【作者】 周耐根；

【导师】 周浪；

【作者基本信息】 南昌大学 ， 材料物理与化学， 2005， 博士

【摘要】 薄膜晶体缺陷主要形成于原子沉积生长过程之中，而现有实验分析手段的空间和时间分辨能力都无法胜任对原子尺度微观过程的研究。我们以面心立方金属为对象、采用三维分子动力学方法对几种薄膜缺陷形成的原子机理与控制方法进行了原子模拟研究。原子间相互作用力采用EAM多体势函数计算。研究内容包括：外延薄膜沉积生长的分子动力学模型、模拟方法与相应程序的建立及对原子沉积过程的基本研究；<111>外延生长薄膜中失配位错、孪晶与一种应力致生长织构的结构、形成机制及可能的控制方法；在纳米晶柱阵列衬底上外延生长高质量、易剥离薄膜晶体的可能性。研究发现： (1) 保持表面原子级平整可使薄膜在超过临界厚度数十倍的情况下仍不形成失配位错。但这种结构对微扰十分敏感，表面仅单原子层厚的微小凹凸或高温下的热扰动都能使失配位错迅速形成。 (2) 负失配条件下，失配位错成核于一种发生在薄膜表层的类似于“局部熔融—重结晶”的过程，它起自薄膜内部压应力与表面台阶共同作用下被挤出的一个倒四面体构型的原子团。其结构为伯格斯矢量与失配方向一致的、滑移面与生长面平行的全刃位错，个别情况下也会呈现为由两个部分位错夹着一片层错组成的Shockley扩展位错。 (3) 正失配条件下，失配位错的结构与成核机制出现两类情况。当失配度f_x≥0.05时，位错结构与成核机制与负失配条件下类似，不同之处是局部熔融源自与表面相交的滑移台阶；当f_x≤0.04时，失配位错直接形成于由表面向内部推进的局部滑移。其伯格斯矢量与失配方向成60°夹角。该位错形成后迅速从薄膜表层沿其滑移系向薄膜与衬底间界面滑移。 (4) 在适当几何条件下，采用纳米晶柱阵列衬底可以在不形成失配位错的情况下释放外延薄膜中的失配应变，有效地抑制失配位错的形成，获得高质量、易剥离外延薄膜。 (5) 在<111>生长中，表面沉积原子在入射碰撞和热运动迁移过程中随机占更多还原

【Abstract】 Crystal defects in thin films mostly form in the atomic deposition processes, while current experimental means do not have enough resolution power in both space and time to analyze any processes at atomistic scale. Using three dimensional molecular dynamics method, and taking FCC metals as prototypes, we have carried out atomistic simulation studies of the formation mechanisms of thin film crystal defects and their control. EAM many-body potentials are adopted to calculate the inter-atomic forces. The work conducted mainly include establishing the molecular dynamics model, the simulation methods and codes for deposition of thin films; fundamental studies of the atomistic deposition; the structures, formation mechanisms and possible control methods of misfit dislocations, twins, and a stress-driven growth texture in <111> epitaxial films; the possibility of growing high quality and easy-to-peel-off epitaxial films on nano pillar crystals arrays. The results show that(1) An epitaxial film can maintain dislocation-free if its surface maintain flat at atomic scale, even when it is tens times thicker than its critical thickness. This structure is, however, very sensitive to disturbances. A single atomic layer variation on surface or merely thermal disturbances at elevated temperatures will trigger formation of the misfit dislocations.(2) For the epitaxial films with negative mismatch, the misfit dislocation nucleates in a local surface fusion-crystallization process. The local fusion begins with a surface step triggered squeeze-out of an inverse mini-tetrahedron. The dislocation formed is a perfect edge dislocation with its Burgers vector paralleled to the misfit and its sliding plane paralleled to the interface. Occasionally, the dislocation appears in form of Shockley type extended dislocation.(3) For the epitaxial films with positive mismatch, two kinds of structures and nucleation mechanisms have been identified for the misfit dislocations, depending onmagnitude of the mismatch f_x. When f_x ≥0.05, they are similar to those in the films with negative mismatch, except that the local fusion is originated from a cross-surface glide; When f_x ≤0.04, the misfit dislocation forms directly as a result of a partial更多还原