V. E. Kan

Formation mechanisms of nanocomposite layers based on multiwalled carbon nanotubes and non-stoichiometric tin oxide

Nanocomposite layers based on multiwalled carbon nanotubes (MWCNTs) and non-stoichiometric tin oxide (SnOx) have been grown by magnetron deposition and CVD methods. In the case of the CVD method, the study of the structure and phase composition of obtained nanocomposite layers has shown that a tin oxide “superlattice” is formed in the MWCNT layer volume, fixed by SnOx islands on the MWCNT surface. During magnetron deposition, the MWCNT surface is uniformly coated with tin oxide islands, which causes a change in properties of individual nanotubes. Electrical measurements have revealed the sensitivity of nanocomposite layers to (NO2)− molecule adsorption, which is qualitatively explained by a change in the conductivity of the semiconductor fraction of p-type MWCNTs.

Fabrication of por-Si/SnOx nanocomposite layers for gas microsensors and nanosensors

Two-phase nanocomposite layers based on porous silicon and nonstoichiometric tin oxide were fabricated by various methods. The structure, as well as elemental and phase composition, of the obtained nanocomposites were studied using transmission and scanning electron microscopy, Raman spectroscopy, Auger electron spectroscopy, and X-ray photoelectron spectroscopy. The results obtained confirm the formation of nanocomposite layers with a thickness as large as 2 μm thick and SnOx stoichiometry coefficients x = 1.0–2.0. Significant tin diffusion into the porous silicon matrix with Deff ≈ 10−14 cm2 s−1 was observed upon annealing at 770 K. Test sensor structures based on por-Si/SnOx nanocomposite layers grown by magnetron deposition showed fairly high stability of properties and sensitivity to NO2.

An observation of the radial breathing mode in the Raman spectra of CVD-grown multi-wall carbon nanotubes

Abstract MWCNTs grown by chemical vapor deposition on SiO 2 /Si substrates were investigated by Raman spectroscopy, transmission electron microscopy (TEM), Auger spectroscopy, and X-ray photoelectron spectroscopy before and after an annealing at 390 °C for 120 min in air or chemical treatment with a HCl solution. The Raman spectroscopy was focused on the low-frequency (250-300 cm −1 ) band. It is found that the positions and full widths at half maximum of the peaks forming the 250-300 cm −1 Raman band change little with the annealing or chemical treatment. The measured inner diameters of small-diameter CNTs from TEM agree well with those from Raman spectroscopy. These indicate that the low-frequency band originates from the radial breathing oscillations of carbon atoms in the inner walls of small-diameter MWCNTs.

Carbon deposits on a resistive FeCrAl catalyst for the suboxidative pyrolysis of methane

The carbon deposits forming upon the suboxidative pyrolysis of methane on resistive FeCrAl catalysts heated with electric current were studied. The suboxidative pyrolysis of methane was carried out in a flow reactor at the ratio CH4: O2 = 15: 1 in a catalyst-coil temperature range of 600–1200°C; a cold reaction mixture (∼20°C) was supplied. The morphology and structure of the carbon deposits and changes in the composition and structure of the catalyst were characterized by scanning electron microscopy, transmission electron microscopy with EDX analysis, Raman spectroscopy, and X-ray diffraction analysis. Various forms of carbon deposits, including branched nanotubes, and metal carbides formed by catalyst constituents were detected. It was found that the carbon deposits on the catalyst surface were morphologically different from the deposits on quartz reactor walls. The reasons for these differences were considered.

Origin of the low-frequency band in Raman spectra of multi-walled carbon nanotubes synthesized by the CVD method

The origin of the low-frequency band (250–300 cm−1) in the Raman spectra of multi-walled carbon nanotubes (MWCNTs) produced by the CVD method has been studied. The studies performed by Raman spectroscopy, transmission electron microscopy, Auger spectroscopy, and X-ray photoelectron spectroscopy after chemical and thermal treatments allow the assumption that this band belongs to radial vibrations of carbon atoms in internal walls of MWCNTs.

Effect of the catalyst on structural and electrophysical characteristics of the layers of nitrogen-containing carbon nanotubes obtained by gas phase synthesis

The morphological, structural, and electrophysical properties of the layers of nitrogen-containing carbon nanotubes synthesized by pyrolysis of acetonitrile on a silicon oxide-silicon substrate with a Ni layer catalyst, Fe volumetric catalyst obtained by the thermal decomposition of ferrocene ((C5H5)2Fe), and their combination were studied. It was found that the type of catalyst affects the morphology, thickness, homogeneity, structure, and defect content of the obtained films and individual nanotubes. The electrophysical characteristics of the carbon nanotubes are similar and have an activation dependence on temperature.

Study of the interaction mechanisms between absorbed NO 2 and por -Si/SnO x nanocomposite layers

The interaction mechanisms between NO2 molecules and the surface of por-Si/SnOx nanocomposites obtained by magnetron deposition and chemical vapor deposition (CVD) are studied by infrared absorption spectroscopy and electron paramagnetic resonance methods. The observed increase in the free carrier concentration in the por-Si/SnOx nanocomposite layers is explained by a change in the charge state of Pb centers due to the formation of neutral “surface defect-adsorbed NO2 molecule” complexes with free carrier generation in the crystallite bulk. In the nanocomposite layers grown by the CVD method, the increase in the free hole concentration during NO2 adsorption is much less pronounced in comparison with the composite grown by magnetron deposition, which is caused by the competing interaction channel of NO2 molecules with electrically neutral Pb centers.

Adsorption of hemoglobin molecules on porous silicon

It is established that hemoglobin can be immobilized in pores and on the surface of porous silicon. This is confirmed by the data of atomic force microscopy and Fourier-transform IR spectroscopy.

Formation and properties of the buried isolating silicon-dioxide layer in double-layer “porous silicon-on-insulator” structures

The oxidation of mesoporous silicon in a double-layer “macroporous silicon–mesoporous silicon” structure is studied. The morphology and dielectric properties of the buried insulating layer are investigated using electron microscopy, ellipsometry, and electrical measurements. Specific defects (so-called spikes) are revealed between the oxidized macropore walls in macroporous silicon and the oxidation crossing fronts in mesoporous silicon. It is found that, at an initial porosity of mesoporous silicon of 60%, three-stage thermal oxidation leads to the formation of buried silicon-dioxide layers with an electric-field breakdown strength of Ebr ~ 104–105 V/cm. Multilayered “porous silicon-on-insulator” structures are shown to be promising for integrated chemical micro- and nanosensors.