Adsorption of carbon dioxide and ammonia in transition metal-doped boron nitride nanotubes.

Density functional theory calculations were carried out to analyze the performance of single-walled boron nitride nanotubes (BNNT) doped with Ni, Pd, and Pt as a sensor of CO2 and NH3. Binding energies, equilibrium distances, charge transference, and molecular orbitals, as well as the density of states, are used to study the adsorption mechanism of the gas species on the surface of the nanotube. Our results suggest a considerable rise in the adsorption potential of BNNTs when the doping scheme is employed, as compared with adsorption in pristine nanotubes. Ni-doped nanotubes are observed to be the best candidates for adsorption of both carbon dioxide and ammonia. Graphical Abstract Molecular orbitals distribution for CO2 adsorption on a Boron Nitride Nanotube.

Stability conditions of armchair graphene nanoribbon bipolarons.

Graphene nanoribbons are 2D hexagonal lattices with semiconducting band gaps. Below a critical electric field strength, the charge transport in these materials is governed by the quasiparticle mechanism. The quasiparticles involved in the process, known as polarons and bipolarons, are self-interacting states between the system charges and local lattice distortions. To deeply understand the charge transport mechanism in graphene nanoribbons, the study of the stability conditions for quasiparticles in these materials is crucial and may guide new investigations to improve the efficiency for a next generation of graphene-based optoelectronic devices. Here, we use a two-dimensional version of the Su-Schrieffer-Heeger model to investigate the stability of bipolarons in armchair graphene nanoribbons (AGNRs). Our findings show how bipolaron stability is dependent on the strength of the electron-phonon interactions. Moreover, the results show that bipolarons are dynamically stable in AGNRs for electric field strengths lower than 3.0 mV/Å. Remarkably, the system's binding energy for a lattice containing a bipolaron is smaller than the formation energy of two isolated polarons, which suggests that bipolarons can be natural quasiparticle solutions in AGNRs. Graphical Abstract Charge localization of bipolarons in armchair garphene nanoribbons.

Polaron formation at impurity-endowed lattices.

In semiconducting materials, lattice deformities can play the role of localizing the charge carriers. Polarons are understood as attractive interactions between charge and lattice deformations that result in a single structure composed by a charged particle surrounded by a cloud of phonons. These composite quasi-particles are vital structures when it comes to charge transport mechanism in a wide range of semiconducting materials. In the present work, we investigated the drift of an electron and the subsequent polaron formation in impurity-endowed lattices in the framework of a one-dimensional tight-binding model. Primarily, we scrutinized electronic dynamics in lattices containing two sources of disorders: a barrier and a well. The dispersion of the gamma distribution gives an idea of the extension of the disorder region in the lattice. We studied the dynamics of an injected electron interacting with the lattice vibrations where we consider, for a given degree of disorder, different velocities of the incoming particle. Our results show that there are different kinds of propagation/localization for the electron according to the assumed initial velocity. Importantly, we obtained the critical values for the impurity strength to promote the quenching of Bloch oscillations and the localization of polarons.

Bloch Oscillations in Fibonacci lattices: polaron formation.

We investigated the dynamics of an electron subjected to a uniform electric field in the scope of a tight-binding electron-phonon interacting approach. We aimed at describing the transport in a one-dimensional lattice in which the on-site energies are distributed according to a Fibonacci sequence. Within this physical picture, we obtained a novel dynamical process with no counterpart in ordered lattices. Our findings showed that in low-disorder limit, the electron performs spatial Bloch oscillations, generating, in the turning points of its trajectory, composite quasi-particles-namely, polarons. When it comes to highly disordered systems, two strongly localized polarons are formed in the region where the oscillating charge is confined, thus propagating excitations that are present in the lattice.

Dynamic Formation of Bipolaron-Exciton Complexes in Conducting Polymers.

The recombination dynamics of two oppositely charged bipolarons within a single polymer chain is numerically studied in the scope of a one-dimensional tight-binding model that considers electron-electron and electron-phonon (e-ph) interactions. By scanning among values of e-ph coupling and electric field, novel channels for the bipolaron recombination were yielded based on the interplay between these two parameters. The findings point to the formation of a compound species formed from the coupling between a bipolaron and an exciton. Depending on the electric field and e-ph coupling strengths, the recombination mechanism may yield two distinct products: a trapped (and almost neutral) or a moving (and partially charged) bipolaron-exciton. These results might enlighten the understanding of the electroluminescence processes in organic light-emitting devices.