Surface Dynamics During Environmental Degradation of Crystal Surfaces. Revision 1.

Whitman, P. K. ; De Yoreo, J. J. ; Land, T. A. ; Miller, E. L. ; Suratwala, T. I. ; Thorsness, C. B. ; Wheeler, E. K.

Technical Information Center Oak Ridge Tennessee

关键词: Crystal surfaces;    Degradation;    Physics;    Chemistry;    Etching;   

RP-ID  :  DE200515013517

学科分类：工程和技术（综合）

美国|英语

来源: National Technical Reports Library

【 摘 要 】

While a great deal of effort has been invested into understanding the physics and chemistry of environmental attack on metal surfaces, little attention has been given to degradation of dielectric crystalline surfaces used for optical applications. Although it is generally possible to isolate such surfaces in vacuum chambers or purged environments, this is not always the case. In addition, even when nominal isolation from the outside world is possible, contamination either present on the surface as a result of finishing the optic or introduced to the surface within the vacuum environment can lead to surface degradation. This problem may be particularly pronounced when the surface has a porous anti-reflective or high reflective coating that acts like a getter for volatile contaminants. Furthermore, the ever increasing internal quality of these materials and the rising demand of UV applications such as UV photolithography has led to their widespread use in high power UV systems where surface degradation is even more pronounced. The National Ignition Facility is the quintessential high power UV system. Its successful deployment and operation depends on the ability of a number of optical surfaces to survive high fluence UV environments. Recently, the formation of pits with distinct geometrical features was discovered on the surface of the sol-coated KH(sub 2)PO(sub 4) (KDP) and KD(sub 2)PO(sub 4) (DKDP) crystals used for optical switching and frequency conversion on Nova, Omega, and Bearnlet after they were coated with anti-reflective coatings. These pits scattered up to 10% of the incident light, resulting in both a loss of energy on target and the potential to produce collateral laser damage through beam modulation and/or contamination from structural material ablated by the scattered light. We have identified these pits as the product of dissolution by water that is adsorbed into the coating. However, the kinetics of pit formation varied dramatically as the surface type was varied from 'as-grown' to mechanically finished to thermally annealed or as the sol coating method and chemistry were varied. The purpose of this proposal was to develop a fundamental understanding of the physics and chemistry of the environmental degradation processes at crystal surfaces.