Nanocones Research Articles

Dynamical holographic Moirés in a TEM

A new electron interferometry method has been developed and implemented in a transmission electron microscope to quantitatively analyse magnetic and electric properties emanating from objects using holograms free of artifacts and with a frequential sensitivity. This method, called dynamical holographic Moirés (DHM), is based on the double-exposure technique consisting in the superimposition of two different holograms. We improved this technique by acquiring the superimposed holograms for two well-defined excitation states of the sample and with a control of the superimposition frequency. The variations of magnetic and electrostatic fields between both excitation states can then be extracted directly from the amplitude part of the so-called interferogram. We demonstrate the efficiency of this method by studying quantitatively the magnetic field generated by a hard disk drive writing head excited by a DC and an AC current. Double exposure measurements have also been performed to study in situ electrostatic properties of a biased carbon nanocone tip. Our method opens the route to dynamical studies using the unique combination of nanoscale resolution and electromagnetic sensitivity of electron interferometry.

The fifth geometric-arithmetic index of bridge graph and carbon nanocones

As an important topological index, the fifth geometric-arithmetic index is used to test the chemical properties of chemical compounds, nanomaterials and drugs. In this paper, by means of graph structure analysis and edge dividing technology, the formulate for calculating the fifth geometric-arithmetic index of bridge graph is given. Furthermore, we present the fifth geometric-arithmetic index of carbon nanocones .

Nanostructured semiconductor solar absorbers with near 100% absorption and related light management picture

Optical behaviors of both polycrystalline silicon (Si) and gallium arsenide (GaAs) nanocone (NC)-capped nanowire (NW) arrays are systematically investigated and a full light management picture is presented. The study demonstrates that compared to shape- and environment-sensitive optical resonance modes, including leaky modes and guided longitudinal resonances, optimization of light harvesting based on light scattering is more operable to guide related device fabrication. Under this consideration, near 100% absorption above the bandgap energy is realized for GaAs NC-capped NW arrays with an effective thickness of only ~1000 nm through balancing antireflection and light scattering in the optical systems. Further study under oblique incidence shows that light absorption for the optimized NC-capped NW arrays is almost insensitive to the incident angle, indicating excellent omnidirectional light management in the NC-capped NW configuration.

An “In Silico” Study of Drug Vectorization by a Carbon Nanocone

An “<i>In Silico</i>” Study of Drug Vectorization by a Carbon Nanocone

Structural and EELS studies on Doped Carbon Nanostructures for Cold Field Emission

Along with the development of cold field emissi on technology, more and more microscopes equipped with cold field emission gun (C-FEG ) are applied in scien tific research. Thanks to the lower working temperature, the service time of emitter has been ex tended. In the meantime, this technology allows to emit electrons from smaller emission radius compared to thermionic emission and Schottky emission [1]. Based on this property, higher curre nt density, higher brightness, be tter special coherence and lower energy distribution of the emission can be expected, wh ich also means that a better electron beam can be obtained [2]. For the further improvement of cold field emission, new emitter materials have been explored. As a rolled-up graphe ne sheet, carbon nanotubes (CNTs) have the similar property, for instance, low work function, high mechanic performan ce, high melting point, high carrier mobility [3-4]. In addition, CNTs have small apex radius curvature for its quasi-one -dimensional character at nanoscale. Therefore, CNTs are capable of working under the operating condition of cold field emission [5]. Furthermore, carbon nanocones are considered as candi date as well [6]. Significant improvements of such kind of carbon nanocones are demonstrated by repl acing the regular tungste n tip in transmission electron microscope [7]. For a higher performance of the cold field emission application, the electronic band structure of carbon nano-object can be modulat ed through the introduction of heteroatoms and a lower work function can be expected [8,9]. Our work is devoted to th e doping of these carbon nanostructures by nitrogen and/or boron, and to the evaluation of these doped carbon nano-objects by a characterization for the cold field emission application.

