Lowest Subband Energy Research Articles

Blind image watermarking scheme based on lowest energy contourlet transform coefficient and modified arnold cat/ikeda maps

<span>The widespread of global internet has led to the need for developing new methods of protecting multimedia information from exploitation, alteration or forgery, illegal distribution, and manipulation. An attacker is quickly and illegally distributing or changing multimedia information by using various means of computer technology. For detecting this manipulation, this paper suggests blind watermark image inside a host image for observing in the receiver. If the watermark image was retrieved, then the host image was not attacked or manipulated. While if not retrieved, in this case, the image was attacked. The proposed method is depending on a decomposition of the host image using lowest energy sub-bands of Contourlet transform (4-levels), with scrambling by Ikeda map of the watermark image, and selecting new positions by modified Arnold Cat map. This will produce more security and safety, as well as provide more difficulty or prevent hacking. The obtained results confirm the robustness against attacks and more effectiveness of the presented scheme compared with the other similar works. Also, using lowest energy sub-bands will expand area of embedding and this part will be considered in the future works with the color images.</span>

Hybrid k·p tight-binding model for subbands and infrared intersubband optics in few-layer films of transition-metal dichalcogenides: MoS2 , MoSe2 , WS2 , and WSe2

We present a density functional theory parametrized hybrid $\mathrm{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{p}$ tight-binding model for electronic properties of atomically thin films of transition-metal dichalcogenides, $2\mathrm{H}\ensuremath{-}M{X}_{2}\phantom{\rule{0.16em}{0ex}}(M=\mathrm{Mo},\phantom{\rule{0.16em}{0ex}}\mathrm{W};\phantom{\rule{0.16em}{0ex}}X=\mathrm{S}$, Se). We use this model to analyze intersubband transitions in $p$- and $n$-doped $2\mathrm{H}\text{\ensuremath{-}}M{X}_{2}$ films and predict the line shapes of the intersubband excitations, determined by the subband-dependent two-dimensional electron and hole masses, as well as excitation lifetimes due to emission and absorption of optical phonons. We find that the intersubband spectra of atomically thin films of the 2H-$M{X}_{2}$ family with thicknesses of $N=2$ to 7 layers densely cover the infrared spectral range of wavelengths between 2 and $30\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{m}$. The detailed analysis presented in this paper shows that for thin $n$-doped films, the electronic dispersion and spin-valley degeneracy of the lowest-energy subbands oscillate between odd and even number of layers, which may also offer interesting opportunities for quantum Hall effect studies in these systems.

SO(4) Landau models and matrix geometry

We develop an in-depth analysis of the SO(4) Landau models on S3 in the SU(2) monopole background and their associated matrix geometry. The Schwinger and Dirac gauges for the SU(2) monopole are introduced to provide a concrete coordinate representation of SO(4) operators and wavefunctions. The gauge fixing enables us to demonstrate algebraic relations of the operators and the SO(4) covariance of the eigenfunctions. With the spin connection of S3, we construct an SO(4) invariant Weyl–Landau operator and analyze its eigenvalue problem with explicit form of the eigenstates. The obtained results include the known formulae of the free Weyl operator eigenstates in the free field limit. Other eigenvalue problems of variant relativistic Landau models, such as massive Dirac–Landau and supersymmetric Landau models, are investigated too. With the developed SO(4) technologies, we derive the three-dimensional matrix geometry in the Landau models. By applying the level projection method to the Landau models, we identify the matrix elements of the S3 coordinates as the fuzzy three-sphere. For the non-relativistic model, it is shown that the fuzzy three-sphere geometry emerges in each of the Landau levels and only in the degenerate lowest energy sub-bands. We also point out that Dirac–Landau operator accommodates two fuzzy three-spheres in each Landau level and the mass term induces interaction between them.

Annealing-induced phase transition in zinc phthalocyanine ultrathin films

We report the evidence of post-annealing-induced phase transition in zinc phthalocyanine (ZnPc) ultrathin (~20 nm) films upon annealing at 200 °C. The signatures of phase transition are observed in their morphological, structural, and ultrafast spectroscopic properties. X-ray diffraction measurement shows that α-phase nanospheres transform to β-phase nanorods that have a high degree of crystallinity with an excellent ordering along the c-direction in a monoclinic arrangement. Tight packing of molecules in the β-crystallites allows a red-shift and intensity gain of the lowest-energy subband in the Q-band and subsequently increases the electronic coupling in both intercolumn and intracolumn paths.

