Uncommon 2D diamond-like carbon nanodots derived from nanotubes: atomic structure, electronic states, and photonic properties.

In this article, we report the results of a relatively facile fabrication of carbon nanodots from single-walled and multi-walled carbon nanotubes (SWCNTs and MWCNTs). The results of X-ray photoelectron spectroscopy (XPS) and Raman measurements show that the obtained carbon nanodots are quasi-two-dimensional objects with a diamond-like structure. Based on the characterization results, a theoretical model of the synthesized carbon nanodots was developed. The measured absorption spectra demonstrate the similarity in the local atomic structure of carbon nanodots synthesized from single-walled and multi-walled carbon nanotubes. However, the photoluminescence (PL) spectra of nanodots synthesized from both sources turned out to be completely different. Carbon dots fabricated from MWCNTs exhibit PL spectra similar to those of nanoscale carbon systems with sp3 hybridization and a valuable edge contribution. At the same time nanodots synthesized from SWCNTs exhibit PL spectra which are typical for quantum dots with an estimated size of ∼0.6-1.3 nm.

Room temperature p-orbital magnetism in carbon chains and the role of group IV, V, VI, and VII dopants.

The study of magnetism without the involvement of transition metals or rare earth ions is considered the key to the fabrication of next generation spintronic devices. Several recent reports claim that optimizing the occupation number of the mixed p-orbitals is the correct way to reinforce p-orbital magnetism in bulk crystals. We provide experimental evidence that the kinked monoatomic carbon chains, the so-called linear-chained carbon, generate intrinsic ferromagnetism even above room temperature. According to our ab initio calculations, unconventional magnetism has its origin in the p-shells. In contrast, the linear monoatomic carbon chains are non-magnetic. Although the optimized differential spin density of states at the Fermi level (SDOS) of the kinked carbon chains is higher than that of bulk Fe, the magnetic moment is as low as 0.3µB. In order to enhance the magnetic response, we decided to tune the p-orbital magnetism by adding dopants from groups IV to VII of the periodic table. We observed that the strength of the p-orbital magnetism and the sign of the exchange interaction depend not only on the kink angle, but also on the concentration of lone pair electrons, free radical electrons, lateral chain spacing, internal electric dipole, dative covalent bonds and the Bohr radius of the dopants. Surprisingly, the V and VII-doped carbon chains show a strong non-zero SDOS, which has its origin in the p-shells. The VII-doped carbon chains give the SDOS of the opposite sign. Our best system, the arsenic-doped carbon chain, exhibits a strong local magnetic moment of 1.5µB, which is comparable to that of the bulk Fe of 2.2µB, with the mean exchange-correlation energy reaching a 63% ratio relative to that of the bulk Fe.

Structural ordering in a silica glass matrix under Mn ion implantation.

Mn(+)-implanted, amorphous SiO(2) samples were synthesized using pulsed-ion implantation without thermal annealing. The crystal and electronic structures have been studied using x-ray diffraction and synchrotron-based soft x-ray absorption and emission spectroscopy at the Si and Mn L(2,3) edges. We find a combination of small MnO clusters and Si crystallites at shallow depths while tetrahedral Mn coordination is found deeper in the host target. Through a combination of techniques, we find that the implantation process simultaneously decreases the long-range order in the near-surface region and increases order deeper in the SiO(2) host. Our results suggest Mn substitution into Si sites at deep levels catalyzes the formation of α-quartz, providing insight into the complex interactions that determine the local structure around the impurities as well as the overall changes to the crystallinity of implanted SiO(2).