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Abstract

A series of studies were performed to aid in the development of a magnetron sputter system which would have the ability to deposit protective optical multilayers for operation in the infrared. Diamond-like carbon was to be used as the top protective layer, while germanium carbide was chosen for the underlying layers due to its tunable refractive index. The microstructural, optical, mechanical and electrical properties of the diamond-like carbon films were investigated as a function of argon sputter gas pressure, substrate bias and reactive gas partial pressure (H₂, O₂, and N₂). The films were characterized by spectroscopic ellipsometry, scanning and transmission microscopy, electron diffraction, resistivity and hardness measurements, along with infrared spectroscopy. It was found that the pseudo-bandgap and JR transparency increased with an increase in the sputter gas pressure, along with a decrease in the hardness. This appeared to be, in part, due to an increase in the amount of hydrogen incorporation and the development of a polymer phase in the film matrix. It was felt that the primary source of hydrogen was outgassing from surfaces inside the vacuum deposition chamber. Increasing the substrate bias resulted in an increase in the film density only. The optimum diamond-like films were deposited at low sputter gas pressures (1 Pa). A widening of the pseudo-bandgap was observed for an increase in the H₂ partial pressure up to a value of 0.1 Pa. The films deposited in a nitrogen/argon mix exhibited up to an order of magnitude increase in the deposition rate over the films deposited in pure argon. The optical properties of these materials were intermediate to those for the hydrogenated and unhydrogenated films. Germanium and carbon multilayers were deposited to determine if interdiffusion between the individual layers would result in germanium carbide. The purpose of this investigation was to attempt to overcome the limitations on the carbon alloy fraction in conventional sputter techniques due to a poisoning of the germanium target from the hydrocarbon gas. The optical and microstructural properties of the multilayers were studied as a function of pressure and substrate bias through in-situ ellipsometry. It was found that a good deal of interdiffusion occurs at higher pressures (2 Pa) but at the cost of an increase in the film porosity. A novel control system was developed by monitoring the film growth through in-situ ellipsometry. This routine has the capability to determine both the thickness and the optical constants of the individual layers in a multilayer stack. A Fabry-Perot filter consisting of 21 quarter-wave layers was deposited with a peak transmission of 65 %. It is shown how this routine can be extended to optically absorbing materials such as carbon.