Magnetic nanoparticles with average size 30 nm were utilized to build three-dimensional framework structures—nanotrusses. In dual-phase Ni/NiO nanoparticles, there is a strong correlation between the amount of magnetic Ni and the final size and shape of the nanotruss. As it decreases, the length of the individual nanowires within the trusses also decreases, caused by a higher degree of branching of the wires. The position and orientation of the non-magnetic material within the truss structure was also investigated for the different phase compositions. For lower concentrations of NiO phase, the electrically conducting Ni-wire framework is maintained through the preferential bonding between the Ni crystals. For larger concentrations of NiO phase, the Ni-wire framework is interrupted by the NiO. The ability to use nanoparticles that are only partly oxidized in the growth of nanotruss structures is of great importance. It opens the possibility for using not only magnetic metals such as pure Ni, Fe, and Co, but also to use dual-phase nanoparticles that can strongly increase the efficiency of e.g. catalytic electrodes and fuel cells.

Dehydroabietic acid (DHAA) is a naturally occurring component of pine resin that was recently shown to open voltage-gated potassium (KV) channels. The hydrophobic part of DHAA anchors the compound near the channel’s positively charged voltage sensor in a pocket between the channel and the lipid membrane. The negatively charged carboxyl group exerts an electrostatic effect on the channel’s voltage sensor, leading to the channel opening. In this study, we show that the channel-opening effect increases as the length of the carboxyl-group stalk is extended until a critical length of three atoms is reached. Longer stalks render the compounds noneffective. This critical distance is consistent with a simple electrostatic model in which the charge location depends on the stalk length. By combining an effective anchor with the optimal stalk length, we create a compound that opens the human KV7.2/7.3 (M type) potassium channel at a concentration of 1 µM. These results suggest that a stalk between the anchor and the effector group is a powerful way of increasing the potency of a channel-opening drug.

Tunable nanostructures that feature a high surface area are firmly attached to a conducting substrate and can be fabricated efficiently over significant areas, which are of interest for a wide variety of applications in, for instance, energy storage and catalysis. We present a novel approach to fabricate Fe nanoparticles using a pulsed-plasma process and their subsequent guidance and self-organization into well-defined nanostructures on a substrate of choice by the use of an external magnetic field. A systematic analysis and study of the growth procedure demonstrate that nondesired nanoparticle agglomeration in the plasma phase is hindered by electrostatic repulsion, that a polydisperse nanoparticle distribution is a consequence of the magnetic collection, and that the formation of highly networked nanotruss structures is a direct result of the polydisperse nanoparticle distribution. The nanoparticles in the nanotruss are strongly connected, and their outer surfaces are covered with a 2 nm layer of iron oxide. A 10 mu m thick nanotruss structure was grown on a lightweight, flexible and conducting carbon-paper substrate, which enabled the efficient production of H-2 gas from water splitting at a low overpotential of 210 mV and at a current density of 10 mA/cm(2).

The morphology and physical properties of thin films deposited by vapor condensation on solid surfaces are predominantly set by the processes of island nucleation, growth, and coalescence. When deposition is performed using pulsed vapor fluxes, three distinct nucleation regimes are known to exist depending on the temporal profile of the flux. These regimes can be accessed by tuning deposition conditions; however, their effect on film microstructure becomes marginal when coalescence sets in and erases morphological features obtained during nucleation. By preventing coalescence from being completed, these nucleation regimes can be used to control microstructure evolution and thus access a larger palette of film morphological features. Recently, we derived the quantitative criterion to stop coalescence during continuous metal vapor flux deposition on insulating surfaceswhich typically yields 3-dimensional growthby describing analytically the competition between island growth by atomic incorporation and the coalescence rate of islands [Lu et al., Appl. Phys. Lett. 105, 163107 (2014)]. Here, we develop the analytical framework for entering a coalescence-free growth regime for metal vapor deposition on insulating substrates using pulsed vapor fluxes, showing that there exist three distinct criteria for suppressing coalescence that correspond to the three nucleation regimes of pulsed vapor flux deposition. The theoretical framework developed herein is substantiated by kinetic Monte Carlo growth simulations. Our findings highlight the possibility of using atomistic nucleation theory for pulsed vapor deposition to control morphology of thin films beyond the point of island density saturation. (C) 2015 AIP Publishing LLC.

The morphology transition from the thermodynamically favorable to the unfavorable phase during growth of freestanding copper nanoclusters is studied by molecular dynamics simulations. We give a detailed description of the kinetics and thermodynamics of the process. A universal mechanism of a solid-solid transition, from icosahedral to decahedral morphology in the nanoclusters, is proposed. We show that a formation of distorted NC during the growth process with islands of incoming atoms localized in certain parts of the grown particle may shift the energy balance between Ih and Dh phases in favor of the latter leading to the morphology transition deep within the thermodynamic stability field of the former. The role of diffusion in the morphology transition is revealed. In particular, it is shown that fast diffusion should suppress the morphology transition and favor homogeneous growth of the nanoclusters.

