碳热还原制备碳化硅纳米线及其性能研究

【作者】 罗晓刚；

【导师】 马文会；

【作者基本信息】 昆明理工大学 ， 有色金属冶金， 2010， 硕士

【摘要】 第三代宽带隙半导体SiC材料以其大的禁带宽度,高的熔点和硬度、高的热导率、高的临界击穿电场、高的电子饱和迁移率、抗辐射能力强以及机械性能好等特性,是制作大功率、高频、低能耗、耐高温和抗辐照器件的理想材料而受到人们的广泛关注。最近研究表明,与块体SiC材料相比SiC纳米线具有优异的光、电和机械等性能,在金属基、陶瓷基和聚合物基增强复合材料,制备发光二极管、大功率晶体管等电子和光电子纳米器件,场发射阴极材料,光催化,储氢和自清洁薄膜等许多领域都有着广泛的应用前景。因此研究SiC纳米线的制备及性能具有重要的意义。本文采用碳热还原Si02在常压无金属催化剂的条件下制备SiC纳米线,结合X射线粉末衍射(XRD)、傅立叶红外光谱(FT-IR)、扫描电子显微镜(SEM)、X射线能谱仪(EDS)、透射电子显微镜(TEM)等分析测试方法,分析了SiC纳米线的成分、形貌和微观结构。研究了影响碳热还原制备SiC纳米线的工艺参数,反应过程热力学并提出了SiC纳米线的生长机理。最后对制备的SiC纳米线的发光性能、场发射性能和光催化性能进行了研究。论文主要包括以下几个方面：1.在常压下,以竹炭为碳源,C和Si02的摩尔比为3,在反应电流536A(1400℃)下反应20分钟,制备了p-SiC纳米线,纳米线具有核-壳结构,内层为单晶p-SiC,外层为无定形Si02。纳米线分布紊乱,表面粗糙,直径在50～200 nm之间,长度可达几百微米,沿着<111>方向生长。2.研究了碳源、配碳量、反应电流和反应时间等实验参数对碳热还原制备SiC纳米线形貌的影响,并提出了生长机理。研究结果表明,不同实验参数下所制备产物的晶体结构都为p-SiC,但形貌差别很大。在不同的配碳量下分别制备了片状、竹节状、宝塔状和珠状的SiC纳米结构；反应电流(温度)对SiC纳米线的形貌具有决定性的影响,在较低的反应电流(温度)下,过饱和度太小不能形成稳定的晶核,SiC纳米线的产率低；电流(温度)太高时,过饱和度太大有利于生成SiC纳米颗粒而不利于SiC纳米线的生成；反应时间对SiC纳米线的产率和直径影响不大,随着反应时间的延长,纳米线的长度不断增加,表面逐渐光滑。由于在反应过程中没有引入金属催化剂,而且FE-SEM和TEM分析表明纳米线尖端没有金属催化剂小滴,我们制备的纳米线是以气-固生长机制生长。3.研究了SiC纳米线的室温光致发光性能、场发射性能和光催化性能。在275 mn波长的光激发下,SiC纳米线在300 nm处有强的紫外光发射峰；SiC纳米线的场发射性能可通过退火热处理来增强,在700℃退火3h之前和之后的开启场强分别为9.5V/μm和7.5 V/gm,其场发射机理为量子隧道机理；在紫外光照射6h后,SiC纳米线降解亚甲基蓝溶液效率高达72.2%。更多还原

【Abstract】 Silicon carbide (SiC), as one of the third-generation semiconductor materials, has been attracting extensive interest due to its outstanding properties, such as wide band gap, high melt point, high hardness, high thermal conductivity, high breakdown electric field, high electron velocity, high resistance to radiation, good mechanical property and can be used as a promise material for preparing high power device, high frequency device, low energy consumption device, high temperature device and high radiation device. Compared with bulk SiC material, SiC nanowires have superior optical, electric and mechanical properties. SiC nanowires can be used as reinforced element for metal-, ceramic-and polymer-matrix composites and to prepare luminescence diode, high power transistor and other optical, electric nanodevices. It also has widely potential application in the fields of field emission cathode material, photocatalyst, hydrogen storage material and self-cleaning coating. So, it is very significant to study the preparation and property of SiC nanowires.In this paper, SiC nanowires were prepared via carbothermic reduction of silica under normal atmosphere pressure without catalyst. The composition, morphology and microstructure of the SiC nanowires were characterized by X-ray powder diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) equipped with energy disperse spectrum (EDS), and transmission electron microscopy (TEM). The parameters, thermodynamics of reaction process and the growth mechanism of SiC nanowires were investigated. Finally, the photoluminescence property, field emission property and photocatalytic degradation property of as-synthesized SiC nanowires were also investigated. The main results obtained in this paper are given as below:1. Under normal atmosphere pressure,β-SiC nanowires were synthesized in C/SiO2 mole ratio of 3 and at reaction current 536 A (1400℃) for 20 min by using bamboo carbon as carbon source. Theβ-SiC nanowires have a core-shell structure with crystalline SiC core and amorphous SiO2 shell. The nanowires with diameter of 50-200 nm and length from tens to hundreds of micrometers have a rough surface morphology, and the SiC nanowires grow along<111> direction.2. The effect of the carbon source, mole ratio of C/SiO2, reaction current and reaction time on the morphology of the SiC nanowires synthesized by carbothermic reduction is discussed and the growth mechanism has also been elucidated. The results indicated that under different experiment parameters the synthesized products were allβ-SiC but with different morphology. The platelet-, bamboo-, pagoda-, and bead-like SiC nanostructure are obtained. The reaction current (temperature) has a crucial effect on the morphology of SiC nanowires. When the current (temperature) is low; the supersaturation degree is too low to form stable nucleation, and then lead to reduce the yield of SiC nanowires; when the current (temperature) is high, the SiC nanoparticles are easily formed due to high supersaturation degree, while the formation of SiC nanowires is restrained. The reaction time has little effect on the yield and diameter of SiC nanowires. With the increasing of time, the length and surface of SiC nanowires are gradually become long and smooth, respectively. During the experiment, no metallic catalyst was introduced and no metallic droplets were detected in the nanowires’tips confirmed by FE-SEM and TEM characterization.Thus, the growth of nanowires in our experiment was not following the conventional metal-catalyst VLS mechanism. Based on the experiment results, we proposed the vapor-solid mechanism for the growth of SiC nanowires.3. The photoluminescence, field emission and photocatalytic degradation property of SiC nanowires are investigated. Under 275 nm excitation at room temperature, the SiC nanowires exhibit a strong ultraviolet emission peak at 300 nm. The field emission property of SiC nanowires can be enhanced by annealing treatment and the turn-on field of SiC nanowires before and after annealing at 700℃for 3 h is 9.5 V/μm and 7.5 V/μm, respectively. The field emission is done by quantum-tunneling mechanism; In addition, the as-synthesized silicon carbide nanowires have a high photocatalytic degradation activity (72.20%) to Methylene blue after 6 h degradation.更多还原