Single-Walled Carbon Nanotubes Acting as Controllable Transport Channels

The motion and equilibrium distribution of water molecules adsorbed inside neutral and negatively charged singlewalled carbon nanotubes (SWNTs) have been studied using molecular dynamics simulations (MDSs) at room temperature based on CHARMM (Chemistry at HARvard Molecular Mechanics) potential parameters. We find that water molecules have a conspicuous electropism phenomenon and regular tubule patterns inside and outside the charged tube wall. The analyses of the motion behaviour of water molecules in the radial and axial directions show that by charging the SWNT, the adsorption efficiency is greatly enhanced, and the electric field produced by the charged SWNTs prevents water molecules from flowing out of the nanotube. However, water molecules can travel through the neutral SWNT in a fluctuating manner. This indicates that by electrically charging and uncharging the SWNTs, one can control the adsorption and transport behaviour of polar molecules in SWNTs for using as a stable storage medium or long transport channels. The transport velocity can be tailored by changing the charge on the SWNTs, which may have a further application as modulatable transport channels.     

Vibrational study on styrene functionalized porous silicon: A method for determining the relative yield of different grafting routes

A new semi-quantitative method providing the relative efficiency of three different organic functionalization reactions onto porous silicon has been set up, based on infrared absorption data. Compared to previously reported techniques, it enables a direct titration of the grafted molecules. We demonstrated that grafting of Si-styrenyl moieties by ethylaluminium dichloride mediated hydrosilylation of phenylacetylene leads to higher yields than organometallic addition onto either hydrogenated or brominated silicon.     

Raman spectral features of longer polyynes HC2 nH ({\sf n=4}–8) in SWNTs

Size-selected linear hydrocarbon molecules, polyynes HC_2nH, were contacted in solutions with single-wall carbon nanotubes (SWNTs) prepared from laser-ablated metal/carbon composite rods (Rh/Pt/C) to produce polyyne-encapsulating SWNTs, HC_2nH@SWNT(RhPt). New Raman spectral features were observed at 2120, 2061, 2017, 1982, and 1963 cm^-1 for five polyynes of n=4–8, respectively, and identified as the vibrational excitation of symmetric stretching modes of the molecules inside the SWNTs. The Raman spectra were compared with those observed for polyynes on Ag islands (SERS) and in solutions. The filling factor was investigated from the concentration dependence of the Raman intensity for HC₁₀H@SWNT(NiCo) to give an estimate of one polyyne molecule per ~350 carbon atoms of SWNTs, providing a picture for head-to-tale filling of aligned C₁₀H₂ molecules inside the SWNTs.     

Random telegraph noise in carbon nanotubes and peapods

The switching of resistance between two discrete values, known as random telegraph noise (RTN), was observed in individual single-walled carbon nanotubes (SWNTs) and C₆₀-filled SWNTs (the so-called peapods). The RTN has been studied as a function of bias-voltage and gate-voltage as well as temperature. By analyzing the features of the RTN, we identify three different types of RTN existing in the SWNT related systems. While the RTN can be generated by the various charge traps in the vicinity of the SWNTs, the RTN for metallic SWNTs is mainly due to reversible defect motions between two metastable states, activated by inelastic scattering with ballistic electrons. On the other hand, the noise for peapods can be attributed to the motion of C₆₀ molecules in hollow space of SWNTs.     

Effect of purification on the electron structure and field emission characteristics of a carbonaceous material containing single-wall carbon nanotubes

A carbonaceous material containing single-wall carbon nanotubes (SWNTs) has been synthesized by arc-discharge evaporation of graphite with a catalytic additive of nickel and cobalt powders. The synthesized SWNTs were purified from an amorphous carbon component (soot) and the catalyst particles by boiling in nitric acid. A comparison of the X-ray fluorescence spectra measured before and after this treatment showed that acid etching significantly decreased the content of soot in the material. The material enriched with SWNTs is characterized by a reduced threshold for the appearance of the field emission current, which is explained by a decrease in the screening effect of soot. The current-voltage characteristics of SWNTs exhibit a hysteresis, which is suggested to be due to the adsorption of molecules and radicals on the surface and at the ends of carbon nanotubes.     

Nonlocal conductance modulation by molecules: scanning tunneling microscopy of substituted styrene heterostructures on H-terminated Si(100)

One-dimensional organic heterostructures consisting of contiguous lines of CF3- and OCH3-substituted styrene molecules on silicon are studied by scanning tunneling microscopy and ab initio simulation. Dipole fields of OCH3-styrene molecules are found to enhance conduction through molecules near CF3-styrene/OCH_{3}-styrene heterojunctions. Those of CF3-styrene depress transport through the nearby silicon. Thus the choice of substituents and their attachment site on host molecules provide a means of differentially tuning molecule and substrate transport at the molecular scale.     

