Table 2. Surface composition of doped graphene samples derived from XPS studies.

Samples	C at.%	O at.%	N at.%	S at.%
NS-G	85.1	13.7	0.9	0.3
N-G	85.5	14.2	0.3	—
S-G	86.5	13.4	—	0.1
NS-G005	84.2	14.9	0.7	0.2
NS-G1	83.2	12.3	1.3	3.2