Finite deformation of single-walled carbon nanocones under axial compression using a temperature-related multiscale quasi-continuum model

A temperature-related multiscale quasi-continuum (QC) model is presented herein for the investigation of the finite deformation behaviors, especially buckling and post-buckling, of open-tip single-walled carbon nanocones (SWCNCs) in thermal environments. The hyper-elastic constitutive model is established with the use of so-called temperature-related higher-order Cauchy–Born (THCB) rule as the kinematic description for the deformation of SWCNCs. The corresponding meshless computational scheme is developed to accomplish the numerical simulation of the deformation responses of SWCNCs. The numerical results reveal that the present approach is effective and efficient for the prediction of the buckling behaviors of SWCNCs at finite temperature. It is found that the buckling and post-buckling of SWCNCs are strongly dependent on the rotation angle of cutting lines, the top radius, the height and the apex angle. The mechanical properties and buckling of SWCNCs with large top radius and apex angle are close to those of graphene.

Tapered carbon nanocone tips obtained by dynamic oxidation in air

We present a facile approach to sharpen dull carbon nanocone tip to make the materials more appropriate for AFM applications.

Fabrication of Au Doped Silicon Nano Cones and Their Gas Sensing Properties to NO2 at Room Temperature

In the present work, A new structure of silicon nano cones (SiNCs) doped by Au was successfully fabricated for room temperature (RT, 300 K) NO2 detection. And this novel structure at the nanoscale was synthesized by a combination of nanosphere lithography and metal-assisted chemical etching (MACEth). The spaces among SiNCs were helpful for diffusion and the adsorption and desorption of gas molecules. Gas sensing properties of the SiNCs doped by Au were systematically examined by measuring the change of resistance toward to NO2 with different concentration in the range of 0.25–3 ppm at RT. Experimental results showed that the gold doping could contribute to enhance gas sensitivity. The Au doped silicon nano cones sensors exhibited a low sensitivity to other gases even at high concentration. This demonstrated excellent selectivity. Moreover, the sensors showed satisfactory sensing stability and repeatability. The improvement in gas sensing properties might be attributed to the Schottky barrier between SiNCs and gold grains, and the probable gas sensing mechanism was also further discussed.

Dynamic stability analysis of single walled carbon nanocone conveying fluid

This report aims the study of dynamic stability of single walled carbon nanocone for some axial length conditions and declination angles of 60°, 120° and 240°. For dynamic stability analysis of Single Walled Carbon Nanocone (SWCNC), the mode shapes and frequencies of the carbon nanocone are extracted using the molecular mechanics approach. The mechanical properties of SWCNC were obtained by the Molecular Mechanics (MM) method. The obtained parameters are used for extraction of the conical shell virtual model of nanocone with the same dimensions. The equations of coupled fluid-structural dynamics of SWCNC are derived using the modal expansion for the structural displacements of the conical shell. In addition, for a velocity field, dimensionless frequencies were drawn according to the dimensionless velocities and critical dimensionless velocity of the fluid was obtained at the first mode of dynamics instability. For validation of these results, one test case is selected and a good agreement is found between the obtained carbon nanotube results using shell-like model and those reported in the literature. Using the developed model, the dimensionless divergence velocities were drawn according to the axial length of carbon nanocone for declination angles of 60° and 240°.

High Stability Electron Field Emitters Synthesized via the Combination of Carbon Nanotubes and N₂-Plasma Grown Ultrananocrystalline Diamond Films.

An electron field emitter with superior electron field emission (EFE) properties and improved lifetime stability is being demonstrated via the combination of carbon nanotubes and the CH4/N2 plasma grown ultrananocrystalline diamond (N-UNCD) films. The resistance of the carbon nanotubes to plasma ion bombardment is improved by the formation of carbon nanocones on the side walls of the carbon nanotubes, thus forming strengthened carbon nanotubes (s-CNTs). The N-UNCD films can thus be grown on s-CNTs, forming N-UNCD/s-CNTs carbon nanocomposite materials. The N-UNCD/s-CNTs films possess good conductivity of σ = 237 S/cm and marvelous EFE properties, such as low turn-on field of (E0) = 3.58 V/μm with large EFE current density of (J(e)) = 1.86 mA/cm(2) at an applied field of 6.0 V/μm. Moreover, the EFE emitters can be operated under 0.19 mA/cm(2) for more than 350 min without showing any sign of degradation. Such a superior EFE property along with high robustness characteristic of these combination of materials are not attainable with neither N-UNCD films nor s-CNTs films alone. Transmission electron microscopic investigations indicated that the N-UNCD films contain needle-like diamond grains encased in a few layers of nanographitic phase, which enhanced markedly the transport of electrons in the N-UNCD films. Moreover, the needle-like diamond grains were nucleated from the s-CNTs without the necessity of forming the interlayer that facilitate the transport of electrons crossing the diamond-to-Si interface. Both these factors contributed to the enhanced EFE behavior of the N-UNCD/s-CNTs films.

