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

技术：光刻图案化和外延生长为实现大规模纳米结构阵列的快速制造提供了一个可行的候选方案。最近的研究表明，在图案化的衬底表面上，分子束外延(MBE)生长的GaAs(001)存在暂态不稳定性。横向尺寸超过与厚度相关的临界值的结构高度增加，而小于该值的结构高度衰减。该项目旨在研究在不同横向长度尺度上形成图案的GaAs(001)表面生长不稳定性的影响因素。这项研究弥合了微米和纳米之间的差距，在微米和纳米之间，连续统描述是有效的，而纳米是原子尺度过程更直接地进入进化的过程。该项目采用综合实验/理论方法。在实验中，用电子束光刻技术在衬底上制作了尺寸为10‘S的沟槽结构，用于在控制温度、生长速率和As_2/Ga流量比的情况下生长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。进行动力学蒙特卡罗(KMC)计算，以与在较小结构上生长过程中的观察相比较。我们的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，它在连续统极限中具有CKPZ形式，但具有在原子尺度上表现出来的修正项。这项研究采用多尺度方法来确定KMC计算中使用的速率和能量参数，利用基于密度泛函理论(DFT)的精确量子分子动力学(从头计算)方法的存在，可以准确地预测这些参数。非技术性：该项目解决了材料科学中具有高度技术相关性的热门领域的基础研究问题。它的目标是在用于电子、光电和自旋电子器件的模型衬底上实现定向自组织和粗糙度控制的预测能力。通过这个项目，研究生和本科生将接受跨学科领域的培训。这项研究项目的结果将被引入两门本科课程的课程中，其中一门是马里兰大学新设立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.