Influence of Surface States on Electronic Band Structure and Electron Density in InAs Nanowires and InAs Shell Nanowires

We report on a theoretical study of the impact of surface states on the electronic band structure and on the electron density in intrinsic cylindrical InAs nanowires and InAs shell nanowires (nanotubes). Solving coupled Poisson and Schroedinger equations we show that the electric field induced by the positively charged donor-type surface states bends the conduction band. For a surface states density above 1012 cm-2 the Fermi level is pinned above the conduction band edge in the vicinity of the neutrality level. Downwards bending of the conduction band leads to the formation of a triangular-shaped n-type channel at the nanowire surface and a square-shaped n-type channel in the nanotube. The square-type profile of the conduction band in the nanotubes enables to reach a higher electron density in comparison with nanowires, if the shell thickness exceeds 15 nm. In nanotubes, the stronger confinement leads to the occupation of only the lowest energy subband, whereas in the triangular well of InAs nanowires typically at least subbands are occupied.

Spin transistor operation driven by the Rashba spin-orbit coupling in the gated nanowire

A theoretical description has been proposed for the operation of the spin transistor in the gate-controlled InAs nanowire. The calculated current-voltage characteristics show that the electron current flowing from the source (spin injector) to the drain (spin detector) oscillates as a function of the gate voltage, which results from the precession of the electron spin caused by the Rashba spin-orbit interaction in the vicinity of the gate. We have studied the operation of the spin transistor under the following conditions: (A) the full spin polarization of electrons in the contacts, zero temperature, and the single conduction channel corresponding to the lowest-energy subband of the transverse motion and (B) the partial spin polarization of the electrons in the contacts, the room temperature, and the conduction via many transverse subbands taken into account. For case (A), the spin-polarized current can be switched on/off by the suitable tuning of the gate voltage, for case (B) the current also exhibits the pronounced oscillations but with no-zero minimal values. The computational results obtained for case (B) have been compared with the recent experimental data and a good agreement has been found.

Mode Space Approach for Tight Binding Transport Simulation in Graphene Nanoribbon FETs

A mode space (MS) tight binding approach for the simulation of armchair graphene nanoribbon FETs is discussed. It makes use of slab-dependent modes and a novel criterion for mode selection, going beyond the one based on the lowest energy subbands. For ideal ribbons, we show that by splitting the modes into decoupled groups, the new method provides results almost identical to the real space (RS) with a speedup of more than one order of magnitude. Even in the presence of edge roughness, which tends to couple the modes, the MS approach still offers a sizable computational advantage with respect to the RS, while retaining a good accuracy.

10.1007/s11447-008-2010-3

The temperature dependence of electron mobility is examined. We calculate the contribution to the electron scattering rate from the surface level atoms (SLAs), proposed in [10]. This contribution is substantial at low temperatures T < 0.5, when the He vapor concentration is exponentially small. We also study the effect of depopulation of the lowest energy subband, which leads to an increase in the electron mobility at high temperature. The results explain certain long-standing discrepancies between the existing theory and experiment on electron mobility on the surface of liquid helium.

A quantum mechanical formulation of electron transport induced wind forces in metallic single-walled carbon nanotubes

In this paper the forces induced on the atoms of the lattice due an electric current (electron transport induced wind forces) are calculated based on quantum mechanics. These forces are calculated in metallic single-walled armchair carbon nanotubes (SWCNTs) from the momentum transfer between the charge carriers and the lattice in a quantum mechanical framework. Energy and phonon dispersion relations are the main input for the formulation proposed. Scattering of electrons with longitudinal acoustic and longitudinal optical phonons are considered to be the only scattering mechanisms that are responsible for the momentum exchange. The current–voltage characteristics are also predicted using the same framework and show good agreement with experimental data. The study shows that using the constant effective charge number for SWCNT is inaccurate at higher electric field forces due to saturation of the lowest energy subband. The thermal effect on the effective charge number appears to be very important, due to the increasing scattering probabilities at higher temperatures.

