Comment on Inverse problem from discrete spectrum in the D = 2 dimensional space (2014 Phys. Scr. 989 085201)

We analyse a method for the construction of the potential-energy function from the moments of the ground-state density. The sum rule on which some expressions are based appear to be wrong, as well as the moments and potential-energy functions derived for some illustrative examples.

Dispersion Size-Consistency

A multivariate adiabatic connection (MAC) framework for describing dispersion interactions in a system consisting of non-overlapping monomers is presented. By constraining the density to the physical ground-state density of the supersystem, the MAC enables a rigorous separation of induction and dispersion effects. The exact dispersion energy is obtained from the zero-temperature fluctuation-dissipation theorem and partitioned into increments corresponding to the interaction energy gained when an additional monomer is added to a -monomer system. The total dispersion energy of an -monomer system is independent of any partitioning into subsystems. This statement of dispersion size consistency is shown to be an exact constraint. The resulting additive separability of the dispersion energy results from multiplicative separability of the generalized screening factor defined as the inverse generalized dielectric function. Many-body perturbation theory (MBPT) is found to violate dispersion size-consistency because perturbative approximations to the generalized screening factor are nonseparable; on the other hand, random phase approximation-type methods produce separable generalized screening factors and therefore preserve dispersion size-consistency. This result further explains the previously observed increase in relative errors of MBPT for dispersion interactions as the system size increases. Implications for electronic structure theory and applications to supramolecular materials and condensed matter are discussed.

Study of the impact of interface traps associated with SiNX passivation on AlGaN/GaN MIS-HEMTs

In this work, we show that a bilayer SiNx passivation scheme which includes a high-temperature annealed SiNx as gate dielectric, significantly improves both ON and OFF state performance of AlGaN/GaN MISHEMTs. From devices with different SiNx passivation schemes, surface and bulk leakage paths were determined. Temperature-dependent MESA leakage studies showed that the surface conduction could be explained using a 2-D variable range hopping mechanism along with the mid-gap interface states at the GaN(cap)/ SiNx interface generated due to the Ga-Ga metal like bonding states. It was found that the high temperature annealed SiNx gate dielectric exhibited the lowest interface state density and a two-step C-V indicative of a superior quality SiNx/GaN interface as confirmed from conductance and capacitance measurements. High-temperature annealing helps in the formation of Ga-N bonding states, thus reducing the shallow metal-like interface states. MISHEMT measurements showed a significant reduction in gate leakage and a 4-orders of magnitude improvement in the ON/OFF ratio while increasing the saturation drain current (IDS) by a factor of 2. Besides, MISHEMTs with 2-step SiNx passivation exhibited a relatively flat transconductance profile, indicative of lower interface states density. The dynamic Ron with gate and drain stressing measurements also showed about 3x improvements in devices with bilayer SiNx passivation.

Effect of Point Defects on Electronic Properties and Structure of Talc (001) Surface by First Principles

The surface structure and electronic properties of Mg vacancy defects on talc (001) and impurity defects with Fe, Mn, Ni, Al, and Ca replacing Mg atoms were calculated by using density functional theory. The calculation results show that the order of impurity substitution energy is Mn < Ni < Al < Ca < Fe. This indicates that Fe impurity defects are most easily formed in talc crystals. The covalent bonding between Si atoms and reactive oxygen atoms adjacent to impurity atoms is weakened and the ionic property is enhanced. The addition of Fe, Mn, and Ni atoms makes the surface of talc change from an insulator to a semiconductor and enhances its electrical conductivity. The analysis of electron state density shows that surface states composed of impurity atoms 4S orbital appear near the Fermi level.

pH-Responsive N^C-Cyclometalated Iridium(III) Complexes: Synthesis, Photophysical Properties, Computational Results, and Bioimaging Application

Herein we report four [Ir(N^C)2(L^L)]n+, n = 0,1 complexes (1–4) containing cyclometallated N^C ligand (N^CH = 1-phenyl-2-(4-(pyridin-2-yl)phenyl)-1H-phenanthro[9,10-d]imidazole) and various bidentate L^L ligands (picolinic acid (1), 2,2′-bipyridine (2), [2,2′-bipyridine]-4,4′-dicarboxylic acid (3), and sodium 4,4′,4″,4‴-(1,2-phenylenebis(phosphanetriyl))tetrabenzenesulfonate (4). The N^CH ligand precursor and iridium complexes 1–4 were synthesized in good yield and characterized using chemical analysis, ESI mass spectrometry, and NMR spectroscopy. The solid-state structure of 2 was also determined by XRD analysis. The complexes display moderate to strong phosphorescence in the 550–670 nm range with the quantum yields up to 30% and lifetimes of the excited state up to 60 µs in deoxygenated solution. Emission properties of 1–4 and N^CH are strongly pH-dependent to give considerable variations in excitation and emission profiles accompanied by changes in emission efficiency and dynamics of the excited state. Density functional theory (DFT) and time-dependent density functional theory (TD DFT) calculations made it possible to assign the nature of emissive excited states in both deprotonated and protonated forms of these molecules. The complexes 3 and 4 internalize into living CHO-K1 cells, localize in cytoplasmic vesicles, primarily in lysosomes and acidified endosomes, and demonstrate relatively low toxicity, showing more than 80% cells viability up to the concentration of 10 µM after 24 h incubation. Phosphorescence lifetime imaging microscopy (PLIM) experiments in these cells display lifetime distribution, the conversion of which into pH values using calibration curves gives the magnitudes of this parameter compatible with the physiologically relevant interval of the cell compartments pH.

