Single NV centers in diamond coupled by hyperfine interaction (hfi) to neighboring 13 C nuclear spins are now widely used in emerging quantum technologies as elements of quantum memory adjusted to a nitrogen-vacancy (NV) center electron spin qubit. For nuclear spins with low flip-flop rate, single shot readout was demonstrated under ambient conditions. Here we report on a systematic search for such stable NV− 13 C systems using density functional theory to simulate the hfi and spatial characteristics of all possible NV− 13 C complexes in the H-terminated cluster C 510 [NV] -H 252 hosting the NV center. Along with the expected stable 'NV-axial− 13 C' systems wherein the 13 C nuclear spin is located on the NV axis, we found for the first time new families of positions for the 13 C nuclear spin exhibiting negligible hfi-induced flipping rates due to near-symmetric local spin density distribution. Spatially, these positions are located in the diamond bilayer passing through the vacancy of the NV center and being perpendicular to the NV axis. Analysis of available publications showed that, apparently, some of the predicted non-axial near-stable NV− 13 C systems have already been observed experimentally. A special experiment performed on one of these systems confirmed the prediction made.

Single nitrogen-vacancy (NV) centers in diamond coupled to neighboring nuclear spins are promising candidates for room-temperature applications in quantum information processing, quantum sensing and metrology. Here we report on a systematic density functional theory simulation of hyperfine coupling of the electronic spin of the NV center to individual 13 C nuclear spins arbitrarily disposed in the H-terminated C 291 [NV] -H 172 cluster hosting the NV center. For the 'families' of equivalent positions of the 13 C atom in diamond lattices around the NV center we calculated hyperfine characteristics. For the first time the data are given for a system where the 13 C atom is located on the NV center symmetry axis. Electron paramagnetic resonance transitions in the coupled electron-nuclear spin system 14 NV-13 C are analyzed as a function of the external magnetic field. Previously reported experimental data from Dréau et al (2012 Phys. Rev. B 85 134107) are described using simulated hyperfine coupling parameters.

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Black silicon (bSi) refers to an etched silicon surface comprising arrays of microcones that effectively suppress reflection from UV to near-infrared (NIR), while simultaneously enhancing the scattering and absorption of light. This makes bSi covered with an nm-thin layer of plasmonic metal, i.e. gold, an attractive substrate material for sensing of bio-macromolecules and living cells using surface-enhanced Raman spectroscopy (SERS). The performed Raman measurements accompanied with finite element numerical simulation and density functional theory analysis revealed that at the 785 nm excitation wavelength, the SERS enhancement factor of the bSi/Au substrate is as high as 10 8 due to a combination of the electromagnetic and chemical mechanisms.This finding makes the SERS-active bSi/Au substrate suitable for detecting trace amounts of organic molecules. We demonstrate the outstanding performance of this substrate by highly sensitive and specific detection of a small organic molecule of 4-mercaptobenzoic acid and living C6 rat glioma cells nucleic acids/proteins/lipids. Specifically, the bSi/Au SERS-active substrate offers a unique opportunity to investigate the living cells' malignant transformation using characteristics protein disulfide Raman bands as a marker. Our findings evidence that bSi/Au provides a pathway to the highly sensitive and selective, scalable, and low-cost substrate for the lab-on-a-chip SERS biosensors that can be integrated into silicon-based photonics device.

In this paper we study the effect of absorption peak correlation in finite length carbon nanotubes and graphene nanoribbons. It is shown, in the orthogonal π-orbital tight-binding model with the nearest neighbor approximation, that if the ribbon width is a half of the tube circumference the effect takes place for all achiral ribbons (zigzag, armchair and bearded), and corresponding tubes, starting from lengths of about 30 nm. This correlation should be useful in designing nanoribbon-based optoelectronics devices fully integrated into a single layer of graphene.

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