Computer modelling of mixed metal fluorides for optical applications

This paper describes a new computational method for predicting the optical behaviour of doped inorganic materials. There is considerable interest in using inorganic materials in photonic devices, and in many cases, the optical properties of these materials depend on doping by ions such as those from the rare earth series. Among the inorganic materials of interest are the mixed metal fluorides (e.g. BaLiF(3), BaY(2)F(8), YLiF(4), LiCaAlF(6), LiSrAlF(6)), doped with trivalent rare earth ions. The paper describes the use of Mott-Littleton calculations to determine the optimum location for dopant ions, followed by crystal field calculations which make direct use of the output of the Mott-Littleton calculations to calculate the optical properties of the dopant ion taking into account its symmetry and the positions of the surrounding ions, including any vacancies or interstitial ions present by virtue of charge compensation. It is then possible to predict whether a given dopant ion at a particular site in a material will have favourable optical properties.     

Amphoteric doping of carbon nanotubes by encapsulation of organic molecules: electronic properties and quantum conductance

In order to investigate and optimize the electronic transport processes in carbon nanotubes doped with organic molecules, we have performed large-scale quantum electronic structure calculations coupled with a Green's function formulation for determining the quantum conductance. Our approach is based on an original scheme where quantum chemistry calculations on finite systems are recast to infinite, non-periodic (i.e., open) systems, therefore mimicking actual working devices. Results from these calculations clearly suggest that the electronic structure of a carbon nanotube can be easily manipulated by encapsulating appropriate organic molecules. Charge transfer processes induced by encapsulated organic molecules lead to efficient n- and p-type doping of the carbon nanotube. Even though a molecule can induce p and n doping, it is shown to have a minor effect on the transport properties of the nanotube as compared to a pristine tube. This type of doping therefore preserves the intrinsic properties of the pristine tube as a ballistic conductor. In addition, the efficient process of charge transfer between the organic molecules and the nanotube is shown to substantially reduce the susceptibility of the pi electrons of the nanotube to modification by oxygen while maintaining stable doping (i.e., no dedoping) at room temperature.     

纳米管掺杂聚合物稳定蓝相液晶的电场响应性能

通过将不同尺寸的多壁碳纳米管(MWNTs)掺杂到聚合物稳定蓝相(PSBP)液晶中研究了体系的蓝相温度稳定性和电场响应性能。 小尺寸MWNTs的加入使PSBP电诱导反射波谱宽化的阈值电压显著降低。 MWNTs掺杂PSBP液晶光子晶体的电响应阈值场强降低至0.1 V/μm,在1.3 V/μm电场下反射光谱谱带宽度可从20 nm拓宽至310 nm。 该材料在反射型显示、可调滤光片等领域具有潜在应用价值。     

Structural,nonlinear optical,and vibration properties of the C40H10 buckybowl modified with nitrogen atoms

Possible isomers of buckybowl with various N contents (5–15%) were systematically searched with density functional theory (DFT) calculations. N doped buckybowls are predicted to be more stable than the well‐known C₄₈N₁₂ azafullerene. The N‐doping pattern in buckybowl presents different character from that of fullerenes. Vibrational properties of the heterobuckybowls vary with the relative positions of substituted atoms in buckybowl. The modified electronic properties of buckybowl by N doping lead to enhancement of the second hyperpolarizabilities, which implies that heterobuckybowls could be potential nonlinear optical materials and possible building blocks for molecular electronics and photonic devices. © 2015 Wiley Periodicals, Inc.     

Theoretical study of the structure and optical properties of carbon-doped rutile and anatase titanium oxides

The structure and optical properties of carbon-doped titanium oxides, TiO2, in the rutile and anatase forms have been investigated theoretically from first principles. Two possible doping sites were studied, carbon at an oxygen site (anion doping) and carbon at a titanium site (cation doping). The calculated structures suggest that cation-doped carbon atoms form a carbonate-type structure, whereas anion-doped carbon atoms do not invoke any significant structural change. A density-of-states analysis revealed three in-gap impurity states for anion doping. The optical properties of anion-doped cells qualitatively agree with the experimentally reported visible-light absorbance values. We ascribe part of the absorption to transitions from the valence band to one of the impurity states. These transitions should be able to promote photocatalytic reactions, because electron holes in the valence band are considered to be crucial for this process. Neither in-gap impurity states nor visible-light absorbance were observed in the case of cation doping. The effect of oxygen vacancies was also investigated. Introduction of oxygen vacancies into anion-doped TiO2 populates the impurity states and thus suppresses photocatalysis. The interaction of a doped carbon atom with an oxygen vacancy at a finite spatial separation was also carried out. The possibility of either a carbon-oxygen vacancy pair or higher carbon-oxygen vacancy complex existing is discussed.     

