摘要
一维纳米材料由于高的比表面积、大的长径比、对电子传输的限域等优点在催化、电子等领域一直受到人们关注。一维半导体纳米材料可有效避免纳米颗粒敏感材料中团聚现象的发生,对提高半导体气体传感器的灵敏度,响应恢复特性,改善元件的选择特性具有重要作用。目前对二元及三元纳米纤维网络的气敏特性研究较频繁,有序排列纳米纤维的研究只停留在有机纳米纤维材料的制备阶段。探索多元固溶体及有序排列的纳米纤维敏感材料的制备工艺,揭示它们气敏机制的特异性是一维敏感材料的有意义的研究方向。
本论文围绕着α-Fe2O3内米带,三元固溶体LaFeO3纳米带和纳米纤维、四元固溶体LaxSr1-xFeO3纳米纤维以及有序排列的In2O3纳米纤维的制备、表征、气敏特性和敏感机理方面展开研究,得到了一些有意义的结果。
利用静电纺丝方法,经过600℃高温烧结工艺制备出α-Fe2O3纳米带材料,SEM表征得知纳米带的表面粗糙,带的宽度约为200-400 nm,厚度约为25-30nm。基于a-Fe2O3纳米带的气敏元件在285℃对浓度500 ppm的乙醇气体灵敏度为4.9,响应时间在10 s以内,恢复时间在24 s以内。
利用静电纺丝的方法,经过600℃高温煅烧制备出LaFeO3内米带和纳米纤维材料。通过SEM照片可知LaFeO3内米带的表面光滑,纳米带的宽度200-300LaFeO3纳米纤维的直径均匀,约80-90 nm。并利用化学共沉淀的方法制备出直径在30 nm左右的LaFeO3纳米颗粒材料。通过三种不同形貌的LaFeO3材料气敏特性的对比测试得出纳米带和纳米纤维相对纳米粒子都具有较低的电阻,并且这些一维纳米材料对乙醇气体的最佳工作温度较低,分别为170℃和200℃。在各自的最佳工作温度时LaFeO3纳米纤维材料对500 ppm乙醇的灵敏度为47,而LaFeO3纳米带对500 ppm的乙醇灵敏度仅为8.6。在工作温度均为200℃时,LaFeO3纳米纤维材料与纳米带和纳米颗粒材料相比具有快速的响应恢复速度,此时LaFeO3纳米纤维对200 ppm乙醇的响应和恢复时间分别为11 s和19 s。LaFeO3纳米纤维材料与纳米带和纳米粒子材料相比对乙醇气体具有更高的灵敏度和快速的响应恢复速度,这与纳米纤维的一维几何形貌有着密切关系。纳米纤维具有高的比表面积,引起外界气体分子大量迅速吸附,提高了纳米纤维材料的灵敏度；由于吸附气体产生的表面空间电荷层沿纤维轴向方向重叠,形成连续的载流子传输通道,导致纳米纤维材料表现出快速的响应恢复特性。
首次制备出四元固体溶LaxSr1-xFeO3 (x=0.6,0.7,0.8)内米纤维,这些纳米纤维的直径均匀,在50-80 nm之间。通过对乙醇气敏特性的测试,La0.7Sr0.3FeO3纳米纤维材料对乙醇的灵敏度明显高于其它比例时的灵敏度。La0.7Sr0.3FeO3纳米纤维在工作温度为185℃时对500 ppm乙醇的灵敏度为40.4,此时它的响应恢复时间分别为11 s和10 s。实验中对比测试了La0.7Sr0.3FeO3纳米纤维元件和市售的MQ-3乙醇气敏元件的敏感特性。Lao.7Sro.3FeO3纳米纤维元件的灵敏度峰值出现在170℃,而MQ-3乙醇气体传感器灵敏度的峰值出现在315℃,同时Lao.7Sro.3FeO3纳米纤维在250 s以内就完成了一个响应恢复周期的测试,而MQ-3乙醇气体传感器在脱离乙醇气体时却无法恢复到正常的空气阻值。通过与市售传感器的对比测试,可以看出一维纳米材料具有低的工作温度和高的灵敏度以及快速的响应恢复速度,在气体传感器领域有着非常可观的应用前景。
采用两块平行的导电磁铁(8 cm×5 cmxl.5 cm)作为静电纺丝中的收集装置,在静电纺丝过程中带电喷射流受到磁场力的牵引和静电荷的排斥作用,纳米纤维被有序的搭接在平行磁铁的空隙上。In2O3纳米纤维经过煅烧后纤维的表面光滑,直径均匀,大约在80-90 nm范围内。实验测得有序排列的In2O3纳米纤维气体传感器的在工作温度为275℃时对1 ppm的NO2的响应时间和恢复时间分别问0.6 s和4 s,在工作温度为245℃时对1 ppm的C12的响应时间和恢复时间分均为0.7 s。相比之下,此时无序排列的In2O3纳米纤维传感器对NO2气体的响应和恢复时间分别为1.3 s和13.1 s,而对Cl2气体的响应和恢复时间分别为1 s和7 s,明显比有序排列的纳米纤维所需的时间长。当有序排列的纳米纤维吸附空气中的氧分子时导致纳米纤维表面形成一层空间电荷区,在沿着纤维轴向的方向这些空间电荷区发生重叠,甚至出现“平带”现象,在这个连续的载流子的传输通道中,由于势垒高度较小,电子的传输过程中受到的散射几率变小,所以有序排列的纳米纤维材料表现出快速的响应恢复速度。
通过水热法合成ZnSnO3空心微球材料,它的直径在400-600 nm范围内。此种材料在工作温度为380℃时对500 ppm的正丁烷灵敏度值为5.79,响应时间为0.3 s,恢复时间为0.65 s,灵敏度和响应恢复速度明显高于实心ZnSnO3微球材料。这主要因为ZnSnO3空心微球材料表面相对比较疏松,有利于气体的吸附和扩散,所以材料相对实心微球表现出较好的灵敏度和响应恢复特性。
总之,本论文通过上述实验和相关结果,证明了纳米纤维优异的气敏特性；不但首次获得了具有敏感特性的多元固溶体,还首次将有序排列的纳米材料应用到气体传感器领域,进一步证实了有序纤维可有效的提高元件的响应恢复特性。
One dimensional (1D) nano-materials have driven much attention in catalyst and electronics due to their large specific surface area, large aspect ratio and electronic-transport confinement effect. 1D semiconductor nano-materials overcome the nanoparticles aggregation phenomenon and have important effect on enhancing response, shortening response and recovery time and improving selectivity of gas sensors. To date, researches are focused on binary and ternary-component solid solutions semiconductor materials, and the study on aligned nanofibers are still in the preparation of organic materials stage. The study on multi-compound-system and aligned sensitive nanofibers and their gas sensing properties is significative direction in 1 D sensitive meterials.