紫外激光和压力共同作用下C60-peapod的聚合相变研究

采用气相扩散方法将C₆₀分子填充到单壁碳纳米管(SWNTs)中，制备出高填充比率的豆荚形纳米材料C₆₀@SWNT，又称为peapod.用金刚石对顶砧(DAC)装置获得高压，在高压下同时利用紫外激光处理样品，通过激光和压力的共同作用研究了C₆₀分子在碳管内的聚合相变.在21.5GPa高压下，同时紫外激光(325nm)照射30min后，拉曼光谱表明C₆₀分子在碳管内发生了聚合，形成一维链状O相聚合结构，且该相变是不可逆的. 关键词： 60 peapod')" href="#">C₆₀ peapod 紫外激光 高压 拉曼光谱     

Standing or lying C70s encapsulated in carbon nanotubes with different diameters

Single-walled carbon nanotubes (SWNTs) encapsulating C₇₀s, so-called C₇₀ peapods, were synthesized in high yield by a vapor-phase doping method. Raman spectra, high resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) measurement indicate that the tube diameter is one of the important factors to determine the orientation of C₇₀ molecules inside the SWNTs. SWNTs with different diameters give different alignment of C₇₀ molecules. The lying orientation is favorable over the standing orientation in thin nanotube, i.e. 1.36 nm nanotubes, whereas the standing orientation is favorable in thick nanotubes, i.e. 1.49 and 1.61 nm nanotubes.     

One-step preparation of water-soluble single-walled carbon nanotubes

A novel one-step process using potassium persulfate (KPS) as oxidant is proposed in this paper to prepare water-soluble single-walled carbon nanotubes (SWNTs). The process without the need for organic solvents and acids is a low-cost, eco-friendly, facile method. Morphology observation by atomic force microscopy (AFM) indicates that the KPS-treated SWNTs were effectively debundled without obvious shortening in their length. The functional groups and thermal stability of the treated SWNTs were analyzed by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). XPS results show that several functional groups such as potassium carboxylate (-COOK), carbonyl (-CO) and hydroxyl (-C-OH) groups were formed on the surfaces of the SWNTs, while the TGA results reveal that the quantity of the functional groups can reach to approximately 20%.     

Photochromic Properties and Surface Enhanced Raman Scattering Spectra of Indoline Spiropyran in Silver-Based Nanocomposite Films

The structure and photochromic transformations of composite organometallic nanosystems composed of Ag nanoparticles covered with a layer of indoline-spiropyran (ISP) molecules from solutions were studied by spectrophotometry, surface Raman scattering spectroscopy (SERS) and quantum chemistry. Analysis of experimental data showed that studied nanostructured systems have photochromic properties, manifested in the reversible photo-induced changes both of the electronic-absorption spectra and of the relative intensity of the SERS bands. The open form of ISP, formed in the organometallic nanostructured film as a result of photochromic transformations, has an adsorption geometry, and, possibly, a conformation different from that formed as a result of chemisorption of ISP molecules on silver colloids.     

Novel donor-acceptor materials for organic light-emitting diodes based on α-cinnamoyl cyclic ketene dithioacetals

A new family of α-cinnamoyl cyclic ketene dithioacetals (CCKDA) based on a typical donor-π-acceptor structure were designed and synthesized. These unsymmetrical π-conjugated molecules consisted of different electron-donating moiety and the same ketene dithioacetals acceptor. The introduction of different donor moieties changed energy level parameters of the molecules and allowed a fine tuning of their optical and electrical properties. It is promising to apply these compounds in organic light-emitting diodes (OLED) as light-emitting and electron-transporting materials.     

Surfactant-nanotube interactions in water and nanotube separation by diameter: atomistic simulations

A non-destructive sorting method to separate single-walled carbon nanotubes (SWNTs) by diameter was recently proposed. By this method, SWNTs are suspended in water by surfactant encapsulation and the separation is carried out by ultracentrifugation in a density gradient. SWNTs of different diameters are distributed according to their densities along the centrifuge tube. A mixture of two anionic surfactants, namely sodium dodecylsulfate (SDS) and sodium cholate (SC), presented the best performance in discriminating nanotubes by diameter. Unexpectedly, small diameter nanotubes are found at the low density part of the centrifuge tube. We present molecular dynamics studies of the water-surfactant-SWNT system to investigate the role of surfactants in the sorting process. We found that surfactants can actually be attracted towards the interior of the nanotube cage, depending on the relationship between the surfactant radius of gyration and the nanotube diameter. The dynamics at room temperature showed that, as the amphiphile moves to the hollow cage, water molecules are dragged together, thereby promoting the nanotube filling. The resulting densities of filled SWNT are in agreement with measured densities.     

XPS Spectra of organometallic phenyl compounds of P,As, Sb and Bi

XPS spectra of 54 organometallic compounds of group V elements with various coordinations are measured in the solid state. Core level binding energy data for the various atoms present in the molecules are given.     

