Production of Gas Phase Zinc Oxide Nanoclusters by Pulsed Laser Ablation

We present experimental results on the photoluminescence (PL) of gas-suspended zinc oxide nanoclusters prepared during ablation of sintered ZnO targets by a pulsed ArF laser in the presence of oxygen ambient gas. The PL spectra in the UV spectral region correspond to the exciton recombination in the nanoclusters which are crystallized and cooled down to the temperature of the ambient gas in the ablation chamber. The time evolution of the spectra as well as their dependence on the ambient gas pressure are discussed.Comment: EMRS-2004, Strasbourg, France. Paper N-I.

Establishing the fundamental magnetic interactions in the chiral skyrmionic Mott insulator Cu2OSeO3 by terahertz electron spin resonance

The recent discovery of skyrmions in Cu$_2$OSeO$_3$ has established a new platform to create and manipulate skyrmionic spin textures. We use high-field electron spin resonance (ESR) spectroscopy combining a terahertz free electron laser and pulsed magnetic fields up to 64 T to probe and quantify its microscopic spin-spin interactions. Besides providing direct access to the long-wavelength Goldstone mode, this technique probes also the high-energy part of the excitation spectrum which is inaccessible by standard low-frequency ESR. Fitting the behavior of the observed modes in magnetic field to a theoretical framework establishes experimentally that the fundamental magnetic building blocks of this skyrmionic magnet are rigid, highly entangled and weakly coupled tetrahedra.Comment: 5 pages, 3 Figure

Silicon clusters produced by femtosecond laser ablation: Non-thermal emission and gas-phase condensation

Neutral silicon clusters Si_n (up to n = 7) and their cations Si_n+ (up to n = 10) have been produced by femtosecond laser ablation of bulk silicon in vacuum and investigated using time-of-flight mass spectrometry. Two populations of the Si_n+ clusters with different velocity and abundance distributions in the ablation plume have been clearly distinguished. Possible mechanisms of cluster formation (Coulomb explosion, gas-phase condensation, phase explosion) are discussed

Enhancement of Exciton Emission from Zno Nanocrystalline Films by Pulsed Laser Annealing

Pulsed ArF laser annealing in air and in hydrogen atmosphere improves the optical properties of ZnO nanostructured films. Independently on the ambient atmosphere, laser annealing produces two major effects on the photoluminescence (PL) spectra: first, the efficiency of the exciton PL increases due to decrease of the number of non-radiative recombination centers; second, the intensity of the defect-related orange band decreases because of the removing of excessive oxygen trapped into the films during deposition. However, annealing in the ambient air also increases the intensity of the green band related to oxygen vacancies. We show that the combination of laser annealing and passivation of oxygen vacancies by hydrogen results in films free of defect-related emission and keeps intact their nanostructural character

A graphene electron lens

International audienceAn epitaxial layer of graphene was grown on a pre patterned 6H-SiC(0001) crystal. The graphene smoothly covers the hexagonal nano-holes in the substrate without the introduction of small angle grain boundaries or dislocations. This is achieved by an elastic deformation of the graphene by ~0.3% in accordance to its large elastic strain limit. This elastic stretching of the graphene leads to a modification of the band structure and to a local lowering of the electron group velocity of the graphene. We propose to use this effect to focus two-dimensional electrons in analogy to simple optical lenses

Strange Exotic States and Compact Stars

We discuss the possible appearance of strange exotic multi-quark states in the interior of neutron stars and signals for the existence of strange quark matter in the core of compact stars. We show how the in-medium properties of possible pentaquark states are constrained by pulsar mass measurements. The possibility of generating the observed large pulsar kick velocities by asymmetric emission of neutrinos from strange quark matter in magnetic fields is outlined.Comment: 10 pages, invited talk given at the International Conference on Strangeness in Quark Matter 2006 (SQM2006), UCLA, USA, March 26-31, 2006, Journal of Physics G in press, refs. adde

Comparative analysis of the organization of medical care in the terrorist attack on Dubrovka and Beslan

The article discusses the features of medical care in emergency situations. The most important aspects of first aid are investigated. The author analyzes statistical data from previous years and considers the most important points for reducing losses and complications among the child population. A comparative description of erroneous actions in organizing assistance in a terrorist attack in a theater center during the musical “Nord-Ost” on Dubrovka and Beslan is carried out.В статье описаны особенности оказания медицинской помощи в чрезвычайных ситуациях. Исследуются наиболее важные аспекты первой помощи. Авторами анализируются статистические данные прошлых лет и обсуждаются наиболее значимые моменты с целью понижения потерь и осложнений среди населения. Проведена сравнительная характеристика ошибочных действий при организации помощи при теракте в театральном центре во время мюзикла “Норд-Ост” на Дубровке и в Беслане

CHOICE OF CONDITIONS FOR GAS OUTFLOW IN VACUUM AND CONFIGURATIONS OF A FORMING UNIT FEEDING A WORKING SUBSTANCE INTO THE PLASMA VOLUME

The paper presents formulated requirements to the gas-dynamic device designed for working substance feeding into the ionization zone of plasmas facilities. The role of geometrical factors in formation of a supersonic flow is determined, as well as, the role of gasdynamic factors in attainment of necessary parameters beyond the forming element. The conditions for gas-dynamic flow clustering minimization in the course of outflow in vacuum