This paper introduces the fabrication, characterization, gas sensing properties and sensing mechanism ofα-Fe2O3 nanobelts, ternary-component solid solution LaFeO3 nanobelts and nanofibers, quaternary-component solid solution LaxSr1-xFeO3 nanofibers and aligned In2O3 nanofibers, and lists some meaningful results.
α-Fe2O3 nanobelts were fabricated by an electrospinning method followed by a calcination in air at 600℃process, the SEM photographs showed that the surface of belts are rough, the width and thickness of the belts are about 200 to 400 nm and 25 to 30 nm, respectively. Gas sensors based onα-Fe2O3 nanobelts have a response of 4.9, a response time less than 10 s and recovery time less than 24 s to 500 ppm ethanol at 285℃.
LaFeO3 nanobelts and nanofibers were also fabricated by an electrospinning method followed by a calcination in air at 600℃process, the SEM photographs showed that the surface of belts are smooth and the width of the belts range from 200 to 300 nm; the diameters of LaFeO3 nanofibers are uniform in the range of 80 to 90 nm. LaFeO3 nanoparticles with diameters of around 30nm were prepared by a chemistry co-precipitation method. Contrastive experiment of gas sensing properties of these three morphologies LaFeO3 materials showed that LaFeO3 nanobelts and nanofibers have lower resistance compare with LaFeO3 nanoparticles and show lower optimum operating temperatures (170℃and 200℃, respectively). Under each optimum operating temperature, the response of LaFeO3 nanofibers material was 47 to 500 ppm ethanol, while that of LaFeO3 nanobelts material was only 8.6. When the operating temperature is 200℃and the concentration of ethanol is 200 ppm, the response and recovery time of LaFeO3 nanofibers were 11 s and 19 s, respectively, which were faster compared with LaFeO3 nanoparticles and nanobelts. The reason why LaFeO3 nanofibers showed higher response and faster response/recovery properties compared with LaFeO3 nanoparticles and nanobelts is closely allied to the geometric morphologies of the nanofibers. The high specific surface area property of nanofibers result in the rapid speed and large amounts of adsorption of gas molecules and this follows the enhancing of the response; the overlap of the surface space-charge layer along the fiber direction leads to the formation of a continuous electron transport tunnel, and this result in the improving of response/recovery property.
Quaternary-component solid solution LaxSr1-xFeO3 (x=0.6,0.7,0.8) nanofibers were successfully prepared for the first time, the diameters of the gained nanofibers are uniform and in the range of 50 to 80 nm. When x takes different values,0.6,0.7 and 0.8, the contrastive experiment of gas sensing properties of LaxSr1-xFeO3 nanofibers showed that La0.7Sr0.3Fe03 nanofibers have higher response than the other ratios. At 185℃, to 500 ppm ethanol, the response of La0.7Sr0.3FeO3 nanofibers was 40.4, and the response and recovery time were 11 s and 10 s, respectively. Compared with commercial available product MQ-3 ethanol gas sensor, La0.7Sr0.3FeO3 nanofibers based sensors showed highest response at 170℃, while MQ-3 ethanol gas sensor showed highest response at 315℃, at the same time, La0.7Sr0.3FeO3 nanofibers based sensors completed a response and recovery period in 250 s, while MQ-3 ethanol gas sensor could not recover when break away ethanol. The above results show that the new one dimensional materials have low operating temperature, high response and fast response/recovery and are promising materials in gas sensor.
Two conductive parallel-positioned magnets (8 cm×5 cmxl.5 cm) were used as collector in electro spinning process. During electro spinning, the electrostatic repulsion force and magnetic field which the charged jet experienced strech the fibers across the gap to form aligned arrays. The calcinated aligned In2O3 nanofibers had smooth surface, uniform diameter of 80 to 90 nm. The experiments results showed that at 275℃, the response and recovery time of aligned In2O3 nanofibers to 1 ppm NO2 are 0.6 s and 4 s, respectively, and at 245℃, the response and recovery time of aligned In2O3 nanofibers to 1 ppm Cl2 are both 0.7 s. While, the response and recovery time of randomly deposited In2O3 nanofibers to NO2 are 1.3 s and 13.1 s, respectively, and that to Cl2 are 1 s and 7 s, respectively. These results show that the aligned nanofibers have shorter response and recovery time. To aligned nanofibers, when oxygen molecules adsorption takes place, there are surface space-charge layers fonned at the surface of the nanofibers, these surface charge spaces overlap along the fibers, sometimes, even form flat band, in this continuous electron transport tunnel, due to the relatively lower potential barriers, the electron scattering probability decreases during transport process, and result in the fast response/recovery property of aligned nanofibers.
Hollow ZnSnO3 microspheres were prepared by hydrothermal method, the diameter of the hollow ZnSnO3 microspheres was in the range of 400 nm to 600 nm. To 500 ppm butane, the reponse of the hollow ZnSnO3 microspheres materials was 5.79 at 380℃, and the response and recovery time were 0.3 s,0.65 s, respectively. The response and response/recovery properties of the gained hollow ZnSnO3 microspheres materials are sufficient better than that of solid ZnSnO3 microspheres materials, this can be explained as the surface of hollow ZnSnO3 microspheres are relatively loosen, and this is conducive to adsorption and desorption of gas molecules, so the hollow ZnSnO3 microspheres materials showed better response and response/recovery properties.
