A. A. Eliseev

Preparation of ordered magnetic iron nanowires in the mesoporous silica matrix

Abstract We report the synthesis of magnetic nanocomposites using mesoporous silica as a host material. Iron nanoparticles were incorporated into the pores of mesoporous silica. During the synthesis, a hydrophobic metal complex, Fe(CO)5, was introduced into the hydrophobic part of the as-prepared mesoporous silica–surfactant composite. The suggested method results in the formation of iron nanowires inside the silica framework. Particles shape and size are in good agreement with the shape and size of the pores. Particles are uniform and well ordered in the silica matrix. Thus, mesoporous silica serves as nanoreactor for the formation of Fe-nanoparticles. The magnetic susceptibility measurements indicate superparamagnetic properties of all samples. This approach leads to functional materials with nanosized active elements in amorphous silica matrix, which could find application as high-density data storage devices.

Magnetoplasmonic nanostructures based on nickel inverse opal slabs

Nanostructured nickel surfaces representing periodically arranged spherical voids in a nickel film are obtained by electrochemical deposition through a self-assembled opaline template. Excitation of surface plasmon-polaritons (SPPs) on the surface of the sample is experimentally observed as the Wood’s anomaly in the reflectance spectra. Transversal magneto-optical Kerr effect (TMOKE) spectra are measured at the different angles of incidence and azimuthal angles. The two- to-threefold enhancement of TMOKE caused by the excitation of mixed plasmons in two selected azimuthal configurations is observed.

IRON-CONTAINING NANOCOMPOSITES BASED ON ZSM-5 ZEOLITE

Here we report synthesis and investigation of Fe/ZSM-5 magnetic nanocomposites. Intercalation of iron was performed by ion-exchange procedure and by impregnation of ZSM-5 zeolite in H+ form by Fe(CO)5. Magnetic nanocomposites were prepared by thermal treatment of impregnated samples in hydrogen flow at different temperatures. Chemical composition, structure and physical properties of the samples were characterized by chemical analysis, TGA, XRD, TEM, Mossbauer spectroscopy and SQUID magnetization measurements. Nanocomposites prepared by reduction of cation-exchanged zeolite indicate paramagnetic behavior even at 4 K. Repeatable ion-exchange/reduction procedure used to enrich ZSM-5 matrix with iron led to formation of bulk iron. Fe/ZSM-5 nanocomposites prepared by thermal decomposition of Fe(CO)5 in the channels of ZSM matrix reveal their ferromagnetic behavior even at room temperature. The coercivity at 300 K for annealed samples attain 670 Oe for the crystallization temperature of 450°C. According XRD, TEM and Mossbauer data iron nanoparticles were formed in the cavities of zeolite.

Optical properties of γ-ferric oxide nanoparticles in a mesoporous silica matrix

Magnetic γ-Fe2O3/SiO2 nanocomposites have been synthesized by impregnating a mesoporous silica matrix with a hexane solution of γ-ferric oxide nanoparticles. The subsequent heat treatment of samples in the course of synthesis influences the optical properties of the final nanostructural material. It is established that an increase in the temperature of annealing (crystallization) leads to a decrease in the energies of both direct and indirect allowed electron transitions to the conduction band.

Environmental control of electron-phonon coupling in barium doped graphene

Two-dimensional superconductivity in alkali- and alkaline-Earth-metal doped monolayer graphene has been explained in the framework of electron–phonon coupling (EPC) and experiments yielded superconducting transition temperatures (T C ) up to 6 K. In contrast to bulk graphite intercalation compounds, the interface of doped graphene with its environment affects its physical properties. Here we present a novel and well-defined BaC8 interface structure in Ba-doped single-layer graphene on Au and Ge substrates. We use angle-resolved photoemission spectroscopy in combination with ab initio modelling to extract the Eliashberg function and EPC for both substrates. This allows us to quantitatively assess the environmental effects for both Au and Ge substrates on superconductivity in graphene. We show that for semiconducting Ge substrates, the doping level and EPC are higher. Our study highlights that both dopant order and the metallicity of the substrate can be used to control EPC and hence superconductivity.

