Supplementary Information

Transcription

1 Supplementary Information Supplementary Figure S1: Structure and composition of Teflon tape. (a) XRD spectra of original Teflon tape and Teflon tape subjected to annealing at 150 o C under Ar atmosphere. Our X-ray diffraction (XRD) study of the both original and annealed Teflon tape has shown a crystalline pseudo-hexagonal structure with a=b=5.66 Å and c=19.5 Å, similar as reported by Bunn et al. 22. Bunn reported that the Teflon tape is highly crystalline below 20 o C while there is partial disordering of the crystalline regions above 20 o C. Our XRD measurement was carried out at 23 o C. Base on our XRD results, it can be observed that a small disordering occurs in the crystalline regions (hump at degree), which is consistent with Bunn s observations. (b) Raman spectra of original Teflon tape and Teflon tape subjected to Ar annealing at 150 o C. Both Teflon tapes show crystalline structures and no observable difference is found between them in the Raman spectra. The peaks are described in Table S1. (c) EDS of Teflon tape after annealing at 150 o C under Ar atmosphere. Only C and F have been detected and no other magnetic impurities are found. Like the XPS results, EDS spectrum of original Teflon tape is also similar to that of the annealed one. (d) XPS of Teflon tape after annealing at 150 o C under Ar atmosphere. Only C and F have been detected and no other magnetic impurities are found. It should be noted that XPS spectrum of original Teflon tape is similar to that of the annealed one. 1

2 Supplementary Figure S2: DSC and TGA results. (a) Differential scanning calorimetry (DSC) and (b) Thermogravimetric analysis (TGA) of original Teflon tape. The thermal DSC and TGA analysis are usually to investigate the both melting and decomposition temperature of polymers. DSC is a thermo-analytical technique, in which the amount of heat energy required to increase the temperature of sample is recorded. The trough of DSC curve indicates the melting process (extra heat is required to change phase) and the minimum is approximately the melting temperature. TGA is to determine changes in weight in relation to change in temperature. A derivative weight loss curve is used to determine a specific temperature where the weight loss is most apparent. Thus, this temperature can be assigned as decomposition temperature. Comparing both DSC and TGA results, the melting temperature of Teflon tape is 345 o C (melting does not involved any weight loss in TGA) and thermal decomposition temperature of Teflon tape is 589 o C and 614 o C (both shown in DSC and TGA). 2

3 Supplementary Figure S3: Calculation of formation energy of C-C bond. (a) Calculated energies of ferromagnetic state (dashed green line) and antiferromagnetic state (solid red line), respectively, for the head-to-head configuration of carbon dangling bonds. (b) The energy difference between ferromagnetic and antiferromagnetic states (E FM E AFM ) as a function of C-C distance in the head-to-head configuration and for two parallel Teflon chains with C-dangling bonds, respectively. All results are obtained based on hybrid functional (PBE0). 3

4 Supplementary Figure S4: Spin-density isosurface. (a) Side view of 2D C-dangling bonds of Teflon tape after adsorption of H 2 O molecules with spin-density isosurface. The spin density is defined as the difference between spin-up and spin-down electron densities, ρ -ρ. The blue, red, pink and sky blue balls represent the fluorine, carbon, oxygen and hydrogen atoms, respectively. (b) Differential charge density isosurface between C-dangling bond in 2D of Teflon tape and adsorbed H 2 O molecule. (c) Spin-polarized density of states (DOS) of 2D C-dangling bonds adsorbed by H 2 O molecules with Fermi energy indicated by dash line. These figures illustrate that ferromagnetic coupling is greatly reduced when C-dangling bonds attached with H 2 O and antiferromagnetic coupling is favorable instead of a strong ferromagnetism without H 2 O molecule attachment. All results are obtained based on hybrid functional (PBE0). 4

5 Supplementary Figure S5: Temperature dependence of magnetization. (a) Saturation magnetization of Teflon tape annealed in Ar at different temperatures (from 50 o C to 150 o C) and (b) fitted activation energy E a by the formula: M=M 0 (-E a /kt), where M is saturation magnetization at a particular temperature, and M 0 is the saturation magnetization after Ar annealing at 150 o C and E a is activation energy to break C-H 2 O bonds. The E a can be estimated as 0.19 ev, which is in the same order to 0.4 ev as the value of the calculated bonding energy. 5

6 Supplementary Table S1: A summary of different models used for our first-principles calculation/evaluation for possible ferromagnetism. All results are obtained based on hybrid functional (PBE0). Models Model 1: Isolated C-dangling bond C-dangling bond Remark Paramagnetism (C dangling carries a magnetic moment of 1µ B ) Model 2: 2 C-dangling bonds in the head-head configuration Antiferromagnetism (As described in Figure S3a, a relatively strong antiferromagnetic coupling appears with a separation around 3 Å. The system is paramagnetic, if the separation exceeds 4 Å) Model 3: 2 C-dangling bonds in the parallel configuration Antiferromagnetism (As described in Figure S3a, a relatively strong antiferromagnetic coupling appears with a separation around 3 Å. The system is paramagnetic, if the separation exceeds 4 Å) Model 4: 1D chain of C-dangling bonds. Ferromagnetism: E FM-AFM = -59 mev (see details in Figure 5a) Model 5: 2D network of C-dangling bonds. All dangling bonds are in the same plane. Ferromagnetism: E FM-AFM = -82 mev (see details in Figure 5b) 6

7 Model 6: 2D network. C dangling bonds are not in the same plane. The neighbored C dangling bonds are shifted by one unit along the Teflon chain (as shown in Side-view). Ferromagnetism: E FM-AFM = - 41 mev (the curve of E FM-AFM shows a negative peak with -41 mev at the chain separation around 5 Å) Model 7: 2D network. C dangling bonds are not in the same plane. The neighbored C dangling bonds are shifted by two units along the Teflon chain (as shown in Side-view). Side-view Paramagnetism (no magnetic exchange coupling was found in our first-principles calculation) Model 8: 2D C-dangling network with H2O attachment Antiferromagnetism (see details in Figure 5b) 7

8 Model 9: two 1D-chains with C-dangling bonds in head-to-head configuration Our calculation has shown that antiferromagnetism appears at the head-to-head separation d around 3 Å. If the separation is larger than 4 Å, head-to-head interactions become d insignificant. Ferromagnetism appears, as the system can be considered as two 1D chains. Ferromagnetism is resulted from lateral interactions as shown in Model 4. Model 10: two 2D-network with C-dangling bonds in head-to-head configuration Side -view d Our calculation has shown that antiferromagnetism appears iat the head-to-head separation d around 3 Å. If the separation is larger than 4 Å. Head-to-head interactions become insignificant. Ferromagneism appears, as the system can be considered as two 2D networks. Ferromagnetism is resulted from lateral interactions as shown in Model 5. 8

9 Supplementary Table S2: Bonding energy E b for C-dangling bond to bond with H, OH or H 2 O [where E b = E (Teflon+molecule) (E (Teflon) +E (molecule) )]. 9