In conclusion, in this paper, the experiments results showed the outstanding gas sensing properties of nanofibers, multi-component solid solutions with sensitive characteristics were successfully prepared for the first time, and applied aligned nanofibers to gas sensor, and demonstrated that aligned nanofibers can improve the response/recovery property.
引文
[1]BRATTEIN W H, BARDEEN J. Surface properties of germanium [J]. Bell. Syst. Tec. J., 1953,1:1-41.
[2]SEIYAMA T, KATO A, FUJIISHI K, NAGATANI M. A new detector for gaseous components using semiconductive thin films [J]. Anal. Chem.,1962,34:1502-1503.
[3]SEIYAMA T, KAGAWA S. Study on a detector for gaseous components using semicon-ductive thin films [J]. Anal. Chem.,1966,38:1069-1073.
[4]TAGUCHIN. Japan, Patent 45-38200 [P].1962.
[5]PARK C O, AKBAR S A. Ceramics for chemical sensing [J]. J. Mater. Sci.,2003,38: 4611-4637.
[6]GOPEL W, REINHARDT G. Metal oxide sensors:New devices through tailoring interfaces on the atomic scale [J] Sensors Update,1996,1:49-120.
[7]QUARANTA F, RELLA R, SICILIANO P, CAPONE S, EPIFANI M, VASANELLI L, LICCIULLI A, ZOCCO A. A novel gas sensor based on SnO2/Os thin film for the detection of methane at low temperature [J]. Sens. Actuators B,1999,58:350-355.
[8]SAVAGE N, CHWIEROTH B, GINWALLA A, PATTON B R, AKBAR S A, DUTTA P K. Composite np semiconducting titanium oxides as gas sensors [J]. Sens. Actuators B,2001,79: 17-27.
[9]TAKADA T. A new method for gas identification using a single semiconductor sensor [J]. Sens. Actuators B,1998,52:49-52.
[10]GARDNER J W, BARTLETT P N. Sensors and Sensory Systems for an Electronic Nose [M]. NATO ASI Series E:Applied Science,1992,212.
[11]CHAMBON L, GERMAIN J P, PAULY A, DEMARNE V, GRISEL A. Ozone sensing properties of NbO2 thin films for health and safety applications [J]. Sens. Actuators B,1999,23: 138-147.
[12]XU C, TAMAKI J, MIURA N, YAMAZOE N. Correlation between Gas Sensitivity and Crystallite Size in Porous SnO2-Based Sensors[J]. Chem. Lett.,1990,3:441-444.
[13]XU C, TAMAKI J, MIURA N, YAMAZOE N. Grain size effects on gas sensitivity of porous SnO2-based elements [J]. Sens. Actuators B 1991,3:147-155.
[14]TAMAKI J, ZHANG Z, FUJIMORI K, AKIYAMA M, HARADA T, MIURA N, YAMAZOE N. Grain-size effects in tungsten oxide-based sensor for nitrogen oxide [J]. J. Electrochem.Soc.,1994,141:2207-2210.
[15]LU F, LI Y, DONG M, WANG X. Nanosized tin oxide as the novel material with simultaneous detection towards CO,H2 and CH4 [J]. Sens. Actuators B,2000,66:225-227.
[16]ANSARI Z A,ANSARI S G,KO T, OH J H. Effect of MoO3 doping and grain size on SnO2-enhancement of sensitivity and selectivity for CO and H2 gas sensing [J] Sens. Actuators B, 2002,87:105-114.
[17]SOMORJAI G A. Introduction to Surface Chemistry and Catalysis [M] John Wiley & Sons, New York,1994.
[18]WANG Q, OSTAFIN A E. Metal Nanoparticles in Catalysis [M] American Scientific, Stevenson Ranch, CA, USA,2004.
[19]GOPEL W, SCHIERBAUM K D. SnO2 sensors:current status and future prospects [J]. Sens. Actuators B,1995,26-27:1-12.
[20]MORRISON S R. Selectivity in semiconductor gas sensors [J] Sens. Actuators,1987,12: 425-440.
[21]KOHL D. The role of noble metals in the chemistry of solid-state gas sensors [J] Sens. Actuators B,1990,1:158-165.
[22]AKIYAMA M, TAMAKI J, MIURA N, YAMAZOE N. Tungsten Oxide-Based Semiconductor Sensor Highly Sensitive to NO and NO2 [J]. Chem. Lett.,1991,1611-1614.
[23]PAGNIER T, BOULOVA M, GALERIE A, GASKOV A, LUCAZEAU G. Tungsten oxide reactivity versus CH4, CO and NO2 molecules studied by Raman spectroscopy [J]. Sens. Actuators B,2001,71:134-139.
[24]CHOWDHURI A, SHARMA P, GUPTA V, SREENIVAS K, RAO K. H2S gas sensing mechanism of SnO2 films with ultrathin CuO dotted islands [J] J. Appl. Phys.2002,92: 2172-2180.
[25]CHOWDHURI A, GUPTA V, SREENIVAS K. Metal and metal oxide nanoparticles in chemiresistors:does the nanoscale matter? [J]. Rev. Conserv.2003,4:75-78.
[26]YAMAZOE N, SAKAI G, SHIMANOE K. Oxide semiconductor gas sensors [J]. Catal. Surv. Asia.,2003,1:63-75.
[27]G URLO A, BARSAN N, LVANOVSKAYA M, WEIMAR U, GOPEL W, In2O3 and MoO3-In2O3 thin film semiconductor sensors:interaction with NO2 and O3 [J]. Sens. Actuators B, 1998,47:92-99.
[28]CABOT A, ARBIOL J, MORANTE J R, WEIMAR U, BARSAN N, GOPEL W. Analysis of the noble metal catalytic additives introduced by impregnation of as obtained SnO2 sol-gel nanocrystals for gas sensors [J]. Sens. Actuators B 2000,70:87-100.
[29]SBERVEGLIERI G Gas Sensors—Principles Operation and Developmens [M]. Kluwer Academic Publishers, The Netherlands,1992.
