Supporting Information for Review Only

Photochemical doping of graphene oxide thin films with nitrogen for electrical conductivity improvement

Xinyu Li,1,2Fuchi Liu1, Nujiang Tang,1,a) Tao Tang,1 Xiancong He1, Ming Li2, YuanLiu,1 and Youwei Du1

1Physics Department & Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing 210093, People’s Republic of China

2College of Science, GuilinUniversity of Technology, Guilin 541004, PR China

Fig.S1. XPS spectra of GO and the NGO samples obtained at different irradiation time.

The bonding configuration of doped nitrogen and the surface composition of corresponding nitrogen-containing chemical structures were examined using XPS. Fig. S1 shows that the overall nitrogen content in N-graphene changes with microwave irradiation power. The peaks at about 285, 400, and 536 eV can be assigned to the binding energy of C1s, N1s, and O1s, respectively. The XPS spectra of NGO as well as undoped RGO(Fig. S2) indicate that the RGO contain ca. 20% of oxygen and no signal concerning nitrogen could be detected, implying the existence of N doping element in the NGO samples. Compared to GO, the NGO samples show clear decrease in the peak intensities of the oxygen functional groups. It may be thatconsiderable amount of oxygen-containing functional groups of GO were removed during irradiation. Moreover, The contents of nitrogen increased with the increase of irradiation time, however,the atomic content of oxygen was dropped from 25.2% for RGO-60 to 10.08% for NGO-120, the contents of carbon remains stable, indicating that oxygen-containing functional groups were effectively removed during irradiation. This is due to the formation of C−N bonds and the recovery to sp2 graphitic lattice of defected NGO by irradiation in NH3 atmosphere.

Fig. S2. (a)XPS spectra of GO and the RGO samples obtained at different irradiation time. (b) Contents of oxygen in the RGO samples.

Fig. S3. Temperature-dependent sheet resistance of NGO films measured in the range of 10-300 K. Inset: Semilog plot of the resistance R vs T-1/3 of the samples.

The resistance versus temperature (Rs–T) characteristics of RGO-60 films are presented in Fig. S3, one can see the resistivity of all films decreased with increasing T, showing a ‘semiconducting’ behaviour.We have plottedthe natural logarithm of the conductance ln R as a function of T−1/3 which is shown in Fig. S3 along with a best fit line from the 2D-VRHmodel, RGO-60 filmshowed lower conductivity than the NGO film with almost the same thickness,it may be the reason that NGO has high content of N by photochemical doping of GO, and the N-doping can effectively enhance its conductivity, RGO films contain more oxygen groups than RGO-60 films, RGO films has rather worse electrical properties due to the presence of a relatively higher oxygen-containing groupsin agreement with the XPS spectrum.

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