Collaborative Research: Connecting Mesoscale Dynamics of Metallic Films on Semiconductors to Nanoscale Phenomena

电子设备，如计算机和智能手机，是我们技术社会的核心。这种设备目前是基于半导体技术，它涉及在金属和半导体之间进行电接触。通过研究和理解金属如何沉积在半导体材料上的细节，该项目将允许开发新的方法来生长低维纳米结构，如极细的电线和非常薄的薄膜。该项目将最先进的实验与复杂的理论技术结合起来，使用由数千万到数百万原子组成的模型来探索控制制造纳米结构预测特性的物理。这些方法的结合将促进低维纳米结构的优化设计和制造。这种结构在制造未来的电子设备方面非常有用，从而保持美国在纳米技术方面的技术领先地位。参与该项目的学生不仅将在涉及金属-半导体界面的令人兴奋的研究领域获得深入的物理理解，而且还将参与与pi持续互动的当地K-12学生和教师的外展活动，特别是通过美国物理学会物理教师教育联盟（APS PhysTEC）。所有pi都定期指导本科生研究人员，并积极参与招募女性和代表性不足的少数民族学生，特别是通过APS桥梁计划。本课题将研究几种金属在半导体系统上的生长机制。该项目的目标是控制低维（一维和二维）纳米结构的生长，阐明在这些系统中观察到的新颖而复杂的集体扩散行为，并了解量子行为如何影响外延生长，以促进新材料的优化设计和制造。一套互补的实验和理论技术将应用于系统地研究Ag、Au和Pb纳米结构在Ge和Si单晶表面的初始生长阶段和结构演变。原子的有序和结合位点，以及形成岛的大小和形状，将通过扫描隧道显微镜（STM）和低能电子显微镜/衍射（LEEM/LEED）来确定，并与基于密度泛函理论（DFT）的模拟预测进行比较。将研究数百万原子的不寻常集体行为和量子尺寸效应（QSE），以阐明机制的细节。扫描隧道光谱（STS）和角分辨光发射光谱（ARPES）将用于测量局域态密度、k分辨能带结构和量子阱态；这些结果将与DFT计算结果进行比较，以了解控制纳米结构特征的因素，并制定有关未来生长的基本机制和过程的物理图景。将确定与半导体表面结合的金属的键序势（BOP），并将其用于岛屿生长和运动的自学习动力学蒙特卡罗（SLKMC）模拟。这些大规模的模拟将提高对集体运动的物理起源的理解，并提出可能显示不寻常物理现象的额外实验系统。硅基和锗基材料的使用将使电子设备的技术应用迅速发展。

Nontechnical AbstractElectronic devices, such as computers and smartphones, are at the heart of our technological society. Such devices currently are based on semiconductor technology, which involves making electrical contacts between metals and semiconductors. By studying and understanding the details of how metals can be deposited onto semiconductor materials, this project will allow the development of novel methods to grow low dimensional nanostructures, such as extremely thin wires and very thin films. The project connects state-of-the-art experiments to observe the growth properties of the materials with sophisticated theoretical techniques using models consisting of tens to millions of atoms to explore the physics governing the predicted properties of the fabricated nanostructures. Working in conjunction, these methods will facilitate the optimal design and creation of these low dimensional nanostructures. Such structures could be very useful in making future electronic devices, thus maintaining the technological leadership of the U.S. in nanotechnology. Students working on the project will not only gain in-depth physical understanding in the exciting research areas involving metal-semiconductor interfaces but also will engage in outreach activities with local K-12 students and teachers with whom the PIs have on-going interactions, especially through the American Physical Society Physics Teacher Education Coalition (APS PhysTEC). All PIs regularly mentor undergraduate researchers and are actively engaged in recruiting women and underrepresented minority students, particularly through the APS Bridge Program.Technical AbstractThis project will study the growth mechanisms of several metal on semiconductor systems. The objectives of this project are controlling the growth of low-dimensional (1D and 2D) nanostructures, elucidating the novel and complex collective diffusion behavior which has been observed for these systems, and understanding how quantum behavior can influence epitaxial growth in order to facilitate the optimal design and fabrication of novel materials. A complementary set of experimental and theoretical techniques will be applied to examine systematically the initial growth stages and structural evolution of Ag, Au, and Pb nanostructures on single crystal surfaces of Ge and Si. The atomic ordering and adatom binding sites, as well as sizes and shapes of formed islands, will be determined by scanning tunneling microscopy (STM) and low energy electron microscopy/diffraction (LEEM/LEED) and compared with predictions from density functional theory (DFT)-based simulations. Unusual collective behavior of millions of atoms and quantum size effects (QSE) will be investigated to elucidate details of the mechanisms. Scanning tunneling spectroscopy (STS) and angle-resolved photoemission spectroscopy (ARPES) will be used to measure local density of states, k-resolved band structure, and quantum well states; these results will be compared with DFT calculations to understand the factors controlling the nanostructure characteristics and to formulate the physical picture about the basic mechanisms and processes for future growth. Bond order potentials (BOP) will be determined for metals bound to semiconductor surfaces and used for self-learning kinetic Monte Carlo (SLKMC) simulations of the growth and movement of islands. These large-scale simulations will improve understanding of the physical origin of the collective motions and suggest additional experimental systems that may display unusual physical phenomena. The use of Si and Ge-based materials would enable rapid development of technological applications for electronic devices.