[30]VYSHATKO N P, KHARTON V V, SHAULA A L, MARQUES F M B. Powder X-ray diffraction study of LaCo0.5Ni0.5O3-δ and LaCo0.5Fe0.5O3-δ[J]. Powder Diffr.,2003,18:159-161.
[31]ERNNA G, JOSHI B C, RUNTHALA D P, GUPTA R P. Oxide materials for development of integrated gas sensors-a comprehensive review [J]. Crit. Rev. Solid State Mater. Sci.,2004,29: 111-188.
[32]MEIXNER H, LAMPE U. Metal oxide sensors [J]. Sens. Actuators B,1996,33:198-202.
[33]YAMAZOE N, KUROKAWA Y, SEIYAMA T. Effects of additives on semiconductor gas sensors [J]. Sens. Actuators B,1983,4:283-289.
[34]MAEKAWA T, TAMAKI J, MIURA N, YAMAZOE N. Gold-loaded tungsten oxide sensor for detection of ammonia in air [J]. Chem. Lett.,1992,21:639-642.
[35]EGASHIRA M, SHIMIZU Y, TAKAO Y. Trimethylamine sensor based on semiconductive metal oxides for detection of fish freshness [J]. Sens. Actuators B,1990,1:108-112.
[36]AKIYAMA M, ZHANG Z, TAMAKI J, MIURA N, YAMAZOE N. Tungsten oxide-base semiconductor sensor for detection of nitrogen oxides in combustion exhaust [J]. Sens. Actuators B,1993,13-14:619-620.
[37]NAKANARA T, TAKAHATA K, MATSUURA S. High sensitive SnO2 gas sensor, I. Detection of volatile sulphides, Proc. Symp. Chemical Sensors, Honolulu, HI, USA, Oct.,1987, 18-23:55-64.
[38]MAEKAWA T, TAMAKI J, MIURA N, YAMAZOE N. Sensing behavior of CuO-loaded SnO2 element for H2S detection [J]. Chem. Lett.,1991,575-578.
[39]MAEKAWA T, TAMAKI J, MIURA N, YAMAZOE N, MATSUSHIMA S. Development of tin dioxide-based ethanol gas sensor [J]. Sens. Actuators B,1992,9:63-69.
[40]TAKADA T, KOMATSU K. O3 gas sensor of thin film semiconductor ln2O3 [J].4th Conf Solid-State Sensors andActuatorn (Transducers 87), Tokyo, Japan, June 2-5,1987,693-696.
[41]OKAYAMA Y. Hydrogen gas sensor. Proc.6th Sensor Symp., Tsukuha, Japan, May 29-30, 1986,101-105.
[42]YAMAZOE N, MUTO Y, SEIYAMA T. Tin oxide gas sensor insensitive to ethanol gas [J]. Hyomen Kagaku,1984,5:241-247.
[43]YAMAURA H, TAMAKI J, MORIYA K, MIURAN, YAMAZOE N. Selective CO detection by using indium oxide-based semiconductor gas sensor [J]. J. Electrochem. Soc.,1996,143: 36-37.
[44]YAMAURA H, TAMAKI J, MORIYA K, MIURAN, YAMAZOE N. Highly selective CO sensor using indium oxide doubly promoted by cobalt oxide and gold [J]. J. Electrochem. Soc., 1997,144:158-160.
[45]ANNO Y, MAEKAWA T, TAMAKI J, ASANO Y, HAYASHI K, MIURAN, YAMAZOE N. Zinc-oxide-based semiconductor sensors for detecting acetone and capronaldehyde in the vapour of consomme soup [J]. Sens. Actuators B,1995,24-25:623-627.
[46]SHEN Y, YAMAZAKI T, LIU Z, MENG D, KIKUTA T, NAKATANI N, SAITO M, MORI M. Microstructure and H2 gas sensing properties of undoped and Pd-doped SnO2 nanowires [J]. Sens. Actuators B,2009,135:524-529.
[47]HSUEH T J, HSU C L, CHANG S J, CHEN I C. Laterally grown ZnO nanowire ethanol gas sensors [J]. Sens. Actuators B,2007,126:473-477.
[48]GAO T, WANG.T H Catalytic growth of In2O3 nanobelts by vapor transport [J]. J. Cryst. Growth,2006,290:660-664.
[49]LIU J F, WANG X, PENG Q, LI Y D. Vanadium Pentoxide Nanobelts:Highly Selective and Stable Ethanol Sensor Mateials [J]. Adv. Mater.,2005,17:764-767.
[50]HEO Y W, TIEN L C, NORTON D P, KANG B S, REN F, GILA B P, PEARTON S J. Electrical transport properties of single ZnO nanorods [J]. Appl. Phys. Lett.,2004,85: 2002-2004.
[51]XUE X Y, FENG P, WANG Y G, WANG T H. Extremely high oxygen sensing of individual ZnSnO3 nanowires arising from grain boundary barrier modulation [J]. Appl. Phys. Lett.,2007, 91:022111.
[52]HUANG H, LEE Y C, TAN O K, ZHOU W, PENG N, ZHANG Q. High sensitivity SnO2 single-nanorod sensors for the detection of H2 gas at low temperature [J]. Nanotechnology,2009, 20:115501.
[53]SYSOEV V V, GOSCHNICK J, SCHNEIDER T, STRELCOV E, KOLMAKOV A. GRADIENT A. Microarray Electronic Nose Based on Percolating SnO2 Nanowire Sensing Elements [J]. Nano Leet.,2007,7:3182-3188.
[54]QURASHI A, YAMAZAKI T, MAGHRABY E M E, KIKUTA T. Fabrication and gas sensing properties of In2O3 nanopushpins [J]. Appl. Phys. Lett.,2009,95:153109.
[55]ZENG Z M, WANG K, ZHANG Z X, CHEN J J, ZHOU W L. The detection of H2S at room temperature by using individual indium oxide nanowire transistors [J]. Nanotechnology,2009,20: 045503.
[56]ZHAO Y M, ZHU Y Q. Room temperature ammonia sensing properties of W18O49 nanowires [J]. Sens. Actuators B,2009,137:27-31.
