We report observations of acoustoelectric effects in carbon nanotubes. We excite sound in &mgr;m long ropes of single walled carbon nanotubes suspended between two metallic contacts by applying radio-frequency electric field. The sound is detected by measuring either the dc resistance of the tubes in a region of strong temperature dependence (in the vicinity of superconducting or metal-insulator transition), or their critical current. We show that, depending on the excitation power, the vibrations produce either electron heating or phase coherence breaking.

A single multiwalled carbon nanotube with an outside diameter of about 12 nm and an inside diameter of about 4 nm has been isolated in order to measure its electrical properties (resistivity, transverse magnetoresistance and temperature dependence of resistance). The semi-metallic character of the conductance of the selected nanotube is concluded from these measurements.

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Core/shell Si/SiO x nanoparticles (Si/SiO x -NP) having bright red-infrared photoluminescence were obtained by a three-stage synthesis based on the thermal disproportionation of microdispersed SiO. Transformation patterns of structure and spectroscopic properties of the material during passage through all process stages (starting from initial SiO microparticles and up to the Si/SiO x -NP sols) have been revealed by using Raman, photoluminescence and ESR spectroscopy, XPS, XRD, and electron microscopy. Thermal annealing of SiO microparticles (stage I) results in formation of amorphous-crystalline Si nanophase in the matrix of SiO 2 , as well as generation of paramagnetic P b centres with the concentration up to 4 9 10 18 particles/g. At the annealing temperature, T an [ 900°C, a rapid growth of nanocrystal sizes takes place, and, simultaneously, a rapid growth of paramagnetic P b centre concentration occurs. Elimination of SiO 2 from the annealed sample by etching in HF (stage II) stimulates further crystallization of amorphous-crystalline core, caused by stress relaxation inside the Si core when removing SiO 2 matrix. Functionalization of nanoparticle surface (stage III) allows obtaining core/shell Si/SiO x -NP with a bright red-infrared photoluminescence and their sols. Average size of the crystalline Si core increases from 4.7 to 11.1 nm when T an at the stage I rises from 350 to 1100°C. At relatively low T an = 350°C, the nanoparticles with monocrystalline Si cores are mainly formed, while at T an [ 1100°C, a large number of polycrystalline Si nanoparticles are also observed. Our TEM images have revealed the existence of monocrystalline Si nanoparticles having significantly different contrast even at comparable nanoparticle sizes. We attribute that to the formation of both bulk (with a high TEM contrast) and flat (2D) Si nanocrystals (with a low TEM contrast) in the course of SiO annealing.