【作者】 任招娣；

【导师】 杜丕一；

【作者基本信息】 浙江大学 ， 材料学， 2012， 博士

【摘要】 硅化钛具有低电阻率、较高的热稳定性以及化学稳定性等诸多优异的性能,且由于其可以与硅工艺兼容而具有重要的研究价值。自1991年碳纳米管发现以来,一维纳米材料的研究引起了人们广泛的关注,硅化钛纳米线的制备、性能及应用研究也逐渐开展起来。本文使用SiH4和TiCl4为前驱体,N2为稀释气体和载气,通过常压化学气相沉积在玻璃基板及硅基板上制备了硅化钛薄膜及硅化钛纳米线,并将这种硅化钛纳米线／硅化钛薄膜一体结构用作场发射的阴极以及电介质薄膜的底电极进行研究,探索了其形成过程、场发射性能以及作为电介质薄膜电极的应用前景。具体内容如下：1.研究了各种沉积条件对硅化钛薄膜形成及其导电性的影响。结果表明,低TiCl4下形成的是Ti5Si3薄膜,而高SiH4/TiCl4下形成的是面心正交的TiSi2薄膜,所形成的晶相种类均不随其他沉积条件的变化而变化。当SiH4/TiCl4处于中间位置时,高温下形成的是Ti5Si3薄膜,低温下形成的是TiSi2薄膜。热力学自由能的变化在不同薄膜的形成中起了关键作用。2.研究了Ti5Si3薄膜、TiSi2薄膜及两种相的混合相薄膜上TiSi (?)内米线、纳米钉及火箭状纳米线的形成及形成机理。结果表明,TiSi (?)目的各向异性生长造成了纳米线的形成。纳米线的形态、直径及密度受沉积温度,源气体浓度等的影响。纳米线的形成还极大的受薄膜种类、结晶程度等的影响,结晶程度越高,纳米线越容易形核。TiSi2薄膜上形成的纳米线的直径小于Ti5Si3上的。纳米线能否形成极大的取决于沉积条件,而不依赖于基板,纳米线相对基板的准直性与其下薄膜的平整度等相关性较大。3.研究了各种不同形貌的硅化钛纳米线/硅化钛薄膜一体结构的场发射性能,并研究了薄膜成分、纳米线直径、纳米线分布、纳米线形态以及电极间距等对硅化钛纳米线/硅化钛薄膜场发射性能的影响。结果表明,TiSi火箭状纳米线/TiSi2薄膜场发射开关电场可低至2.33V/μm(电流密度超过10μA/cm2时的电场),最大电流密度可达917.43μA/cm2(电场强度为4.18V/μm)。纳米线直径越小,则其尖端电场越强；与火箭状纳米线及普通纳米线相比,钉状纳米线的尖端场强更强；束状分布的纳米线具有更高的尖端场强及更大的场发射体密度。纳米线尖端的场强越强,尖端数量越多,则其开关电场越低,场发射电流密度越大。TiSi纳米线/TiSi2薄膜具有比TiSi纳米线/Ti5Si3薄膜更低的开关电场及更大的场发射电流密度。4.使用溶胶-凝胶及射频-磁控溅射法,在Ti5Si3薄膜、TiSi纳米线/Ti5Si3薄膜、TiSi纳米线/Ti5Si3+TiSi2薄膜及ITO上制备了BT、BST及PST等电介质薄膜,研究了硅化钛薄膜及纳米线上电介质薄膜的介电性能。结果表明,与ITO基板相比,Ti5Si3薄膜、TiSi (?)内米线/Ti5Si3薄膜、TiSi纳米线/Ti5Si3+TiSi2薄膜上形成的电介质薄膜的结晶性更好,电容更大,损耗更低,且电容和损耗对频率的依赖性更低；与Ti5Si3薄膜相比,纳米线上形成的电介质薄膜的电容更大,损耗更低；与TiSi纳米线/Ti5Si3薄膜相比,TiSi纳米线/Ti5Si3+TiSi2薄膜上形成的电介质薄膜的电容更大,损耗更低。非氧化物硅化钛相的存在使得硅化钛薄膜上制备的电容相较ITO具有更低的频率依赖性。纳米线极大的比表面积及其周围局域增强电场的存在引起了硅化钛纳米线／硅化钛薄膜及上制备的电介质薄膜更大的电容,更低的损耗以及电容和损耗对频率的更低依赖性。更多还原