[57]LIU Z F, YAMAZAKI T, SHEN Y B, KIKUTA T, NAKATANI N, KAWABATA T. Room temperature gas sensing ofp-type TeO2 nanowires [J]. Appl. Phys. Lett.,2007,90:173119.
[58]LIU J F, WANG X, PENG Q, LI Y D. Preparation and gas sensing properties of vanadium oxide nanobelts coated with semiconductor oxides [J]. Sens. Actuators B,2006,115:481-487.
[59]KOLMAKOV A, MOSKOVITS M. Chemical sensing and catalysis by one-dimensional metal-oxide nanostructures [J]. Annu. Rev. Mater. Res.,2004,34:151-180.
[60]PARK W I, YI G C, KIM M, PENNYCOOK S J. Quantum confinement observed in ZnO/ZnMgO nanorod heterostructures [J]. Adv. Mater.,2003,15:526-29.
[61]KAYE B H, RANDOM A. Walk Through Fractal Dimensions [M]. VCH Verlagsgesellschaft, Weinheim,1989.
[62]WILLIAMS D E, PRATT K F E. Microstructure effects on the response of gas-sensitive resistors based on semiconducting oxides [J]. Sens. Actuators B,2000,70:214-221.
[63]HYODA T, NISHIDA N, SHIMIZU Y, EGASHIRA M. Preparation and gas-sensing properties of thermally stable mesoporous SnO2 [J]. Sens. Actuators B,2002,83:209-215.
[64]BERNASIK A, RADECKA M, REKAS M, SLOMA M. Electrical properties of Cr-and Nb-doped TiO2 thin films [J]. Appl. Surf. Sci.,1993,65-66:240-245.
[65]ZAKRZEWSKA K, RADECKA M, REKAS M. Effect of Nb, Cr, Sn additions on gas sensing properties of TiO2 thin films [J]. Thin Solid Films,1997,310:161-166.
[66]TAN O K, ZHU W, YAN Q, KONG L B. Size effect and gas sensing characteristics of nanocrystalline xSnO2-(1-x)a-Fe2O3 ethanol sensors [J].Sens. Actuators B,2000,65:361-365.
[67]KIM I D, ROTHSCHILD A, LEE B H, KIM D Y, JO S M, TULLER H L. Ultrasensitive Chemiresistors Based on Electrospun TiO2 Nanofibers [J]. Nano Lett.,2006,6:2009-2013.
[68]KUANG Q, LAO C S, WANG Z L, XIE Z X, ZHENG L S. High-Sensitivity Humidity Sensor Based on a Single SnO2 Nanowire [J]. J. Am. Chem. Soc.,2007,129:6070-6071.
[69]YANG F, TAGGART D K., PENNER R M. Fast, Sensitive Hydrogen Gas Detection Using Single Palladium Nanowires That Resist Fracture [J]. Nano Lett.,2009,9:2177-2182.
[70]FORMHALS. Process and Apparatus fob Pbepabing. A. US Patent,1975504 [P].1934-10-2. http://www.google.com.hk/patents?hl=zh-CN&lr=&vid==USPAT1975504&id= X5oAAAAEBAJ &oi=fnd&dq==Formhals.+A.+US+Patent+1975504,+1934.&printsec=abstract#y=onepage&q&f= false
[71]FORMHALS. Method and apparatus for spinning. A. US Patent,2160962 [P].1939-6-6. http://www.google.com.hk/patents?hl=zh-CN&lr=&vid=USPAT2160962&id=9JJuAAAAEBAJ &oi=fnd&dq=Formhals.+A.+US+Patent+2160962.+1939.&printsec=abstract#v=onepage&q=For mhals%2C%20A.%20US%20Patent%202160962%2C%201939.&f=false
[72]FORMHALS. A. US Patent,2187306 [P].1940-1-16. http://www.google.com.hk/patents?hl=zh-CN&lr=&vid=U SPAT2187306&id=Mm5aAAAAEBA J&oi=fnd&dq=Formhals,+A.+US+Patent+2187306.+1940.&printsec=abstract#v=onepage&q=F ormhals%2C%20A.%20US%20Patent%202187306%2C%201940.&f=false
[73]TAYLOR G I. Electrically Driven Jets [J]. Proc. Roy. Soc. London A,1969,313:453-475.
[74]BUCHKO C J, CHEN L C, YU S, MARTIN D C. Processing and microstructural characterization of porous biocompatible protein polymer thin films [J]. Polymer,1999,40, 7397-7047.
[75]BAUMGARTEN P K. Electrostatic spinning of acrylic microfibers [J]. J. Colloid Interface Sci.,1971,36,71-79.
[76]LARRONDO L, MANDLEY R S J. Electrostatic fiber spinning from polymer melts. I. Experimental observations on fiber formation and properties [J]. J. Polym. Sci.:Polymer Physics Edn.,1981,19:909-920.
[77]DOSHI J, RENEKER D H. Electrospinning process and applications of electrospun fibers [J]. J. Electrostatics,1995,35:151-160.
[78]BHARDWAJ N, KUNDU S C. Electrospinning:A fascinating fiber fabrication technique [J] Biotechnol. Adv.,2010,28:325-347.
[79]RAMAKRISHNA S, FUJIHARA K, TEO W E, YONG T, MA Z, RAMASESHAN R. Electrospun nanofibers:solving global issues [J].Mater Today,2006,9:40-50.
[80]RAMASESHAN R, SUNDARRAJAN S, JOSE R, RAMAKRISHNA S. Nanostructured ceramics by electrospinning [J]. J. Appl. Phys.,2007,102:111101.
[81]LI D, XIA Y N. Electrospinning of Nanofibers:Reinventing the Wheel? [J]. Adv. Mater.,.2001,16:1151-1170.
[82]CHONG E J, PHAN T T, LIM I J, ZHANG Y Z, BAY B H, RAMAKISHNA S, LIM C T. Evaluation of electrospun PCL/gelatin nanofibrous scaffold for wound healing and layered dermal reconstitution [J]. Acta. Mater.,2007,3:321-330.
[83]SUKIGARA S, GANDHI M, AYUTSEDE J, MICKLUS M, KO F. Regeneration of Bombyx mori silk by electrospinning-part 1:processing parameters and geometric properties [J]. Polymer, 2003,44:5721-5727.