Continuum study on the oscillatory characteristics of carbon nanocones inside single-walled carbon nanotubes

This article aims to present a comprehensive study on the oscillatory behavior of concentric carbon nanocones (CNCs) inside carbon nanotubes (CNTs) using a continuum approach. To this end, the optimum radius of nanotube for which the nanocone lies on the tube axis is determined based on the distribution of suction energy. Using the Runge–Kutta numerical integration scheme, the equation of motion is solved numerically to attain the time history of displacement and velocity of nanocone. It is observed that the oscillation of nanocone occurs with respect to its axial equilibrium distance which moves further away from the middle axis of nanotube as the number of pentagons increases. A novel semi-analytical expression as a function of geometrical parameters, initial conditions and cone vertex direction is also proposed for the precise evaluation of oscillation frequency. With respect to the proposed frequency expression, a detailed parametric study is conducted to get an insight into the effects of number of pentagons, cone vertex direction and initial conditions on the oscillatory behavior of CNC–CNT oscillators. It is found that nanocones with more pentagons generate greater maximum frequencies inside nanotubes. Furthermore, it is shown that higher maximum frequencies can be achieved if the nanocone enters the nanotube from base.

Particle-on-Film Gap Plasmons on Antireflective ZnO Nanocone Arrays for Molecular-Level Surface-Enhanced Raman Scattering Sensors.

When semiconducting nanostructures are combined with noble metals, the surface plasmons of the noble metals, in addition to the charge transfer interactions between the semiconductors and noble metals, can be utilized to provide strong surface plasmon effects. Here, we suggest a particle-film plasmonic system in conjunction with tapered ZnO nanowire arrays for ultrasensitive SERS chemical sensors. In this design, the gap plasmons between the metal nanoparticles and the metal films provide significantly improved surface-enhanced Raman spectroscopy (SERS) effects compared to those of interparticle surface plasmons. Furthermore, 3D tapered metal nanostructures with particle-film plasmonic systems enable efficient light trapping and waveguiding effects. To study the effects of various morphologies of ZnO nanostructures on the light trapping and thus the SERS enhancements, we compare the performance of three different ZnO morphologies: ZnO nanocones (NCs), nanonails (NNs), and nanorods (NRs). Finally, we demonstrate that our SERS chemical sensors enable a molecular level of detection capability of benzenethiol (100 zeptomole), rhodamine 6G (10 attomole), and adenine (10 attomole) molecules. This work presents a new design platform based on the 3D antireflective metal/semiconductor heterojunction nanostructures, which will play a critical role in the study of plasmonics and SERS chemical sensors.

Interaction between adsorbed hydrogen and potassium on a carbon nanocone containing material as studied by photoemission

Hydrogen adsorption on a potassium doped carbon nanocone containing material was studied by photoelectron spectroscopy and work function measurement. The valence band spectra indicate that there is charge transfer from potassium to carbon. Upon deposition on carbon potassium is in its ionic state for lower doping and shows both ionic and metallic behavior at higher doping. Adsorption of hydrogen facilitates diffusion of potassium on the carbon material as seen by changes in the K2p core level spectrum. Variations in the measured sample work function indicate that hydrogen initially adsorb on the K dopants and subsequently adsorb on the carbon cone containing material.

Three-dimensional modal analysis of carbon nanocones using molecular dynamics simulation

The resonant frequencies of carbon nanocones and their corresponding mode shapes are investigated through molecular dynamics simulations. The three-dimensional vibrational mode shapes are extracted using the time histories of the three coordinates of each atom obtained from conducting one molecular dynamics simulation. Unlike the previous studies, the proposed technique is able to predict precisely all of the possible mode shapes including transverse, radial, torsional, and longitudinal modes within one molecular dynamics run. The effects of length, apex angle, and boundary conditions on the resonant characteristics of carbon nanocones are examined. The results indicate that the apex angle not only affects the resonant frequencies but also influences the shape and order of modal displacements. In addition, it is observed that the sensitivity of the resonant frequencies to the boundary conditions depends on the shape of the modal displacement.

Flexoelectricity in Carbon Nanostructures: Nanotubes, Fullerenes, and Nanocones.

