[en] The Ar₃--HCl tetramer has been identified via the observation of its microwave rotational spectrum using the pulsed nozzle Fourier transform technique. The rotational spectroscopic constants of the ground vibrational state have been obtained for the ³⁵Cl/³⁷Cl isotopes from measurements of the J = 1→2 to J = 4→5 transitions and their hyperfine structure. For Ar₃--H³⁵Cl, the values found for B₀, D/sub J/, D/sub J//sub K/, and chi/sub aa/ are 843.8974(1) MHz, 2.333(2) and 1.818(6) kHz, and 31.006(5) MHz, respectively, and for Ar₃--H³⁷Cl, 825.9811(2) MHz, 2.211(5) and 1.940(12) kHz, and 24.481(8) MHz. The cluster is a symmetric top with the HCl along the C₃ axis, its H end directed towards the Ar₃ trimer. In its torsional oscillations, the HCl makes an average angle of 36.91⁰ with the symmetry axis. The chlorine isotopic substitution leads to values of 3.8510 and 4.0024 A for the Ar--Ar and Ar--Cl distances. The results of the present study are compared with those reported earlier for the Ar/sub m/--HF (m = 1,2,3) and Ar/sub m/--HCl (m = 1,2) clusters

[en] Microwave rotational spectra have been observed for the four ¹⁴N/¹⁵N isotopic species of an (HCN)₂--Ar trimer with the pulsed nozzle Fourier transform method using the Flygare Mark II spectrometer. Thirteen J→J' asymmetric top transitions were measured in the 2.5 to 10 GHz region for the parent ¹⁴N,¹⁴N trimer and nine for each of the other three species. The ¹⁴N nuclear quadrupole hyperfine structure was analyzed for the transitions and the interaction constants and line centers determined. The line centers were fitted to obtain ground vibronic state rotational and quartic centrifugal distortion constants. For the ¹⁴N/¹⁴N trimer these are (in MHz) for A'', B'', and C'': 2013.5993(10), 1759.2756(3), 932.3709(2); and for tau₁, tau₂, tau/sub a//sub a//sub a//sub a/, tau/sub b//sub b//sub b//sub b/, and tau/sub c//sub c//sub c//sub c/: -0.3017(1), -0.0660(1), -0.1700(9), -0.013 71(1), and -0.0088(1). The inertial defect is 3.7881 amu A². The zero-point vibrationally averaged geometry is planar and T shaped with the structure of the linear HCN dimer remarkably unperturbed by presence of the Ar atom. The substitution NxxxN distance in the cluster is 4.453 A compared with 4.461 A in the free dimer. The argon is attracted by the π electrons of the two --CequivalentN groups, being equidistant from them. The ArxxxN(1) and ArxxxN(2) distances are 3.671 and 4.316 A, respectively

[en] Comprehensive investigations of structure and micro plasticity of high-purity fullerites C₆₀ are made. The crystal structure, lattice parameters and phase transitions in the temperature range of 30 to 293 K are studied by using an x-ray diffraction technique. The order-disorder phase transition temperature is found to be T_c = 260 K.The samples display a great number of stacking disorder areas that are responsible for a fcc-sc transition smearing at T_c = ± 3 K. The temperature dependence of the lattice parameter a(T) exhibits three anomalies: one at T_c where a jump in the lattice parameter occurs (Δa/a = 3,3 centre dot 10^-3) and two at T₀ approx= 155 K and T_g approx= 95 K which are related to the onset and the completion of the process of molecule orientation freezing. It is shown that the formation of the orientational glass is followed by a considerable increase in the width of x-ray reflections. The geometry of slip and the temperature dependence of microhardness, H_V, are studied within the temperature range of 81 to 293 K. A { 111 } <110> type system is shown to be the only system of slip in the fcc and sc phases. The magnitude of H_V depends on the plane of indentation:H_V¹¹¹ > H_V¹⁰⁰. Below T_c it increases sharply (by about 30%). The temperature interval of the anomaly decreases after the crystal is annealed in vacuum. At T< T₀ the dependence H_V(T) becomes appreciably steeper. The hardness of C₆₀ normalized to elastic shear modulus is found to be higher than that of typical molecular crystals, the homo logic temperatures being comparable