Quantum-mechanical effects in nanometer scale MuGFETs

Solving the Poisson and Schrödinger equations self-consistently in two dimensions reveals quantum-mechanical effects that influence the electron concentration, the threshold voltage and the subthreshold slope of MuGFETs. The average electron concentration needed to reach the threshold voltage depends on the gate configuration and on the device geometry. The dependence of the energy of the subbands on the different gate configurations is studied, and the relation between threshold voltage and the lowest subband energy is investigated. Due to a dynamic threshold voltage effect, the drain current is lower in the quantum-based drain current model than in classical simulations. This dynamic increase of threshold voltage is due to an increase of the subband energy with the electron concentration. This effect degrades the subthreshold slope. It is observed in non-symmetrical devices (FinFET, tri-gate), but not in symmetrical structures (GAA). This gives symmetrical devices like GAA nanowires an intrinsic advantage compared to the other types of devices.

Electron mobility on the surface of liquid Helium: influence of surface level atoms and depopulation of lowest subbands

The temperature dependence of electron mobility is examined. We calculate the contribution to the electron scattering rate from the surface level atoms (SLAs), proposed in [10]. This contribution is substantial at low temperatures T < 0.5, when the He vapor concentration is exponentially small. We also study the effect of depopulation of the lowest energy subband, which leads to an increase in the electron mobility at high temperature. The results explain certain long-standing discrepancies between the existing theory and experiment on electron mobility on the surface of liquid helium.

Self-consistent calculation for valence subband structure and hole mobility in p-channel inversion layers

Using six- and eight-band k⋅p models—with parameters calibrated against the bulk band structure obtained using non-local empirical pseudopotentials—we have employed a new hybrid self-consistent method to calculate the valence subband structure in p-channel inversion layers of InAs, InSb, GaAs, In0.53Ga0.47As, and GaSb. This method involves two separate stages: first, density-of-states (DOS) of the three lowest-energy subbands (heavy, light, and split-off holes) is calculated using the triangular-well approximation. Then, the self-consistent calculation is performed using the DOS previously obtained, but shifting each subband by the amount obtained from the self-consistent eigenvalues obtained during the self-consistent iteration. Finally, we present results regarding the hole mobility in Ge p-channel inversion layers. The results are compared to those obtained employing the subband structure computed with the triangular-well approximation and also with experimental data.

Manipulation of spin states by dipole polarization switching

A ferromagnetic/ferroelectric hybrid double quantum disk structure is proposed, capable of manipulating spin states. Switching of spontaneous electric polarization of the ferroelectric quantum disk changes the potential profile of the system and induces ground state transition. Two carrier spin states are separated into ferroelectric semiconductor and diluted magnetic semiconductor disks via asymmetric Zeeman splitting of the coupled quantum disks. The proof of the spin separation resulting from the dipole polarization switching is shown by the probability density change of the lowest energy subband. Evolution of the spin state is also predicted from the subband energy diagram as a function of the bias voltage.

Modulation of the Curie temperature in ferromagnetic/ferroelectric hybrid double quantum wells

We propose a ferromagnetic/ferroelectric hybrid double quantum well structure, and present an investigation of the Curie temperature (Tc) modulation in this quantum structure. The combined effects of applied electric fields and spontaneous electric polarization are considered for a system that consists of a Mn \delta-doped well, a barrier, and a p-type ferroelectric well. We calculate the change in the envelope functions of carriers at the lowest energy sub-band, resulting from applied electric fields and switching the dipole polarization. By reversing the depolarizing field, we can achieve two different ferromagnetic transition temperatures of the ferromagnetic quantum well in a fixed applied electric field. The Curie temperature strongly depends on the position of the Mn \delta-doped layer and the polarization strength of the ferroelectric well.

