ZnO超长微米线的制备及光学性质的研究
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摘要
作为新一代宽禁带半导体,ZnO被认为是最具功能性的材料之一。在室温下ZnO的禁带宽度为3.37 eV,激子束缚能高达60 meV,是制备下一代紫外光发光二极管(LED)和激光器的最佳候选材料之一。同时ZnO具有许多其它优异的特性,比如化学和热学稳定性、压电和生物适应性等,使其在压电传感器、表面声波器件、生物化学器件和生物医学器件等诸多领域有着重要而广泛的应用。由于ZnO微米/纳米线的特殊六角结构可以作为共振腔,于是基于ZnO微米/纳米线受激辐射现象的研究成为了热点之一。
本文利用简单新颖的上游生长模式化学气相沉积方法在小石英管(SQT)端口处制备得到ZnO微米“森林”和超长ZnO微米线结构,在下游衬底上得到ZnO薄膜。由扫描电镜(SEM)图像可以看出所制备的ZnO微米线晶体结构完美,并具有超长生长可控性,为受激辐射研究打下了基础。
应用VS生长机制和回流效应对上下游ZnO微纳结构的形成进行了分析,从气流和温度两个方面分析了ZnO微米线和微米“森林”的产生机理。SQT的小尺寸使气体不能顺利越过反应源到达下游区,而产生回流现象,一组对比实验证明了回流效应的存在。石英与ZnO大的晶格失配导致了ZnO微米线的形成,ZnO微米“森林”是以ZnO微米线为“树干”,逐步生长出“树枝”、“树叶”的。
分别对生长在上游和下游的ZnO结构进行了PL测试。生长在衬底上的ZnO薄膜只有可见光区发光峰,而生长在SQT端口的具有线状结构的ZnO还具有紫外光区发光峰,并且结构越好紫外发光峰越强。对单根ZnO微米线的光学性质进行了研究,实验结果显示,随着微米线尺寸的减小,紫外发光峰的波长减小,向蓝紫光方向移动,发生了蓝移。使用He-Cd(λ=325 nm)激光器作为激发光源,对单根ZnO微米线的受激辐射情况进行了初步研究,在可见光区发现了共振现象,说明本实验制备的ZnO微米线在结构上可以作为WGM共振模式的载体。其紫外光区的受激辐射特性还有待进一步研究。
Among semiconducting nanomaterials, Zinc oxide (ZnO) is a wide band gap semiconductor and has been recognized as one of the most functional materials. ZnO had a wide direct band gap of 3.37 eV and a large exciton binding energy of 60 meV at room temperature. It has been regarded as one of the most promising candidates for the next generation of UV light emitting diode (LED) and laser devices. On account of its many other exciting properties, such as chemical and thermal stability, piezoelectric properties and biocompatibility, ZnO has a variety of applications piezoelectric nanosensors, surface acoustic wave (SAW) device, biochemical device and biomedical device. Because ultralong ZnO microwires with perfect hexagonal morphology can be used as resonant cavity, it has attracted increasing interests.
A novel chemical vapor deposition (CVD) system with an upstream growth pattern was exploited to prepare the ultralong ZnO microwires and ZnO microforest. ZnO film was deposited on the substrate in the downstream region. SEM (scanning electron microscopy) images clearly showed the ultralong ZnO microwires with perfect hexagonal morphology. Here, we achieved the controllable growing of ultralong ZnO microwires, which provided the basis for the study of stimulated emission.
The growth processes of ZnO microwires and microforest have been analyzed with vapor-solid (VS) growth mechanism and the special backflow effect. The novel CVD method is attributed to the special gas flow and the temperature distribution in the small quartz reacting tube (SQT). Due to the small size of the inner quartz tube, airflow cannot pass through the reactant source, which leads to the backflow effect. A comparison experiment demonstrated there is a backflow effect. Because the lattice mismatch between ZnO and quartz is very large, the ZnO island-like thin film grow into ZnO microwire in the upstream growth region. ZnO microforest is based on ZnO microwire as its trunk. The growth process is form trunks to branches, and finally to leaves.
Different ZnO structures have been investigated by PL spectra. PL spectra of ZnO films grown on the substrate showed an emission peaks in the visible region. PL spectra of ZnO microwires showed an emission peaks in the UV region. And the intensity is stronger when the ZnO structure is better. For individual ZnO microwire, the peak position moved towards the UV direction with the decrease of the scale. It's the blue shift phenomenon. Using He-Cd laser as the incident source, resonance phenomenon appeared in the visible region for individual ZnO microwire. It shows that the ZnO microwire can be the WGM mode resonant cavity. The further research of stimulated emission to the ZnO microwires is needed.
