Doping of Carbon Nanotubes with Encapsulated Phosphorus Chains.

Single-walled carbon nanotubes (SWCNTs) are a perfect host for the formation of one-dimensional phosphorus structures and to obtain hybrid materials with a large P-C ratio. This work presents a procedure for high-yield phosphorus filling of commercial Tuball SWCNTs and efficient removal of phosphorus deposits from the external nanotube surface. We probed white and red phosphorus as precursors, varied the synthesis temperature and the ampoule shape, and tested three solvents for sample purification. High-resolution transmission electron microscopy and Raman spectroscopy indicated crystallization of interior phosphorus in a form resembling fibrous red phosphorus. An aqueous sodium hydroxide solution allowed removing the majority of external phosphorus particles. Thermogravimetric analysis of the product determined ∼23 wt % (∼10 atom %) of phosphorus, and the X-ray photoelectron spectroscopy (XPS) data showed that ca. 80% of it is in the form of elemental phosphorus. Externally purified SWCNTs filled with phosphorus were used to study the interaction between the components. Raman spectroscopy and core-level XPS revealed p-type SWCNT doping. Valence-band XPS data and density functional theory calculations confirmed the transfer of the SWCNT electron density to the encapsulated phosphorus.

Single-Walled Carbon Nanotubes with Red Phosphorus in Lithium-Ion Batteries: Effect of Surface and Encapsulated Phosphorus.

Single-walled carbon nanotubes (SWCNTs) with their high surface area, electrical conductivity, mechanical strength and elasticity are an ideal component for the development of composite electrode materials for batteries. Red phosphorus has a very high theoretical capacity with respect to lithium, but has poor conductivity and expends considerably as a result of the reaction with lithium ions. In this work, we compare the electrochemical performance of commercial SWCNTs with red phosphorus deposited on the outer surface of nanotubes and/or encapsulated in internal channels of nanotubes in lithium-ion batteries. External phosphorus, condensed from vapors, is easily oxidized upon contact with the environment and only the un-oxidized phosphorus cores participate in electrochemical reactions. The support of the SWCNT network ensures a stable long-term cycling for these phosphorus particles. The tubular space inside the SWCNTs stimulate the formation of chain phosphorus structures. The chains reversibly interact with lithium ions and provide a specific capacity of 1545 mAh·g-1 (calculated on the mass of phosphorus in the sample) at a current density of 0.1 A·g-1. As compared to the sample containing external phosphorus, SWCNTs with encapsulated phosphorus demonstrate higher reaction rates and a slight loss of initial capacity (~7%) on the 1000th cycle at 5 A·g-1.

Factors Influencing the Performance of Pd/C Catalysts in the Green Production of Hydrogen from Formic Acid.

Formic acid derived from biomass is known to be used for hydrogen production over Pd catalysts. The effects of preparation variables, structure of the carbon support, surface functional composition on the state of Pd, and catalytic properties of the samples in the vapor-phase decomposition of formic acid were studied. In all catalysts derived from Pd acetate, metal particles visible by conventional TEM had similar sizes, but the adsorption capacity towards CO responded strongly to N-doping of the carbon surface. Moreover, a decrease in the CO/Pd values was accompanied by a significant increase in the reaction rate. Taking account of X-ray photoelectron spectroscopy (XPS) and atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF/STEM) data, the trends observed were assigned to a larger fraction of single electron-deficient Pd atoms in the N-doped samples, which do not adsorb CO but interact with formic acid to produce hydrogen. This was confirmed by extended DFT studies. The obtained results are valuable for the development of Pd catalysts on carbon supports for different processes.

Structural peculiarities of single crystal diamond needles of nanometer thickness.

Diamond is attractive for various applications due to its unique mechanical and optical properties. In particular, single crystal diamond needles with high aspect ratios and sharp apexes of nanometer size are demanded for different types of optical sensors including optically sensing tip probes for scanning microscopy. This paper reports on electron microscopy and Raman spectroscopy characterization of the diamond needles having geometrically perfect pyramidal shapes with rectangular atomically flat bases with (001) crystallography orientation, 2-200 nm sharp apexes, and with lengths from about 10-160 µm. The needles were produced by selective oxidation of (001) textured polycrystalline diamond films grown by chemical vapor deposition. Here we study the types and distribution of defects inside and on the surface of the single crystal diamond needles. We show that sp3 type point defects are incorporated into the volume of the diamond crystal during growth, while the surface of the lateral facets is enriched by multiple extended defects. Nitrogen addition to the reaction mixture results in increase of the growth rate on {001} facets correlated with the rise in the concentration of sp3 type defects.

Virus-Templated Near-Amorphous Iron Oxide Nanotubes.

We present a simple synthesis of iron oxide nanotubes, grown under very mild conditions from a solution containing Fe(II) and Fe(III), on rod-shaped tobacco mosaic virus templates. Their well-defined shape and surface chemistry suggest that these robust bionanoparticles are a versatile platform for synthesis of small, thin mineral tubes, which was achieved efficiently. Various characterization tools were used to explore the iron oxide in detail: Electron microscopy (SEM, TEM), magnetometry (SQUID-VSM), diffraction (XRD, TEM-SAED), electron spectroscopies (EELS, EDX, XPS), and X-ray absorption (XANES with EXAFS analysis). They allowed determination of the structure, crystallinity, magnetic properties, and composition of the tubes. The protein surface of the viral templates was crucial to nucleate iron oxide, exhibiting analogies to biomineralization in natural compartments such as ferritin cages.

The mechanism of {113} defect formation in silicon: clustering of interstitial-vacancy pairs studied by in situ high-resolution electron microscope irradiation.

We report the direct visualization of point defect clustering in {113} planes of silicon crystal using a transmission electron microscope, which was supported by structural modeling and high-resolution electron microscope image simulations. In the initial stage an accumulation of nonbonded interstitial-vacancy (I-V) pairs stacked at a distance of 7.68 Å along neighboring atomic chains located on the {113} plane takes place. Further broadening of the {113} defect across its plane is due to the formation of planar fourfold coordinated defects (FFCDs) perpendicular to chains accumulating I-V pairs. Closely packed FFCDs create a sequence of eightfold rings in the {113} plane, providing sites for additional interstitials. As a result, the perfect interstitial chains are built on the {113} plane to create an equilibrium structure. Self-ordering of point defects driven by their nonisotropic strain fields is assumed to be the main force for point defect clustering in the {113} plane under the existence of an energy barrier for their recombination.