【作者】 张小朋；

【导师】 杜善义； 朱嘉琦；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2013， 博士

【摘要】 氧化铝具有优异的力学、光学、热学等性能，是一种具有广泛应用的陶瓷材料。一方面，利用氧化铝的高硬度和光学透过性，可以用作红外窗口的透明保护膜。但目前一般工艺条件下制得的氧化铝薄膜呈现非晶态，无法充分发挥其机械保护作用，而高质量晶态氧化铝薄膜的制备方法，存在着沉积温度高，工艺复杂以及成本昂贵等问题，严重限制了其作为中红外透明保护材料的应用范围，如何在较低的温度下使用比较简单的工艺方法制得晶态氧化铝薄膜是目前研究的一个热点。另一方面，将氧化铝作为一种单层材料制作成金属/氧化铝纳米多层膜时，多层膜可以具有很低的热导率，而且具有较好的力学性能，是一类结构功能一体化的薄膜材料，在热障涂层领域和热电薄膜材料领域有着广泛的应用前景。目前，对金属/氧化铝纳米多层膜界面特性、力学性能优化机理和导热机制的认识还存在分歧和不足，需要进一步工作的开展。针对上述问题，本文采用射频反应磁控溅射制备了氧化铝薄膜，并系统地研究了氧化铝薄膜生长工艺条件与其结构、力学和光学等性能之间的内在联系；通过设计在薄膜制备过程间歇利用反溅技术进行辅助，实现了较低温度下制备高质量的晶态氧化铝薄膜。另一方面，本文采用磁控溅射方法制备了铜（钼）/氧化铝纳米多层膜，并研究了多层厚度周期对多层膜结构的力学和热学等性能的影响机制。XRD研究表明采用磁控溅射法制备的氧化铝薄膜呈现非晶态，且随着衬底温度升高，氧化铝薄膜未实现晶化，薄膜硬度基本保持不变，维持在13.6GPa。此外，衬底偏压对氧化铝薄膜的晶态影响同样不明显。在薄膜制备过程间歇利用反溅技术进行辅助，氧化铝薄膜出现较明显的晶化现象。纳米硬度分析表明，采用反溅模式磁控溅射法制备的氧化铝薄膜，随着沉积温度由室温增加到600oC，氧化铝薄膜的硬度先增大后减小，在450oC时达到最高值15.7GPa。这是由于随着沉积温度提高到600oC时，反溅过程中离子撞击所照成的损伤会占据主导作用，使得氧化铝的晶态形核变得困难，从而导致薄膜硬度下降。与非晶态氧化铝薄膜相比，采用反溅模式制备的晶态氧化铝薄膜折射率得到了提高。通过调整沉积时长，制备了一系列厚度周期不同的铜/氧化铝纳米多层膜和钼/氧化铝纳米多层膜。掠入射X射线反射分析表明，多层膜中铜单层、钼单层和氧化铝单层的密度比其相应体材料的密度稍小。铜（钼）/氧化铝界面的界面粗糙度和氧化铝/铜（钼）界面的界面粗糙度均呈现随距衬底距离的增大而增大的趋势，后者大于前者。随着铜（钼）/氧化铝多层膜厚度周期的逐渐变小，多层膜的纳米硬度逐渐增大，多层膜厚度周期减小到20¹00nm临界周期时，多层膜的纳米硬度开始减小。该临界厚度周期的存在表明纳米多层膜在压头下变形模式可能存在由位错运动主导到由晶粒间滑动主导的转变。铜（钼）/氧化铝多层膜的划擦响应行为与氧化铝薄膜的划擦响应行为有显著不同。氧化铝薄膜的摩擦系数曲线光滑连续，而铜（钼）/氧化铝多层膜的摩擦系数以较快的速率增加到一定值后，摩擦系数值发生震荡。在划擦初期压头纵向载荷较小时，铜（钼）/氧化铝多层膜的耐划擦性能优于氧化铝薄膜。表明多层膜中金属膜层的弹性变形和局部塑性变形改变了压头处的接触边界条件，导致摩擦系数较大，而氧化铝薄膜可容纳的应变量较小，对压头处接触边界条件的改变不如金属/氧化铝多层膜显著，因此摩擦系数较小。随着层界面密度的增加，铜（钼）/氧化铝多层膜的热导率逐渐减小。当铜/氧化铝多层膜和钼/氧化铝多层膜的层界面密度增大到约0.2nm^-1时，相应多层膜的热导率分别减小到约1.6W·m^-1K^-1和1.8W·m^-1·K^-1。相同层界面密度的钼/氧化铝多层膜的热导率比铜/氧化铝多层膜略大，这可能是由于钼的电导率比铜的电导率小，钼/氧化铝多层膜在界面处散射掉的电子携带的热量较小。铜/氧化铝多层膜在从室温到500°C的温度下比较稳定；在600°C⁸00°C之间，铜单层和氧化铝单层反应生成CuAlO2晶态相，但是单质铜相依然存在；在900°C¹000°C之间，单质铜相消失，铜/氧化铝多层膜完全破坏。钼/氧化铝多层膜在从室温到600°C的温度下比较稳定；在700°C⁸00°C之间，钼单层和氧化铝单层反应生成Al₂（MoO₄）₃晶态相；在900°C¹000°C之间，多层膜中生成Al₂（MoO₄）₃和MoSi₂相。从室温到1000°C，钼/氧化铝多层膜中单质钼相始终存在。与铜/氧化铝多层膜相比，钼/氧化铝多层膜的热稳定性较好，这是因为钼的熔点比铜的熔点高，在相同温度下铜的扩散能力更强，化学性质更活泼。本文通过设计反溅辅助技术，在较低温度下制备了高质量的晶态氧化铝薄膜，为低温沉积高质量晶态氧化铝薄膜提供了一种新的途径，从而能有效地降低晶态氧化铝薄膜生产成本，并有助于拓展其应用范围。另一方面，获得了具有较优异力学和热学性能的铜（钼）/氧化铝多层周期薄膜，对其在热障涂层和热电薄膜材料方面的应用具有潜在的价值。更多还原

【Abstract】 Al₂O₃is one of the important ceramics materials, has excellent mechanicaloptical and thermal properties. Al₂O₃is as infrared transparent protective materialdue to its high hardness and transparent. But Al₂O₃films have been synthesizedthrough common methods are always amorphous and can’t realize mechanicalprotection. However, high quality crystalline Al₂O₃films obtain at the highsynthesis temperature and expensive cost, and the application in mid-infraredtransparent protective films is limited. Multiple periodic metal/Al₂O₃thin filmspossess unique properties such as low thermal conductivity and high mechanicalproperties which have great advantage in the applications of thermal barrier coatingand thermoelectric films. Currently insufficient research is relative to the interfacesof multiple periodic metal/Al₂O₃thin films, mechanical