Atomic Layer Deposition Barrier Layers on Large Silver-coated Mirrors

即使所有令人眼花缭乱的技术已经带来了对天文观测的影响，并且该技术的进一步发展反过来又受到天文应用的启发，仍然很难制造出在所有光波长下都具有高度反射性但在现场使用中足够耐用的金属镜面涂层。传统的铝涂层是耐用的，但不是在所有波长下都具有高反射性。 银具有更好的全波长反射率，但会在短时间内形成针孔并剥落，除非使用巧妙的方法将其存款在玻璃镜坯上。 这种方法的发展是本研究的目标，也是对未来许多不同类型仪器具有深远应用的目标。提高耐久性、高反射率银涂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气相工艺，利用自限制表面反应。ALD涂层具有几种期望的性质，特别是优异的膜结构、保形覆盖以及优异的厚度均匀性和控制。 ALD现在是广泛用于硅晶片工业的成熟工艺。然而，迄今为止，ALD仅限于相对较小的衬底尺寸，并且由于其速度相对较慢，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，以获得比单独使用PVD更耐用的薄膜。 所提出的工艺是一种混合工艺，其中大部分涂层用PVD工艺完成，阻挡层用ALD系统添加。 ALD沉积速度的改进也计划允许在合理的时间内涂覆更大的衬底。该项目具有巨大的更广泛的影响，因为它可以显着提高各种天文仪器的实际性能。 此外，学生将参与其中，并有一个强烈的承诺，以平实的语言解释的研究和它的结果。该项目的资金是由美国国家科学基金会的天文科学部通过其先进技术和仪器计划提供。

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.