Collaborative Research: Using Nanoscale Patterning to Reveal the Atomic-scale Effects which Drive Unstable Growth on GaAs (001)

技术：光刻图像化之后的外延生长提供了一个可行的候选人，以实现快速制造纳米级结构的大阵列。最近的研究揭示了GaAs（001）分子束外延生长（MBE）在图案衬底表面的瞬态不稳定性。横向尺寸超过与厚度相关的临界值的结构高度增加，而小于此值的结构高度衰减。本项目旨在研究不同横向长度尺度的砷化镓（001）表面的生长不稳定性。这项研究弥补了微米尺度和纳米尺度之间的差距，微米尺度上的连续描述是有效的，而纳米尺度上的原子尺度过程更直接地进入了进化。该项目采用实验/理论相结合的方法。在实验中，利用电子束光刻技术在衬底上制造出尺寸小至10纳米的沟槽结构，用于在控制的温度、生长速率和As2/Ga通量比下生长GaAs。利用光刻和电子束光刻相结合的方法制备纳米/微米混合结构。动力学蒙特卡罗（KMC）计算将与在较小结构上生长过程中的演化观测进行比较。目标是理解连续统方程中各项系数的物理意义。第二个更雄心勃勃的理论目标是找到一个方程，它在连续体极限下具有CKPZ形式，但具有在原子尺度上表现出来的校正项。本研究采用多尺度方法确定用于KMC计算的速率和能量参数，利用基于密度泛函理论（DFT）的精确量子分子动力学（从头算）方法的存在，可以准确预测这些参数。非技术：该项目涉及材料科学主题领域的基础研究问题，具有高技术相关性。它旨在实现在模型衬底GaAs表面的定向自组织和粗糙度控制的预测能力，用于电子，光电和自旋电子器件。通过这个项目，研究生和本科生将接受跨学科领域的培训。这个研究项目的结果将被引入到两门本科课程的课程中，其中一门是马里兰大学新创建的跨学科纳米科学与技术辅修课程。

Technical: Lithographic patterning followed by epitaxial growth provides a viable candidate to achieve rapid fabrication of large arrays of nanometer scale structures. Recent research reveals a transient instability in molecular beam epitaxial (MBE) growth of GaAs(001) on patterned substrate surfaces. Structures whose lateral dimensions exceed a thickness-dependent critical value increase in height, while those smaller than this value decay. This project is to investigate the effects responsible for growth instabilities of GaAs(001) surfaces patterned at various lateral length scales. The research bridges the gap in the scale between micrometers, where a continuum description is valid, and nanometers, where atomic scale processes enter more directly into the evolution. The project uses an integrated experimental/theoretical approach. In experiments, electron beam lithography is used to produce groove structures of dimensions as small as a few 10's of nanometers on substrates, which are used to grow GaAs at controlled temperatures, growth rates and As2/Ga flux ratios. A combination of photo lithography and electron beam lithography is utilized to fabricate hybrid nanometer/micrometer structures. Kinetic Monte Carlo (KMC) calculations are to be carried out for comparison with observations of the evolution during growth on the smaller structures. The goal is to understand the physical significance of the coefficients of the terms in the continuum equation. A second, more ambitious theoretical goal is to find an equation which has the CKPZ form in the continuum limit, but with correction terms that manifest themselves at the atomic scale. The research adopts a multi-scale approach in determining the rate and energy parameters for use in the KMC calculations, taking advantage of the existence of accurate quantum molecular dynamics (ab initio) methods based on density functional theory (DFT) that can accurately predict these parameters.Non-technical: The project addresses basic research issues in a topical area of materials science with high technological relevance. It aims at achieving a predictive capability for directed self organization and roughness control at the surface of a model substrate, GaAs, for applications in electronic, optoelectronic and spintronic devices. Through this project, graduate and undergraduate students will receive training in an interdisciplinary field. The results from this research projects will be introduced into the curriculum of two undergraduate courses, including one for a newly created Interdisciplinary NanoScience and Technology Minor program at the University of Maryland.