In the Introduction, “The implantation of the NV centers by PIII has been previously reported, but in those cases, diamond films were deposited on silicon wafers that were then negatively biased.35,36”, shall be modified as follows: “The implantation of the nitrogen-vacancy related color centers has been previously reported, but in those cases, diamond films were deposited on silicon wafers that were then negatively biased.35,36” We have recently checked our EPR equipment (Jeol JESFA200) and found out that there was a problem with the LFS board which controls the power supply of the magnetic field. This component was found to be malfunctioning and was replaced recently. Consequently, we remeasured the standard and the 5 min irradiated samples and the results are shown in Figure C1. Please note that Figure C1 and Figure C2 are not to be included as additional figures and in the original article; these are incorporated to aid our explanations on why the corrections are needed. In Figure C1, the standard sample refers to the commercial fluorescent nanodiamond product with an average diameter of 140 nm and the NV- content of 3.5 ppm, which was purchased from Ada´mas Nanotechnologies. The 5 min irradiated sample, on the other hand, refers to the sample that was treated for 5 min by the plasma immersion ion implantation technique, and then annealed, oxidized, and acid cleaned. These two samples are the exact same samples used for EPR analysis in our original article. As can be seen in the figure, the signals from the NV- centers of the standard and the 5 min irradiated samples appeared at g = 4.27 and g = 4.24, respectively. This result indicates that in the original article, the EPR results contained systematic errors arising from the magnetic field calibration. To double check if our analysis conditions are suitable, we also acquired the EPR spectra of another as-purchased, commercially available detonation nanodiamond (DND) powder (Ray Techniques Ltd. RT-DND, highly purified). As we can see in Figure C2a, the EPR spectrum of our original raw sample (US Research Nanomaterials) does not show a clear and distinct peak at g = 4.27, as in our original article. On the other hand, a signal at g = 4.26 appears on the other DND powder, as in Figure C2b. This implies that there are no problems with the EPR measurement setup after the replacement of the LFS board, and it also suggests that not all pristine DND powders show a distinct NV- signal in their EPR spectra. From these results, the measured magnetic field intensity was recalculated, and Figure 8 of our original publication was revised. In the Results and Discussion, the previous incorrect interpretation of Figure 8, “Although an intense paramagnetic signal at g = 2 along with a unique hyperfine structure coming from P1 centers is a characteristic feature of NDs,54 there is only a sharp peak at g = 1.9 in our samples. Indeed, this may be related to the small size of our diamonds because as the ND particle becomes smaller, hyperfine patterns gradually diminish and the associated g factor decreases.55 It was hypothesized that this phenomenon occurs because “In small particles the electron wave function of a surface paramagnetic center is delocalized over the whole nanoparticle.”55 Hence, the absence of hyperfine structures and shift in the ND signature peak is related to this phenomenon because our ND particles are, on average, below 5 nm in diameter, as confirmed using AFM, XRD, and TEM. Figure 8b shows the comparison of the EPR spectra of the raw, standard, and 7.5 min irradiated samples. The standard sample, which has an average diameter of 140 nm and NV- content of 3.5 ppm, was purchased from Adamas Nanotechnologies. As can be seen in this figure, the raw sample does not show any signal in this range, but the standard and nitrogen-ion-implanted samples show peaks at g = 4.16 and 4.06, respectively. The standard sample’s peak intensity is considerably less, and its line width is much narrower than our sample. To distinguish the peak from background noise, the sample’s spectra were again acquired; this time, the magnetic field was swept several times. Figure 8c shows the obtained data. Although the standard sample contains NV- centers, its g value does not exactly match the conventional g value of 4.27. As discussed earlier, this may be related to the size effect. Based on these results, we can infer that our peak with a g factor of 4.06 is attributed to the NV- center”, shall be rewritten as follows: “We can see an intense signal at g = 2.04, which comes from the paramagnetic nitrogen, P1 center (S = 1/2).1 In general, this signal is accompanied by a hyperfine pattern, but such a structure does not appear in our samples, since in ultrasmall detonation nanodiamonds, this characteristic feature is absent.2 Also, in Figure 8b, a relatively weak signal in the half magnetic field region at around g = 4.24, which stems from the forbidden transition of NV- centers (S = 1) is observed.1” The text, “Figure 8d shows the original spectra of the asreceived, non-irradiated, and nitrogen-ion-implanted samples”, shall be deleted. In the Conclusions, the statement, “Intriguingly, we observed considerable broadening together with the shift of P1 centers’ and the NV- centers’ signals. This finding agrees with the previous studies on EPR analysis of ultrasmall NDs, where smaller NDs were shown to have indistinct hyperfine patterns and smaller g factors. It was hypothesized that the size effect and nonuniformity in size may have caused peak shift and peak broadening”, shall be modified as follows: “Intriguingly, we observed considerable broadening. The cause of this broadening is not yet clear, but possible explanation may include nonuniform size distribution.” Before we end, we acknowledge our error in the EPR measurement; the peak shift did not occur. However, this correction does not affect the conclusion of our work.
ASJC Scopus subject areas
- Materials Science(all)