Figures at a glance
Figure 1: Micro-Raman characteristics of the isotopically modified graphene. 
a, Raman map (2,530~2,730 cm−1) of the 2D bands. The colour bar shown below indicates the dosing sequence for the four regions. b, Raman spectra of graphene measured at the positions labelled by the coloured circles in a. c, SEM image of graphene transferred onto the SiNx holey membrane. d, Raman maps of graphene transferred onto the SiNx holey membrane. From left to right, three Raman maps showing the integrated intensity of the 2D band of 0.01% 13C (2,630~2,730 cm−1), the 50:50 12C/13C mixture (2,560~2,660 cm−1) and 99.2% 13C (2,530~2,630 cm−1) graphene, respectively. The x-axis shows counts (cts) from the CCD (charge-coupled device). The arrows indicate wrinkles and cracks in some samples, which were excluded from the thermal measurements.
Figure 2: Thermal conductivity K of the suspended graphene film with 13C isotope concentrations of 0.01%, 1.1% (natural abundance), 50% and 99.2%, respectively, as a function of the temperature measured with the micro-Raman spectrometer. 
The solid lines are a guide to the eye only. The experimental errors were estimated by means of the square-root-sum error propagation approach, including the following error sources: the Raman peak position calibration, temperature resolution of the Raman measurement method, and the uncertainty of the laser absorption.
Figure 3: Thermal conductivity of graphene as a function of its isotopic composition. 
a, Histograms of K for graphene films with 0.01%, 1.1%, 50% and 99.2% 13C isotopic concentration at ~380 K. The solid lines represent fits to the experimental data with the normal distribution. b, The average value of the measured thermal conductivity K as a function of 13C concentration at ~380 K. The MD simulations results for K are shown as yellow squares for comparison.