The morphology of thin metal films and nanostructures synthesized from the vapor phase on insulating substrates is strongly influenced by the coalescence of islands. Here, we derive analytically the quantitative criterion for coalescence suppression by combining atomistic nucleation theory and a classical model of coalescence. Growth simulations show that using this criterion, a coalescence-free growth regime can be reached in which morphological evolution is solely determined by island nucleation, growth, and impingement. Experimental validation for the ability to control the rate of coalescence using this criterion and navigate between different growth regimes is provided by in situ monitoring of Ag deposition on SiO2. Our findings pave the way for creating thin films and nanostructures that exhibit a wide range of morphologies and physical attributes in a knowledge-based manner.

The morphology and physical properties of thin films deposited by vapor condensation on solid surfaces are predominantly set by the initial surface processes of nucleation, island growth and coalescence. When deposition is performed using pulsed vapor fluxes, three distinct nucleation regimes are known to exist depending on the temporal profile of the flux. While these regimes can be accessed by tuning deposition conditions, their effect on film microstructure becomes marginal when coalescence sets in and erases morphological features obtained during nucleation. By preventing coalescence from being completed, these nucleation regimes can be used in a straightforward manner to control microstructure evolution and thus access a larger palette of film morphological features. Recently, we proposed a mechanism and derived the quantitative criterion to stop coalescence during continuous vapor flux deposition, based on a competition between island growth by atomic incorporation and the coalescence rate of islands [Lü et al., Appl. Phys. Lett. 105, 163107 (2014)]. In the present study, we develop the analytical framework for entering a coalescence-free growth regime for thin film deposition using pulse vapor fluxes, showing that there exist three distinct criteria corresponding to the three nucleation regimes of pulsed vapor flux deposition. The theoretical framework developed herein is substantiated by kinetic Monte Carlo growth simulations. Our findings highlight the possibility of using classical nucleation theory for pulsed vapor deposition to design materials which have an inherent tendency to coalesce.

A recently developed method of nanoclusters growth in a pulsed plasma is studied by means of molecular dynamics. A model that allows one to consider high-energy charged particles in classical molecular dynamics is suggested, and applied for studies of single impact events in nanoclusters growth. In particular, we provide a comparative analysis of the well-studied inert gas aggregation method and the growth from ions in a plasma. The importance to consider of the angular distribution of incoming ions in the simulations of the nanocluster growth is underlined. A detailed study of the energy transfer from the incoming ions to a nanocluster, as well as the diffusion of incoming ions on the cluster surface, is carried out. Our results are important for understanding and control of the nanocluster growth process.

Climate change is predicted to have major implications for global biodiversity. Dispersal and evolution may become crucial for species survival, as species must either adapt or migrate to track the changing climate. However, migration and evolution do not occur in vacuum – the biotic community in which these processes play out may modulate their effect on biodiversity. Here, we use an eco-evolutionary, spatially explicit, multi-species model that allows us to examine the interactive effects of competition, adaptation and dispersal on species richness in plant communities under global warming. We find that there is a larger decline in global species richness when interspecific competition is strong. Furthermore, there is a three-way interaction between interspecific competition, evolution and dispersal that creates a complex pattern of biodiversity responses, in which both evolution and dispersal can either increase or decrease the magnitude of species loss. This interaction arises for at least two reasons: 1) different levels of dispersal, evolution and competition creates differences in local and global community structure before climate change, and 2) competitive interactions determine whether the benefits of dispersal and/or evolution (climate tracking and adaptation) outweighs the risks (competitive exclusion).

The initial formation stages (i.e., island nucleation, island growth, and island coalescence) set characteristic length scales during growth of thin films from the vapour phase. They are, thus, decisive for morphological and microstructural features of films and nanostructures. Each of the initial formation stages has previously been well-investigated separately for the case of Volmer-Weber growth, but knowledge on how and to what extent each stage individually and all together affect the microstructural evolution is still lacking. Here we address this question using growth of Ag on SiO₂ from pulsed vapour fluxes as a case study. By combining in situ growth monitoring, ex situ imaging and growth simulations we systematically study the growth evolution all the way from nucleation to formation of a continuous film and establish the effect of the vapour flux time domain on the scaling behaviour of characteristic growth transitions (elongation transition, percolation and continuous film formation). Our data reveal a pulsing frequency dependence for the characteristic film growth transitions, where the nominal transition thickness decreases with increasing pulsing frequency up to a certain value after which a steady-state behaviour is observed. The scaling behaviour is shown to result from differences in island sizes and densities, as dictated by the initial film formation stages. These differences are determined solely by the interplay between the characteristics of the vapour flux and time required for island coalescence to be completed. In particular, our data provide evidence that the steady-state scaling regime of the characteristic growth transitions is caused by island growth that hinders coalescence from being completed, leading to a coalescence-free growth regime.