Inversion Electron Density Research Articles

Inversion of spectral information obtained during hypersonic impact

A large number of space activities are generating a high amount of undesirable space debris, which causes inevitable damage to spacecraft and satellites. Moreover, the damage assessment of ultrahigh-speed debris is a challenging task that requires both theoretical and ground-level experimental simulations. One should note that the location and damage degree can be preliminarily determined by measuring the impact flash spectrum, which provides basic data for damage assessment. Herein, the radiation spectrum of an ultrahigh-speed collision between plastic projectile and aluminum target is measured by using spectroscopic technology. The surface temperature of the colliding material, electron temperature, and electron density in the plasma are simultaneously retrieved by using a single-frame spectrum. The single-frame spectrum is separated into a continuous spectrum and a line spectrum by using continuous thermal radiation spectrum inversion material interface temperature and line spectrum inversion electron temperature and electron density in the plasma.

Orientation and Shape Effects on Ballistic Transport Properties in Gate-All-Around Rectangular Germanium Nanowire nFETs

The electron transport properties of square and rectangular cross-sectional germanium nanowire (GeNW) field-effect transistors (FETs) with [001], [110], [111], and [112] crystal orientations are investigated. The electronic states of GeNWs are calculated by using an <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sp</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s*</i> tight-binding model coupled to a Poisson equation self-consistently. A semiclassical ballistic FET model is used to evaluate the electron transport characteristics. For the square cross section, electron injection velocity dominates the drive current in GeNW FETs because the inversion electron density in the GeNW channels is mainly determined by the capacitance of the gate insulator, and a [110] GeNW FET achieves the highest drive current of all the orientations. In the case of rectangular cross section, the electron density in GeNWs is dependent on their orientations and cross-sectional geometries due to the small quantum capacitance, and the difference of the density of states of GeNWs significantly affects the drive current. A [112] GeNW FET on a (11̅0) face exhibits the highest injection velocity of all the calculated FETs but low drive current because of its insufficient density of states. As a result, a [110] GeNW FET on a (001) face, which has both large density of states and high injection velocity, achieves the highest drive current.

Mismatch of dielectric constants at the interface of nanometer metal-oxide-semiconductor devices with high-K gate dielectric impacts on the inversion charge density

The comparison of the inversion electron density between a nanometer metal-oxide-semiconductor (MOS) device with high-K gate dielectric and a SiO2 MOS device with the same equivalent oxide thickness has been discussed. A fully self-consistent solution of the coupled Schrodinger–Poisson equations demonstrates that a larger dielectric-constant mismatch between the gate dielectric and silicon substrate can reduce electron density in the channel of a MOS device under inversion bias. Such a reduction in inversion electron density of the channel will increase with increase in gate voltage. A reduction in the charge density implies a reduction in the inversion electron density in the channel of a MOS device. It also implies that a larger dielectric constant of the gate dielectric might result in a reduction in the source–drain current and the gate leakage current.

Remote surface roughness effects on inversion electron density in nano-MOSFET

In this paper the remote surface roughness effects on channel electron density of nano MOSFET is discussed by solving the coupled Schrodinger equation and Poisson equation. The results demonstrate that the remote surface roughness could largely affect the density of inversion channel electron, and the change of electron density by this effect has been found to have approximately linear relationship to the remote surface roughness. This implies that the mobility degradation effect by remote surface roughness scattering can be partially erased for the on-state current.

A new method of asymmetric Abel inversion for magnetic equilibrium configuration state in tokamaks

It is difficult to obtain the asymmetrical factor along the observation direction parallel to the plasma mid-plane when the detected radiation is also in the mid-plane. This paper considers the magnetic surfaces and Grad?Shafranov shift, and develops a new method for inverse asymmetric electron density information, during magnetic equilibrium configuration in a tokamak.

Effective mass divergence in the infinite- U Hubbard model

To clarify the property of Mott transition in the strong correlation limit, we investigate the infinite- U Hubbard model using high-temperature expansion method. The free energies in various lattices are obtained as a function of inverse temperature and electron density. If we assume the low temperature behavior as S ∝ T , we can extrapolate the series down to T = 0 with remarkable accuracy and find that the specific heat coefficient γ diverges with n → 1 . Furthermore, it is revealed that the divergence is scaled as γ ∝ ( 1 - n ) - x with x ∼ 1.7 – 1.8 , which is almost irrespective of lattice structure.

