R. B. Vasiliev

CuO/SnO2 thin film heterostructures as chemical sensors to H2S

Abstract CuO/SnO2 heterostructures as well as SnO2(CuO) polycrystalline films have been studied for H2S sensing. Gas sensing properties of these materials have been compared in conditions: 25–300 ppm H2S in N2 at 100–250°C. A shorter response time of the heterostructures as compared to that of the SnO2(CuO) films has been found. It is suggested that the improvement of dynamic sensor properties of SnO2/CuO heterostructures is caused by the localization of electrical barrier between CuO and SnO2 layers.

Microstructure and electrophysical properties of SnO2, ZnO and In2O3 nanocrystalline films prepared by reactive magnetron sputtering

The influence of oxygen concentration in the plasma-forming gas on the microstructure, phase composition and electrical conductivity has been investigated for SnO2, ZnO and In2O3 films grown by reactive magnetron sputtering method. The evolution of the oxide microstructure and resistivity under annealing at 400 8C was also studied. The nanocrystallite size remains unaltered for all the investigated films, while the agglomerate size varies significantly depending on the type of oxide and annealing duration. The agglomerate size growth leads to reduction of film resistance and conductivity activation energy. # 2002 Elsevier Science B.V. All rights reserved.

Effect of interdiffusion on electrical and gas sensor properties of CuO/SnO2 heterostructure

The influence of annealing on the electrical and H2S gas sensor properties of p-CuO/n-SnO2 heterostructures has been investigated. The heterostructures were prepared by magnetron sputtering technique with subsequent oxidation. The depth composition was analyzed by the secondary neutral mass-spectrometry (SNMS) method. The Sn and Cu interdiffusion coefficients at 573 K were estimated as 3×10−14 cm2 s−1 and 1×10−15 cm2 s−1, respectively. Resistance behavior and high H2S gas sensitivity are associated with the formation of a transitional layer at CuO–SnO2 interface due to interdiffusion processes.

Electroluminescence of CdSe/CdS quantum dots and the transfer of the exciton excitation energy in an organic light-emitting diode

A light emitting diode has been developed on the basis of multilayer nanostructures in which CdSe/CdS semiconductor colloidal quantum dots serve as emitters. Their absorption, photo-, and electroluminescence spectra have been obtained. The strong influence of the size effect and the density of particles in the layer on the spectral and electrophysical characteristics of the diode has been demonstrated. It has been shown that the rates of the transfer of the exciton excitation energy from organic molecules to quantum dots increase strongly even at a small increase in the radius of the core (CdSe) of a particle and depend strongly on the thickness of the shell (CdS) of the particle. The optimal arrangement of the layer of quantum dots with respect to the p-n junction has been estimated from the experimental data. The results demonstrate that the spectral characteristics and rates of the electron processes in light-emitting devices based on quantum dots incorporated into an organic matrix can be efficiently controlled.

Fluorescent immunolabeling of cancer cells by quantum dots and antibody scFv fragment

Semiconductor quantum dots (QDs) coupled with cancer-specific targeting ligands are new promising agents for fluorescent visualization of cancer cells. Human epidermal growth factor receptor 2/neu (HER2/neu), overexpressed on the surface of many cancer cells, is an important target for cancer diagnostics. Antibody scFv fragments as a targeting agent for direct delivery of fluorophores offer significant advantages over full-size antibodies due to their small size, lower cross-reactivity, and immunogenicity. We have used quantum dots linked to anti-HER2/neu 4D5 scFv antibody to label HER2/neu-overexpressing live cells. Labeling of target cells was shown to have high brightness, photostability, and specificity. The results indicate that construction based on quantum dots and scFv antibody can be successfully used for cancer cell visualization.

Surface states effect on photoluminescence of CdS colloidal nanocrystals

CdS colloidal nanocrystals with an average size of 4.5 nm and oleic acid as surfactant were studied using photoluminescence spectroscopy and time-correlated single photon counting technique at different temperatures. Observed spectra revealed three thermally activated luminescence bands at 2.15, 1.76, and 1.37 eV in addition to conventional band edge recombination of the nanocrystals. We present a kinetic model based on concept of single emitters which quantitatively describes the luminescence of the ensemble of the nanocrystals in the temperature range 10–300 K. We determined activation energies (18.2 and 8.6 meV) for transitions responsible for the luminescence. The 1.76 eV band most probably emerges from the intrinsic defects on the surface of CdS, whereas bands at 2.15 and 1.37 eV result from the influence of oleic acid bonded to the surface of the nanocrystals.

Mechanism of electronic-excitation transfer in organic light-emitting devices based on semiconductor quantum dots

The results of an experimental study of organic light-emitting diodes (LEDs) with luminescent layers based on two types of CdSe/CdS semiconductor quantum dots (QDs) with an average CdSe core diameter of 3 and 5 nm and a characteristic CdS shell thickness of 0.5 nm are presented. The dependences of the LED efficiency on the QD concentration are determined. The experimental data are used to determine the mechanism of electronic-excitation transfer from the organic matrix to the semiconductor QDs. Ways of optimizing the design of the LEDs in order to improve their efficiency are suggested on this basis.

THE BAIKAL NEUTRINO TELESCOPE — RESULTS AND PLANS

New results from the Baikal neutrino telescope NT200, based on the first 5 years of operation (1998–2003), are presented. We derive an all-flavor limit on the diffuse flux of astrophysical neutrinos between 20 TeV and 50 PeV, extract an enlarged sample of high energy muon neutrino events, and obtain limits on the flux of high energy atmospheric muons. In 2005, the upgraded telescope NT200+ will be commissioned: 3 additional distant strings with only 12 photo-multipliers each will rise the effective volume to 20 Mton at 10 PeV for this largest running neutrino telescope in the Northern hemisphere.

BAIKAL experiment: status report

We review the present status of the Baikal Neutrino Project and present the results obtained with the deep underwater neutrino telescope NT-200.We review the present status of the Baikal Neutrino Project and present the results obtained with the deep underwater neutrino telescope NT-200

Lake Baikal Neutrino Experiment: Selected Results

We review the present status of the Lake Baikal neutrino experiment and present selected physics results obtained during the consecutive stages of the stepwise upgrade of the detector: from NT-36 to NT-96. The results cover atmospheric muons, neutrino events, neutrinos of very high energy, searches for neutrino events from WIMP annihilation, searches for magnetic monopoles, and environmental studies. We also describe an air Cherenkov array developed for studying the angular resolution of NT-200.