mechanisms, and thermalproperty.Aiming at the above problems, Al₂O₃films is synthesized by radio frequencyreactive magnetron sputtering, and the relationship between deposition conditionsand the structure, the mechanical and optical properties has been studied.Cu（Mo）/Al₂O₃nano-multilayers have been prepared by using radio frequencyreactive magnetron sputtering, and the relationship between the thickness period andthe structure, mechanical,and thermal properties of Cu（Mo）/Al₂O₃nano-multilayershas been indicated.The XRD results reveal that Al₂O₃films obtained at room temperature bymagnetron sputtering is amorphous, and Al₂O₃films don’t crystallize with thedeposition temperature increasing. The hardness of Al₂O₃films is stable to13.6GPaby varying synthesis temperature. The effect of the bias voltage on thecrystallization of Al₂O₃is not notable.The resputtering technique has been designed and this technique is used tosynthesize crystalline Al₂O₃films. The nano-hardness of Al₂O₃films prepared byresputtering technique increased from13.6GPa to15.7GPa along with thedeposition temperature increasing from room temperature to450°C. But thenano-hardness of Al₂O₃films obtained at600°C decreased to14.5GPa. In this case,the damage caused by ion bombardment is dominant when the deposited temperature reaches a critical value, and the damage makes the nucleation difficultso the hardness of films decreases. The refractive index of crystal Al₂O₃filmsprepared by resputtering assisted technology increases compared with amorphousAl₂O₃films. Crystal Al₂O₃films have excellent mechanical property and middleinfrared transmittance, and the industrial application of Al₂O₃films realizes throughlow-cost deposited technique.Two different multilayer systems of Cu/Al₂O₃and Mo/Al₂O₃were deposited byRF-sputtering system, in which the thickness of each layer can be adjusted bycontrolling deposition time. The size of the grains in the metallic layers can betailored by the thickness of the metallic layer and the influence of the thicknessbecomes weaker for the thicker case, while stronger for the thinner case. It can beconfirmed by analysis of GIXRD that the densities of the Cu, Mo and Al₂O₃areslightly smaller than that of the corresponding bulk states. The roughness of theinterface between metal and Al₂O₃is varied for different deposition sequenceswhich include metal/Al₂O₃and Al₂O₃/metal patterns, in which the Al₂O₃wasdeposited before the metal layer for the former system and the sequence reverses forthe latter case. The roughness of the interfaces for both patterns increases with theincreasing distance from the substrate to the top of the multilayers. And it is notedthat the roughness of Al₂O₃/metal interface is larger than that of the metal/Al₂O₃interface.The nano-hardness of the Cu（Mo）/Al₂O₃system decreases with the periodicthickness of the metallic and Al₂O₃layers and then increases with further reductionthe thickness period after reaching a critical