Free electron model

About: Free electron model is a research topic. Over the lifetime, 4678 publications have been published within this topic receiving 103535 citations.

A pseudo-lucky electron model for simulation of electron gate current in submicron NMOSFET's

Abstract: An energy parameterized pseudo-lucky electron model for simulation of gate current in submicron MOSFET's is presented in this paper. The model uses hydrodynamic equations to describe more correctly the carrier energy dependence of the gate injection phenomenon. The proposed model is based on the exponential form of the conventional lucky electron gate current model. Unlike the conventional lucky electron model, which is based on the local electric fields in the device, the proposed model accounts for nonlocal effects resulting from the large variations in the electric field in submicron MOSFET's. This is achieved by formulating the lucky electron model in terms of an effective-electric field that is obtained by using the computed average carrier energy in the device and the energy versus field relation obtained from uniform-field Monte Carlo simulations. Good agreement with gate currents over a wide range of bias conditions for three sets of devices is demonstrated.

Maximal spontaneous photon emission and energy loss from free electrons

Abstract: Free-electron radiation such as Cerenkov1, Smith–Purcell2 and transition radiation3,4 can be greatly affected by structured optical environments, as has been demonstrated in a variety of polaritonic5,6, photonic-crystal7 and metamaterial8–10 systems. However, the amount of radiation that can ultimately be extracted from free electrons near an arbitrary material structure has remained elusive. Here we derive a fundamental upper limit to the spontaneous photon emission and energy loss of free electrons, regardless of geometry, which illuminates the effects of material properties and electron velocities. We obtain experimental evidence for our theory with quantitative measurements of Smith–Purcell radiation. Our framework allows us to make two predictions. One is a new regime of radiation operation—at subwavelength separations, slower (non-relativistic) electrons can achieve stronger radiation than fast (relativistic) electrons. The other is a divergence of the emission probability in the limit of lossless materials. We further reveal that such divergences can be approached by coupling free electrons to photonic bound states in the continuum11–13. Our findings suggest that compact and efficient free-electron radiation sources from microwaves to the soft X-ray regime may be achievable without requiring ultrahigh accelerating voltages. Calculating the amount of radiation that can ultimately be extracted from free electrons near an arbitrary material structure is a challenge. Now, an upper limit to the spontaneous photon emission of electrons is demonstrated, regardless of geometry.

Effects of geometry and impurities on quantum rings in magnetic fields

Abstract: We investigate the effects of impurities and changing ring geometry on the energetics of quantum rings under different magnetic field strengths. We show that as the magnetic field and/or the electron number are/is increased, both the quasiperiodic Aharonov-Bohm oscillations and various magnetic phases become insensitive to whether the ring is circular or square in shape. This is in qualitative agreement with experiments. However, we also find that the Aharonov-Bohm oscillation can be greatly phase shifted by only a few impurities and can be completely obliterated by a high level of impurity density. In the many-electron calculations we use a recently developed fourth-order imaginary time projection algorithm that can exactly compute the density matrix of a free electron in a uniform magnetic field.

Band structure, evanescent states, and transport in spin tunnel junctions

Abstract: First-principles based electronic structure calculations provide important insight into spin-dependent transport in tunnelling junctions with magnetic electrodes. They have shown that Bloch electrons are qualitatively different from free electrons in determining the tunnelling probability and magnetoresistance of tunnelling junctions, and that tunnelling wavefunctions within the barrier region are usually different from those modelled by a simple barrier potential. Several factors are important in determining the tunnelling current and magnetoresistance of a tunnelling junction. These include the symmetry of the Bloch wavefunctions, the presence or absence of interface resonance states, the nature of the chemical bond between the electrode atoms and the atoms in the barrier layer, and the complex bands (evanescent states) within the barrier layer.