90.