value. Especially, the critical periodthicknesses of Cu/Al₂O₃and Mo/Al₂O₃systems both fall in the range of about20¹00nm. The emergence of the critical period thickness reveals that the transitionof the deformation mode occurs. The dominant transition is believed to change fromdislocation motion to inter-grains slide in the multilayers under the load ofnano-indenter.The scratch-response behavior is quite different between the Cu（Mo）/Al₂O₃multilayers and the Al₂O₃film. The curve of friction coefficient for the Al₂O₃film issmooth and continual while shaked for the metal/Al₂O₃multilayers after a criticalfriction coefficient is reached. In the early stage of the scratch experiment, theperformance of anti-scratch is superior in the Cu（Mo）/Al₂O₃systems compared to the Al₂O₃. It is believed that the boundary conditions between the indenter andsamples is varied by elastic and plastic deformations. The variance of the boundaryconditions induces the increase of the frictional coefficient. In contrast, the frictionalcoefficient is rather smaller response to the variance of the boundary condition dueto the smaller strain that the Al₂O₃can endure.The thermal conductivity of the Cu（Mo）/Al₂O₃multilayers is graduallydecreasing with the density of the state of interface above a threshold value. Thethermal conductivities decease to1.6W·m^-1K1and1.8W·m^-1·K^-11respectivelywhen the density of interface states increase up to about0.2nm-1for both theCu/Al₂O₃and Mo/Al₂O₃systems. The thermal conductivity of the Mo/Al₂O₃systemis slightly larger than that of the Cu/Al₂O₃system possibly due to the smallerelectrical conductivity in metal Mo which can induce smaller dissipation of thermalenergy.The Cu/Al₂O₃system is stable from room temperature to500°C, whilecrystalline phase CuAlO2is formed by the reaction between Cu and Al₂O₃in thetemperature range of600°C⁸00°C along with some remaining Cu phase. TheCu/Al₂O₃multilayers is destroyed above900oC with the complete disappearance ofmetallic Cu. The Mo/Al₂O₃multilayers stably existed up to600°C. In the700°C⁸00°C range, Mo reacts with Al₂O₃to form crystalline Al₂（MO4）3phase.Among900°C¹000°C, two phases of Al₂（MoO₄）₃and MoSi₂are formed. It is notedthat pure Mo can still exist up to1000°C in Mo/Al₂O₃system. It can be concludedthat the thermal stability of the Mo/Al₂O₃system is better than that of Cu/Al₂O₃system which may partially due to the higher melting point of Mo compared to Cu.In that case, the diffusion is stronger for Cu than that for Mo at same temperature.High quality crystalline Al₂O₃films have been obtained at relative lowtemperature by using resputtering assisted technology. This method is a new way toget high quality crystalline Al₂O₃films at low temperature and will have potential inapplications and the cost will decrease. Cu（Mo）/Al₂O₃nano-multilayers that possessexcellent mechnical and thermal properties have potential in the application ofthermal barrier coating and thermoelectric films.更多还原