Andrey N. Baranov

Bio: Andrey N. Baranov is an academic researcher from Moscow State University. The author has contributed to research in topics: Nanorod & Cathodoluminescence. The author has an hindex of 20, co-authored 124 publications receiving 1153 citations. Previous affiliations of Andrey N. Baranov include Centre national de la recherche scientifique & Russian Academy of Sciences.

Strain relief and island shape evolution in heteroepitaxial metal growth

Abstract: Atomistic scale calculations reveal that cobalt islands on Cu~001!, as they grow in size, undergo unusual shape evolution. The strain relief in the Co islands is predicted to have a strong effect on the shape of the islands and the morphology of the substrate in the early stage of the film growth. We show that strain and stress at the interface vary strongly on an atomic scale. Our results demonstrate that the strain relief in the early stage of heteroepitaxy is more complicated than suggested by simple considerations based on the lattice mismatch of bulk materials. The classical rule used to predict heteroepitaxial growth is based on the lattice mismatch between film and substrate. 1 However, several recent experiments 2‐4 have shown that the scenario of the strain relaxation at metal interfaces is more complicated than expected from the lattice misfit. In contradiction to lattice mismatch consideration, a tremendous compressive stress in Ni on W~110! below 0.5 monolayer ~ML! was measured. 2 Also, for Fe, Co, and Cu on W~110! compressive stress was found, while tensile stress is expected from mismatch arguments. 3 A giant compressive surface stress for the first few monolayers of silver on Pt~111! was reported, which is far beyond the stress induced by the misfit. 4 The results of stress measurements in the submonolayer range give clear evidence that continuum elasticity relying on bulk reference data is of questionable relevance for films thinner than 10 A. 2 Ab initio studies have shown that for very thin cobalt films the comparison of the bulk lattice parameters of the two materials is inappropriate to study strained Co layers on Cu~001!. 5

2.7–3.9 μm InAsSb(P)/InAsSbP low threshold diode lasers

Abstract: Lasing has been obtained in the wavelength range 2.7–3.9 μm in double heterostructure diode lasers with an active region made of InAs alloys. The devices were grown by liquid‐phase epitaxy. Typical values of threshold current at 80 K were as low as 40 mA and the maximum operating temperature was 180 K. The blue shift of lasing modes was observed with current. This was explained by the increase of the carrier density in the active region above threshold due to intervalence band absorption.

Resistive Switching in Al/Graphene Oxide/Al Structure

Abstract: We report resistive switching behaviors in an Al/graphene oxide/Al planar structure. Graphene oxide was synthesized by a modified Hummer's method from graphite rods. The planar structures were fabricated on a Si/SiO2 substrate by spin-coating graphene oxide suspensions and patterning Al electrodes by photolithography. Both diode-like (rectifying) and resistor-like (nonrectifying) behaviors were observed in the device switching characteristics. Electrical characterization of the Al/graphene oxide interface using the induced current identified a potential barrier near the interface and its spatial modulation, caused by local changes of resistance at a bias voltage, which correlated well with the resistive switching of the whole structure. The mechanism of the observed local resistance changes near the electrode and the associated resistive switching of the entire structure is associated with the electrodiffusion of oxygen and the formation of sp2 graphene clusters in an sp3 insulating graphene oxide layer formed near the electrode by a pre-forming process.

Unusual x-ray excited luminescence spectra of NiO suggest self-trapping of the d - d charge-transfer exciton