本文利用简单新颖的上游生长模式化学气相沉积方法在小石英管(SQT)端口处制备得到ZnO微米“森林”和超长ZnO微米线结构,在下游衬底上得到ZnO薄膜。由扫描电镜(SEM)图像可以看出所制备的ZnO微米线晶体结构完美,并具有超长生长可控性,为受激辐射研究打下了基础。
应用VS生长机制和回流效应对上下游ZnO微纳结构的形成进行了分析,从气流和温度两个方面分析了ZnO微米线和微米“森林”的产生机理。SQT的小尺寸使气体不能顺利越过反应源到达下游区,而产生回流现象,一组对比实验证明了回流效应的存在。石英与ZnO大的晶格失配导致了ZnO微米线的形成,ZnO微米“森林”是以ZnO微米线为“树干”,逐步生长出“树枝”、“树叶”的。
分别对生长在上游和下游的ZnO结构进行了PL测试。生长在衬底上的ZnO薄膜只有可见光区发光峰,而生长在SQT端口的具有线状结构的ZnO还具有紫外光区发光峰,并且结构越好紫外发光峰越强。对单根ZnO微米线的光学性质进行了研究,实验结果显示,随着微米线尺寸的减小,紫外发光峰的波长减小,向蓝紫光方向移动,发生了蓝移。使用He-Cd(λ=325 nm)激光器作为激发光源,对单根ZnO微米线的受激辐射情况进行了初步研究,在可见光区发现了共振现象,说明本实验制备的ZnO微米线在结构上可以作为WGM共振模式的载体。其紫外光区的受激辐射特性还有待进一步研究。
Among semiconducting nanomaterials, Zinc oxide (ZnO) is a wide band gap semiconductor and has been recognized as one of the most functional materials. ZnO had a wide direct band gap of 3.37 eV and a large exciton binding energy of 60 meV at room temperature. It has been regarded as one of the most promising candidates for the next generation of UV light emitting diode (LED) and laser devices. On account of its many other exciting properties, such as chemical and thermal stability, piezoelectric properties and biocompatibility, ZnO has a variety of applications piezoelectric nanosensors, surface acoustic wave (SAW) device, biochemical device and biomedical device. Because ultralong ZnO microwires with perfect hexagonal morphology can be used as resonant cavity, it has attracted increasing interests.
A novel chemical vapor deposition (CVD) system with an upstream growth pattern was exploited to prepare the ultralong ZnO microwires and ZnO microforest. ZnO film was deposited on the substrate in the downstream region. SEM (scanning electron microscopy) images clearly showed the ultralong ZnO microwires with perfect hexagonal morphology. Here, we achieved the controllable growing of ultralong ZnO microwires, which provided the basis for the study of stimulated emission.
The growth processes of ZnO microwires and microforest have been analyzed with vapor-solid (VS) growth mechanism and the special backflow effect. The novel CVD method is attributed to the special gas flow and the temperature distribution in the small quartz reacting tube (SQT). Due to the small size of the inner quartz tube, airflow cannot pass through the reactant source, which leads to the backflow effect. A comparison experiment demonstrated there is a backflow effect. Because the lattice mismatch between ZnO and quartz is very large, the ZnO island-like thin film grow into ZnO microwire in the upstream growth region. ZnO microforest is based on ZnO microwire as its trunk. The growth process is form trunks to branches, and finally to leaves.
Different ZnO structures have been investigated by PL spectra. PL spectra of ZnO films grown on the substrate showed an emission peaks in the visible region. PL spectra of ZnO microwires showed an emission peaks in the UV region. And the intensity is stronger when the ZnO structure is better. For individual ZnO microwire, the peak position moved towards the UV direction with the decrease of the scale. It's the blue shift phenomenon. Using He-Cd laser as the incident source, resonance phenomenon appeared in the visible region for individual ZnO microwire. It shows that the ZnO microwire can be the WGM mode resonant cavity. The further research of stimulated emission to the ZnO microwires is needed.
引文
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[2]马洪磊,薛成山.纳米半导体[M].北京：国防工业出版社,2009.
[3]Hong W-K, Jo G, Sohn J I, et al. Tuning of the Electronic Characteristics of ZnO Nanowire Field Effect Transistors by Proton Irradiation [J].ACS Nano,2010,4(2): 811-818.
[4]Ling B, Zhao J L, Sun X W, et al. Color tunable light-emitting diodes based on p+-Si/p-CuA102/n-ZnO nanorod array heterojunctions [J].Appl. Phys. Lett.,2010, 97(1):013101.
[5]Czekalla C, Sturm C, Rudiger S-G, et al. Whispering gallery mode lasing in zinc oxide microwires [J]. Appl. Phys. Lett.,2008,92(24):241102.
[6]Dai J, Xu C X, Ding R, et al. Combined whispering gallery mode laser from hexagonal ZnO microcavities [J].Appl. Phys. Lett.,2009,95(19):191117.
[7]Zhang Y, Zhou H, Liu S W, et al. Second-Harmonic Whispering-Gallery Modes in ZnO Nanotetrapod [J].Nano Lett.,2009,9(5):2109-2112.
[8]Sun K, Zhang H, Hu L, et al. Growth of ultralong ZnO microwire and its application in isolatable and flexible piezoelectric strain sensor [J].Phys. Status Solidi A, 2010,207(2):488-492.
[9]Calestani D, Zha M, Mosca R, et al. Growth of ZnO tetrapods for nanostructure-based gas sensors [J]. Sens. Actuators B,2010,144:472-478.
