M. Jonson

Viscoelastic Acoustic Response of Layered Polymer Films at Fluid-Solid Interfaces: Continuum Mechanics Approach

We have derived the general solution of a wave equation describing the dynamics of two-layer viscoelastic polymer materials of arbitrary thickness deposited on solid (quartz) surfaces in a fluid environment. Within the Voight model of viscoelastic element, we calculate the acoustic response of the system to an applied shear stress, i.e. we find the shift of the quartz generator resonance frequency and of the dissipation factor, and show that it strongly depends on the viscous loading of the adsorbed layers and on the shear storage and loss moduli of the overlayers. These results can readily be applied to quartz crystal acoustical measurements of the viscoelasticity of polymers which conserve their shape under the shear deformations and do not flow, and layered structures such as protein films adsorbed from solution onto the surface of self-assembled monolayers.

Effect of inelastic scattering on resonant and sequential tunneling in double barrier heterostructures

We demonstrate that the current through a double barrier heterostructure is independent of whether the electron tunneling mechanism is sequential or Fabry–Perot like. For typical experimental parameters we show that inelastic scattering, which destroys the phase coherence, is an important effect that strongly reduces the probability for coherent tunneling. As a result, the tunneling will be mainly incoherent (sequential). However, in a model calculation where the degree of coherency can be varied, we find that the tunneling current does not depend on which of the two mechanisms dominate as long as the resonant energy is well defined.

Electron correlations in inversion layers

The two-dimensional electron gas (2DEG) is a widely used model for the electrons in the inversion layer of certain MOSFET devices. The sensitivity of a number of physical quantities of the 2DEG to a proper treatment of many-body effects has been examined. This was achieved by calculating the plasmon dispersion, pair correlation function, exchange and correlation energy and the self-energy at the Fermi level using three different approximations to the many-body problem, namely: (i) the RPA; (ii) the Hubbard approximation (HA); and (iii) the self-consistent STLS approximation of Singwi et al. (1968). The RPA and HA were found to be less satisfactory approximations for a 2DEG than for a 3DEG.

Quantum spin fluctuations as a source of long-range proximity effects in diffusive ferromagnet-super conductor structures

We show that quantum spin fluctuations in inhomogeneous ferromagnets drastically affect the Andreev reflection of electrons and holes at a ferromagnet-superconductor interface. As a result, a strong long-range proximity effect appears, associated with electron-hole spin-triplet correlations and persisting on a length scale typical for non-magnetic materials, but anomalously large for ferromagnets.

Exchange and correlation in inhomogeneous electron systems

Abstract An exchange-correlation functional with a nonlocal density dependence is proposed. It fulfills a sum rule stating that the exchange-correlation hole should contain on electron, atom. We have used this functional as well as an earlier proposed approximation to calculate the exchange energy of atoms. The errors in the local density approximation are reduced by an order of magnitude, indicating that these improved functionals should be very useful for more complicated systems.

Electronic superlattices in corrugated graphene

We theoretically investigate electron transport through corrugated graphene ribbons and show how the ribbon curvature leads to an electronic superlattice with a period set by the corrugation wavelength. Transport through the ribbon depends sensitively on the superlattice band structure which, in turn, strongly depends on the geometry of the deformed sheet. In particular, we find that for ribbon widths where the transverse level separation is comparable to the band edge energy, a strong current switching occurs as a function of an applied back gate voltage. Thus, artificially corrugated graphene sheets or ribbons can be used for the study of Dirac fermions in periodic potentials. Furthermore, this provides an additional design degree of freedom for graphene-based electronics.

The dynamical image potential for tunneling electrons

Abstract The exchange-correlation (XC) potential (image potential) felt by an electron tunneling from a metal through a classically forbidden region into vacuum is calculated by a Greens function technique. The resulting XC-potential reduces to the classical image potential if x, where x 2 m ω s κ and κ = {2 m ( V −ω)} 1 2 , is large. For small x dynamical corrections to the classical result become important.

Giant lasing effect in magnetic nanoconductors

We propose a new principle for a compact solid-state laser in the 1–100 THz regime. This is a frequency range where attempts to fabricate small-size lasers up to now have met severe technical problems. The proposed laser is based on a new mechanism for creating spin-flip processes in ferromagnetic conductors. The mechanism is due to the interaction of light with conduction electrons; the interaction strength, being proportional to the large exchange energy, exceeds the Zeeman interaction by orders of magnitude. On the basis of this interaction, a giant lasing effect is predicted in a system where a population inversion has been created by tunneling injection of spin-polarized electrons from one ferromagnetic conductor to another—the magnetization of the two ferromagnets having different orientations. Using experimental data for ferromagnetic manganese perovskites with nearly 100% spin polarization, we show the laser frequency to be in the range 1–100 THz. The optical gain is estimated to be of order 107 cm−1, which exceeds the gain of conventional semiconductor lasers by 3 or 4 orders of magnitude. A relevant experimental study is proposed and discussed.

Dynamics of viscous amphiphilic films supported by elastic solid substrates

The dynamics of amphiphilic films deposited on a solid surface is analysed for the case in which shear oscillations of the solid surface are excited. The two cases of surface and bulk shear waves are studied with the film exposed to a gas or to a liquid. By solving the corresponding dispersion equation and the wave equation while maintaining the energy balance, we are able to connect the surface density and the shear viscosity of a fluid amphiphilic overlayer with the experimentally accessible damping coefficient, phase velocity, dissipation factor, and resonant frequency shifts of shear waves.

Carbon “peapods”—a new tunable nanoscale graphitic structure (Review)

We consider the electronic properties of empty single-wall nanotubes (SWNT) and SWNT filled with fullerene molecules (carbon “nano-peapods”). The first part of the review (Sec. II) is devoted mostly to the Luttinger liqued properties of individual metallic SWNT coupled to metallic electrodes or to superconducting leads. The discovery of carbon “nano-peapods” and their elastic, electric and thermal properties are reviewed in the second part of the paper (Sec. III). We suggest in particular how fullerene and metallofullerene molecules can be released from a “nano-peapod” by a purely electrostatic method.