Application of the Standard Tapping Mode of an Atomic-Force Microscope for Local Investigations of the Electronic System of Carbon Nanotubes under Vacuum Conditions

Instruments and Experimental Techniques - The possibility of local investigations of the electronic system of carbon nanotubes (CNTs) at a pressure of P < 10–2 mbar is shown using the...     

Spatial kinetics in fast reactors

The analysis of the solution to the spatial nonstationary equation of neutron transport is presented by the example of a fast reactor. Experiments in spatial kinetics conducted recently at the complex of critical assemblies (fast physical stand) and computations of their data using the TIMER code (for solving the nonstationary equation in multidimensional diffusion approximation for direct and inverse problems of reactor kinetics) have shown that kinetics of fast reactors substantially differs from kinetics of thermal reactors. The difference is connected with influence of the delayed neutron spectrum on rates of the process in a fast reactor.     

Conditions for Instability of One Class of Nonlinear Nonautomomous Dynamic Systems

Consideration was given to the conditions for instability of the equilibrium states of a nonlinear nonautonomous dynamic systems obeying an ordinary vector differential equation of arbitrary order whose right-hand side satisfies the following conditions: (i) for any t 0, div 0$$ " align="middle" border="0"> almost everywhere on the set H that is a neighborhood of the equilibrium point of the system and (ii) at any point . The equilibrium states of such systems can be both stable and unstable. For one class of these systems, sufficient instability conditions were given, which enables one to carry out studies using only the information about the right-hand side of the system.     

Kinetics of interaction of HIV fusion protein (gp41) with lipid membranes studied by real-time AFM imaging

One of the most important steps in the process of viral infection is a fusion between cell membrane and virus, which is mediated by the viral envelope glycoprotein. The study of activity of the glycoprotein in the post-fusion state is important for understanding the progression of infection. Here we present a first real-time kinetic study of the activity of gp41 (the viral envelope glycoprotein of human immunodeficiency virus—HIV) and its two mutants in the post-fusion state with nanometer resolution by atomic force microscopy (AFM). Tracking the changes in the phosphatidylcholine (PC) and phosphatidylcholine–phosphatidylserine (PC:PS) membrane integrity over one hour by a set of AFM images revealed differences in the interaction of the three types of protein with zwitterionic and negatively charged membranes. A quantitative analysis of the slow kinetics of hole formation in the negatively charged lipid bilayer is presented. Specifically, analysis of the rate of roughness change for the three types of proteins suggests that they exhibit different types of kinetic behavior.     

Self-assembly routes towards creating superconducting and magnetic arrays

Using self-assembly from colloidal suspensions of polystyrene latex spheres we prepared well-ordered templates. By electrochemical deposition of magnetic and superconducting metals in the pores of such templates highly ordered magnetic and superconducting anti-dot nano-structures with 3D architectures were created. Further developments of this template preparation method allow us to obtain dot arrays and even more complicated structures. In magnetic anti-dot arrays we observe a large increase in coercive field produced by nanoscale (50–1000nm) holes. We also find the coercive field to demonstrate an oscillatory dependence on film thickness. In magnetic dot arrays we have explored the genesis of 3D magnetic vortices and determined the critical dot size. Superconducting Pb anti-dot arrays show pronounced Little-Parks oscillations in T_c and matching effects in magnetization and magnetic susceptibility. The spherical shape of the holes results in significantly reduced pinning strength as compared to standard lithographic samples. Our results demonstrate that self-assembly template methods are emerging as a viable, low cost route to prepare sub-micron structures.     

Temperature dependence of the gain of lasers based on quantum-dot arrays with an inhomogeneously broadened density of states

A model making it possible to describe analytically the temperature dependence of the optical gain and threshold current density in lasers based on quantum-dot arrays characterized by inhomogeneous broadening of the density of states is proposed. At high temperatures the dependence obtained is universal, i.e., it is determined exclusively by the broadening of the density of states, not by its specific form. Fiz. Tekh. Poluprovodn. 33, 1395–1400 (November 1999)     

Carrier heating in quantum wells under optical and current injection of electron-hole pairs

Carrier heating in GaAs/AlGaAs quantum wells (QWs) under optical interband pumping in the spontaneous-emission mode has been studied. The electron temperature was determined as a function of the pumping intensity. The effect of the electric field on the photoluminescence spectrum was examined. The change in the carrier concentration with the drive current in the spontaneous- and stimulated-emission modes in InGaAsSb/InAlGaAsSb QWs was determined from electroluminescence spectra. The rise in the temperature of hot carriers, which results in the increase in the carrier concentration with the drive current, was roughly estimated.     

Optical anisotropy of InAs quantum dots

The optical anisotropy of InAs quantum dots (QDs) synthesized in the regime of either continuous or submonolayer deposition on a singular GaAs(100) surface have been studied using polarized photoluminescence measurements. It is established that an isolated array of QDs formed in a continuous deposition regime possesses a weak (<1–2%) optical anisotropy, whereas the vertical matching (coupling) of such QDs via less than 15-nm-thick spacer layers leads to an 8% linear polarization of PL along the [0$ \bar 1 $ \bar 1 1] crystallographic direction. QDs formed in the regime of submonolayer deposition exhibit a strong (17–20%) anisotropy of emission from the ground and excited states of QDs in the same crystallographic direction.