Optical Properties Of Nanotubes Research Articles

Effect of the Deposition of Vanadium-Oxide on the Photocatalytic Activity of TiO2 Nanotubes and Its Photodiode Performance Interfaced with CH3NH3PbI3 Single Crystal

In this study, we report the influence of vanadium oxide (VO), as a photosensitive component, on the photoactivity of TiO2 nanotubes (TNTs). A series of TNTs of varying tube diameter were synthesized by the anodization of titanium foils at different voltages, while vanadium oxide was deposited on TNTs by wet chemical deposition. An improvement in the optical properties of nanotubes was observed after the deposition of vanadium oxide. An improvement in the optical properties (redshift in UV-Vis spectra) of TNTs and TNT/VO was noted. The photocatalytic activity was improved with increasing tube diameter, while it was weakened after the deposition of VO. Furthermore, photoactivity was investigated in photodiodes based on TNTs or TNT/VO and single crystals of CH3NH3PbI3. The photoelectric measurement revealed that different TNT diameters did not influence the I-V characteristic of the photodiodes, while the deposition of VO improved the photocurrent for smaller TNTs.

Graphene Nanoribbon Bending (Nanotubes): Interaction Force between QDs and Graphene

Carbon materials in different shapes—such as fullerene molecules (0D), nanotubes and graphene nanoribbons (1D), graphene sheets (2D), and nanodiamonds (3D)—each have distinct electrical and optical properties. All graphene-based nanostructures are expected to exhibit extraordinary electronic, thermal, and mechanical properties. Moreover, they are therefore promising candidates for a wide range of nanoscience and nanotechnology applications. In this work, we theoretically studied and analyzed how an array of quantum dots affects a charged graphene plate. To that end, the array of quantum dots was embedded on the graphene plate. Then, considering the interaction between QDs and graphene nanoribbons, we transformed the charged plate of a graphene capacitor into a nanotube using the bipolar-induced interaction and the application of an external electromagnetic field. In this work, the dimensions of the graphene plate were 40 nm × 3100 nm. The bending process of a charged graphene plate is controlled by the induced force due to the applied electromagnetic field and the electric field induced by the quantum dots. Finally, using the predetermined frequency and amplitude of the electromagnetic field, the graphene nanoribbon was converted into a graphene nanotube. Since the electrical and optical properties of nanotubes are different from those of graphene plates, this achievement has many practical potential applications in the electro-optical industry.

Electronic and optical properties of ultra-small diameter armchair carbon and boron nitride nanotubes by PBE, TB-mBJ and YS-PBE0 functionals

We have investigated the electronic and optical properties of ultra-small (3,3), (4,4) and (5,5) armchair single walled nanotubes carbon (C-SWNTs) and boron nitride (BN-SWNTs) using three density functional methods of different categories, namely, PBE, TB-mBJ and hybrid functional YS-PBE0. A density functional theory (DFT) within the full-potential linearized augmented-plane wave (FP-LAPW) method, was used to study the structures, electronic and optical properties of these nanotubes. The calculation of optical properties has been performed under electric fields polarized both parallel and perpendicular with respect to the nanotube axis. The results show that the hybrid functional YS-PBE0 perform the best for calculations of band gap of BN-SWNTs (5.27–5.54 eV), while for C-SWNTs the PBE and TB-mBJ functionals obtain band gap range (0.16–0.28 eV) with smaller errors compared to experimental values and confirming the semiconducting behavior of the studied C-SWNTs. The dielectric function is anisotropic for all tubes and is larger in the parallel direction. The results show also that for C-SWNTs, the static refractive index is higher than those of BN-SWNTs and it has an inverse correlation with the C-SWNTs diameter. This proves that for optoelectronic applications, it is improve to use the BN-SWNTs doped than intrinsic.

(Invited) Low Temperature Photoluminescence of Individual SWNTs Emitting at Telecommunication Wavelengths

In the quest for a nanoscale light emitter, carbon nanotubes have exceptional assets: they have a diameter dependent band-gap compatible with telecom wavelengths, they can possibly be operated at room temperature due to huge exciton binding energies and they emit anti-bunched photons, as required for quantum telecommunications. Here, we will present a complete set of low temperature photoluminescence (PL) experiments on single SWNTs emitting at the telecommunication wavelengths showing statistically relevant narrow line widths. These nanotubes are produced with a high temperature synthesis method (laser ablation – L-SWNTs), which is known to lead to a higher crystalline quality. The narrowing of the lines will be discussed in terms of a reduction of the exciton-phonon coupling in L-SWNTs. An exciton localization up to 6 times larger than in CVD-grown SWNTs is reported suggesting that the crystalline quality play a major role in the optical properties of nanotubes at low temperature. This study shows that several degrees of exciton localization are achievable in SWNTs. Therefore, identification of high crystalline quality nanotubes is a key step towards the control of exciton localization, going continuously from 0D to 1D confinement.

Optical properties of single‐walled carbon nanotubes filled with CuCl by gas‐phase technique

Single‐walled carbon nanotubes (SWCNTs) have unique electronic and optical properties, which are attractive in various applications. These properties can be further improved by functionalization. In this work, it is shown that filling nanotubes with CuCl leads to improvement of their electro‐conductive and optical transmission properties up to outstanding level. The improvement is due to the significant p‐type doping of the functionalized nanotubes. That leads to a huge increase in nanotubes charge carrier density and the considerable decrease of the nanotubes absorption via Pauli blocking. The functionalization was realized via a gas‐phase filling of SWCNTs with CuCl. We demonstrate the effect of huge doping on optical properties of nanotubes with different average diameters. The observed sufficient stability of the CuCl@SWCNT composite is proved to be due to the formation of quasi‐one‐dimensional (1D) CuCl crystal inside nanotubes. AC‐HRTEM image of 1D CuCl crystal formed inside SWCNT.

