Influence of Encapsulated Water on Luminescence Energy, Line Width, and Lifetime of Carbon Nanotubes: Time Domain Ab Initio Analysis

In a broad range of applications, carbon nanotubes (CNTs) are in direct contact with a condensed-phase environment that perturbs CNT properties. Experiments show that water molecules encapsulated inside of semiconducting CNTs reduce the electronic energy gap, enhance elastic and inelastic electron–phonon scattering, and shorten the excited-state lifetime. We rationalize the observed effects at the atomistic level using real-time time-dependent density functional theory combined with nonadiabatic molecular dynamics. Encapsulated water makes the nanotube more rigid, suppressing radial breathing modes while enhancing and slightly shifting the optical G-mode. Water screens Coulomb interactions and shifts charge carrier energies and wave functions. The screening, together with distortion of the CNT geometry and lifting of orbital degeneracy, produces a luminescence red shift. Enhanced elastic and inelastic electron–phonon scattering explains line width broadening and shortening of the excited-state lifetime. The influence of water on the CNT properties is similar to that of defects; however, in contrast to defects, water creates no new phonon modes or electronic states in the CNTs. The atomistic understanding of the influence of the condensed-phase environment on CNT optical, electronic, and vibrational properties, and electron–vibrational dynamics guides design of novel CNT-based materials

Chemical Ordering and Surface Segregation in Cu–Pt Nanoalloys: The Synergetic Roles in the Formation of Multishell Structures

We performed Monte Carlo simulations coupled with MAEAM potentials to study the surface segregation and chemical ordering patterns in Cu–Pt nanoalloy particles for a broad range of sizes, shapes, composition, and temperature. It was found that both the Cu segregation on the surface and the chemical ordering in the core are the general rules and usually compete with each other. Surface segregation of Cu is enhanced with increasing particle size or surface openness or global Cu composition. Despite their different morphologies, most of the types of ordered phases in the core region are the same as bulk alloys. Due to the modification or suppression effects of surface segregation, the degrees of chemical ordering shift to the Pt-richer side and are more apparent in a large-sized particle. Particularly, at a narrow composition range, the multishell structures (onion-ring or multishell/maze-like core) form in (truncated) octahedrons, illustrating a subtle synergy between the segregated Cu {111} facets and the L1₁ ordering. The possibility and advantage of transformation from these multishell structures to Pt multilayer shell/single Cu-rich core ORR catalysts by selective etching of Cu were also discussed

Growth performance of different icefish populations in Lake Erhai.

<p>Month by month (6/2010-5/2011) comparisons by lake section of mean (A) total length (B) body weight, and (C) condition factors of icefish in Lake.Erhai. Data are presented as mean±1 SE.</p

Sampling sites and heat map of Lake Erhai.

<p>(A) Location of icefish sampling sites in three discrete sections of Lake Erhai and (B) heat map for four months of the year documenting observed average water temperature variations across Lake Erhai.</p

Reproductive traits of different icefish populations in Lake Erhai.

<p>(A) Predicted maturation probability for female icefish as a function of total length in the northern warmwater (solid line), mid-lake (dashed line) and southern coldwater (dotted line) sections of Lake Erhai. (B) Box plot of median egg diameter of female icefish captured from each of the three lake sections. (C) Box plot of median absolute fecundity of female icefish captured from each of the three lake sections. (D) Box plot of median relative fecundity of female icefish captured from each of the three lake sections. (E) Box plot of median gonad somatic index (GSI) of female icefish captured from each of the three lake sections. On all panels, letters denote means that do not differ significantly from one another.</p