Microstructural patterning of thin films using extrinsic seed crystals

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。根据不同的应用，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，并且能够在高温下工作而不会出现故障。这些性能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，如果可以控制薄膜的微观结构，则可以根据需要改变其性能，从而大大提高其性能。最终的结果将是电子设备的功耗更低，太阳能电池板的效率更高，切割工具的寿命更长，等等。该奖项支持基础研究，使金属合金薄膜的制造具有精确控制的微观结构，并解决与金属合金中晶体形成和生长有关的关键问题。研究活动与教育和推广工作相结合，包括对本科生的指导计划，为在校学生提供实践活动和示范，鼓励他们从事材料科学和工程方面的职业，以及对研究生进行材料合成和表征方面的培训。设计具有独特物理和机械性能的薄膜需要明确控制广泛的微观结构参数，包括平均晶粒尺寸，晶粒尺寸分散，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。基于以下假设，一种新的合成方法的发展解决了这个基本问题：嵌入适当种子晶体的非晶前驱体膜可以被控制地结晶，以获得精确定制的微观结构。为了验证上述假设，采用磁控溅射法合成了嵌入精心选择的种子晶体的非晶NiTi薄膜，并通过受控热退火进行了结晶。结合先进的透射电镜技术，揭示了种子晶体在非晶膜中的空间分布和取向如何影响结晶膜的最终微观结构。除了定制薄膜的整体晶粒尺寸分布、织构和相组成外，该方法还可以用于特定位置的这些参数变化，从而实现对机械和物理性能的局部控制。教育和推广活动包括材料研究大使（MRAs）计划，通过该计划，各种各样的本科生被招募到这个项目中工作并进行推广活动。mra邀请学生参观亚利桑那州立大学（ASU）进行实践活动，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。

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.