Synthesis and oxygen vacancy-related photocatalytic properties of ZnO nanotubes grown by thermal evaporation

ZnO nanotubes with breaches in the walls (Breached ZnO nanotubes) with diameters of 50–200 nm and lengths up to several micrometers have been produced in high yield on glass substrates by heating Zn powder at 600–700 °C at a total gas pressure of 20 Pa. We assume formation of ZnO nanotubes involves four steps: formation of Zn vapor; formation of ZnO nanoplates; transformation of ZnO nanoplates into ZnO nanoleaves; and transformation of ZnO nanoleaves into ZnO nanotubes. The optical properties of nanotubes were studied by use of photoluminescence spectroscopy; strong green emission related to oxygen vacancies was observed. Study of the degradation of methyl orange (MO) revealed that the photocatalytic activity of the nanotubes was high, because of their high surface-to-volume ratios and abundant oxygen vacancies near their surfaces. This type of high-surface-area ZnO nanotube has potential for environmental applications.

Microscopic and spectroscopic investigation of MoS2 nanotubes/P3HT nanocomposites

Blends of conductive polymer poly(3-hexylthiophene) (P3HT) and size controlled MoS2 nanotubes (NTs) were prepared focusing on procedures which do not alter the electrical and optical properties of nanotubes, i.e., without surfactants. After disassembly of as-grown hedgehog-like self-assemblies of the MoS2 NTs, relatively homogeneous dispersions of the NTs in P3HT were prepared. Thin films of these blends were prepared via spin coating. The NTs were found efficiently wetted by the P3HT and nearly completely immersed in the films. The surface structure was composed of pure P3HT lamellae. Photoluminescence spectra taken on P3HT/MoS2 NT thin films revealed a quenching effect, which depends on the concentration of NTs. Results of optical microscopy and spectroscopy investigations, scanning tunnelling microscopy and scanning electron microscopy studies are shown.

Electronic structure and optical spectra of semiconducting carbon nanotubes functionalized by diazonium salts

We report density functional (DFT) calculations on finite-length semiconducting carbon nanotubes covalently and non-covalently functionalized by aryl diazonium moieties and their chlorinated derivatives. For these systems, we investigate (i) an accuracy of different functionals and basis sets, (ii) a solvent effect, and (iii) the impact of the chemical functionalization on optical properties of nanotubes. In contrast to B3LYP, only long-range-corrected functionals, such as CAM-B3LYP and wB97XD, properly describe the ground and excited state properties of physisorbed molecules. We found that physisorbed cation insignificantly perturbs the optical spectra of nanotubes. In contrast, covalently bound complexes demonstrate strong redshifts and brightening of the lowest exciton that is optically dark in pristine nanotubes. However, the energy and oscillator strength of the lowest state are dictated by the position of the molecule on the nanotube. Thus, if controllable and selective chemical functionalization is realized, the PL of nanotubes could be improved.

Time-Resolved Investigation of Excitation Energy Transfer in Carbon Nanotube–Porphyrin Compounds

Single-Wall Carbon Nanotubes (SWNTs) non-covalently functionalized with organic molecules have proven to be a very promising light-harvesting system. The goal is to combine the unique transport and optical properties of nanotubes with the wide tunability of organic molecules properties. Among those molecules, porphyrins, a precursor of photosynthetic centers, show a strong absorption in the visible that is already used in dye sensitized hybrid solar cells [1]. Porphyrins link to SWNTs through π-stacking interaction which preserves most of the intrinsic properties of the SWNTs, in contrast with covalent functionalization. Moreover, the coupling is still strong enough to induce new functionalities. It was recently shown that efficient excitation energy transfer (EET) can occur in such system [2,3]. The very high quantum yield reported in this system suggests that the EET mechanism must occur on an ultrafast time-scale [4]. In order to characterize the nature of the EET mechanism, we investigate its dynamics at a subpicosecond time scale, by means of pump-probe spectroscopy. We show that the ground state recovery time of porphyrin in the compound is reduced by several orders of magnitude compared to the case or free porphyrin (Fig. 1). Concomitantly, a strong bleaching signal is observed on the optical resonances of the nanotubes showing an ultrafast population build-up upon excitation of the porphyrin (Fig. 2). We conclude that the energy transfer occurs on a time scale shorter than 100fs and that the surrounding of SWNTs by porphyrins does not affect the relaxation dynamics.

Synthesis and characterization of ion-exchangeable titanate nanotubes.

Titanate nanotubes were synthesized under hydrothermal conditions. The optimized synthesis (100-180 degrees C, longer than 48 h), thermal and hydrothermal stability, ion exchangeability and consequent magnetic and optical properties of the titanate nanotubes were systematically studied in this paper. First, nanotubes with monodisperse pore-size distribution were prepared. The formation mechanism of the titanate nanotubes was also studied. Second, the thermal and hydrothermal stability were characterized with X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FTIR), and Raman spectroscopy. Results showed that sodium ions played a significant role in the stability of the frameworks. Third, the selective ion exchangeability was demonstrated with a series of ions. The ion substitution also enlarged the BET surface area of the titanate nanotubes to 240 m(2) x g(-1). Combination of these two features implied that these nanotubes might be functionalized by substitution of different transitional-metal ions and consequently used for selective catalysis. Magnetism, photoluminescence, and UV/Vis spectra of the substituted titanate nanotubes revealed that the magnetic and optical properties of the nanotubes were modifiable.