Effective mass (solid-state physics)

About: Effective mass (solid-state physics) is a research topic. Over the lifetime, 12539 publications have been published within this topic receiving 295485 citations.

A hybrid elastic metamaterial with negative mass density and tunable bending stiffness

Abstract: Achieving vibration and/or wave attenuation with locally resonant metamaterials has attracted a great deal of attention due to their frequency dependent negative effective mass density Moreover, adaptive phononic crystals with shunted piezoelectric patches have also demonstrated a tunable wave attenuation mechanism by controlling electric circuits to achieve a negative effective stiffness In this paper, we propose an adaptive hybrid metamaterial that possesses both a negative mass density as well as an extremely tunable stiffness by properly utilizing both the mechanical and electric elements A multi-physical analytical model is first developed to investigate and reveal the tunable wave manipulation abilities in terms of both the effective negative mass density and/or bending stiffness of the hybrid metamaterial The programmed flexural wave manipulations, broadband negative refraction and waveguiding are then illustrated through three-dimensional (3D) multi-physical numerical simulations in hybrid metamaterial plates Our numerical results demonstrate that the flexural wave propagation can essentially be switched between “ON/OFF” states by connecting different shunting circuits

Quantum confinement in Si and Ge nanostructures

Abstract: We apply perturbative effective mass theory as a broadly applicable theoretical model for quantum confinement (QC) in all Si and Genanostructures including quantum wells(QWs), wires (Q-wires), and dots(QDs). Within the limits of strong, medium, and weak QC, valence and conduction band edge energy levels (VBM and CBM) were calculated as a function of QD diameters, QW thicknesses, and Q-wire diameters. Crystalline and amorphous quantum systems were considered separately. Calculated band edge levels with strong, medium, and weak QC models were compared with experimental VBM and CBM reported from X-ray photoemission spectroscopy (XPS), X-ray absorption spectroscopy (XAS), or photoluminescence(PL). Experimentally, the dimensions of the nanostructures were determined directly, by transmission electron microscopy(TEM), or indirectly, by x-ray diffraction (XRD) or by XPS. We found that crystalline materials are best described by a medium confinement model, while amorphous materials exhibit strong confinement regardless of the dimensionality of the system. Our results indicate that spatial delocalization of the hole in amorphous versus crystalline nanostructures is the important parameter determining the magnitude of the band gap expansion, or the strength of the quantum confinement. In addition, the effective masses of the electron and hole are discussed as a function of crystallinity and spatial confinement.

Large Enhancement and Tunable Band Gap in Silicene by Small Organic Molecule Adsorption

Abstract: Adsorption of eight organic molecules (acetone, acetonitrile, ammonia, benzene, methane, methanol, ethanol, and toluene) onto silicene has been investigated using van der Waals density functional theory calculations (DFT-D). The calculated values of the adsorption energies vary from −0.11 to −0.95 eV. Quantitatively, these values are higher than the corresponding adsorption energies of the molecules adsorbed on graphene. In addition, electronic structure calculations have been performed. The obtained values of the band gap range from 0.006 to 0.35 eV for acetonitrile to acetone, respectively. Furthermore, the effective mass of the electron is estimated and found to be comparatively small, which is expected to result in high electron mobility. In addition, we study the effect of Li atoms doped in pristine and acetone adsorbed silicene. In particular, we focus on the variation of the adsorption energy with respect to the number of Li atoms in the systems. Our results suggest new approaches for the use of si...

Electronic surface states of liquid helium

Abstract: Electrons at the surface of liquid $^{4}\mathrm{He}$ are potentially valuable probes of both static and dynamic properties of the interface. Two species of surface state are discussed. One of these is localized just above the interface, weakly bound by the image force. The existence of this state has been confirmed by direct spectroscopic observation. Measurements of parallel field mobility and life-time on the surface are discussed and compared with predictions. The other surface state is an electron bubble held below the interface with an applied field. A resonance experiment in this geometry determines an effective mass different from the bulk liquid value. Studies of field emission from the bubbles lead to an evaluation of other bubble properties.

Highest-Occupied-Molecular-Orbital Band Dispersion of Rubrene Single Crystals as Observed by Angle-Resolved Ultraviolet Photoelectron Spectroscopy

Abstract: The electronic structure of rubrene single crystals was studied by angle-resolved ultraviolet photoelectron spectroscopy. A clear energy dispersion of the highest occupied molecular orbital-derived band was observed, and the dispersion width was found to be 0.4 eV along the well-stacked direction. The effective mass of the holes was estimated to be $0.65(\ifmmode\pm\else\textpm\fi{}0.1){m}_{0}$. The present results suggest that the carrier conduction mechanism in rubrene single crystals can be described within the framework of band transport.