Electron Transmission Properties Research Articles

Effect of magnetic field on the transmission properties of electrons in a four-terminal quantum waveguide

We investigate the quantum-mechanical transmission of electrons in a four-terminal quantum waveguide (FTQW) subjected to an inhomogeneous magnetic field perpendicular to the FTQW plane with the use of the mode-matching technique. An electron incident through one channel of the waveguide can travel into the other three channels in the quantum ballistic regime. The results show that in zero field the transmission coefficients in two channels perpendicular to the main wire are of similar behavior, but different from that of the channel parallel to the main wire. However, in an applied magnetic field, the transmission coefficients in two channels perpendicular to the main wire exhibit quite difference from each other and depend sensitively on geometric parameters. When different magnetic configurations are applied in the structure, the transmission exhibits various patterns such as step drop, wide valley, sharp peak, and so on. Our results show that one may control the transmission property of the FTQW to match practical requirements in devices by adjusting magnetic configurations or structural parameters.

Electronic conductance in binomially tailored quantum wire

We have studied the electronic transmission properties through binomially tailored waveguide quantum wires with Dirac delta function potentials. The potential's strength is weighted according to the binomial distribution law. We have assumed that single free-electron channel is incident on the structure and the scattering of electrons is solely from the geometric nature of the problem. We have used the transfer matrix method to study the electron transmission. We found that this structure pattern allows us to have well-defined allowed conduction bands due to transmission resonance. We also found that the electronic conductance spectrum depends on the number of the Dirac delta function potential in the quantum wire. When the number of Dirac delta function potentials in the structure and their strengths are increased, both well-defined conductance bands and sharper and narrower forbidden bands are formed.

Electron transmission through a doped semi-conducting atomic wire

The electron transmission properties of a semiconducting wire are investigated via the tight-binding approximation. The wire is modeled as a chain of sp-hybrid orbitals, including overlap effects. The transmission probability is calculated using the tensorial Green function method. An impurity in the chain is shown to be able to serve as a switch for transmission through either its Coulomb integral or its overlap.

Electronic transport in a Cantor stub waveguide network

We theoretically investigate the character of electronic eigenstates and transmission properties of a one-dimensional array of stubs with Cantor geometry. Within the framework of real space renormalization group (RSRG) and transfer matrix methods we analyze the resonant transmission and extended wave functions in a Cantor array of stubs, which lack translational order. Apart from resonant states with high transmittance we unravel a whole family of wave functions supported by such an array clamped between two-infinite ordered leads, which have an extended character in the RSRG scheme but, for such states the transmission coefficient across the lead-sample-lead structure decays following a power law as the system grows in size. This feature is explained from renormalization group ideas and may lead to the possibility of trapping of electronic, optical, or acoustic waves in such hierarchical geometries.

Electron emission from solids under electron irradiation: a Monte Carlo study

We have implemented a Monte Carlo simulation method to study electron emission from solid surfaces under electron irradiation at energies of up to 100 keV. Calculations are performed for the yields and energy distributions of the emitted electrons in backscattering and transmission geometries for Al and Au metals. For transmission studies the film thicknesses range from a few nanometres to micrometres. The method is demonstrated to predict correctly the electron backscattering and transmission properties, and gives a qualitatively reasonable description of the low-energy (E < 50 eV) secondary electron emission. For the exit surface of thin films we predict a universal behaviour according to which the maximum low-energy secondary electron yield is obtained when ∼50–70% of the incident electrons are transmitted through the film. This corresponds to film thicknesses of ∼0.75 times the mean depth of penetration of the electron with the same kinetic energy in a bulk target.

Embedding method for conductance of DNA

Using a technique based on embedding in a local-orbital formalism, the electronic structure and electron transmission properties of long biological molecules may be calculated. The electronic structure is found by adding one structural unit at a time to the molecule, and calculating an embedding potential for adding the next structural unit. At present an extended H\"uckel scheme is used to evaluate the matrix elements. The transmission is also calculated within the embedding scheme, taking the molecule-metal contacts into account. Results for the density of states and transmission are presented for several structures of DNA. The transmission is highly energy dependent, and is also greatly influenced by the orbitals to which contact is made. The implications of these calculations for conductance are discussed.

