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

技术支持：光刻图案化之后的外延生长提供了一个可行的候选人，以实现快速制造的大型阵列的纳米尺度结构。最近的研究揭示了在图案化衬底表面上分子束外延（MBE）生长GaAs（001）的瞬态不稳定性。结构的横向尺寸超过厚度依赖的临界值增加的高度，而那些小于这个值衰减。本计画旨在探讨不同横向长度尺度之砷化镓（001）表面图案化对成长不稳定性的影响。这项研究弥合了微米和纳米尺度之间的差距，在微米尺度下，连续描述是有效的，而在纳米尺度下，原子尺度的过程更直接地进入进化。该项目采用综合实验/理论方法。在实验中，电子束光刻用于在衬底上产生尺寸小至几十纳米的沟槽结构，其用于在受控温度、生长速率和As 2/Ga通量比下生长GaAs。利用光刻和电子束光刻的组合来制造混合纳米/微米结构。动力学蒙特卡罗（KMC）计算进行比较与观察过程中的演变对较小的结构。我们的目标是了解连续介质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。该研究采用多尺度方法确定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（ab initio）方法，可以准确预测这些参数。非技术性：该项目涉及材料科学领域的基础研究问题，具有高度的技术相关性。它的目的是实现在模型衬底，GaAs，在电子，光电子和自旋电子器件的应用程序的表面的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。从这个研究项目的结果将被引入到两个本科课程的课程，其中包括一个新创建的跨学科纳米科学和技术未成年人计划在马里兰州的大学。

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.