Search

Reactions of composition-selected cerium oxide cluster cations, Ce n O m + (n = 2–6; m ⩽ 2n), with O2 have been studied under single collision conditions. The formation of Ce n O m + 2 + is observed only for Ce n O m + with the average oxidation number (AON) of ∼3 for Ce atoms, Ce(III) clusters. In contrast, Ce(II) clusters with AON Ce n O m + 1 + , Ce n - 1 O m + , and Ce n - 2 O m - 2 + , after the oxidation of the parent clusters. Combined with collision-induced dissociation studies, it is concluded that O2 is bound weakly to the Ce(III) cluster, whereas O2 added to the Ce(II) cluster is incorporated as atoms rapidly and then the cluster decomposes.

Reactions of size-selected copper cluster cations, Cu n + (n = 3–7) and Cu n O m + (n = 3–5; m = 1 and 2), with nitrous oxide molecules, N2O, have been investigated by use of a tandem mass spectrometer. N2O molecules adsorb sequentially on the odd-sized Cu n + to produce Cu n + (N2O)l, while the even-sized clusters give the reaction products, such as Cu n - 1 O + (N2O)l, involving both the oxidation and the N2O adsorption. Preadsorption of oxygen atoms promotes the sequential N2O-adsorption significantly, and in particular, Cu 3 O + (N2O)3, Cu 4 O 2 + (N2O)3, and Cu 5 O 2 + (N2O)4 are produced dominantly from Cu 3 O + , Cu 4 O 2 + , and Cu 5 O 2 + , which shows the saturation of the adsorption with N2O.

Photodissociation spectra of Co n + (CH 3 OH) 3 ( n = 1–3) were measured in the region of 2800–6800 cm −1 . A broad near-infrared (-IR) absorption was observed in the spectra of n = 2 and 3, in addition to the vibrational absorption in the mid-IR region. With the aid of a calculation based on time-dependent density functional theory (TD-DFT), the near-IR absorption is assigned to the electronic transitions between the levels located near the highest occupied and the lowest unoccupied levels of Co n + (CH 3 OH) 3 , in which one or two methanol molecules dissociate to CH 3 and OH fragments and the fragments adsorb on the bridge sites of Co n + .

We systematically studied the support materials for chemical vapor deposition of single-wall carbon nanotubes (SWNTs). Four support materials with iron catalysts were investigated: silicon dioxide, aluminum film, boehmite, and γ-alumina. The boehmite and the γ-alumina were progressively converted from evaporated aluminum film. The iron catalysts on the aluminum film, the boehmite, and the γ-alumina produced a good SWNT yield in the growth temperature range of 650–800 °C, while the catalysts on silicon dioxide produced a poor SWNT yield. The X-ray diffraction patterns suggested that the catalyst particle sizes were kept small on these aluminum-based support materials.

We have established two new methods that enable incorporation of guest molecules into single-wall carbon nanotubes in liquid phases. Owing to their unique mechanisms, we call them nano-extraction and nano-condensation methods. To make Single-wall carbon nanotubes (SWNTs) that have incorporated C 60 ((C 60 ) n @SWNT) through nano-extraction, we put C 60 and SWNTs in ethanol for 1 day, during which the C 60 molecules deposited themselves inside the SWNTs. In the case of nano-condensation, we formed thin layers of C 60 -toluene saturated solution on SWNT surfaces and then obtained (C 60 ) n @SWNT within a few seconds. Reasonable explanations for these incorporation mechanisms are presented.

We report on chemical vapor deposition (CVD) of single-wall carbon nanotubes (SWNTs) on sapphire substrates coated with thin Fe films. The dependence of the SWNTs growth on orientation of the crystallographic face of the sapphire substrate, i.e., defined as A-, R-, and C-faces, was investigated. It was found when the CVD was performed at 800 °C, the largest quantity of SWNTs was produced on the A-face substrate, followed by the R- and C-face substrates. This result implies that the SWNT growth can be controlled by choosing the orientation of the sapphire substrates.

Synthesis of single-wall carbon nanotubes (SWNTs) was carried out by irradiating a graphite–Co/Ni target at room temperature with CO 2 laser pulses with durations of 1–20 ms. The length and bundle structure of SWNTs depended on the pulse duration. Most of the SWNTs formed by 1 ms laser pulses were individual tubes only 30–70 nm long. We discuss the growth dynamics of individual and bundled SWNTs based on the successive formation of metal nucleation sites in carbon–metal composite particles.

Two common methods of oxidation, gas-phase oxidation by heat treatment in oxygen gas and liquid-phase oxidation using nitric acid, were applied to single-wall carbon nanotubes (SWNT). The heat treatment in oxygen showed that thinner SWNTs burn more quickly. The nitric acid treatment showed that SWNTs are relatively inert to oxidation using acids. When the nitric acid treated samples were further oxidized by heat treatment in oxygen, selective oxidation of thinner SWNTs occurred.

