We study the optical properties of MoS2 nanotubes (NTs) with walls comprising dozens of monolayers. We reveal strong peaks in micro-photoluminescence (μ-PL) spectra when detecting the light polarized along the NT axis. We develop a model describing the optical properties of the nanotubes acting as optical resonators which support the quantization of whispering gallery modes inside the NT wall. The experimental observation of the resonances in μ-PL allows one to use them as a contactless method of the estimation of the wall width. Our findings open a way to use such NTs as polarization-sensitive components of nanophotonic devices.

This work is devoted to the development and optimization of the parameters of graphene-based sensors. The graphene films used in the present study were grown on semi-insulating 6H-SiC substrates by thermal decomposition of SiC at the temperature of ~1700 °C. The results of measurements by Auger and Raman spectroscopies confirmed the presence of single-layer graphene on the silicon carbide surface. Model approach to the theory of adsorption on epitaxial graphene is presented. It is demonstrated that the Green-function method in conjunction with the simple substrate models permit one to obtain analytical results for the charge transfer between adsorbed molecules and substrate. The sensor structure was formed on the graphene film by laser. Initially, a simpler gas sensor was made. The sensors developed in this study demonstrated sensitivity to the NO2 concentration at the level of 1–0.01 ppb. The results obtained in the course of development and the results of testing of the graphene-based sensor for detection of protein molecules are also presented. The biosensor was fabricated by the technology previously developed for the gas sensor. The working capacity of the biosensor was tested with an immunochemical system constituted by fluorescein and monoclonal antibodies (mAbs) binding this dye.

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We report the results of experimental and theoretical studies of phonon modes in GaN/AlN superlattices (SLs) with a period of several atomic layers, grown by submonolayer digital plasma-assisted molecular-beam epitaxy, which have a great potential for use in quantum and stress engineering. Using detailed group-theoretical analysis, the genesis of the SL vibrational modes from the modes of bulk AlN and GaN crystals is established. Ab initio calculations in the framework of the density functional theory, aimed at studying the phonon states, are performed for SLs with both equal and unequal layer thicknesses. The frequencies of the vibrational modes are calculated, and atomic displacement patterns are obtained. Raman spectra are calculated and compared with the experimental ones. The results of the ab initio calculations are in good agreement with the experimental Raman spectra and the results of the group-theoretical analysis. As a result of comprehensive studies, the correlations between the parameters of acoustic and optical phonons and the structure of SLs are obtained. This opens up new possibilities for the analysis of the structural characteristics of short-period GaN/AlN SLs using Raman spectroscopy. The results obtained can be used to optimize the growth technologies aimed to form structurally perfect short-period GaN/AlN SLs.

The electrical transport in graphene interfaced with different ions in solution gated graphene field effect transistors (GFETs) is the subject of active studies due to its importance in sensor fabrication. Most of the developed GFET biological sensors use graphene that has been modified. The difficulty in the modification procedure and the reduction in quality of graphene that it causes are important drawbacks for applications. Therefore, we focus on GFETs based on unmodified graphene gated by aqueous solutions containing lysine amino acids. We observed that an increase in the ionic concentration of lysine in these solutions leads to a suppression of unipolar electron conductance of graphene in GFETs. This dependence is opposite to the dependence typically observed in gating solutions containing smaller atomic ions. We attribute the observed suppression to electric field screening of the graphene surface from water molecules by lysine ions which are larger and have lower charge density compared to atomic ions. This novel phenomenon leads to an overall decrease of surface charge density in molecular layers formed at the graphene interface and can be applied in GFET sensors with unmodified graphene that detect the presence and concentration of large molecules in the gating solutions.