Defect and Surfactant Mediated Growth of High Quality Single Crystal Metallic Thin Films

技术综述：缺陷介导法(DMG)和表面活性剂介导法(SMG)是制备高质量外延单晶金属材料的新型电化学沉积方法。DMG包括与将要成为外延覆盖层的金属可逆地共沉积，这是一种中介金属。该介体(例如，铅)被重复地作为亚单分子层沉积在膜表面上，然后在膜生长时通过电化学势的循环完全剥离。每个循环在生长的薄膜表面产生新的核，增加在之前循环中形成的表面簇。通过适当地选择沉积通量和循环频率，可以保持高密度的二维团簇，导致当二维团簇最终结合时，薄膜材料的单层被完成。以这种方式，获得了二维而不是三维的薄膜生长。SMG使用最多一层介体金属作为表面活性剂，在沉积过程中持续保持在表面，导致二维生长。使用这些方法，可以在常温下电沉积原子扁平的单晶薄膜(不含介体金属)，并且对于在常温沉积过程中经常表现出三维生长的系统，其薄膜质量与通过分子束外延生长获得的薄膜质量相似。要研究的具体体系包括：在Au上的铜，在铜上的镍，以及在硅上的铜、银、镍和钴。这项工作的新特点将是实时监测DMG和SMG过程中薄膜应力的产生，并将应力行为与形貌演变关联起来。这在科学和技术上都很有意义，因为应力行为与生长的微观结构特征有关，如果DMG和SMG生产的系统要用于技术应用(例如，用于互连的硅上铜)，则重要的是表征应力。应力的实时监测还将用于优化生长条件和在沉积过程中监测薄膜质量。非技术摘要：生产用于薄膜应用(例如微电子)的高质量单晶材料的能力对于维持和推进许多重要技术至关重要。缺陷和表面介导的电化学生长是最近开发的以廉价方式生产此类材料的方法，是可以并入现有和下一代技术的过程。这项研究将研究具有科学和工业重要性的合成材料系统，并包括用于质量表征和控制的实时应力监测。这将是第一次在这些合成方法中使用应力测量，并将极大地增强将它们转化为技术上可行的工艺的潜力。这项工作将与亚利桑那州立大学(ASU)和IBM托马斯·J·沃森研究中心的研究人员合作进行。与该项目相关的外展活动包括通过实地考察、指导和实践模块让中学生参与科学-技术-工程-数学(STEM)教育。这些学生将来自巴尔的摩市公立学校，他们在STEM教育中的代表性和服务不足。

TECHNICAL SUMMARY:Defect mediated growth (DMG) and surfactant mediated growth (SMG) are novel electrochemical deposition methods of producing extremely high-quality epitaxial single-crystal metallic materials. DMG involves reversibly co-depositing with the metal that is to become the epitaxial overlayer a mediator metal. This mediator (e.g., Pb) is repeatedly deposited as a submonolayer on the film surface and then completely stripped by the cycling of the electrochemical potential as the film is grown. Each cycle creates new nuclei on the surface of the growing film, adding to the surface clusters that developed on previous cycles. A high density of two-dimensional clusters can be maintained by appropriately choosing the deposition flux and cycling frequency, resulting in a monolayer of the film material being completed when the two-dimensional clusters eventually coalesce. In this manner, two-dimensional rather than three-dimensional film growth is obtained. SMG uses up to a monolayer of the mediator metal acting as a surfactant that is continuously maintained at the surface during deposition, resulting in two-dimensional growth. Using these approaches, atomically flat single-crystal films (free of the mediator metal) can be electrodeposited at ambient temperature, and the film quality is similar to that obtained by molecular beam epitaxial growth for systems that often display three-dimensional growth during ambient temperature deposition. Specific systems to be studied include Cu on Au, Ni on Cu, and Cu, Ag, Ni, and Co on Si. New features of this work will be the in situ monitoring of the thin film stress generation in real time during DMG and SMG and correlating the stress behavior with the morphological evolution. This of interest both scientifically and technologically, as the stress behavior is associated with microstructural features of growth, and it is important to characterize the stress if DMG and SMG-produced systems are to be used in technological applications (e.g., Cu on Si for interconnects). Real-time monitoring of the stress will also be used to optimize growth conditions and to monitor film quality during deposition.NON-TECHNICAL SUMMARY:The ability to produce high-quality single-crystal materials for thin film applications (e.g., microelectronics) is critical for maintaining and advancing many important technologies. Defect and surface mediated electrochemical growth are recently developed methods of producing such materials in an inexpensive manner and are processes that can be incorporated into existing and next-generation technologies. The research will investigate synthesizing material systems of both scientific and industrial importance and includes real-time stress monitoring for quality characterization and control. This will be the first time stress measurements will be employed during these synthesis methods and will greatly enhance the potential of converting them into technologically viable processes. This work will be conducted in collaboration with researchers at Arizona State University (ASU) and at IBM Thomas J. Watson Research Center. Outreach activities associated with this project include engaging middle-school students in science-technology-engineering-mathematics (STEM) education through field trips, mentoring, and hands-on modules. The students will be from the Baltimore City Public Schools who are both underrepresented and underserved in STEM education.