Raman studies of phase and atomic compositions of GeSi nanosystems after pulsed annealing

The phase and elemental compositions of GeSi heterostructures deposited on non-refractory substrates are analyzed by using a non-destructive express technique, i.e., the Raman spectroscopy. It is shown that application of pulsed laser annealing allows one to vary the elemental composition and size of nanocrystals formed from solid alloys of germanium and silicon.     

A mechanism of current noise reduction in systems of ion beam formation from vacuum arc plasma

The influence of a residual gas plasma on the ion beam transport in the drift chamber of an ion source based on the vacuum arc discharge was numerically simulated by the pellet injection method. The plasma formed as a result of ionization of the residual gas causes a change in the potential profile in the drift chamber. This leads to the appearance of an extended slow ion transport zone (occurring at a virtual anode potential) and to a change in the mechanism of suppression of the ion current noise as compared to the well-known mechanism operative in an equipotential vacuum gap. The results of model calculations show that the modified mechanism is related to a spatial redistribution of the density of ions (in the beam characterized by a certain scatter of velocities) in the slow ion transport zone.     

Initial stage of gas discharge in an inhomogeneous electric field

A model of the initial stage of gas discharge has been developed within the framework of the particle in cell (PIC) method, with allowance for the space charge and particle collisions described using the Monte Carlo (MC) numerical simulation technique. The PIC/MC simulations of the initial stage of discharge under conditions of the electric field strength to gas pressure ratio E/P > 1 kV/(cm Torr) showed that a beam of runaway electrons is formed within ∼10 ps near the cathode, which consists of both emitted electrons and those generated as a result of the gas ionization. The duration of the beam pulse is determined primarily by plasma screening of the external electric field near the cathode and amounts to 10–20 ps.     

Formation and study of <Emphasis Type="Italic">p–i–n</Emphasis> structures based on two-phase hydrogenated silicon with a germanium layer in the <Emphasis Type="Italic">i</Emphasis>-type region

Four pairs of p–i–n structures based on polymorphous Si:H (pm-Si:H) are fabricated by the method of plasma-enhanced chemical vapor deposition. The structures in each pair are grown on the same substrate so that one of them does not contain Ge in the i-type layer while the other structure contains Ge deposited by molecular-beam epitaxy as a layer with a thickness of 10 nm. The pair differ from one another in terms of the substrate temperature during Ge deposition; these temperatures are 300, 350, 400, and 450°C. The data of electron microscopy show that the structures formed at 300°C contain Ge nanocrystals (nc-Ge) nucleated at nanocrystalline inclusions at the pm-Si:H surface. The nc-Ge concentration increases as the temperature is raised. The study of the current–voltage characteristics show that the presence of Ge in the i-type layer decreases the density of the short-circuit current in p–i–n structures when they are used as solar cells, whereas these layers give rise to an increase in current at a reverse bias under illumination. The obtained results are consistent with known data for structures with Ge clusters in Si; according to these data, Ge clusters increase the coefficient of light absorption but they also increase the rate of charge-carrier recombination.     

Formation and structural features of silicon quantum dots in germanium

The formation of Si quantum dots on Ge is studied. Fundamental differences were found between the nucleation and growth of quantum dots on substrates with different orientations, related to both the formation of a SiGe solid solution layer and the shape of quantum dots. The temperature interval of formation of Si nanocrystals on Ge (111) is determined. It is shown that a change in the epitaxy temperature from 480 to 400 °C increases the silicon content in quantum dots from 58 to 75%. The effect of surfactants (in particular, hydrogen) on the nucleation and growth of silicon nanoislands is analyzed, showing that the use of hydrogen as a surfactant leads to a decrease in the size of quantum dots and a substantial increase in their density. The observed effects are attributed to the suppression of surface diffusion of atoms in the presence of hydrogen.     

Double-Channel Electron Transport in Suspended Quantum Point Contacts with in-Plane Side Gates

Semiconductors - The conductance of a suspended quantum point contact fabricated on the basis of GaAs/AlGaAs heterostructures with a two-dimensional electron gas and equipped with side gates...     

Effect of cathode emissivity on runaway electron beam formation in gas-filled diode with inhomogeneous electric field

Mechanisms of the formation of runaway electron beams at the initial stage of breakdown in a gasfilled diode with sharply inhomogeneous electric field have been studied by numerical simulations using a specially developed PIC/MC code. It is established that a beam of runaway electrons can be generated either immediately at the cathode or at a discharge plasma boundary. The obtained dependence of the runaway electron beam current on the state of the cathode surface (emissivity) has the characteristic shape.     

Use of Statistical Analysis Methods for Estimating the Reliability of First-Year Carbon Steel and Zinc Corrosion Loss Predictions Calculated Using Dose-Response Functions

Protection of Metals and Physical Chemistry of Surfaces - The following parameters have been used to estimate the reliability of predicted first-year corrosion losses of carbon steel and zinc (...     

Ion separation with respect to charge in a beam transported via a flat gap

The transport of a beam of variously charged ions via a flat equipotential vacuum gap is theoretically described. The values of the critical beam current density are determined. The current density and the average ion charge in a beam past the gap are expressed as functions of the injected beam parameters (current density, average charge, and initial energy). Regimes featuring the effective separation of singly and doubly charged ions are found.