Helicity and Electron-Correlation Effects on Transport Properties of Double-Walled Carbon Nanotubes

Starting from selection rules for intershell tunneling in double-walled nanotubes with commensurate (c-DWNTs) and incommensurate (i-DWNTs) shells, we show that for i-DWNTs the coupling is negligible between lowest energy subbands, but it becomes important as the higher subbands become populated. In turn the elastic mean-free path of i-DWNTs is reduced for increasing energy, with additional suppression at subband onsets and crossings. At low energies, a Luttinger liquid theory for DWNTs with metallic shells is derived. Interaction effects are more pronounced in i-DWNTs than in c-DWNTs.

Curie-temperature modulation by electric fields in Mnδ-doped asymmetric double quantum wells

We present an investigation of the Curie temperature ${(T}_{c})$ modulation in semiconductor quantum wells. The combined effects of applied electric fields and p-type doping are considered for a system that consists of a Mn $\ensuremath{\delta}$-doped well, a barrier, and a p-type-doped well. The amount of supplied holes from the p-type-doped well to the Mn $\ensuremath{\delta}$-doped well is controlled by the applied electric fields. We calculate the change in the envelope functions of carriers at the lowest-energy subband resulting from applied electric fields. By applying 1.5 meV/nm electric fields, we can enhance ${T}_{c}$ up to 8 times than that without the fields. The ferromagnetic transition temperature strongly depends on a position of the Mn $\ensuremath{\delta}$-doped layer and asymmetry of quantum wells.

Magnetic-field-induced recovery of resonant tunneling into a disordered quantum well subband

We investigate how the disorder produced by a layer of self-assembled InAs quantum dots affects the electronic states of a GaAs quantum well incorporated in a double barrier resonant tunneling diode. The disorder strongly suppresses the resonant peak in the current due to electron tunneling into the lowest energy subband of the quantum well. However, the peak is recovered by the application of an in-plane magnetic field, which provides a means of tuning the in-plane momentum of the tunneling electrons. Analysis of these data and of Landau level formation when the field is applied perpendicular to the quantum well plane provides information about the length-scale of disorder potential in the well.

Nonlinear hole transport through a submicron-size channel

We investigate hole transport through a submicron-size channel fabricated from a modulation-doped p-type GaAs/(AlGa)As single-quantum-well heterostructure. The intense electric field in the channel accelerates the holes beyond the inflection point of the lowest energy subband dispersion curve. This leads to current saturation and negative differential conduction effects in the current–voltage characteristics.

Two-dimensional electron systems in inversion layers of p-type Hg0.8Zn0.2Te metal-insulator-semiconductor structures

Strong oscillations on capacitance and conductance have been observed in p-type Hg0.8Zn0.2Te metal-insulator-semiconductor structures, made by using a recent process for the interface passivation. This behaviour is attributed to a two-dimensional electron gas in the n-inversion layer and the variation of the conductance maximums with temperature indicates that the dominant perpendicular transport mechanism for electrons is an incoherent two-step tunnelling through deep levels in the gap. Three models have been used to describe the quantum confinement: the simple variational method, the triangular potential approximation and the propagation matrix method. The later approach takes into account the non parabolicity of the conduction band structure and uses a finite height barrier at the insulator-semiconductor interface. A very good agreement between experimental and calculated values for the two lowest subband energy is obtained.

Phonon-limited inversion layer electron mobility in extremely thin Si layer of silicon-on-insulator metal-oxide-semiconductor field-effect transistor

Phonon-limited inversion layer electron mobility in extremely thin (100) Si layers of silicon-on-insulator field-effect transistors has been studied at 300 K using a relaxation time approximation and a one-dimensional self-consistent calculation. For the Si layer thickness tSi of more than approximately 5 nm, the mobility behavior as a function of an effective vertical electric field is found to be almost identical with that of bulk Si inversion layers. For a thickness of less than that, however, the mobility behavior is considerably affected by the change in the electronic structures due to a confinement effect. As the Si layer thickness decreases, the phonon-limited electron mobility μph increases to a maximum at tSi of ∼3 nm and decreases monotonically. The increase in mobility results from the increase of the fraction of electrons in the lowest energy subband that has a higher mobility than other subbands. The mobility decrease in the extremely thin tSi region is attributed to the enhancement of phonon scattering rates caused by a reduction of the spatial widths of the subbands.