[10]Lei Y, Yan X, Luo N, et al. ZnO nanotetrapod network as the adsorption layer for the improvement of glucose detection via multiterminal electron-exchange [J]. Colloids Surf. A:Physicochem. Eng. Aspects,2010,361:169-173.
[11]王新强,杜国同,姜秀英等.ZnO薄膜研究进展[J].半导体光电,2000,21(4)：233-237.
[12]Ozgur U, Alivov Ya I, Liu C, et al. Comprehensive review of ZnO materials and devices [J]. J. Appl Phys.,2005,98:041301.
[13]Tang Z K, Wang G K L, Yu P, et al. Appl. Phys. Lett. [J].1998,72(25):3270.
[14]Chen Y F, Bagnall D and Yao T F. ZnO as a novel photonic material for the UV region [J]. Materials Science and Engineering B-Solid State Materials for Advanced Technology,2000,75(2-3):190-198.
[15]Ham H, Shen G Z, Cho J H, et al. Vertically aligned ZnO nanowires produced by a catalyst-free thermal evaporation method and their field emission properties [J]. Chemical Physics Letters,2005,404:69-73.
[16]Lee W, Jeong M-C, Myoung J-M. Catalyst-free growth of ZnO nanowires by metal-organic chemical vapour deposition (MOCVD) and thermal evaporation [J]. Acta Materialia,2004,52:3949-3957.
[17]Zhang H Z, Sun X C, Wang R M, et al. Growth and formation mechanism of c-oriented ZnO nanorod arrays deposited on glass [J]. Journal of Crystal Growth,2004,269: 464-471.
[18]Shen G Z, Cho J H, Lee C J. Morphology-controlled synthesis, growth mechanism and optical properties of ZnO nanonails [J]. Chemical Physics Letters,2005,401: 414-419.
[19]Chen Y F, Wang R M, Zhang H Z, et al. TEM investigations on ZnO nanobelts synthesized via a vapor phase growth [J]. Micron,2004,35:481-487.
[20]Huang Y H, Zhang Y, He J, et al. Fabrication and characterization of ZnO comb-like nanostructures [J]. Ceramics International,2006,32:561-566.
[21]Xu C X, Sun X W, Dong Z L, et al. Self-organized nanocomb of ZnO fabricated by Au-catalyzed vapor-phase transport [J]. Journal of Crystal Growth,2004,270: 498-504.
[22]Li F, Ding Y, Gao P X, et al. Single-Crystal Hexagonal Disks and Rings of ZnO: Low-Temperature, Large-Scale Synthesis and Growth Mechanism [J]. Angewandte Chemie,2004,116(39):5350-5354.
[23]Hughes W L, Wang Z L. Formation of Piezoelectric Single-Crystal Nanorings and Nanobows [J]. J. AM. CHEM. SOC.,2004,126:6703-6709.
[24]Lei Y, Yan X Q, Luo N, et al. ZnO nanotetrapod network as the adsorption layer for the improvement of glucose detection via multiterminal electron-exchange [J]. Colloids and Surfaces A:Physicochem. Eng. Aspects.2010,361:169-173.
[25]Kong X Y, Wang Z L. Spontaneous Polarization-Induced Nanohelixes, Nanosprings, and Nanorings of Piezoelectric Nanobelts [J].2003,3(12):1625-1631.
[26]Ko S H, Lee D, Kang H W, et al. Nanoforest of Hydrothermally Grown Hierarchical ZnO Nanowires for a High Efficiency Dye-Sensitized Solar Cell [J]. Nano Lett. 2011,11(2):666-671.
[27]Wang X D, Song J H, Wang Z L. Single-crystal nanocastles of ZnO [J]. Chemical Physics Letters,2006,424:86-90.
[28]Gao P X, Wang Z L. Nanopropeller arrays of zinc oxide [J]. Applied Physics Letters, 2004,84(15):2883-2885.
[29]Pan Z W, Dai Z R and Wang Z L. Nanobelts of semiconducting oxides [J]. Science, 2001,291 (5510):1947-1949.
[30]Huang M H, Mao S, Feick H, et al. Room-temperature ultraviolet nanowire nanolasers [J]. Science,2001,292(5523):1897-1899.
[31]Wang Z L. Nanostructures of zinc oxide [J]. Materials Today,2004,7(6):26-33.
[32]Wang X D, Zhou J, Lao C S, et al. In situ field emission of density-controlled ZnO nanowire arrays [J]. Advanced Materials,2007,19(12):1627-1631.
[33]Chang S-P, Chang S-J, Lu C-Y, et al. A ZnO nanowire-based humidity sensor [J].
[34]Lao C S, Park M-C, Kuang Q, et al. Giant Enhancement in UV Response of ZnO Nanobelts by Polymer Surface-Functionalization [J]. J. AM. CHEM. SOC.,2007,129:12096-12097.
[35]Wang Z L. Nanopiezotronics [J]. Adv. Mater.,2007,19:889-892.
[36]Gao P X, Song J H, Liu J, et al. Nanowire Piezoelectric Nanogenerators on Plastic Substrates as Flexible Power Sources for Nanodevices [J]. Adv. Mater.,2007,19: 67-72.
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