123 research outputs found
Nanotubular Boron-Carbon Heterojunctions
Linear nanotubular boron-carbon heterojunctions are systematically
constructed and studied with the help of ab initio total energy calculations.
The structural compatibility of the two classes of materials is shown, and a
simple recipe that determines all types of stable linear junctions is
illustrated in some detail. Our results also suggest the compatibility of
various technologically interesting types of nanotubular materials, leading to
novel types of nanotubular compound materials, and pointing out the possibility
of wiring nanotubular devices within heterogeneous nanotubular networks.Comment: 7 pages, 5 figures, accepted by J. Chem Phy
Superior Hardness and Stiffness of Diamond Nanoparticles
We introduce a computational approach to estimate the hardness and stiffness
of diamond surfaces and nanoparticles by studying their elastic response to
atomic nanoindentation. Results of our ab initio density functional
calculations explain the observed hardness differences between different
diamond surfaces and suggest bond stiffening in bare and hydrogenated fragments
of cubic diamond and lonsdaleite. The increase in hardness and stiffness can be
traced back to bond length reduction especially in bare nanoscale diamond
clusters, a result of compression that is driven by the dominant role of the
surface tension.Comment: 7 pages, 3 figure
Broad boron sheets and boron nanotubes: An ab initio study of structural, electronic, and mechanical properties
Based on a numerical ab initio study, we discuss a structure model for a
broad boron sheet, which is the analog of a single graphite sheet, and the
precursor of boron nanotubes. The sheet has linear chains of sp hybridized
sigma bonds lying only along its armchair direction, a high stiffness, and
anisotropic bonds properties. The puckering of the sheet is explained as a
mechanism to stabilize the sp sigma bonds. The anisotropic bond properties of
the boron sheet lead to a two-dimensional reference lattice structure, which is
rectangular rather than triangular. As a consequence the chiral angles of
related boron nanotubes range from 0 to 90 degrees. Given the electronic
properties of the boron sheets, we demonstrate that all of the related boron
nanotubes are metallic, irrespective of their radius and chiral angle, and we
also postulate the existence of helical currents in ideal chiral nanotubes.
Furthermore, we show that the strain energy of boron nanotubes will depend on
their radii, as well as on their chiral angles. This is a rather unique
property among nanotubular systems, and it could be the basis of a different
type of structure control within nanotechnology.Comment: 16 pages, 17 figures, 2 tables, Versions: v1=preview, v2=first final,
v3=minor corrections, v4=document slightly reworke
Constricted Boron Nanotubes
The recent discovery of pure boron nanotubes raises questions about their
detailed atomic structure. Previous simulations predicted tubular structures
with smooth or puckered surfaces. Here, we present some novel results based on
ab initio simulations of bundled single-wall zigzag boron nanotubes (ropes).
Besides the known smooth and puckered modifications, we found new forms that
are radially constricted, and which seem to be energetically superior to the
known isomers. Furthermore, those structures might be interpreted as
intermediate states between ideal tubular phases and the known bulk phases
based on boron icosahedra.Comment: 11 pages, 4 figure
Multi-Mode Love-Wave SAW Magnetic-Field Sensors
A surface-acoustic-wave (SAW) magnetic-field sensor utilizing fundamental, first- and second-order Love-wave modes is investigated. A 4.5 μ m SiO2 guiding layer on an ST-cut quartz substrate is coated with a 200 n m (Fe90Co10)78Si12B10 magnetostrictive layer in a delay-line configuration. Love-waves are excited and detected by two interdigital transducers (IDT). The delta-E effect in the magnetostrictive layer causes a phase change with applied magnetic field. A sensitivity of 1250 ° / m T is measured for the fundamental Love mode at 263 M Hz . For the first-order Love mode a value of 45 ° / m T is obtained at 352 M Hz . This result is compared to finite-element-method (FEM) simulations using one-dimensional (1D) and two-and-a-half-dimensional (2.5 D) models. The FEM simulations confirm the large drop in sensitivity as the first-order mode is close to cut-off. For multi-mode operation, we identify as a suitable geometry a guiding layer to wavelength ratio of h GL / λ ≈ 1.5 for an IDT pitch of p = 12 μ m . For this layer configuration, the first three modes are sufficiently far away from cut-off and show good sensitivity
Functionalizing graphene by embedded boron clusters
We present a model system that might serve as a blueprint for the controlled
layout of graphene based nanodevices. The systems consists of chains of B7
clusters implanted in a graphene matrix, where the boron clusters are not
directly connected. We show that the graphene matrix easily accepts these
alternating boron chains, and that the implanted boron components may
dramatically modify the electronic properties of graphene based nanomaterials.