High-quality manganese-doped zinc sulfide quantum rods with tunable dual-color and multiphoton emissions

We report a simple, fast and green phosphine-free colloidal chemistry to synthesize high-quality wurtzite-type Mn-doped ZnS quantum rods (QRs) with tunable diameters (1.6-5.6 nm), high aspect ratios (up to 50), variable Mn doping levels (0.18-1.60%), and high quantum yields (up to 45%). The electron paramagnetic resonance spectra with modeling reveal the successful doping of paramagnetic Mn(2+) ions in the host ZnS QRs. The Mn-doped ZnS QRs demonstrate tunable dual-color (orange and blue) emissions by tuning the doping levels and UV excitation wavelengths. The orange emission with long decay lifetime (3.3 ms) originates from the doped Mn(2+) states, while the blue emission with fast decay lifetime (0.31 ns) is attributed to the QR surface states. The bright two- and three-photon excitation upconversion luminescence from the Mn-doped ZnS QRs have been observed using tunable near-infrared femtosecond laser. Our strategy provides a versatile route to programmably control the optical properties of anisotropic semiconductor nanomaterials, which may create new opportunities for photonic devices and bioimaging applications.     

Modification of carbon nano-objects in low-temperature plasma for use in polymer nanocomposites

Literature on the modification of carbon nanotubes and nanofibers in a low-temperature plasma has been surveyed. Basic techniques for the treatment of nano-objects in discharges of various types and various devices used in these processes have been described. Instrumental methods for the investigation of plasma-modified carbon nanotubes and nanofibers and the properties of composites prepared from them with different polymer matrices have been discussed.     

Advances in Photonic Devices Based on Optical Phase-Change Materials

Phase-change materials (PCMs) are important photonic materials that have the advantages of a rapid and reversible phase change, a great difference in the optical properties between the crystalline and amorphous states, scalability, and nonvolatility. With the constant development in the PCM platform and integration of multiple material platforms, more and more reconfigurable photonic devices and their dynamic regulation have been theoretically proposed and experimentally demonstrated, showing the great potential of PCMs in integrated photonic chips. Here, we review the recent developments in PCMs and discuss their potential for photonic devices. A universal overview of the mechanism of the phase transition and models of PCMs is presented. PCMs have injected new life into on-chip photonic integrated circuits, which generally contain an optical switch, an optical logical gate, and an optical modulator. Photonic neural networks based on PCMs are another interesting application of PCMs. Finally, the future development prospects and problems that need to be solved are discussed. PCMs are likely to have wide applications in future intelligent photonic systems.     

Molecular dynamics simulation of anticancer drug delivery from carbon nanotube using metal nanowires

In this study, we have investigated delivery of cisplatin as the anticancer drug molecules in different carbon nanotubes (CNTs) in the gas phase using molecular dynamics simulation. We examined the shape and composition of the releasing agent by using the different nanowires and nanoclusters. We also investigated the doping effect on the drug delivery process using N-, Si, B-, and Fe-doped CNTs. Different thermodynamics, structural, and dynamical properties have been studied by using the pure and different doped CNTs in this study. Our results show that the doping of the CNT has significant effect on the rate of the drug releasing process regardless of the composition of the releasing agent. © 2019 Wiley Periodicals, Inc.     

Wall‐ and Hybridisation‐Selective Synthesis of Nitrogen‐Doped Double‐Walled Carbon Nanotubes

Controlled nitrogen‐doping is a powerful methodology to modify the properties of carbon nanostructures and produce functional materials for electrocatalysis, energy conversion and storage, and sensing, among others. Herein, we report a wall‐ and hybridisation‐selective synthetic methodology to produce double‐walled carbon nanotubes with an inner tube doped exclusively with graphitic sp²‐nitrogen atoms. Our measurements shed light on the fundamental properties of nitrogen‐doped nanocarbons opening the door for developing their potential applications.     

Effects of a chemically modified multiwall carbon nanotubes on electro-optical properties of PDLC films

Polymer dispersed liquid crystal (PDLC) films are fabricated by well-known polymerization-induced phase separation method. In this paper, the dispersion of multi-walled carbon nanotubes (MWCNT) in liquid crystals has been enhanced by chemical modification and we have investigated their effects on the morphology, electro-optical properties and conductivity of the PDLC films. Results indicated that the threshold voltage and the saturation voltage of PDLC films decreased with the increase of the doping concentration of MWCNT or chemically modified MWCNT, because carbon nanotubes can enhance the electric field by reducing the resistivity of the medium and increasing the capacitance of the cells. It can be viewed obviously that the contrast ratio of the PDLC films doped with the chemically modified MWCNT is higher than that of the MWCNT.     

