25 research outputs found
Reversible switching of surface texture by hydrogen intercalation
The interaction of atomic hydrogen with a single layer of hexagonal boron
nitride on rhodium leads to a removal of the h-BN surface corrugation. The
process is reversible as the hydrogen may be expelled by annealing to about 500
K whereupon the texture on the nanometer scale is restored. This effect is
traced back to hydrogen intercalation. It is expected to have implications for
applications, like the storage of hydrogen, the peeling of sp2-hybridized
layers from solid substrates or the control of the wetting angle, to name a
few.Comment: 4 pages and 4 figure
Ion implantation in nanodiamonds: Size effect and energy dependence
Nanoparticles are ubiquitous in nature and are increasingly important for technology. They are subject to bombardment by ionizing radiation in a diverse range of environments. In particular, nanodiamonds represent a variety of nanoparticles of significant fundamental and applied interest. Here we present a combined experimental and computational study of the behaviour of nanodiamonds under irradiation by xenon ions. Unexpectedly, we observed a pronounced size effect on the radiation resistance of the nanodiamonds: particles larger than 8 nm behave similarly to macroscopic diamond (i.e. characterized by high radiation resistance) whereas smaller particles can be completely destroyed by a single impact from an ion in a defined energy range. This latter observation is explained by extreme heating of the nanodiamonds by the penetrating ion. The obtained results are not limited to nanodiamonds, making them of interest for several fields, putting constraints on processes for the controlled modification of nanodiamonds, on the survival of dust in astrophysical environments, and on the behaviour of actinides released from nuclear waste into the environment
Comparison of Free Energy Surfaces Calculations from Ab Initio Molecular Dynamic Simulations at the Example of Two Transition Metal Catalyzed Reactions
We carried out ab initio molecular dynamic simulations in order to determine the free energy surfaces of two selected reactions including solvents, namely a rearrangement of a ruthenium oxoester in water and a carbon dioxide addition to a palladium complex in carbon dioxide. For the latter reaction we also investigated the gas phase reaction in order to take solvent effects into account. We used two techniques to reconstruct the free energy surfaces: thermodynamic integration and metadynamics. Furthermore, we gave a reasonable error estimation of the computed free energy surface. We calculated a reaction barrier of ÎF = 59.5 ± 8.5 kJ molâ1 for the rearrangement of a ruthenium oxoester in water from thermodynamic integration. For the carbon dioxide addition to the palladium complex in carbon dioxide we found a ÎF = 44.9 ± 3.3 kJ molâ1 from metadynamics simulations with one collective variable. The investigation of the same reactions in the gas phase resulted in ÎF = 24.9 ± 6.7 kJ molâ1 from thermodynamic integration, in ÎF = 26.7 ± 2.3 kJ molâ1 from metadynamics simulations with one collective variable, and in ÎF = 27.1 ± 5.9 kJ molâ1 from metadynamics simulations with two collective variables
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PEGâpeptide conjugates
The remarkable diversity of the self-assembly behavior
of PEGâpeptides is reviewed, including self-assemblies formed by PEGâpeptides with ÎČ-sheet and α-helical (coiled-coil) peptide sequences. The modes of self-assembly in solution and in the solid state are discussed. Additionally, applications in bionanotechnology and synthetic materials science are summarized