Impact of oxide/4H-SiC interface state density on field-effect mobility of counter-doped n-channel 4H-SiC MOSFETs

We investigated the effect of interface state density on the field-effect mobility (μ FE) of 4H-SiC counter-doped MOSFETs. We fabricated counter-doped MOSFETs with three types of gate oxides i.e., SiO2, Al2O3 formed via atomic layer deposition, and Al2O3 formed via metal layer oxidation (MLO). A maximum μ FE of 80 cm2/Vs was obtained for the MLO-Al2O3 FET, and this value was 60% larger than that of the SiO2 FET. In addition, we evaluated the electron mobility in the neutral channel (μ neutral) and the rate of increase in the free electron density in the neutral channel with respect to the gate voltage (dN neutral/dV G), which are factors determining μ FE. μ neutral depended only on the channel depth, independent of the type of gate oxide. In addition, dN neutral/dV G was significantly low in the SiO2 FET because of carrier trapping at the high density of interface states, whereas this effect was smaller in the Al2O3 FETs.

Influence of Thermal Post-deposition on Trap States in Sol-gel Indium Zinc Oxide TFTs

In solution-processed oxide thin-film transistors, post-deposition thermal processing significantly changes the film’s transport properties and is essential for high-performance devices. The mobility, bias stability and trapping-detrapping related hysteresis are improved with higher processing temperatures, which is generally attributed to decreased concentrations of localized states that act as electron traps. Fabricating and characterizing 29 devices, we provide further experimental evidence that post-deposition processing indeed leads to enhanced channel electron mobility in sol-gel indium zinc oxide TFTs, and, on the basis of a simple model, we extract physical parameters that yield a quantitative assessment of the changes in the densities and the properties of the localized trap states. The data is obtained for sol-gel indium zinc oxide thin films and TFTs subjected to thermal postdeposition processing from 300 to 500 0<\sup>C. The extracted parameters indicate that the trap state density in the bulk semiconductor and at the interface decrease by factors of 5 and 3, respectively. Furthermore, the localized states become shallower, and the band mobility increases with higher processing temperatures. <br>

First-principles calculations of magnetic and mechanical properties of Fe-based nanocrystalline alloy Fe80Si10Nb6B2Cu2

Based on the first-principles calculation method of density functional theory (DFT), the crystal structure, band structure, magnetic moment, density of state, elastic constant and population analysis of Fe80Si10Nb6B2Cu2 are calculated. The calculation results show that the Fe-based nanocrystalline alloy of this composition has a stable structure, strong resistance to deformation, high hardness and is an alloy with good flexibility. The energy band structure of spin-up and spin-down is basically the same, and the energy gap is 0 eV, showing metallicity. The asymmetry of the electronic state density between the spin-up and spin-down states indicates that the alloy is ferromagnetic, with a magnetic moment of 84.15 μ; the Fe element plays a decisive role in the magnetic properties of this alloy.

Synergistic effects in MOS capacitors with an Au/HfO2-SiO2/Si structure irradiated with neutron and gamma ray

The properties of oxide trapped charges and interface state density in the metal oxide semiconductor (MOS) capacitors with an Au/HfO2-SiO2/Si structure were investigated under irradiation of 14 MeV neutron and 60Co gamma-ray. In the mixed neutron and gamma irradiation environment, the formation of the oxide trapped charges in the HfO2-SiO2 layer is determined by the total deposited ionization energy, i.e. the sum of ionization energy deposition of the neutrons and the accompanying gamma rays, while the influence of the displacement damage caused by 14 MeV neutrons can be ignored. The interface state density depends not only on the ionizing energy loss (IEL) but also the non-ionizing energy loss (NIEL), and NIEL plays a major role below the critical neutron fluence of 4.5×1012 n/cm2. The synergistic effect of the interface state is observed increases with energy deposition in the oxide at lower fluences, while decreasing above the critical fluence. These results confirm the existence of the synergistic effect of neutron and gamma irradiation in damaging HfO2 MOS devices.