受调制的衬底对薄膜生长形貌的影响.pdf

摘 要 本文采用动力学蒙特卡洛(Kinetic Monte Carlo)模拟方法研究了在应变场 或量子尺寸效应调制的衬底上纳米结构的自组织生长。 首先我们发展了一个多尺度的动力学蒙特卡洛模型研究应变诱导的量子点 超晶格的自组织堆栈生长。这个模型考虑了长程的弹性相互作用并利用原子级 的 KMC 方法模拟量子点的外延生长。覆盖层下面的岛在覆盖层表面产生的应 变场调制势能表面,进而影响生长过程中岛的形核以及空间分布。我们的模拟 结果表明,膨胀区域的应变提高了量子点的形核几率,从而导致量子点的堆栈 生长在垂直方向上排成一列。随着量子点堆栈生长的进行,应变场分布变得越 来越均匀,从而导致了量子点在水平方向上的自组织生长。进一步的分析表明, 虽然在膨胀应变区域原子的扩散势垒增大了,但是在膨胀区域原子密度也很大, 昀终导致随着膨胀应变增大形核几率增大。 另外,我们还设计了一种自组织生长金属纳米结构的模型。金属纳米结构 生长在以具有一定“式样”pattern的 Si111表面为衬底、表面平整、量子尺 寸效应调制的 Pb111薄膜上。扫描隧道显微镜实验发现由于量子尺寸效应,被 覆盖的台阶在表面的作用就像是一个真实的“台阶”。这种有趣的实验现象为 我们提供了一种以自组织的方式制备功能金属纳米结构的潜在途径,例如在以 具有一定“式样”pattern的 Si111表面为衬底的、平整的 Pb111薄膜上生长 纳米线,其中 Pb111薄膜表面的量子尺寸效应是可以人为控制的。我们同样利 用动力学蒙特卡洛方法研究在量子尺寸效应调制的 Pb111/Si111衬底上在各 种条件下生长纳米线的情况。 关键词:动力学蒙特卡洛 KMC;自组织生长;应变;量子尺寸效应QSE I Abstract In the thesis, Kinetic Monte Carlo simulation method is used to investigate the self-assembly growth of nanostructures on substrates modulated by strain field or Quantum Size EffectFirst, a multiscale realistic kinetic Monte Carlo model is developed to study the strain-induced self-assembly of stacked quantum dots superlattice. Our model integrates the long-range elastic interaction and realistic atomistic kMC simulation of epitaxial growth. The strain field on the spacer layers induced by the buried QDs modulates the potential energy surface and thus affects the nucleation and spatial arrangement of the islands. Our results show that in the tensile region, strain enhances the nucleation, leading to the vertical alignment of the stacked QDs. With the QD superlattice further stacked, the strain field becomes more uniform which leads to the lateral self-organization of QDs. More detailed analysis shows that although the diffusion barrier is increased by the tensile strain, the adatom density in the tensile region is increased, and the nucleation is finally enhanced as the tensile strain becomes strongerIn addition, a mechanism of self-assembly of metallic nanostructures on a quantum-modulated flat Pb111 thin film with patt