Carbon, isotropic polymer deposition

Most isotropic etchants exhibit a loading effect, wherein a measurable depletion of the active etchant results from consumption in the etch process. In these cases, the overall etch rate depends upon the area of film to be etched. Under extreme circumstances, with carbon-based etch gases, etchant depletion can be so severe that polymer deposition occurs instead of etching. An analysis (85) of the loading effect, which has been extended (86) to include multiple etchant loading and other etchant loss processes, indicates that the etch rate (R) for N wafers each of area A is given by... 

Layer-by-layer (LBL) assembly technique has been proven as a well-established approach to build composites or function-specific multilayer assemblies. Mamedov et al. fabricated isotropic polymer/SWNT composites by LBL deposition method to preserve SWNT dispersion [98]. Zhang et al. prepared PVA/poly(vinyl pyrolidone)/SDS (sodium dodecyl sulfate)/SWNT composite films by LBL technique with good nanotube dispersion and load transfer from polymer matrix to the carbon nanotubes [99]. With the aid of a surfactant, super-tough PVA/SWNT fibers were also fabricated by LBL method with SWNT loading as high as 60 wt% [100]. 

Recently, success was achieved in depositing pyrolitic carbon onto the surfaces of blood vessel implants made of polymers. This type of carbon is called ultra low temperature isotropic (ULTI) carbon instead of low temperature isotropic (LTI) carbon. The deposited carbon has excellent compatibility with blood and is thin enough not to interfere with the flexibility of the grafts [Park and Lakes, 1992]. 

As will be seen below, we obtained similar and sometimes even better results with carbon layers. It is well known that so-called isotropic carbon is especially compatible with blood /7/. It is deposited as pyrolytic carbon in a fluidized bed of a hydrocarbon-noble gas mixture at relatively low pyrolysis temperatures between 1200 and 1500 C (LT = low temperature). Since this process can on ly be used with a heat-stable substrate material with low thermal expansion coefficients, we (and others /8/) used vacuum-coating processes for the deposition of similar coatings onto polymers. In our work we used two processes with one, the results of which will be reported in sect. 5, the carbon is separated out of a hydrocarbon-noble gas mixture in the set-up shown in Fig.2. However, not heat, as in pyrolysis, but rather a glow discharge is used for the decomposition. 

---