Fullerene in a metal-organic matrix: design of the electronic structure

We present a theoretical study of a new hybrid compound, where the C60 molecules are encapsulated in a recently discovered metal-organic framework (MOF). Being placed in a rigid skeleton, the fullerene molecules form a cubic crystal, while the intermolecular distance of the fullerenes is tuned by the choice of appropriate organic linkers of the MOF structure. The resulting C60 crystal shows a density of conduction states considerably higher than any of the fullerene crystals considered so far, which is a key factor influencing the transition temperature of the superconducting state. This constitutes a new approach of tuning the density of states of a fullerene crystal.     

Hydrogen adsorption in microporous alkali-doped carbons (activated carbon and single wall nanotubes)

Adsorption of hydrogen gas was tested in microporous doped carbons: activated carbon (1600 m²/g) and single wall carbon nanotubes (SWNTs). The isotherms of adsorption of LiC₁₈ and KC₂₄ doped microporous activated carbons were determined in the range [0–30 bar] at room temperature and 77 K. The chemisorption ratio observed at room temperature increases with increasing the alkali/carbon rate. The isotherm profiles of doped activated carbon at 77 K show no clear enhancement of the sorption ratio compared to the raw activated carbon.The adsorption sites of potassium doped SWNTs with closed end were determined by neutron diffraction experiment using deuterium gas. The K-doped SWNTs were found only slightly intercalated by K ions so that empty cavities are preserved in between the tubes. At room temperature, the chemisorption of deuterium was not observed in doped SWNTs bundles, but only in the KC₈ graphite intercalation compound impurities. At low temperature, the isotherms analysis and neutron diffraction experiments have shown that D₂ molecules are physisorbed in the free interstitial voids in between the tubes within the bundles.     

单壁碳纳米管:纳米发电机和纳米马达

简要回顾了单壁碳纳米管的发现及研究现状,介绍了一种新颖的悬空单壁碳纳米管的制备方法;在此基础上,通过新的一种四电极方法,用实验证明水分子可以进入两端开口的单壁碳纳米管内,由于水分子偶极子与碳纳米管中载流子的相互产生相互耦合作用,载流子的定向运动(电流)可以使水产生定向运动(纳米马达);同时,水的运动又会使碳纳米管中的载流子产生定向运动而产生一个电动势(纳米发电机).     

Synthesis and characterization of SWNT-heavy alkali metal intercalation compounds,effect of host SWNTs materials

Singlewall carbon nanotubes (SWNTs) produced by electric-arc and laser ablation methods were characterized by X-ray diffraction before and after the reaction with alkali metals (M=K, Rb, and Cs). Reaction with annealed SWNTs gave MC₈ composition at saturation. The alkali metal lattice showed short range order incommensurate with graphene cylinders of SWNTs. X-ray diffractogram simulations have enabled the study of the influence of SWNTs structure on that of intercalation compounds. Chemically-purified bundles, constituted of open SWNTs, can be intercalated inside and between the tubes forming disordered structures. Annealed or pristine bundles were intercalated only between the tubes leading to short or long range ordered structure depending on host crystallinity and alkali metal (K, Rb or Cs). The expansion of the 2D SWNTs lattice after intercalation is comparable to graphite intercalation compounds. Some 2D arrangements of SWNTs and K atoms are proposed and discussed to reproduce XRD results. ¹³C NMR and ESR studies of annealed doped SWNTs emphasize the fact that the intercalation compounds of SWNTs are metallic.     

CVD synthesis and purification of single-walled carbon nanotubes on aerogel-supported catalyst

Single-walled carbon nanotubes (SWNTs) were synthesized by disproportionation of carbon monoxide on an aerogel-supported Fe/Mo catalyst. A simple acidic treatment followed by an oxidation process produced a high purity (>99%) of SWNTs. The nanotubes obtained are bundled SWNTs and free of amorphous-carbon coating. Several factors that affect the yield and the quality of the SWNTs were also studied. This method shows great promise for large-scale production of SWNTs. Received: 30 August 2001 / Accepted: 3 December 2001 / Published online: 4 March 2002     

Tunable UV laser photolysis of organometallics with product detection by laser mass spectroscopy: Trimethylaluminum

We use tunable UV laser light in the region 200–320 nm, produced by frequency doubling the output of a dye laser, for the decomposition of organometallic compounds. This method has been applied to TMA, trimethylaluminum Al(CH₃)₃. Only the TMA monomer absorbs UV light for >220 nm. TMA decomposes by one-photon absorption mainly into two channels: aluminum atoms Al plus organic fragments, and aluminummonomethyl AlCH₃ molecules plus organic fragments. The ratio [Al]/[AlCH₃] is wavelength dependent. We present a mechanism to explain the photolysis of trimethyl compounds of group III elements (Al, Ga, In).