TEM Imaging of Mass-selected Polymer Molecules

Polyethylene glycol (PEG) molecules with masses below 1300amu are electrosprayed (ES) from solution, mobility-selected at high resolution in a differential mobility analyzer (DMA), collected on a grid and imaged by transmission electron microscopy (ES–DMA–TEM). The DMA resolves individual n-mers, and selects only one out of the many present in the original sample. Ion identity is established from parallel mass spectra (ES-MS). The images reveal spherical particles 1.46nm in diameter, in good agreement with the known ion mass and bulk density. The DMA-selection technique opens new paths for the study of very small particles.     

Effect of acceleration by internal and external force fields on particle motion in intermediate regimes between the hydrodynamic and free-molecular limits

The kinetic theory of gases is applied to analyze slow translational motion of low-concentration particles driven by an external force in a homogeneous gas. The analysis takes into account the diffusion due to the difference in acceleration between particles and molecules in internal and external force fields. A general expression is derived for the particle drag force in hydrodynamic, free-molecular, and intermediate regimes. This expression reduces to a simple relation between the drag force and its values in the hydrodynamic and free-molecular limits and the force of intermolecular interaction between particles and gas molecules. In the case of spherically symmetric potential of interaction between the particle and molecules, the drag force is the harmonic mean of its limit values.     

Performance and early applications of a versatile double aberration-corrected JEOL-2200FS FEG TEM/STEM at Aalto University

Applications relevant to carbon based nano-materials have been explored using a newly installed JEOL-2200FS field emission gun (FEG) (scanning) transmission electron microscope (S)TEM which is integrated with two CEOS aberration correctors for both the TEM image-forming and the STEM probe-forming lenses. The performance and utility of this newly commission hardware has been reviewed with a particular focus on operation at an acceleration voltage of 80 kV, thus bringing the primary electron beam voltage below the knock-on threshold for carbon materials and opening up a range of possibilities for the study of carbon-based nanostructures in the aberration-corrected electron microscope. The ability of the microscope to obtain both atomic TEM images and high-quality electron diffraction patterns from carbon nanotubes was demonstrated. The chiral structure of a double-walled carbon nanotube was determined from its diffraction pattern. The aberration corrected TEM imaging technique facilitates a unique approach to accurate determination of single-walled carbon nanotube diameters. On the other hand, the probe-corrected high angle annular dark field (HAADF) STEM imaging performance allows for the detection of single gold atoms at 80 kV and was used to study the graphite interlayer spacing in a multi-walled carbon nanotube.     

The synthesis of few-walled carbon nanotubes by the catalytic pyrolysis of methane and the kinetics of their accumulation

The kinetic dependences of the accumulation of carbon during pyrolysis of CH₄ mixed with H₂ on an Mo-Co/MgO catalyst with the atomic ratio Mo: Co: Mg = 3: 1: 76 at atmospheric pressure, temperature 900°C, and various CH₄ and H₂ partial pressures were determined by direct thermogravimetric measurements in combination with electron microscopic examination. The main solid pyrolysis products were found to be carbon nanotubes with two to five walls. The outside diameter of nanotubes changed from ～3 to 9 nm. A kinetic model of the accumulation of carbon was suggested. The model took into account the formation of two products, nanotubes and carbon deposited on their surface, process reversibility, and catalyst deactivation by nanotubes formed.     

Synthesis of nanoparticles using vapor-phase decomposition of copper(II) acetylacetonate

Experimental data on the synthesis of crystalline Cu, Cu₂O, and CuO nanoparticles obtained earlier by the vapor-phase decomposition of copper(II) acetylacetonate (Cu(acac)₂) were systematized and generalized. Studies were performed using a laminar flow reactor at atmospheric pressure within the ranges of precursor partial vapor pressure P _prec = 0.06–44 Pa and reactor temperature from 432 to 1216°C. The decomposition of Cu(acac)₂ was studied in an inert nitrogen atmosphere and in the presence of various reagents (water vapors, H₂, O₂, and CO). The composition of synthesized particles varied from pure copper to its oxides (Cu₂O and CuO) depending on experimental conditions and used reagents. A semi-empirical kinetic model was proposed for describing the product dynamics. The hypothesis on the predominant role of copper dimers in a particles growth was stated. It was established that the composition of products is determined by the surface reactions on growing particles and is dependent on the ratio between the concentrations of the gaseous reagents. Calculated phase diagrams of the products of Cu(acac)₂ decomposition in the presence of various reagents were in good agreement with experimental data. The proposed method of construction of the phase diagram of decomposition products can be employed for other systems. It was established that, upon the Cu(acac)₂ decomposition in the presence of CO, carbon nano-onions were formed in addition to copper nanoparticles.Translated from Kolloidnyi Zhurnal, Vol. 67, No. 1, 2005, pp. 5–25.Original Russian Text Copyright © 2005 by Nasibulin, Shurygina, Kauppinen.     

Synthesis of boron nitride multi-walled nanotubes by laser ablation technique

Carbon nanotubes are known as prospective material for the optoelectronics, vacuum electronics, non-linear optics and for the composite material synthesis. Boron nitride nanotubes (BNNTs) were obtained only recently. It is expected that these nanotubes possess the unique properties. BN is much more chemically inert than carbon. Its oxidation temperature is above 1000°C as the graphite is totally oxidized already at 650°C. BNNTs are wide-gap semiconductors with the 6 eV gap. In case of the introducing of the carbon atoms into the BN nanotube wall its bandgap may be varied in wide range. This property is important for the UV optics.     

Ion-induced nucleation of dibutyl phthalate vapors on spherical and nonspherical singly and multiply charged polyethylene glycol ions

Dibutyl phthalate vapor nucleation induced by positive polyethylene glycol (PEG) ions with controlled sizes and charges was experimentally studied. The ions were produced by electrospray ionization, classified in a high-resolution differential mobility analyzer, and studied in a nano condensation nucleus counter of the mixing type. Ionic radii of PEG varied from 0.52 to 1.56 nm, including from singly to quadruply charged ions. Some of these ions are fully stretched chains, other are spherical, and others have intermediate forms, all of them having been previously characterized by mobility and mass spectrometry studies. Activation of PEG1080(+2) requires a supersaturation almost as high as that required for small singly charged ions and higher than for PEG1080(+). This anomaly is explained by the Coulombic stretching of the ion into a long chain, where the two charged centers appear to be relatively decoupled from each other. The critical supersaturation for singly charged spherical ions falls below Thomson's (capillary) theory and even below the already low values seen previously for tetraheptyl ammonium bromide clusters. Spherical PEG4120(+2) falls close to the Thomson curve. The trends observed for slightly nonspherical PEG4120(+3) and highly nonspherical (but not quite linear) PEG4120(+4) are intermediate between those of multiply charged spheres and small singly charged ions.