Engineering topics

Pavlov, V. V.

Publications and source records attributed to Pavlov, V. V..

4 records

DOE OSTI2018

Photocharging Dynamics in Colloidal CdS Quantum Dots Visualized by Electron Spin Coherence

We use a time-resolved technique with three laser pulses (pump, orientation and probe) to study the photocharging dynamics with picosecond resolution on a long timescale ranging from ps to ms in CdS colloidal quantum dots. The detection is based on measuring the coherent spin dynamics of electrons, allowing us to distinguish the type of carrier in the dot core (electron or hole). We find that although initially negative photocharging happens because of fast hole trapping on surface states, eventually it evolves to positive photocharging due to electron trapping and hole detrapping. The positive photocharging lasts up to hundreds of microseconds at room temperature.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Growth and Structural, Magnetic, and Magnetooptical Properties of ZnO Films Doped with a Fe{sup 57} 3d Impurity

ZnO films obtained by high-frequency magnetron sputtering and doped with a Fe{sup 57} metallic 3d impurity by the diffusion method are studied. The type of local environment of Fe{sup 57} impurity atoms on varying the deposition parameters of ZnO films is determined by Mössbauer spectroscopy. It is established that the ground state of Fe{sup 57} impurity atoms corresponds to metallic iron in the magnetically ordered state and there is a small fraction of Fe{sup 57} atoms with a local environment corresponding to the complex oxide Fe{sub 3}O{sub 4}, having the magnetically ordered state; there is also a fraction of iron atoms in the paramagnetic state. The magnetic and magnetooptical parameters of the films were measured using magnetooptic Kerr effect. The spectral dependences of the polar magnetooptic Kerr effect in ZnO(Fe{sup 57}) films are measured in a photon energy range of 1.5–4.5 eV and simulated by the effective-medium method. It is established that ZnO(Fe{sup 57}) possess an easy-plane magnetic anisotropy with a magnetization lying in the film plane.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2015

Room-temperature ferromagnetism in cerium dioxide powders

Room-temperature ferromagnetism is detected in a CeO{sub 2} powder with a grain size of about 35 nm and a low (<0.1 at %) manganese and iron content. The ferromagnetism in a CeO{sub 2} sample with a submicron crystallite size and the same manganese and iron impurity content is lower than in the nanocrystalline sample by an order of magnitude. Apart from ferromagnetism, both samples exhibit EPR spectra of localized paramagnetic centers, the concentration of which is lower than 0.01 at %. A comparative analysis of these results shows that the F-center exchange (FCE) mechanism cannot cause ferromagnetism. This conclusion agrees with the charge-transfer ferromagnetism model proposed recently.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1977

Ergatic dynamic control systems

Synthesis and analysis of systems containing a man in their control circuits are considered. The concepts of ergonomics and ergatic systems are defined, and tasks and problems of ergonomics are outlined. The synthesis of the structure of an astronautic ergatic organism is presented, as well as the synthesis of nonstationary ergatic systems. Problems of selecting the criteria for complex systems are considered, and the results are presented from a study of ergatic control systems with any degree of human participation.

Pavlov, V. V.↗