[en] Short communication

[en] Many experiments on the mechanics of nanostructures require the creation of rigid clamps at specific locations. In this work, electron-beam-induced deposition (EBID) has been used to deposit carbon films that are similar to those that have recently been used for clamping nanostructures. The film deposition rate was accelerated by placing a paraffin source of hydrocarbon near the area where the EBID deposits were made. High-resolution transmission electron microscopy, electron-energy-loss spectroscopy, Raman spectroscopy, secondary-ion-mass spectrometry, and nanoindentation were used to characterize the chemical composition and the mechanics of the carbonaceous deposits. The typical EBID deposit was found to be hydrogenated amorphous carbon (a-C:H) having more sp²- than sp³-bonded carbon. Nanoindentation tests revealed a hardness of ∼4 GPa and an elastic modulus of 30-60 GPa, depending on the accelerating voltage. This reflects a relatively soft film, which is built out of precursor molecular ions impacting the growing surface layer with low energies. The use of such deposits as clamps for tensile tests of poly(acrylonitrile)-based carbon nanofibers loaded between opposing atomic force microscope cantilevers is presented as an example application

[en] Scanning tunneling microscopy (STM) has been used to obtain images and current--voltage (I--V) curves of carbon nanotubes produced by arc discharge of carbon electrodes. The STM I--V curves indicate that carbon nanotubes with diameters from 2.0 to 5.1 nm have a metallic density of states. Using STM, we also observe nanometer-size graphene sheets which are four graphite layers thick. The STM images of carbon nanotubes are in good agreement with transmission electron microscope images. copyright 1995 American Vacuum Society

No abstract available

[en] An apparent enhanced solubility of single-wall carbon nano tubes (SWNTs) in the deuterated form of the standard 3 : 1 sulfuric (H₂SO₄) to nitric (HNO₃) acid mixture treatment is reported and attributed to the stronger interaction of deuterium bonds with the single-wall carbon nano tube surface. UV-Visible spectroscopy was used to characterize the apparent enhanced solubility of the SWNTs treated in deuterated forms of the acid mixture in comparison to the standard acid mix, while FTIR was used to analyze the nature of the functional groups generated on the SWNTs as a result of the different acid treatments. The apparent enhanced solubility reported here is consistent with the limited number of computational and experimental results published in the literature regarding the interaction of carbon nano tubes with deuterated solvents; however, a detailed understanding of the underlying mechanism responsible for this observation is currently lacking. The apparent increased solubility observed here could potentially be utilized in many applications where carbon nano tube dispersion is required.

[en] Highlights: • Scanning μLEED measurements performed with a very small electron beam (250 nm) can provide precise quantitative information about structural variations with high spatial resolution. • We have developed the source extraction and photometry-spot profile analysis tool for quantitative evaluation of scanning μLEED data with high throughput. • The application of this tool to evaluate scanning μLEED data obtained for defective graphene on Cu(111) reveals a rich rotational domain structure. -- Abstract: Micro-low energy electron diffraction (μLEED) is frequently used in conjunction with low energy electron microscopy (LEEM) to learn about local surface structural features in small selected areas. Scanning μLEED measurements performed with a very small electron beam (250 nm) can provide precise quantitative information about structural variations with high spatial resolution. We have developed the Source Extraction and Photometry (SEP) – Spot Profile Analysis (SPA) tool for evaluating scanning μLEED data with high throughput. The capability to automate diffraction peak identification with SEP-SPA opens up the possibility to investigate systems with complex diffraction patterns in which diffraction peak positions vary rapidly for small lateral displacements on the surface. The application of this tool to evaluate scanning μLEED data obtained for defective graphene on Cu(111) demonstrates its capabilities. A rich rotational domain structure is observed in which a majority of the graphene is co-aligned with the Cu(111) substrate and the significant remainder comprises domains with large rotations and small sizes that are comparable to the small beam size.