HRTEM of 1DSnTe@SWNT nanocomposite located on thin layers of graphite

The method for imaging of highly sensitive nanostructures unstable under electron beam irradiation is introduced. To reduce charge and thermally generated beam damage, highly conductive multilayered graphene or thin graphite layers were used as supports for nanostructures. Well‐defined crystalline structure of graphite layers enables image reconstruction by Fourier filtering and allows maintaining high quality of images. The approach was tested for imaging of highly sensitive quasi one‐dimensional SnTe nanocrystals hosted inside single‐walled carbon nanotubes. Relying on the filtered images and the image simulation, the structure of one‐dimensional SnTe was established as a chain of fcc NaCl type unit cells, connected by the [001] edges with <110> direction coinciding with nanotube axis.

Stability of Tetragonal ZrO2 toward External Influences

The response of the nonequilibrium phase T-ZrO2 to various physicochemical influences was studied by x-ray diffraction analysis. The results indicate a significant sensitivity of the T-ZrO2 → M-ZrO2 phase transition to some of the influences: pressing at elevated temperatures (100–250°C) accelerates the formation of the equilibrium phase, whereas Al2O3 additions notably slow down the process (stabilize the metastable phaseT-ZrO2). Mechanochemical treatment and freezing at 77 K have no effect on the character of the phase transition.

Atomically precise semiconductor--graphene and hBN interfaces by Ge intercalation.

The full exploration of the potential, which graphene offers to nanoelectronics requires its integration into semiconductor technology. So far the real-world applications are limited by the ability to concomitantly achieve large single-crystalline domains on dielectrics and semiconductors and to tailor the interfaces between them. Here we show a new direct bottom-up method for the fabrication of high-quality atomically precise interfaces between 2D materials, like graphene and hexagonal boron nitride (hBN), and classical semiconductor via Ge intercalation. Using angle-resolved photoemission spectroscopy and complementary DFT modelling we observed for the first time that epitaxially grown graphene with the Ge monolayer underneath demonstrates Dirac Fermions unaffected by the substrate as well as an unperturbed electronic band structure of hBN. This approach provides the intrinsic relativistic 2D electron gas towards integration in semiconductor technology. Hence, these new interfaces are a promising path for the integration of graphene and hBN into state-of-the-art semiconductor technology.

The structure and continuous stoichiometry change of 1DTbBrx@SWCNTs

HRTEM and HAADF STEM of 1DTbBrx@SWCNT meta‐nanotubes reveal three structural modifications of 1D nanocrystals within single wall carbon nanotube channels attributed to a different stoichiometry of the guest crystal. For SWCNTs with diameters Dm > 1.4 nm a most complete tetragonal unit cell is observed. When crystallization occurs inside SWCNT with Dm < 1.4 nm 1D TbBrx crystal deforms a nanotube to elliptical shape in cross section. In this case the 1D crystal unit cell becomes monoclinic, with possible loss of a part of bromine atoms. Two modifications of a monoclinic unit cell appear. One of them is characterized by single or pair vacancies in the structure of the 1D crystal. Another structure is explained by peripheral and central bromine atoms loss. An appearance of such modifications can be stimulated by electron irradiation. The loss of bromine atoms is in agreement with chemical analysis data. Electronic properties of obtained meta‐nanotubes are investigated using optical absorption and Raman spectroscopy. It is shown that intercalation of terbium bromide into SWCNTs leads to acceptor doping of SWCNTs. According to local EDX analysis and elemental mapping this doping can arise from significant stoichiometry change in 1D nanocrystal indicating an average Tb:Br atomic ratio of 1:2.8 ± 0.1.

Synthesis of nanocomposites on basis of single-walled carbon nanotubes intercalated by manganese halogenides

In this work MnCl2@SWNT and MnBr2@SWNT nanocomposites were prepared via capillary filling of single-walled carbon nanotube channels by melts of manganese halogenides with slow cooling to room temperature for better crystallization. Electronic properties of MnHal2@SWNT nanocomposites have been investigated by X-ray photoelectron spectroscopy, optical absorption spectroscopy and Raman spectroscopy. It was found that the manganese halogenides show acceptor behavior and there is the charge transfer from the carbon nanotube walls to intercalated nanocrystals.