Evidence of Carboxyl Modification of Hydrogen-Free Diamond-Like Carbon Films Assisted by Radio Frequency Plasma in Vacuum

Table 1

Sample-modification-process parameters, and the estimated coverage rate of the carboxyl groups based on XPS data.

Sample	Step  1	Step  2		Step  3	O/C (At.%)	Coverage (first method)	Coverage (second method)
		RF power (W)	Time (min)
S1	√	—	—	—	18.1%	—	—
S2	√	—	—	√	10.0%	<10%	<10%
S3	√	0	60	√	15.7%	23%	17%
S4	√	20	10	√	—	—	—
S5	√	20	60	√	19.9%	44%	43%
S6	√	20	60	√	18.8%	40%	60%