Nucleation and Growth of Thin Films and Nanostructures

本研究计划研究金属纳米粒子和超薄金属薄膜在非晶态衬底上的成核和生长。将研究化学生长方法，包括化学气相沉积和原子层沉积。这项研究将集中于测量非晶态衬底上缺陷位置的浓度，并阐明当成核开始或稳定的金属团簇被捕获时缺陷位置的化学性质。该计划将探索固有缺陷的化学性质，以及故意在衬底上产生的缺陷。设计用来化学滴定不同缺陷位置的荧光探针分子将被用来测量缺陷的浓度以及它们的空间分布。不同的缺陷影响形核和金属吸附原子捕获的方式将被确定。该研究还将探索抑制/阻止已建立的金属岛生长的方法，并强制更高的形核密度作为获得光滑和超薄连续薄膜的途径。该计划将使用Ru、Co和W金属，以及二氧化硅、氧化铝和二氧化钛作为载体。总体目标是了解和描述允许金属形核发生的表面化学，并确定是否有可能控制颗粒的生长以最大化氧化物衬底上的形核密度。将探索基片表面和薄膜界面上的结合和反应。用X射线光电子能谱和低能离子散射谱跟踪薄膜的成分和化学结合。将使用一整套表征设备来研究薄膜，包括荧光、原子力显微镜、X射线散射光谱和高分辨率电子显微镜。智能优点：金属薄膜在传感器、光学和微电子领域有应用，随着应用和系统的临界尺寸或尺寸的减小，金属薄膜的厚度也必须减小到最多几十个原子直径，并且必须具有特定的微结构。纳米颗粒被用于先进的计算机存储器设计、催化和量子计算体系结构；在所有情况下，都需要最大限度地提高颗粒密度和均匀性。这项研究有望对金属薄膜和金属纳米颗粒如何在无定形氧化物表面成核并启动岛状生长有一个总体的理解。成核和生长的概念对于纳米颗粒和多晶膜是常见的。所探讨的成核和生长问题超出了为该项目选择的材料系统的范围。广泛的影响：这项研究的动机是超薄金属薄膜和非晶态衬底上的纳米粒子在电极、传感器、光学、热障、催化剂和扩散障碍等应用中所起的核心作用。有大量的文献指出缺陷在成核和生长中可能起的作用，然而，很少有关于非晶态表面的研究测量和表征这些缺陷的性质。该计划寻求使用化学探针来滴定不同的缺陷。荧光信号强度表明，这些探针对0.001个甚至可能0.0001个单分子层具有敏感性。如果成功，这些探测器可以用来更广泛地探索氧化物。此外，本程序解决并试图描述在薄膜从吸附原子到成核岛再到结合的连续薄膜的过程中影响薄膜演化的界面和表面反应。

This research program investigates the nucleation and growth of metal nanoparticles and ultra thin metal films on amorphous substrates. Chemical growth methods will be studied that include chemical vapor deposition and atomic layer deposition. The research will focus on measuring the concentration and elucidating the chemical nature of defect sites on amorphous substrates were nucleation is initiated or where stable metal clusters are trapped. The program will probe the chemical nature of inherent defects and defects that are purposefully generated on the substrates. Fluorescent probe molecules designed to chemically titrate different proposed defect sites will be used to measure the concentration of the defects and possibly also their spatial distribution. The way the different defects affect nucleation and metal adatom trapping will be established. The research will also explore approaches to inhibit/block the growth of established metal islands and force a higher nucleation density as a route to smooth and ultra thin continuous films. The program will involve ruthenium, cobalt and tungsten metals, and silicon dioxide, aluminum oxide, and titanium dioxide as the supports. The overall objectives are to understand and describe the surface chemistry that allows metal nucleation to occur, and to determine if it is possible to control the growth of particles to maximize the nucleation density on the oxide substrate. Bonding and reactions at the substrate surface and at the film interface will be explored. Film composition and chemical bonding will be followed using X-ray photoelectron spectroscopy and low energy ion scattering spectroscopy. A full complement of characterization facilities will be used to study the films, including fluorimetry, atomic force microscopy, X-ray scattering spectroscopy, and high resolution electron microscopy.Intellectual Merit: Metal films find applications in sensors, optics and microelectronics, and as the critical dimensions or size of the applications and systems decrease, the metal films thickness also must decrease to tens of atomic diameters at most and must have a specific microstructure. Nanoparticles are used in advanced computer memory design, catalysis and quantum computing architectures; in all cases, there is a need to maximize the particle density and uniformity. This research is expected to develop a general understanding of how metal films and metal nanoparticles nucleate on amorphous oxide surfaces and initiate island growth. Nucleation and growth concepts are common to nanoparticles and polycrystalline films. The nucleation and growth issues explored transcend the material systems selected for this project.Broader Impacts: This research is motivated by the central role ultra thin metal films and nanoparticles on amorphous substrates have in applications such as electrodes, sensors, optics, thermal barriers, catalysts and diffusion barriers. There is an extensive literature pointing to the possible role of defects in nucleation and growth, however, there are few studies on amorphous surfaces that have measured and characterized the nature of these defects. This program seeks to use chemical probes designed to titrate the different defects. The fluorescence signal intensity suggest a sensitivity to 0.001 and possibly 0.0001 monolayers with these probes. If successful, the probes could be used to explore oxides more generally. Further this program addresses and seeks to describe the interfacial and surface reactions that affect the evolution of a film as it transforms from adsorbed adatoms to nucleated islands to a coalesced, continuous film.