A. Gorbunov

Diameter grouping in bulk samples of single-walled carbon nanotubes from optical absorption spectroscopy

The influence of the synthesis parameters on the mean characteristics of single-wall carbon nanotubes in soot produced by the laser vaporization of graphite has been analyzed using optical absorption spectroscopy. The abundance and mean diameter of the nanotubes were found to be most influenced by the furnace temperature and the cobalt/nickel catalyst mixing ratio. Via an analysis of the fine structure in the optical spectra, the existence of preferred nanotube diameters has been established and their related fractional abundance could be determined. The results are consistent with nanotubes located mainly around the armchair axis.

Solid–Liquid–Solid Growth Mechanism of Single-Wall Carbon Nanotubes

Abstract Reasons are presented which suggest that the liquefaction of the catalytic particles is a decisive condition for formation of single wall carbon nanotubes (SWNTs) by physical synthesis techniques. It is argued that the SWNT growth mechanism is a kind of solid–liquid–solid graphitization of amorphous carbon or other imperfect carbon forms catalyzed by molten supersaturated carbon–metal nanoparticles. The assumption of low temperature melting of these nanoparticles in contact with amorphous carbon followed by its precipitation in the form of SWNTs allows to explain qualitatively the experimentally observed SWNT growth rates and temperature dependence of the SWNT yield. Guidelines for increasing SWNT yield are proposed.

Cross-beam pulsed laser deposition: General characteristic

Physical background of the operation of the cross-beam pulsed laser deposition (CBPLD) is considered. In this modification of PLD, gas-dynamic interaction of two plasma plumes from separate targets is used for particulate elimination from the plasma flux to the substrate. The interaction of the plasma plumes by CBPLD in a vacuum was investigated with the help of ion collectors and optical spectroscopy. A minimal plasma number density in the intersection region necessary for an efficient plume interaction amounts to ≈1.4×1015 cm−3 in the geometry of the experiments. For the materials with relatively high evaporation rates, the plasma density in the plume intersection region is larger than this value during almost the entire plume existing time, and the ablated material can be effectively utilized for the deposition of films. CBPLD demonstrates a very good effectiveness of the particulate removal from the plasma flux, and it is reasonable to suggest that CBPLD is one of the most effective working methods fo...

Ultrathin film deposition by pulsed laser ablation using crossed beams

A high vacuum pulsed laser deposition system is described where an intersection of two ablation plumes from twinned simultaneously irradiated targets is used. This system allows thin film and multilayer deposition of a wide variety of materials (including low melting point metals like tin) practically without droplet contamination. The intersection region acts as a filter for droplets and high energy plasma particles. The use of twinned targets of different materials facilitates preparation of artificially mixed supersaturated thin film solid state solutions used as a media for sub-micrometer and nanometer-scale surface processing. Special design of the target holder that can carry simultaneously up to 24 targets and computer control of the deposition process make it possible to change easily targets without venting the deposition chamber and to deposit arbitrary multilayer combinations of various materials.

Impact of catalyst coarsening on the formation of single-wall carbon nanotubes

The single-wall carbon nanotube (SWCN) yield as a function of the gas flow velocity for different catalyst contents in a furnace-based pulsed laser evaporation method is shown to depend sensitively on the size distribution and growth conditions of the condensed catalyst nanoparticles in the gas phase. In particular, accelerated particle coarsening should be avoided. Consequently, a high number density of small catalyst nanoparticles leads to a high nanotube yield within the timescale of a few hundred milliseconds. Hence, the attainment of enhanced particle growth control will enable a high yield evaporation-based synthesis of high-quality SWCNT.

Structural and magnetic phase transformation in metastable Fe-Cr alloys induced by ion irradiation

Unusual metastable paramagnetic phases have been observed in Fe–Cr thin films (thickness about 40 nm) fabricated by pulsed laser deposition. In the present article, x-ray diffraction and Mossbauer spectroscopy have been applied to follow the structural and magnetic phase transformation in these alloys induced by ion irradiation with a projected range positioned in the center of the films. It has been found that the critical dose for the transformation to the more stable body-centered cubic (bcc) structure depends on the initial phase of the film and the ion mass. The initial body-centered tetragonal phase, which forms in the alloys with low Cr content (∼30 at. %), can be completely transformed to the bcc phase already by a dose of 5×1015 Cr/cm2, whereas the primitive orthorhombic phase of roughly equiatomic Fe–Cr alloys is about four times more resistant against ion bombardment. A five times higher Ne ion dose is required to induce the same transformation as by the Cr bombardment. The observed effects are...

X-ray investigation of metastable crystalline phases in co-deposited Fe–Cr alloy nanometer films

Abstract Fe100−xCrx (x=24.5–61.7, 100 at.%) alloy nanometer films prepared by crossed-beam pulsed laser deposition were examined by wide-angle X-ray scattering. On varying the Cr content, x, a change of phase content is observed starting from the known body-centered cubic phase at low Cr content. Indications for three new metastable Fe–Cr phases were found to form in body-centered tetragonal, face-centered orthorhombic and primitive orthorhombic lattice types, respectively.

LATERAL SELF-LIMITATION IN THE LASER-INDUCED OXIDATION OF ULTRATHIN METAL FILMS

cw‐laser‐induced local oxidation of ultrathin (3–60 nm) titanium films on glass in air is studied. It is shown, that the brightening of the films upon through‐oxidation forms a negative feedback to this highly nonlinear process. It offers the possibility of stable writing of oxide line structures narrower than the diffraction limited focused laser spot. The optimum metal film thickness is of the order of the light absorption length in the metal. Transparent isolated oxide lines and gratings with periods down to 250 nm and line width down to 165 nm were recorded in 6–15 nm thick Ti films on glass by using the radiation of the Ar ion laser (λ=488, 514 nm).

Formation of unusual intermetallic phases by vacuum PLD

Abstract Unusual phase formation in Fe–Cr alloys co-deposited by pulsed laser deposition (PLD) is reported. Contrary to expectations to obtain a continuous series of supersaturated body centered cubic (b.c.c.) solid solutions, the structure of alloys develops from a tetragonally distorted b.c.c. at low Cr-content to an ordered primitive orthorhombic crystal structure of the A15 type at nearly equiatomic composition. It seems to be the first observation of an ordering of restrictedly soluble components under the bombardment of hyperthermal species in PLD. The film formation in PLD can be described in the frames of subplantation model of Lifshitz et al. where the phase that forms is a product of kinetic factors like defect formation beneath the free surface and their disintegration rather than thermodynamic driving forces.

Comparative study of interfaces of Fe–Al multilayers prepared by direct and crossed-beam pulsed laser deposition

Abstract Fe/Al multilayers with different composition were prepared by conventional, direct-pulsed laser deposition (DPLD) and crossed-beam pulsed laser deposition (CBPLD). Films were studied by means of X-ray reflectometry, wide-angle X-ray scattering and X-ray absorption fine structure experiments. Ballistic simulations of the deposition processes were performed. It is found that adjacent Fe and Al layers are partially intermixed during the deposition, forming Fe–Al transition layers of a few nm in thickness. Both DPLD and CBPLD multilayers have comparable interfaces. In Fe-rich layers, a b.c.c. solid solution is formed. Al-rich layers of approximately 5 nm in nominal thickness are amorphous. DPLD samples have a higher Al content and a significant number of incorporated Al droplets.