Phosphaalkenes with Inverse Electron Density: Electrochemistry, Electron Paramagnetic Resonance Spectra, and Density Functional Theory Calculations of Aminophosphaalkene Derivatives

Cyclic voltammetry of Mes*PC(NMe2)2 (1) and Mes*PC(CH3)NMe2 (2) shows that, in solution in DME, these compounds are reversibly oxidized at 395 and 553 mV, respectively. Electrochemical oxidation or reaction of 1 (or 2) with [Cp2Fe]PF6 leads to the formation of the corresponding radical cation, which was characterized by its electron paramagnetic resonance (EPR) spectra. Experimental 31P and 13C isotropic and anisotropic coupling constants agree with density functional theory (DFT) calculations showing that the unpaired electron is strongly localized on the phosphorus atom, in accord with the description Mes*P•−(C(NMe2)2)+. Electrochemical reduction of 1 is essentially irreversible and leads to a radical species largely delocalized on the C(NMe2)2 moiety; this neutral radical results from the protonation of the phosphorus atom and corresponds to Mes*(H)P−•C(NMe2)2. No paramagnetic species is obtained by reduction of 2. The presence of the amino groups, responsible for the inverted electron distribution at ...

Organophosphorus compounds - 60 1. Reactions of phosphatriafulvenes with nucleophilic partners

The phosphatriafulvenes 1a,b - phosphaalkenes with inverse electron density - react primarily at the three-membered ring with nucleophilic reagents. From their reactions with organolithium compounds 2a-c and Grignard reagents 5a,b the cyclopropenylphosphines 4a-f are obtained after addition of chlorotrimethylsilane; of these products only 4a, d, and e were isolated and characterized. Methanolysis of products 4a-f yields the primary ( 7a-d) and secondary phosphines ( 9a,b) via cleavage of the PSi bond. Compound 1b reacts with the ynamines 10a,b through cleavage of the three-membered ring to yield the 1-phospha-1,3,5-hexadienynes 11a (X-ray structure) and 11b. The same phosphatriafulvene reacts with the cyclobutadienes 17a,b to furnish initially the 2-phosphabicyclohexenes 18a,b which, on stirring in chloroform at room temperature, undergo [2 + 2] cycloreversion to give the open-chain isomers 20a,b.

ChemInform Abstract: Organophosphorus Compounds. Part 51. Phosphatriafulvenes ‐ Phosphaalkenes with Inverse Electron Density.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Unusually‐Coordinated Phosphorus Compounds. Part 39. Phosphatriafulvenes ‐ Phosphaalkenes with Inverse Electron Density.

AbstractThe cyclopropanone (I) reacts with the lithium phosphides (II) to give the ylides (III).

Theory of self-consistency effects in the electronic structure of inversion layers in a perpendicular magnetic field

Abstract Recently a new kind of magnetic-field-dependent self-consistent calculation was developed for quantum wells and for inversion layers with two or more populated subbands in a perpendicular magnetic field. Numerical results show for inversion layers in bicrystals that qualitatively new features of the Landau level spectrum, of the inversion electron density, and of the subband occupation occur. It is shown here in an almost analytical way qualitatively why these new structures occur in inversion layers in systems like bicrystals, δ-doping layers, and MIS-structures. This is achieved by analyzing the dependence of the band bending and of the subband energies on the magnetic-field-dependent occupation of the Landau levels according to their ordering and to their degeneration. Analytical estimates are given which yield results in good agreement with the numerical ones. Most important is the behaviour of the spectrum where Landau levels coming from different subbands are crossing each other.

Theory of self-consistency effects in the electronic structure of inversion layers in a perpendicular magnetic field

Recently a new kind of magnetic-field-dependent self-consistent calculation was developed for quantum wells and for inversion layers with two or more populated subbands in a perpendicular magnetic field. Numerical results show for inversion layers in bicrystals that qualitatively new features of the Landau level spectrum, of the inversion electron density, and of the subband occupation occur. It is shown here in an almost analytical way qualitatively why these new structures occur in inversion layers in systems like bicrystals, δ-doping layers, and MIS-structures. This is achieved by analyzing the dependence of the band bending and of the subband energies on the magnetic-field-dependent occupation of the Landau levels according to their ordering and to their degeneration. Analytical estimates are given which yield results in good agreement with the numerical ones. Most important is the behaviour of the spectrum where Landau levels coming from different subbands are crossing each other.

Phosphatriafulvenes - phosphaalkenes with inverse electron density

The phosphatriafulvenes 3a,b, accessible from the cyclopropenone 1 and the lithium phosphides 2, possess inverse electron density as indicated by structure B; this can also be deduced from ab initio calculations. In accord with the electronic structure, methyllithium attacks at a carbon atom of the three-membered ring (to 4 5 ), carboxylic acid chlorides effect P -acylation (to 6), and dimethyl acetylenedicarboxylate inserts into the P/Si bond (to 8).