Enhanced dielectric and electro-optical properties of a newly synthesised ferroelectric liquid crystal material by doping gold nanoparticle-decorated multiwalled carbon nanotubes

In this article, a newly synthesised ferroelectric liquid crystal (FLC) material, namely LAHS 22, has been characterised. The characterisation of the FLC material has been performed using dielectric relaxation spectroscopy, differential scanning calorimetry and polarisation optical microscopy. We observed an enhancement in the dielectric and electro-optical properties of the FLC material by incorporating gold nanoparticles (GNPs)-decorated multiwalled carbon nanotubes (MWCNTs). The GNPs-decorated MWCNTs cause an increment in dielectric dispersion (up to kHz), absorption, spontaneous polarisation and rotational viscosity of the FLC material. The pure and GNPs-decorated MWCNTs doped FLC cells were analysed by means of various dielectric spectroscopic and optical measurements. The observed enhancement in the dielectric and electro-optical properties of the FLC material has also been studied with concentration of GNPs-decorated MWCNTs in FLC material. The GNPs-decorated MWCNTs/FLC composites are not only of fundamental importance, but also useful materials for device applications such as liquid crystal displays and memory devices.     

Preparation and characterization of anthracenecarboxylic acid doped polyaniline thin films

Doped polyaniline films were prepared with electrochemistry method. A small conjugated molecule, anthracenecarboxylic acid(2-ACA), was used as the dopant, considering its electrical activeness due to the conjugated π-π* structure. Film morphology of doped and undoped polyaniline samples was investigated. The corresponding changes in optical and electrical properties after ACA doping were discussed. By measuring and calculating their energy level distribution, a promising application of polyaniline thin films as buffer layer in optic-electric devices is expectable.     

碳纳米管-聚合物复合材料的研究进展

本文综述了两类碳纳米管-聚合物复合材料的制备方法,碳纳米管/复合材料的力学、光、电化学等性质,以及当前研究的焦点和存在的问题,侧重讨论碳纳米管与聚合物相互作用的机理,并展望两类复合材料的应用前景。     

Preparation and optical properties of ThO(2) and Eu-doped ThO(2) nanotubes by the sol-gel method combined with porous anodic aluminum oxide template

In this paper, we report the synthesis of thorium oxide and Eu-doped thorium oxide nanotubes for the first time using the sol-gel method in porous anodic aluminum oxide template. Transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were applied to characterize the morphology and structure of the as-prepared nanotubes. It has been demonstrated that Eu(3+) ions were homogeneously doped into the ThO(2) crystal lattice. The optical properties resulting from Eu-doped products were investigated by means of photoluminescence spectroscopy. Strong visible light emissions were observed at low doping concentration, and the luminescent intensity decreased at high doping concentration. The luminescent centers were concluded to be the Eu(3+) ions in the cubic (O(h)) sites rather than the C(3v) sites, which accounted well for the decrease of luminescent intensity at high doping concentration.     

Generating suspended single-walled carbon nanotubes across a large surface area via patterning self-assembled catalyst-containing block copolymer thin films

Using self-assembled block copolymers as templates, catalytically active nanostructures with controlled size and space have been produced. A self-assembled polystyrene-b-polyferrocenylsilane thin film and monolayer of surface micelles of cobalt-complexed polystyrene-b-poly(2-vinylpyridine) are fully compatible with novolac-based conventional photoresists. Combining bottom-up self-assembly of catalyst-containing block copolymers with top-down microfabrication processing, plateaus covered with arrays of catalytically active nanostructures have been generated. Spatially selective growth of suspended single-walled carbon nanotubes over a large surface area has been achieved. Greatly enhanced Raman signals have been detected from the suspended tubes. This facile method of creating highly ordered catalyst nanostructures on top of posts enables the rational synthesis of suspended carbon nanotubes, thus facilitating the study of CNT properties by optical methods and enabling the fabrication of devices based on suspended CNTs.     

