Higher coverage gas adsorption on the surface of carbon nanotubes: evidence for a possible new phase in the second layer

We present adsorption isotherm results for Ne, CH4, and Xe on bundles of close-ended single-wall carbon nanotubes, for coverages above the completion of the first layer. We find a small, sharp, substep present in the second-layer data for Ne and CH4, and a weaker feature, that produces an isothermal compressibility peak, for Xe. The size and location of the feature allows its tentative identification as a new, second-layer, one-dimensional phase, in which the atoms sit atop high binding energy sites in the second layer.     

Total cross-section measurements for 2–400 eV positrons in the rare gases

Experimentally determined values of the total scattering cross-sections for positrons in the energy range 2–400 eV on He, Ne, Ar, Kr and Xe are presented.     

An investigation of the efficiencies of various buffer gases in Na-Xe spin exchange

Measurements of the efficiencies of He, Ne and Xe as buffer gases in Na-Xe spin exchange are presented, and earlier values determined for N₂ revised slightly. The spin-rotation coupling of Na-Xe van der Waals molecules is also measured and found to be consistent with recent theoretical work.     

Experimental verification of a zero-dimensional model of the kinetics of XeCl* discharges by Xe*-, Cl*-, Ne*-, and H*-density measurements

Absorption spectroscopic measurements of effective particle number densities of excited Xe, Ne, Cl, and H performed on a small scale discharge with well-defined current and voltage pulses are compared with the results of model calculations over a wide range of discharge parameters. The reaction kinetic pathways determining the ionization and dissociative attachment rates have been verified by the good agreement obtained during the quasi-steady-state phase of the discharge for Xe and H. To reproduce the rise times of the excited Xe particle number densities during the ignition phase, the electron collision excitation cross sections of ground state Xe published by Puech and Mizzi [1] had to be enhanced by about 25%. From the Ne measurements it is concluded that the electron collision excitation cross sections of ground state Ne published by Puech and Mizzi [1] may be too large near the threshold. Measurements of excited Cl particle number densities are unsuitable to check the attachment kinetics of HCl, because these densities are mainly determined by reactions not involving the formation of Cl^– ions.     

Photoelectron momentum distributions of Ne and Xe dimers in counter-rotating circularly polarized laser fields

The strong-field ionization of dimers is investigated theoretically in counter-rotating circularly polarized laser fields. By numerically solving the two-dimensional (2D) time-dependent Schrödinger equation (TDSE) with the single-electron approximation (SEA) frame, we present the photoelectron momentum distributions (PMDs) and photoelectron angular distribution (PADs) of aligned Ne and Xe dimers. It is found that the PMDs and PADs strongly depend on the time delays by counter-rotating circularly polarized laser pulses. The results can be explained by the ultrafast photoionization model and the evolution of electron wave packets for Ne and Xe dimers. Besides, We make a comparison of PMDs between Ne atom and Ne dimer.     

Diffraction by finite-size crystalline bundles of single wall nanotubes

We calculate the diffraction spectrum of finite-size crystalline bundles of single wall carbon nanotubes (SWNT). The general profile of the spectrum as well as the width and position of the (1 0) diffraction peaks of the 2-D lattice of bundles depend on the tubes symmetry, distribution of tubes diameters and diameter of the bundles. Consequently, any attempt to derive the mean-diameter of the tubes from a diffraction spectrum requires to consider the diameters distribution of the tubes and the size of the bundles. Experimental diffraction profiles of various single wall nanotubes samples are well fitted by the calculated spectra. Received 16 December 1998     

Solar wind and cosmogenic rare gases in Luna 16 and 20 soils and their correlation with cosmic ray produced fossil tracks in lunar samples

The elemental and isotopic composition of Ne, Ar, Kr and Xe were measured in the bulk soil samples obtained from Luna 16 and 20 missions. The average cosmic ray exposure ages for the Luna 16 soils is higher than that of Luna 20 soils. The trapped solar wind composition is deduced by correcting for the cosmogenic component and is found to be in good agreement with the values published by others. The correlation between the solar wind gases and cosmic ray tracks in lunar samples is quantitatively studied and some systematic features regarding lunar regolith dynamics are tentatively established.     

