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