Single-wall carbon nanotubes (SWNT) were formed by laser ablation or arc discharge using a C target containing Ni and Y, each with an atomic percentage of 0.3%. The carbonaceous deposit rich in SWNTs contained Ni and a small quantity of Y. The carbonaceous deposit poor in SWNTs contained C, Ni and Y, or C and Y. We concluded that the SWNT formation was catalyzed by Ni, but not by Ni coexisting with Y or by Y itself.

Experiments on single-wall carbon-nanotube (SWNT) formation by laser ablation were performed using a target composed of C, Ni, and Co. The pulse-to-pulse time (p–p) intervals of Nd:YAG laser beams were varied between 0.1 and 120 s. Since SWNTs were formed at all p–p intervals, we concluded that a single laser-beam pulse could form SWNTs. The amount of spider-web-like deposits containing SWNTs decreased as the p–p interval became longer. The structures of the SWNTs and of the non-SWNT carbon deposits had little dependence on the p–p interval.

During laser ablation to form single-wall carbon nanotubes, the composition at the surface of a target composed of C, Ni and Co became metal-rich and the yield of single-wall carbon nanotubes decreased. This problem was solved by applying double-target laser ablation where separate carbon and metal-alloy targets were simultaneously irradiated by the laser light.

Collision-induced reaction of Ar+n (n=2−15) with Kr was studied at collision energies from 0.1 to 2.0 eV (center-of-mass) by means of a tandem mass-spectrometer equipped with octopole ion guides. The reaction was found to proceed via Ar-atom evaporation from Ar+n, charge transfer from Ar+n to Kr or fusion of Ar+n with Kr. The absolute cross sections for these processes were measured as functions of the size of the parent cluster ion and the collision energy. The evaporation process was explained by collisional excitation of the parent cluster ion followed by a unimolecular dissociation of the “hot” parent cluster ion through evaporation. The charge transfer was found to proceed most efficiently in the n⩽6 range probably because of its energetics. On the other hand, the fusion process is energetically allowed in the entire size range studied and its cross section can be approximated by the geometrical cross section of Ar+n.

The way pentagons are distributed on a closed surface consisting of hexagons and pentagons determines the surface topology. Here, we present high-resolution electron microscopy images of carbon nano-tubes and nano-partcles, and show the symmetric and asymmetric distribution of pentagons at their end surfaces. From many observed morphologies it is concluded that no preferred distribution, leading to energetically favorable shapes, exists for the tip ends. It is also seen that the arrangements of pentagons show signatures for helicity in the hexagonal network of carbon on the tube surfaces.

C 60 thin film crystals have been fabricated on the (001) surface of alkali halide substrates, KCl, KBr, and NaCl, and their structures have been studied. TEM observations show that the hexagonal close packing (hcp) with lattice parameters a = 10.0 A and c = 16.3 A and the face-centered cubic (fcc) with a = 14.2 A coexist in the C 60 thin film crystals. The ratio of hcp to fcc is very dependent on the kind of substrate and on the temperature during crystal growth. The coexistence of two phases is considered to be related to the difficulties in achieving alkali-doped M 3 C 60 thin films.

Dissociative reactions of a rare-gas cluster ion, Arn−1Xe+ (n=13, 19 and 25), in collision with an Ar atom were investigated by use of the molecular dynamics method. It was found that evaporation of Ar atoms from Arn−1Xe+ proceeded dominantly at collision energies below ≈ 10 eV, while the Xe+ was ejected from the cluster ion with an increasing efficiency as the collision energy increased above ≈ 10 eV. The cross sections of the Xe+ ejection were obtained and compared with calculations based on a cage-vibrational excitation model proposed. This model was found to predict the cross section of the Xe+ ejection from a large cluster ion.

The vibrational motions of nearly spherical Ar 13 , Ar 30 and Ar 55 clusters were studied by use of the molecular dynamics method and were analyzed in terms of the modes of a dense-sphere vibration. Breathing, quadruple spheroidal and quadruple torsional vibrations were extracted from the motion of Ar atoms in these clusters and the frequency spectra for these modes were determined. The vibrational modes were found to be well separated from one another. This mode analysis is generally applicable to the investigation of the collective vibrations of clusters, which accompany structural changes.

The breathing vibration of Ar N cluster, N =13,20,25,30 and 55, was investigated by use of a dense sphere model, in which the cluster were approximated by a dense sphere; the breathing vibration corresponds to the symmetric stretch vibration of the dense sphere. The average distance ( r ), which is an index of the breathing motion, and its variance ( s 2 ) of all the Ar atoms with respect to the center of mass were calculated as a function of time by use of the molecular dynamics method. The frequency spectrum of r ( r spectrum) was derived from the time evolution of r . The frequency of the breathing vibration, f MD , obtained from the r spectrum was compared with that of the symmetric stretch vibration, f DS , calculated analytically based on the dense sphere model. As the cluster size increase, f MD , had a tendency to agree with f DS .