Radiation chemical yields for loss of ether and carbonate ester bonds in PADC films exposed to proton and heavy ion beams

Chemical modification along ion tracks in PADC films has been studied by means of FT-IR spectrometry, which was exposed to proton and heavy ions of He, C, Ne, Ar, Fe, Kr and Xe with energies around the Bragg peaks. This study covers a wide region of the stopping power ranging from 10 to 10,000 keV/μm. Removal cross sections for the loss of ether and carbonate ester bonds are assessed for each ion, as a function of the stopping power. Chemical damage parameters like the damage density, the effective track core radius and the radiation chemical yields, G values (scissions/100 eV), for each bond are also derived. We have found anomalous dependence of these parameters on the stopping power. The G value for the loss of carbonate ester bond decreased from 20 for proton down to 5 for C and Ne ions, and then increased with atomic number of heavy ions up to 8 for Xe ion. Radial dose distribution for each ion has been also calculated. Results are discussed from the viewpoint of polymeric structure of PADC that consists of two parts with different radio-sensitivities.     

Visible and near-infrared excited-state dynamics of single-walled carbon nanotubes

Excited-state lifetimes of isolated single-walled semiconducting carbon nanotubes (SWNTs) have been measured for the first time; these excited states, observed over the 400- to 1800-nm spectral domain, possess lifetimes that range from several ps to more than 100 ps. Sub-ps to ps decay components are assigned to relaxation in SWNT bundles. Interrogation of the samples with different SWNT mean diameters further confirms the dependence of the excited-state lifetime on roll-up vector. The ratio of fast and slow decaying component contributions in the first van Hove band can be viewed as a measure of the bundle content. PACS 78.67.Ch; 78.47.+p; 61.46.+w; 73.22.-f     

Evidence of 1D behavior of He4 confined within carbon-nanotube bundles

We present the first low-temperature thermodynamic investigation of the controlled physisorption of He4 gas in carbon single-wall nanotube (SWNT) samples. The vibrational specific heat measured between 100 mK and 6 K demonstrates an extreme sensitivity to outgassing conditions. For bundles with a few number of nanotubes the extra contribution to the specific heat, C(ads), originating from adsorbed He4 at very low density displays 1D behavior, typical for He atoms localized within linear channels as grooves and interstitials, for the first time evidenced. For larger bundles, C(ads) recovers the 2D behavior akin to the case of He4 films on planar substrates (grafoil).     

Pressure derivatives of isothermal bulk modulus of rare gas solids

In the present study we have derived the expression for the bulk modulus using the Hildebrand approximation and the lattice potential energy for rare gas solids (RGS). The derived relation is further used to derive the expression for first and second order pressure derivatives of the bulk modulus for RGS. The derived relations are also used to compute the values of these constants in the case of Ne, Ar, Kr and Xe which are compared with the available values.     

An experimental investigation of the pressure and concentration dependence of muonic Coulomb capture and cascade in gases

Muonic Coulomb capture ratios and x-ray intensity patterns in four binary mixtures of the gases N₂, Ne, Ar, Kr, and Xe have been measured at three atomic ratios. An influence of the concentration has been established. The Lyman series intensity patterns of pure N₂, Ne, Ar, Kr, and Xe were measured at pressures between 0.4 and 51 bar and found to depend on the pressure. Possible explanations are discussed.     

High‐pressure Brillouin study of the elastic properties of rare‐gas solid xenon at pressures up to 45 GPa

The pressure dependences of three adiabatic elastic constants, adiabatic bulk modulus, refractive index, and elastic anisotropy, as well as Cauchy deviation of fcc solid Xe have been determined up to 10 GPa at 296 K by high‐pressure Brillouin scattering spectroscopy. The characteristics of elastic properties at high pressure of rare‐gas solid Xe are investigated by comparison with the previous studies on Ne, Ar, and Kr. Above 10 GPa, the occurrence of splitting in the Brillouin signals and the direction dependence of acoustic velocities for solid Xe clearly show partial phase transformation to the hcp structure reported by the previous X‐ray diffraction and Raman scattering studies. The shear elastic modulus in the hcp phase of solid Xe has also been estimated at pressures up to 45 GPa by using the pressure dependence of the Raman wavenumber shift for the E_2g mode. Copyright © 2008 John Wiley & Sons, Ltd.     

