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

缺陷介导生长（DMG）和表面活性剂介导生长（SMG）是生产极高质量外延单晶金属材料的新型电化学沉积方法。DMG涉及与要成为外延覆盖层的金属可逆地共沉积介体金属。该介体（例如，Pb）作为亚单层重复沉积在膜表面上，然后随着膜的生长通过电化学电势的循环完全剥离。每一个循环都在生长的薄膜表面上产生新的原子核，并将其添加到前一个循环中形成的表面簇中。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簇，导致当二维簇最终聚结时完成膜材料的单层。以这种方式，获得二维而不是三维膜生长。 SMG使用高达单层的介体金属作为表面活性剂，其在沉积期间连续保持在表面，导致二维生长。使用这些方法，原子级平坦的单晶膜（不含介体金属）可以在环境温度下电沉积，并且膜的质量类似于通过分子束外延生长获得的，用于在环境温度沉积期间经常显示三维生长的系统。待研究的具体系统包括在Au上的Cu、在Cu上的Ni以及在Si上的Cu、Ag、Ni和Co。这项工作的新特点将是在原位监测薄膜应力产生的真实的时间在DMG和SMG和相关联的应力行为与形态的演变。这在科学和技术上都是令人感兴趣的，因为应力行为与生长的微观结构特征相关联，并且如果DMG和SMG生产的系统要用于技术应用（例如，用于互连的Si上的Cu）。应力的实时监测也将用于优化生长条件和监测沉积期间的膜质量。非技术性概述：生产用于薄膜应用的高质量单晶材料的能力（例如，微电子）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这种材料的方法，并且是可以并入现有和下一代技术的工艺。该研究将研究具有科学和工业重要性的合成材料系统，包括用于质量表征和控制的实时应力监测。这将是首次在这些合成方法中采用应力测量，并将大大提高将其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。与该项目相关的外联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教育中代表性不足，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.