V. M. Fomin

Superfast motion of catalytic microjet engines at physiological temperature.

There is a great interest in reducing the toxicity of the fuel used to self-propel artificial nanomachines. Therefore, a method to increase the efficiency of the conversion of chemicals into mechanical energy is desired. Here, we employed temperature control to increase the efficiency of microjet engines while simultaneously reducing the amount of peroxide fuel needed. At physiological temperatures, i.e. 37 °C, only 0.25% H(2)O(2) is needed to propel the microjets at 140 μm s(-1), which corresponds to three body lengths per second. In addition, at 5% H(2)O(2), the microjets acquire superfast speeds, reaching 10 mm s(-1). The dynamics of motion is altered when the speed is increased; i.e., the motion deviates from linear to curvilinear trajectories. The observations are modeled empirically.

Atomic-scale structure of self-assembled In(Ga)As quantum rings in GaAs

We present an atomic-scale analysis of the indium distribution of self-assembled In(Ga)As quantum rings (QRs) which are formed from InAs quantum dots by capping with a thin layer of GaAs and subsequent annealing. We find that the size and shape of QRs as observed by cross-sectional scanning tunneling microscopy (X-STM) deviate substantially from the ring-shaped islands as observed by atomic force microscopy on the surface of uncapped QR structures. We show unambiguously that X-STM images the remaining quantum dot material whereas the AFM images the erupted quantum dot material. The remaining dot material shows an asymmetric indium-rich crater-like shape with a depression rather than an opening at the center and is responsible for the observed electronic properties of QR structures. These quantum craters have an indium concentration of about 55% and a diameter of about 20nm which is consistent with the observed electronic radius of QR structures.

Photoluminescence of spherical quantum dots

In order to interpret the phonon-assisted optical transitions in semiconductor quantum dots, a theory is developed comprising the exciton interaction with both adiabatic and Jahn-Teller phonons and also the external nonadiabaticity (pseudo-Jahn-Teller effect). The effects of nonadiabaticity of the exciton-phonon system are shown to lead to a significant enhancement of phonon-assisted transition probabilities and to multiphonon optical spectra that are considerably different from the Franck-Condon progression. The calculated relative intensity of the phonon satellites and its temperature dependence compare well with the experimental data on the photoluminescence of CdSe quantum dots, both colloidal and embedded in glass.

Theory of electron energy spectrum and Aharonov-Bohm effect in self-assembled Inx Ga1-x As quantum rings in GaAs

We analyze theoretically the electron energy spectrum and the magnetization of an electron in a strained

Photoluminescence of Tetrahedral Quantum-Dot Quantum Wells

{\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}∕\mathrm{Ga}\mathrm{As}

Multiphonon Raman scattering in semiconductor nanocrystals: importance of nonadiabatic transitions

self-assembled quantum ring (SAQR) with realistic parameters, determined from the cross-sectional scanning-tunneling microscopy characterization of that nanostructure. The SAQRs have an asymmetric indium-rich craterlike shape with a depression rather than an opening at the center. Although the real SAQR shape differs strongly from an idealized circular-symmetric open ring structure, the Aharonov-Bohm oscillations of the magnetization survive.

ELECTRONIC STRUCTURE AND PHONON-ASSISTED LUMINESCENCE IN SELF-ASSEMBLED QUANTUM DOTS

Taking into account the tetrahedral shape of a quantum-dot quantum well (QDQW) when describing excitonic states, phonon modes, and the exciton-phonon interaction in the structure, we obtain within a nonadiabatic approach a quantitative interpretation of the photoluminescence spectrum of a single CdS/HgS/CdS QDQW. We find that the exciton ground state in a tetrahedral QDQW is bright, in contrast to the dark ground state for a spherical QDQW. The position of the phonon peaks in the photoluminescence spectrum is attributed to interface optical phonons. We also show that the experimental value of the Huang-Rhys parameter can be obtained only within the nonadiabatic theory of phonon-assisted transitions.

On the superconducting phase boundary for a mesoscopic square loop

Multi-phonon Raman scattering in semiconductor nanocrystals is treated taking into account both adiabatic and non-adiabatic phonon-assisted optical transitions. Because phonons of various symmetries are involved in scattering processes, there is a considerable enhancement of intensities of multi-phonon peaks in nanocrystal Raman spectra. Cases of strong and weak band mix- ing are considered in detail. In the first case, fundamental scattering takes place via internal electron-hole states and is participated by s- and d-phonons, while in the second case, when the intensity of the one-phonon Raman peak is strongly influenced by the interaction of an electron and of a hole with in- terface imperfections (e. g., with trapped charge), p-phonons are most active. Calculations of Raman scattering spectra for CdSe and PbS nanocrystals give a good quantitative agreement with recent experimental results.

Electron and hole states in quantum dot quantum wells within a spherical eight-band model

We present photoluminescence (PL) measurements on an ensemble of InAs/GaAs self-assembled quantum dots embedded in GaAs. We observe a transition from an inhomogeneously broadened photoluminescence band under non-resonant excitation into up to five phonon-assisted bands under selective excitation. We interpret the phonon-assisted PL as being indicative of an enhanced electron–phonon interaction. We also perform theoretical calculations of the single-particle energy spectrum of self-assembled quantum dots, in the framework of the single-band effective-mass approximation for electrons and using the Luttinger Hamiltonian for holes. Finally, by taking advantage of the computed wave functions we evaluate the Huang-Rhys parameter: We find an enhancement of the electron–phonon interaction that partially accounts for the experimental results.

Bipolaron binding in quantum wires

Abstract A self-consistent solution of the Ginzburg-Landau equations for a mesoscopic superconducting square loop has been obtained. It has been shown that the inhomogeneous distribution of the amplitude of the order parameter inside the loop leads to the appearance of certain areas where it is much more difficult to rotate the superconducting condensate and which therefore sustain much higher applied magnetic fields. The interplay between the square symmetry of the loop and the cylindrical symmetry of the magnetic field results in different oscillatory superconducting phase boundaries which correspond to various phase boundary definitions. The most “realistic” criterion to define the phase boundary magnetic field( H )-temperature( T ) is formulated; it allows to obtain a good agreement between the calculated H ( T ) curve and the experimentally observed one.