Microstructural patterning of thin films using extrinsic seed crystals

非技术概述薄膜具有广泛的应用范围，从计算机芯片和太阳能电池到切割工具、光学透镜和生物医学设备。根据应用的不同，薄膜需要表现出特定的机械和物理性能。例如，用于计算机芯片的金属薄膜必须具有高导电性，并能够在高温下无故障地运行。这些特性在很大程度上取决于薄膜的微观结构(晶体的大小、形状和取向)。因此，如果能够控制薄膜的微结构，就可以随心所欲地改变其性能，这将导致其性能的显著提高。最终的结果将是电子设备的能耗更低，太阳能电池板的效率更高，刀具的寿命更长，仅举几例。该奖项支持能够制造具有精确可控微结构的金属合金薄膜的基础研究，并解决与晶体如何在金属合金中形成和生长相关的关键问题。研究活动与教育和外联工作相结合，包括为本科生提供指导计划，为在校学生提供实践活动和示范，以鼓励他们在材料科学和工程领域从事职业，以及对研究生进行材料合成和表征方面的培训。技术概述设计具有独特物理和机械性能的薄膜需要明确控制各种微观结构参数，包括平均晶粒度、晶粒度分散度、织构和相组成。但是，尽管薄膜加工技术取得了实质性的进步，我们独立调整多个微结构参数的能力仍然有限。这一基本问题是通过开发一种新的合成方法来解决的，该方法基于以下假设：嵌入适当种子晶体的非晶态前驱体薄膜可以被可控地晶化以获得精确定制的微结构。为了验证所提出的假设，采用磁控溅射法制备了镶嵌有精选种子晶体的非晶态NiTi薄膜，并用可控热退火方法进行了晶化处理。结合先进的电子显微镜技术，揭示了晶种晶体在非晶态薄膜中的空间分布和取向对晶化薄膜的最终微结构的影响。该方法除了可以调整薄膜的总体颗粒尺寸分布、织构和相组成外，还可以用于这些参数的特定位置的变化，从而实现对机械和物理性能的局部控制。教育和外展活动包括材料研究大使(MRA)计划，通过该项目招募不同的本科生参与该项目并开展外展活动。MRA邀请访问亚利桑那州立大学(ASU)的学生进行动手活动，并访问当地中学进行演示并向学生介绍材料研究。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical SummaryThin films have a wide variety of applications ranging from computer chips and solar cells to cutting tools, optical lenses and biomedical devices. Depending on the application, the thin films need to exhibit specific mechanical and physical properties. For example, thin metallic films used in computer chips must have high electrical conductivity and be able to operate at elevated temperatures without failure. These properties are determined to a large extent by the microstructure (size, shape and orientation of crystals) of the thin films. Therefore, if the microstructure of the thin films can be controlled, their properties can be altered as desired, which will lead to considerable improvement in their performance. The ultimate result would be lower power consumption in electronic devices, greater efficiency in solar panels, higher lifetimes for cutting tools, to name a few. This award supports fundamental research that enables the fabrication of metallic alloy films with precisely controlled microstructures and addresses critical questions related to how crystals form and grow in metallic alloys. The research activities are integrated with education and outreach efforts that include a mentoring program for undergraduates, hands-on activities and demonstrations for school students to encourage them to pursue careers in materials science and engineering, and training of graduate students in materials synthesis and characterization. Technical SummaryDesigning thin films with unique physical and mechanical properties requires explicit control over a wide range of microstructural parameters including the mean grain size, grain size dispersion, texture and phase composition. But despite substantial advances in thin film processing techniques, our ability to independently tune multiple microstructural parameters is still limited. This fundamental problem is addressed by the development of a novel synthesis method based on the following hypothesis: Amorphous precursor films embedded with appropriate seed crystals can be controllably crystallized to obtain precisely tailored microstructures. To validate the proposed hypothesis, amorphous NiTi films embedded with carefully chosen seed crystals are synthesized by magnetron sputtering and crystallized by controlled thermal annealing. A combination of advanced transmission electron microscopy techniques are used to reveal how the spatial distribution and orientation of seed crystals in the amorphous films influence the final microstructure the crystallized films. Apart from tailoring the overall grain size distribution, texture and phase composition of thin films, the method can be used for location specific variation of these parameters, which enables local control of the mechanical and physical properties. Education and outreach activities include the Materials Research Ambassadors (MRAs) program through which a diverse set of undergraduate students are recruited to work on this project and perform outreach activities. The MRAs engage school students visiting Arizona State University (ASU) with hands-on activities, and visit local middle schools to perform demonstrations and introduce students to materials research.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.