Vacuum Technology & Coating.

I would like highlight the above journal which for those of you with internet access can be viewed at either www.vactechmag.com or www.vtcmag.com

In the March 2008 edition (Vol 9, No 3) there are a couple of articles that I think will interest many of you.

The first is one of the ‘Guides to vacuum technology’ and is ‘Outgassing – part 1 Desorption of molecules from surfaces’ by Luke Hinkle   This article starts by defining outgassing as being one of 4 phenomena comprising 1) surface desorption, 2) Contamination evaporation, 3) Diffusion from the bulk or 4) Sublimation.  The article then goes on to outline a ‘battle plan’ to minimise the problem which consists of two parts the first is to reduce the presence of water on surfaces and the second is to stimulate the molecules to assist them leaving the surface.    The article then goes on to describe the options for preventing the original absorption of material on the surfaces such as by venting using dry air or nitrogen.  To speed up the removal of any material there are various options such as baking the system, using ultra-violet radiation or bombarding the surface with energetic ions.  Water is held onto the surface by a binding energy approximately 100 times greater than its average thermal kinetic energy.  In the normal course of events the water molecule once attached to a surface can experience thermal agitation that is, in general, insufficient to free it from the surface.   The use of any of the above methods of adding energy increase the thermal agitation and more of the molecules will shake free of the surface. 

This gives a flavour of the article which goes into much more detail.

The second article is ‘Plasma Chemistry’ by Abe Belkind & Kurt Becker.  Virtually all vacuum deposition processes make use of plasma cleaning and in addition there are an increasing number of plasma enhanced deposition processes and plasma etching processes.  As such this article could well be of great interest to many readers for a wide variety of different reasons. The article gives a detailed description of the chemistry that occurs within a plasma including the formation of ions and radicals in all their different forms.  The article then proceeds to describe how the plasma can be used in a number of these different applications including some other non vacuum applications such as ozone generation for water treatment or as used for car exhaust cleaning.

Although this article may not change the way you use the plasma on your own system it does at least explain how the chemistry occurs and what the limitations might be.