Abstract: Luminescence spectra of NiO have been investigated under vacuum ultraviolet (VUV) and soft X-ray (XUV) excitation. Photoluminescence (PL) spectra show broad emission bands centered at about 2.3 and 3.2 eV. The PL excitation (PLE) spectral evolution and lifetime measurements reveal that two mechanisms with short and long decay times, attributed to the d($e_g$)-d($e_g$) and p($\pi$)-d charge transfer (CT) transitions in the range 4-6\,eV, respectively, are responsible for the observed emissions, while the most intensive p($\sigma$)-d CT transition at 7\,eV appears to be a weak if any PL excitation mechanism. The PLE spectra recorded in the 4-7\,eV range agree with the RIXS and reflectance data. Making use of the XUV excitation allows us to avoid the predominant role of the surface effects in luminescence and reveal bulk luminescence with puzzling well isolated doublet of very narrow lines with close energies near 3.3\,eV characteristic for recombination transitions in self-trapped \emph{d}-\emph{d} CT excitons formed by coupled Jahn-Teller Ni$^+$ and Ni$^{3+}$ centers. This conclusion is supported both by a comparative analysis of the luminescence spectra for NiO and solid solutions Ni$_{x}$Zn$_{1-x}$O, and by a comprehensive cluster model assignement of different \emph{p}-\emph{d} and \emph{d}-\emph{d} CT transitions, their relaxation channels. To the best of our knowledge it is the first observation of the self-trapping for \emph{d}-\emph{d} CT excitons. Our paper shows the time resolved luminescence measurements provide an instructive tool for elucidation of the \emph{p}-\emph{d} and \emph{d}-\emph{d} CT excitations and their relaxation in 3d oxides.

Band parameters for III–V compound semiconductors and their alloys

Abstract: We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

Enhancing solar cell efficiency: the search for luminescent materials as spectral converters

Abstract: Photovoltaic (PV) technologies for solar energy conversion represent promising routes to green and renewable energy generation. Despite relevant PV technologies being available for more than half a century, the production of solar energy remains costly, largely owing to low power conversion efficiencies of solar cells. The main difficulty in improving the efficiency of PV energy conversion lies in the spectral mismatch between the energy distribution of photons in the incident solar spectrum and the bandgap of a semiconductor material. In recent years, luminescent materials, which are capable of converting a broad spectrum of light into photons of a particular wavelength, have been synthesized and used to minimize the losses in the solar-cell-based energy conversion process. In this review, we will survey recent progress in the development of spectral converters, with a particular emphasis on lanthanide-based upconversion, quantum-cutting and down-shifting materials, for PV applications. In addition, we will also present technical challenges that arise in developing cost-effective high-performance solar cells based on these luminescent materials.

Challenges and Prospects in Solar Water Splitting and CO2 Reduction with Inorganic and Hybrid Nanostructures

Abstract: The inexorable rise of carbon dioxide level in the atmosphere, already exceeding 400 ppm, highlights the need for reduction of CO2 emissions. Harvesting solar energy to drive reverse chemical reactions to fuel combustion offers a possible solution. The produced chemical fuels (e.g. hydrogen, methane, or methanol) are also a convenient means of energy storage, not available in photovoltaic cells. This Review is focused on the heterogeneous photocatalytic water splitting and on CO2 reduction with nanostructured semiconductors, metals, and their hybrids. The stages of light absorption, charge separation and transfer, and surface reactions are discussed, together with possible energy-loss mechanisms and means of their elimination. Many novel materials have been developed in this active field of research, and this Review describes the concepts underpinning the continued progress in the field. The approaches which hold promise for substantial improvement in terms of efficiency, cost, and environmental sustainab...

Carbon Coated ZnFe2O4 Nanoparticles for Advanced Lithium‐Ion Anodes

Abstract: The preparation and electrochemical characterization of a new material consisting of carbon coated ZnFe2O4 nanoparticles is presented. This material, which offers an interesting combination of alloying and conversion mechanisms, is capable of hosting up to nine equivalents of lithium per unit formula, corresponding to an exceptional specific capacity, higher than 1000 mAh g−1. Composite electrodes of such a material, prepared using environmentally friendly sodium carboxymethyl cellulose as binder, showed the highest, ever reported, specific capacity and high rate performance upon long-term testing. Furthermore, in situ X-ray diffraction analysis allowed identifying the reduction process occurring upon initial lithiation.