Understanding Reaction Mechanisms and Controlling Reactive Surface Species During Atomic Layer Deposition of Metal Chalcogenides

By and large, the progress of technology in areas such as computer chips and solar cells is driven by decreasing scale, coupled with increasing intricacies in device architecture. For example, development of advanced thin film solar cells will require the ability to uniformly coat nanometer sized inverse-opal patterns or random nanowire configurations over surface areas as large as a cubic meter. Atomic layer deposition (ALD) is a technique uniquely suited for the deposition of films on intricate nanostructures, as ALD’s defining characteristic is that film growth is controlled by two complementary and self-limiting surface reactions, which give uniform growth in a non-line-of-sight fashion. Unfortunately, this industrially mature technology has not been extensively studied from a fundamental chemistry standpoint. Complicating matters is the difficult task of studying chemistry at the gas-solid interface. In this talk, Weimer will discuss a portion of his Ph.D. work on the development of new precursors to control the reaction of chemical species on a solid surface and spectroscopic techniques to reveal chemical surface mechanisms. Specifically, In and V precursors were developed to work in concert to grow a new intermediate band-gap material, V_xIn_3-xS₃, which shows dual absorption events. Next, advanced ex situ spectroscopic measurements were used in concert with solution reactions to discover the growth and termination mechanism during SnO₂ deposition from a cyclic stannylene precursor and different oxygen sources. Finally, a novel mobile ALD reactor was designed and built for in situ X-ray synchrotron measurements of ALD surface chemistry and morphology. This new tool provides an exciting glimpse into a seldom studied realm of ALD, hard X-ray spectroscopy under actual deposition conditions.