【Abstract】 Titanium silicide has received great interests due to its low resistivity, high thermal and chemical stability as well as high compatibility with Si technology. One-dimentional nanostructures have been given great concerns since CNT was reported in 1991. Titanium silicide nanowires thus receive great developments in its preparation, properties and applications. In this paper, titanium silicide thin films and nanowires are prepared on glass and Si substrates with APCVD method by using SiH4 and TiCl4 as precursors of Si and Ti, respectively, and N2 as diluted gas and carrier gas. The field emission properties of the titanium silicide thin films and nanowires are investigated. The titanium silicide thin films and nanowires as-prepared are also used as electrode substrates for preparing dielectric thin films. The formation and the field emission property of the thin films and the nanowires as well as the applications for it being used as electrodes in dielectric thin films are investitated. The paper mainly focuses on the following aspects.1. Preparation and the electrical properties of the titanium silicide thin films at different deposition conditions. It shows that the Ti5Si3 crystalline phases with hexagonal structure are formed at lower SiH4/TiCl4 while TiSi2 crystalline phases with face-centered orthorhombic structure are formed at higher SiH4/TiCl4. Species of the phases as-prepared are independence on the others deposition conditions in these cases. However, species of the phases in the thin films can be adjusted by the others deposition conditions, such as the deposition temperature, with a moderate SiH4/TiCl4. A higher temperature favors the formation of the Ti5Si3 phases while a lower temperature favors the formation of the TiSi2 phases. The thermodynamics is critical in forming the phases.2. Formation of the TiSi nanowires with morphologies of nanowires, nanopins and rocket nanowires, on different thin films of the Ti5Si3, the TiSi2, and the mixture of them. It shows that the TiSi nanowires are formed due to its anisotropic growth of the TiSi crystal planes. The nucleation and growth of the nanowires depend not only on the deposition temperature, the concentration of the source gases, but also on the properties of the thin films underneath the nanowires. The higher the contents of the crystalline phase in the thin films, the easier the nucleation of the nanowires is. The formation of the nanowires depends seriously on the deposition conditions in the CVD process other than the substrates. The verticality of the nanowires to the substrate depends mainly on the properties of the thin films underbeneath.3. Field emission properties of the titanium silicide thin films and TiSi nanowires. Effects of the thicknesses, morphologies and the distribution of the nanowires as well as the species of the thin films on the field emission properties of the TiSi nanowires/titanium silicide thin films were investigated. It shows that the turn on voltage of the TiSi rocket nanowire with thin films underneath is as low as 2.33V/μm (when the current density larger than 10μA/cm2) and the current density is 917.43μA/cm2 as the electric field reaches 4.18V/μm. The lower the thickness of the nanowires is, the stronger the intensity of the electric field at the tip is. Intensity of the electric field at the tip of the nanopins is larger compared with that of normal nanowires and rocket nanowires. The bunch nanowires have the lower screening effect of the electric field and thus can get both lower turn on voltage and larger current density. The turn on voltage of the nanowires prepared on TiSi2 thin film is lower than that of Ti5Si3 thin film and the current density of the former is also larger than that the latter.4. Ti5Si3 thin films, TiSi nanowire/Ti5Si3 thin films and TiSi nanowire/Ti5Si3 and TiSi2 thin films were used as electrodes and substrates for preparing BT, BST and PST thin films by Sol-gel method and RF-sputtering method respectively. The dielectric properties of the BT, BST and PST thin films as-prepared were also investigated. It shows that the dielectric thin films formed on the titanium silicide thin films with nanowires have higher crystallinity, higher capacitance, low dielectric loss and lower dependence of the capacitance and dielectric loss on the frequency than that of ITO. Furthermore, the capacitance of the dielectric thin films formed on the titanium silicide thin films with nanowires is larger than that on titanium silicide thin films without nanowires. The capacitance of the dielectric thin films formed on the TiSi nanowire/Ti5Si3 and TiSi2 thin films is larger than that of Ti5Si3 thin films. Nonoxide titanium silicide gives the dielectric thin films prepared on the titanium silicide thin films the lower dependence of the dielectric properties on the frequency than that of ITO while the large surface area of the nanowires and large electric field around the nanowires give the higher capacitance and lower dependence of the dielectric properties on the frequency of the titanium silicide thin films with nanowires than the titanium silicide thin films without nanowires.更多还原