Cu,Ni, Co掺杂对Fe碳纳米管的结构及电催化性能的影响

在制备含铁碳纳米管(Fe@NCNTs)的过程中分别加入铜(Cu)、 镍(Ni)和钴(Co)盐, 得到3种双金属碳纳米管材料(CuFe@NCNTs, NiFe@NCNTs和CoFe@NCNTs). 通过扫描电子显微镜(SEM)、 N₂气吸附-脱附曲线测试、 X射线衍射(XRD)、 X射线光电子能谱(XPS)和拉曼光谱(Raman)对3种双金属碳纳米管的结构和组成进行了 表征, 证明3种双金属均可得到碳纳米管结构. 3种材料均表现出双功能电催化活性[氧还原反应(ORR)和氧 析出反应(OER)]; 锌-空气电池(ZABs)性能测试结果表明, CuFe@NCNTs基ZABs具有最大的峰值功率密度 (53 mW/cm²), NiFe@NCNTs和CoFe@NCNTs基ZABs具有更好的倍率性能, 3种双金属碳纳米管ZABs的循环稳定性均优于Pt/C-IrO₂ ZABs.     

Dispersions, novel nanomaterial sensors and nanoconjugates based on carbon nanotubes

Nanomaterials are structures with dimensions characteristically much below 100 nm. The unique physical properties (e.g., conductivity, reactivity) have placed these nanomaterials in the forefront of emerging technologies. Significant enhancement of optical, mechanical, electrical, structural, and magnetic properties are commonly found through the use of novel nanomaterials. One of the most exciting classes of nanomaterials is represented by the carbon nanotubes. Carbon nanotubes, including single-wall carbon nanotubes, multi-wall carbon nanotubes, and concentric tubes have been shown to possess superior electronic, thermal, and mechanical properties to be attractive for a wide range of potential applications They sometimes bunch to form “ropes” and show great potential for use as highly sensitive electronic (bio)sensors due to the very small diameter, directly comparable to the size of single analyte molecules and that every single carbon atom is in direct contact with the environment, allowing optimal interaction with nearby molecules. Composite materials based on integration of carbon nanotubes and some other materials to possess properties of the individual components with a synergistic effect have gained growing interest. Materials for such purposes include conducting polymers, redox mediators and metal nanoparticles. These tubes provide the necessary building blocks for electronic circuits and afford new opportunities for chip miniaturization, which can dramatically improve the scaling prospects for the semiconductor technologies and the fabrication of devices, including field-effect transistors and sensors. Carbon nanotubes are one of the ideal materials for the preparation of nanoelectronic devices and nanosensors due to the unique electrical properties, outstanding electrocatalytic properties, high chemical stability and larger specific surface area of nanotubes. Carbon nanotubes are attractive material for supercapacitors due to their unique one-dimensional mesoporous structure, high specific surface area, low resistivity and good chemical stability. Nanoscaled composite materials based on carbon nanotubes have been broadly used due to their high chemical inertness, non-swelling effect, high purity and rigidity. The integration of carbon nanotubes with organics, biomaterials and metal nanoparticles has led to the development of new hybrid materials and sensors. Hybrid nanoscale materials are well established in various processes such as organic and inorganic compounds, nucleic acid detachment, protein separation, and immobilization of enzymes. Those nanostructures can be used as the building blocks for electronics and nanodevices because uniform organic and metal coatings with the small and monodisperse domain sizes are crucial to optimize nanoparticle conductivity and to detect changes in conductivity and absorption induced by analyte adsorption on these surfaces. The highly ordered assembly of zero-dimensional and one-dimensional nanoparticles is not only necessary for making functional devices, but also presents an opportunity to develop novel collective properties.     

Electronic Structure of Doped Boron Nitride Nanotubes as Potential Catalysts of Photochemical Water Splitting

Semiconductors with band gap widths of 1.5–2.8 eV are used as catalysts for hydrogen production by photochemical water splitting. The electronic states of BN nanotubes doped with Group III–V nontransition elements have been studied by quantum-chemical methods. It has been found that nanotubes with a small excess of boron or with carbon atoms substituted for some boron atoms can be used as candidates for creation of such catalysts since they have optical absorption in this spectral range.     

The effect of 3<Emphasis Type="Italic">d</Emphasis>-metal dopants on the electronic structure of carbon nanotubes

In the course of synthesis of nanotubes, atoms of transition metals used as a catalyst can be substituted for carbon atoms. The electronic properties of semiconducting (13,0) and metallic (5,5) nanotubes doped with Co and Ni atoms have been calculated by ab initio quantum-chemical methods. The total and partial densities of states have been determined. The conclusion has been made that Co and Ni substituted for carbon disturb the electronic structure of metallic and semiconducting nanotubes. Such dopants can be detected by spectral and electrical measurements.