and 1 5 ma cm 2 respectively for each run total pressure was 0 4 pa during tpo with argon and oxygen partial pressures of 0 28 and 0 12 pa respectively sputter cleaning and plasma heating were also carried out prior to pulsed tpo as elucidated in example 1 instead of keeping the oxygen flow constantly on throughout the treatment its flow was periodically pulsed whilst the argon flow was kept constant the duration of this pulsed tpo treatment was 165 minutes then a plasma heat step at 700 u00b0 c was performed immediately after tpo for 75 minutes similarly to tpo plasma heating can be carried out at a total pressure range of of 0 1 to 1 0 pa preferably 0 4 pa workpiece bias voltages during plasma heating may vary from u2212 100 to u2212 1000 v preferably u2212 200 v to minimize surface roughening filament heater current is periodically adjusted to keep a constant current density in the workpiece current density should be set in the range of 0 1 to 4 0 ma cm 2 preferably 1 5 ma cm 2 radiant heaters may be required to achieve treatment temperature if plasma heating is to be performed at.