This suggests a functionalization of graphene nanomaterials, where the
semiconducting properties might be supplemented by parts of the graphene matrix
itself, but the basic wiring will be provided by alternating chains of
implanted boron clusters that connect these areas.Comment: 10 pages, 2 figures, 1 tabl
A scanning probe microscope for magnetoresistive cantilevers utilizing a nested scanner design for large-area scans
Meier T, Foerste A, Tavassolizadeh A, et al. A scanning probe microscope for magnetoresistive cantilevers utilizing a nested scanner design for large-area scans. Beilstein Journal of Nanotechnology. 2015;6:451-461.We describe an atomic force microscope (AFM) for the characterization of self-sensing tunneling magnetoresistive (TMR) cantilevers. Furthermore, we achieve a large scan-range with a nested scanner design of two independent piezo scanners: a small high resolution scanner with a scan range of 5 x 5 x 5 mu m(3) is mounted on a large-area scanner with a scan range of 800 x 800 x 35 mu m(3). In order to characterize TMR sensors on AFM cantilevers as deflection sensors, the AFM is equipped with a laser beam deflection setup to measure the deflection of the cantilevers independently. The instrument is based on a commercial AFM controller and capable to perform large-area scanning directly without stitching of images. Images obtained on different samples such as calibration standard, optical grating, EPROM chip, self-assembled monolayers and atomic step-edges of gold demonstrate the high stability of the nested scanner design and the performance of self-sensing TMR cantilevers
Comparison of structural transformations and superconductivity in compressed Sulfur and Selenium
Density-functional calculations are presented for high-pressure structural
phases of S and Se. The structural phase diagrams, phonon spectra,
electron-phonon coupling, and superconducting properties of the isovalent
elements are compared. We find that with increasing pressure, Se adopts a
sequence of ever more closely packed structures (beta-Po, bcc, fcc), while S
favors more open structures (beta-Po, simple cubic, bcc). These differences are
shown to be attributable to differences in the S and Se core states. All the
compressed phases of S and Se considered are calculated to have weak to
moderate electron-phonon coupling strengths consistent with superconducting
transition temperatures in the range of 1 to 20 K. Our results compare well
with experimental data on the beta-Po --> bcc transition pressure in Se and on
the superconducting transition temperature in beta-Po S. Further experiments
are suggested to search for the other structural phases predicted at higher
pressures and to test theoretical results on the electron-phonon interaction
and superconducting properties
Improved efficiency of organic solar cells using Au NPs incorporated into PEDOT:PSS buffer layer
Au based plasmonic phenomenon inside the hole transport layer poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) of an organic solar cell based on blend of poly(3-hexylthiophene) (P3HT) and [6:6]-phenyl-C61-butyric acid (PCBM) is investigated. The concentration of the Au nanoparticles synthesized by wet chemical reduction is one of the key factors to strong light trapping when the spherical gold nanoparticles are blended into the PEDOT:PSS solution. Studies of the influence of the concentration of nanoparticles distribution in the PEDOT:PSS were carried out using UV–Vis spectroscopy and atomic force microscopy. Electrical characteristics of the pristine device and of device with metallic nanostructures were analyzed from J –V characteristics to observe the plasmonic effects on the performance in the P3HT:PCBM organic solar cells. The origin of the photocurrent enhancements with varying Au nanoparticles concentrations on PEDOT:PSS are discussed.The University of theWitwatersrand, Material
Physics Research Institute, School of Physics & Chemistry; and MMU facilities at Wits, NRF and
Material Energy Research Group (MERG).http://scitation.aip.orgcontent/aip/journal/advaam2017Physic
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