Host–Guest Hybrid Redox Materials Self‐Assembled from Polyoxometalates and Single‐Walled Carbon Nanotubes

The development of next‐generation molecular‐electronic, electrocatalytic, and energy‐storage systems depends on the availability of robust materials in which molecular charge‐storage sites and conductive hosts are in intimate contact. It is shown here that electron transfer from single‐walled carbon nanotubes (SWNTs) to polyoxometalate (POM) clusters results in the spontaneous formation of host–guest POM@SWNT redox‐active hybrid materials. The SWNTs can conduct charge to and from the encapsulated guest molecules, allowing electrical access to >90% of the encapsulated redox species. Furthermore, the SWNT hosts provide a physical barrier, protecting the POMs from chemical degradation during charging/discharging and facilitating efficient electron transfer throughout the composite, even in electrolytes that usually destroy POMs

Atomic-Scale Time-Resolved Imaging of Krypton Dimers, Chains and Transition to a One-Dimensional Gas

Single-atom dynamics of noble-gas elements have been investigated using time-resolved transmission electron microscopy (TEM), with direct observation providing for a deeper understanding of chemical bonding, reactivity, and states of matter at the nanoscale. We report on a nanoscale system consisting of endohedral fullerenes encapsulated within single-walled carbon nanotubes ((Kr@C60)@SWCNT), capable of the delivery and release of krypton atoms on-demand, via coalescence of host fullerene cages under the action of the electron beam (in situ) or heat (ex situ). The state and dynamics of Kr atoms were investigated by energy dispersive X-ray spectroscopy (EDS), electron energy loss spectroscopy (EELS), and X-ray photoelectron spectroscopy (XPS). Kr atom positions were measured precisely using aberration-corrected high-resolution TEM (AC-HRTEM), aberration-corrected scanning TEM (AC-STEM), and single-atom spectroscopic imaging (STEM-EELS). The electron beam drove the formation of 2Kr@C120 capsules, in which van der Waals Kr2 and transient covalent [Kr2]+ bonding states were identified. Thermal coalescence led to the formation of longer coalesced nested nanotubes containing more loosely bound Krn chains (n = 3–6). In some instances, delocalization of Kr atomic positions was confirmed by STEM analysis as the transition to a one-dimensional (1D) gas, as Kr atoms were constrained to only one degree of translational freedom within long, well-annealed, nested nanotubes. Such nested nanotube structures were investigated by Raman spectroscopy. This material represents a highly compressed and dimensionally constrained 1D gas stable under ambient conditions. Direct atomic-scale imaging has revealed elusive bonding states and a previously unseen 1D gaseous state of matter of this noble gas element, demonstrating TEM to be a powerful tool in the discovery of chemistry at the single-atom level

Testing various facets of the equivalence principle using lunar laser ranging

Abstract More than 42 years of lunar laser ranging provides an excellent basis for the determination of various parameters of the Earth-Moon system and for tests related to gravitational physics. In this paper, we focus on tests of the equivalence principle with the Earth and Moon as test bodies in the gravitational field of the Sun as well as a test of a possible violation of the equivalence principle as a result of the coupling of the galactic dark matter with the ordinary matter of the Earth and the Moon. Tests were carried out for three different data sets with observations from 1969 to 2011, 1986 to 2011, and one set with data only from the Apache Point Observatory. No significant deviation from the predictions of general relativity was found within the reached accuracy of 3.6 × 10 −4 for the Nordtvedt parameter η and 1.6 × 10 −13 for the mass ratio (m g /m i ) EM of gravitational and inertial masses between the Earth and the Moon. PACS numbers: 95.55. Pe, 04.80.Cc, 95.35.+

Lunar laser ranging test of the Nordtvedt parameter and a possible variation in the gravitational constant

Context. Forty years of lunar laser ranging (LLR) data provide an excellent basis to determine various parameters of the Earth-Moon system as well as parameters related to gravitational physics. Aims. We update the Institut für Erdmessung (IfE) LLR model taking the effect of a fluid lunar core into consideration. The temporal variation in the gravitational constant Ġ/G0 and the strong equivalence principle, parameterized by the Nordtvedt parameter η, are investigated. Methods. A set of LLR observations from 1970 to 2009 was analysed and the parameters were determined by a least squares adjustment in two runs. After solving for classical Newtonian parameters (e.g. initial conditions for the lunar orbit and rotation) in the first run, relativistic parameters were determined in the second run. Results. The upper limits to the gravitational constant and the Nordtvedt parameter were found to be Ġ/G0 = (−0.7 ± 3.8) × 10-13  yr-1 and η = (−0.6 ± 5.2) × 10-4

Identification of magnetic properties of few nm sized FePt crystalline particles by characterizing the intrinsic atom order using aberration corrected S/TEM

Hard-magnetic nanomaterials like nanoparticles of FePt are of great interest because of their promising potential for data storage applications. The magnetic properties of FePt structures strongly differ whether the crystal phases are face centered cubic (fcc) or face centered tetragonal (fct). We evaluated aberration corrected HRTEM, electron diffraction and aberration corrected HAADF-STEM as methods to measure the chemical degree of order S that describes the ordering of Pt and Fe atoms within the crystals unit cells. S/TEM experiments are accompanied by image calculations. The findings are compared with results obtained from X-ray diffraction on a FePt film. Our results show that STEM is a reasonable fast approach over HRTEM and electron diffraction to locally determine the chemical degree of order S. Copyright 2010 Elsevier B.V. All rights reserved