532 research outputs found
Chemically active substitutional nitrogen impurity in carbon nanotubes
We investigate the nitrogen substitutional impurity in semiconducting zigzag
and metallic armchair single-wall carbon nanotubes using ab initio density
functional theory. At low concentrations (less than 1 atomic %), the defect
state in a semiconducting tube becomes spatially localized and develops a flat
energy level in the band gap. Such a localized state makes the impurity site
chemically and electronically active. We find that if two neighboring tubes
have their impurities facing one another, an intertube covalent bond forms.
This finding opens an intriguing possibility for tunnel junctions, as well as
the functionalization of suitably doped carbon nanotubes by selectively forming
chemical bonds with ligands at the impurity site. If the intertube bond density
is high enough, a highly packed bundle of interlinked single-wall nanotubes can
form.Comment: 4 pages, 4 figures; major changes to the tex
BN domains included into carbon nanotubes: role of interface
We present a density functional theory study on the shape and arrangement of
small BN domains embedded into single-walled carbon nanotubes. We show a strong
tendency for the BN hexagons formation at the simultaneous inclusion of B and N
atoms within the walls of carbon nanotubes. The work emphasizes the importance
of a correct description of the BN-C frontier. We suggest that BN-C interface
will be formed preferentially with the participation of N-C bonds. Thus, we
propose a new way of stabilizing the small BN inclusions through the formation
of nitrogen terminated borders. The comparison between the obtained results and
the available experimental data on formation of BN plackets within the single
walled carbon nanotubes is presented. The mirror situation of inclusion of
carbon plackets within single walled BN nanotubes is considered within the
proposed formalism. Finally, we show that the inclusion of small BN plackets
inside the CNTs strongly affects the electronic character of the initial
systems, opening a band gap. The nitrogen excess in the BN plackets introduces
donor states in the band gap and it might thus result in a promising way for
n-doping single walled carbon nanotubes
Mechanically activated catalyst mixing for high-yield boron nitride nanotube growth
Boron nitride nanotubes (BNNTs) have many fascinating properties and a wide range of applications. An improved ball milling method has been developed for high-yield BNNT synthesis, in which metal nitrate, such as Fe(NO(3))(3), and amorphous boron powder are milled together to prepare a more effective precursor. The heating of the precursor in nitrogen-containing gas produces a high density of BNNTs with controlled structures. The chemical bonding and structure of the synthesized BNNTs are precisely probed by near-edge X-ray absorption fine structure spectroscopy. The higher efficiency of the precursor containing milling-activated catalyst is revealed by thermogravimetric analyses. Detailed X-ray diffraction and X-ray photoelectron spectroscopy investigations disclose that during ball milling the Fe(NO(3))(3) decomposes to Fe which greatly accelerates the nitriding reaction and therefore increases the yield of BNNTs. This improved synthesis method brings the large-scale production and application of BNNTs one step closer
Subsequent Hematopoietic Stem Cell Transplantation (HSCT) Associated with Longer Survival in Patients with Relapsed/Refractory (R/R) Acute Myelogenous Leukemia (AML) After Clo+Ara-C or Ara-C Alone: A Landmark Analysis from the Classic I Trial
Magnetic Boron Nitride Nanoribbons with Tunable Electronic Properties
We present theoretical evidence, based on total-energy first-principles
calculations, of the existence of spin-polarized states well localized at and
extended along the edges of bare zigzag boron nitride nanoribbons. Our
calculations predict that all the magnetic configurations studied in this work
are thermally accessible at room temperature and present an energy gap. In
particular, we show that the high spin state, with a magnetic moment of 1
at each edge atom, presents a rich spectrum of electronic behaviors as
it can be controlled by applying an external electric field in order to obtain
metallic semiconducting half-metallic
transitions.Comment: 12 pages, 5 figures, 2 table
Colonization, disability, and the intranet: the ethnic cleansing of space?
The article analyzes teacher’s emplacement of the image of disability within school’s intranet sites in England. The image unearthed within such sites was problematic as it did not display a positive or realistic image of disability or disabled people. Within the article historical archaeology and colonialism are employed as theoretic framework to interpret this artifact of disability. The article also provides an ethnographic subscript to the creation of a space of possibilities and how this became striated by missionary teachers who colonized this brave new intranet world. Deciphering of the organization and representation of the disabled indigene, through this theoretical framework, unearthed a cartography inscribed by the scalpel of old world geometry
Single step process for the synthesis of carbon nanotubes and metal/alloy-filled multiwalled carbon nanotubes
A single-step approach for the synthesis of multi-walled nanotubes (MWNT) filled with nanowires of Ni/ternary Zr based hydrogen storage alloy has been illustrated. We also demonstrate the generation of CO-free hydrogen by methane decomposition over alloy hydride catalyst. The present work also highlights the formation of single-walled nanotubes (SWNT) and MWNTs at varying process conditions. These carbon nanostructures have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution TEM (HRTEM), Energy dispersive X-ray analysis (EDX) and Raman spectroscopy. This new approach overcomes the existing multi-step process limitation, with possible impact on the development of future fuel cell, nano-battery and hydrogen sensor technologies
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