Electronic structure and conductance of large molecules and DNA

Using a new technique based on embedding in a local orbital formalism, the electronic structure and electron transmission properties of long biological molecules are calculated, in particular DNA. The electronic structure is found by adding one structural unit at a time to the molecule, and calculating an embedding potential for adding the next structural unit. At present, an extended Hückel scheme is used for the Hamiltonian. The transmission is also calculated within the embedding scheme, taking the molecule–metal contacts into account. The results for transmission depend greatly on the orbitals to which contact is made, and also on energy. The implications of these calculations for conductance are discussed.

Electronic structure and conductance of large molecules and DNA

Using a new technique based on embedding in a local orbital formalism, the electronic structure and electron transmission properties of long biological molecules are calculated, in particular DNA. The electronic structure is found by adding one structural unit at a time to the molecule, and calculating an embedding potential for adding the next structural unit. At present, an extended Hückel scheme is used for the Hamiltonian. The transmission is also calculated within the embedding scheme, taking the molecule–metal contacts into account. The results for transmission depend greatly on the orbitals to which contact is made, and also on energy. The implications of these calculations for conductance are discussed.

Overlap effects on electron transmission through doped molecular wires

The electron transmission properties of a molecular wire, containing a single impurity, are investigated in the context of the tight-binding approximation. The inclusion of overlap gives rise to nonorthogonal orbitals, whose treatment requires a tensorial formalism to obtain the Green function arising in the Lippmann-Schwinger equation approach to the transmission probability $T(E).$ The presence of overlap has profound effects on the $T(E)$ curves. In particular, two antiresonances appear, which are governed by different conditions. The $T(E)$ behavior, throughout the parametric space in question, is described in detail. It is clear that a viable theory of electron transmission should take account of overlap. The tensorial procedure, adopted here, provides a direct means of doing so.

Characteristics of transmission of electrons in a quantum wire tangentially attached to a superconductor ring threaded by magnetic flux

We present numerical investigations of the transmission properties of electrons in a normal quantum wire tangentially attached to a superconductor ring threaded by magnetic flux. A point scatterer with a δ -function potential is placed at node to model scattering effect. We find that the transmission characteristics of electrons in this structure strongly depend on the normal or superconducting state of the ring. The transmission probability as a function of the energy of incident electrons, in the case of a superconductor ring threaded by one quantum magnetic flux, emerges one deep dip, imposed upon the first broad bump in spectrum. This intrinsic conductance dip originates from the superconductor state of the ring. When increasing the magnetic flux from one quantum magnetic flux to two, the spectrum shifts toward higher energy region in the whole. This conductance dip accordingly shifts and appears in the second bump. In the presence of a point-scatterer at the node, the spectrum is substantially modified. Based on the condition of the formation of the standing wave functions in the ring and the broken of the time-reserve symmetry of Schrodinger equation after switching magnetic flux, the characteristics of transmission of electrons in this structure can be well understood.

Electronic Transmission Properties of Two-Dimensional Quasi-Lattice

In the framework of the tight binding model, the electronictransmission properties of two-dimensional Penrose lattices with freeboundary conditions are studied using the generalized eigenfunctionmethod (Phys. Rev. B 60(1999)13 444). The electronic transmissioncoefficients for Penrose lattices with different sizes and widths arecalculated, and the result shows strong energy dependence because ofthe quasiperiodic structure and quantum coherent effect. Around theFermi level E = 0, there is an energy region with zero transmissionamplitudes, which suggests that the studied systems are insulating.The spatial distributions of several typical electronic states withdifferent transmission coefficients are plotted to display thepropagation process.

Characterization of hot electron transmission tunneling through the gap potential in scanning hot electron microscopy

With the emitter/gap-potential/tip structure, we have studied the hot electron (HE) transmission properties used in scanning hot electron microscopy (SHEM). The rational and practical gap potential profile between two electrodes has been constructed based on the electrostatic image force and the jellium model. The transmission probability calculated using the constructed potential profile in this paper differs from that using conventional profiles appreciably. Dependencies of the transmission probability on the gap separation, HE energy, and the tunnel voltage have been made clear.

Linear and non-linear conduction regimes in broken down gate oxides

We have investigated conduction properties of gate oxides in metal-oxide–semiconductor structures in which dielectric breakdown has occurred. The measurements were performed on p- and n-type substrate samples with oxide thickness ranging from 2.0 to 13.5 nm. It is shown that the post-breakdown differential conductance has two typical modes, which, in terms of the physics of mesoscopic conducting systems, are referred to as linear and non-linear conduction regimes. In this work, we propose an analytic model for the conductance based on the electron transmission properties of quantum point contacts, which captures the essential features and consistently explains both breakdown modes.

