Single Wall Carbon Nanotubes Filled with Metallocenes: a First Example of Non-Fullerene Peapods

We report the synthesis and analysis of metallocenes (ferrocene, chromocene, ruthenocene, vanadocene, tungstenocene-dihydride) encapsulated in single wall carbon nanotubes (SWNTs). In the case of ferrocene, efficient filling of the SWNTs was accomplished from both the liquid and the vapor phase. The other two metallocenes were filled from the vapor phase. High resolution transmission electron microscopy reveals single molecular chains of metallocenes inside SWNTs. Molecules move under the electron beam in the SWNTs indicating the absence of strong chemical bonds between each other and the SWNT wall. Their movement freezes after short illumination as a result of irradiation damage. Energy dispersive X-ray spectrometry confirms the presence of iron, chromium, ruthenium, vanadium and tungsten

Structure and properties of C\u3csub\u3e60\u3c/sub\u3e@SWNT

Our recent achievement of high-yield C60@SWNT synthesis facilitates characterization by various techniques, including selected area electron diffraction (SAD) and Raman spectroscopy. The obtained SAD patterns show that interior C60 molecules sit on a simple 1-D lattice having a parameter of 1.00 nm. Simulated SAD patterns and real-space measurements both support this determination and do not indicate a lattice with a more complex basis, e.g. a dimer basis. Empty and bulk-filled SWNTs (22%, 56%, and 90% yields), each subjected to identical processing steps, were examined by room temperature Raman spectroscopy. Systematic differences are seen between the spectra of filled and unfilled SWNTs, particularly with respect to the G- and RBM-bands of the nanotubes. We present a possible explanation for this behavior

Reproducible synthesis of C\u3csub\u3e60\u3c/sub\u3e@SWNT in 90% yields

In previous works, we have shown our discovery of C60@SWNT and first described the general mechanism of filling, which involves the vapor phase transport of C60 molecules to openings in the SWNTs\u27 walls. Here, we discuss the high-yield synthesis of C60@SWNT by refinements to our method. Yields are measured by a calibrated weight uptake technique, a methodology that is not subject to many of the potential pitfalls inherent to other techniques that have been applied. At certain processing conditions, yields exceeding 90% were obtained and corroborated by transmission electron microscopy. From our data, we determine the parameters most important for creating endohedral SWNT supramolecular assemblies by the vapor phase method. Our results pave the way for successful single-tube measurements and for high-yield filling with non-fullerenes

Processing of single wall carbon nanotubes and implications for filling experiments

Single wall carbon nanotubes (SWNTs) have been processed in different schemes to get clean material for use in various filling experiments. The SWNTs synthesized by different methods require different processing schemes, and this is presumably due to heterogeneous nature of the various contaminants present along with the carbon nanotubes. For the pulsed laser synthesized SWNTs, a combination of nitric acid, hydrogen peroxide and hydrochloric acid treatment gives best results and the purified SWNTs give best ever filling fraction for fullerene, C60 of ~90%. The processing improves the surface cleanliness of SWNTs, in turn giving greater access for the target molecules, and hence the higher filling fraction. For the carbon arc produced SWNTs, air oxidation followed by treatment with nitric acid has been found to work best and the processed SWNTs have been used for filling experiments with metal chlorides. Both these processing schemes still leave a small fraction of catalyst impurities in the final material, thus the material quality of filled material and hence its properties depend on the processed material used for the filling experiments

Composition dependence of the in-plane copper-oxygen bond-stretching LO phonon mode in yttrium barium copper oxide

Composition dependence of the in-plane Cu-O bond-stretching LO mode in YBa2Cu3O6+x was investigated in order to gain insight into the microscopic mechanism of the metal-insulator transition in cuprates. We report experimental results suggesting the presence of spatial electronic inhomogeneities in superconducting YBa2Cu 3O6+x. These results were obtained by time-of-flight inelastic neutron scattering measurements on YBa2Cu3O6+x single crystals with different oxygen concentrations (x = 0.15, 0.35, 0.6, 0.7 and 0.95). In addition to the well-known zone boundary softening of the in-plane Cu-O bond-stretching longitudinal optical phonon mode, our results showed an insulator-like unsoftened branch coexisting with the softened branch at intermediate doping. We also determined that the extent of softening was the same for all doping levels and was equal to 14 meV. It has been proposed that this phonon softening is the result of strong electron-phonon coupling. In addition, we found that the spectral weight of the softened mode at the zone boundary increased while the intensity of the unsoftened branch decreased with increasing doping. This suggests a nano-scale electronic phase separation in superconducting YBa2Cu3O6+x. Lattice dynamical calculations have been carried out to study the evolution of phonon modes upon doping. The lattice dynamical models assuming a homogeneous, one-component system were not able to reproduce the experimentally observed phonon behavior. To explain out experimental findings, we propose a two-phase scenario for underdoped cuprates. The effect of doping---phonon softening---is confined to a certain volume fraction of the material, and this volume fraction is increasing with doping. Furthermore, triple-axis and time-of-flight inelastic neutron scattering measurements on the underdoped YBa2Cu3 O6.6 performed at different temperatures revealed that a new mode appeared at 65 meV at higher temperatures (200 K and above). This mode is dispersionless and might indicate the presence of polarons in YBa 2Cu3O6.6 at higher temperatures, possibly shedding light on nature of transition from the insulating parent compound to metallic cuprates

Composition dependence of the in-plane copper-oxygen bond-stretching LO phonon mode in yttrium barium copper oxide

