Atomic Layer Deposition Barrier Layers on Large Silver-coated Mirrors

即使所有令人眼花缭乱的技术都被用于天文观测，而这些技术的进一步发展又受到天文学应用的启发，要制造出一种金属反射镜涂层，在所有的光学波长上都具有高反射率，但又足够耐用，可以在野外使用，仍然很困难。传统的铝涂层很耐用，但在所有波长下的反射率都不高。银具有更好的全波长反射率，但除非采用巧妙的方法将其沉积在玻璃镜面上，否则银会在短时间内形成针孔并脱落。这些方法的发展是本研究的目标，也是一个对许多不同类型的未来仪器具有深远应用的目标。提高耐用性、高反射率银镀层的技术方法的本质是原子层沉积（ALD）。ALD是一种相对较新的连续化学蒸汽工艺，利用了自限制表面反应。ALD涂层有几个理想的性能，特别是优良的膜结构，保形覆盖，以及优良的厚度均匀性和控制。ALD是目前广泛应用于硅片工业的成熟工艺。然而，到目前为止，ALD仅限于相对较小的衬底尺寸，并且由于其相对较慢的速度，很少用于光学。该项目将在传统物理气相沉积（PVD）沉积的银上放置ALD阻挡层，以获得比单独PVD更耐用的薄膜。因此，所提出的工艺是一种混合工艺，大部分涂层采用PVD工艺完成，阻挡层采用ALD系统添加。还计划改进ALD沉积速度，以便在合理的时间内涂层更大的基底。这个项目有着巨大而广泛的影响，因为它极大地提高了大量天文仪器的实际性能。此外，学生将参与，并有一个强烈的承诺，以简单的语言解释的研究和它的结果。该项目由美国国家科学基金会天文科学部通过其先进技术和仪器计划提供资金。

Even with all the dazzling technology that has been brought to bear on astronomical observations, and the furthering of that technology in turn that has been inspired by astronomical applications, it is still difficult to make a metal mirror coating that is highly reflective at all optical wavelengths yet durable enough to last in field use. Traditional aluminum coatings are durable, but not highly reflective at all wavelengths. Silver has better all-wavelength reflectance, but will develop pin-holes and flake away in a short time unless clever methods are used to deposit it on a glass mirror blank. The development of such methods is the goal of this investigation, and a goal with far-reaching applications to many different kinds of future instruments.The essence of the technical approach to improved durability, high-reflectance silver coatings, is Atomic Layer Deposition (ALD). ALD is a relatively new, sequential chemical vapor process taking advantage of self-limiting surface reactions. ALD coatings have several desirable properties, notably excellent film structure, conformal coverage, and excellent thickness uniformity and control. ALD is now a mature process used widely in the silicon wafer industry. To date, however, ALD has been limited to relatively small substrate sizes and is rarely used for optics, owing to its relatively slow speed. This project will place ALD barrier layers on top of silver deposited by conventional physical vapor deposition (PVD) to get films more durable than PVD alone. The process proposed is a thus hybrid process, with most of the coating done with PVD processes and the barrier layers added with the ALD system. Improvements in ALD deposition speed are also planned to allow coating of larger substrates in reasonable times.This project has immense broader impacts in that it enables dramatically improved practical performance of a vast range of astronomical instrumentation. In addition, students will be involved, and there is a strong commitment to plain-language explication of the research and its results.Funding for this project is being provided by NSF's Division of Astronomical Sciences through its Advanced Technologies and Instrumentation program.