Calculations of Magnetotransport Properties of InSb Bicrystals with Several Populated Q2D Subbands

AbstractThe magnetic subband structure of the quasi two‐dimensional electron gas in an inversion layer with several populated electric subbands in InSb bicrystals is calculated using a straightforward and accurate method developed recently. The oscillating part of the magnetoresistance and the magnetic field dependence of the Hall resistance are evaluated by using the Ando model. Two different assumptions concerning the Fermi level position in dependence on the magnetic field are presented and discussed. A good description of the magnetotransport data determined in previous experiments is achieved. It is shown that the simple model of δ‐like Landau energy levels and the resulting discontinous magnetic field dependence of the Fermi energy for a fixed inversion electron density is not able to describe the magnetotransport behaviour determined in the experiments. Estimates of the electron mobilities in the electric subbands from the Landau level broadening lead us to the conclusion that the mobilities obtained from the onset of the Shubnikovde Haas‐oscillations are lower limits.

Cyclotron and spin resonance in electron inversion layers on InSb.

Cyclotron and electron spin resonance in inversion layers on InSb are studied by far-infrared laser and Fourier-transform spectroscopy. For the interpretation of the optical spectra the occupancies of electric subbands in magnetic fields have been derived from Shubnikov--de Haas measurements. Cyclotron masses and effective Land\'e g factors are given as a function of inversion electron density and of cyclotron energy, i.e., magnetic field. We emphasize nonparabolic and polaron effects and discuss the experimental results with a three-level model in magnetic fields. Since until present no self-consistent calculations in the presence of magnetic fields exist for InSb, we employ the triangular-well approximation for the electrostatic surface potential to obtain a qualitative description of our experiments. At weak magnetic fields good quantitative agreement is obtained between experiments and existing Hartree calculations performed in the absence of magnetic fields.

Temperature and density dependence of inversion electron cyclotron resonance in InSb

Cyclotron resonance (CR) in inversion layers on p-InSb has been measured at laser energies h(cross) omega =10.4 and 26.6 meV as a function of temperature (T approximately=4-200K) and inversion electron density (n5 approximately=0.2-2*1012 cm-2) to investigate the CR lineshape. In particular, the authors study quantum oscillations and their influence on sub-band CR. They find that quantum oscillations show the same periodicity and temperature dependence as the corresponding Shubnikov-de Haas oscillations of the static conductivity. The experimental peak position of sub-band CR is not significantly (<or approximately=5%) affected by quantum oscillations. Cyclotron masses can most reliably be extracted at elevated temperatures (T approximately=50K) when the oscillations are smeared out.

New mobility-measurement technique on inverted semiconductor surfaces near the conduction threshold

A new experimental technique has been demonstrated which has a sensitivity of ${10}^{8}$ electrons/${\mathrm{cm}}^{2}$ in a semiconductor surface inversion channel. Combined with surface-conductivity measurements, the electron (or hole) conductivity mobility can be determined unambiguously near the conduction threshold, which is not possible by previous measurement methods of conductance or transconductance versus perpendicular surface electric field (or gate voltage). The new technique measures the input admittance or impedance of the surface channel and interprets the result by a distributed-transmission-line model. The distributed capacitance element associated with the inversion layer electrons is a direct measure of the inversion electron density, ${C}_{N}=\frac{{q}^{2}{N}_{\mathrm{INV}}}{{k}_{B}T}$. Electron mobilities in the $n$-type surface inversion layers on $p$-type silicon with high and low densities of oxide charge scattering centers have been measured down to ${10}^{8}$ electrons/${\mathrm{cm}}^{2}$. A monotonic mobility decrease with decreasing electron densities has been observed in contrast to previous published data which showed unexplained mobility peaks near the conduction threshold.

Intersubband spectroscopy by photoconductivity and absorption in inversion layers onp−Si(100)

Subband spectroscopy in an inversion layer on $p\ensuremath{-}\mathrm{Si}(100)$ is done simultaneously in photoconductivity and absorption. The resonances observed are investigated in their dependence on inversion electron density ${N}_{s}$ and depletion charge ${N}_{\mathrm{dep}}$ and are interpreted as transitions from the ground subband to higher subbands of the two valleys with heavy mass perpendicular to the surface. Absorption and photoconductivity give identical resonance positions and similar lineshape. The dependence of the subband splitting on ${N}_{s}$ and ${N}_{\mathrm{dep}}$ is found to agree with the measurements of Kneschaurek et al. and the most recent theory by Ando. Agreement with the photoconductivity results of Wheeler and Goldberg and the hot-electron-induced emission experiment of Gornik and Tsui can only be achieved if the latter results are assumed to correspond to a much lower ${N}_{\mathrm{dep}}$ than derived from the substrate resistivity at 300 K. In contrast to the results of Wheeler and Goldberg the amplitude of the photoconductivity signal exhibits a strong temperature dependence between 1.7 and 6 K.