Thermal vacancies in one-dimensional Xe adsorbate chains in grooves of nanotube bundles

The specific heat C _P of quasi-one-dimensional Xe adsorbate chains in grooves on the outer surface of closed single-walled carbon nanotube bundles in the temperature interval of 2–55 K has been measured. Experimental data have been compared to the theoretical C _V values. The sharp increase in the difference C _P ? C _V above 30 K has been explained within the model of formation of single thermal vacancies in the one-dimensional Xe adsorbate chains. The enthalpy, entropy, and concentration of thermal vacancies have been determined.     

Chemical cross sections induced by ions in solid organic detectors: Experimentation and simulation

Chemical ester bond scission induced by incoming ions in polyethylene terephthalate (PET), bisphenol A polycarbonate (PC), polyallyl diglycol carbonate (PADC), have been systematically determined by FT-IR transmission measurements. The studied ions (H, He, C, Ne, I, Ar, Fe, Kr, Xe) have LET ranging from 10 to 10 000 keV μm⁻¹. We discuss the opportunity to simulate the experimental chemical cross section obtained with an approach based on the dose deposited by the secondary electrons removed by the incoming ion. Such an approach has been already successfully applied for LR115.     

Synthesis and structure of pristine and alkali-metal-intercalated single-walled carbon nanotubes

8 (M=K or Cs). No crystalline structure was observed in the reacted materials by X-ray diffraction. In situ metal deposition, TEM, and electron energy loss spectroscopy (EELS) measurements were performed on individual SWNT bundles at 300 K. The results showed that alkali metals can be reversibly intercalated into the SWNT bundles. Although intercalation induced structural disorder, individual nanotubes and to a large extent the bundles maintained their structural integrity after intercalation and de-intercalation. Received: 10 February 1998     

Anisotropic intermolecular forces. I. Rare gas—hydrogen chloride systems

Anisotropic potential energy surfaces for Ne.HCl, Kr.HCl and Xe.HCl are obtained by simultaneous least squares fitting to molecular beam spectra and rotational line broadening cross sections. A revised potential surface for Ar.HCl is also presented. The potentials are all very similar in shape, with the absolute minimum at the linear rare gas-HCl geometry in each case. The absolute well depths and well depth anisotropies increase steadily as the size of the rare gas atom increases.

The potentials should be reliable in the region of the absolute minimum and on the repulsive wall of the potential. The molecular beam spectra for Ne.HCl can be fitted only by a potential with a significant secondary minimum at the linear Ne.Cl-H geometry, but the existing data for the more anisotropic Ar, Kr and Xe systems are not sensitive to the presence of this potential feature. The potential surfaces for these systems have accordingly been constrained to have a similar secondary minimum near the linear rare gas-ClH geometry. Experiments which would provide further information on the intermolecular potentials are suggested and predictions of the results are made.     

产生惰性气体高价离子的新方法

此文介绍了一种产生惰性气体高价离子的新方法。在飞行时间质谱仪（ＴＯＦ－ＭＳ）上，把聚焦后的３０８ｎｍ激光掠射到不锈钢栅网上，产生超短脉冲的电子束，利用这种电子束来轰击惰性气体（Ｈｅ，Ｎｅ，Ａｒ，Ｋｒ，Ｘｅ），产生高价离子，并给出了这些离子的飞行时间质谱。这些高价离子可能是电子逐次电离气体原子产生的。这种方法可作为飞行时间质谱的一种理想的“软电离”的“点”离子源     

Formation mechanism of carbon nanotubes in the gas-phase synthesis from colloidal solutions of nanoparticles

Single- and multi-wall carbon nanotubes have been synthesized by the gas-phase catalytic reaction of colloidal solutions of metal nanoparticles using a vertical flow reactor. The reverse micelle solution of the Co–Mo nanoparticles with the mean diameter of 11 nm dissolved in toluene was injected directly into the reactor maintained at 1200 °C. The nanoparticles and the solvent act as the catalyst and carbon source, respectively. When the concentration of the thiophene additive is low (1 wt.%), the formation of SWNT bundles preferentially occurred. The SWNT bundles were present together with the relatively small metal nanoparticles with the diameter of 0.5–5.5 nm. It is likely that the original nanoparticles with the diameter of 11 nm break into smaller ones, 1–2 nm diameters, which is suitable for the SWNT growth. The synactic effect of Co and Mo was also observed.