Interactions of hydrogen with amorphous hafnium oxide

We used density functional theory (DFT) calculations to study the interaction of hydrogen with amorphous hafnia ( a − HfO 2 ) using a hybrid exchange-correlation functional. Injection of atomic hydrogen, its diffusion towards electrodes, and ionization can be seen as key processes underlying charge instability of high-permittivity amorphous hafnia layers in many applications. Hydrogen in many wide band gap crystalline oxides exhibits negative-U behavior (+1 and − 1 charged states are thermodynamically more stable than the neutral state) . Our results show that in a − HfO 2 hydrogen is also negative-U, with charged states being the most thermodynamically stable at all Fermi level positions. However, metastable atomic hydrogen can share an electron with intrinsic electron trapping precursor sites [Phys. Rev. B 94, 020103 (2016).] forming a [ e − t r + O – H ] center, which is lower in energy on average by about 0.2 eV. These electron trapping sites can affect both the dynamics and thermodynamics of the interaction of hydrogen with a − HfO 2 and the electrical behavior of amorphous hafnia films in CMOS devices

Solitons of two-component Bose-Einstein condensates modulated in space and time

In this paper we present soliton solutions of two coupled nonlinear Schodinger equations modulated in the bspace and time. The approach allows us to obatin solitons with large variety of solutions depending on the nonlinearity and the potential profiles. As examples we show three cases with soliton solution in such system, one of them with potential varying between repulsive and attractive behavior and the others with nonlinearity localized and delocalized, respectively.Comment: 18 pages, 8 figure

Calculating adiabatic evolution of the perturbed DNLS/MNLS solitons

A symbolic computation technique is developed to calculate adiabatic evolution equations for parameters of the perturbed DNLS/MNLS solitons obtained by the recently developed direct perturbation theory [X.-J. Chen and J. Yang, Phys. Rev. E {\bf 65}, 066608(2002)]. Effects of the intrapulse Raman scattering, third-order group velocity dispersion, and narrow-banded filters with nonlinear gain on the MNLS solitons are studied as examples.Comment: 10 pages, 1 figure. to be published on Phys. Lett.

Deep electron and hole polarons and bipolarons in amorphous oxide

Amorphous (a)-HfO2 is a prototype high dielectric constant insulator with wide technological applications. Using ab initio calculations we show that excess electrons and holes can trap in a-HfO2 in energetically much deeper polaron states than in the crystalline monoclinic phase. The electrons and holes localize at precursor sites, such as elongated Hf-O bonds or undercoordinated Hf and O atoms, and the polaronic relaxation is amplified by the local disorder of amorphous network. Single electron polarons produce states in the gap at ∼2 eV below the bottom of the conduction band with average trapping energies of 1.0 eV. Two electrons can form even deeper bipolaron states on the same site. Holes are typically localized on undercoordinated O ions with average trapping energies of 1.4 eV. These results advance our general understanding of charge trapping in amorphous oxides by demonstrating that deep polaron states are inherent and do not require any bond rupture to form precursor sites