CAREER: Probing Crystallization of Atomic Layers Using In Situ Electron Diffraction

职业：利用原位电子衍射探测原子层的结晶

• 批准号: 1752956
• 负责人: Nick Strandwitz
• 金额: $ 59.98万
• 依托单位: Lehigh University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-07-01 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1752956&HistoricalAwards=false
• 关键词: CAREER; Probing; Crystallization; Atomic; Layers

NON-TECHNICAL DESCRIPTION: Control of atomic scale structure in ultra-thin films on non-planar substrates is critical to next generation optical, electrical, biological, and magnetic materials and devices. In particular, nanoscale control of materials is essential to enable further decreases in the feature sizes and growth of materials in three dimensional architectures that are being developed for applications such as logic circuitry, memories, and photovoltaics. This research investigates the fundamental rearrangement of single atomic layers on surfaces during thin film growth, and provides important knowledge regarding the factors that influence transformation of disordered layers of atoms into ordered, crystalline arrangements. The primary experimental platform utilizes an electron beam to probe the structure of atomically-thick layers during growth and thermal processing. The research also uses atomically-resolved electron microscopy to probe the structure of these films. The knowledge generated from this research allows for an enhanced control and understanding of the formation of nanoscale crystalline materials that can be created on three dimensional (non-planar) surfaces and impacts a wide variety of fields in nanoelectronics, computing, photovoltaics, and nanoscale mechanical systems. This research activity is integrated with a university thin film course, a hands-on equipment laboratory, and an industrial outreach effort. Graduates typically find employment in national laboratory or industry. TECHNICAL DETAILS: This research elucidates the fundamental transformations that occur during atomic layer deposition and annealing by utilizing in situ reflection high energy electron diffraction (RHEED). Current atomic layer deposition (ALD) processes are often limited in terms of the structural control that is available due to precursor decomposition at high temperatures, which presents a significant barrier to precisely controlled three dimensional epitaxial architectures that are integral to next generation electronics. Therefore, this work separates the precursor chemisorption steps (ALD component) that result in amorphous layers from thermal processing that provides energy needed to induce crystallization in the model material system gallium oxide. Importantly, electron diffraction is probing in real time the structural transformations that occur to reveal the effect of ambient atmosphere, substrate structure, and orientation with adlayer thicknesses in the range of 0.5-10 nm. Analytical electron microscopy is providing precise structural and compositional details of the films and film-substrate interfaces including defect characteristics. This research captures a slow-motion picture of the structural changes that occur during many traditional thin film epitaxy techniques, and yields new relationships that control crystallization of ultra-thin layers and thus impacts the thin film/epitaxy communities. Undergraduate and graduate students are trained during the research. Industrial engagements are pursued with the Lehigh University Office of Economic Engagement. Mentorship and outreach are conducted with Lehigh University's Clare Booth Scholarship Program, Mountaintop Experience, and a local science center.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

非技术描述：控制非平面基板上超薄膜的原子尺度结构对下一代光学、电学、生物和磁性材料和器件至关重要。特别是，材料的纳米级控制对于进一步减小特征尺寸和三维结构中材料的生长至关重要，这些结构正在开发用于逻辑电路，存储器和光伏等应用。本研究探讨了薄膜生长过程中表面单原子层的基本重排，并提供了影响无序原子层向有序晶体排列转变的因素的重要知识。主实验平台利用电子束来探测原子厚层在生长和热加工过程中的结构。该研究还使用了原子分辨电子显微镜来探测这些薄膜的结构。从这项研究中产生的知识可以增强对纳米级晶体材料形成的控制和理解，这些材料可以在三维（非平面）表面上创建，并影响纳米电子学，计算，光伏和纳米级机械系统的各种领域。这项研究活动与大学薄膜课程、动手设备实验室和工业推广工作相结合。毕业生通常在国家实验室或工业部门就业。技术细节：本研究阐明了利用原位反射高能电子衍射（RHEED）在原子层沉积和退火过程中发生的基本转变。当前的原子层沉积（ALD）工艺通常在结构控制方面受到限制，由于前驱体在高温下分解，这对精确控制下一代电子产品不可或缺的三维外延结构提出了重大障碍。因此，这项工作将导致非晶层的前驱体化学吸附步骤（ALD组件）与在模型材料系统氧化镓中提供诱导结晶所需能量的热加工分离。重要的是，电子衍射可以实时探测发生的结构转变，以揭示环境气氛，衬底结构和取向对衬底厚度在0.5-10 nm范围内的影响。分析电子显微镜提供了薄膜和薄膜-衬底界面的精确结构和成分细节，包括缺陷特征。这项研究捕捉了许多传统薄膜外延技术中发生的结构变化的慢动作画面，并产生了控制超薄层结晶的新关系，从而影响了薄膜/外延群落。在研究过程中对本科生和研究生进行培训。工业合作是与利哈伊大学经济合作办公室进行的。指导和外展是由里海大学的克莱尔·布斯奖学金项目、山顶体验和当地科学中心进行的。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。