arXiv subjects

Yevgeniy S. Puzyrev

Publications and source records attributed to Yevgeniy S. Puzyrev.

5 recordsLinked to original sources

arXiv2015

The Effect of Intrinsic Crumpling on the Mechanics of Free-Standing Graphene

Free-standing graphene is inherently crumpled in the out-of-plane direction due to dynamic flexural phonons and static wrinkling. We explore the consequences of this crumpling on the effective mechanical constants of graphene. We develop a sensitive experimental approach to probe stretching of graphene membranes under low applied stress at cryogenic to room temperatures. We find that the in-plane stiffness of graphene is between 20 and 100 N/m at room temperature, much smaller than 340 N/m (the value expected for flat graphene). Moreover, while the in-plane stiffness only increases moderately when the devices are cooled down to 10 K, it approaches 300 N/m when the aspect ratio of graphene membranes is increased. These results indicate that softening of graphene at temperatures less than 400 K is caused by static wrinkling, with only a small contribution due to flexural phonons. Together, these results explain the large variation in reported mechanical constants of graphene devices and paves the way towards controlling their mechanical properties.

cond-mat.mes-hall↗

arXiv2015

Theory of inelastic multiphonon scattering and carrier capture by defects in semiconductors. Application to capture cross sections

Inelastic scattering and carrier capture by defects in semiconductors are the primary causes of hot-electron-mediated degradation of power devices, which holds up their commercial development. At the same time, carrier capture is a major issue in the performance of solar cells and light-emitting diodes. A theory of nonradiative inelastic scattering by defects, however, is non-existent, while the the- ory for carrier capture by defects has had a long and arduous history. Here we report the construction of a comprehensive theory of inelastic scattering by defects, with carrier capture being a special case. We distinguish between capture under thermal equilibrium conditions and capture under non-equilibrium conditions, e.g., in the presence of electrical current or hot carriers where carriers undergo scattering by defects and are described by a mean free path. In the thermal-equilibrium case, capture is mediated by a non-adiabatic perturbation Hamiltonian, originally identified by Huang and Rhys and by Kubo, which is equal to linear electron-phonon coupling to first order. In the non-equilibrium case, we demonstrate that the primary capture mechanism is within the Born-Oppenheimer approximation, with coupling to the defect potential inducing Franck-Condon electronic transitions, followed by multiphonon dissipation of the transition energy, while the non-adiabatic terms are of secondary importance. We report density-functional-theory calculations of the capture cross section for a prototype defect using the Projector-Augmented-Wave which allows us to employ all-electron wavefunctions. We adopt a Monte Carlo scheme to sample multiphonon configurations and obtain converged results. The theory and the results represent a foundation upon which to build engineering-level models for hot-electron degradation of power devices and the performance of solar cells and light-emitting diodes.

cond-mat.mtrl-sci↗

arXiv2015

High On/Off Ratio Memristive Switching of Manganite-Cuprate Bilayer by Interfacial Magnetoelectricity

Memristive switching serves as the basis for a new generation of electronic devices. Memristors are two-terminal devices in which the current is turned on and off by redistributing point defects, e.g., vacancies, which is difficult to control. Memristors based on alternative mechanisms have been explored, but achieving both the high On/Off ratio and the low switching energy desirable for use in electronics remains a challenge. Here we report memristive switching in a La0.7Ca0.3MnO3/PrBa2Cu3O7 bilayer with an On/Off ratio greater than 10^3 and demonstrate that the phenomenon originates from a new type of interfacial magnetoelectricity. Using results from first-principles calculations, we show that an external electric-field induces subtle displacements of the interfacial Mn ions, which switches on/off an interfacial magnetic "dead" layer, resulting in memristive behavior for spin-polarized electron transport across the bilayer. The interfacial nature of the switching entails low energy cost about of a tenth of atto Joule for write/erase a "bit". Our results indicate new opportunities for manganite/cuprate systems and other transition-metal-oxide junctions in memristive applications.

cond-mat.str-el↗

arXiv2015

Two-dimensional nanovaristors at grain boundaries account for memristive switching in polycrystalline BiFeO3

Memristive switching in polycrystalline materials is widely attributed to the formation and rupture of conducting filaments, believed to be mediated by oxygen-vacancy redistribution. The underlying atomic-scale processes are still unknown, however, which limits device modeling and design. Here we combine experimental data with multi-scale calculations to elucidate the entire atomic-scale cycle in undoped polycrystalline BiFeO3. Conductive atomic force microscopy reveals that the grain boundaries behave like two-dimensional nanovaristors while, on the return part of the cycle, the decreasing current is through the grains. Using density-functional-theory and Monte-Carlo calculations we deduce the atomic-scale mechanism of the observed phenomena. Oxygen vacancies in non-equilibrium concentrations are initially distributed relatively uniformly, but they are swept into the grain boundaries by an increasing voltage. A critical voltage, the SET voltage, then eliminates the barrier for hopping conduction through vacancy energy levels in grain boundaries. On the return part of the cycle, the grain boundaries are again non-conductive, but the grains show nonzero conductivity by virtue of remote doping by oxygen vacancies. The RESET voltage amounts to a heat pulse that redistributes the vacancies. The realization that nanovaristors are at the heart of memristive switching in polycrystalline materials may open possibilities for novel devices and circuits.

cond-mat.mtrl-sci↗

arXiv2012

Probing charge scattering mechanisms in suspended graphene by varying its dielectric environment

Graphene with high carrier mobility μ is required both for graphene-based electronic devices and for the investigation of the fundamental properties of graphene's Dirac fermions. It is largely accepted that the mobility-limiting factor in graphene is the Coulomb scattering off of charged impurities that reside either on graphene or in the underlying substrate. This is true both for traditional graphene devices on SiO2 substrates and possibly for the recently reported high-mobility suspended and supported devices. An attractive approach to reduce such scattering is to place graphene in an environment with high static dielectric constant κ that would effectively screen the electric field due to the impurities. However, experiments so far report only a modest effect of high-κ environment on mobility. Here, we investigate the effect of the dielectric environment of graphene by studying electrical transport in multi-terminal graphene devices that are suspended in liquids with κ ranging from 1.9 to 33. For non-polar liquids (κ<5) we observe a rapid increase of μ with κ and report a record room-temperature mobility as large as ~60,000 cm2/Vs for graphene devices in anisole (κ=4.3), while in polar liquids (κ>18) we observe a drastic drop in mobility. We demonstrate that non-polar liquids enhance mobility by screening charged impurities adsorbed on graphene, while charged ions in polar liquids cause the observed mobility suppression. Furthermore, using molecular dynamics simulation we establish that scattering by out-of-plane flexural phonons, a dominant scattering mechanism in suspended graphene in vacuum at room temperature, is suppressed by the presence of liquids. We expect that our findings may provide avenues to control and reduce carrier scattering in future graphene-based electronic devices.

cond-mat.mes-hall↗