Structural modification of nanosized diamonds (ND) irradiated with 100 keV 15N ions for various doses was investigated using transmission electron microscopy (TEM) and Raman spectroscopy. Raman active modes showing a long-range order of diamond were observed for samples dosed with 1015 cm−2. However, the formation of a graphitic phase was observed, from TEM images, for ion doses as low as 1014 cm−2. The threshold dose for complete transformation of ND (sp3 to sp2) due to this implant is found to be greater than 1015cm−2. The technique could prove valuable to tailor carbon nanostructures with controlled fractions of sp3–sp2 bonding.

Comment on "Quantitative analysis of annealing-induced structure disordering in ion-implanted amorphous silicon," by Ju-Yin Cheng et al.,We use fluctuation electron microscopy to characterize medium-range order in ion-implanted amorphous silicon. In fluctuation microscopy, intensity fluctuation in a dark-field image contains the information of high-order atomic correlations in the length scale of 1-3 nm. In this study, we heated as-implanted silicon at 500, 550, and 580°C for various times. Our results indicate that in the beginning amorphous silicon is a disordered phase with robust medium-range order. Thermal annealing leads to disordering of the structure. Furthermore, we find that the activation energy of the disordering is about 2.7 eV, close to the activation energy for thermal relaxation ͑about 2.2 eV͒. Our finding suggests a strong correlation between structure disordering and thermal relaxation.

Medium-range order in ion-implanted amorphous silicon has been observed using fluctuation electron microscopy. In fluctuation electron microscopy, variance of dark-field image intensity contains the information of high-order atomic correlations, primarily in medium-range order length scale (1–3 nm). Thermal annealing greatly reduces the order and leaves a random network. It appears that the free energy change previously observed on relaxation may therefore be associated with randomization of the network. In this paper, we discuss the origin of the medium-range order during implantation, which can be interpreted as a paracrystalline state, that is, a disordered network enclosing compacts of highly topologically ordered grains on the length scale of 1–3 nm with significant strain fields.

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In this article, we report the grafting of multi-walled carbon nanotubes on silica nanowires by directly growing nanotubes on the surfaces of the nanowires via chemical vapor deposition (CVD) using ferrocene and xylene as Fe catalyst precursor and carbon source, respectively. The grafted carbon nanotubes are a few micrometers long with diameters of 10 to approximately 30 nm, and grow uniformly along the lengths of the nanowires. The distribution density of the grafted carbon nanotubes on the silica nanowires can be tuned by simply adjusting the CVD growth temperature. Our method provides a simple approach for synthesizing nanometer scale grafted heterostructures between nanotubes and nanowires, which could be used to design and construct high-performance filters, chemical sensors and reinforced composites.