Papers by Keyword: Chirality

Abstract: Single-walled carbon nanotubes (SWCNTs) as a promising candidate in a wide range of applications have shown great potentials in optical, electronic, magnetic and mechanical fields. Precisely due to their excellent characteristics and performances, it has attracted widespread attention, and much progress has been made during recent decades. However, due to the huge challenge in controlled synthesis and purification, obtaining SWCNTs with consistent chirality has seriously limited their high-end industrial applications. In this article, we will review the approaches recently developed in chirality-controlled preparation of SWCNTs. Among them, we will introduce the mechanism of templated growth of SWCNTs from chiral affinities, including cloning and seeds designing strategies. The preparation of SWCNTs catalyzed by noble metal and assisted with weak oxidant have been illustrated as well. Meanwhile, we will also discuss some chirality-selective separation approaches, which pay more attention to post-processing strategies by purifying the chiral SWCNTs with functional reagents. We expect that these strategies in controlling the chirality of CNTs will shed more light on the mechanism and process for atomic structural control of CNTs, and may also be applicable in the controlled synthesis of other nanomaterials.

Abstract: The present paper investigates the nonlocal buckling of Zigzag Triple-walled carbon nanotubes (TWCNTs) under axial compression with both chirality and small scale effects. Based on the nonlocal continuum theory and the Timoshenko beam model, the governing equations are derived and the critical buckling loads under axial compression are obtained. The TWCNTs are considered as three nanotube shells coupled through the van der Waals interaction between them. The results show that the critical buckling load can be overestimated by the local beam model if the small-scale effect is overlooked for long nanotubes. In addition, a significant dependence of the critical buckling loads on the chirality of zigzag carbon nanotube is confirmed, and these are then compared with: A single-walled carbon nanotubes (SWCNTs); and Double-walled carbon nanotubes (DWCNTs). These findings are important in mechanical design considerations and reinforcement of devices that use carbon nanotubes.

Abstract: Currently, composite materials composed of a matrix and reinforcing components are widely used as a structural material for various engineering devices designed to operate under extreme loads of different types. By modifying a composite with structure-sensitive inclusions, such as a single-wall carbon nanotube, the mechanical properties, especially elastic characteristics, of the resulting material can be significantly improved. The results of investigation of a single-walled carbon nanotubes chirality influence on its elastic properties are presented. Various configurations of nanotubes, such as zigzag and armchair are considered. The dependences of the nanotube bulk modulus and shear modulus of its diameter are shown.

Abstract: We have analyzed the chirality of terahertz (THz) wave emission from a square chiral metamaterial. The sample was manufactured with a periodic structure formed by a square pattern of chiral with different depth on a silver film. We have yield the specific polarization rotation in the THz region when the THz wave is emitted from a square chiral metamaterial. The THz emissions from these chiral metamaterials were elliptic polarization. A square chiral metamaterial was shown circular dichroism and optical activity properties at different frequencies. The ellipticity and rotation angle will reach a maximum value at a frequency of 1.2 THz and 0.6 THz, respectively. The results were indicated the possibility to controlled the polarization with chiral metamaterial structures.

Abstract: We have studied the interaction of the positron with chiral left-or right-handed quartz crystals. In Doppler-broadening experiments, using a mono-energetic positron beam there is a differential depth profile for positrons implanted in LH or RH z-cut quartz as identified by a shape parameter (S). Further, in bulk positron annihilation lifetime spectroscopy (PALS) experiments, the lifetime (τ ₂) attributed to free annihilation of the positron interacting with the chiral lattice exhibits a larger value for the LH quartz, and the associated intensity (I₂) is also significantly different—RH quartz is consistently 10% greater than the LH crystal. The τ ₃ lifetime and its intensity, I₃, attributed to positronium interacting with defects in the quartz, also appears to exhibit differences between the enantiomeric sets of crystals. These observations may demonstrate chiral recognition using a positron annihilation technique, pave the way for a broad range of positron experiments, and may help inform hypotheses of chirality recognition, selection, or induction by beta radiation.

Abstract: In this work, an improved technique for chirality assignment of single wall carbon nanotubes (SWCNT) is proposed which work for both isolated and bundles SWCNTs. The technique exploits the (2n+m) family pattern both in optical transitions vs diameter plot and Raman G-mode frequency vs diameter plot of SWCNTs. Using two different plots can give accurate value of the family of unknown SWCNTs that can be used to find chiral index (n, m) of unknown SWCNT unambiguously in most of the cases. Unlike existing methods, graphical comparison or pattern recognition with an existing Kataura plot is not required here. Chirality of 13 SWCNTs are assigned here using this technique. Validity of assigned chirality is cross checked from previous experimental reports. The technique is especially useful for determining chirality of isolated SWCNT.

Abstract: In this work, effect of chirality on gas adsorption property of semiconducting single-wall carbon nanotubes (SWCNTs) is reported for the first time. First principles simulation of the interaction of three different chirality SWCNTs with different gas molecules is performed maintaining equilibrium tube–molecule distance. Results are obtained employing density functional theory, using the Atomistic toolkit simulation package (ATK-DFT). Nanotube density of states is observed to vary significantly due to interaction with different types of gases as well as for same gas if chirality of SWCNTs varies. The most significant finding is, the change in DOS near Fermi level is highest in mod 2 type semiconducting SWCNT for different gas molecules irrespective of donor or acceptor. Thus, proper selection of chirality of SWCNT is important to make nanotube based gas sensor and mod 2 types semiconducting SWCNTs should get preference over mod 1 type as a sensing element so as to get better sensitivity.

Abstract: An asymmetrical chiral metamaterial at microwave frequency is constructed by using four double-layered L-shaped strips which are rotated by 90⁰ with respect to their adjacent metal strip. These different size strips allows another degree of freedom in the equalizing the orthogonal components of the electric fields at the output interface with 90^o phase difference when the x-polarized wave excites the structure. The proposed structure exhibits the properties of chiral medium such as optical activity and circular dichroism. The L shaped chiral objects can be etched on double side substrate. The effect of structure on different electromagnetic parameter like chirality, optical activity and reflection characteristics are analyzed. Due to the strong chirality the structure posses negative refractive index for either left circularly or right circularly polarized wave. In this paper, a numerical study in the frequency domain of the electromagnetic-wave propagation through these types of structures is achieved by using the commercial software Computer Simulation Technology (CST) microwave studio.

Abstract: The elastic buckling behaviors of graphene nanosheets are investigated via molecular structural mechanics based finite element method. The size-and chirality-dependent critical buckling stresses of monolayer and bilayer graphene nanosheets are calculated for different geometrical dimensions and boundary constraints, respectively. By analogy with classical buckling theory of elastic plate, the analytical expressions of critical buckling stress are derived for the graphene nanosheets with different boundary constraints, and the comparisons of analytical results with the counterparts obtained by molecular structural mechanics simulation show a good consistency.

Abstract: Metamaterials composed of metallic strips on both side of the substrate are analyzed at microwave frequencies. The rectangular shaped metallic foils are rotated by 90^o with respect to their adjacent metal strip on each side of the substrate. The twist angle between the cross strips on opposite sides of substrate is 40^o. The proposed structure exhibits the properties of chiral medium such as optical activity and circular dichroism due to their cross coupling between the electric and magnetic fields. The rectangular shaped chiral objects can be easily fabricated on double side substrate. Both transmission and reflection resonances are illustrated. The chiral configuration of this metamaterial structure is analyzed in commercial software Computer Simulation Technology (CST) microwave studio and negative refractive index is observed. Moreover, other electromagnetic structural parameters such as chirality, optical activity and polarization effect are discussed.