Electronic transmission properties in a mesoscopic necklace with inhomogeneous magnetic flux.

The electronic transmission properties and the energy spectrum of a mesoscopic necklace with inhomogeneous flux is calculated. We found interesting transmission behavior that is quite different from the case with homogenous flux. In this model, the transmission depends on both the modulation mode and the amplitude of the flux. The electronic transmission properties can be explained from the energy spectrum of the system.

Resonances in GaAs/AlxGa1?xAs Heterojunctions Due to Si Shallow Donors Related Protrusions

We investigate the role of protrusions due to individual Si shallow donors on the electron transmission properties through GaAs/AlxGa1—xAs heterojunctions. Our theoretical calculations show that the protrusions can change remarkably the electron transmission properties, being even capable of producing resonances. The modifications on the electron transmission are stronger when the individual dopant is localized in the AlxGa1—iix. As alloy side, but they also depend how far is the individual dopant from the GaAs/AlxGa1—xAs heterojunction interface. When the existence of two simultaneous individual dopants is considered, the electron transmission can present more than one resonance peak.

Electronic transport in random-side-chain polymers

We investigate the electronic transmission properties of polymers which consist of a dimerized backbone chain with randomly distributed side chains of length 2m. The system is connected to perfect left-hand and right-hand metallic leads, and the transmission spectrum is computed. We find 2m-2 high-transmission and 2 low-transmission peaks which reflect resonant extended states in the random system and the gap edges of the dimerized backbone chain, respectively. The temperature dependence of the conductivity is shown to be very sensitive to the position of the Fermi level. The tunnelling current at zero temperature in the presence of a bias voltage gives a region of negative differential conductivity, which is due to a competition between the opening of a transmission window by the applied bias and the suppression of the transmission peaks by the electric field.

Electronic transmission properties in a mesoscopic necklace with nonlinear impurities

The electronic transmission properties of a necklace of loop system with nonlinear impurities is studied. It shows a multivalued dependence of the transmitted intensity on the input intensity in this nonlinear system. For the transmission-energy relation, if the nonlinearity parameter is zero, there exists a range in the lower-energy region where no transmitting is permitted. If the nonlinearity parameter is nonzero, there will be transmitting peaks in the originally transmitting inhibited region of the corresponding linear system.

Electron Transmission Through Nonabrupt GaAs/AlxGa1-xAs Double-Barriers Subjected to an Electric Field

It is shown that the existence of nonabrupt interfaces modify electric field effects on the electron transmission through a GaAs/AlxGa1-xAs double-barrier. When the applied electric intensity is 25 kV/cm, and the abrupt well and barriers are 100 A wide, interfaces as thin as two GaAs lattice parameters are responsible for shifts at least of 10 meV in the electron tunneling resonance energies. The type of interface potential and electron effective mass description changes significantly theoretical results related to the electric field influence on the electron transmission properties.

Transmission properties of coupled atomic wires

Electron transmission properties of a configuration consisting of two infinite monatomic chains, which are coupled to each other by either a direct bond or through a finite atomic bridge, are studied via the tight-binding model. A method, based on the multi-channel Lippmann - Schwinger equation, is used to obtain analytical expressions for the scattering matrix, from which transmission probabilities are calculated for several special chain configurations. In particular, we study cases where the bridge is subjected to a constant potential and an electric field, which is generated by a potential difference between the two infinite chains. The results of the theory are very useful for qualitative evaluations of the transmission properties of simple atomic circuits and molecular switches.

Exact results for infinite and finite Sierpinski gasket fractals: extended electron states and transmission properties

We present an exact calculation to show that an infinite Sierpinski gasket fractal supports an infinite number of extended electron states. We work within the real space renormalization group (RSRG) scheme and show that by analysing the recursion relations for the Hamiltonian parameters one can extract the eigenvalues for an infinity of eigenstates that are of extended character. We also calculate the transmission coefficient for fractals of arbitrarily large generation. For the energy eigenvalues corresponding to the extended electron states, the transmission coefficient exhibits a novel feature. It turns out to be scale invariant with a value between zero and one depending upon the initial choice of the on-site potentials and the nearest-neighbour hopping integrals.