[84]MCKEE M G, LAYMAN J M, CASHION M P, LONG T E. Phospholipid non-woven electrospin membranes [J]. Science,2006,311:353-355.
[85]DEITZEL J M, KLEINMEYER J, HARRIS D, TAN N C B. The effect of processing variables on the morphology of electrospun nanofibers and textiles [J]. Polymer,2001,42: 261-272.
[86]DOSHI J, RENEKER D H. Electrospinning process and applications of electrospun fibers [J]. J. Electrost,1995,35:151-156.
[87]KWON I K, MATSUDA T. Co-electrospun nanofiber fabrics of poly (1-lactide-co-ε-caprolactone) with type I collagen or heparin [J]. Biomacromolecules,2005,6: 2096-2105.
[88]MCKEE M G, WILLES G L, COLBY R H, LONG T E. Correlations of solution rheology with electrospun fiber formation of linear and branched polyesters [J]. Macromolecules,2004,37: 1760-1767.
[89]ZHANG C, YUAN X, WU L, HAN Y, SHENG J. Study on morphology of electrospun poly (vinyl alcohol) mats [J]. Eur. Polym. J.2005b,41:423-432.
[90]YUAN X Y, ZHANG Y Y, DONG C H, SHENG J. Morphology of ultrafine polysulfone fibers prepared by electrospinning [J]. Polym. Int.,2004,53:1704-1710.
[91]MEGELSKI S, STEPHENS J S, CHASE D B, RABOLT J F. Micro-and nanostructured surface morphology on electrospun polymer fibers [J]. Macromolecules,2002,35:8456-8466.
[92]KIM K H, JEONG L, PARK H N, SHIN S Y, PARK W H, LEE S C, et al. Biological efficacy of silk fibroin nanofiber membranes for guided bone regeneration [J]. Afr. J. Biotechnol 2005a,120:327-339.
[93]WANNATONG L, SIRIVAT A, SUPAPHOL P. Effects of solvents on electrospun polymeric fibers:preliminary study on polystyrene [J]. Polym. Int.,2004,53:1851-1859.
[94]WANG X, UM I C, FANG D, OKAMOTO A, HSIAO B S, CHU B. Formation of water-resistant hyaluronic acid nanofibers by blowing-assisted electro-spinning and non-toxic post treatments [J]. Polymer,2005b,46:4853-4867.
[95]SUNDARAY B, SUBRAMANIAN V, NATARAJAN T S, XIANG R Z, CHANG C C, FANN W S. Electrospinning of continuous aligned polymer fibers [J]. Appl. Phys. Lett.,2004, 84:1222-1224.
[96]XU C Y, INAI R, KOTAKI M, RAMAKRISHNA S. Aligned biodegradable nanofibrous structure:a potential scaffold for blood vessel engineering [J]. Biomaterials,2004,25:877-886.
[97]KI C S, KIM J W, HYUN J H, LEE K H, HATTORI M, RAH D K, et al. Electrospun three dimensional silk fibroin nanofibrous scaffold [J]. J. Appl. Polym. Sci.,2007,106:3922-3928.
[98]BUCHKO C J, CHEN LC, SHEN Y, MARTIN D C. Processing and microstructural characterization of porous biocompatible protein polymer thin films [J]. Polymer,1999,40: 7397-7407.
[99]MIT-UPPATHAM C, NITHITANAKUL M, SUPAPHOL P. Ultrafine electrospun polyamide-6 fibers:effect of solution conditions on morphology and average fiber diameter [J]. Macromol. Chem. Phys.,2004,205:2327-2338.
[100]CAI S S, LIU Y C, SHU X Z, PRESTWICH G D. Injectable glycosaminoglycan hydrogels for controlled release of human basic fibroblast growth factor [J]. Biomaterials,2005,26: 6054-6067.
[101]BAUMGARTEN P K. Electrostatic spinning of acrylic microfibers [J]. J. Colloid. Interf. Sci.,1971,36:71-79.
[102]FONG H, RENEKET D H. Electrospinning and formation of nanofibers. In:Salem D R, editor. Structure formation in polymeric fibers. Munich, Hanser,2001,225-246.
[103]TABAR H R. Modeling the nano-scale phenomena in condensed matter physics via computer based numerical simulations [J]. Physics Reports 2000,325:239-310.
[104]SHIN Y M, HOHMAN M M, BRENNER M P, RUTLEDGE G C. Electrospinning:A whipping fluid jet generates submicron polymer fibers [J]. Appl. Phys. Lett.,2001,78: 1149-1151.
[105]KOOMBHONGSE S, RENEKER D H. Branched and split fiber from electrospinning process, Bookof Abstracts. In:New Frontiers in Fiber Science, Spring Meeting 2001. Available from:http://www.tx.ncsu.edu/itatm/volume1specialissue/posters/posters part1.pdf.
[106]RENEKER D H, YARIN A L, FONG H, KOOMBHONGSE S. Bending instability of electrically charged liquid jets of polymer solutions in electrospinning [J]. J. Appl. Phys.,2000, 87,4531-4547.
[107]HOHMAN M M, SHIN M, RUTLEDGE G, BRENNER M P. Electrospinning and electrically forced jets. I. Stability theory [J]. Phys. Fluids,2001,13:2201-2220.
[108]SHKADOV V Y, SHUTOV A A. Disintegration of a charged viscous jet in a high electric field [J]. Fluid Dyn. Res.,2001,28:23-29.
[109]YARIN A L, KOOMBHONGSE S, RENEKER D H. Bending instability in electrospinning of nanofibers [J]. J. Appl. Phys.,2001,89:3018-3026.
[110]SHIN Y M, HOHMAN M M, BRENNER M P, RUTLEDGE G C. Electrospinning:A whipping fluid jet generates submicron polymer fibers [J]. Appl. Phys. Lett.,2001,78: 1149-1151.
[111]RENEKER D H, YARIN A L, FONG H, KOOMBHONGSE S. Bending instability of electrically charged liquid jets of polymer solutions in electrospinning [J]. J. Appl. Phys.,2000, 87:4531-4547.