Composition dependence of the in-plane Cu-O bond-stretching LO mode in YBa2Cu3O6+x was investigated in order to gain insight into the microscopic mechanism of the metal-insulator transition in cuprates. We report experimental results suggesting the presence of spatial electronic inhomogeneities in superconducting YBa2Cu 3O6+x. These results were obtained by time-of-flight inelastic neutron scattering measurements on YBa2Cu3O6+x single crystals with different oxygen concentrations (x = 0.15, 0.35, 0.6, 0.7 and 0.95). In addition to the well-known zone boundary softening of the in-plane Cu-O bond-stretching longitudinal optical phonon mode, our results showed an insulator-like unsoftened branch coexisting with the softened branch at intermediate doping. We also determined that the extent of softening was the same for all doping levels and was equal to 14 meV. It has been proposed that this phonon softening is the result of strong electron-phonon coupling. In addition, we found that the spectral weight of the softened mode at the zone boundary increased while the intensity of the unsoftened branch decreased with increasing doping. This suggests a nano-scale electronic phase separation in superconducting YBa2Cu3O6+x. Lattice dynamical calculations have been carried out to study the evolution of phonon modes upon doping. The lattice dynamical models assuming a homogeneous, one-component system were not able to reproduce the experimentally observed phonon behavior. To explain out experimental findings, we propose a two-phase scenario for underdoped cuprates. The effect of doping---phonon softening---is confined to a certain volume fraction of the material, and this volume fraction is increasing with doping. Furthermore, triple-axis and time-of-flight inelastic neutron scattering measurements on the underdoped YBa2Cu3 O6.6 performed at different temperatures revealed that a new mode appeared at 65 meV at higher temperatures (200 K and above). This mode is dispersionless and might indicate the presence of polarons in YBa 2Cu3O6.6 at higher temperatures, possibly shedding light on nature of transition from the insulating parent compound to metallic cuprates

Effects of Particle Size on the Attenuated Total Reflection Spectrum of Minerals

This study focuses on particle size effect on monomineralic powders recorded using attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy. Six particle size fractions of quartz, feldspar, calcite, and dolomite were prepared (<2, 2–4, 4–8, 8–16, 16–32, and 32–63 mm). It is found that the width, intensity, and area of bands in the ATR FTIR spectra of minerals have explicit dependence on the particle size. As particle size increases, the intensity and area of IR bands usually decrease while the width of bands increases. The band positions usually shifted to higher wavenumbers with decreasing particle size. Infrared spectra of minerals are the most intensive in the particle size fraction of 2–4 mm. However, if the particle size is very small (<2 mm), due to the wavelength and penetration depth of the IR light, intensity decreases. Therefore, the quantity of very fine-grained minerals may be underestimated compared to the coarser phases. A nonlinear regression analysis of the data indicated that the average coefficients and indices of the power trend line equation imply a very simplistic relationship between median particle diameter and absorbance at a given wavenumber. It is concluded that when powder samples with substantially different particle size are compared, as in regression analysis for modal predictions using ATR FT-IR, it is also important to report the grain size distribution or surface area of samples. The band area of water (3000–3620 cm–1) is similar in each mineral fraction, except for the particles below 2 mm. It indicates that the finest particles could have disproportionately more water adsorbed on their larger surface area. Thus, these higher wavenumbers of the ATR FT-IR spectra may be more sensitive to this spectral interference if the number of particles below 2 mm is considerable. It is also concluded that at least a proportion of the moisture could be very adhesive to the particles due to the band shift towards lower wavenumbers in the IR range of 3000–3620 cm–1

Obliquity‐driven mountain permafrost‐related fluvial magnetic susceptibility cycles in the Quaternary mid‐latitude long‐term (2.5 Ma) fluvial Maros Fan in the Pannonian Basin

Magnetic susceptibility (MS) of the Quaternary long‐term mid‐latitude Maros fluvial fan (Pannonian Basin) was recorded to understand the stratigraphical features of source‐proximal fluvial depositional settings. Three fully cored 500‐m‐deep boreholes were sampled at 0.5‐m intervals; low‐field and frequency dependent MS were measured, and complementary hysteresis and SEM‐EDAX investigations were performed on selected samples. Logged susceptibility data were also used to log correlations established by a simultaneous comparison of wireline log and laboratory measurements. Time‐series analyses of the susceptibility records reveal a ~41‐ka and ~100‐ka cyclicity. Towards the source‐distal sections the intensity of the ~41‐ka cycles decreases, while that of the ~100‐ka cycles remains strong. Stratigraphical and spectral similarities were observed between the Maros fluvial fan and Chinese loess records; however, based on complementary magnetic data, the magnetic phase of the Maros Fan sections is related to the detrital magnetite that originates from the catchment during early postglacial permafrost degradations. The amplification of the ~41‐ka cycles can be attributed to the very high susceptibility values in source‐proximal settings and to the special stratigraphical feature of the distributive fluvial systems. This comprises the increased avulsion frequency on the fluvial fans in ‘glacial recession periods’, in concert with the ‘early postglacial’ occurrence of the permafrost‐related magnetite originating from the catchment. As a local phenomenon, this is significant since it records the obliquity‐driven variations in permafrost development in a catchment. However, fluvial and alluvial fans are widespread depositional landforms within the Eurasian mountain range and were possibly the same during the Quaternary deglaciations. Thus, obliquity‐driven magnetic susceptibility variations in source‐proximal fan deposits attached or adjacent to regions of loess deposition should also be considered when scanning for potential source material of aeolian deposits