Patent ID: 7541069

Claim:
A method of modifying an internal surface of a workpiece comprising: coupling at least one first opening of said workpiece to a gas source to function as an entrance and coupling at least one second opening of said workpiece to a vacuum source to function as an exit; connecting a biasing system so as to apply a negative pulsed DC voltage to said workpiece, including selecting a duty cycle such that: (a) when said voltage is in an “on” condition, a negative voltage is applied to said conductive workpiece such that positive source gas ions within said gas generated in an interior of said conductive workpiece are attracted to said internal surfaces and react chemically to modify said internal surfaces; and (b) when said voltage is in an “off” condition, said positive source gas ions are sufficiently replenished within said interior to provide uniformity in coating said internal surfaces; flowing gas having a surface modifying material through said workpiece from said at least one first opening to said at least one second opening to implement a first coating cycle; with said workpiece remaining in situ, reversing said flow of gas through said workpiece to implement a second coating cycle; repeating said first and said second coating cycles to provide a uniform coating on said internal surfaces of said conductive workpiece, said repeating being adjustable for different said conductive workpieces of varying diameters and lengths; decreasing a pressure gradient in said interior when said voltage is in said “on” condition, thereby decreasing said flow through said workpiece; and increasing said pressure gradient in said interior when said voltage is in said “off” condition, thereby increasing said flow through said workpiece.