[112]HOHMAN M M, SHIN M, RUTLEDGE G, BRENNER M P. Electrospinning and electrically forced jets. Ⅱ Applications[J]. Phys. Fluids,2001,13:2221-2236.
[113]KIM H S, KIM K, JIN H J, CHIN I J. Morphological characterization of electrospun nano-fibrous membranes of biodegradable poly(L-lactide) and poly(lactidecoglycolide) [J]. Macromol. Symp.,2005,224:145-154.
[114]LIU H, HSIEH Y L. Ultrafine fibrous cellulose membranes from electrospinning of cellulose acetate [J]. J. Polym. Sci. Part B:Polym. Phys.,2002,40:2119-2129.
[115]BAJI A, MAI Y W, WONG S C, ABTAHI M, CHEN P. Electrospinning of polymer nanofibers:Effects on oriented morphology, structures and tensile properties [J]. Compos. Sci. Technol.,2010,70:703-718.
[116]THERON A, ZUSSMAN E, YARIN A L. Electrostatic field-assisted alignment of electrospun nanofibres [J]. Nanotechnology,2001,12:384-390.
[117]KATTA P, ALESSANDRO M, RAMSIER R D, CHASE G G. Continuous electrospinning of aligned polymer nanofibers onto a wire drum collector [J]. Nano Lett.,2004,4:2215-2218.
[118]FENNESSEY S F, FARRIS R J. Fabrication of aligned and molecularly oriented electrospun polyacrylonitrile nanofibers and the mechanical behavior of their twisted yarns [J]. Polymer,2008,45:4217-4225.
[119]MATHEW G, HONG J P, RHEE J M, LEE H S, NAH C. Preparation and characterization of properties of electrospun poly(butylene terephthalate) nanofibers filled with carbon nanotubes [J]. Polym. Test.,2005,24:712-717.
[120]BOLAND E D, WNEK G E, SIMPSON D G,PALOWSKI K J, BOWLIN G L. Tailoring tissue engineering scaffolds using electrostatic processing techniques:a study of poly(glycolic acid) electrospinning [J]. J. Macromol. Sci.:Pur. Appl. Chem.,2001a; 38:1231-1243.
[121]DERSCH R, LIU T, SCHAPER A K. Electrospun nanofibers:internal structure and intrinsic orientation [J]. J. Polym. Sci.:Part A:Polym. Chem.,2003,41:545-553.
[122]XU C Y, INAI R, KOTAKI M, RAMAKRISHNA S. Aligned biodegradable nanofibrous structure:a potential scaffold for blood vessel engineering [J]. Biomaterials,2004,25:877-886.
[123]TEO W E, RAMAKRISHNA S. A review on electrospinning design and nanofibre assemblies [J]. Nanotechnology 2006,17:89-106.
[124]KIM G H, KIM W D. Formation of oriented nanofibers using electrospinning [J]. Appl. Phys. Lett.,2006,88:233101.
[125]TEO W E, RAMAKRISHNA S. Electrospun fibre bundle made of aligned nanofibres over two fixed points [J]. Nanotechnology,2005,16:1878-1884.
[126]WONG S C, BAJI A, LENG S W. Effect of fiber diameter on tensile properties of electrospun poly(-caprolactone) [J]. Polymer,2008,21:4713-4722.
[127]HUANG Z M, ZHANG Y Z, KOTAKI M, RAMAKRISHNA S. A review on polymer nanofibers by electrospinning and their applications in nanocomposites [J]. Compos. Sci. Technol.,2003,63,2223-2253.
[128]LI D, WANG Y L, XIA Y N. Electrospinning nanofibers as uniaxially aliged arrays and layer-by-layer stacked films [J]. Adv. Mater.,2004,16:361-366.
[129]YANG D Z, ZHANG J F, ZHANG J, NIE J, Aligned Electrospun Nanofibers Induced by Magnetic Field [J], J. Appl. Polym. Sci.,2008,110:3368-3372.
[130]DEITZEL J M, KLEINMEYER J, HIRVONEN J K, BECK T N C. Controlled deposition of electrospun poly(ethylene oxide) fibers [J]. Polymer,2001,42:8163-8170.
[131]FAN H T, XU X J, MA X K, ZHANG T. Preparation of LaFeO3 nanofibers by electrospinning for gas sensors with fast response and recovery [J]. Nanotechnology,2011,22: 115502.
[132]ZHANG Y, LI J, LI Q, ZHU L, LIU X, ZHONG X, MENG J, CAO X. Preparation of In2O3 ceramic nanofibers by electrospinning and their optical properties [J], Scripta Mater.,2007,56: 409-412.
[133]QI Q, ZHANG T, LIU L, ZHENG X, Synthesis and toluene sensing properties of SnO2 nanofibers [J], Sens. Actuators B 2009,137:471-475.
[134]WAN Q, LI Q H, CHEN Y J, WANG T H, HE X L, LI J P, LIN C L. Fabrication and ethanol sensing characteristics of ZnO nanowire gas sensors [J]. Appl. Phys. Lett.,2004,84: 3654-3656.
[135]CHEN Y J, XUE X Y, WANG Y G, WANG T H. Synthesis and ethanol sensing characteristics of single crystalline SnO2 nanorods [J], Appl. Phys. Lett.,2005,87:233503.
[136]SCOTT R W J, YANG S M, CHABANIS G, COOMBS N, WILLIAMS D E, OZIN G A. Tin Dioxide Opals and Inverted Opals:Near-Ideal Microstructures for Gas Sensors [J]. Adv. Mater.,2001,13:1468-1472.
[137]ALBERT K J, LEWIS N S, SCHAUER C L, SOTZING G A, STITZEL S E, VAID T P, D WALT R. Cross-Reactive Chemical Sensor Arrays [J]. Chem. Rev.,2000,100:2595-2626.
[138]BARSAN N, KOZIEJ D, WEIMAR U. Metal oxide-based gas sensor research:How to? [J]. Sens. Actuators B,2007,121:18-35.
