【作者】 王晓姹；

【导师】 白海力；

【作者基本信息】 天津大学 ， 材料物理与化学， 2007， 博士

【摘要】 碳氮薄膜以其良好的力学、电学和光学性质,在磁盘磁头保护、硬质刀具、冷阴极发射、空间防护等领域具有广阔的应用前景。目前,纳米级铁磁性金属颗粒薄膜体系、超硬纳米级多层膜体系是凝聚态物理和材料科学领域的研究热点。碳氮薄膜具有导电性可控以及高硬度等特点,尝试在这些复合体系中使用碳氮材料具有重要意义。本论文采用对向靶磁控溅射法制备了碳氮薄膜、过渡族金属（Ni、Fe、Co、Cu、Ti）?碳氮基纳米颗粒薄膜以及氮化钛/碳氮（TiN/CN）多层膜,对它们的化学成份、微观结构、磁性质、电输运特性和力学性质进行了系统研究。通过对纯碳氮薄膜的研究,发现薄膜中的氮含量并不随氮气分压的升高而增大,而是在氮气分压为20%时达到饱和（33%）。纯碳膜主要由sp³杂化的C原子组成,随着氮气分压的升高,碳氮薄膜中sp²杂化的C原子数目增加,类石墨结构区域的尺寸增大,薄膜结构趋于有序化。薄膜中的环状sp²层的尺寸始终很小,并且薄膜中存在着大量缺陷。薄膜的光学和电学性质主要由薄膜中的缺陷态决定,而薄膜的力学性质则与薄膜中sp³ C的含量密切相关。在室温下采用共溅射法制备了系列过渡族金属?碳氮基纳米颗粒薄膜。在磁性金属（Fe、Co、Ni）?碳氮基纳米颗粒薄膜中观察到了自旋相关的低温磁电阻显著增强现象,磁电阻在3 K和90 kOe的磁场下可以达到–59%。在外加磁场由0增大至90 kOe的过程中,薄膜的磁电阻一直增大,出现弱饱和现象;当温度高于20 K后,薄膜的磁电阻都接近于0;而当温度低于20 K时,磁电阻随温度的降低而急剧增大,并遵循log |MR|∝-T关系。通过改变碳氮母体的绝缘性以及磁性金属含量可以对磁电阻进行调制,而磁电阻随磁场和温度的变化关系并不改变。基于高阶隧穿模型,考虑新的自旋极化率随温度的变化关系P = P₀ exp（-βT^α）,我们解明了低温磁电阻增强现象的物理机制。在TiN/CN多层膜中观察到“超硬度现象”。多层膜的硬度随着氮化钛层的结晶而大幅度提高,这说明非晶态和晶态薄膜的形变过程不同,只有当多层膜的晶态物质占一定比例,薄膜形变以位错缺陷的形变过程为主时,才会出现超硬度现象。采用Bhattacharya-Nix经验方程对纳米压痕测得的硬度值进行了拟合,从而较准确地估计了薄膜硬度的真实值。我们发现对于硬度较大的薄膜,其硬度的测量值与实际值的差距较大。更多还原

【Abstract】 Amorphous CNx films have been extensively investigated due to their excellent mechanical, optical and electrical properties and practical applications in magnetic disk coatings, cast machining, cold-cathode-emission and space protection etc. Recently, ferromagnetic metal composite materials and superhard nanomultilayers become the focuses in the field of condensed matter physics and materials science. Carbon nitride films have controllable conductivity and high hardness, and can be used as one of the component in above systems.Carbon nitride films, transition metal (Ni, Fe, Co, Cu, Ti)-CN nanocomposite films and TiN/CN multilayers were fabricated using facing-target reactive sputtering. Their chemical composition, microstructure, magnetic, electrical transport and mechanical properties were studied systematically.It was found that the N concentration in the carbon nitride films does not change with the nitrogen partial pressure PN linearly, which rises quickly to a saturate value of～33% at a PN of 20%, and does not change with further increasing PN. The pure C films are mainly composed of sp3 C atoms. Increasing PN makes both the number of sp2 C atoms and the size of aromatic sp2-hybridized C clusters increase, while the sp2 C cluster remains a rather small size. The optical and electrical properties of the films are mainly determined by the defects existing in the films and the mechanical properties correlate closely with the sp3 C content.An enhanced spin-dependent magnetoresistance (MR) was observed at low temperatures in the (Fe, Co, Ni)-CNx nanocomposite films fabricated at room temperature. The maximum MR reaches–59% at 3 K and 90 kOe. The MR has a weak saturation trend with increasing field to 90 kOe. Above 20 K, the MR is very small (<1%), but as temperature is below 20 K, it follows the relation of log MR∝?T. The maximum MR, MR enhancement and carrier transport mechanism can be tailored by changing the insulation of the CNx matrix through tuning PN or altering the Ni content in the films. The enhancement of the low-temperature negative MR was clarified by introducing a new relation of spin polarization P with T, P = P0 exp(?βTα), into the high-order tunneling model. TiN/CN multilayers were fabricated and superhardness phenomenon was observed. When the two components (TiN and CN) in the multilayer are amorphous, no enhancement in hardness can be observed. While with the crystallization of the TiN layer, the hardness of the multilayers is enhanced greatly and becomes higher than that calculated using the rule of mixtures. The variation of hardness with the crystallinity of TiN layers suggests that the mechanism of the deformation in amorphous TiN/CN multilayers is different from that in the crystalline ones and the dislocation related mechanism in the crystalline multilayers is very important for the appearance of the superhardness effect. The real hardness of the multilayers free from the substrate effect was extracted using Bhattacharya-Nix empirical equation based on the data measured from nanoindentation with continuous stiffness measurement technique. Large deviation between the film’s hardness and measured hardness was found for the films with large hardness.更多还原