P.E. Vickers et al. Carbon 38(2000)675-689 ic(%)composition of the fibre surface measured by XPS after fibres had been dried in an air oven at 122C overnight Atomic(%)concentration Elemental ratios W min nIs Na Is O/C N+O)/C 000 00000 0.l1 13 0.8 elative intensity of the OH ions, which would be appearing in bold. These even-mass ions generally de- expected if a significant number of hydroxyl or carboxylic crease in relative intensity from the untreated fibre surface ing introduced at the after the early stages of oxidation, with the ot be observed if th the ion assigned with the composition of C, H, NO, which present as phenol groups or attached to aromatic systems, appears unaffected by oxidation. The general observation owing to the increased stability to fragmentation. is consistent with the XPs data, which shows a slight A feature that is generally observed in the positive decrease in surface nitrogen concentration, and is also in ToF-SIMS spectra is that the vast majority of ions present agreement with the findings of Alexander and Jones [18] are even-electron ions. This phenomenon arises firstly who observed a change in peak shape in the n Is signal because odd-electron ions are radicals and as a result more They assigned the nitrogen present in the untreated fibre to prone to fragmentation to an even-electron ion and aa protonated amine structure and proposed that the oxi- neutral fragment (radical), and secondly because the dined fibres possessed nitrogen atoms in a configuration method of secondary ion production(sputtering) produces ions that tend to have low internal energies(and therefore decrease in initial nitrogen content and change in chem Bht unlikely to be radicals). This can prove useful in assigning environment is real, then this suggests that nitrogen is organic secondary ions, because the only trivalent element incorporated into the outer layers of the fibre during ommonly found in organic systems is nitrogen, and as a manufacture, where the fibres are subjected to high tem- result, even-electron ions containing an odd number of peratures in inert(N2, Ar)atmospheres. This outer layer is nitrogen atoms will appear at an even mass: charge ratio, then probably removed during the initial stages of oxida- generally most useful for positive ions of low-moderate tion to reveal the residual nitrogen left over from the pan mass precursor. intensity with treatment for a number of even-mass ions in XPS and ToF-SIms both indicate that the surface the positive spectrum, and possible ion assignments are composition of the fibre is modified as a result of the given in Table 4, with the most plausible ion compositions elec ical oxidation process. However, they do not §252出一若 ☆一OH =:°·Ca Fig. 2. Variation of simple ions, Na, Ca, CH, O, OH and Cl, with fibre treatment.680 P.E. Vickers et al. / Carbon 38 (2000) 675 –689 Table 3 Atomic (%) composition of the fibre surface measured by XPS after fibres had been dried in an air oven at 1228C overnight Fibre Atomic (%) concentration Elemental ratios 21 W min g C 1s O 1s N 1s Cl 2p Na 1s Ca 2p O/C (N1O)/C 0 91.7 3.6 3.5 0.3 0.3 0.5 0.04 0.08 25 88.2 7.7 2.7 0.3 0.6 0.4 0.09 0.12 50 86.9 9.7 2.0 0 0.9 0.5 0.11 0.14 100 86.6 9.0 2.5 0.2 1.0 0.6 0.10 0.13 200 83.5 11.6 3.0 0.3 0.9 0.8 0.14 0.17 2 relative intensity of the OH ions, which would be appearing in bold. These even-mass ions generally de￾expected if a significant number of hydroxyl or carboxylic crease in relative intensity from the untreated fibre surface acid groups were being introduced at the surface. How- after the early stages of oxidation, with the exception of 1 ever, this may not be observed if the oxygen atoms are the ion assigned with the composition of C H NO , which 2 2 present as phenol groups or attached to aromatic systems, appears unaffected by oxidation. The general observation owing to the increased stability to fragmentation. is consistent with the XPS data, which shows a slight A feature that is generally observed in the positive decrease in surface nitrogen concentration, and is also in ToF-SIMS spectra is that the vast majority of ions present agreement with the findings of Alexander and Jones [18] are even-electron ions. This phenomenon arises firstly who observed a change in peak shape in the N 1s signal. because odd-electron ions are radicals and as a result more They assigned the nitrogen present in the untreated fibre to prone to fragmentation to an even-electron ion and a a protonated amine structure and proposed that the oxi￾neutral fragment (radical), and secondly because the dised fibres possessed nitrogen atoms in a configuration method of secondary ion production (sputtering) produces more similar to a tertiary aromatic nitrogen. If the slight ions that tend to have low internal energies (and therefore decrease in initial nitrogen content and change in chemical unlikely to be radicals). This can prove useful in assigning environment is real, then this suggests that nitrogen is organic secondary ions, because the only trivalent element incorporated into the outer layers of the fibre during commonly found in organic systems is nitrogen, and as a manufacture, where the fibres are subjected to high tem￾result, even-electron ions containing an odd number of peratures in inert (N , Ar) atmospheres. This outer layer is 2 nitrogen atoms will appear at an even mass:charge ratio, then probably removed during the initial stages of oxida￾generally most useful for positive ions of low-moderate tion to reveal the residual nitrogen left over from the PAN mass. Fig. 3 shows the variation in normalised ion precursor. intensity with treatment for a number of even-mass ions in XPS and ToF-SIMS both indicate that the surface the positive spectrum, and possible ion assignments are composition of the fibre is modified as a result of the given in Table 4, with the most plausible ion compositions electrochemical oxidation process. However, they do not 1 1 22 2 2 Fig. 2. Variation of simple ions, Na , Ca , CH , O , OH and Cl , with fibre treatment