[139]SBERVEGLIERI G, BARATTO C, COMINI E, FAGLIA G, FERRONI M, PONZONI A, VOMIERO A. Synthesis and characterization of semiconducting nanowires for gas sensing [J]. Sens. Actuators B,2007,121:208-213.
[140]BELMONTRE J C, MANZANO J, ARBILO J, CIRERA A, PUIGCORBEJ, VILA A, SABATEN, GRACIA I, CANEC, MORANTE J R. Micromachined twin gas sensor for CO and O2 quantification based on catalytically modified nano-SnO2 [J]. Sens. Actuators B,2006,114: 881-892.
[141]VARGHESE O K, GONG D, PAULOSE M, ONG K G, GRIMES C A. Hydrogen sensing using titania nanotubes [J]. Sens. Actuators B,2003,93:338-344.
[142]IVANOVSKAYA M, KOTSIKAU D, FAGLIA G, NELLI P. Influence of chemical composition and structural factors of Fe2O3/In2O3 sensors on their selectivity and sensitivity to ethanol [J]. Sens. Actuators B,2003,96:498-503.
[143]GOU X L, WANG G X, YANG J, PARK J, WEXKER D. Chemical synthesis, characterisation and gas sensing performance of copper oxide nanoribbons [J]. J. Mater. Chem., 2008,18,965-969.
[144]JIMENEZ I, CENTENO M A, SCOTTI R, MORAZZONI F, ARBIOL J, CNRNET A, MORANTE J R. NH3 interaction with chromium-doped WO3 nanocrystalline powders for gas sensing applications [J]. J. Mater. Chem.,2004,14:2412-2420.
[145]FRANKE M E, KOPLIN T J, SIMON U. Metal and metal oxide nanoparticles in chemiresistors:does the nanoscale matter? [J]. Small,2006,2:36-50.
[146]ZHANG Y, XIANG Q, XU J Q, XU P C, PAN Q Y, LI F. Self-assemblies of Pd nanoparticles on the surfaces of single crystal ZnO nanowires for chemical sensors with enhanced performances [J]. J. Mater. Chem.,2009,19:4701-4706.
[147]GIBSON P W, SCHREUDER-GIBSON H L, RIVEN D. Electrospun fiber mats:transport properties [J]. AIChE J.,1999,45:190-195.
[148]ANGADJIVAND S A, SCHWARTA M G, EITZMAN P D, JONES M E. Method and apparatus for making a nonwoven fibrous electret web from free-fiber and polar liquid. US patent 6375886 [P].2002-4-23. http://www.google.com.hk/patents?hl=zh-CN&lr=&vid=USPAT6375886&id=GkUJAAAAEBAJ &oi=fnd&dq=S.A.+Angadiivand,+M.G.+Schwartz.+P.D.+Eitzman,+M.E.+Jones,+US+patent+6, 375,886+(2002).&printsec=abstract#v=onepage&q&f=false
[149]FERTALA A, HAN W B, KO F K. Mapping critical sites in collagen Ⅱ for rational design of gene-engineered proteins for cell-supporting materials [J]. J. Biomed. Mater. Res.,2001,57: 48-58.
[150]JIN H J, FRIDRIKH S, RUTLEDGE G C, KAPLAN D. Electrospinning Bombyx mori silk with poly (ethylene oxide) [J]. Biomacromolecules,2002,6:1233-1239.
[151]KOLMAKOV A, KLENOV D 0, LILACH Y, STEMMER S, MOSKOVITS M. Enhanced gas sensing by individual SnO2 nanowires and nanobelts functionalized with Pd catalyst particles [J]. Nano Lett.2005,5:667-673.
[152]ZHANG Y, XIANG Q, XU J Q, XU P C, PAN Q Y, LI F. Self-assemblies of Pd nanoparticles on the surfaces of single crystal ZnO nanowires for chemical sensors with enhanced performances [J]. J. Mater. Chem.2009,19,4701-4706.
[153]COBLEY C M, CAMPBELL D J, XIA Y N. Tailoring the optical and catalytic properties of gold-silver nanoboxes and nanocages by introducing palladium [J]. Adv. Mater.,2008,20: 748-752.
[154]LU X M, AU L, MCLELLAN J, LI Z Y, MARQUEZ M, XIA Y N. Fabrication of cubic nanocages and nanoframes by dealloying Au/Ag alloy nanoboxes with an aqueous etchant based on Fe(NO3)3 or NH4ON [J]. Nano Lett.,2007,7:1764-1769.
[155]PARK S, LIM J, CHUNG S, MIRKIN C A. Self-assembly of mesoscopic metal-polymer amphiphiles [J]. Science,2004,303:348-351.
[156]LIU B, ZENG H C. Fabrication of ZnO "Dandelions" via a modified Kirkendall process [J]. J. Am. Chem. Soc.,2004,126:16744-16746.
[157]YANG H G, ZENG H C. Preparation of hollow anatase TiO2 nanospheres via Ostwald ripening [J]. J. Phys. Chem. B,2004,108:3492-3495.
[158]JIANG P, BERTONE J F, COLVIN V L. A lost-wax approach to monodisperse colloids and their crystals [J]. Science,2001,291:453-457.
[159]BAE J S, YUN D H, PARK C O, HWANG J S. Improved selectivity of oxide semiconductor type gas sensor using compensating element [J]. Sens. Actuators B,2001,75: 160-165.
[160]FENG Y L, WANG S J, FENG B, WANG R, HE Y, ZHANG T. Development of an auto test system for humidity sensors [J]. Sens. Actuators A,2009,152:104-109.
[161]EGASHIRA M, SHIMIZU Y, TAKAO Y, SAKO S. Variations in I-V characteristics of oxide semiconductors induced by oxidizing gases [J]. Sens. Actuators B,1996,35:62-67.
[162]CHOI K I, KIM H R, LEE J H. Enhanced CO sensing characteristics of hierarchical and hollow In2O3 microspheres [J]. Sens. Actuators B,2009,138:497-503.
[163]XUA J Q, JIA X H, LOU X D, XI G X, HAN J J, GAO Q H, Selective detection of HCHO gas using mixed oxides of ZnO/ZnSnO3 [J]. Sens. Actuators B,2007,120:694-699.