We report theoretical analysis of the electronic flexoelectric effect associated with nanostructures of sp(2) carbon (curved graphene). Through the density functional theory calculations, we establish the universality of the linear dependence of flexoelectric atomic dipole moments on local curvature in various carbon networks (carbon nanotubes, fullerenes with high and low symmetry, and nanocones). The usefulness of such dependence is in the possibility to extend the analysis of any carbon systems with local deformations with respect to their electronic properties. This result is exemplified by exploring of flexoelectric effect in carbon nanocones that display large dipole moment, cumulative over their surface yet surprisingly scaling exactly linearly with the length, and with sine-law dependence on the apex angle, dflex ~ L sin(α). Our study points out the opportunity of predicting the electric dipole moment distribution on complex graphene-based nanostructures based only on the local curvature information.

Enhanced Mechanical Stability of Gold Nanotips through Carbon Nanocone Encapsulation.

Gold is a noble metal that, in comparison with silver and copper, has the advantage of corrosion resistance. Despite its high conductivity, chemical stability and biocompatibility, gold exhibits high plasticity, which limits its applications in some nanodevices. Here, we report an experimental and theoretical study on how to attain enhanced mechanical stability of gold nanotips. The gold tips were fabricated by chemical etching and further encapsulated with carbon nanocones via nanomanipulation. Atomic force microscopy experiments were carried out to test their mechanical stability. Molecular dynamics simulations show that the encapsulated nanocone changes the strain release mechanisms at the nanoscale by blocking gold atomic sliding, redistributing the strain along the whole nanostructure. The carbon nanocones are conducting and can induce magnetism, thus opening new avenues on the exploitation of transport, mechanical and magnetic properties of gold covered by sp2 carbon at the nanoscale.

Double-walled carbon nanocones: stability and electronic structure

We have applied first-principles calculations, based on the density functional theory, to investigate the stability and electronic properties of double-walled carbon nanocones, 60°60°, 120°120° and 60°120° with different rotation angles between the walls. We have shown that the most favorable double-walled nanocone studied here is that of angles of 60°60°, with rotation angle of 36° and distance between apexes of 4.22 A. We have found that, the interaction between the walls of rotated double-walled nanocones introduce geometric distortion in gap states, such as in Fermi level. These results should have consequences on the field emission properties of double-walled carbon nanocones. Additionally, we also investigated the spin polarization of such structures, and we have found unpaired electrons, which induces a total spin from 1 and 1/2 for 60°60° and 60°120° double cones, respectively.

Vibration analysis of single-walled carbon nanocones using multiscale atomistic finite element method incorporating Tersoff–Brenner potential

This research work addresses the free and forced vibration characteristics of single-walled carbon nanocones (SWCNCs) using multiscale atomistic finite element method (AFEM) incorporating Tersoff–Brenner (TB) potential. The multibody interatomic TB potential is used to represent the energy between two carbon atoms. Based on the TB potential, new set of force constant parameters is established for carbon nanocones, and the equivalent geometric and elastic properties of the space frame element to represent carbon–carbon bond are derived which are consistent with the material constitutive relations. The eigenvalues of clamped and cantilevered SWCNCs with different disclination angles are extracted using AFEM, and the effect of these angles on the resonant frequencies is investigated. A computational sine sweep test is carried out on the atomic structure of SWCNCs within the frequency range of 0–10 THz to investigate the steady-state forced vibration response under harmonic excitation. The frequency response of the SWCNCs to the cyclic and impulse load over an applied frequency range is calculated. Based on the forced vibration response spectra, the resonant frequency components of SWCNCs are identified. The results have been validated using molecular dynamics simulation.

Mie resonance-mediated antireflection effects of Si nanocone arrays fabricated on 8-in. wafers using a nanoimprint technique.

We fabricated 8-in. Si nanocone (NC) arrays using a nanoimprint technique and investigated their optical characteristics. The NC arrays exhibited remarkable antireflection effects; the optical reflectance was less than 10% in the visible wavelength range. The photoluminescence intensity of the NC arrays was an order of magnitude larger than that of a planar wafer. Optical simulations and analyses suggested that the Mie resonance reduced effective refractive index, and multiple scattering in the NCs enabled the drastic decrease in reflection.PACS: 88.40.H-; 88.40.jp; 81.07.Gf

Influences of vacancy defects on buckling behaviors of open-tip carbon nanocones

Abstract