Calculations of the Probability of Positron Trapping by a Vacancy in a Metal and the Estimation of the Vacancy Contribution to the Work Function of Electrons and Positrons

The probabilities of the localization of positrons in monovacancies of Al and Cu have been calculated as functions of the energy and temperature. The vacancy was simulated by a void with a radius equal to the radius of the Wigner—Seitz cell in the model of stable jellium. Using the Fermi—Dirac golden rule for transitions, the formula for the rate of positron trapping by a vacancy has been derived as the function of the positron energy. For the thermalized positrons, the rate of localization near the triple point proved to be, on the order of magnitude, close to the rate of annihilation. Within the framework of our previously proposed models, the contribution of vacancies to the work function of electrons and positrons has been demonstrated based on the example of Al. The physical situations where the vacancy effect can manifest have been considered.     

Piecewise parabolic negative magnetoresistance of two-dimensional electron gas with triangular antidot lattice

Extraordinary piecewise parabolic behavior of the magnetoresistance has been experimentally detected in the two-dimensional electron gas with a dense triangular lattice of antidots, where commensurability magnetoresistance oscillations are suppressed. The magnetic field range of 0–0.6 T can be divided into three wide regions, in each of which the magnetoresistance is described by parabolic dependences with high accuracy (comparable to the experimental accuracy) and the transition regions between adjacent regions are much narrower than the regions themselves. In the region corresponding to the weakest magnetic fields, the parabolic behavior becomes almost linear. The observed behavior is reproducible as the electron gas density changes, which results in a change in the resistance by more than an order of magnitude. Possible physical mechanisms responsible for the observed behavior, including so-called “memory effects,” are discussed.     

Elastic Properties of Suspended Conducting GaAs/AlGaAs Nanostructures by Means of Atomic Force Microscopy

This paper demonstrates the applicability of nanoindentation technique using atomic-force microscope cantilever for studying the elastic properties of suspended semiconductor structures on the basis of relatively thick GaAs/AlGaAs membranes in the case when their stiffness significantly exceeds that of the cantilever of atomic-force microscope, which is confirmed by the agreement between the experimentally determined values of both relative and absolute stiffness measured at different points of the investigated structure with theoretical predictions.     

Variational calculations of positron characteristics in metals

Energies of the formation of monovacancies, as well as the binding energies and work functions of quasi-free and localized positrons and positroniums have been calculated in terms of the gradient version of the density-functional method using the stable-jellium model. The calculations show that for the metals possessing negative positron work function, the presence of vacancies in the subsurface region can lead to the change in the sign of the work function. The same effect of the change in the sign of the work function of a quasi-free positron can be caused by the presence of a dielectric coating on the metal surface. Comparison with the experiment is performed.     

Electron work function and the surface tension of a metallic surface with an insulating coating

The electron work function, contact potential difference, and surface tension of elastically deformed faces of metal with an insulating coating have been calculated within the Kohn-Sham method. The calculations demonstrate the opposite deformation dependences of the electron work function and contact potential difference. An insulating coating leads to a negative change in the work function and a positive change in the contact potential difference. It is shown that the measurements of the contact potential difference of a deformed face by the Kelvin method give only the change in the value of the one-electron effective potential on the plane of a virtual image behind the surface rather than the value of the electron work function. The calculated values of the electron work function and surface tension for Al, Au, Cu, and Zn are in agreement with the results of experiments for polycrystals and first-principles calculations.